2,260,000 Shares AMERICAN DENTAL PARTNERS, INC. COMMON STOCK ($.01 PAR VALUE) UNDERWRITING AGREEMENT

Exhibit 1.1

2,260,000 Shares

AMERICAN DENTAL PARTNERS, INC.

COMMON STOCK ($.01 PAR VALUE)

UNDERWRITING AGREEMENT

August 18, 2009

XXXXXX X. XXXXX & CO. INCORPORATED

000 Xxxx Xxxxxxxxx Xxxxxx

Xxxxxxxxx, Xxxxxxxxx 00000

Ladies and Gentlemen:

American Dental Partners, Inc., a Delaware corporation (the “Company”), proposes to issue and sell to the Underwriter named in Schedule I hereto (the “Underwriter”) 2,260,000 shares of the Common Stock, ($.01 Par Value) of the Company (the “Firm Shares”).

The Company also proposes to issue and sell to the Underwriter up to an additional 339,000 shares of Common Stock, ($.01 Par Value) of the Company (the “Additional Shares”), if and to the extent that you, Xxxxxx X. Xxxxx & Co. Incorporated (referred to herein as either “Baird” or “Manager”), as Manager of the offering, shall have determined to exercise the right to purchase such shares of common stock granted to the Underwriter in Section 2 hereof. The Firm Shares and the Additional Shares, are hereinafter collectively referred to as the “Shares.” The shares of Common Stock, ($.01 Par Value) of the Company to be outstanding after giving effect to the sales contemplated hereby, are hereinafter referred to as the “Common Stock.”

The Company has prepared and filed, in accordance with the Securities Act of 1933, as amended (the “Securities Act”), and the rules and regulations thereunder, with the Securities and Exchange Commission (the “Commission”) a registration statement on Form S-3, as amended, (Registration No. 333-160157, including a prospectus, relating to the Shares, which registration statement and prospectus incorporate or are deemed to incorporate by reference documents that the Company has filed, or will file, with the Commission in accordance with the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and the rules and regulations thereunder. The registration statement as amended at the time it becomes effective for purposes of Section 11 of the Securities Act (as such section applies to the Underwriter), including the documents filed as part thereof and information contained or incorporated by reference in the prospectus or otherwise deemed to be part of the registration statement at the time of effectiveness pursuant to Rule 430A or Rule 430B under the Securities Act, is hereinafter referred to as the “Registration Statement.” The Company has also filed with, or transmitted for filing to, or shall promptly after the date of this Agreement file with or transmit for filing to, the Commission a prospectus supplement (in the form first used to confirm sales of the Shares (or in the form first made available to the Underwriter by the Company to meet requests of purchasers pursuant to Rule 173 under the Securities

Act), the “Prospectus Supplement”) pursuant to Rule 424 under the Securities Act. The term “Base Prospectus” means the prospectus dated August 7, 2009 relating to the Shares, in the form in which it has most recently been filed with the Commission as part of the Registration Statement on or prior to the date of this Agreement. The term “Prospectus” means the Base Prospectus as supplemented by the Prospectus Supplement. The term “Preliminary Prospectus” means any preliminary form of Prospectus (including without limitation the preliminary Prospectus Supplement dated August 18, 2009, filed with the Commission pursuant to Rule 424).

For purposes of this Agreement, “free writing prospectus” has the meaning set forth in Rule 405 under the Securities Act; “Time of Sale Prospectus” means the Base Prospectus and the Preliminary Prospectus, together with the free writing prospectuses, if any, each identified in Schedule II hereto (each, a “Permitted Free Writing Prospectus”), and other information conveyed to purchasers of the Shares at or prior to the Time of Sale as set forth in Schedule II hereto; “Time of Sale” means 9:00 p.m. (Central Time) on the date of this Agreement; and “road show” has the meaning set forth in Rule 433(h)(4) under the Securities Act. As used herein, the terms “Registration Statement,” “Base Prospectus,” “Preliminary Prospectus,” “Time of Sale Prospectus” and “Prospectus” shall include the documents, if any, deemed to be incorporated by reference therein, including, unless the context otherwise requires, the documents, if any, filed as exhibits to such incorporated documents. The terms “supplement,” “amendment” and “amend” as used herein with respect to the Registration Statement, the Base Prospectus, the Time of Sale Prospectus, any Preliminary Prospectus, the Prospectus or any free writing prospectus shall include all documents subsequently filed by the Company with the Commission pursuant to the Exchange Act that are deemed to be incorporated by reference therein.

1. Representations and Warranties of the Company. The Company represents and warrants to and agrees with the Underwriter on the date hereof, on the Closing Date and on each Option Closing Date, if any, that:

(a) The Registration Statement has become effective under the Securities Act; no stop order suspending the effectiveness of the Registration Statement or preventing or suspending the use of any Preliminary Prospectus or the Prospectus is in effect, and no proceedings for such purpose are pending before or to the Company’s knowledge threatened by the Commission.

(b) The Base Prospectus and any Preliminary Prospectus filed as part of the registration statement as originally filed or as part of any amendment thereto, or filed pursuant to Rule 424 under the Securities Act, complied when so filed in all material respects with the Securities Act and the rules and regulations thereunder (including, without limitation, Rule 430B(a) or 430A(b)).

(c) (i) Each document, if any, filed or to be filed pursuant to the Exchange Act and incorporated by reference in the Time of Sale Prospectus or the

Prospectus complied or will comply when so filed in all material respects with the Exchange Act and the applicable rules and regulations of the Commission thereunder; (ii) each part of the Registration Statement, when such part became effective, did not contain and each such part, as amended or supplemented, if applicable, will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading; (iii) the Registration Statement, as of the date hereof, does not contain and, as amended or supplemented, if applicable, will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading; (iv) the Registration Statement complies and, as amended or supplemented, if applicable, will comply in all material respects with the Securities Act; the conditions to the use of Form S-3 in connection with the offering and sale of the Shares as contemplated hereby have been satisfied; the Registration Statement meets, and the offering and sale of the Shares as contemplated hereby complies with, the requirements of Rule 415 under the Securities Act (including without limitation Rule 415(a)(5)); (iv) at no time during the period that begins on the earlier of the date of the Preliminary Prospectus and the date on which the Preliminary Prospectus was filed with the Commission and ends immediately prior to the execution of this Agreement did any Preliminary Prospectus contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading; (v) the Time of Sale Prospectus does not, and at the Time of Sale, at the Closing Date (as defined in Section 4) and, if applicable, each Option Closing Date (as defined in Section 5), the Time of Sale Prospectus, as then amended or supplemented by the Company, if applicable, will not, contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading; (vi) each Permitted Free Writing Prospectus does not conflict with the information contained in the Registration Statement, the Time of Sale Prospectus or the Prospectus; (vii) each road show, when considered together with the Time of Sale Prospectus, does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading; and (viii) the Prospectus, as of the date it is filed with the Commission pursuant to Rule 424, at the Closing Date and at each Option Closing Date, if any, will comply in all material respects with the Securities Act (including without limitation Section 10(a) of the Securities Act) and will not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided, however, that the representations and warranties set forth in this Section 1(c) do not apply to statements or omissions in the Registration Statement, the Time of Sale Prospectus, any Preliminary Prospectus, any Permitted Free Writing Prospectus, any road show or the Prospectus or any amendments or supplements thereto based upon information relating to the Underwriter furnished to the Company in writing by such Underwriter through the Manager expressly for use therein, it being agreed that the only information

furnished by the Underwriter to the Company expressly for use therein are the statements contained in the underwriter table in, and the fourth and twelfth paragraphs of, the “Underwriting” section of the Prospectus Supplement (and preliminary Prospectus Supplement) and the last paragraph of the cover page of the preliminary Prospectus Supplement.

(d) Prior to the execution of this Agreement, the Company has not, directly or indirectly, offered or sold any Shares by means of any “prospectus” (within the meaning of the Securities Act) or used any “prospectus” (within the meaning of the Securities Act) in connection with the offer or sale of the Shares, in each case other than the Base Prospectus, the Preliminary Prospectus and/or the Permitted Free Writing Prospectuses; the Company has not, directly or indirectly, prepared, used or referred to any free writing prospectuses, without the prior written consent of Baird, other than the Permitted Free Writing Prospectuses and road shows furnished or presented to the Manager before first use. Each Permitted Free Writing Prospectus has been prepared, used or referred to in compliance with Rule 163 or with Rules 164 and 433 under the Securities Act; assuming that such Permitted Free Writing Prospectus is so sent or given after the Registration Statement was filed with the Commission (and after such Permitted Free Writing Prospectus was, if required pursuant to Rule 433(d) under the Securities Act, filed with the Commission), the sending or giving, by the Underwriter, of any Permitted Free Writing Prospectus will satisfy the provisions of Rule 164 and Rule 433 (without reliance on subsections (b), (c) and (d) of Rule 164); the conditions set forth in one or more of subclauses (i) through (iv), inclusive, of Rule 433(b)(1) under the Securities Act are satisfied, and the registration statement relating to the offering of the Shares contemplated hereby, as initially filed with the Commission, includes a prospectus that, other than by reason of Rule 433 or Rule 431 under the Securities Act, satisfies the requirements of Section 10 of the Securities Act; neither the Company nor the Underwriter is disqualified, by reason of subsection (f) or (g) of Rule 164 under the Securities Act, from using, in connection with the offer and sale of the Shares, free writing prospectuses pursuant to Rules 164 and 433 under the Securities Act; each Permitted Free Writing Prospectus that the Company has filed, or is required to file, pursuant to Rule 433(d) under the Securities Act or that was prepared by or behalf of or used or referred to by the Company complies or will comply in all material respects with the requirements of the Securities Act; no Permitted Free Writing Prospectus conflicts with the information contained in the Registration Statement, any Preliminary Prospectus, Time of Sale Prospectus or Prospectus; and, to the Company’s knowledge, no free writing prospectus (if any) prepared by or on behalf of or used by the Underwriter contains any “issuer information” within the meaning of Rule 433(h)(2) under the Securities Act, except as contemplated by Section 7(a)(ii) hereof.

(e) The Company was not an “ineligible issuer” (as defined in Rule 405 under the Securities Act) as of the eligibility determination date for purposes of Rules 164 and 433 under the Securities Act with respect to the offering of the Shares contemplated by the Registration Statement.

(f) In accordance with Rule 5110(c)(7)(C)(i) of the Financial Industry Regulatory Authority (“FINRA”), the Shares have been registered with the Commission on Form S-3 under the Securities Act pursuant to the standards for such Form S-3 in effect prior to October 21, 1992.

(g) The Common Stock is listed on the NASDAQ Global Select Market (“NASDAQ”), and the Company has not received any notice from the NASDAQ regarding the delisting of such shares from the NASDAQ. The Shares are duly listed, and admitted and authorized for trading, subject to official notice of issuance, on the NASDAQ. To the Company’s knowledge, there are no affiliations or associations between (i) any member of the FINRA and (ii) the Company or any of the Company’s officers, directors or 5% or greater security holders or any beneficial owner of the Company’s unregistered equity securities that were acquired at any time on or after the 180th day immediately preceding the date the Registration Statement was initially filed with the Commission, except as disclosed in the Registration Statement (excluding the exhibits thereto), the Time of Sale Prospectus and the Prospectus.

(h) The Company has been duly incorporated, is validly existing as a corporation in active status under the laws of the jurisdiction of its incorporation, has the corporate power and authority to own its property and to conduct its business as described in the Time of Sale Prospectus and is duly qualified to transact business and is in good standing (or similar status) in each jurisdiction in which the conduct of its business or its ownership or leasing of property requires such qualification, except to the extent that the failure to be so qualified or be in good standing would not (i) have a material adverse effect on the assets, business, condition (financial or otherwise) or results of operation of the Company and its subsidiaries, taken as a whole, (ii) prevent or materially interfere with the authority or ability of the Company to perform its obligations in all material respects under this agreement or the consummation of the transactions contemplated hereby, or (iii) result in the delisting of shares of Common Stock from the NASDAQ (the occurrence of any such effect, prevention, interference or result described in the foregoing clauses (i), (ii) or (iii) being herein referred to as a “material adverse effect”).

(i) Attached hereto as Exhibit C is a complete and correct list of all of the subsidiaries of the Company, including their jurisdiction of organization and direct equity owners. Exhibit C also identifies each subsidiary that is a “significant subsidiary” as defined in Rule 405 (each, a “Significant Subsidiary”). Each subsidiary of the Company has been duly organized, is validly existing as a corporation or limited liability company in good standing (or similar status) under the laws of the jurisdiction of its organization, has the corporate power and authority to own its property and to conduct its business as described in the Time of Sale Prospectus and is duly qualified to transact business and is in good standing (or similar status) in each jurisdiction in which the conduct of its business or its ownership or leasing of property requires such qualification, except to the extent that

the failure to be so qualified or be in good standing would not have a material adverse effect; all of the issued shares of capital stock or other equity interests of each subsidiary of the Company have been duly and validly authorized and issued, are fully paid and non-assessable and, except as set forth on Exhibit C and except for directors’ qualifying shares, are owned directly or indirectly by the Company, except as described in the Time of Sale Prospectus, free and clear of all liens, encumbrances, equities or claims. There are no outstanding options, warrants or other rights of any description, contractual or otherwise, entitling any person to subscribe for or purchase any shares of capital stock or other equity interests of any Significant Subsidiary, except as disclosed on Exhibit D hereto.

(j) This Agreement has been duly authorized, executed and delivered by the Company, and is a valid and binding agreement of the Company enforceable in accordance with its terms.

(k) The authorized and outstanding capitalization of the Company is as set forth in the Time of Sale Prospectus and will be as set forth in the Prospectus, subject, in each case, to the issuance of shares of Common Stock upon exercise of stock options disclosed as outstanding in the Time of Sale Prospectus and the Prospectus, as the case may be, and the grant of equity incentive awards under existing equity incentive plans described in the Time of Sale Prospectus and the Prospectus. The authorized capital stock of the Company conforms and will conform as to legal matters to the description thereof contained in the Time of Sale Prospectus and the Prospectus.

(l) The shares of Common Stock outstanding prior to the issuance of the Shares to be sold by the Company have been duly authorized, are validly issued, fully paid and non-assessable, have been issued in compliance in all material respects with applicable securities laws and were not issued in violation of any preemptive or similar rights. All prior offers and sales of securities by the Company were made in compliance in all materials respects with the Securities Act and all other applicable laws and regulations.

(m) The Shares to be sold by the Company have been duly authorized and, when issued and delivered in accordance with the terms of this Agreement, will be validly issued, fully paid and non-assessable, and the issuance of such Shares will not be subject to any preemptive or similar rights.

(n) Neither the execution and delivery by the Company of, nor the performance by the Company of its obligations under, this Agreement, conflict with, contravene, result in a breach or violation of, or imposition of any lien, charge or encumbrance upon any assets of the Company or any of its subsidiaries pursuant to, or constitute a default under (i) any statute, law, rule, regulation, judgment, order or decree of any governmental body, regulatory or administrative agency or court having jurisdiction over the Company or any subsidiary; (ii) the charter or bylaws of the Company or any of its Significant Subsidiaries; or (iii) any contract, agreement,

obligation, covenant or instrument to which the Company or any of its Significant Subsidiaries (or any of their respective assets) is subject or bound, except to the extent that such breach, violation, imposition or default would not have a material adverse effect.

(o) No approval, authorization, consent or order of or filing with any federal, state, local or foreign governmental or regulatory commission, board, body, authority or agency, or of or with any self-regulatory organization or other non-governmental regulatory authority (including, without limitation, the NASDAQ), or approval of the Company’s shareholders, is required in connection with the issuance and sale of the Shares or the consummation of the transactions contemplated hereby, other than (i) registration of the Shares under the Securities Act, which has been effected, (ii) filing of the Time of Sale Prospectus and the Prospectus Supplement, (iii) the filing of a supplemental listing application and related materials with the NASDAQ, (iv) any necessary qualification under the securities or blue sky laws of the various states of the United States, or other jurisdictions in which the Shares are being offered by the Underwriter, or (v) any such consents, approvals, orders and registrations or qualifications as may be required by FINRA.

(p) Neither the Company nor any Significant Subsidiary is, nor with the giving of notice or passage of time or both, would be, in violation or in breach of: (i) its respective charter or bylaws; (ii) any statute, ordinance, order, rule or regulation applicable to the Company or such Significant Subsidiary; (iii) any order or decree of any court, regulatory body, arbitrator, administrative agency or other instrumentality of the United States or other country or jurisdiction having jurisdiction over the Company or such Significant Subsidiary; or (iv) any provision of any agreement, lease, franchise, license, indenture, permit, mortgage, deed of trust, evidence of indebtedness or other instrument to which the Company or such Significant Subsidiary is a party or by which any property owned or leased by the Company or such Significant Subsidiary is bound or affected, except, in each case above, for such violations or breaches as do not or would not have a material adverse effect.

(q) There are no actions, suits, claims, investigations or proceedings pending or, to the Company’s knowledge, threatened or contemplated to which the Company or any of its subsidiaries or any of their respective directors or officers is or would be a party or of which any of their respective properties is or would be subject at law or in equity, before or by any federal, state, local or foreign governmental or regulatory commission, board, body, authority or agency, or before or by any self-regulatory organization or other non-governmental regulatory authority (including, without limitation, the NASDAQ, (i) other than any such action, suit, claim, investigation or proceeding accurately described in the Time of Sale Prospectus which, if resolved adversely to the Company or any of its subsidiaries, would not, individually or in the aggregate, have a material adverse effect or (ii) that are required to be described in the Time of Sale Prospectus and are not so described.

(r) The Company is not, and after giving effect to the offering and sale of the Shares and the application of the proceeds thereof as described in the Prospectus will not be, required to register as an “investment company” as such term is defined in the Investment Company Act of 1940, as amended.

(s) The financial statements included or incorporated by reference in the Registration Statement, the Time of Sale Prospectus and the Prospectus, together with the related notes, present fairly the consolidated financial position of the Company and its subsidiaries as of the dates indicated and the consolidated results of operations, cash flows and changes in shareholders’ equity of the Company for the periods specified and have been prepared in compliance with the requirements of the Securities Act and Exchange Act and in conformity with U.S. generally accepted accounting principles applied on a consistent basis during the periods involved; the financial statement schedules, if any, incorporated by reference into the Registration Statement, the Time of Sale Prospectus and the Prospectus present fairly, in all material respects, the information required to be stated therein on a basis consistent with the consolidated financial statements of the Company contained therein; and the other financial and statistical data contained or incorporated by reference in the Registration Statement, the Time of Sale Prospectus and the Prospectus that are derived from the Company’s financial statements and/or books and records are accurately and fairly presented and prepared on a basis consistent with the financial statements and books and records of the Company; there are no financial statements (historical or pro forma) that are required to be included or incorporated by reference in the Registration Statement, the Time of Sale Prospectus or the Prospectus that are not included or incorporated by reference as required; the Company and its subsidiaries do not have any material liabilities or obligations, direct or contingent (including any off-balance sheet obligations), not described in the Time of Sale Prospectus and the Prospectus. PricewaterhouseCoopers LLP, which has expressed its opinion with respect to the consolidated financial statements and schedules of the Company, is an independent registered public accounting firm as required by the Securities Act.

(t) All statistical or market-related data included or incorporated by reference in the Time of Sale Prospectus, the Prospectus and the Permitted Free Writing Prospectuses are based on or derived from sources that the Company reasonably believes to be reliable and accurate, and the Company has obtained the written consent to the use of such data from such sources to the extent required. Each “forward-looking statement” (within the meaning of Section 27A of the Securities Act or Section 21E of the Exchange Act) contained or incorporated by reference in the Registration Statement, the Time of Sale Prospectus, the Prospectus and the Permitted Free Writing Prospectuses has been made or reaffirmed, as of the date made or reaffirmed, with a reasonable basis and in good faith.

(u) The Company and its subsidiaries (i) are in compliance with any and all applicable federal, state and local laws and regulations relating to the protection of human health and safety, the environment or hazardous or toxic substances or

wastes, pollutants or contaminants (“Environmental Laws”), (ii) have received all permits, licenses or other approvals required of them under applicable Environmental Laws to conduct their respective businesses and (iii) are in compliance with all terms and conditions of any such permit, license or approval, except where such noncompliance with Environmental Laws, failure to receive required permits, licenses or other approvals or failure to comply with the terms and conditions of such permits, licenses or approvals would not have a material adverse effect. The Company and its subsidiaries are not subject to any costs or liabilities associated with Environmental Laws (including, without limitation, any capital or operating expenditures required for clean-up, closure of properties or compliance with Environmental Laws or any permit, license or approval, any related constraints on operating activities and any potential liabilities to third parties) which would have a material adverse effect.

(v) There are no contracts, agreements or understandings between the Company and any person granting such person the right to require the Company to file a registration statement under the Securities Act with respect to any securities of the Company or to require the Company to include such securities with the Shares registered pursuant to the Registration Statement.

(w) There is no transaction, relationship, obligation, agreement or other document required to be described in the Registration Statement, the Time of Sale Prospectus and the Prospectus or to be filed or deemed to be filed as an exhibit to the Registration Statement by the Securities Act, which has not been described or filed as required. All such contracts or agreements to which the Company or any Significant Subsidiary is a party have been duly authorized, executed and delivered by the Company or such Significant Subsidiary, constitute valid and binding agreements of the Company or such Significant Subsidiary, and are enforceable by and against the Company or such Significant Subsidiary, in accordance with the respective terms thereof.

(x) Except as disclosed in the Time of Sale Prospectus or the Prospectus, neither the Company nor any Significant Subsidiary is a party to a letter of intent, accepted term sheet or similar instrument or any binding agreement that contemplates an acquisition, disposition, transfer or sale of the assets (as a going concern) or capital stock of the Company or of any subsidiary or business unit or any similar business combination transaction which would be material to the Company and its subsidiaries taken as a whole.

(y) Subsequent to the respective dates as of which information is given in each of the Registration Statement, the Time of Sale Prospectus and the Prospectus, (i) there has not occurred any material adverse change, or any development involving a prospective material adverse change, in the assets, business, condition (financial or otherwise), management, operations or earnings of the Company and its subsidiaries, taken as a whole; (ii) the Company and its subsidiaries have not incurred any material liability or obligation, direct or contingent, nor

entered into any material transaction; (iii) the Company has not purchased any of its outstanding capital stock, nor declared, paid or otherwise made any dividend or distribution of any kind on its capital stock other than ordinary and customary dividends; and (iv) there has not been any material change in the capital stock, short-term debt or long-term debt of the Company and its Significant Subsidiaries, except in each case as described in each of the Registration Statement, the Time of Sale Prospectus and the Prospectus, respectively.

(z) The Company and its subsidiaries have good and valid title in fee simple to all real property and good and valid title to all personal property reflected as owned by them in the Company’s consolidated financial statements which is material to the business of the Company and its subsidiaries, in each case free and clear of all liens, encumbrances and defects except such as are described in the Time of Sale Prospectus or such as do not materially affect the value of such property and do not interfere with the use made and proposed to be made of such property by the Company and its subsidiaries or as sold in the ordinary course of business after the end of the period covered by such financial statements; and any real property and buildings held under lease by the Company and its subsidiaries are held by them under valid, subsisting and enforceable leases with such exceptions as are not material and do not interfere with the use made and proposed to be made of such property and buildings by the Company and its subsidiaries, in each case except as described in the Time of Sale Prospectus.

(aa) Each of the Company and its subsidiaries owns or possesses adequate rights to use all inventions, patent applications, patents, trademarks (both registered and unregistered), trade names, service names, copyrights, trade secrets and other proprietary information described in the Registration Statement, the Time of Sale Prospectus and the Prospectus as being owned, used or licensed by it or which is necessary for the conduct of, or material to, its businesses (collectively, the “Intellectual Property”), and the Company is unaware of any claim to the contrary or any challenge by any other person to the rights of the Company or any of its subsidiaries with respect to the Intellectual Property except for any claim that, if resolved adversely to the Company or any subsidiary would not have a material adverse effect. Neither the Company nor any of its subsidiaries has infringed or is infringing the intellectual property of a third party, and neither the Company nor any of its subsidiaries has received notice of a claim by a third party to the contrary, except for any claim that, if resolved adversely to the Company or any subsidiary, would not have a material adverse effect.

(bb) No material labor dispute with the employees of the Company or any of its subsidiaries exists, except as described in the Time of Sale Prospectus, or, to the knowledge of the Company, is imminent; and the Company is not aware of any existing, threatened or imminent labor disturbance by the employees of any of its principal suppliers, manufacturers or contractors that could have a material adverse effect. To the best of the Company’s knowledge, neither the Company nor any of its subsidiaries is in violation of any provision of the Employee Retirement Income Security Act of 1974, as amended, or the rules and regulations promulgated thereunder, except for such violations as would not have a material adverse effect.

(cc) The Company and each of its subsidiaries are insured by insurers of recognized financial responsibility against such losses and risks and in such amounts as are customary in the businesses in which they are engaged; neither the Company nor any of its subsidiaries has been refused any insurance coverage sought or applied for except as would not have a material adverse effect; and neither the Company nor any of its subsidiaries has any reason to believe that it will not be able to renew its existing insurance coverage as and when such coverage expires or to obtain similar coverage from similar insurers as may be necessary to continue its business at a cost that would not have a material adverse effect.

(dd) The Company and its subsidiaries possess all certificates, authorizations and permits issued by the appropriate federal, state or foreign regulatory authorities necessary to conduct their respective businesses, except as would not have a material adverse effect, and neither the Company, nor any of its subsidiaries has received any notice of proceedings relating to the revocation or modification of any such certificate, authorization or permit, which, singly or in the aggregate, if the subject of an unfavorable decision, ruling or finding, would have a material adverse effect.

(ee) Except as otherwise would not have a material adverse effect, no subsidiary of the Company is subject to any material direct or indirect prohibition on paying any dividends to the Company, on making any other distribution on such subsidiary’s capital stock, on repaying to the Company any loans or advances to such subsidiary from the Company or on transferring any of such subsidiary’s property or assets to the Company or any other subsidiary of the Company, except as described in the Time of Sale Prospectus.

(ff) The Company maintains “internal control over financial reporting” (as defined in Rules 13a-15 and 15d-15 under the Exchange Act) in compliance with the requirements of the Exchange Act. The Company’s internal control over financial reporting is a process designed by the Company’s principal executive officer and principal financial officer, or under their supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles and is effective in performing the functions for which it was established. Except as described in the Time of Sale Prospectus, since the end of the Company’s most recent audited fiscal year, there has been (i) no significant deficiency or material weakness in the design or operation of the Company’s internal control over financial reporting (whether or not remediated) which is reasonably likely to adversely affect the Company’s ability to record, process, summarize and report financial information, and (ii) no change in the Company’s internal control over financial reporting that has materially affected, or is reasonably likely to materially affect, the Company’s internal control over financial reporting.

(gg) The Company maintains “disclosure controls and procedures” (as such term is defined in Rules 13a-15 and 15d-15 under the Exchange Act) consisting of controls and other procedures designed to ensure that information the Company is required to disclose in reports it files or submits under the Exchange Act is recorded, processed, summarized and reported within the time periods specified by the Commission’s rules and forms and that such information is accumulated and communicated to management, including the Company’s Chief Executive Officer and Chief Financial Officer. The principal financial officers (or their equivalents) of the Company have made all certifications required by the Xxxxxxxx-Xxxxx Act of 2002 and any related rules and regulations promulgated by the Commission (the “Xxxxxxxx-Xxxxx Act”), and the statements made in each such certification are accurate; the Company, its subsidiaries and its directors and officers are each in compliance in all material respects with the applicable provisions of the Xxxxxxxx-Xxxxx Act.

(hh) Neither the Company nor any of its subsidiaries has sent or received any communication not subsequently rescinded regarding termination of, or intent not to renew, any of the contracts or agreements referred to or described in the Time of Sale Prospectus or the Prospectus, or referred to or described in, or filed as an exhibit to, the Registration Statement, except as would not have a material adverse effect and no such termination or non-renewal has been threatened by the Company or any of its subsidiaries or, to the Company’s knowledge, any other party to any such contract or agreement.

(ii) All tax returns required to be filed by the Company or any of its Significant Subsidiaries have been filed, and all taxes and other assessments of a similar nature (whether imposed directly or through withholding) including any interest, additions to tax or penalties applicable thereto due or claimed to be due from such entities have been timely paid, other than those being contested in good faith and for which adequate reserves have been provided, or that would not have a material adverse effect.

(jj) Neither the Company nor any of its subsidiaries nor, to the knowledge of the Company, any director, officer, agent, employee or affiliate of the Company or any of its subsidiaries is aware of or has taken any action, directly or indirectly, that would result in a violation by such persons of the Foreign Corrupt Practices Act of 1977, as amended, and the rules and regulations thereunder; and the Company and its subsidiaries have instituted and maintain policies and procedures designed to ensure continued compliance therewith, including without limitation a system of internal accounting controls sufficient to provide reasonable assurances that (i) transactions are executed in accordance with management’s general or specific authorization, (ii) transactions are recorded as necessary to permit preparation of financial statements in conformity with generally accepted accounting principles and to maintain accountability for assets, (iii) access to assets is permitted only in accordance with management’s general or specific authorization, and (iv) the recorded accountability for assets is compared with the existing assets at reasonable intervals and appropriate action is taken with respect to any differences.

(kk) Except as described in the Time of Sale Prospectus, the Company has not sold, issued or distributed any shares of Common Stock during the six-month period preceding the date hereof, including any sales pursuant to Rule 144A under, or Regulation D or S of, the Securities Act, other than shares issued pursuant to employee benefit plans, qualified equity incentive plans or other employee compensation plans or pursuant to outstanding options, rights or warrants.

2. Agreements to Sell and Purchase. The Company hereby agrees to issue and sell 2,260,000 Shares to the Underwriter at a price of $11.34 per share (the “Purchase Price”), and the Underwriter, upon the basis of the representations and warranties herein contained, but subject to the conditions herein set forth, agrees to purchase from the Company at the Purchase Price the number of Firm Shares (subject to such adjustments to eliminate fractional shares as the Manager may determine) set forth opposite the name of such Underwriter set forth in Schedule I hereto.

Moreover, the Company hereby agrees to issue and sell up to 339,000 Additional Shares to the Underwriter at the Purchase Price, and the Underwriter, upon the basis of the representations and warranties contained herein, but subject to the terms and conditions herein set forth, shall have the right (but not the obligation) to purchase up to the Additional Shares at the Purchase Price. The Manager may exercise this right on behalf of the Underwriter in whole or from time to time in part by giving written notice not later than 30 days after the date of this Agreement. Any exercise notice shall specify the number of Additional Shares to be purchased by the Underwriter and the date on which such shares are to be purchased. Each purchase date must be at least one business day after the written notice is given and may not be earlier than the closing date for the Firm Shares or later than ten business days after the date of such notice. Additional Shares may be purchased as provided in Section 4 hereof solely for the purpose of covering over-allotments made in connection with the offering of the Firm Shares. On each day, if any, that Additional Shares are to be purchased (an “Option Closing Date”), the Underwriter agrees, severally and not jointly, to purchase the number of Additional Shares (subject to such adjustments to eliminate fractional shares as the Manager may determine) that bears the same proportion to the total number of Additional Shares to be purchased on such Option Closing Date as the number of Firm Shares set forth in Schedule I hereto opposite the name of such Underwriter bears to the total number of Firm Shares.

3. Terms of Public Offering. The Company is advised by the Manager that the Underwriter proposes to make a public offering of the Shares as soon after this Agreement has become effective as in the Manager’s judgment is advisable. The Company is further advised by the Manager that the Shares are to be offered to the public initially at $12.00 per share (the “Public Offering Price”).

4. Payment and Delivery. Payment for the Firm Shares to be sold by the Company shall be made to the Company in Federal or other funds immediately available in Boston, Massachusetts against delivery of such Firm Shares for the account of the Underwriter at 11:00 a.m., Eastern Time, on August 21, 2009 or at such other time on the same or such other date, not later than ten business days after the date hereof as the Manager and the Company may agree. The time and date of such payment are hereinafter referred to as the “Closing Date.”

Payment for any Additional Shares shall be made to the Company in Federal or other funds immediately available in Boston, Massachusetts against delivery of such Additional Shares for the respective accounts of the Underwriter at 11:00 a.m., Eastern Time, on the date specified in the corresponding notice described in Section 2 or at such other time on the same or on such other date, in any event not later than ten business days after the expiration of the notice, as the Manager and the Company shall agree.

The Firm Shares and Additional Shares shall be registered in such names and in such denominations as the Manager shall request in writing not later than one full business day prior to the Closing Date or the applicable Option Closing Date, as the case may be. The Firm Shares and Additional Shares shall be delivered to the Manager on the Closing Date or an Option Closing Date, as the case may be, for the respective accounts of the Underwriter, with any transfer taxes payable in connection with the transfer of the Shares to the Underwriter duly paid, against payment of the Purchase Price therefor.

5. Conditions to the Underwriter’s Obligations. The several obligations of the Underwriter are subject to the condition that all representations and warranties on the part of the Company contained in this Agreement are, on the date hereof, on the Closing Date and on each Option Closing Date, if any, true and correct, the condition that the Company has performed its obligations required to be performed prior to the Closing Date and the following further conditions:

(a) Subsequent to the execution and delivery of this Agreement and prior to the Closing Date and each Option Closing Date, if any:

(i) there shall not have occurred any downgrading, nor shall any notice have been given of any intended or potential downgrading or of any review for a possible change that does not indicate the direction of the possible change, in the rating (if any) accorded any of the securities of the Company or any of its subsidiaries by any “nationally recognized statistical rating organization,” as such term is defined for purposes of Rule 436(g)(2) under the Securities Act; and

(ii) there shall not have occurred any change, or any development involving a prospective change, in the assets, business, condition (financial or otherwise), management, operations, earnings or prospects of the Company

and its subsidiaries, taken as a whole, from that set forth in the Time of Sale Prospectus that, in the Manager’s good faith judgment, is material and adverse and that makes it, in the Manager’s good faith judgment, impracticable or inadvisable to offer or sell the Shares on the terms and in the manner contemplated in the Time of Sale Prospectus.

(b) The Underwriter shall have received on the Closing Date and each Option Closing Date, if any, a certificate, dated the Closing Date or such Option Closing Date, as the case may be, and signed by the Chief Executive Officer and Chief Financial Officer of the Company, to the effect that the representations and warranties of the Company contained in this Agreement are true and correct as of the Closing Date or such Option Closing Date, as the case may be, and that the Company has complied in all material respects with all of the agreements and satisfied all of the conditions on its part to be performed or satisfied hereunder on or before the Closing Date or such Option Closing Date, as the case may be. The delivery of the certificate provided for in this Section 5(b) shall constitute a representation and warranty of the Company as to the statements made in such certificate.

(c) The Underwriter shall have received on the Closing Date and each Option Closing Date, if any, an opinion of Xxxxx & Xxxxxxxxx, LLP, outside counsel for the Company, dated the Closing Date or such Option Closing Date, as the case may be, in form and substance reasonably satisfactory to counsel for the Underwriter to the effect set forth in Exhibit A hereto. In rendering such opinion, Xxxxx & Xxxxxxxxx, LLP, may rely as to matters of fact (but not as to legal conclusions), to the extent they deem proper, on certificates of responsible officers of the Company and its subsidiaries and of public officials. The opinion of Xxxxx & Xxxxxxxxx, LLP shall be rendered to the Underwriter at the request of the Company and shall so state therein.

(d) The Underwriter shall have received on the Closing Date and each Option Closing Date, if any, an opinion of Xxxxx & Lardner LLP, counsel for the Underwriter, dated the Closing Date or such Option Closing Date, as the case may be, in form and substance reasonably satisfactory to the Underwriter. In rendering such opinion, Xxxxx & Xxxxxxx LLP, may rely as to matters of fact (but not as to legal conclusions), to the extent they deem proper, on certificates of responsible officers of the Company and its subsidiaries and of public officials.

(e) The Underwriter shall have received, on each of the date hereof, the Closing Date and each Option Closing Date, if any, a letter dated the date hereof, the Closing Date or the Option Closing Date, as the case may be, in form and substance satisfactory to the Underwriter, from PricewaterhouseCoopers LLP, independent public accountants, containing statements and information of the type ordinarily included in accountants’ “comfort letters” to underwriters with respect to the financial statements and certain financial information contained in the Registration Statement, the Time of Sale Prospectus and the Prospectus; provided that the letter delivered on the Closing Date shall use a “cut-off date” not earlier than the date hereof.

(f) No stop order suspending the effectiveness of the Registration Statement or preventing or suspending the use of any Preliminary Prospectus, the Time of Sale Prospectus or the Prospectus shall have been issued, and no proceedings for such purpose shall have been instituted or threatened by the Commission; no notice of objection of the Commission to the use of the Registration Statement shall have been received; and all requests for additional information on the part of the Commission shall have been complied with to the Manager’s satisfaction.

(g) The “lock-up” agreements, each substantially in the form of Exhibit B hereto, between the Manager and the executive officers and directors of the Company relating to sales and certain other dispositions of shares of Common Stock or certain other securities, delivered to the Manager on or before the date hereof, shall be in full force and effect on the Closing Date.

(h) The Shares shall have been approved for listing on the NASDAQ subject to notice of issuance.

The several obligations of the Underwriter to purchase Additional Shares hereunder are subject to the delivery to the Manager on the applicable Option Closing Date of such documents as the Manager may reasonably request, including certificates of officers of the Company, legal opinions and an accountants’ comfort letter, and other matters related to the issuance of such Additional Shares.

6. Covenants of the Company. The Company covenants with the Underwriter as follows:

(a) To furnish to the Manager, without charge, two signed copies of the Registration Statement (including exhibits thereto) and to furnish to the Manager in Boston, Massachusetts, without charge, prior to 11:00 a.m. Eastern Time on the business day next succeeding the date of this Agreement and during the period mentioned in Section 6(f) or 6(g) below, as many copies of the Time of Sale Prospectus, the Prospectus and any supplements and amendments thereto or to the Registration Statement as the Manager may request.

(b) Before amending or supplementing the Registration Statement, the Time of Sale Prospectus or the Prospectus, to furnish to the Manager a copy of each such proposed amendment or supplement and not to file any such proposed amendment or supplement to which the Manager objects, and to file with the Commission within the applicable period specified in Rule 424(b) under the Securities Act any prospectus required to be filed pursuant to such Rule.

(c) To furnish to the Manager a copy of each proposed free writing prospectus to be prepared by or on behalf of, used by, or referred to by the Company and not to use or refer to any proposed free writing prospectus to which the Manager reasonably objects.

(d) Not to take any action that would result in the Underwriter or the Company being required to file with the Commission pursuant to Rule 433(d) under the Securities Act a free writing prospectus prepared by or on behalf of the Underwriter that the Underwriter otherwise would not have been required to file thereunder.

(e) To advise the Manager promptly of any request by the Commission for amendments or supplements to the Registration Statement, Base Prospectus, any Preliminary Prospectus, Prospectus Supplement or Prospectus or for additional information with respect thereto, or of notice of institution of proceedings for, or the entry of a stop order, suspending the effectiveness of the Registration Statement or preventing or suspending the use of any Preliminary Prospectus, the Time of Sale Prospectus or the Prospectus; and if the Commission should enter such a stop order, to use its best efforts to obtain the lifting or removal of such order as soon as possible.

(f) If the Time of Sale Prospectus is being used to solicit offers to buy the Shares at a time when the Prospectus is not yet available to prospective purchasers and any event shall occur or condition exist as a result of which it is necessary to amend or supplement the Time of Sale Prospectus in order to make the statements therein, in the light of the circumstances, not misleading, or if any event shall occur or condition exist as a result of which the Time of Sale Prospectus conflicts with the information contained in the Registration Statement then on file, or if, in the good faith opinion of counsel for the Underwriter, it is necessary to amend or supplement the Time of Sale Prospectus to comply with applicable law, forthwith to prepare, file with the Commission and furnish, at its own expense, to the Underwriter and to any dealer upon request, either amendments or supplements to the Time of Sale Prospectus so that the statements in the Time of Sale Prospectus as so amended or supplemented will not, in light of the circumstances when delivered to a prospective purchaser, be misleading or so that the Time of Sale Prospectus, as amended or supplemented, will no longer conflict with the Registration Statement, or so that the Time of Sale Prospectus, as amended or supplemented, will comply with applicable law.

(g) If, during such period after the first date of the public offering of the Shares as in the good faith opinion of counsel for the Underwriter the Prospectus (or in lieu thereof the notice referred to in Rule 173(a) under the Securities Act) is required by law to be delivered in connection with sales by an Underwriter or dealer, any event shall occur or condition exist as a result of which it is necessary to amend or supplement the Prospectus in order to make the statements therein, in the light of the circumstances when the Prospectus (or in lieu thereof the notice referred to in

Rule 173(a) under the Securities Act) is delivered to a purchaser, not misleading, or if, in the good faith opinion of counsel for the Underwriter, it is necessary to amend or supplement the Prospectus to comply with applicable law, forthwith to prepare, file with the Commission and furnish, at its own expense, to the Underwriter and to the dealers (whose names and addresses Manager will furnish to the Company) to which Shares may have been sold by Manager on behalf of the Underwriter and to any other dealers upon request, either amendments or supplements to the Prospectus so that the statements in the Prospectus as so amended or supplemented will not, in the light of the circumstances when the Prospectus (or in lieu thereof the notice referred to in Rule 173(a) under the Securities Act) is delivered to a purchaser, be misleading or so that the Prospectus, as amended or supplemented, will comply with applicable law.

(h) If, at any time during the period when a prospectus is required by the Securities Act to be delivered (whether physically or through compliance with Rule 172 under the Securities Act or any similar rule) in connection with any sale of Shares, the Registration Statement shall cease to comply with the requirements of the Securities Act with respect to eligibility for the use of the form on which the Registration Statement was filed with the Commission, to (i) promptly notify the Manager, (ii) promptly file with the Commission a new registration statement under the Securities Act, relating to the Shares, or a post-effective amendment to the Registration Statement, which new registration statement or post-effective amendment shall comply with the requirements of the Securities Act and shall be in a form reasonably satisfactory to the Manager, (iii) use its reasonable best efforts to cause such new registration statement or post-effective amendment to become effective under the Securities Act as soon as practicable, (iv) reasonably promptly notify the Manager of such effectiveness and (v) take all other action necessary or appropriate to permit the public offering and sale of the Shares to continue as contemplated in the Prospectus; all references herein to the Registration Statement shall be deemed to include each such new registration statement or post-effective amendment, if any;

(i) To file within the time period required by the Commission all reports and any definitive proxy or information statements required to be filed by the Company with the Commission pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act subsequent to the date of the Prospectus and for so long as the delivery of a prospectus (or, in lieu thereof, the notice referred to in Rule 173(a) under the Securities Act) is required in connection with the offering or sale of the Shares (the “Prospectus Delivery Period”).

(j) Promptly to furnish such information or to take such action as the Manager may reasonably request and otherwise to qualify the Shares for offer and sale under the securities or “blue sky” laws of such jurisdictions as the Manager shall reasonably request, and to comply with such laws so as to permit the continuance of sales and dealings therein in such jurisdictions for as long as may be necessary to complete the distribution of the Shares; provided, however, that the Company shall

not be required to qualify as a foreign corporation or to file a consent to service of process in any jurisdiction (excluding service of process with respect to the offer and sale of the Shares); and to promptly advise the Manager of the receipt by the Company of any notification with respect to the suspension of the qualification of the Shares for offer or sale in any jurisdiction or the initiation or threatening of any proceeding for such purpose.

(k) To make generally available to the Company’s security holders and to the Manager as soon as practicable an earning statement covering a period of at least twelve months beginning after the effective date of the Registration Statement (as defined in Rule 158(c) under the Securities Act), which shall satisfy the provisions of Section 11(a) of the Securities Act and Rule 158 thereunder.

(l) To use its best efforts to cause the Shares to be listed on the NASDAQ and to maintain the listing of the Common Stock, including the Shares, on the NASDAQ.

(m) During the period beginning on the date of the Underwriting Agreement and continuing to and including 60 days after the date of the Prospectus, and without the prior written consent of Xxxxx with the authorization to release the lock-up letter on behalf of the Underwriter, not to (i) to issue, offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock, (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether such transaction described in clause (i) or (ii) above is to be settled by delivery of the Common Stock or such other securities, in cash or otherwise, (iii) file any registration statement with the Commission relating to the offering of any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock, or (iv) publicly announce an intention to effect any transaction specified in clause (i), (ii) or (iii). The restrictions contained in the preceding sentence shall not apply to (i) the Shares to be sold hereunder, (ii) the grant of equity awards pursuant to the Company’s equity incentive plans under the terms of such plans in effect on the date hereof, provided such equity awards are granted consistent with the Company’s past practice, (iii) the net exercises of options under the Company’s equity incentive plans to the extent that such net exercises may be deemed dispositions of shares of Common Stock, or to the withholding of shares to pay income taxes upon the vesting of restricted shares of Common Stock, or (iv) the issuance by the Company of shares of Common Stock upon the exercise of an option, or stock appreciation right or the conversion of a security outstanding on the date of the Underwriting Agreement which have been disclosed in the Time of Sale Prospectus. Notwithstanding the foregoing, if (1) during the last 17 days of the 60-day restricted period the Company issues an earnings release or material news or a material event relating to the Company occurs; or (2) prior to the expiration of the 60-day

restricted period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the 60-day period, the restrictions imposed by this agreement shall continue to apply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event. The Company shall promptly notify Xxxxx of any earnings release, news or event that may give rise to an extension of the initial 60-day restricted period.

(n) To prepare, if the Manager so requests, a final term sheet relating to the offering of the Shares, containing only information that describes the final terms of the Shares or the offering in a form consented to by the Manager, and to file such final term sheet within the period required by Rule 433(d)(5)(ii) under the Securities Act following the date the final terms have been established for the offering of the Shares.

(o) To pay the fees applicable to the Registration Statement in connection with the offering of the Shares within the time required by Rule 457(r) under the Securities Act.

(p) To comply with Rule 433(d) under the Securities Act (without reliance on Rule 164(b) under the Securities Act) and with Rule 433(g) under the Securities Act.

(q) Not to take, directly or indirectly, any action designed, or which will constitute, or has constituted, or might reasonably be expected to cause or result in the stabilization or manipulation of the price of any security of the Company to facilitate the sale or resale of the Shares.

(r) Not, at any time at or after the execution of this Agreement, to offer or sell any Shares by means of any “prospectus” (within the meaning of the Securities Act) or use any “prospectus” (within the meaning of the Securities Act) in connection with the offer or sale of the Shares, except in each case other than the Prospectus.

(s) To maintain a transfer agent and, if necessary under the jurisdiction of incorporation of the Company, a registrar for the Common Stock.

(t) To apply the net proceeds to the Company from the sale of the Shares in the manner set forth under the caption “Use of Proceeds” in the Prospectus Supplement.

7. Agreements of the Underwriter. The Underwriter covenants with the Company as to the following:

(a) It has not and will not use, authorize use of, refer to, or participate in the planning for use of, any “free writing prospectus” (which term includes use of any written information furnished to the Commission by the Company and not

incorporated by reference into the Registration Statement or any press release issued by the Company) other than a free writing prospectus that (i) is not an “issuer free writing prospectus” (as defined in Rule 433 under the Securities Act) and (ii) contains only (A) information describing the preliminary terms of the Shares or their offering, (B) information permitted under Rule 134 under the Securities Act or (C) information that describes the final terms of the Shares or their offering and that is included in the final term sheet of the Company; provided that if the Underwriter uses such term sheet, the Underwriter shall notify the Company and provide a copy of such term sheet to the Company, prior to, or substantially concurrently with, the first use of such term sheet; provided further that Underwriter may use any underwriter free writing prospectus approved by the Company in advance in writing and that the Underwriter may use a term sheet substantially in the form of numbered point 2 on Schedule II without the consent of the Company.

(b) (i) It has not offered or sold and will not offer or sell any Shares to persons in the United Kingdom except to persons whose ordinary activities involve them in acquiring, holding, managing or disposing of investments (as principal or agent) for the purposes of their businesses or otherwise in circumstances which have not resulted and will not result in an offer of transferable securities to the public in the United Kingdom within the meaning of Section 102B of the Financial Services and Markets Xxx 0000 (“FSMA”); (ii) it has only communicated or caused to be communicated and will only communicate or cause to be communicated any invitation or inducement to engage in investment activity (within the meaning of Section 21 of the FSMA) received by it in connection with the issue or sale of any Shares in circumstances in which Section 21(l) of the FSMA does not apply to the Company or in which the communication is exempt under the Financial Services and Markets Xxx 0000 (Financial Promotions) Order 2005; and (iii) it has complied and will comply with all applicable provisions of the FSMA with respect to anything done by it in relation to the Shares in, from or otherwise involving the United Kingdom.

(c) In relation to each Member State of the European Economic Area which has implemented the Prospectus Directive (each, a “Relevant Member State”), and on and after the date on which the Prospectus Directive is implemented in that Relevant Member State (the “Relevant Implementation Date”), it has not made and will not make an offer of Shares to the public in that Relevant Member State prior to the publication of a prospectus in relation to the Shares which has been approved by the competent authority in that Relevant Member State or, where appropriate, approved in another Relevant Member State and notified to the competent authority in that Relevant Member State, all in accordance with the Prospectus Directive, except that it may, on and after the Relevant Implementation Date, make an offer of Shares to the public in that Relevant Member State at any time:

(i) to legal entities which are authorized or regulated to operate in the financial markets or, if not so authorized or regulated, whose corporate purpose is solely to invest in securities;

(ii) to any legal entity which has two or more of (1) an average of at least 250 employees during the last financial year; (2) a total balance sheet of more than €43,000,000 and (3) an annual net turnover of more than €50,000,000, as shown in its last annual or consolidated accounts; or

(iii) in any other circumstances which do not require the publication by the Company of a prospectus pursuant to Article 3 of the Prospectus Directive.

(d) For the purposes of this provision, the expression an “offer of shares of Shares to the public” in relation to any Shares in any Relevant Member State means the communication in any form and by any means of sufficient information on the terms of the offer and the Shares to be offered so as to enable an investor to decide to purchase or subscribe for the Shares, as the same may be varied in that Relevant Member State by any measure implementing the Prospectus Directive in that Relevant Member State and the expression “Prospectus Directive” means Directive 2003/71/EC and includes any relevant implementing measure in each Relevant Member State.

(e) It has not offered or sold and will not offer or sell any Shares to persons in Canada except in material compliance with the securities registration laws of Ontario, Canada.

(f) It is not subject to any pending proceeding under Section 8A of the Securities Act with respect to the offering (and will promptly notify the Company if any such proceeding against it is initiated during the Prospectus Delivery Period)

8. Expenses. Whether or not the transactions contemplated in this Agreement are consummated or this Agreement is terminated, the Company agrees to pay or cause to be paid all expenses incident to the performance of its obligations under this Agreement, including: (i) the fees, disbursements and expenses of the Company’s counsel and the Company’s accountants in connection with the registration and delivery of the Shares under the Securities Act and all other fees or expenses in connection with the preparation and filing of the Registration Statement, any Preliminary Prospectus, the Time of Sale Prospectus, the Prospectus, any free writing prospectus prepared by or on behalf of, used by, or referred to by the Company and amendments and supplements to any of the foregoing, including all printing costs associated therewith, and the mailing, shipping and delivering of copies thereof to the Underwriter and dealers, in the quantities hereinabove specified during the Prospectus Delivery Period, (ii) all costs and expenses related to the transfer and delivery of the Shares to the Underwriter, including any transfer or other taxes payable thereon, (iii) the cost of printing or producing any securities or blue

sky memorandum in connection with the offer and sale of the Shares under the securities laws of the jurisdictions in which the Shares may be offered or sold and all expenses in connection with the qualification of the Shares for offer and sale under such securities laws as provided in Section 6(l) hereof, including filing fees and the reasonable fees and disbursements of counsel for the Underwriter in connection with such qualification and in connection with the Blue Sky or Legal Investment memorandum, (iv) all costs and expenses incident to listing the Shares on the NASDAQ, (v) the cost of printing certificates representing the Shares, (vi) the costs and charges of any transfer agent, registrar or depositary, (vii) the costs and expenses of the Company relating to investor presentations on any “road show” undertaken in connection with the marketing of the offering of the Shares, including, without limitation, expenses associated with the preparation or dissemination of any road show, expenses associated with the production of road show slides and graphics, fees and expenses of any consultants engaged in connection with the road show presentations with the prior approval of the Company, travel and lodging expenses of the representatives and officers of the Company and any such consultants, (except to the extent provided in the following paragraph), (viii) the document production charges and expenses associated with printing this Agreement, (ix) all expenses in connection with any offer and sale of the Shares outside of the United States, including filing fees and the reasonable fees and disbursements of counsel for the Underwriter in connection with offers and sales outside of the United States, and (x) all other costs and expenses incident to the performance of the obligations of the Company hereunder for which provision is not otherwise made in this Section.

The Underwriter will pay all of its costs and expenses, including fees and disbursements of its counsel (including but not limited to any travel and lodging expenses of the Underwriter’s representatives in connection with the road show), stock transfer taxes payable on resale of any of the Shares by them and any advertising expenses connected with any offers they may make. Notwithstanding the above, if the sale of the Shares provided for herein is not consummated because any condition to the obligations of the Underwriter set forth in Section 5 is not satisfied, because of any termination of this Agreement by the Underwriter pursuant to Section 10 hereof or because of any refusal, inability or failure on the part of the Company to perform any obligation or covenant hereunder or comply with any provision hereof other than by reason of a default by the Underwriter, the Company will reimburse the Underwriter through the Manager on demand for all out-of-pocket expenses (including reasonable fees and disbursements of counsel) reasonably incurred by the Underwriter in connection with this Agreement or the offering contemplated hereby.

9. Indemnity and Contribution. (a) The Company agrees to indemnify and hold harmless the Underwriter, each person, if any, who controls the Underwriter within the meaning of either Section 15 of the Securities Act or Section 20 of the Exchange Act, and each affiliate of the Underwriter within the meaning of Rule 405 under the Securities Act from and against any and all losses, claims, damages and

liabilities (including, without limitation, any legal or other expenses reasonably incurred in connection with defending or investigating any such action or claim) caused by, arising out of or based upon (i) any untrue statement or alleged untrue statement of a material fact contained in the Registration Statement or any amendment thereof, or any omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, or (ii) any untrue statement or alleged untrue statement of a material fact contained in any Preliminary Prospectus, the Time of Sale Prospectus, any issuer free writing prospectus as defined in Rule 433(h) under the Securities Act, any issuer information that the Company has filed, or is required to file, pursuant to Rule 433(d) of the Securities Act, any road show not constituting a free writing prospectus, or the Prospectus or any amendment or supplement thereto, or any omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein, in light of the circumstances in which there were made, not misleading; provided, however, that the Company shall not be liable under this Section 9(a) to the extent that such losses, claims, damages or liabilities are caused by, arise out of or are based upon any such untrue statement or omission or alleged untrue statement or omission made therein in reliance upon and in conformity with information relating to the Underwriter furnished to the Company in writing by such Underwriter through the Manager expressly for use therein.

(b) The Underwriter agrees to indemnify and hold harmless the Company, the directors of the Company, the officers of the Company who sign the Registration Statement and each person, if any, who controls the Company within the meaning of either Section 15 of the Securities Act or Section 20 of the Exchange Act from and against any and all losses, claims, damages and liabilities (including, without limitation, any legal or other expenses reasonably incurred in connection with defending or investigating any such action or claim) caused by, arising from or based upon (i) any untrue statement or alleged untrue statement of a material fact contained in the Registration Statement or any amendment thereof or any omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, or (ii) any untrue statement or alleged untrue statement of a material fact contained in any Preliminary Prospectus, the Time of Sale Prospectus, any issuer free writing prospectus as defined in Rule 433(h) under the Securities Act, any Company information that the Company has filed, or is required to file, pursuant to Rule 433(d) of the Securities Act, any road show not constituting a free writing prospectus, or the Prospectus or any amendment or supplement thereto, or any omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein, in light of the circumstances in which there were made, not misleading, in each case to the extent, but only to the extent, that such untrue statement or omission or alleged untrue statement or omission was made therein in reliance upon and in conformity with information relating to the Underwriter furnished to the Company in writing by such Underwriter through the Manager expressly for use therein.

(c) In case any proceeding (including any governmental investigation) shall be instituted involving any person in respect of which indemnity may be sought pursuant to Section 9(a) or 9(b) such person (the “indemnified party”) shall promptly notify the person against whom such indemnity may be sought (the “indemnifying party”) in writing and the indemnifying party, upon request of the indemnified party, shall retain counsel reasonably satisfactory to the indemnified party to represent the indemnified party and any others the indemnifying party may designate in such proceeding and shall pay the fees and disbursements of such counsel related to such proceeding. In any such proceeding, any indemnified party shall have the right to retain its own counsel, but the fees and expenses of such counsel shall be at the expense of such indemnified party unless (i) the indemnifying party and the indemnified party shall have mutually agreed to the retention of such counsel or (ii) the named parties to any such proceeding (including any impleaded parties) include both the indemnifying party and the indemnified party and representation of both parties by the same counsel would be inappropriate due to actual or potential differing interests between them. It is understood that the indemnifying party shall not, in respect of the legal expenses of any indemnified party in connection with any proceeding or related proceedings in the same jurisdiction, be liable for (i) the fees and expenses of more than one separate firm (in addition to any local counsel) for the Underwriter and all persons, if any, who control the Underwriter within the meaning of either Section 15 of the Securities Act or Section 20 of the Exchange Act or who are affiliates of the Underwriter within the meaning of Rule 405 under the Securities Act, and (ii) the fees and expenses of more than one separate firm (in addition to any local counsel) for the Company, its directors, its officers who sign the Registration Statement and each person, if any, who controls the Company within the meaning of either such Section, and that all such fees and expenses shall be reimbursed as they are incurred. In the case of any such separate firm for the Underwriter and such control persons and affiliates of the Underwriter, such firm shall be designated in writing by Baird. In the case of any such separate firm for the Company, and such directors, officers and control persons of the Company, such firm shall be designated in writing by the Company. The indemnifying party shall not be liable for any settlement of any proceeding effected without its written consent, but if settled with such consent or if there be a final judgment for the plaintiff, the indemnifying party agrees to indemnify the indemnified party from and against any loss or liability by reason of such settlement or judgment. Notwithstanding the foregoing sentence, if at any time an indemnified party shall have requested an indemnifying party to reimburse the indemnified party for fees and expenses of counsel as contemplated by the second and third sentences of this paragraph, the indemnifying party agrees that it shall be liable for any settlement of any proceeding effected without its written consent if (i) such settlement is entered into more than 30 days after receipt by such indemnifying party of the aforesaid request and (ii) such indemnifying party shall not have reimbursed the indemnified party in accordance with such request prior to the date of such

settlement. No indemnifying party shall, without the prior written consent of the indemnified party, effect any settlement of any pending or threatened proceeding in respect of which any indemnified party is or could have been a party and indemnity could have been sought hereunder by such indemnified party, unless such settlement includes an unconditional release of such indemnified party from all liability on claims that are the subject matter of such proceeding.

(d) To the extent the indemnification provided for in Section 9(a) or 9(b) is unavailable to an indemnified party or insufficient in respect of any losses, claims, damages or liabilities referred to therein, then each indemnifying party under such paragraph, in lieu of indemnifying such indemnified party thereunder, shall contribute to the amount paid or payable by such indemnified party as a result of such losses, claims, damages or liabilities (i) in such proportion as is appropriate to reflect the relative benefits received by the indemnifying party or parties on the one hand and the indemnified party or parties on the other hand from the offering of the Shares or (ii) if the allocation provided by clause (i) above is not permitted by applicable law, in such proportion as is appropriate to reflect not only the relative benefits referred to in clause (i) above but also the relative fault of the indemnifying party or parties on the one hand and of the indemnified party or parties on the other hand in connection with the statements or omissions that resulted in such losses, claims, damages or liabilities, as well as any other relevant equitable considerations. The relative benefits received by the Company on the one hand and the Underwriter on the other hand in connection with the offering of the Shares shall be deemed to be in the same respective proportions as the net proceeds from the offering of the Shares (before deducting expenses) received by the Company and the total underwriting discounts and commissions received by the Underwriter, in each case as set forth in the table on the cover of the Prospectus, bear to the aggregate Public Offering Price of the Shares. The relative fault of the Company on the one hand and the Underwriter on the other hand shall be determined by reference to, among other things, whether the untrue or alleged untrue statement of a material fact or the omission or alleged omission to state a material fact relates to information supplied by the Company or by the Underwriter and the parties’ relative intent, knowledge, access to information and opportunity to correct or prevent such statement or omission.

(e) The Company and the Underwriter agree that it would not be just or equitable if contribution pursuant to this Section 9 were determined by pro rata allocation or by any other method of allocation that does not take account of the equitable considerations referred to in Section 9(d). The amount paid or payable by an indemnified party as a result of the losses, claims, damages and liabilities referred to in Section 9(d) shall be deemed to include, subject to the limitations set forth above, any legal or other expenses reasonably incurred by such indemnified party in connection with investigating or defending any such action or claim. Notwithstanding the provisions of this Section 9, the Underwriter shall not be required to contribute any amount in excess of the amount by which the total price at which the Shares underwritten by it and distributed to the public were offered to

the public exceeds the amount of any damages that the Underwriter has otherwise been required to pay by reason of such untrue or alleged untrue statement or omission or alleged omission. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. The remedies provided for in this Section 9 are not exclusive and shall not limit any rights or remedies which may otherwise be available to any indemnified party at law or in equity.

(f) The indemnity and contribution provisions contained in this Section 9 shall remain operative and in full force and effect regardless of (i) any termination of this Agreement, (ii) any investigation made by or on behalf of the Underwriter, any person controlling the Underwriter or any affiliate of the Underwriter, or the Company, its officers or directors or any person controlling the Company and (iii) acceptance of and payment for any of the Shares.

10. Termination. The Underwriter may terminate this Agreement by notice given by the Manager to the Company, if after the execution and delivery of this Agreement and prior to the Closing Date (a) trading generally shall have been suspended or materially limited or minimum prices shall have been established on, or by, as the case may be, any of the New York Stock Exchange, the American Stock Exchange, or the NASDAQ Global Market, (b) trading of any securities of the Company shall have been suspended or materially limited on any exchange or in any over-the-counter market, (c) a material disruption in securities settlement, payment or clearance services in the United States shall have occurred, (d) any moratorium or material limitation on commercial banking activities shall have been declared by Federal or New York state authorities, (e) there shall have occurred any outbreak or escalation of hostilities, act of terrorism involving the United States or declaration by the United States of a national emergency or war, or (f) any other calamity or crisis or any change in financial, political or economic conditions in the United States or elsewhere, if the effect of any such event specified in clause (e) or (f), in the Manager’s good faith judgment, is material and adverse and makes it, in the Manager’s good faith judgment, impracticable or inadvisable to proceed with the offer, sale or delivery of the Shares on the terms and in the manner contemplated in the Time of Sale Prospectus or the Prospectus (exclusive of any supplement thereto).

11. Effectiveness. This Agreement shall become effective upon the execution and delivery hereof by the parties hereto.

12. Representations and Indemnities to Survive. The respective agreements, representations, warranties, indemnities and other statements of the Company and the Underwriter set forth or made pursuant to this Agreement will remain in full force and effect, regardless of any investigation made by or on behalf of the Underwriter or the Company or any of the officers, directors, employees, agents or controlling persons referred to in Section 9 hereof, and will survive delivery of and payment for the Shares. The provisions of Sections 8 and 9 hereof shall survive the termination or cancellation of this Agreement.

13. Entire Agreement. (a) This Agreement, together with any contemporaneous written agreements and any prior written agreements (to the extent not superseded by this Agreement) that relate to the offering of the Shares, represents the entire agreement between the Company, on the one hand, and the Underwriter, on the other, with respect to the preparation of any Preliminary Prospectus, the Time of Sale Prospectus, the Prospectus, the conduct of the offering, and the purchase and sale of the Shares.

(b) The Company acknowledges that in connection with the offering of the Shares: (i) the Underwriter has acted at arm’s length, is not an agent of, and owes no fiduciary duties to, the Company or any other person; (ii) the Underwriter owes the Company only those duties and obligations set forth in this Agreement and prior written agreements (to the extent not superseded by this Agreement), if any; and (iii) the Underwriter may have interests that differ from those of the Company. The Company waives to the full extent permitted by applicable law any claims it may have against the Underwriter arising from an alleged breach of fiduciary duty in connection with the offering of the Shares.

14. Counterparts. This Agreement may be signed in any number of counterparts, each of which shall be an original, with the same effect as if the signatures thereto and hereto were upon the same instrument.

15. Applicable Law. This Agreement shall be governed by and construed in accordance with the internal laws of the State of New York.

16. Headings. The headings of the sections of this Agreement have been inserted for convenience of reference only and shall not be deemed a part of this Agreement.

17. Amendments or Waivers. No amendment or waiver of any provision of this Agreement, nor any consent or approval to any departure therefrom, shall in any event be effective unless the same shall be in writing and signed by the parties hereto.

18. Notices. All communications hereunder shall be in writing and effective only upon receipt and if to the Underwriter shall be delivered, mailed or sent to the Manager at Xxxxxx X. Xxxxx & Co. Incorporated, 000 Xxxx Xxxxxxxxx Xxxxxx, Xxxxxxxxx, Xxxxxxxxx 00000, Fax: (000) 000-0000 Attention: Xxxxxxx Xxxxxxx, with copies to the Legal Department, Xxxxxx X. Xxxxx & Co. Incorporated, 000 Xxxx Xxxxxxxxx Xxxxxx, Xxxxxxxxx, Xxxxxxxxx 00000, Fax: (000) 000-0000 and Xxxxx & Xxxxxxx LLP, Attention: Xxxx X. Xxxxxx, 000 Xxxxxxxxxx Xxxxxx, Xxxxxx, Xxxxxxxxxxxxx 00000, Fax: (000) 000-0000; and if to the Company shall be delivered, mailed or sent to American Dental Partners, Inc., 000 Xxxxxxxxx Xxxxx, Xxxxx 000,

Xxxxxxxxx, Xxxxxxxxxxxxx 00000, Fax: (000) 000-0000, with a copy to Xxxxx & Xxxxxxxxx, LLP, Attention: Xxx X. Xxxxxxxx, 00 Xxxx Xxxxx Xxxxxx, Xxxxx 0000, Xxxxxxxx, Xxxx 00000, Fax: (000) 000-0000.

[[The balance of this page is intentionally left blank]]

[Signature page to Underwriting Agreement]


Very truly yours,

AMERICAN DENTAL PARTNERS, INC.

By:
Name:
Title:

[Signature page to Underwriting Agreement, continued]


Accepted as of the date hereof

XXXXXX X. XXXXX & CO. INCORPORATED

By:
Name:
Title:

SCHEDULE I


Underwriter	Number of Firm Shares To Be Purchased	Number of Additional Shares To Be Purchased
Xxxxxx X. Xxxxx & Co. Incorporated	2,260,000	339,000

Total:	2,260,000	339,000

SCHEDULE II

Time of Sale Prospectus

1.	Preliminary Prospectus, including Preliminary Prospectus Supplement dated August 18, 2009 and Base Prospectus dated August 7, 2009.

2.	Orally communicated pricing information:

Number of Shares to be Sold: 2,260,000

Offering size (gross offering proceeds assuming no exercise of the over-allotment spread) : $27,120,000.00

Estimated net proceeds to the Company (after underwriting discounts and commissions and offering expenses): $25.3 million

Price per share: $12.00

Underwriting discount and commissions per share: $0.66

Trade date: August 18, 2009

Closing date: August 21, 2009

3.	Free writing prospectus containing a final term sheet, dated August 18, 2009

EXHIBIT A

FORM OF OPINION OF COMPANY’S COUNSEL

TO BE DELIVERED PURSUANT TO SECTION 5(c)

1. The Company is validly existing as a corporation in good standing under the laws of the jurisdiction of its incorporation, and has the corporate power and authority to own its property and to conduct its business as described in the Time of Sale Prospectus;

2. Each Significant Subsidiary of the Company (a “Significant US Subsidiary”) is validly existing as a corporation or limited liability company in good standing (or similar concept) under the laws of the jurisdiction of its organization, has the corporate power and authority to own its property and to conduct its business as described in the Time of Sale Prospectus, and, to such counsel’s knowledge, except such as are described in the Time of Sale Prospectus with respect to [Arizona subsidiary], the Company owns directly or indirectly and beneficially all of the issued and outstanding capital stock of each Significant US Subsidiary;

3. The Company has an authorized capitalization as set forth in the Time of Sale Prospectus and the Prospectus, and the authorized capital stock of the Company conforms in all material respects as to legal matters to the description thereof contained in each of the Time of Sale Prospectus and the Prospectus;

4. The shares of Common Stock outstanding prior to the issuance of the Shares to be sold by the Company have been duly authorized and are validly issued, fully paid and non-assessable;

5. The Shares to be sold by the Company have been duly authorized and, when issued and delivered in accordance with the terms of this Agreement, will be validly issued, fully paid and non-assessable, and the issuance of such Shares will not be subject to any preemptive or similar rights pursuant to federal or Delaware law, the terms of the Company’s Certificate of Incorporation or bylaws, or the terms of other agreements or instruments known to such counsel;

6. This Agreement has been duly authorized, executed and delivered by the Company;

7. To our knowledge after due inquiry, neither the execution and delivery by the Company of, nor the performance by the Company of its obligations under, this Agreement will conflict with, contravene, result in a breach or violation of, or imposition of any lien, charge or encumbrance upon any property or assets of the Company or any Significant US Subsidiary, or constitute a default under (i) any

statute, law, rule, regulation, judgment, order or decree of any governmental body, regulatory or administrative agency or court known to such counsel and having jurisdiction over the Company or any subsidiary; (ii) the charter or bylaws of the Company or any of its Significant Subsidiaries; or, to such counsel’s knowledge, (iii) any contract, agreement, obligation, covenant or instrument to which the Company or any of its Significant Subsidiaries (or any of their respective assets) is subject or bound, and which is filed as an exhibit to the Registration Statement; and no consent, approval, authorization or order of, or qualification with, any U.S. governmental body or agency is required for the performance by the Company of its obligations under this Agreement, except such as may be required by the securities or “blue sky” laws of the various jurisdictions in connection with the offer and sale of the Shares;

8. The statements relating to legal matters, documents or proceedings included in (A) the Base Prospectus under “Description of Capital Stock” and (B) the Registration Statement in Item 15, in each case fairly and accurately summarize in all material respects such matters, documents or proceedings;

9. The Company is not, and after giving effect to the offering and sale of the Shares and the application of the proceeds thereof as described in the Prospectus will not be, required to register as an “investment company” as such term is defined in the Investment Company Act of 1940, as amended; and

10. In the opinion of such counsel (1) each document filed pursuant to the Exchange Act and incorporated by reference in the Registration Statement, the Time of Sale Prospectus and the Prospectus (except for the financial statements and notes thereto, pro forma financial data and other financial, statistical and accounting data and related schedules included therein, as to which such counsel need not express any opinion) appeared on its face to be appropriately responsive as of its filing date in all material respects to the requirements of the Exchange Act and the applicable rules and regulations of the Commission thereunder and (2) the Registration Statement, the Time of Sale Prospectus and the Prospectus (except for the financial statements and financial schedules and other financial and statistical data included therein, as to which such counsel need not express any belief) appear on their face to be appropriately responsive in all material respects to the requirements of the Securities Act and the applicable rules and regulations of the Commission thereunder.

In rendering such opinions, such counsel may rely as to matters of fact on certificates of officers of the Company and public officials

* * *

In addition to such opinions, counsel shall state that nothing has come to the attention of such counsel that causes such counsel to believe that (1) the Registration Statement or the prospectus included therein (except for the financial statements and notes thereto, pro forma financial data and other financial, statistical and accounting data and related schedules included therein, as to which

such counsel need not express any belief) at the time the Registration Statement became effective for purposes of Section 11 of the Securities Act (as such section relates to the Underwriter) contained any untrue statement of a material fact or omitted to state a material fact required to be stated therein or necessary to make the statements therein not misleading, (2) the Time of Sale Prospectus (except for the financial statements and notes thereto, pro forma financial data and other financial, statistical and accounting data and related schedules included therein, as to which such counsel need not express any belief) as of the Time of Sale or, as amended or supplemented, if applicable, as of the Closing Date contained or contains any untrue statement of a material fact or omitted or omits to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading or (3) the Prospectus (except for the financial statements and notes thereto, pro forma financial data and other financial, statistical and accounting data and related schedules included therein, as to which such counsel need not express any belief) as of its date or, as amended or supplemented, if applicable, as of the Closing Date contained or contains any untrue statement of a material fact or omitted or omits to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading.

EXHIBIT B

[FORM OF LOCK-UP LETTER TO BE SIGNED BY

OFFICERS AND DIRECTORS]

, 2009

XXXXXX X. XXXXX & CO. INCORPORATED

000 Xxxx Xxxxxxxxx Xxxxxx

Xxxxxxxxx, Xxxxxxxxx 00000

Ladies and Gentlemen:

The undersigned understands that Xxxxxx X. Xxxxx & Co. Incorporated (“Baird”) (the “Manager”) proposes to enter into an Underwriting Agreement (the “Underwriting Agreement”) with American Dental Partners, Inc., a Delaware corporation (the “Company”), providing for the public offering (the “Public Offering”) by the Underwriter (the “Underwriter”) of [# of Shares Offered] shares (the “Shares”) of the Common Stock ($.01 Par Value) of the Company (the “Common Stock”).

To induce the Underwriter that may participate in the Public Offering to continue their efforts in connection with the Public Offering, the undersigned hereby agrees that, without the prior written consent of the Underwriter, it will not, during the period commencing on the date hereof and ending 60 days after the date of the final prospectus relating to the Public Offering (the “Restricted Period”), (1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock, (2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (1) or (2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise, (3) file any registration statement with the Commission relating to the offering of any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock, or (4) publicly announce an intention to effect any transaction specified in clause (1), (2) or (3). The foregoing sentence shall not apply to (a) transactions relating to shares of Common Stock or other securities acquired in open market transactions after the completion of the Public Offering, provided that no filing under Section 16(a) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”) shall be required or shall be voluntarily made in connection with subsequent sales of Common Stock or other securities acquired in such open market transactions, (b) transfers of shares of Common Stock or any security convertible into Common Stock as a bona fide gift, (c) transfers by will or intestate succession to the undersigned’s family or to a trust, the beneficiaries of which are exclusively the

undersigned or members of the undersigned’s family, (d) distributions of shares of Common Stock or any security convertible into Common Stock to limited partners or stockholders of the undersigned or (e) the net exercises of options under the Company’s equity incentive plans to the extent that such net exercises may be deemed dispositions of shares of Common Stock, or to the withholding of shares to pay income taxes upon the vesting of restricted shares of Common Stock,; provided that in the case of any transfer or distribution pursuant to clause (b), (c) or (d), (i) each donee or distributee shall sign and deliver a lock-up letter substantially in the form of this letter and (ii) no filing under Section 16(a) of the Exchange Act, reporting a reduction in beneficial ownership of shares of Common Stock, shall be required or shall be voluntarily made during the Restricted Period. In addition, the undersigned agrees that, without the prior written consent of the Underwriter, it will not, during the Restricted Period, make any demand for or exercise any right with respect to, the registration of any shares of Common Stock or any security convertible into or exercisable or exchangeable for Common Stock. The undersigned also agrees and consents to the entry of stop transfer instructions with the Company’s transfer agent and registrar against the transfer of the undersigned’s shares of Common Stock except in compliance with the foregoing restrictions.

If:

(1) during the last 17 days of the Restricted Period the Company issues an earnings release or material news or a material event relating to the Company occurs; or

(2) prior to the expiration of the Restricted Period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the Restricted Period;

then the restrictions imposed by this agreement shall continue to apply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event, unless Baird waives such extension in writing.

The undersigned shall not engage in any transaction that may be restricted by this agreement during the 34-day period beginning on the last day of the Restricted Period unless the undersigned requests and receives prior written confirmation from the Company that the restrictions imposed by this agreement have expired.

The undersigned understands that the Company and the Underwriter are relying upon this agreement in proceeding toward consummation of the Public Offering. The undersigned further understands that this agreement is irrevocable and shall be binding upon the undersigned’s heirs, legal representatives, successors and assigns.

Whether or not the Public Offering actually occurs depends on a number of factors, including market conditions. Any Public Offering will only be made pursuant to an Underwriting Agreement, the terms of which are subject to negotiation between the Company and the Underwriter.

Very truly yours,

(Name)

(Address)

EXHIBIT C

AMERICAN DENTAL PARTNERS, INC. SUBSIDIARIES

ADP-CFK, LLC

ADP of New York, LLC

American Dental Partners of Alabama, LLC

American Dental Partners of Arizona, LLC

American Dental Partners of California, Inc.

American Dental Partners of Louisiana, LLC

American Dental Partners of Maryland, LLC

American Dental Partners of Michigan, LLC

American Dental Partners of Minnesota, LLC

American Dental Partners of Missouri, LLC

American Dental Partners of North Carolina, LLC

American Dental Partners of Ohio, Inc.

American Dental Partners of Oklahoma, LLC

American Dental Partners of Pennsylvania, LLC

American Dental Partners of Tennessee, LLC

American Dental Partners of Texas, LLC

American Dental Partners of Virginia, LLC

American Dental Partners of Wisconsin, LLC

American Dental Professional Services, LLC

Apple Park Associates, Inc.

Care for Kids – USA, LLC

Care for Kids of Arizona, LLC

CFK of Texas, LLC

Edgewater Indemnity Company, Inc.

Focus Practice Consultants, LLC

Metropolitan Dental Holdings, Inc.

Metropolitan Dental Management, Inc.

PDHC, Ltd.

Xxxx Dental Lab, Inc.

ZetaSys, LLC

EXHIBIT D

OPTIONS TO ACQUIRE EQUITY INTERESTS IN ANY SUBSIDIARIES

The existing minority members in CFK-USA, LLC (“CFK-USA”), who currently hold a combined 15% membership interest in CFK-USA will be offered the right to acquire up to a 15% membership interest, in the aggregate, in CFK of Texas, LLC (“CFK-TX”), which is currently an indirect wholly-owned subsidiary of the Company. To acquire those interests, the minority members will be required to provide their pro rata shares of the funds requested pursuant to a capital call to be made by CFK-TX.

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2,260,000 Shares AMERICAN DENTAL PARTNERS, INC. COMMON STOCK ($.01 PAR VALUE) UNDERWRITING AGREEMENT

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