<PAGE>
 
                                                                   EXHIBIT 10(H)
                                                                                

                                AMENDMENT NO. 2
                                      TO
                        AMERICAN DENTAL PARTNERS, INC.
             AMENDED AND RESTATED 1996 DIRECTORS STOCK OPTION PLAN
             -----------------------------------------------------


     The American Dental Partners, Inc. Amended and Restated 1996 Directors
Stock Option Plan, as previously amended (the "Plan"), is hereby amended
pursuant to the following provisions:

     1.     Definitions
            -----------

     All capitalized terms used in this amendment which are not otherwise
defined herein shall have the respective meanings given such terms in the Plan.

     2.     Change in Control.
            ----------------- 

     Section 10 of the Plan is hereby deleted from the Plan in its entirety and
replaced with the following:

     (S)10. Change in Control.
            ----------------- 
 
            (a)  Accelerated Vesting and Company Purchase Option.
                 ----------------------------------------------- 

          Notwithstanding any provision of the Plan or any Stock Option
     Agreement to the contrary (unless such Stock Option Agreement contains a
     provision referring specifically to this (S)10 and stating that this (S)10
     shall not be applicable to the Option evidenced by such Stock Option
     Agreement), if a Change in Control (as defined below) occurs, then: 

               (i)  Any and all Options theretofore granted and not fully vested
          shall thereupon become vested and exercisable in full and shall remain
          so exercisable in accordance with their terms; provided that no Option
          which has previously been exercised or otherwise terminated shall
          become exercisable; and

               (ii) The Company may, at its option, terminate any or all
          unexercised Options and portions thereof not more than 30 days after
          such Change in Control; provided that the Company shall, upon such
          termination and with respect to each Option so terminated, pay to the
          optionee (or such optionee's transferee, if applicable) theretofore
          holding such Option cash in an amount equal to the difference between
          the fair market value (as defined in (S)5(b), above) of the Shares
          subject to the Option at the time the Company exercises its option
          under this (S)10(a)(ii) and the exercise price of the Option, less
          applicable withholding taxes; and provided further that if such fair
          market value is less than such exercise price, then the Board may, in
          its sole discretion, terminate such Option without any payment.
<PAGE>
 
     (b)  Definition of Change in Control.
          ------------------------------- 

     For purposes of the Plan, a "Change in Control" shall mean the happening of
any of the following:

          (i)   The direct or indirect acquisition by any "person" as defined in
     (S)3(a)(9) of the 1934 Act and as used in (S)(S)13(d) and 14(d) thereof,
     including a "group" within the meaning of (S)13(d) of the 1934 Act
     (hereinafter, simply a "Person"), of "beneficial ownership" (within the
     meaning of Rule 13d-3 under the 1934 Act) of securities of the Company
     representing more than 50% of the combined voting power of the Company's
     then outstanding voting securities entitled to vote generally in the
     election of directors of the Company (the "Company Voting Securities");
     provided that: (A) the Company, any subsidiary of the Company, any employee
     benefit plan sponsored or maintained by the Company or any subsidiary of
     the Company (including any trustee of such plan acting as trustee), any
     person who was a stockholder of the Company on the effective date of the
     Plan (an "Existing Stockholder"), and any affiliate of an Existing
     Stockholder; and (B) the provisions of this subsection (i) shall not apply
     to (1) any acquisition of securities from the Company or any of its
     subsidiaries, or (2) any acquisition of securities pursuant to a Business
     Combination (as defined below) which satisfies clauses (A), (B), and (C) of
     subsection (iii) of this (S)10(b);

          (ii)  When, during any period of 24 consecutive months during the
     existence of the Plan, the individuals who, at the beginning of such period
     constitute the Board (the "Incumbent Directors") cease for any reason other
     than death to constitute at least at least a majority of the Board;
     provided, however, that a director who was not a director at the beginning
     of such 24-month period shall be deemed to have satisfied such 24-month
     requirement (and be an Incumbent Director) if such director was elected by,
     or on the recommendation of or with the approval of, at least two-thirds of
     the directors who then qualified as Incumbent Directors either actually
     (because they were directors at the beginning of such 24-month period) or
     by prior operation of this (S)10 (b)(ii); or

          (iii)  Approval by the stockholders of the Company of a
     reorganization, merger, consolidation, or recapitalization of the Company,
     or a sale or other disposition of all or substantially all of the assets of
     the Company, or the acquisition of the assets of another corporation (any
     such transaction, a "Business Combination"), or the consummation of a
     business Combination for which stockholder approval is not obtained,
     unless, in any such case, following such Business Combination: (A) all or
     substantially all of the individuals and entities who were the beneficial
     owners of the Company Voting Securities outstanding immediately prior to
     such Business Combination beneficially own, directly or indirectly,
     immediately following such Business Combination, more than 50% of the
     combined voting power of the then outstanding voting securities entitled to
     vote generally in the election of directors of the corporation resulting
     from such Business Combination in substantially the same proportions as
     their ownership of the Company Voting Securities immediately prior to such
     Business Combination,

                                      -2-
<PAGE>
 
     and (B) at least a majority of the members of the board of directors of the
     corporation resulting from such Business Combination were Incumbent
     Directors at the time of the execution of the initial agreement, or of the
     action of the Board, providing for such Business Combination; or

          (iv)  Approval by the stockholders of the Company of a complete
     liquidation or dissolution of the Company.

     4.   Effective Date; Construction
          ----------------------------

     The effective date of this amendment is November 6, 1998, and this
amendment shall be deemed to be a part of the Plan as of such date and shall be
applicable to all Options granted prior to that date, as well as Options
hereafter granted. In the event of any inconsistencies between the provisions of
the Plan and this amendment, the provisions of this amendment shall control.
Except as modified by this amendment, the Plan shall continue in full force and
effect without change.

                                      -3-
<PAGE>
 
                                                                   EXHIBIT 10(H)
                                                                                

                                AMENDMENT NO. 3
                                      TO
                        AMERICAN DENTAL PARTNERS, INC.
             AMENDED AND RESTATED 1996 DIRECTORS STOCK OPTION PLAN
             -----------------------------------------------------

     The American Dental Partners, Inc. Amended and Restated 1996 Directors
Stock Option Plan, as previously amended by Amendment No. 1 dated October 27,
1997 and Amendment No. 2 dated November 6, 1998 (collectively, the "Plan"), is
hereby amended pursuant to the following provisions:

     1.  Definitions
         -----------

     All capitalized terms used in this amendment which are not otherwise
defined herein shall have the respective meanings given such terms in the Plan.

     2.  Shares Subject To Plan
         ----------------------

     The total number of Shares for which Options may be granted under the Plan,
as provided under (S)4 of the Plan, as previously adjusted pursuant to (S)9 of
the Plan, is increased by 25,000 Shares to a total of  85,000 Shares.

     3.  Effective Date; Construction
         ----------------------------

     The effective date of this amendment is February 26, 1999, and this
amendment shall be deemed to be a part of the Plan as of such date.  In the
event of any inconsistencies between the provisions of the Plan and this
amendment, the provisions of this amendment shall control.  Except as modified
by this amendment, the Plan shall continue in full force and effect without
change.

     This amendment shall be submitted to the stockholders of the Company for
approval as soon as reasonably practicable, but in any event not later than 12
months after the date of this amendment.  Notwithstanding the preceding
paragraph or any other provisions of this amendment to the contrary, if this
amendment is not approved by the stockholders of the Company within such 12-
month period, this amendment and all options granted with respect to the
additional shares of Common Stock subject to the Plan as a result of this
amendment shall automatically become null and void and have no further force or
effect.