Document:

<PAGE>

                                                                    Exhibit 4.17

                      RESTRICTED STOCK PURCHASE AGREEMENT
                      -----------------------------------

     THIS RESTRICTED STOCK PURCHASE AGREEMENT (this "Agreement") is dated as of
                                                     ---------
the 6th day of March, 1997, by and between OraPharma, Inc., a Delaware
corporation (the "Corporation"), and Michael Kishbauch ("Employee").
                  -----------                            --------

                              W I T N E S S E T H:
                              - - - - - - - - - -

     WHEREAS, Employee is currently the President of the Corporation; and

     WHEREAS, Employee wishes to purchase, and the Corporation wishes to sell to
Employee, 672,925 shares of the Corporation's common stock, $.001 par value per
share ("Common Stock") at a price of $.001 per share (the "OCPS"); and
        ------------                                       ----

     WHEREAS, such shares of Common Stock will be issued to Employee in order to
provide an incentive to Employee to exercise his best efforts on behalf of, and
to remain as an employee of, the Corporation, subject to the terms and
provisions of this Agreement.

     NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties do hereby agree as
follows:

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

     As used in this Agreement, the following terms shall have the following
respective meanings:

     "Common Shares" shall mean the issued and outstanding shares of the
      -------------
Corporation's Common Stock, at the applicable time.

     "Equity Stock" shall have the meaning set forth in Rule 3a11-1 under the
      ------------
Securities Exchange Act of 1934, as amended, and any successor statute and the
rules and regulations thereunder, as shall be in effect from time to time.

     "Family" shall include any spouse, lineal ancestor or descendant, or
      ------
sibling, any trust for the exclusive benefit of any of the foregoing, or any
corporation, limited partnership, limited liability company or other entity
majority controlled by any of the foregoing individuals or trusts.

     "Stockholders" shall mean the Investors and the Founders, both as defined
      ------------
in that certain Stockholders Agreement dated the date hereof by and among the
Corporation and certain stockholders of the Corporation.
<PAGE>

     "Group" shall mean as to (a) a partnership, any or all of its general or
      -----
limited partners or any "affiliate" thereof (as defined by Rule 405 promulgated
under the Securities Act), (b) a trust, any of the beneficiaries, settlers or
grantors now existing or hereafter arising of, or any Person under common
control with, such trust, (c) a corporation, any of its stockholders, any
subsidiary of such corporation or any corporation which is under common control
with such corporation, or any directors, officers or employees of such
corporation, and (d) a limited liability company, any of its members.

     "New Securities" shall mean any Equity Stock, including, but not limited
      --------------
to, shares of Common Stock, any security which is convertible into or
exercisable or exchangeable for Common Stock, or any right, option or warrant to
acquire any Common Stock of the Corporation.

     "Person" shall mean and include a natural person, a corporation, a limited
      ------
liability company, a partnership, a trust, an unincorporated organization and a
government or any department, agency or political subdivision thereof.

     "Preferred Shares" shall mean the Corporation's Series A Preferred Stock,
      ----------------
$.001 par value per share, and Series B Preferred Stock, $.001 par value per
share, issued or to be issued to certain of the Stockholders pursuant to the
Stock Purchase Agreement dated February 26, 1997 among the Corporation and such
Stockholders, as the same may be amended.

     "Pro Rata Fraction" shall mean a fraction, the numerator of which shall be
      -----------------                             ---------
the number of shares of Common Stock then owned by such Stockholder and the
denominator of which shall be the aggregate number of shares of Common Stock
-----------
then owned by all Stockholders.  For the purpose of calculating the Pro Rata
Fraction, each Preferred Share shall be deemed to represent the number of shares
of Common Stock into which the Preferred Share is then convertible.

     "Public Offering" shall mean a distribution of New Securities in a firm
      ---------------
commitment underwritten public offering to the general public pursuant to a
registration statement filed with and declared effective by the Securities and
Exchange Commission pursuant to the Securities Act.

     "Securities Act" shall mean the Securities Act of 1933, as amended, and any
      --------------
successor statute and the rules and regulations of the Securities and Exchange
Commission thereunder, as shall be in effect at the applicable time.

     "Shares" shall mean the 672,925 shares of Common Stock purchased by
      ------
Employee hereunder.

     "Termination of Employment" shall mean the termination of the employment
      -------------------------
relationship between the Corporation and Employee.

                                      -2-
<PAGE>

     "Transfer" shall include any direct or indirect sale, assignment, transfer,
      --------
pledge (but not including a pledge in favor of the Corporation), hypothecation
or other disposition of any Shares or of any legal or beneficial interest
therein.

     SECTION 2.     Sale to Employee of Common Stock.  Subject to the terms and
                    --------------------------------
conditions contained herein, the Corporation hereby sells, transfers and assigns
to Employee, and Employee hereby purchases from the Corporation, the Shares.
The Corporation hereby acknowledges receipt from Employee of payment of the OCPS
(or $672.93 in the aggregate).  Employee covenants and agrees to forward to the
Corporation, if, as and when filed, a copy of any forms filed by Employee with
the Internal Revenue Service with respect to the Shares pursuant to Section
83(b) of the Internal Revenue Code of 1986, as amended.

     SECTION 3.     Termination of Employment.  (a) (i)  In the event of the
                    -------------------------
Termination of Employment of Employee for any reason, the Corporation shall have
the right to purchase from Employee, and if the Corporation exercises its option
pursuant to this Section 3, Employee shall sell to the Corporation upon the
exercise of such right, up to the number of Shares (rounded up to the nearest
whole Share) at the OCPS determined in accordance with the following table:

 If the Termination of Employment
    Occurs On or Prior to the        Percentage of Shares
         Following Dates            Subject to Repurchase
----------------------------------  ----------------------

       September 9, 1997                     100%
       December 9, 1997                       80%
       March 9, 1998                          75%
       June 9, 1998                           70%
       September 9, 1998                      65%
       December 9, 1998                       60%
       March 9, 1999                          55%
       June 9, 1999                           50%
       September 9, 1999                      45%
       December 9, 1999                       40%
       March 9, 2000                          35%
       June 9, 2000                           30%
       September 9, 2000                      25%
       December 9, 2000                       20%
       March 9, 2001                          15%
       June 9, 2001                           10%
       September 9, 2001                       5%
       After September 9, 2001                 0%

          (ii) The number of Shares subject to purchase pursuant to this Section
3(a) shall be adjusted to give effect to any stock dividend, or other
distribution of stock made on or in respect of such Shares, or any subdivision,
combination or reclassification of the outstanding capital stock of the
Corporation or received in exchange for the Shares.

     (b) In order to exercise the option to purchase Employee's Shares under
this Section 3, the Corporation shall deliver a written notice to Employee,
indicating its election to purchase the Shares and specifying the number of
Shares which the Corporation elects to purchase and the purchase price therefor,
within 30 days after Employee's Termination of Employment.

     (c) The repurchase of Shares hereunder shall be made on a date within 90
days of the Termination of Employment, by delivery of payment to the Employee,
by check or wire transfer, against receipt of one or more certificates, properly
endorsed, evidencing the Employee's Shares to be so purchased.  If the
repurchase is not consummated by such date, the Corporation may deliver to
Employee by check or wire transfer the applicable repurchase price for the
Shares to be repurchased and may cancel the certificates evidencing such Shares
on the books and records of the Corporation.

                                      -3-
<PAGE>

     SECTION 4.     Legend on Shares and Notice of Transfer.
                    ---------------------------------------

          4.1  Restrictive Legends.  (a) Each certificate evidencing Shares, and
               -------------------
each certificate evidencing Shares held by subsequent transferees of any such
certificate, shall (unless otherwise permitted by the provisions of Section 4.2
hereof) be stamped or otherwise imprinted with a legend in substantially the
following form:

     THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED FOR
     INVESTMENT AND HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933,
     AS AMENDED, OR ANY STATE SECURITIES LAW.  THESE SECURITIES MAY NOT BE SOLD
     OR TRANSFERRED IN THE ABSENCE OF SUCH REGISTRATION OR ANY EXEMPTION
     THEREFROM UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR ANY APPLICABLE
     STATE SECURITIES LAW.

          (b) Each certificate evidencing Shares, and each certificate
evidencing Shares held by subsequent transferees of any such certificate, shall
(unless otherwise permitted by the provisions of Section 4.2 hereof) also be
stamped or otherwise imprinted with a legend in substantially the following
form:

     ADDITIONALLY, THE TRANSFER OF THESE SECURITIES IS SUBJECT TO THE TERMS AND
     CONDITIONS OF A RESTRICTED STOCK PURCHASE AGREEMENT DATED AS OF MARCH 6,
     1996, AMONG ORAPHARMA, INC. AND THE HOLDER OF RECORD OF THIS CERTIFICATE
     AND NO SALE, ASSIGNMENT, TRANSFER, PLEDGE, HYPOTHECATION OR OTHER
     DISPOSITION OF SUCH SECURITIES SHALL BE VALID OR EFFECTIVE EXCEPT IN
     ACCORDANCE WITH SUCH AGREEMENT AND UNTIL SUCH TERMS AND CONDITIONS HAVE
     BEEN FULFILLED.  COPIES OF SUCH AGREEMENT MAY BE OBTAINED AT NO COST BY
     WRITTEN REQUEST MADE BY THE HOLDER OF RECORD OF THIS CERTIFICATE TO THE
     SECRETARY OF ORAPHARMA, INC.

          4.2  Notice of Transfer.  (a) Employee, and any other holder of any
               ------------------
Shares by acceptance thereof, agrees that, prior to any Transfer of any Shares,
such holder will give written notice to the Corporation of such holder's
intention to effect such Transfer and to comply in all other respects with the
provisions of this Section 4.2. Each such notice shall contain (i) a statement
setting forth the intention of said holder's prospective transferee with respect
to its retention or disposition of said Shares; and (ii) unless waived by the
Corporation, an opinion of counsel for said holder (who may be the inside or
staff counsel employed by said holder), as to the necessity or non-necessity for
registration under the Securities Act and applicable state securities laws in
connection with such Transfer and stating the factual and statutory basis relied
upon by counsel.  The following provisions shall then apply:

               (i) If the proposed Transfer of Shares may be effected without
     registration or qualification under the Securities Act and any applicable
     state securities laws, then the registered holder of such Shares shall be
     entitled to Transfer such Shares in accordance with Section 5 hereof and
     the intended method of disposition specified in the statement delivered by
     said holder to the Corporation.

               (ii) If the proposed Transfer of such Shares may not be effected
     without registration under the Securities Act or registration or
     qualification under any applicable state securities laws, the registered
     holder of such Shares shall not be entitled to Transfer such Shares
     pursuant to Section 5 hereof until the requisite registration or
     qualification is effective.

          (b) Notwithstanding the provisions of Section 4.2(a), in the case of a
Transfer by a holder to a member of such holder's Family or Group, no such
opinion of counsel shall be necessary; provided, that the transferee agrees in
                                       --------
writing to be subject to this Agreement to the same extent as if such transferee
were originally a signatory to this Agreement.

          (c) Each certificate evidencing the Shares issued upon such Transfer
(and each certificate evidencing any untransferred balance of such Shares) shall
bear the legend set forth in Section 4.1(a) hereof unless (i) in the opinion of
counsel (acceptable to the Corporation) addressed to the Corporation the
registration of future Transfers is not required by the applicable provisions of
the Securities Act or applicable state securities laws; (ii) the Corporation
shall have waived the requirement of such legend; or (iii) in the reasonable
opinion of counsel to the Corporation, such Transfer shall have been made in
connection with an effective registration statement filed pursuant to the
Securities Act or in compliance with the requirements of Rule 144 or Rule 144A
(or any similar or successor rule) promulgated under the Securities Act, and in
compliance with applicable state securities laws.

                                      -4-
<PAGE>

          (d) Each certificate evidencing the Shares issued upon such Transfer
(and each certificate evidencing any untransferred balance of such Shares) shall
bear the legend set forth in Section 4.1(b) hereof, for so long as this
Agreement remains in effect.  In the event of the termination of this Agreement,
the holder of Shares may request that the Corporation issue a new certificate
not bearing the legend set forth in Section 4.1(b) hereof.

     SECTION 5.     Covenants of Employee and Corporation.
                    -------------------------------------

          5.1  Prohibited Transfers.
               --------------------

          (a) Employee agrees that he shall not Transfer any of his Shares which
are subject to repurchase pursuant to Section 3 above at any time.  Employee
further agrees that he shall not Transfer any of his Shares which are no longer
subject to repurchase pursuant to Section 3 above without the prior written
consent of the holders of a majority of the outstanding Common Shares held by
the Stockholders, except as provided for in Section 5.2.

          (b) Notwithstanding anything to the contrary contained herein,
Employee (and any permitted transferee of Employee) may Transfer all of its, his
or her Shares:  (i) if the stockholder is a limited partnership or a trust, to
any member of the Group of which Employee (or such permitted transferee) is a
member; provided, that such transferee shall agree in writing with the
        --------
Corporation, prior to and as a condition precedent to such Transfer, to be bound
by all of the provisions of this Agreement; (ii) if the stockholder is a
corporation, to any member of its Group; provided, that such transferee shall
                                         --------
agree in writing with the Corporation, prior to and as a condition precedent to
such Transfer, to be bound by all of the provisions of this Agreement; (iii) to
any member of the Family of Employee (or such permitted transferee); provided,
                                                                     --------
that such transferee shall agree in writing with the Corporation, prior to and
as a condition precedent to such Transfer, to be bound by all of the provisions
of this Agreement and, provided, further, that the interests in any Family
                       --------  -------
trusts shall be non-transferable; and (iv) by will or the laws of descent and
distribution, in which event each such transferee shall be bound by all of the
provisions of this Agreement to the same extent as if such transferee were the
deceased Employee (or permitted transferee).

          (c) If requested in writing by the managing underwriters, if any, of
any Public Offering, Employee agrees not to offer, sell, contract to sell or
otherwise dispose of any Shares except as part of such Public Offering within
thirty (30) days before or one hundred and eighty (180) days after the effective
date of the registration statement filed with respect to said offering, and the
Corporation hereby also so agrees; provided, however, that this restriction will
                                   --------
not apply to transfers permitted under Section 5.1(b) provided such transferee
agrees to be bound by the restriction contained in this Section 5.1(c).
Notwithstanding the foregoing, in the event that Employee shall have accepted an
offer to purchase Offered Shares (as defined below) which have been offered
pursuant to Section 5.2(a), Employee shall not be prohibited from consummating
such sale, provided, that the purchaser agrees to be bound by the restrictions
           --------
contained in this Section 5.1(c).

                                      -5-
<PAGE>

         5.2  Right of First Offer on Dispositions.
              ------------------------------------

          (a) Except as provided in Section 5.1(b), if Employee desires to
Transfer all or any part of its Shares pursuant to this Section 5.2 and is not
otherwise prohibited from Transferring his Shares pursuant to Section 5.1(a),
Employee shall submit a written offer (the "Offer") to sell such Shares (the
                                            -----
"Offered Shares") to the Stockholders and the Corporation, which Offer shall
 --------------
specify the number of Offered Shares proposed to be sold, the total number of
Shares owned by Employee, and the terms and conditions, including price, at
which the Shares are being offered.

          (b) Each of the Stockholders shall have the right to purchase its Pro
Rata Fraction of the Offered Shares.

          (c) The Corporation shall have the right to purchase all of the
remaining Offered Shares, on the same terms and conditions specified in the
Offer, in excess of the Offered Shares accepted by the Stockholders.

          (d) The Stockholders shall have a right of oversubscription such that,
if any Stockholder fails to accept the Offer as to its full Pro Rata Fraction,
it shall have the right to purchase up to the balance of the Offered Shares not
so purchased.  Such right of oversubscription may be exercised by such
Stockholder by accepting the offer as to more than its Pro Rata Fraction.

          (e) If a Stockholder desires to purchase all or any part of the
Offered Shares on the same terms and conditions specified in the Offer, such
Stockholder (a "Purchasing Stockholder") shall communicate in writing to
                ----------------------
Employee and the Corporation its election to purchase (an "Acceptance"), which
                                                           ----------
Acceptance shall state the number of Offered Shares the Purchasing Stockholder
desires to purchase and shall be delivered in person or mailed to Employee at
the address set forth in the Offer, with a copy to the Corporation and the other
Stockholder, within 20 days of the date the Offer was made by Employee pursuant
to Section 5.2(a).

          (f) If the Corporation desires to purchase all or any part of the
Offered Shares on the same terms and conditions specified in the Offer, the
Corporation shall deliver its Acceptance to Employee and the Stockholders, which
Acceptance shall state the number of Offered Shares the Corporation desires to
purchase and shall be delivered in person or mailed to Employee at the address
set forth in the Offer, with a copy to the Stockholder, within 20 days of the
date the Offer was made by Employee pursuant to Section 5.2(a).

          (g) If the Corporation and the Stockholders elect to purchase all of
the Offered Shares, sale of the Offered Shares pursuant to this Section 5.2
shall be made at the offices of the Corporation on the 45th day following the
expiration of the 20-day period described above (or if such 45th day is not a
business day, then on the next succeeding business day).  Such sales shall be
effected by Employee's delivery to each Purchasing Stockholder or the
Corporation, as the case may be, of a certificate or certificates evidencing the
Offered Shares to be purchased by it, him or her, duly endorsed for transfer to
the Purchasing Stockholder or the Corporation, as the case may be, which Offered
Shares shall be delivered free and clear of all liens, charges, claims and
encumbrances of any nature whatsoever, against payment to Employee of the
purchase price therefor by the Corporation or such Purchasing Stockholder, as
the case may be.  Payment for the Offered Shares shall be made as provided in
the Offer or by wire transfer or certified check.

          (h) If the Purchasing Stockholders and the Corporation do not elect to
purchase all of the Offered Shares, then the Offered Shares may be sold by
Employee at any time within 150 days after the date the Offer was made by
Employee pursuant to Section 5.2(a).  Any such sale shall be upon terms and
conditions, including price, not less favorable to Employee than those specified
in the Offer.  Any Offered Shares not sold within such 150-day period shall
continue to be subject to the requirements of a prior offer pursuant to this
Section 5.2.

          5.3  Drag Along.  Subject to Section 5.2 above, anything in this
               ----------
Agreement to the contrary notwithstanding, in the event that (i) the Board of
Directors of the Corporation by unanimous vote or unanimous written consent
and/or the holders of sixty-six and two-thirds of the then outstanding Common
Shares by vote or written consent approves a transaction pursuant to which any
Person or Persons not affiliated with any of the Stockholders will acquire 50%
or more of the Common Shares of the Corporation (by stock purchase, merger or
otherwise) or all or substantially all of the assets of the Corporation, upon
the written request of the holders of sixty-six and two-thirds of the Common
Shares, Employee agrees to offer to sell all of his Shares, and to sell all of
his Shares, to such Person or Persons or to vote all of his Shares in favor of
the sale of assets, as the case may be, in either case upon the terms and
conditions of the transaction approved by the Board of Directors of the
Corporation and/or the holders of sixty-six and two-thirds of the Common Shares;
provided, however, that Employee's obligation to sell his Shares pursuant to
--------  -------
this Section 5.3 shall only apply if all of the Shares are to be sold on the
same terms and conditions.  For purposes of this Section 5.3, each Preferred
Share shall be deemed to be the number of shares of Common Stock into which the
Preferred Share is then convertible.

                                      -6-
<PAGE>

     SECTION 6.     Representations.
                    ---------------

          6.1  Representations of Employee.  In connection with Employee's
               ---------------------------
purchase of the Shares, Employee hereby represents and warrants to the
Corporation as follows:

          (a)  Investment Intent; Capacity to Protect Interests.  Employee is
               ------------------------------------------------
purchasing the Shares solely for his own account for investment and not with a
view to or for sale in connection with any distribution of the Shares or any
portion thereof and not with any present intention of selling, offering to sell
or otherwise disposing of or distributing the Shares or any portion thereof in
any transaction other than a transaction exempt from registration under the
Securities Act.  Employee also represents that the entire legal and beneficial
interest of the Shares is being purchased, and will be held, for his account
only, and neither in whole or in part for any other person.

          (b)  Restricted Securities. Employee understands and acknowledges that
               ---------------------
the sale of the Shares has not been registered under the Securities Act; that
the Shares must be held indefinitely unless subsequently registered under the
Securities Act or an exemption from such registration is available; and that the
Corporation is under no obligation to register the Shares.

          (c)  Disposition under Rule 144.  Employee understands that the Shares
               --------------------------
are restricted securities within the meaning of Rule 144 promulgated under the
Securities Act; that the exemption from registration under Rule 144 will not be
available in any event for at least two years from the date of purchase of any
payment for the Shares, and even then will not be available unless (i) a public
trading market then exists for the Shares, (ii) adequate information concerning
the Corporation is then available to the public, and (iii) other terms and
conditions of Rule 144 are complied with; and that any sale of the Shares may be
made only in limited amounts in accordance with such terms and conditions.

          (d)  Accredited Investor.  Employee is an "accredited investor", as
               -------------------
defined in Rule 501 under the Securities Act.

          6.2  Representations of the Corporation.  The Corporation represents
               ----------------------------------
to Employee that:

          (a) The execution, delivery and performance by the Corporation of this
Agreement and all transactions contemplated by this Agreement have been duly
authorized by all action required by law, its Certificate of Incorporation, its
Bylaws or otherwise.

          (b) This Agreement has been duly executed and delivered by the
Corporation and constitutes the legal, valid and binding obligation of the
Corporation enforceable against it in accordance with its terms.

     SECTION 7.     Withholding.  Upon the request of the Corporation, Employee
                    -----------
shall promptly pay to the Corporation, or make arrangements satisfactory to the
Corporation regarding payment of, any Federal, state or local taxes of any kind
required by law to be withheld with respect to the Shares (or any distributions
of other securities or property (including cash) thereon or issued in
replacement thereof).

     SECTION 8.     Remedies.  In case any one or more of the covenants and/or
                    --------
agreements set forth in this Agreement shall have been breached by any party
hereto, the party entitled to the benefit of such covenants or agreements may
proceed to protect and enforce its rights either by suit in equity and/or by
action at law, including, but not limited to, (a) an action for damages as a
result of any such breach, (b) an action for specific performance of any such
covenant or agreement contained in this Agreement, and/or (c) a temporary or
permanent injunction, in any case without showing any actual damage.  The
rights, power and remedies of the parties under this Agreement are cumulative
and not exclusive of any other agreement or law.  No single or partial assertion
or exercise of any right, power or remedy of a party hereunder shall preclude
any other or further assertion or exercise thereof.  Any purported Transfer in
violation of the provisions of this Agreement shall be null and void ab initio.
                                                                     -- ------

                                      -7-
<PAGE>

     SECTION 9.     Successors and Assigns.  Except as otherwise expressly
                    ----------------------
provided herein, this Agreement shall bind and inure to the benefit of the
Corporation, Employee, the respective successors or heirs, distributees and
personal representatives and permitted assigns of the Corporation and Employee,
and each other person who shall properly become a registered holder of any
Shares that have not theretofore been sold to the public pursuant to a
registration statement under the Securities Act or Rule 144 or Rule 144A (or any
similar or successor rule).

     SECTION 10.    Entire Agreement.  This Agreement contains the entire
                    ----------------
agreement among the parties with respect to the subject matter hereof and
supersedes other prior and contemporaneous arrangements or understandings with
respect thereto.

     SECTION 11.    Notices.  All notices, consents and other communications
                    -------
under this Agreement shall be in writing and shall be deemed to have been duly
given (a) when delivered by hand, (b) one (1) business day after the business
day of transmission, if sent by telex or telecopier (with receipt confirmed),
provided that a copy is mailed by registered mail, return receipt requested, or
(c) one (1) business day after the business day of deposit with the carrier, if
sent by Express Mail, Federal Express or other express delivery service (receipt
requested), in each case to the appropriate addresses, telex numbers and
telecopier numbers set forth below (or to such other addresses or telecopy
numbers as a party may designate as to itself by notice to the other parties):

     (a)  If to Employee:

          37 Hancock Court
          Flemington, New Jersey 08822

     (b)  If to the Corporation:

          OraPharma, Inc.
          1200 Route 22 East
          Suite 2000
          Bridgewater, NJ 08807
          Attention:  Chief Executive Officer
          Telecopier No.: (908) 806-6199

     with a copy to:

          Sills Cummis Zuckerman Radin
            Tischman Epstein & Gross, P.A.
          One Riverfront Plaza
          Newark, New Jersey 07102
          Telecopier No.: (201) 643-6500
          Attention:  Ira A. Rosenberg, Esq.

     SECTION 12.    Changes.  The terms and provisions of this Agreement may
                    -------
not be modified or amended, or any of the provisions hereof waived, temporarily
or permanently, without the prior written consent of each of the parties hereto.

                                      -8-
<PAGE>

     SECTION 13.      Counterparts.  This Agreement may be executed in any
                      ------------
number of counterparts, and each such counterpart shall be deemed to be an
original instrument, but all such counterparts together shall constitute but one
agreement.

     SECTION 14.      Headings.  The benefits of the various sections of this
                      --------
Agreements have been inserted for convenience of reference only and shall not be
deemed to be part of this Agreement.

     SECTION 15.      Nouns and Pronouns.  Whenever the context may require, any
                      ------------------
pronouns used herein shall include the corresponding masculine feminine or
neuter forms, and the singular form of names and pronouns shall include the
plural and vice-versa.

     SECTION 16.      Severability.  Any provision of this Agreement that is
                      ------------
prohibited or unenforceable in any jurisdiction shall, as to such jurisdiction,
be ineffective to the extent of such prohibition or unenforceability.  Such
prohibition or unenforceability in any one jurisdiction shall not invalidate or
render unenforceable such provision in any other jurisdiction.

     SECTION 17.      Governing Law; Jurisdiction.  This Agreement and (unless
                      ---------------------------
otherwise provided) all amendments hereof and waivers and consents hereunder
shall be governed by the internal law of the State of New Jersey, without regard
to the conflicts of law principles thereof.

                                      -9-
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of
the date and year first written above.

WITNESS                       ORAPHARMA, INC.

------------------------      By:----------------------------
                                 Michael Kishbauch, President

WITNESS

-----------------------------------------------------
                                    Michael Kishbauch

                                      -10-
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of
the date and year first written above.

WITNESS                       ORAPHARMA, INC.

/s/  Dorinda Alevritis                   By:  /s/  Michael Kishbauch
----------------------                      ------------------------------
                                             Michael Kishbauch, President

WITNESS

/s/  Dorinda Alevritis                   By:  /s/  Michael Kishbauch
----------------------                      -----------------------------
                                             Michael Kishbauch, President

                                      -11-
<PAGE>

                AMENDMENT TO RESTRICTED STOCK PURCHASE AGREEMENT
                ------------------------------------------------

     This AMENDMENT TO RESTRICTED STOCK PURCHASE AGREEMENT (this "Amendment") is
                                                                  ---------
dated as of the 3rd day of September, 1999, by and between OraPharma, Inc., a
Delaware corporation (the "Corporation") and Michael D. Kishbauch (the
                           -----------
"Stockholder").
------------

                                  WITNESSETH:
                                  ----------

     WHEREAS, the Corporation and the Stockholder have previously entered into a
Restricted Stock Purchase Agreement pursuant to which the Stockholder purchased
from the Corporation shares of the Corporation's Common Stock, $.001 par value
per share (the "Agreement"); and
                ---------

     WHEREAS, the parties now desire to amend the Agreement as set forth herein.

     NOW, THEREFORE, for full and adequate consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto, intending to
be legally bound, hereby agree as follow:

     1.   A new Section 3(d) is hereby added to the Agreement to read in its
entirety as follows:

          "Notwithstanding anything contained in this Agreement to the contrary,
          if in connection with the consummation of a Change of Control the
          employment by the Corporation (or its successor) of the Stockholder is
          terminated by the Corporation (or such successor) without Cause, the
          Corporation's right to repurchase the Shares from the Stockholder
          pursuant to this Section 3 shall be terminated, effective immediately
          prior to consummation of such Change of Control.

               For purposes hereof, a 'Change of Control' shall mean any of the
               following:

                    (i) any person or entity, other than a person or entity who
               is a beneficial owner of the Corporation's securities before the
               consummation of the transaction, becomes, after such
               consummation, the beneficial owner, directly or indirectly, of
               securities of the Corporation representing fifty percent (50%) or
               more of the combined voting power of the Corporation's then
               outstanding securities;

                    (ii) the Corporation consummates a merger, consolidation or
               reorganization the result of which is that the persons or
               entities who were stockholders of the Corporation immediately
               prior to consummation of such transaction own less than fifty
               percent (50%) of the equity of the corporation or entity
               surviving or resulting from such transaction;

                                      -12-
<PAGE>

                    (iii)  the sale in one or more series of transactions of all
               or substantially all of the assets of the Corporation; or

                    (iv) the dissolution or liquidation of the Corporation.

               For purposes hereof  'Cause' shall mean any of the following:

                    (i) the Stockholder is convicted of, pleads guilty to or
               confesses to (y) a felony, or (z) any act of fraud,
               misappropriation, embezzlement, dishonesty or disloyalty which
               damages the Corporation (or its successor) in any material
               respect;

                    (ii) substantial and repeated failure by the Stockholder to
               follow the direction of the Chief Executive Officer or Board of
               Directors of the Corporation (or its successor) and such failure
               is not cured within thirty (30) days after the Stockholder
               receives notice thereof from the Corporation (or its successor);

                    (iii)  failure by the Stockholder to meet reasonable
               performance objectives; or

                    (iv) gross negligence or willful misconduct of the
               Stockholder with respect to the Corporation (or its successor)."

     2.   This Amendment may be executed in several counterparts, each of which,
when executed and delivered, shall be deemed an original, and all of which
together shall constitute one agreement.

     3.   This Amendment shall be governed by and construed and interpreted in
accordance with the laws of the Commonwealth of Pennsylvania, without giving
effect to principles of conflicts law.

     4.   In the event there is a conflict between this Amendment and the
Agreement, the terms of this Amendment shall prevail.

     5.   Except as amended hereby, the Agreement shall remain in full force and
effect in accordance with its terms.

                                      -13-
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed and delivered as of the day and year first above written.

                              ORAPHARMA, INC.

Witnessed By:/s/  James A. Ratigan                  By:/s/ Michael D. Kishbauch
             ---------------------                     ------------------------
                  James A. Ratigan                         Michael D. Kishbauch

Witnessed By:/s/  James A. Ratigan                     /s/ Michael D. Kishbauch
             ---------------------                     ------------------------
                  James A. Ratigan                         Michael D. Kishbauch

                                      -14-<PAGE>

                                                                    Exhibit 4.18

                      RESTRICTED STOCK PURCHASE AGREEMENT
                      -----------------------------------

     THIS RESTRICTED STOCK PURCHASE AGREEMENT (this "Agreement") is dated as of
                                                     ---------
the 19th day of March, 1997, by and between OraPharma, Inc., a Delaware
corporation (the "Corporation"), and James R. Law ("Employee").
                  -----------                       --------

                             W I T N E S S E T H:
                             - - - - - - - - - -

     WHEREAS, Employee is currently an employee of the Corporation; and

     WHEREAS, Employee wishes to purchase, and the Corporation wishes to sell to
Employee, 178,750 shares of the Corporation's common stock, $.001 par value per
share ("Common Stock") at a price of $.001 per share (the "OCPS"); and
        ------------                                       ----

     WHEREAS, such shares of Common Stock will be issued to Employee in order to
provide an incentive to Employee to exercise his best efforts on behalf of, and
to remain as an employee of, the Corporation, subject to the terms and
provisions of this Agreement.

     NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties do hereby agree as
follows:

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

     As used in this Agreement, the following terms shall have the following
respective meanings:

     "Common Shares" shall mean the issued and outstanding shares of the
      -------------
Corporation's Common Stock, at the applicable time.

     "Equity Stock" shall have the meaning set forth in Rule 3a11-1 under the
      ------------
Securities Exchange Act of 1934, as amended, and any successor statute and the
rules and regulations thereunder, as shall be in effect from time to time.

     "Family" shall include any spouse, lineal ancestor or descendant, or
      ------
sibling, any trust for the exclusive benefit of any of the foregoing, or any
corporation, limited partnership, limited liability company or other entity
majority controlled by any of the foregoing individuals or trusts.

     "Stockholders" shall mean the Investors and the Founders, both as defined
      ------------
in that certain Stockholders Agreement dated the date hereof by and among the
Corporation and certain stockholders of the Corporation.
<PAGE>

     "Group" shall mean as to (a) a partnership, any or all of its general or
      -----
limited partners or any "affiliate" thereof (as defined by Rule 405 promulgated
under the Securities Act), (b) a trust, any of the beneficiaries, settlers or
grantors now existing or hereafter arising of, or any Person under common
control with, such trust, (c) a corporation, any of its stockholders, any
subsidiary of such corporation or any corporation which is under common control
with such corporation, or any directors, officers or employees of such
corporation, and (d) a limited liability company, any of its members.

     "New Securities" shall mean any Equity Stock, including, but not limited
      --------------
to, shares of Common Stock, any security which is convertible into or
exercisable or exchangeable for Common Stock, or any right, option or warrant to
acquire any Common Stock of the Corporation.

     "Person" shall mean and include a natural person, a corporation, a limited
      ------
liability company, a partnership, a trust, an unincorporated organization and a
government or any department, agency or political subdivision thereof.

     "Preferred Shares" shall mean the Corporation's Series A Preferred Stock,
      ----------------
$.001 par value per share, and Series B Preferred Stock, $.001 par value per
share, issued or to be issued to certain of the Stockholders pursuant to the
Stock Purchase Agreement dated February 26, 1997 among the Corporation and such
Stockholders, as the same may be amended.

     "Pro Rata Fraction" shall mean a fraction, the numerator of which shall be
      -----------------                             ---------
the number of shares of Common Stock then owned by such Stockholder and the
denominator of which shall be the aggregate number of shares of Common Stock
-----------
then owned by all Stockholders.  For the purpose of calculating the Pro Rata
Fraction, each Preferred Share shall be deemed to represent the number of shares
of Common Stock into which the Preferred Share is then convertible.

     "Public Offering" shall mean a distribution of New Securities in a firm
      ---------------
commitment underwritten public offering to the general public pursuant to a
registration statement filed with and declared effective by the Securities and
Exchange Commission pursuant to the Securities Act.

     "Securities Act" shall mean the Securities Act of 1933, as amended, and any
      --------------
successor statute and the rules and regulations of the Securities and Exchange
Commission thereunder, as shall be in effect at the applicable time.

     "Shares" shall mean the 178,750 shares of Common Stock purchased by
      ------
Employee hereunder.

     "Termination of Employment" shall mean the termination of the employment
      -------------------------
relationship between the Corporation and Employee.

                                       2
<PAGE>

     "Transfer" shall include any direct or indirect sale, assignment, transfer,
      --------
pledge (but not including a pledge in favor of the Corporation), hypothecation
or other disposition of any Shares or of any legal or beneficial interest
therein.

     SECTION 2.  Sale to Employee of Common Stock.  Subject to the terms and
                 --------------------------------
conditions contained herein, the Corporation hereby sells, transfers and assigns
to Employee, and Employee hereby purchases from the Corporation, the Shares. The
Corporation hereby acknowledges receipt from Employee of payment of the OCPS (or
178.75 in the aggregate). Employee covenants and agrees to forward to the
Corporation, if, as and when filed, a copy of any forms filed by Employee with
the Internal Revenue Service with respect to the Shares pursuant to Section
83(b) of the Internal Revenue Code of 1986, as amended.

     SECTION 3.  Termination of Employment.  (a) (i)  In the event of the
                 -------------------------
Termination of Employment of Employee for any reason, the Corporation shall have
the right to purchase from Employee, and if the Corporation exercises its option
pursuant to this Section 3, Employee shall sell to the Corporation upon the
exercise of such right, up to the number of Shares (rounded up to the nearest
whole Share) at the OCPS determined in accordance with the following table:

<TABLE>
<CAPTION>
     If the Termination of Employment
          Occurs On or Prior to the          Percentage of Shares
              Following Dates                Subject to Repurchase
              ---------------                ---------------------
     <S>                                     <C>
              June 19, 1997                           80%
              September 19, 1997                      75%
              December 19, 1997                       70%
              March 19, 1998                          65%
              June 19, 1998                           60%
              September 19, 1998                      55%
              December 19, 1998                       50%
              March 19, 1999                          45%
              June 19, 1999                           40%
              September 19, 1999                      35%
              December 19, 1999                       30%
              March 19, 2000                          25%
              June 19, 2000                           20%
              September 19, 2000                      15%
              December 19, 2000                       10%
              March 19, 2001                           5%
              After March 19, 2001                     0%
</TABLE>

          (ii)   The number of Shares subject to purchase pursuant to this
Section 3(a) shall be adjusted to give effect to any stock dividend, or other
distribution of stock made on or in respect of such Shares, or any subdivision,
combination or reclassification of the outstanding capital stock of the
Corporation or received in exchange for the Shares.

                                       3
<PAGE>

     (b)  In order to exercise the option to purchase Employee's Shares under
this Section 3, the Corporation shall deliver a written notice to Employee,
indicating its election to purchase the Shares and specifying the number of
Shares which the Corporation elects to purchase and the purchase price therefor,
within 30 days after Employee's Termination of Employment.

     (c)  The repurchase of Shares hereunder shall be made on a date within 90
days of the Termination of Employment, by delivery of payment to the Employee,
by check or wire transfer, against receipt of one or more certificates, properly
endorsed, evidencing the Employee's Shares to be so purchased. If the repurchase
is not consummated by such date, the Corporation may deliver to Employee by
check or wire transfer the applicable repurchase price for the Shares to be
repurchased and may cancel the certificates evidencing such Shares on the books
and records of the Corporation.

     SECTION 4.  Legend on Shares and Notice of Transfer.
                 ---------------------------------------

          4.1    Restrictive Legends.  (a)  Each certificate evidencing Shares,
                 -------------------
and each certificate evidencing Shares held by subsequent transferees of any
such certificate, shall (unless otherwise permitted by the provisions of Section
4.2 hereof) be stamped or otherwise imprinted with a legend in substantially the
following form:

     THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED FOR
     INVESTMENT AND HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
     1933, AS AMENDED, OR ANY STATE SECURITIES LAW. THESE SECURITIES MAY
     NOT BE SOLD OR TRANSFERRED IN THE ABSENCE OF SUCH REGISTRATION OR ANY
     EXEMPTION THEREFROM UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR
     ANY APPLICABLE STATE SECURITIES LAW.

          (b)    Each certificate evidencing Shares, and each certificate
evidencing Shares held by subsequent transferees of any such certificate, shall
(unless otherwise permitted by the provisions of Section 4.2 hereof) also be
stamped or otherwise imprinted with a legend in substantially the following
form:

     ADDITIONALLY, THE TRANSFER OF THESE SECURITIES IS SUBJECT TO THE
     TERMS AND CONDITIONS OF A RESTRICTED STOCK PURCHASE AGREEMENT DATED
     AS OF MARCH 19, 1997, AMONG ORAPHARMA, INC. AND THE HOLDER OF RECORD
     OF THIS CERTIFICATE AND NO SALE, ASSIGNMENT, TRANSFER, PLEDGE,
     HYPOTHECATION OR OTHER DISPOSITION OF SUCH SECURITIES SHALL BE VALID
     OR EFFECTIVE EXCEPT IN ACCORDANCE WITH SUCH AGREEMENT AND UNTIL SUCH
     TERMS AND CONDITIONS HAVE BEEN FULFILLED. COPIES OF SUCH AGREEMENT
     MAY BE OBTAINED AT NO COST BY WRITTEN REQUEST MADE BY THE HOLDER OF
     RECORD OF THIS CERTIFICATE TO THE SECRETARY OF ORAPHARMA, INC.

                                       4
<PAGE>

          4.2    Notice of Transfer.  (a) Employee, and any other holder of any
                 ------------------
Shares by acceptance thereof, agrees that, prior to any Transfer of any Shares,
such holder will give written notice to the Corporation of such holder's
intention to effect such Transfer and to comply in all other respects with the
provisions of this Section 4.2. Each such notice shall contain (i) a statement
setting forth the intention of said holder's prospective transferee with respect
to its retention or disposition of said Shares; and (ii) unless waived by the
Corporation, an opinion of counsel for said holder (who may be the inside or
staff counsel employed by said holder), as to the necessity or non-necessity for
registration under the Securities Act and applicable state securities laws in
connection with such Transfer and stating the factual and statutory basis relied
upon by counsel. The following provisions shall then apply:

                 (i)    If the proposed Transfer of Shares may be effected
     without registration or qualification under the Securities Act and any
     applicable state securities laws, then the registered holder of such Shares
     shall be entitled to Transfer such Shares in accordance with Section 5
     hereof and the intended method of disposition specified in the statement
     delivered by said holder to the Corporation.

                 (ii)   If the proposed Transfer of such Shares may not be
     effected without registration under the Securities Act or registration or
     qualification under any applicable state securities laws, the registered
     holder of such Shares shall not be entitled to Transfer such Shares
     pursuant to Section 5 hereof until the requisite registration or
     qualification is effective.

          (b)    Notwithstanding the provisions of Section 4.2(a), in the case
of a Transfer by a holder to a member of such holder's Family or Group, no such
opinion of counsel shall be necessary; provided, that the transferee agrees in
                                       --------
writing to be subject to this Agreement to the same extent as if such transferee
were originally a signatory to this Agreement.

          (c)    Each certificate evidencing the Shares issued upon such
Transfer (and each certificate evidencing any untransferred balance of such
Shares) shall bear the legend set forth in Section 4.1(a) hereof unless (i) in
the opinion of counsel (acceptable to the Corporation) addressed to the
Corporation the registration of future Transfers is not required by the
applicable provisions of the Securities Act or applicable state securities laws;
(ii) the Corporation shall have waived the requirement of such legend; or (iii)
in the reasonable opinion of counsel to the Corporation, such Transfer shall
have been made in connection with an effective registration statement filed
pursuant to the Securities Act or in compliance with the requirements of Rule
144 or Rule 144A (or any similar or successor rule) promulgated under the
Securities Act, and in compliance with applicable state securities laws.

          (d)    Each certificate evidencing the Shares issued upon such
Transfer (and each certificate evidencing any untransferred balance of such
Shares) shall bear the legend set forth in Section 4.1(b) hereof, for so long as
this Agreement remains in effect. In the event of the termination of this
Agreement, the holder of Shares may request that the Corporation issue a new
certificate not bearing the legend set forth in Section 4.1(b) hereof.

                                       5
<PAGE>

     SECTION 5.  Covenants of Employee and Corporation.
                 -------------------------------------

          5.1    Prohibited Transfers.
                 --------------------

          (a)    Employee agrees that he shall not Transfer any of his Shares
which are subject to repurchase pursuant to Section 3 above at any time.
Employee further agrees that he shall not Transfer any of his Shares which are
no longer subject to repurchase pursuant to Section 3 above without the prior
written consent of the holders of a majority of the outstanding Common Shares
held by the Stockholders, except as provided for in Section 5.2.

          (b)    Notwithstanding anything to the contrary contained herein,
Employee (and any permitted transferee of Employee) may Transfer all of its, his
or her Shares: (i) if the stockholder is a limited partnership or a trust, to
any member of the Group of which Employee (or such permitted transferee) is a
member; provided, that such transferee shall agree in writing with the
        --------
Corporation, prior to and as a condition precedent to such Transfer, to be bound
by all of the provisions of this Agreement; (ii) if the stockholder is a
corporation, to any member of its Group; provided, that such transferee shall
                                         --------
agree in writing with the Corporation, prior to and as a condition precedent to
such Transfer, to be bound by all of the provisions of this Agreement; (iii) to
any member of the Family of Employee (or such permitted transferee); provided,
                                                                     --------
that such transferee shall agree in writing with the Corporation, prior to and
as a condition precedent to such Transfer, to be bound by all of the provisions
of this Agreement and, provided, further, that the interests in any Family
                       --------  -------
trusts shall be non-transferable; and (iv) by will or the laws of descent and
distribution, in which event each such transferee shall be bound by all of the
provisions of this Agreement to the same extent as if such transferee were the
deceased Employee (or permitted transferee).

          (c)    If requested in writing by the managing underwriters, if any,
of any Public Offering, Employee agrees not to offer, sell, contract to sell or
otherwise dispose of any Shares except as part of such Public Offering within
thirty (30) days before or one hundred and eighty (180) days after the effective
date of the registration statement filed with respect to said offering, and the
Corporation hereby also so agrees; provided, however, that this restriction will
                                   --------
not apply to transfers permitted under Section 5.1(b) provided such transferee
agrees to be bound by the restriction contained in this Section 5.1(c).
Notwithstanding the foregoing, in the event that Employee shall have accepted an
offer to purchase Offered Shares (as defined below) which have been offered
pursuant to Section 5.2(a), Employee shall not be prohibited from consummating
such sale, provided, that the purchaser agrees to be bound by the restrictions
           --------
contained in this Section 5.1(c).

          5.2    Right of First Offer on Dispositions.
                 ------------------------------------

          (a)    Except as provided in Section 5.1(b), if Employee desires to
Transfer all or any part of its Shares pursuant to this Section 5.2 and is not
otherwise prohibited from Transferring his Shares pursuant to Section 5.1(a),
Employee shall submit a written offer (the "Offer") to sell such Shares (the
                                            -----
"Offered Shares") to the Stockholders and the Corporation, which Offer shall
---------------
specify the number of Offered Shares proposed to be sold, the total number of

                                       6
<PAGE>

Shares owned by Employee, and the terms and conditions, including price, at
which the Shares are being offered.

          (b)    Each of the Stockholders shall have the right to purchase its
Pro Rata Fraction of the Offered Shares.

          (c)    The Corporation shall have the right to purchase all of the
remaining Offered Shares, on the same terms and conditions specified in the
Offer, in excess of the Offered Shares accepted by the Stockholders.

          (d)    The Stockholders shall have a right of oversubscription such
that, if any Stockholder fails to accept the Offer as to its full Pro Rata
Fraction, it shall have the right to purchase up to the balance of the Offered
Shares not so purchased. Such right of oversubscription may be exercised by such
Stockholder by accepting the offer as to more than its Pro Rata Fraction.

          (e)    If a Stockholder desires to purchase all or any part of the
Offered Shares on the same terms and conditions specified in the Offer, such
Stockholder (a "Purchasing Stockholder") shall communicate in writing to
                ----------------------
Employee and the Corporation its election to purchase (an "Acceptance"), which
                                                           ----------
Acceptance shall state the number of Offered Shares the Purchasing Stockholder
desires to purchase and shall be delivered in person or mailed to Employee at
the address set forth in the Offer, with a copy to the Corporation and the other
Stockholder, within 20 days of the date the Offer was made by Employee pursuant
to Section 5.2(a).

          (f)    If the Corporation desires to purchase all or any part of the
Offered Shares on the same terms and conditions specified in the Offer, the
Corporation shall deliver its Acceptance to Employee and the Stockholders, which
Acceptance shall state the number of Offered Shares the Corporation desires to
purchase and shall be delivered in person or mailed to Employee at the address
set forth in the Offer, with a copy to the Stockholder, within 20 days of the
date the Offer was made by Employee pursuant to Section 5.2(a).

          (g)    If the Corporation and the Stockholders elect to purchase all
of the Offered Shares, sale of the Offered Shares pursuant to this Section 5.2
shall be made at the offices of the Corporation on the 45th day following the
expiration of the 20-day period described above (or if such 45th day is not a
business day, then on the next succeeding business day). Such sales shall be
effected by Employee's delivery to each Purchasing Stockholder or the
Corporation, as the case may be, of a certificate or certificates evidencing the
Offered Shares to be purchased by it, him or her, duly endorsed for transfer to
the Purchasing Stockholder or the Corporation, as the case may be, which Offered
Shares shall be delivered free and clear of all liens, charges, claims and
encumbrances of any nature whatsoever, against payment to Employee of the
purchase price therefor by the Corporation or such Purchasing Stockholder, as
the case may be. Payment for the Offered Shares shall be made as provided in the
Offer or by wire transfer or certified check.

                                       7
<PAGE>

          (h)    If the Purchasing Stockholders and the Corporation do not elect
to purchase all of the Offered Shares, then the Offered Shares may be sold by
Employee at any time within 150 days after the date the Offer was made by
Employee pursuant to Section 5.2(a). Any such sale shall be upon terms and
conditions, including price, not less favorable to Employee than those specified
in the Offer. Any Offered Shares not sold within such 150-day period shall
continue to be subject to the requirements of a prior offer pursuant to this
Section 5.2.

          5.3    Drag Along.  Subject to Section 5.2 above, anything in this
                 ----------
Agreement to the contrary notwithstanding, in the event that (i) the Board of
Directors of the Corporation by unanimous vote or unanimous written consent
and/or the holders of sixty-six and two-thirds of the then outstanding Common
Shares by vote or written consent approves a transaction pursuant to which any
Person or Persons not affiliated with any of the Stockholders will acquire 50%
or more of the Common Shares of the Corporation (by stock purchase, merger or
otherwise) or all or substantially all of the assets of the Corporation, upon
the written request of the holders of sixty-six and two-thirds of the Common
Shares, Employee agrees to offer to sell all of his Shares, and to sell all of
his Shares, to such Person or Persons or to vote all of his Shares in favor of
the sale of assets, as the case may be, in either case upon the terms and
conditions of the transaction approved by the Board of Directors of the
Corporation and/or the holders of sixty-six and two-thirds of the Common Shares;
provided, however, that Employee's obligation to sell his Shares pursuant to
--------  -------
this Section 5.3 shall only apply if all of the Shares are to be sold on the
same terms and conditions. For purposes of this Section 5.3, each Preferred
Share shall be deemed to be the number of shares of Common Stock into which the
Preferred Share is then convertible.

     SECTION 6.  Representations.
                 ---------------

          6.1    Representations of Employee.  In connection with Employee's
                 ---------------------------
purchase of the Shares, Employee hereby represents and warrants to the
Corporation as follows:

          (a)    Investment Intent; Capacity to Protect Interests.  Employee is
                 ------------------------------------------------
purchasing the Shares solely for his own account for investment and not with a
view to or for sale in connection with any distribution of the Shares or any
portion thereof and not with any present intention of selling, offering to sell
or otherwise disposing of or distributing the Shares or any portion thereof in
any transaction other than a transaction exempt from registration under the
Securities Act. Employee also represents that the entire legal and beneficial
interest of the Shares is being purchased, and will be held, for his account
only, and neither in whole or in part for any other person.

          (b)    Restricted Securities.  Employee understands and acknowledges
                 ---------------------
the sale of the Shares has not been registered under the Securities Act; that
the Shares must be held indefinitely unless subsequently registered under the
Securities Act or an exemption from such registration is available; and that the
Corporation is under no obligation to register the Shares.

          (c)    Disposition under Rule 144.  Employee understands that the
                 --------------------------
Shares are restricted securities within the meaning of Rule 144 promulgated
under the Securities Act; that the exemption from registration under Rule 144
will not be available in any event for at least two

                                      -8-

<PAGE>

years from the date of purchase of any payment for the Shares, and even then
will not be available unless (i) a public trading market then exists for the
Shares, (ii) adequate information concerning the Corporation is then available
to the public, and (iii) other terms and conditions of Rule 144 are complied
with; and that any sale of the Shares may be made only in limited amounts in
accordance with such terms and conditions.

          (d)    Accredited Investor.  Employee is an "accredited investor", as
                 -------------------
defined in Rule 501 under the Securities Act.

          6.2    Representations of the Corporation.  The Corporation represents
                 ----------------------------------
to Employee that:

          (a)    The execution, delivery and performance by the Corporation of
this Agreement and all transactions contemplated by this Agreement have been
duly authorized by all action required by law, its Certificate of Incorporation,
its Bylaws or otherwise.

          (b)    This Agreement has been duly executed and delivered by the
Corporation and constitutes the legal, valid and binding obligation of the
Corporation enforceable against it in accordance with its terms.

     SECTION 7.  Withholding.  Upon the request of the Corporation, Employee
                 -----------
shall promptly pay to the Corporation, or make arrangements satisfactory to the
Corporation regarding payment of, any Federal, state or local taxes of any kind
required by law to be withheld with respect to the Shares (or any distributions
of other securities or property (including cash) thereon or issued in
replacement thereof).

     SECTION 8.  Remedies.  In case any one or more of the covenants and/or
                 --------
agreements set forth in this Agreement shall have been breached by any party
hereto, the party entitled to the benefit of such covenants or agreements may
proceed to protect and enforce its rights either by suit in equity and/or by
action at law, including, but not limited to, (a) an action for damages as a
result of any such breach, (b) an action for specific performance of any such
covenant or agreement contained in this Agreement, and/or (c) a temporary or
permanent injunction, in any case without showing any actual damage. The rights,
power and remedies of the parties under this Agreement are cumulative and not
exclusive of any other agreement or law. No single or partial assertion or
exercise of any right, power or remedy of a party hereunder shall preclude any
other or further assertion or exercise thereof. Any purported Transfer in
violation of the provisions of this Agreement shall be null and void ab initio.
                                                                     -- ------

     SECTION 9.  Successors and Assigns.  Except as otherwise expressly provided
                 ----------------------
herein, this Agreement shall bind and inure to the benefit of the Corporation,
Employee, the respective successors or heirs, distributees and personal
representatives and permitted assigns of the Corporation and Employee, and each
other person who shall properly become a registered holder of any Shares that
have not theretofore been sold to the public pursuant to a registration
statement under the Securities Act or Rule 144 or Rule 144A (or any similar or
successor rule).

                                       9
<PAGE>

     SECTION 10. Entire Agreement.  This Agreement contains the entire
                 ----------------
agreement among the parties with respect to the subject matter hereof and
supersedes other prior and contemporaneous arrangements or understandings with
respect thereto.

     SECTION 11. Notices.  All notices, consents and other communications under
                 -------
this Agreement shall be in writing and shall be deemed to have been duly given
(a) when delivered by hand, (b) one (1) business day after the business day of
transmission, if sent by telex or telecopier (with receipt confirmed), provided
that a copy is mailed by registered mail, return receipt requested, or (c) one
(1) business day after the business day of deposit with the carrier, if sent by
Express Mail, Federal Express or other express delivery service (receipt
requested), in each case to the appropriate addresses, telex numbers and
telecopier numbers set forth below (or to such other addresses or telecopy
numbers as a party may designate as to itself by notice to the other parties):

     (a)  If to Employee:

                 J. Ronald Lawter
                 28 Gablewing Circle
                 Newtown, PA 18940

     (b)  If to the Corporation:

                 OraPharma, Inc.
                 1200 Route 22 East
                 Suite 2000
                 Bridgewater, NJ 08807
                 Attention:  Chief Executive Officer
                 Telecopier No.:  (908) 806-6199

          with a copy to:

                 Sills Cummis Zuckerman Radin
                   Tischman Epstein & Gross, P.A.
                 One Riverfront Plaza
                 Newark, New Jersey 07102
                 Telecopier No.:  (201) 643-6500
                 Attention:  Ira A. Rosenberg, Esq.

     SECTION 12. Changes.  The terms and provisions of this Agreement may not
                 -------
be modified or amended, or any of the provisions hereof waived, temporarily or
permanently, without the prior written consent of each of the parties hereto.

     SECTION 13. Counterparts.  This Agreement may be executed in any number
                 ------------
of counterparts, and each such counterpart shall be deemed to be an original
instrument, but all such counterparts together shall constitute but one
agreement.

                                       10
<PAGE>

     SECTION 14. Headings.  The benefits of the various sections of this
                 --------
Agreements have been inserted for convenience of reference only and shall not be
deemed to be part of this Agreement.

     SECTION 15. Nouns and Pronouns.  Whenever the context may require, any
                 ------------------
pronouns used herein shall include the corresponding masculine feminine or
neuter forms, and the singular form of names and pronouns shall include the
plural and vice-versa.

     SECTION 16. Severability.  Any provision of this Agreement that is
                 ------------
prohibited or unenforceable in any jurisdiction shall, as to such jurisdiction,
be ineffective to the extent of such prohibition or unenforceability. Such
prohibition or unenforceability in any one jurisdiction shall not invalidate or
render unenforceable such provision in any other jurisdiction.

     SECTION 17. Governing Law; Jurisdiction.  This Agreement and (unless
                 ---------------------------
otherwise provided) all amendments hereof and waivers and consents hereunder
shall be governed by the internal law of the State of New Jersey, without regard
to the conflicts of law principles thereof.

     IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of
the date and year first written above.

WITNESS                            ORAPHARMA, INC.

/s/ [Signature illegible]          By: /s/ Michael D. Kishbauch
----------------------------           ------------------------------------
                                           Michael D. Kishbauch, President

WITNESS

/s/  Edgar J. Herman                   /s/ James R. Lawter
----------------------------           ------------------------------------
                                           J. Ronald Lawter

                                       11
<PAGE>

               AMENDMENT TO RESTRICTED STOCK PURCHASE AGREEMENT
               ------------------------------------------------

     This AMENDMENT TO RESTRICTED STOCK PURCHASE AGREEMENT (this "Amendment") is
                                                                  ---------
dated as of the 3rd day of September, 1999, by and between OraPharma, Inc., a
Delaware corporation (the "Corporation") and James R. Lawter (the
                           -----------
"Stockholder").
 -----------

                                  WITNESSETH:
                                  ----------

     WHEREAS, the Corporation and the Stockholder have previously entered into a
Restricted Stock Purchase Agreement pursuant to which the Stockholder purchased
from the Corporation shares of the Corporation's Common Stock, $.001 par value
per share (the "Agreement"); and
                ---------

     WHEREAS, the parties now desire to amend the Agreement as set forth herein.

     NOW, THEREFORE, for full and adequate consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto, intending to
be legally bound, hereby agree as follow:

     1.   A new Section 3(d) is hereby added to the Agreement to read in its
entirety as follows:

     "Notwithstanding anything contained in this Agreement to the contrary, if
     in connection with the consummation of a Change of Control the employment
     by the Corporation (or its successor) of the Stockholder is terminated by
     the Corporation (or such successor) without Cause, the Corporation's right
     to repurchase the Shares from the Stockholder pursuant to this Section 3
     shall be terminated, effective immediately prior to consummation of such
     Change of Control."

          For purposes hereof, a "Change of Control" shall mean any of the
          following:

               (i)    any person or entity, other than a person or entity who is
          a beneficial owner of the Corporation's securities before the
          consummation of the transaction, becomes, after such consummation, the
          beneficial owner, directly or indirectly, of securities of the
          Corporation representing fifty percent (50%) or more of the combined
          voting power of the Corporation's then outstanding securities;

               (ii)   the Corporation consummates a merger, consolidation or
          reorganization the result of which is that the persons or entities who
          were stockholders of the Corporation immediately prior to consummation
          of such transaction own less than fifty percent (50%) of the equity of
          the corporation or entity surviving or resulting from such
          transaction;

               (iii)  the sale in one or more series of transactions of all or
          substantially all of the assets of the Corporation; or
<PAGE>

               (iv)   the dissolution or liquidation of the Corporation.

          For purposes hereof, 'Cause' shall mean any of the following:

               (i)    the Stockholder is convicted of, pleads guilty to or
          confesses to (y) a felony, or (z) any act of fraud, misappropriation,
          embezzlement, dishonesty or disloyalty which damages the Corporation
          (or its successor) in any material respect;

               (ii)   substantial and repeated failure by the Stockholder to
     follow the direction of the Chief Executive Officer or Board of Directors
     of the Corporation (or its successor) and such failure is not cured within
     thirty (30) days after the Stockholder receives notice thereof from the
     Corporation (or its successor);

               (iii)  failure by the Stockholder to meet reasonable performance
          objectives; or

               (iv)   gross negligence or wilful misconduct of the Stockholder
          with respect to the Corporation (or its successor)."

     2.   This Amendment may be executed in several counterparts, each of which,
when executed and delivered, shall be deemed an original, and all of which
together shall constitute one agreement.

     3.   This Amendment shall be governed by and construed and interpreted in
accordance with the laws of the Commonwealth of Pennsylvania, without giving
effect to principles of conflicts law.

     4.   In the event there is a conflict between this Amendment and the
Agreement, the terms of this Amendment shall prevail.

     5.   Except as amended hereby, the Agreement shall remain in full force and
effect in accordance with its terms.
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed and delivered as of the day and year first above written.

                              ORAPHARMA, INC.

                              By: /s/ Michael D. Kishbauch
                                 -------------------------------------
                                      Michael D. Kishbauch

                              /s/ James R. Lawter
                              ----------------------------------------
                                  James R. Lawter

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