<PAGE>

THE SECURITIES REPRESENTED BY THE WARRANT DATED DECEMBER 3, 1996 AMENDED HEREBY
AND THIS AMENDMENT HAVE BEEN ACQUIRED FOR INVESTMENT AND HAVE NOT BEEN
REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED OR STATE SECURITIES
LAWS. THESE SECURITIES MAY NOT BE SOLD OR TRANSFERRED IN THE ABSENCE OF SUCH
REGISTRATION OR AN EXEMPTION THEREFROM UNDER SAID ACT OR STATE SECURITIES LAWS.

             ____________________________________________________

                          FIRST AMENDMENT TO WARRANT

  THIS FIRST AMENDMENT TO WARRANT dated as of February 11, 2000, by and between
ORAPHARMA, INC., a Delaware corporation (the "Company") and CANAAN CAPITAL
LIMITED PARTNERSHIP ("Holder").

                                   RECITALS

     A.  The Company and Holder entered into that certain warrant dated December
3, 1996 entitling the Holder, subject to the provisions of such warrant, to
purchase 334 fully paid, validly issued and nonassessable shares of Series A
Preferred Stock, par value $.001 per share, of the Company, at an exercise price
of $1.00 per share (the "Warrant").

     B.   The Company and Holder desire to make certain amendments to the
Warrant.

     NOW, THEREFORE, in consideration of the premises and the mutual covenants
hereinafter contained, the parties hereto agree that the initial paragraph of
the Warrant shall hereby be amended and restated as follows:

           Series A Preferred Stock or Common Stock Purchase Warrant

     This is to certify that, FOR VALUE RECEIVED, CANAAN CAPITAL LIMITED
PARTNERSHIP (the "Holder"), is entitled to purchase, subject to the provisions
                  ------
of this Warrant, from OraPharma, Inc. a Delaware corporation (the "Company"),
                                                                   -------
334 fully paid, validly issued and nonassessable shares of either Series A
Preferred Stock, par value $.001 per share, of the Company (the "Preferred
                                                                 ---------
Stock") or Common Stock, par value, $.001 per share, of the Company (the "Common
-----
Stock"), at an exercise price of $1.00 per share. The number of shares of
Preferred Stock to be received upon the exercise of this Warrant and the price
to be paid for each share of Preferred Stock may be adjusted from time to time
as hereinafter set forth. The number of shares of Common Stock to be received
upon the exercise of this Warrant and the price to be paid for each share of
Common Stock may be adjusted from time to time on terms identical to those
applicable to the Preferred Stock. The shares of Preferred Stock and/or Common
Stock deliverable upon such exercise, and as adjusted from time to time, are
hereinafter sometimes referred to as "Warrant Shares" and the exercise price of
                                      --------------
a share of Preferred Stock or Common Stock in effect at any time and as adjusted
from time to time is hereinafter referred to as the "Exercise Price". In the
                                                     --------------
event the outstanding shares of Preferred Stock are automatically converted into
shares of the Company's Common Stock in accordance with the terms of the
Preferred Stock as set forth in the Company's
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Fourth Restated Certificate of Incorporation, this Warrant shall immediately
become exercisable for shares of the Company's Common Stock on terms identical
to those applicable to the Preferred Stock. In no event shall both the
provisions of Section 4 of the Warrant and the provisions of the Company's
Fourth Restated Certificate of Incorporation be applied concurrently to effect
an increase in the relative equity interest in the Company of the Holder of this
Warrant over the amount of increase which would have occurred if the Holder had
acquired shares of Preferred Stock rather than the Warrant on December 3, 1996.

     This Agreement may be executed in any number of separate counterparts, each
of which shall, collectively, constitute one agreement.

     IN WITNESS WHEREOF, this Agreement has been duly executed as of the date
first written above.

                                   CANAAN CAPITAL LIMITED PARTNERSHIP

                                   By:  Canaan Capital Management
                                        L.P., General Partner
                                   By:  Canaan Capital Partners L.P.,
                                        General Partner


                                        By: /s/ [ILLEGIBLE]
                                           ---------------------------
                                           Name:
                                           Title:


Accepted and Agreed:


ORAPHARMA, INC.


By: /s/ Michael Kishbauch
   -------------------------------------
    Michael Kishbauch, President and CEO