<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 is dated as of February 11, 2000, by and
between ORAPHARMA, INC., a Delaware corporation (the "Company") and CANAAN
S.B.I.C., L.P. ("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 28,125 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 S.B.I.C., L.P. (the
"Holder"), is entitled to purchase, subject to the provisions of this Warrant,
 ------
from OraPharma, Inc. a Delaware corporation (the "Company"), 28,125 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 Fourth Restated Certificate of
<PAGE>

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 S.B.I.C., L.P.

                                        By:  Canaan S.B.I.C. Partners, L.P.,
                                             General Partner

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


Accepted and Agreed:


ORAPHARMA, INC.


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