<PAGE>   1
                                                                     EXHIBIT 4.2

                                                                       EXHIBIT A
                                                             TO CREDIT AGREEMENT




                                            FORM OF REVOLVING CREDIT NOTE

THIS NOTE MAY NOT BE TRANSFERRED EXCEPT IN COMPLIANCE WITH THE TERMS AND
PROVISIONS OF THE THIRD AMENDED AND RESTATED CREDIT AGREEMENT REFERRED TO BELOW.
TRANSFERS OF THIS NOTE MUST BE RECORDED IN THE REGISTER MAINTAINED BY THE
ADMINISTRATIVE AGENT PURSUANT TO THE TERMS OF SUCH THIRD AMENDED AND RESTATED
CREDIT AGREEMENT.


$                                                             New York, New York
 -----

                                                                     -----------


         FOR VALUE RECEIVED, each of the undersigned, Sybron International
Corporation ("Parent"), a Wisconsin corporation, Kerr Corporation ("Kerr"), a
Delaware Corporation, and Nalge Nunc International Corporation ("NNI"), a
Delaware Company (each, a "Revolving Credit Borrower"), severally, hereby

    The unconditionally promises to pay to the order of          (the Lender")
at the office of The Chase Manhattan Bank, located at 270 Park Avenue, New York,
New York 10017, in lawful money of the United States of America and in
immediately available funds, on the Termination Date the lesser of (a) the
principal amount of    DOLLARS ($      ), and (b) the aggregate unpaid principal
amount of all Revolving Credit Loans made by the Lender to such Revolving Credit
Borrower pursuant to subsection 2.1 of the Credit Agreement, as hereinafter
defined. Each Revolving Credit Borrower, severally, further agrees to pay
interest in like money at such office on the unpaid principal amount of
Revolving Credit Loans of such Revolving Credit Borrower from time to time
outstanding at the rates and on the dates specified in subsection 2.19 of such
Credit Agreement.

         The holder of this Note is authorized to endorse on the appropriate
schedules annexed hereto and made a part hereof or on a continuation thereof
which shall be attached hereto and made a part hereof the date, Type and amount
of each Revolving Credit Loan made by such holder to each Revolving Credit
Borrower pursuant to the Credit Agreement and the date and amount of each
payment or prepayment of principal thereof, each continuation thereof, each
conversion of all or a portion thereof to another Type and, in the case of
Eurodollar Loans, the length of each Interest Period and the Eurodollar Rate
with respect thereto. Each such endorsement shall constitute prima facie
evidence of the accuracy of the information endorsed. The failure to make any
such endorsement shall not affect the obligations of the Revolving Credit
Borrower in respect of such Revolving Credit Loan.

         This Note (a) is one of the Revolving Credit Notes referred to in the
Third Amended and Restated Credit Agreement dated as of July        , 1999 (as
amended, supplemented or otherwise modified from time to time, the "Credit
Agreement"), among the Parent, Kerr, NNI, Ormco


<PAGE>   2
                                                                               2



Corporation, a Delaware corporation, Erie Scientific Company, a Delaware
corporation, Barnstead Thermolyne Corporation, a Delaware corporation, Remel,
Inc., a Wisconsin corporation, the Lender, the other banks and financial
institutions from time to time parties thereto, Chase Securities Inc., as
arranger, and The Chase Manhattan Bank, as administrative agent, (b) is subject
to the provisions of the Credit Agreement and (c) is subject to optional and
mandatory prepayment in whole or in part as provided in the Credit Agreement.
This Note is secured and guaranteed as provided in the Loan Documents. Reference
is hereby made to the Loan Documents for a description of the assets in which a
security interest has been granted, the nature and extent of the security and
the guarantees, the terms and conditions upon which the security interests and
each guarantee were granted and the rights of the holder of this Note in respect
thereof.

         Upon the occurrence of any one or more of the Events of Default, all
amounts then remaining unpaid on this Note shall become, or may be declared to
be, immediately due and payable, all as provided in the Credit Agreement.

         All parties now and hereafter liable with respect to this Note, whether
maker, principal, surety, guarantor, endorser or otherwise, hereby waive
presentment, demand, protest and all other notices of any kind, except as
otherwise provided in any of the Loan Documents.

         Unless otherwise defined herein, terms defined in the Credit Agreement
and used herein shall have the meanings given to them in the Credit Agreement.

         THIS NOTE SHALL BE GOVERNED BY, AND CONSTRUED AND INTERPRETED IN
ACCORDANCE WITH, THE LAW OF THE STATE OF NEW YORK.

                                      SYBRON INTERNATIONAL CORPORATION


                                      By:
                                         ---------------------------------------
                                         Name:
                                         Title:



                                      KERR CORPORATION


                                      By:
                                         ---------------------------------------
                                         Name:
                                         Title:



<PAGE>   3


                                      NALGE NUNC INTERNATIONAL
                                      CORPORATION


                                      By:
                                         ---------------------------------------
                                         Name:
                                         Title:















<PAGE>   4



                                                                    Schedule A-1
                                                        to Revolving Credit Note


                                     PARENT
                 LOANS, CONVERSIONS AND REPAYMENTS OF ABR LOANS

<TABLE>
<CAPTION>

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                                Amount                               Amount of ABR Loans
                             Converted to   Amount of Principal of      Converted to          Unpaid Principal
 Date  Amount of ABR Loans    ABR Loans        ABR Loans Repaid       Eurodollar Loans      Balance of ABR Loans  Notation Made By
------------------------------------------------------------------------------------------------------------------------------------
<S>   <C>                   <C>            <C>                      <C>                    <C>                   <C>

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====================================================================================================================================

</TABLE>

<PAGE>   5



                                                                    Schedule A-2
                                                        to Revolving Credit Note


                                      KERR
                  OANS, CONVERSIONS AND REPAMENTS OF ABR LOANS


<TABLE>
<CAPTION>

------------------------------------------------------------------------------------------------------------------------------------

                                Amount                               Amount of ABR Loans
                             Converted to   Amount of Principal of      Converted to          Unpaid Principal
 Date  Amount of ABR Loans    ABR Loans        ABR Loans Repaid       Eurodollar Loans      Balance of ABR Loans  Notation Made By
------------------------------------------------------------------------------------------------------------------------------------
<S>   <C>                   <C>            <C>                     <C>                     <C>                   <C>

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====================================================================================================================================

</TABLE>


<PAGE>   6



                                                                    Schedule A-3
                                                        to Revolving Credit Note


                                       NNI
                  OANS, CONVERSIONS AND REPAMENTS OF ABR LOANS


<TABLE>
<CAPTION>

------------------------------------------------------------------------------------------------------------------------------------

                                Amount                               Amount of ABR Loans
                             Converted to   Amount of Principal of      Converted to          Unpaid Principal
 Date  Amount of ABR Loans    ABR Loans        ABR Loans Repaid       Eurodollar Loans      Balance of ABR Loans  Notation Made By
------------------------------------------------------------------------------------------------------------------------------------
<S>   <C>                   <C>            <C>                      <C>                    <C>                   <C>

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====================================================================================================================================

</TABLE>


<PAGE>   7



                                                                    Schedule B-1
                                                        to Revolving Credit Note

                                     PARENT
      LOANS, CONTINUATIONS, CONVERSIONS AND REPAYMENTS OF EURODOLLAR LOANS



<TABLE>
<CAPTION>

------------------------------------------------------------------------------------------------------------------------------------

                                                                          Amount of        Amount of       Unpaid Principal
                                               Interest Period and      Principal of       Eurodollar         Balance of
          Amount of        Amount Converted    Eurodollar Rate with   Eurodollar Loans  Loans Converted to    Eurodollar    Notation
 Date  Eurodollar Loans   to Eurodollar Loans     Respect Thereto          Repaid           ABR Loans           Loans       Made By
------------------------------------------------------------------------------------------------------------------------------------
<S>   <C>                <C>                  <C>                    <C>               <C>                <C>              <C>

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====================================================================================================================================

</TABLE>


<PAGE>   8



                                                                    Schedule B-2
                                                        to Revolving Credit Note

                                      KERR
      LOANS, CONTINUATIONS, CONVERSIONS AND REPAYMENTS OF EURODOLLAR LOANS



<TABLE>
<CAPTION>

------------------------------------------------------------------------------------------------------------------------------------

                                                                          Amount of        Amount of       Unpaid Principal
                                               Interest Period and      Principal of       Eurodollar         Balance of
          Amount of        Amount Converted    Eurodollar Rate with   Eurodollar Loans  Loans Converted to    Eurodollar    Notation
 Date  Eurodollar Loans   to Eurodollar Loans     Respect Thereto          Repaid           ABR Loans           Loans       Made By
------------------------------------------------------------------------------------------------------------------------------------
<S>   <C>                <C>                  <C>                    <C>               <C>                <C>              <C>

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====================================================================================================================================

</TABLE>


<PAGE>   9



                                                                    Schedule B-3
                                                        to Revolving Credit Note

                                       NNI
      LOANS, CONTINUATIONS, CONVERSIONS AND REPAYMENTS OF EURODOLLAR LOANS


<TABLE>
<CAPTION>

------------------------------------------------------------------------------------------------------------------------------------

                                                                          Amount of        Amount of       Unpaid Principal
                                               Interest Period and      Principal of       Eurodollar         Balance of
          Amount of        Amount Converted    Eurodollar Rate with   Eurodollar Loans  Loans Converted to    Eurodollar    Notation
 Date  Eurodollar Loans   to Eurodollar Loans     Respect Thereto          Repaid           ABR Loans           Loans       Made By
------------------------------------------------------------------------------------------------------------------------------------
<S>   <C>                <C>                  <C>                    <C>               <C>                <C>              <C>

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====================================================================================================================================

</TABLE>