X0201 4 2004-04-13 0 0001028087 AMERICAN DENTAL PARTNERS INC ADPI 0001018067 MANNION MARTIN J C/O SUMMIT PARTNERS 222 BERKELEY ST., 18TH FLOOR BOSTON MA 02116 1 0 0 0 0001018056 STAMPS E ROE IV C/O SUMMIT PARTNERS 222 BERKELEY STREET, 18TH FLOOR BOSTON MA 02116 0 0 0 1 Indirect GP of 10% Owner 0001018073 WOODSUM STEPHEN G C/O SUMMIT PARTNERS 222 BERKELEY STREET, 18TH FLOOR BOSTON MA 02116 0 0 0 1 Indirect GP of 10% Owner 0001018068 AVIS GREGORY M C/O SUMMIT PARTNERS 222 BERKELEY STREET, 18TH FLOOR BOSTON MA 02116 0 0 0 1 Indirect GP of 10% Owner 0001018062 EVANS BRUCE R C/O SUMMIT PARTNERS 222 BERKELEY STREET, 18TH FLOOR BOSTON MA 02116 0 0 0 1 Indirect GP of 10% Owner 0001018059 KORTSCHAK WALTER G C/O SUMMIT PARTNERS 222 BERKELEY STREET, 18TH FLOOR BOSTON MA 02116 0 0 0 1 Indirect GP of 10% Owner 0001018057 ROBERTS THOMAS S C/O SUMMIT PARTNERS 222 BERKELEY ST., 18TH FLOOR BOSTON MA 02116 0 0 0 1 Indirect GP of 10% Owner 0001018075 SUMMIT INVESTORS II LP C/O SUMMIT PARTNERS 222 BERKELEY STREET, 18TH FLOOR BOSTON MA 02116 0 0 0 1 Affiliate of 10% Owner Common Stock 2004-04-13 4 S 0 2361762 15.2 D 0 I Indirect General Partner of 10% Owner 2,272,016 shares held in the name of Summit Ventures IV, L.P. 89,746 shares held in the name of Summit Investors II, L.P. All persons/entities shown here hold all such shares indirectly, with the exception of Summit Investors II, L.P., which holds 89,746 shares directly. The Indirect General Partners of the 10% Owner listed here disclaim beneficial ownership of any of such shares to which they do not have an actual pecuniary interest. Martin J. Mannion 2004-04-14