Class IV preparation design for microfilled and macrofilled composite resin.

The current standard preparation for Class IV composite restorations is the placement of a bevel on all enamel margins. This study evaluated chamfered and beveled preparations for Class IV restorations of lesions with microfilled and macrofilled composite resin. Forty incisors were obtained and standardized lesions for Class IV restorations were formed. Twenty teeth had a 1.5-mm bevel placed and 20 had a 1.5-mm chamfered preparation placed. Half of the beveled and chamfered preparations were restored with microfilled composite resin; the remaining were restored with macrofilled composite resin. All restorations were fractured with an Instron Testing Machine. The mean force (lbs +/- SD) to fracture the restorations were: (beveled, microfilled composite 16.0 +/- 4.4); (chamfered, microfilled composite 30.6 +/- 20.0); (beveled, macrofilled composite 34.9 +/- 18.6); (chamfered, macrofilled composite 48.8 +/- 14.3). The chamfered preparations provided greater restoration fracture resistance than beveled preparations, for both microfilled and macrofilled composite restorations. Scheffe's test indicated traditional beveled, microfilled Class IV composite resin restorations significantly decreased fracture resistance compared to chamfered, macrofilled composite restorations (P less than 0.001).