Restoration techniques and marginal overhang in Class II composite resin restorations

The objective of the study was to compare in vitro interproximal overhang formation of Class II composite resin restoration when using different matrix systems.

240 lower left molar phantom head teeth with an MO-preparation were divided into 12 groups (n=20). In six groups a circumferential matrix (Tofflemire X-thin matrix, HaweNeos 1001-c, SuperCap) was used, combined with either a hand-instrument (PFI49 or OptraContact) or separation ring (Composi-Tight Gold). In the other six groups two sectional matrix systems were used (flexible and dead-soft), with three separation rings (Composi-Tight Gold, Contact Matrix, Palodent BiTine). Matrices were secured with wooden wedges and preparations were restored with composite resin Clearfil AP-X (Kuraray) placed and polymerized in increments. After matrix removal overhang was measured on a standardized digital macroscopic image in mm(2). For analysis a multiple linear regression model was used.

Use of circumferential matrices resulted in less overhang than sectional matrices (-0.85 mm2, p<0.001). A flexible matrix led to less overhang than dead-soft matrices (-0.54mm2, p<0.001), and no difference was found between straight and pre-contoured matrices (p=0.945). The insertion of the OptraContact resulted in a much increased overhang of 2.54 mm2 (p<0.001). The Composi-Tight Gold and the Contact Matrix System rings resulted in less overhang, -0.69 and -0.68 mm(2), respectively (both p<0.001), whereas the Palodent BiTine ring did not.

Use of circumferential matrices or sectional flexible matrices resulted in the least marginal overhang when combined with a Contact Matrix separation ring or a Composi-Tight Gold ring.