Comparison of proximal in vitro tooth contacts in class II restorations with different restorative materials and cavity sizes using a new measurement device

This study used a newly developed proximal contact strength (PCS) device to evaluate the tightness of proximal tooth contact for Class II cavity size restoration with different materials using an auxiliary separation ring system. A measurement device based on the equilibrium of forces acted on the clamp rod converts a pull-out force between interdental spaces on a force sensing resistor to express the PCS. This device was designed using dental floss as the test end and can be moved with constant speed during measurement through a bevel gear that transforms the rotation of motor shaft into linear movement of clamp rod. A manikin model was used with 60 artificial first molars in which an mesial occlusal (MO) preparation was ground. Samples were divided into six groups (each n = 10) for simulating amalgam and resin composite restoration with three different cavity sizes. The different cavities were defined using the ratio of the actual isthmus width to the intercuspal width (W) to 1/3, 2/3 and 1. The PCS value in each sample was measured after restoration. The result showed that the mean PCS value and standard deviation were 2283.1 ± 216.5 gf, 2419.1 ± 375 gf and 1737.6 ± 372.7 g for 1/3 W, 2/3 W and W cavities of the amalgam restoration, respectively. The corresponding PCS values were 1178.0 ± 230.4 gf, 1205.8 ± 249.1 gf and 1247.0 ± 157.5 gf for 1/3 W, 2/3 W and W cavities of the resin composite restoration. PCS values with amalgam restoration were larger than those for resin composite restorations under the same cavity size. Large cavity (W) PCS might be lost with amalgam restoration. No significant difference was found in resin composite restoration PCS among the different cavity sizes.