Effect of Occlusal and Brushing Forces on Combined Wear

Objectives: The purpose of this study was to investigate the effect of occlusal and brushing forces on the combined wear test which was the combination of both occlusal and toothbrush wears. Methods: In the combined wear test, specimens were exposed to both types of wear alternately, after 500 cycles of each type. The alternation was repeated 24 times resulting in a total of 24,000 cycles. A ceramic antagonist which has a round tip (2 mm diameter) was used in the occlusal wear. The antagonist reciprocated on a specimen under 40 N or 80 N with a 1 mm sliding distance. In toothbrush wear, a commercial toothbrush slid on a specimen under 1.5 N or 3N. The sliding distance and speed were 30mm and 40 mm/s, respectively. Four resin composites: Clearfil AP-X (KURARAY, Japan), Z100 (3M, USA), SOLARE P (GC, Japan) and SOLIDEX-F (SHOFU, Japan) were tested in this study. Volume loss and maximum depth after the combined wear test were measured using a computed measuring microscope. Results: Analysis of variance showed that significant differences of volume loss were found among resin composites (p<0.01), between occlusal forces (p<0.01) and between brushing forces (p<0.05). Volume loss was larger when high occlusal force and high brushing force was used in the combined wear test. Analysis of variance showed that significant differences of maximum depth were found among resin composites (p<0.01) and between occlusal forces (p<0.01). At the higher occlusal force maximum depth was greater than at the lower force. Conclusion: Significant differences both in the volume loss and maximum depth after the combined wear test were found between different resin composites. Both occlusal and brushing forces influenced the volume loss of the resin composites, but the maximum depth was influenced only by the occlusal force.