Effect of cusp coverage and water storage on compressive strength of composite restorations of premolars

BACKGROUND: The aim of this study was to assess the effect of cusp coverage and water storage on compressive strength of composite restorations. MATERIAL AND METHODS: This in vitro experimental study was conducted on 40 extracted human maxillary premolar teeth, which were randomly divided into four groups of 10. Mesio-occluso-distal (MOD) cavities were prepared in all teeth. The thickness of composite for cusp coverage was 1.5 mm in groups 1 and 3 and 2.5 mm in groups 2 and 4. Compressive strength (CS) was measured after 24 hours in groups 1 and 2 and after six months of water storage in groups 3 and 4. Two-way ANOVA was used to statistically analyze the data. RESULTS: The mean and standard error (SE) of compressive strength was 795.23 ± 35.18N in Group 1, 1232.52 ± 78.01N in Group 2, 617.18 ± 40.19N in Group 3 and 963.22 ± 50.05N in Group 4. CONCLUSIONS: Statistical analysis showed a significant difference in compressive strength measured after 24 hours (groups 1 and 3) and after six months of water storage (groups 2 and 4). The compressive strength of groups with 2.5 mm cusp coverage was significantly greater than that of groups with 1.5 mm cusp coverage. Key words:Fracture strength, cusp coverage, water absorption, composite resin, compressive strength.