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Comparison of different base materials on fracture strength of mesio-occlusal-distal composite restorations

Objective: The aim of this study was to evaluate the influence of different base materials on fracture strength of mesio-occlusal-distal (MOD) composite restorations. Materials and Methods: Forty-eight extracted, intact maxillary molar teeth with standardized, deep MOD cavities were randomly assigned into four groups according to the base material placed: Control group (CO); no base material, SDR group; bulk-fill flowable composite, CGIC group; chemically curing glass ionomer cement (GIC), and RGIC group; light curing resin reinforced GIC. All the specimens were then restored with a nanocomposite (CeramX Duo/Dentsply) in combination with etch and rinse adhesive following the manufacturer's instructions. After aging fracture, strength of the specimens was tested by the application of a ramped oblique load to the buccal cusp in a universal testing machine. Mean fracture strength values for each group were calculated and compared using one-way ANOVA (P = 0.05). Fracture patterns of the specimens were also evaluated. Results: The mean loads necessary to fracture the samples were as follows: control: 819.22 ± 253.65; SDR: 694.46 ± 266. 55; CGIC: 559.15 ± 277.34; RGIC 861.87 ± 277.28: N. The control and RGIC groups showed significantly higher fracture strength than CGIC and SDR groups (P < 0.05). Although the mean fracture strength value of SDR group was higher than that of CGIC group, the difference between these groups was not statistically significant (P > 0.05). Most frequently observed fracture patterns were adhesive (58.3%) in CO, cohesive (50%) in SDR group, cohesive (83.3%) in CGIC group, and mixed (41.7%) in RGIC group. Conclusions: Resin-modified glass-ionomer cement as a base material or restoration of the tooth only with composite resin resulted in higher fracture strength than composite resin restoration with a conventional glass ionomer base or a flowable bulk-fill material. Fracture pattern distributions diversed according to the base material placed under composite restoration.