The aim of this study was to compare fracture resistance of teeth presenting medium-sized mesial-occlusal-distal (MOD) cavities using different base materials. Thirty-six extracted molars were immersed for 48 h in saline solution (0.1% thymol at 4 °C) and divided into six groups. In group A, the molars were untouched, and in group B, cavities were prepared, but not filled. In group C, we used zinc polycarboxylate cement, in group D—conventional glass ionomer cement, in group E—resin modified glass ionomer cement, and in group F—flow composite. Fracture resistance was tested using a universal loading machine (Lloyd Instruments) with a maximum force of 5 kN and a crosshead speed of 1.0 mm/min; we used NEXYGEN Data Analysis Software and ANOVA Method (p < 0.05). The smallest load that determined the sample failure was 2780 N for Group A, 865 N for Group B, 1210 N for Group C, 1340 N for Group D, 1630 N for Group E and 1742 N for Group F. The highest loads were 3050 N (A), 1040 N (B), 1430 N (C), 1500 N (D), 1790 N (E), and 3320 N (F), the mean values being 2902 ± 114 N (A), 972 ± 65 N (B), 1339 ± 84 N (C), 1415 ± 67 N (D), 1712 ± 62 N (E), and 2334 ± 662 N (F). A p = 0.000195 shows a statistically significant difference between groups C, D, E and F. For medium sized mesial-occlusal-distal (MOD) cavities, the best base material regarding fracture resistance was flow composite, followed by glass ionomer modified with resin, conventional glass ionomer cement and zinc polycarboxylate cement. It can be concluded that light-cured base materials are a better option for the analyzed use case, one of the possible reasons being their compatibility with the final restoration material, also light-cured.

Restoring teeth with second class cavities is a challenge in dentistry. Both the carious process and the preparation of the cavity for the dental restoration reduces the tooth resistance to the masticatory forces. It has been shown that modern aesthetic materials using an adhesive system improve the stress resistance of the restored teeth. There is a series of studies that attempted to determine the type of optimal material that would provide increased resistance to occlusal demands. In the present study we tried to determine the fracture resistance of molars with second class cavities restored with different categories of aesthetic materials. Thus, forty intact molars were divided into five groups of 8 teeth, MOD cavities were prepared and the teeth were restored with three types of materials: nanofilled composite, mycrohibrid composite and ormocer. The teeth of the first group were left unprepared, and those belonging to the second group were subjected to the preparation of MOD cavities but were not filled. Samples were subjected to compression using an Universal Loading Machine (Lloyd Instruments) and the value of the force they failed was recorded. Intact teeth showed the highest resistance to compression and those with MOD cavities prepared but not filled showed the smallest. Of the groups that benefited from restoration with filling material, the teeth restored with ormocer had the highest resistance, followed by those restored with nanofilled composite, and finally by those restored with mycrohibrid composite.