Comparative Evaluation of Fracture Strength of Cusp Coverage with Composite Versus Unsupported Enamel Reinforced with Composite in Posterior Dental Restorations

Background and aim: Efficient bonding techniques should be employed for strengthening tooth structure. Whether to preserve intact dental tissue or to sacrifice some undermined parts can still be challenging. We aimed to evaluate the fracture strength of cusp coverage with composite versus unsupported enamel reinforced with composite in posterior restorations. Materials and methods: In this in-vitro study, over-impressions were made from 36 sound human maxillary premolars using bleaching shields. The teeth were randomly divided into three groups (n=12): group 1) intact teeth, group 2) teeth with MOD cavities without cusp coverage, and group 3) teeth with MOD cavities and 1.5 mm of buccal and palatal cusp coverage. Wide MOD cavities were prepared such that only 1 mm of intact enamel was left unsupported at margins. The cavities were restored using light-cure glass ionomer and P60 composite using the over-impressions to achieve the normal tooth anatomy. The teeth were stored in water at 37°C for a week, and their fracture resistance was assessed using a universal testing machine. The load at fracture was recorded in Newton (N). Data were analyzed using one-way analysis of variance (ANOVA) and Tukey’s test with a 95% confidence interval (CI). Results: The mean±standard deviation (SD) of fracture load was 1834.62±104.04 N in group 1, 750.34±147.46 N in group 2, and 1211.30±210.85 N in group 3. One-way ANOVA revealed significant differences between the groups (P=0.001). Likewise, Tukey’s test showed that the difference between the groups was statistically significant (P<0.05). Conclusion: Using composite in restoring unsupported enamel must be combined with cusp coverage to increase fracture strength

Effect of ferrule preparation on fatigue resistance of teeth restored with quartz-fiber posts

&quot;nBackground and Aim: A key factor in restoring the endodontically treated teeth is ferrule preparation. When the ferrule is absent, occlusal loads may cause the post or root to fracture. The purpose of this in vitro study was to evaluate the effect of ferrule preparation on fatigue resistance of teeth restored with quartz-fiber posts. &quot;nMaterials and Methods: Twenty single-rooted lower premolars having similar dimentions were randomly devided into two groups of 10. In control group the teeth were prepared with 3-mm of remaining coronal tooth structure and in test group teeth were prepared with 1-mm of remaining coronal tooth structure. The teeth were endodontically treated. 9-mm long Post holes were prepared, and D.T. light quartz-fiber(RTD,France) posts were cemented with Panavia F2(Kuraray,Japan).Then the core build up was done with Bisco core build up composite(Bisco,USA) and full metal crowns were cemented with Zinc phosphate(Harvard cement, Germany). All specimens were mounted in acrylic resin blocks and intermittently loaded (180 N) at an angulation of 45- degree to the long axis of the teeth at a frequency of 4 loads per second, until failure occurred. &quot;nResults: There was significant difference between the loads cycles of two groups studied. (p&amp;lt;0.0001). &quot;nConclusion: The results of this study showed that an increased amount of coronal dentin significantly increases the fracture resistance of teeth restored with quartz-fiber posts