Is dentin analogue material a viable substitute for human dentin in fatigue behavior studies?

This study aimed to compare the fatigue performance of a lithium disilicate ceramic cemented on different substrates (human dentin and glass fiber-reinforced epoxy resin - GFRER), treated with different types of conditioning (CTR - without surface conditioning; HF5 - 5% hydrofluoric acid; HF10 - 10% hydrofluoric acid; H3PO4 - phosphoric acid 37%; SAND - sandblasting with aluminum oxide). The occlusal surface of human molars (DENT group) (n = 15) was ground for dentin exposure and the root portion was cut, then the dentin slice (2.0 mm thick) was conditioned with 37% phosphoric acid and a dual-curing dental adhesive was applied. The GFRER in a round-rod format was cut into discs (Ø = 10 mm, 2.0 mm thick). Lithium disilicate glass ceramic blocks (IPS e.max CAD, Ivoclar, Schaan, Liechtenstein) were shaped into a cylinder format and cut, resulting in 90 discs (Ø = 10 mm, 1.5 mm thick). The substrate materials of each group were etched according to the groups and the ceramic was etched with 5% hydrofluoric acid for 30 s. A silane coupling agent was applied over the cementation surface in ceramic and GFRER surfaces and a dual cement was used for cementation (ceramic/GFRER or dentin). The disc/disc sets were submitted to thermocycling (25,000 cycles + storage for 6 months), and then tested in step-wise accelerated cyclic fatigue test. The failure pattern and topography were analyzed and the roughness and contact angle were measured before and after surface treatment. The DENT group presented the lowest load to failure values and number of cycles to failure in fatigue (637.33 N; 118.333), showing no statistical similarity with any of the other tested groups (p < 0.05). The topographic analysis showed that all proposed surface treatments modified the substrate surface when compared to the CTR group. All of the fractographical inspections demonstrated failure by radial crack. Considering the roughness analysis, the post-etched DENT group showed similar roughness to all groups of GFRER materials with their surface treated, except for SAND, which showed greater roughness and statistically different from the other groups. The DENT group (49.5) showed statistically different post-conditioning contact angle values from the HF10 group (96.5) and similar to the other groups. The glass fiber-reinforced epoxy resin was not able to simulate the results presented by the human dentin substrate when cemented to lithium disilicate regarding fatigue failure load and number of cycles for failure, regardless of the surface treatment. Lithium disilicate cemented on dentin analogue overestimates the load values for fatigue failure.

Bovine tooth is a substitute for human tooth on bond strength studies: A systematic review and meta-analysis of in vitro studies.

OBJECTIVES: This study aimed to systematically review the literature to compare the bond strength values achieved from human and bovine teeth of in vitro studies. DATA AND SOURCE: The PubMed/MEDLINE, ISI Web of Science and Scopus electronic databases were searched to select laboratorial studies that evaluated adhesive systems bond strength to human and bovine teeth. No publication year or language restriction was considered. STUDY SELECTION: From 1,285 potentially eligible studies, 15 were selected for full-text analysis, 11 were included in the systematic review and 9 in the meta-analysis. Two authors independently selected the studies, extracted the data and assessed the risk of bias. Mean differences were obtained by comparing bond strength values between human and bovine teeth (overall analysis), and considering enamel and dentin separately (subgroups analysis). Statistical analysis was performed using RevMan5.1, with random effects model, at a significance level of p=0.05. RESULTS: No significant difference was found between human and bovine teeth (p=0.35), either for enamel (p=0.07) or for dentin (p=0.93) substrates. Low to moderate heterogeneity was found on the meta-analysis. All included studies in the systematic review scored between medium and high risk of bias. CONCLUSIONS: Bovine teeth can be a reliable substitute for human ones on bond strength studies of adhesive systems to both enamel and dentin substrates.