Enamel wear opposing different surface conditions of different CAD/CAM ceramics.

OBJECTIVE: The aim of this study was to evaluate bovine enamel wear opposed to four different ceramic substrates (CEREC) in the glazed and polished conditions. METHOD AND MATERIALS: Sixty-three ceramic (IPS Empress CAD, Paradigm C, Vitablocs Mark II) and fourteen composite resin (MZ100) styli were prepared. Ceramics were subdivided into three surface conditions (n = 7), unpolished, polished, and glazed, and the composite resin (n = 7) into unpolished and polished. All styli were used as wear antagonists opposing bovine enamel blocks (8 mm × 9 mm) in an oral wear simulator. Wear tests were conducted at 30 N abrasion and 70 N attrition forces applied at 1.7 Hz for 5,000 simulated mastication cycles. Abrasion and attrition wear were evaluated using an automatic profilometer. Statistical analyses were conducted using Tukey's B rank order test, P = .05. RESULTS: For bovine enamel opposing glazed Vitablocs, abrasion and attrition wear showed a volume loss significantly higher than bovine enamel opposing polished Vitablocs (P < .05). For attrition wear, bovine enamel opposing glazed Vitablocs and untreated Paradigm C showed a volume loss higher than bovine enamel opposing the other ceramic conditions. CONCLUSION: Abrasion and attrition wear of bovine enamel opposing antagonist ceramic was affected according to the ceramic surface condition and the ceramic material. Antagonistic wear against the studied ceramic materials and conditions exhibited wear rates within the range of normal enamel. In addition, the glaze layer presented as a protection, exhibiting fewer cracks and less loss of material on the ceramic surface.

Neutral evolution of synonymous base composition in the Brassicaceae.

The GC content of synonymous sites is elevated in genes from both Brassica oleraceae and Arabidopsis lyrata compared with Arabidopsis thaliana. However, this shift in base composition is independent of gene expression level, and there is no evidence for a similar difference in the frequency of codons preferred by translational selection. The results suggest that composition evolution is caused by a change in mutation bias or biased gene conversion, rather than by a reduction in the efficacy of natural selection in selfing Arabidopsis.