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Tooth enamel wear occurs because of daily mastication and occlusion. This study investigated the wear behavior of bovine teeth against aesthetic restorative materials in vitro. Abrader specimens were fabricated using four tooth-colored restorative materials (zirconia, lithium disilicate glass ceramic, dental porcelain, and resin composite), with bovine tooth enamel as a control. Flattened bovine tooth enamel was used as the substrate specimen. These materials were characterized by Vickers hardness tests and surface roughness measurements. Two-body wear tests between the abrader and substrate specimens were performed, and the worn topographies were evaluated using a contour-measuring instrument and 3D laser microscope. The restorative materials and bovine tooth enamel had similar surface roughness but different hardness and wear behaviors. Bovine teeth showed the largest wear in tooth–tooth contact as the abrader and substrate specimens. Compared to bovine teeth, zirconia, lithium disilicate glass ceramic, and dental porcelain showed greater hardness and less wear on their surfaces, and less substrate wear of the opposite tooth enamel. The lowest hardness resin composite showed intermediate wear on its surface, resulting in the lowest substrate wear. Accordingly, dentists should pay attention to the selection of restorative materials to reconstruct their morphologies owing to different wear behaviors.

A novel one-pot synthetic method was developed for the preparation of optically active cyanohydrin acetates. Racemic cyanohydrins were generated from aldehydes and acetone cyanohydrin by quinidine-catalyzed transhydrocyanation, and the resulting cyanohydrins 2a–j were then acetylated by lipase in a stereoselective manner using isopropenyl acetate as an acylating regent. A variety of aldehydes 1a–j were successfully transformed into the corresponding cyanohydrin acetates 3a–j having 47–95% e.e. without isolating the unstable cyanohydrins 2. Moreover, the reversible nature of base-catalyzed transhydrocyanation allows for in situ racemization of the unreacted cyanohydrins and concurrent kinetic resolution by lipase enabled the preparation of (S)-3b–d with 40–82% e.e. in more than 50% yield. Polymer-supported cinchona alkaloid was also used as a catalyst for this one-pot reaction and showed the comparable chemical and optical yield to that for the soluble monomeric alkaloid. The insoluble polymer and lipase were recovered by filtration and found to have almost the same catalytic activity even after four times of reuse.

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Amongthe methods for racemization testing in peptide synthesis, the GLCmethod is a simple one and the most practicable, especially when a packed column is used. In this method Tfa-Pro-X-OH (X=amino acids) is coupled with H-Val-Pro-OMe, the resulting Tfa-tetrapeptide-OMe is separated by GLC, and the degree of recemization is estimated from the ratio of the peaks separated to the diastereoisomers ldll and llll.1 2) The Tfa-Pro-X-OH used in this method has been prepared in several ways: for example, Tfa-Pro-Val-OH was prepared via Tfa-Pro-Val-O'Bu, which was obtained by direct condensation1 2' of both the amino acid derivatives or by replacement of Z-with the Tfa group from Z-Pro-Val-OlBu.2) It has also been prepared from Z-Pro-Val-OMe by saponification and subsequent replacement of Z-with the Tfa group.3) These methods were, however, fairly laborious in starting from amino acids. In this paper, we report a simpler procedure for preparing such compounds, Tfa-Pro-OH being coupled with H-X-OBzl to give Tfa-Pro-X-OBzl,