The correlation of the vibroacoustic signal with the wear of a ceramic part during frictional interaction with a steel disc

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Changing the structure of the surface layer of ceramic products during operation. Part 2

Kinetics of structure changes of surface layer of ceramic part outside the area of contact interaction during operation was studied with using original technique. The main regularities of this process are established and the influence of defect degree of initial surface layer on the changes occurring was revealed.

Influence of Teeth Preparation Finishing on the Adaptation of Lithium Disilicate Crowns

The polishing step of teeth preparations for crowns is a step often performed, so that there is an increased time during the clinical procedure. The aim of this study is to evaluate the marginal and internal adaptation of all-ceramic CAD/CAM lithium disilicate crowns in polished preparations for crown and nonpolished preparations for crowns. For this purpose, 20 first molars were selected, which were divided into two groups (n=10) G1, teeth that received surface roughening similar to preparation without polishing, and G2 (control), polished preparations. After the preparations were completed the teeth were scanned (Cerec Bluecam, Sirona, Bensheim, Germany), and the crowns were designed and machined using CAD/CAM technology (Sirona, Bensheim, Germany). The adaptation of the pieces was evaluated using polyvinyl siloxane replicas and stereomicroscope photographs with 70x magnifications. The normality test indicated a nonnormal result, so a Man–Whitney nonparametric test was performed. One out of the 24 measured regions showed a statistically significant difference (p=0.0494). With this study it can be concluded that crowns fabricated by CAD/CAM technology performed on unpolished preparations are not influenced by the internal marginal adaptation and the ceramic part and are different from polished preparations.