ABSTRACT
Abstract: The aim of this study is to evaluate the machinability of four CAD/CAM materials (n = 13) assessed by brittleness index, Vickers hardness, and fracture toughness and interaction among such mechanical properties. The materials selected in this in vitro study are Feldspathic ceramic [FC], Lithium-disilicate glass ceramic [LD], leucite-reinforced glass ceramic [LR], and nanofilled resin material [RN]. Slices were made from the blocks following original dimensions 14 × 12 × 3 mm (L × W × H), using a precision slow-speed saw device and then surfaces were regularized through a polishing device. Brittleness index and fracture toughness were calculated by the use of specific equations for each one of the properties. The Vickers hardness was calculated automated software in the microhardness device. One-way Anova and Pearson's correlation were applied to data evaluation. LD obtained the highest values for brittleness index and was not significantly different from FC. LR presented statistically significant difference compared with RN, which had the lowest mean. Vickers hardness showed LD with the highest average, and no statistical difference was found between FC and LR. RN presented the lowest average. Fracture toughness showed FC and LR not statistically different from each other, likewise LD and RN. The brittleness index, considered also as the machinability of a material, showed within this study as positively dependent on Vickers hardness, which leads to conclusion that hardness of ceramics is related to its milling capacity. In addition, fracture toughness of pre-sintered ceramics is compared to polymer-based materials.
Subject(s)
Polymers/chemistry , Ceramics/chemistry , Computer-Aided Design , Resin Cements/chemistry , Dental Porcelain/chemistry , Aluminum Silicates/chemistry , Reference Values , Surface Properties , Materials Testing , Reproducibility of Results , Analysis of Variance , Statistics, Nonparametric , Hardness TestsABSTRACT
Objective: The aim of the present study was to evaluate dentistry students' perceptions about an extramural activity designed to deliver dental care to an indigenous community. Materials and Methods: This was a qualitative investigation involving 4 students of dentistry who had just had the experience of delivering treatment to indigenous Brazilian people. These students answered questions about the relevance of the experience to their personal and professional lives. We performed Content Analysis to data treatment and it was analysed by Social Representation Theory. Results: Two social representations were reached: a) Being capable to promote oral health; b) Facing human feeling and respect each other. Conclusion: We concluded that participation in an extramural project improves the students' understanding of primary health care in dentistry. Such experiences help students develop a sense of cultural respect, comprehensive care, and to understand patients in their totality as social beings with their own values, beliefs, and attitudes regarding oral health care.