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Wear, lifetime and failure mode of materials processed via CAD-CAM


Objectives: To investigate four CAD-CAM materials, two composite/ceramic and two glass-ceramics on: (1) the effect of wear by a chewing simulator on volume loss and surface roughness; (2) the fatigue behavior of disc specimens processed by CAD-CAM technology, before and after the generation of clinically relevant surface defects by means of a wear test in a chewing simulator; and (3) To compare the fatigue behavior of prosthetic crowns made by CAD-CAM technology using a chewing simulation, and considering the failure criterion as the first cracks detected by an acoustic emission detection apparatus. Materials and methods: Four different commercial CAD-CAM materials will be used: composite blocks for indirect use (Lava Ultimate, 3M), ceramic/polymer blocks (Enamic, Vita Zahnfabrik), a lithium dissilicate-based glass-ceramic blocks (IPS e.max CAD, Ivoclar Vivadent), and a lithium silicate based glass-ceramic reinforced with zirconia (Suprinity, Vita Zahnfabrik). In the first part of this project (related to objectives #1 and 2), 39 disc-shaped specimens of each material will be produced and divided into 3 groups. The first group will be used to determine the flexural strength of the materials. The second group will be submitted to wear and fatigue test. First, the specimens will be taken to a profilometer for topography determination. Then, the discs will be subjected to a wear test in which the specimens will be taken to a chewing simulator for a period corresponding to one year of clinical use. After the test, the specimens will be subjected again to the topographic analysis through profilometry for determination of the volume loss, depth of wear and surface roughness. The same specimens will then be subjected to cyclic fatigue for determination of the lifetime of specimens (the worn area will be placed on the tensile side). The third group (control), will not be subjected to wear and will be taken only to the chewing simulator for cyclic fatigue. In the second phase of this project (concerning objective #3), twenty-one specimens in the shape of crowns of each material will be prepared, simulating the first lower molar. The crowns will be cemented in resin composite preparations in a PVC tube. These specimens will be taken to a chewing simulator for the cyclic fatigue test with the aid of an acoustic detector. For disks and crowns, the fatigue test will be the "step-stress" method, which uses three fatigue profiles: slow, moderate, and severe. Fractographic analysis will performed for all specimens (discs and crowns). Wear data and roughness will be analyzed by ANOVA with global significance level of 5%, and fatigue data will be analyzed using the Weibull ++ program/Alta Pro 7 to determine the probability of failure estimated under fatigue, at stress levels of 50 or 100 MPa (disks) and at loads of 70 up to 150 N (crowns), after missions of 1, 3 or 5 million cycles (corresponding to 1, 3 and 5 years of clinical use). (AU)

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