Intaglio dental1/10/2024 Two layers of feldspathic ceramic and their consequent two firings in a vacuum furnace (VACUMAT 6000 M, Vita Zahnfabrik) were performed on each crown. The 0.7-mm-thick framework was veneered using a feldspathic ceramic ( Table 1 VITA VM9 base-dentin, Vita Zahnfabrik) with the stratified technique, simulating a full crown with a flat occlusal surface. The frameworks were ultrasonically and oven-cycle cleaned and then sintered in a ZYrcomat VITA oven (Vita Zahnfabrik), as recommended by the manufacturer. The InLab Cerec MC XL (Sirona Dental Systems) milled 90 identical frameworks in Y-TZP ceramic (VITA In-Ceram YZ for InLab, Vita Zahnfabrik, Bad Säckingen, Germany). 38 The presence of this film may trigger the start of crack propagation, since this glass material has a lower tensile strength.Īfter a polyvinylsiloxane impression was made, a digital design of a plaster cast was obtained with the aid of InLab 3.60 software (Sirona Dental Systems, Bensheim, Germany). 27, 37 However, such a thin glass film is located on the intaglio surface of crowns, which is the area in which tensile stresses are experienced when a crown is mechanically challenged. Promising results related to the bond strength between Y-TZP and resin cement were observed with glazed and Al 2O 3-sandblasted 35, 36 or hydrofluoric acid–etched surfaces. In addition to these surface treatments, surface alterations using Y-TZP ceramic with glazing and etching have been tried. 23, 31, 32 Contradicting this theory, studies by Cattani-Lorente and others 33 and Scherrer and others 34 cited that sandblasting with 30-μm silica particles does not promote a deleterious effect on the mechanical behavior of Y-TZP ceramics. 23- 30 The same is observed for a silica or aluminum oxide coated with silica (SiO 2) coating. 22 Indeed, aging of the sandblasted Y-TZP has a deleterious effect on the materials' strength. However, the mechanical strength of the ceramic is time dependent as a result of a subcritical crack growth that the material may suffer when subjected to cyclic loading in an aqueous environment. The initially present microdefects introduced by the sandblasting seem insufficient to lead to failure. Silica coating by sandblasting improves adhesion between Y-TZP and resin cement 4 however, it seems to lead to material degradation. Sandblasting, silica coating, etching, and glazing are the most commonly used pretreatments. 9, 10, 14- 16 The adhesion between the Y-TZP surface and cements has been widely studied in in vitro research. The results were analyzed using the Kaplan-Meier and Mantel-Cox log rank tests (5%), a one-way analysis of variance, Tukey multiple comparison test, and Weibull nonparametric test.Īt the same time, the loss of retention of Y-TZP crowns (due to a lack of adhesion between the Y-TZP surface and the tooth) was also shown to be a reason for failure. The cement thickness and failure modes were analyzed using a stereomicroscope and scanning electron microscopy. Fatigue resistance was evaluated using stepwise loads at 1.4 Hz until failure: 5000 cycles at maximum load of 200 N, followed by 10,000 cycles at maximum loads of 800, 1000, 1200, and 1400 N. Altogether, six groups of 15 specimens each were tested. Only the PN cements were tested against frameworks that had been sandblasted or glazed. All three cements were tested against frameworks that were alcohol cleaned. One of three luting cements were used: 1) zinc phosphate 2) glass ionomer and 3) adhesive resin cement (PN). Prior to cementation the intaglio surface of the ceramic was treated using one of four treatments: 1) cleaning with isopropyl alcohol 2) application of an overglaze 3) sandblasting with 125 μm aluminum oxide powder and 4) sandblasting with 30 μm silica powder (CJ). Each preparation was restored with a Y-TZP framework made by a CAD/CAM system and veneered using feldspathic ceramic. Ninety identical preparations were machined in a dentin-like epoxy composite. A research design was chosen that attempted to reduce the likelihood of Hertzian cracking and to increase the probability of fracture initiation at the intaglio surface of the framework.
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