Layering of discolored substrates with high-value opaque composites for CAD-CAM monolithic ceramics.

STATEMENT OF PROBLEM: Severely discolored substrates have been shown to limit the use of computer-aided design and computer-aided manufacturing (CAD-CAM) ceramic blocks because they provide insufficient color masking. PURPOSE: The purpose of the in vitro study was to evaluate the effect of a layer of high-value opaque composite resin over discolored substrates to determine its masking ability with CAD-CAM ceramics. MATERIAL AND METHODS: Six ceramic groups (n=10) were tested. A bilayer group of zirconia and porcelain served as the control. The CAD-CAM monolithic groups were translucent zirconia, zirconia-reinforced lithium silicate, lithium disilicate, leucite-reinforced glass-ceramic, and feldspathic ceramic. Five substrates were used: A1 (used as reference), A3.5, C4, and coppery and silvery metals. The substrates were separated as nonlayered or layered (with flowable or restorative opaque composite resins). The tested luting agents were white, opaque, and A1. Color differences (ΔE00) were assessed with the CIEDE2000 formula. A 2-way ANOVA (α=.05) was used to detect significant differences in ΔE00 among the groups for each substrate. The results were compared with acceptability (1.77) and perceptibility (0.81) thresholds. RESULTS: The flowable composite resin layer associated with A1 luting agent ensured ΔE00 lesser the than perceptibility thresholdwith the use of CAD-CAM monolithic ceramics, with the lowest values for zirconia-reinforced lithium silicate in substrates A3.5 (0.53) and C4 (0.32) and for leucite-reinforced glass-ceramic for coppery (0.49) and silvery (0.81) substrates (P<.001). The same benefit was observed when zirconia and porcelain was tested over the silvery substrate. The absence of substrate treatment only provided ΔE00 lesser than the acceptability threshold with CAD-CAM ceramics for the A3.5 background. CONCLUSIONS: The application of a flowable opaque composite resin and the use of a shaded luting agent ensure masking with CAD-CAM monolithic ceramics.

Fatigue performance of adhesively luted glass or polycrystalline CAD-CAM monolithic crowns.

STATEMENT OF PROBLEM: Data comparing the fatigue performance of adhesively luted glass or polycrystalline ceramic systems for computer-aided design and computer-aided manufacturing (CAD-CAM) are scarce. PURPOSE: The purpose of this in vitro study was to evaluate and compare the fatigue performance of monolithic crowns manufactured from glass or polycrystalline CAD-CAM ceramic systems adhesively luted to a dentin analog. MATERIALS AND METHODS: Fifty-four pairs of standardized preparations of dentin analog (NEMA Grade G10) and simplified ceramic crowns of 1.5-mm thickness were obtained with 3 ceramic materials: lithium disilicate (LD) glass-ceramic (IPS e.max CAD); zirconia-reinforced lithium silicate (ZLS) glass-ceramic (Vita Suprinity); and translucent yttrium fully stabilized polycrystalline zirconia (Trans YZ) (Prettau Anterior). The simplified crowns (n=15) were adhesively cemented onto the preparations and subjected to step-stress fatigue test (initial load of 400 N, 20 Hz, 10 000 cycles, followed by 100-N increment steps until failure). Collected data (fatigue failure load [FFL] and cycles for failure [CFF]) were submitted to survival analysis with the Kaplan-Meier and Mantel-Cox post hoc tests (α=.05) and to Weibull analysis (Weibull modulus and its respective 95% confidence interval). Failed crowns were submitted to fractography analysis. The surface characteristics of the internal surface (roughness, fractal dimension) of additional crowns were accessed, and the occlusal cement thickness obtained in each luted system was measured. RESULTS: Trans YZ crowns presented the highest values of FFL, CFF, and survival rates, followed by ZLS and LD (mean FFL: 1740 N>1187 N>987 N; mean CFF: 149 000>92 613>73 667). Weibull modulus and cement thickness were similar for all tested materials. LD presented the roughest internal surface, followed by ZLS (mean Ra: 226 nm>169 nm>93 nm). The LD and ZLS internal surfaces also showed higher fractal dimension, pointing to a more complex surface topography (mean fractal dimension: 2.242=2.238>2.147). CONCLUSIONS: CAD-CAM monolithic crowns of Trans YZ show the best fatigue performance. In addition, ZLS crowns also showed better performance than LD crowns.

Effect of Root Canal Irrigants on the Mechanical Properties of Endodontically Treated Teeth: A Scoping Review.

INTRODUCTION: The aim of this study was to identify through a scoping review whether root canal irrigants influence the mechanical properties of endodontically treated teeth, and which properties could be affected. The protocol of this study, available online (https://osf.io/yc9nb/), followed the Joana Briggs Institute guidelines. Reporting was based on PRISMA Extension for Scoping Reviews. METHODS: We selected studies written in English that evaluated the effect of at least one irrigant on the mechanical properties of endodontically treated teeth. The search and study screening were performed in PubMed and Scopus databases by 2 independent researchers. A descriptive analysis was performed to consider the study design, the characteristics of the irrigants, and the properties tested. RESULTS: The initial search yielded 608 citations, of which 66 were included. On the basis of the collected data, the most commonly used solutions were 17% EDTA, 2.5% or 5% sodium hypochlorite, and 2% chlorhexidine, and the most common tested properties were hardness and strength. Alterations in the modulus of elasticity, stress and strain concentration during preparation, and roughness were also assessed. CONCLUSIONS: The majority of studies corroborated a negative effect of all solutions on the mechanical properties of endodontically treated teeth. Furthermore, increases in the concentration of the solution and in the time of exposure were found to intensify deleterious effects. However, disinfection of the canal is also a crucial factor in endodontic success. Thus, clinicians should consider these factors to mitigate the effects without interfering with antibacterial properties, customizing the choice of the solution to the case in hand.