Effect of total occlusal convergence on fit and fracture resistance of zirconia-reinforced lithium silicate crowns

Abstract

IntroductionComputer-aided design (CAD) and computer-aided manufacturing (CAM) monolithic crowns are gaining momentum. Limited evidence exists about the effect of tooth preparation total occlusal convergence (TOC) on marginal and internal gap distances in addition to load to fracture values.AimThe aim of this study was to evaluate, by microcomputed tomography (µCT), the influence of 12° and 20° TOC on marginal and internal adaptation of zirconia-reinforced lithium silicate (ZLS) crowns. Moreover, values of load to fracture with and without initial cyclic loading (CL) were compared.Material and methodsForty ZLS crowns were fabricated on dies with TOC of 12° and 20°, 20 crowns for each group. µCT was used to compare marginal and internal adaptation. Each specimen was measured at 140 points distributed on all tooth preparation surfaces for 2D gap distance assessment. 3D gap volume was also evaluated. Crowns were then cemented and divided into two subgroups; the first was stored in distilled water (no cyclic loading [NCL] subgroup), the second was subjected to CL (CL subgroup).ResultsFactorial repeated measures ANOVA followed by Bonferroni post hoc in addition to independent and dependent t-tests were used for statistical analysis. Marginal gap, absolute marginal discrepancy, and occlusal gap measurements showed significant differences between the measurement sites. Static load to fracture values showed significant differences between TOC groups for both NCL (P=0.011) and CL (P=0.025) subgroups.ConclusionAn increase of TOC from 12° to 20° did not affect marginal and internal adaptation but resulted in higher values of load to fracture of ZLS crowns. CL simulating 1 year of service did not result in fatigue failure.

Evaluation of zirconia and zirconia‐reinforced glass ceramic systems fabricated for minimal invasive preparations using a novel standardization method

“…When using natural teeth, the researcher can perform various bonding techniques that have a significant influence on the behavior of the materials being investigated. 37,38 In in-vitro studies, the dentin wetness, thickness and the pressure of the tooth pulp are influential variables that try to imitate in-vivo conditions. The modulus of elasticity of natural teeth is essential factor when applying fracture tests as the other materials do not behave as natural teeth.…”

Evaluation of Marginal/Internal Fit and Fracture Load of Monolithic Zirconia and Zirconia Lithium Silicate (ZLS) CAD/CAM Crown Systems

“…A total of 32 crowns were thus fabricated for marginal and internal fit evaluation: Group 1, 16 monolithic Zi crowns; Group 2, 16 monolithic ZLS crowns (n = 16). The sample size of this study was based on earlier related published studies [ 25 , 28 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. Based on the mean differences and standard deviation assumptions, the total sample size was estimated as 24 crown samples (12 for each of the two ‘ceramic material’ groups), at α = 0.05 and power of 85% (G* Power statistical power software v.3.1.9.7) for the marginal and internal gap evaluations.…”

Fracture Resistance of Monolithic Zirconia Crowns on Four Occlusal Convergent Abutments in Implant Prosthesis

“…The results hence rejected the hypothesis described in the introduction. Alammari et al [34] reported that an increase of TOC (from 12 to 20 degree) did not affect marginal and internal fit but resulted in higher load to fracture values of ceramic crowns. A similar finding was reported by Corazza et al [35], who compared the influence of 6 • , 12 • , and 20 • TOC on the fracture load of yttria partially stabilized zirconia veneered with feldspathic porcelain.…”