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. 2018 Dec 31:11:1-8.
doi: 10.2147/CCIDE.S193326. eCollection 2019.

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

Manal Rahma Alammari  1 , Mohamed Hussein Abdelnabi  1   2 , Amal Ali Swelem  1   3
Affiliations

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

Manal Rahma Alammari et al. Clin Cosmet Investig Dent. .

Abstract

Introduction: Computer-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.

Aim: The 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 methods: Forty 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).

Results: Factorial 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.

Conclusion: An 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.

Keywords: CAD; CAM; marginal gap; monolithic crowns; total occlusal convergence; µCT.

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Conflict of interest statement

Disclosure The authors report no conflicts of interest in this work.

Figures

Figure 1
Figure 1
2D adaptation assessment: axial gap (AG) and occlusal gap (OG).
Figure 2
Figure 2
2D adaptation assessment: marginal gap (MG), absolute marginal discrepancy (AMD).
Figure 3
Figure 3
Specimens of the cyclic loading subgroup were held with their bases in a dynamic loading machine (Instron dynamic testing machine).
Figure 4
Figure 4
Specimen placed in a universal testing machine (Instron universal testing machine) and submitted to compressive load test (crunch the crown test) at a cross head speed of 0.5 mm/min.
See this image and copyright information in PMC

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