Load capacity of occlusal veneers of different restorative CAD/CAM materials under lateral static loading

Abstract

Objective: The aim of this in vitro study was to analyze the failure of occlusal veneers made of three different restorative CAD/CAM materials under lateral static loading.

Materials and methods: Sixty standardized semi-anatomical occlusal veneers were fabricated on natural lower molars from three different CAD/CAM materials: hybrid ceramic (Vita Enamic), lithium disilicate (IPS e. max CAD) and translucent zirconia (Bruxzir). The specimens were mechanically loaded by a custom-made device attached to a universal testing machine (MTS 858 Mini Bionix II, MN, USA). Static lateral loading was applied on the buccal cusp of the occlusal veneer until failure. Failure loads were recorded, and the types of failure noted for each group. 3D finite element (FE) models simulating the actual test set-up were further employed to evaluate the stresses within the tooth-restoration complex to help interpret the experimental results.

Results: Occlusal veneers made from zirconia recorded a significantly higher mean failure load (843.1 ± 141.5 N) than specimens of the other two materials (p < 0.05). There was no statistically significant difference between the lithium disilicate (493.21 ± 102.24 N) and the hybrid ceramic (499.6 ± 123.1 N) groups (p = 0.863). 74% of the hybrid ceramic and 84% of the lithium disilicate specimens showed veneer fracture, whereas 78% of the zirconia veneers showed debonding. Comparison of the FE-predicted stresses with the different failure strengths corroborated with the experimental results.

Conclusion: Lateral loading caused failure of occlusal veneers at loads significantly lower than those reported for axial loading. Among the materials tested, zirconia veneers showed the highest resistance to failure, with the main failure mode being debonding under lateral loading. The other two material groups failed mainly by veneer fracture at lower loads.

Highlights: - A novel device was used for testing occlusal veneers under lateral static loading. - 3D-FE analysis explained and corroborated the experimental results. - The relationship between vertical and horizontal forces acting on teeth has been described. - The study highlights the harm of excursive contacts on ceramic restorations.

Keywords: CAD/CAM materials; Debonding; Finite element analysis; Lateral loading; Occlusal veneers; Weibull modulus.