Effect of Different Bonding Substrates on Fracture Resistance of Thin and Ultra-thin Occlusal Veneers constructed using Different CAD/CAM Materials

Objectives: The aim of this study was to compare the fracture resistance of thin and ultra-thin occlusal veneers constructed from ceramics and hybrid ceramics bonded to different bonding substrates after thermomechanical aging.
Materials and Methods: A total of 96 extracted maxillary first premolars were used. The teeth were divided into three groups according to the bonding substrate/protocol: EN, IDS Dentin, DDS Dentin. Each group was further subdivided into two subgroups according to the material of construction: E.max CAD, Vita Enamic. Each subgroup was further subdivided into two subdivisions according to the thickness of the occlusal veneer: Ultrathin, Thin. All the teeth were prepared to receive occlusal veneers. All the occlusal veneers were constructed using CAD/CAM technique. All occlusal veneers were cemented using adhesive resin cement. Thermomechanical aging was applied on all samples. Fracture resistance testing was performed.
Results: There was statistically significant difference between bonding protocols where IDS Dentin showed the statistically significantly highest mean fracture resistance followed by Enamel then DDS Dentin. Vita Enamic showed statistically significantly higher mean fracture resistance than E.max CAD. Ultra-thin occlusal veneers showed statistically significantly lower mean fracture resistance than thin occlusal veneers.
Conclusions: Ultrathin occlusal veneers must be cautiously used when glass ceramics is chosen. However, this minimal thickness could be a favorable option on using hybrid ceramics. Increasing the occlusal thickness to 0.5-0.8mm could be promising upon bonding with either enamel or dentin with both materials used. Ultra-thin occlusal veneers must be used carefully upon bonding to dentin (IDS must be applied).