الفهرس 
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Abstract
Statement of problem: Treating worn dentition with occlusal veneers made from hybrid ceramics seems to be a promising option; however, the wear resistance of these materials remains a primary concern. Objective: Evaluation of wear resistance of occlusal veneers made from two hybrid ceramics (Vita Enamic, Cerasmart) in comparison to wear resistance of human enamel. Materials and methods: An intact mandibular molar was collected and centralized in an epoxy resin base using centralizing device and occlusally reduced by 1 mm to simulate a worn dentition then it was duplicated into sixteen epoxy resin dies. Sixteen occlusal veneers specimens were constructed on their corresponding epoxy resin dies from two hybrid materials; polymer infiltrated ceramic network material (Vita Enamic) and resin nanoceramic material (Cerasmart). Eight unrestored natural mandibular molars were collected and act as a control group. Twenty-four natural maxillary first premolar teeth were collected and only the buccal halves of sectioned teeth was used as antagonists. Occlusal veneers were cemented on the resin dies using dual cure resin cement (RelyX Ultimate). All specimens were loaded into a chewing simulator with a load 49 N and a frequency of 1.6 Hz for 75,000 cycles to represent 6 months of oral function. 3D surface analyzer system were used to detect the roughness pre- and post- the masticatory cycles. For volume loss values, 3D scans of pre- and post- the masticatory cycles were collected then aligned using a reverse-engineering software (Geomagic ControlX). Results : Among specimens; Cerasmart group recorded higher change of roughness than Vita Enamic group while Vita Enamic group had same change of roughness as that of the natural enamel group (C > N = E). however, the highest volume loss was for natural enamel group and the lowest was for Vita Enamic group (N > C > E). Among antagonist’s roughness; antagonists of Vita Enamic recorded higher change of roughness than the other groups, while antagonists of Cerasmart and natural enamel had almost the same change of roughness percentage (E‶ > N‶ ≅ C‶). Among antagonist’s volume loss; antagonists of Vita Enamic group recorded the highest volume loss than the other groups, while antagonists of Cerasmart group detected the least amount of loss than the other groups (E‶ > N‶ > C‶). Conclusions: Cerasmart occlusal veneers were less abrasive (antagonist-friendly) than the other groups. Vita Enamic occlusal veneers had more wear resistance than the other groups. Occlusal veneers from both hybrid materials can be used when treating patients with a worn dentition as they exhibit volume loss and roughness values within the acceptable range.