Ahmed S. Abd El Shakour, Cherif A. Mohsen And Magda I. Ramzy,

ABSTRACT
Objective: The Purpose Of This Study Was To Investigate Fracture Strength Of Two Types Of Hybrid Ceramic Posterior Occlusal Veneers With Different Thicknesses.

Materials and Methods: Eighty Natural Maxillary Molars Of Comparable Size And Morphology Were Selected. Standardization Of The Teeth Preparations Was Accomplished Using A Diamond Saw; Teeth Were Sectioned Horizontally, Removing All Coronal Tooth Structure 4 Mm Occlusal To The CEJs Leaving Exposed Dentin Centrally And Peripheral Enamel. Samples Were Randomly Divided Into Two Groups (n=40) Based On Restorative Materials That Will Be Used: Computer-milled Hybrid Ceramic (ENAMIC) And Resin Nano Ceramic (LAVA ULTIMATE). Each Group Was Divided Into Two Subgroups (20 Samples Each) According To The Type Of Preparation (conventional And Experimental). The Experimental Preparation Had An Additional Preparation Feature. Within Each Subgroup, Specimens Were Subdivided Into Two Classes (consisting Of 10 Specimens Each N=10) Based On Restoration Thickness (0.3, 0.6 Mm). Each Class Was Divided Into 2 Subclasses (n=5) For Testing The Fracture Resistance And The Microleakage. Specimens Were Stored In Distilled Water 37oC For 7 Days. Restorations Were Adhesively Bonded To Their Respective Teeth For Measuring Fracture. Result: The Fracture Strengths (mean � Standard Deviation) Were 2416 � 676, And 1777 � 697, N For Lava Ultimate, And Vita Enamic, Respectively. Lava Ultimate Had Significantly Higher Fracture Strength Than The Vita Enamic (p < 0.05). No Correlation Between Fracture Strengths And Failure Modes Was Found Within Each Material. Most Specimens (48 Out Of 60) Fractured In The Restoration Without Involving Tooth Structures.

Conclusions: The Fracture Strength Of Ultrathin Occlusal Veneers Made From The Novel Ceramic Hybrid Matched The Strength Of CAD/CAM Composite. The Highest Strength Was Found With The Resin Nanoceramic Material.