Wasfi A. Qaid , Mohamed R. Farid And Mohamed F. Haridy,

ABSTRACT
Statement Of Problem: All-ceramic Onlay Has Become More Popular In Dental Clinics Due To Their Lifelike Appearance, Durability, And Biocompatibility. However, Their Drawbacks Include Fracture Susceptibility And Inadequate Marginal Fit And Fracture Susceptibility.

Purpose: The Aim Of This Study Was To Compare Hybrid Ceramic And Pressable Ceramic Onlay Restoration Regarding Vertical Marginal Discrepancy Of Both Materials Following Thermal Cycling.

Materials and Methods: A Total Of Twenty Four Extracted Intact Molar Were Fixed In Epoxy Resin. Standardized Onlay Preparation Was Performed On All Specimens By Computer Numerically Controlled Milling Machine (CNC). The Samples Were Divided Into Two Main Groups (I-Vita Enamic Hybrid Ceramic Materials & II- IPS E.max Press Ceramic Materials) According To The Ceramic Material Used For Construction Of Onlay Restoration. All Onlay Ceramic Restorations Were Fabricated And Treated And Cemented On The Prepared Teeth. All Samples Were Subjected To Thermocycling Between 5C� To 55C� In Water Bath For A Total Of 2000 Cycle With 10 Seconds Dwell Time At Each Bath Using Thermocycling Device. The Marginal Gap Distance Between The Outer Margins Of Each Onlay And The Shoulder Finish Line Of Prepared Tooth In A Vertical Direction Was Measured. The Data From The Two Groups Were Collected, Tabulated And Statistically Analyzed. The Results Were Analyzed Statistically Using Student?s ?t? Test. The Level Of Significance Was Taken At P < 0.05. Result: It Was Found That Vita Enamic Hybrid Ceramic Onlay Group Recorded Statistically Significant (P<0.016), (P<0.001), (P<0.0001), And (P<0.0001) Higher Vertical Marginal Gap Mean Value When Compared To IPS Emax Ceramic Onlay Group.

Conclusions: The Material Used For Fabrication Of The Indirect Ceramic Restorations Has A Crucial Effect On Its Performance Regarding The Marginal Gap. Differences In Marginal Fit Were Recorded For Ceramic Partial Restorations Fabricated By Different Manufacturing Techniques E.g. IPS E.max Press Ceramic Was Better In The Marginal Sealing Values Than The Vita Enamic Ceramic Onlay.