Salwa Osman, Rabab M Ibrahim And Carl H Halim,

ABSTRACT
Aim Of The Study: This Is In Vitro Study Conducted To Analyze The Effect Of Cooling Rate (slow And Rapid Cooling Protocols) On Flexural Strength Of Zirconia Veneered With Two Different Veneering Ceramics. Nano- Fluoroapatite Ceramic For The Conventional Layering Of Zirconia And Fluoroapatite Based Glass Ceramic For Press On Zirconia Technique.

Materials and Methods: Twenty Zirconia Discs Samples (12 Mm Diameter And 0.8 Mm Thickness) Were Milled From Prefabricated ICE Zirkonzahn Zirconia Ceramic Blocks And Divided Into Two Groups According To Veneering Technique, Group A (n= 10) Zirconia Samples Veneered With Conventional Layering Technique Using Nano-fluoroapatite Veneering Ceramic (IPS E-max Ceram) And Group B (n=10) Zirconia Samples Veneered With Press On Zirconia Technique Using Fluoroapatite Veneering Ceramic (IPS E-max Zir-press). Each Group Was Further Sub Divided Into Two Subgroups According To The Cooling Rate Of The Glaze Firing Cycle Of The Veneering Porcelain. Sub Group 1: Slow Cooling Rate Following The Manufacturer Recommendation Of The Glaze Firing Cycle And Sub Group 2: Rapid Cooling Rate. Bi-axial Flexural Strength Test Was Done Using A Computer Controlled Universal Testing Machine (Model LRX-plus; Lloyd Instruments Ltd), Then The Scanning Electron Microscopic Examination For Veneered Zirconia Specimens Was Done By SEM Model Quanta 250 FEG.

Results: One Way ANOVA Followed By Tukey?s Post-hoc Tests Were Performed To Detect Significance Between Subgroups. It Was Found That The Difference Between Conventional Layering Veneering Technique Subgroups Was Statistically Significant (P0.05) As Indicated By Paired T-test. The Difference Between Press On Veneering Technique Subgroups Was Statistically Significant (P0.05) As Indicated By Paired T-test. The Difference Between Slow Cooling Groups Was Statistically Non-significant (P>0.05) As Indicated By Unpaired T-test, It Was Found That Conventional Layering (group A) Recorded Statistically Non-significant Higher Bi-axial Flexure Strength Mean Value Than Press On (group B) It Between Slow Cooling Groups. It Was Found That Press On (group B) Recorded Statistically Non-significant Higher Bi-axial Flexure Strength Mean Value Than Conventional Layering (group A) Between Rapid Cooling Groups. Conclusion: Cooling Protocols Affect Significantly The Bi-axial Flexure Strength Of Veneered Zirconia. The Different Veneering Techniques Used Showed Similar Behavior With The Same Cooling Protocols Used. Considering The Slow Or Rapid Cooling Rate For Both Veneering Techniques Showed No Significant Difference In Their Flexural Strength.