Dina M. Shehawi, Atef. S.Ibrahim And Hany. H. Nasr,

ABSTRACT
Statement Of Problem: Maxillary Anterior Tooth Loss May Cause Esthetic And Functional Problems. Successful Treatment For These Situations May Necessitate A Minimally Invasive Technique To Preserve Sound Remaining Abutment Tooth Structure Objective: The Aim Of This In-vitro Investigation Was The Establishment Of Three Different Proposed Designs Of A Conservative Partial Fixed Restorative Ceramic Approach For Restoring Missing Maxillary Lateral Incisor, Aiming To Assess Their Mechanical Performance Using Two Different Ceramic Materials Employing CAD-CAM Technology Material & Methods: The Same 3 Designs Were Prepared As Previously Mentioned Typodont Model With Typodont Resin Teeth Representing Missing Maxillary Lateral Incisor Case Was Used. Maxillary Central Incisor And Maxillary Canine Were Prepared According To The Following Three Designs: First Design (Group I): Minimal Invasive Preparation Design Second Design (Group II): Palatal Preparation With Proximal Half Grooves. Third Design (Group III): Palatal Preparation With Proximal Half Grooves And Cingulum Indentation.) Optical Impressions Were Taken For The Preparations To Obtain A Model For Each Preparation Of The Three Groups , And All- Ceramic Fixed Partial Dentures (30 IPS E-max CAD And 30 Incoris TZI Ceramic Material) Were Fabricated In Accordance With The Different Designs. Duplicate The Three Master Models For The Purpose Of Production Of Epoxy Models That Were Used As Substrates For Cementation Of The Constructed Resin Bonded Bridge Samples During Testing Procedures. Bridges Were Cemented To The Epoxy Models . Thermo-mechanical Aging Test Was Conducted Using Chewing Simulator Accompanied With Thermo-cyclic Mode.The Test Was Repeated 120,000 Times To Clinically Simulate The 6 Months Chewing Condition, Accompanying Thermocycling According To Previous Studies Temperature Changes Between 5oC And 55oC Using A Frequency Of 3 Hz .Then Fracture Test Was Done By Compressive Mode Of Load Applied At The 135o Angle (through Housing The Sample In Specially Designed 45o Angle Jig) Using A Metallic Rod With Round Tip (3.8 Mm Diameter) Attached To The Upper Movable Compartment Of Testing Machine Traveling At Cross-head Speed Of 1mm/min. Statistical Analysis Was Performed After Collecting All Data.

Results: Regarding The Fracture Resistance Test, For Zirconia Bridges ; It Was Found That Group II Recorded Statistically Significant Highest Fracture Resistance Mean Value (612.72 � 63.8 N) Followed By Group III With Mean Values (530.34 � 27.2 N) While Group I Recorded The Lowest Fracture Resistance Mean Value (500.44 � 79.6 N). These Results Showed Non-significant Difference Between Group III And Group I. For E.max Bridges ; It Was Found That Group III Recorded Statistically Significant Highest Fracture Resistance Mean Value (420.3� 33.4 N) Followed By Group II With Mean Values (391.03 � 12.1 N) While Group I Recorded The Lowest Significant Fracture Resistance Mean Value (321.57 � 16.3 N). Regardless To Preparation Designs, Totally It Was Found That Zirconia Bridges Recorded Statistically Significant Higher Fracture Resistance Mean Value (547.83 � 43.26 N) Than E.max Bridges Mean �SD Values (377.63 � 37.38 N). Irrespective Of Ceramic, Totally It Was Found That Group II Recorded Statistically Significant Highest Fracture Resistance Mean Value (501.88 � 37.9 N) Followed By Group III With Mean Values�SDs (475.32 �30.3 N) While Group I Recorded The Lowest Fracture Resistance Mean Value (411.01 � 47.9 N) . Results Showed Statistically Non-significant Mean Vales Between Group III And Group II.

Conclusions: Within The Limitations Of The Present Study, The Following Conclusions Could Be Drawn: All-ceramic Resin Bonded Fixed Partial Denture (RBFPD) Restoring The Maxillary Lateral Incisor Could Withstand Successfully The Maximum Loads To Which The Anterior Area Is Subjected. Incoris TZI And IPS E-max Blocks Using Cerec-Inlab System Could Be Used Successfully For Construction Of Resin Bonded Fixed Partial Dentures Incoris TZI Resin Bonded Bridges Had Superior Fracture Resistance Than IPS E-max CAD Resin Bonded Bridges. The Design Has Significant Effect On Fracture Resistance, Adding Retentive Means Increases The Fracture Resistance Of Both Materials.