Ahmad K. Mubarak, Manal R. Hassan And Mohammed M. Shalaby,

ABSTRACT
Aim Of The Study: The Aim Of This Study Was To Investigate Fracture Resistance Of Maxillary Posterior Fixed Partial Denture Constructed On Mutilated Abutments Using Finite Element Analysis.

Materials and Methods: Twenty Four 3 Units �3-Y-PS Zirconia� Fixed-fixed Partial Dentures Were Constructed On 48 Uniformly Prepared Abutments (24 Maxillary Second Premolars+24 Maxillary Second Molars). The Zirconia Fixed-fixed Partial Dentures Were Divided According To The Vitality Of The Adjoing Abutments Into Two Main Groups. Group (A): The Adjoining Abutments Were Non Endodontically Treated That Restored With Composite Cores. Group (B): The Adjoining Abutments Were Endodontically Treated Restored With Glass Fiber Posts Cemented With Rely X Cement And Composite Cores Build Up. Each Group Of (A) And (B)were Subdivided Into: Control Group (sound Abutments With No Missed Wall) And Experimental Group. The Experimental Group Consisted Of 3 Subgroups; One Wall Missed (A1 Or B1), Two Walls Missed (A2 Or B2) And Three Walls Missed (A3 Or B3). A Vertical Compressive Load With 3mm Diameter Indenter Was Applied To The Central Fossa Of The Pontic Using Universal Testing Machine. A 5Kg Load Was Applied At A Crosshead Speed Of 1mm/min Until Fracture Occurred. A Finite Element Models Were Conducted To Study Stress Distribution On The Component Of The Fixed-fixed Bridges Of All Studied Groups And Subgroups , Besides, Comparing Between Zirconia And Lithium Disilicate Ceramics(E Max) As Different Bridge Construction Materials.

Results: The Highest Fracture Resistance Mean Value Was Recorded For The Control Group Of The A Abutments (Ac)(3095.22 �284.94N). The Fracture Resistance Means Of The Subgroups Were Recorded As A1(2978.52N)>Bc(2897.1N)>A2(2687.13N)>B1(2341.29N)>B2(2118.76)>A3(1943.32N)>B3(1921.79N). While The Lowest Fracture Resistance Mean Value Was Recorded For B3subgroup (1921.79 �75.26N) Which Is The Non Endodontically Treatd Abutments With 3 Missing Walls (the Most Mutilated Subgroup). Conclusion: The Fracture Resistance Of The Fixed-fixed Partial Denture Was Directly Proportional To The Adjoining Abutments Existing Walls Number. The Zirconia Material Enhanced The Fracture Resistance Of The Fixed Prosthodontics Due Toitshigher Ability For Stress Distribution Than The Lithium Di-silicate Ceramics(E-Max).