Ahmed B. Abdel-Rahman, Manal R. Hassan And Mohamed M. Shalaby,

ABSTRACT

Objectives: To Evaluate The Effect Of Pontic Span Length On The Design Of Inlay Retained Fixed Partial Denture.

Materials and Methods: Two Designs Of Inlay Retained Fixed Partial Denture (IRFPD) Preparation, The First One Is Occluso-mesial And Occluso-distal Box(OD/OM),the Second One Is Mesio-occluso-distal (MOD) In The Two Abutment Were Studied With Two Different Pontic Spaces (7 And 9 Mm) To Restore Missed Upper Second Premolar. Four Inlay Retained Fixed Partial Dentures (IRFPDs) Were Constructed From Full Contour Milled Zirconia To Restore The Four Models. Model (1): Occluso-mesial And Occluso-distal Design Restoring Pontic Span 7mm, Modal (2) MOD Design Restoring Pontic Span 7mm, Model (3): Occluso-mesial And Occluso-distal Design Restoring Pontic Span 9mm And Model (4):MOD Design With Pontic Span Length 9mm. Fracture Resistance Of Each Model Was Performed In Which A Load Was Applied At The Center Of Pontic Occlusally Using A Metallic Rod With Round Tip (3.4 Mm Diameter) Traveling At Cross-head Speed Of 1mm/min. With Tin Foil Sheet In-between To Achieve Homogenous Stress Distribution. The Mode Of Failure Was Observed And Recorded. Four 3D Finite Element Models Were Obtained After Scanning The Four Models In Order To Compare The Stress Falling On The Components Of IRFPD Restored With Lithium Di-silicate Ceramics And Zirconia Under Two Force Direction (vertical And Oblique 30� From Buccal Side) .

Results: OD/OM Designs Showed Higher Fracture Resistance Values Than MOD Inlay Designs, 7 Mm Pontic Span Models Showed Higher Fracture Resistance Value Than 9 Mm Pontic Span Models. The Highest Fracture Resistance Mean Value Was Recorded In Model One (2787.3�34.2N) While The Lowest Fracture Resistance Mean Value Was Recorded In Model Four (1257.5�35.5N). Mode Of Failure Was Cohesive Failure In The Zirconia Framework As Fracture Of The IRFPD At Level Of Connectors Or At Level Of Retainers. The Finite Element Analysis Showed That Zirconia Fixed Partial Dentures Had Higher Fracture Resistance Value Than Lithium Di-silicate Ceramics.

Conclusions: The Fracture Resistance Of IRFPD Was Increased With Conservation Of Tooth Structure And Decreased When Pontic Span Length Increased. It Is Assumed That Zirconia Enhanced The Fracture Resistance Due To Its Ability For Stress Distribution Than Lithium Di-silicate Ceramics.