Influence of Retainer Design on Shear Bond Strength in Fixed Partial Dentures: An In Vitro Comparative Study

Area of Science:

• Dental Materials Science
• Prosthodontics
• Biomaterials Engineering

Background:

• Resin-bonded fixed dental prostheses (RBFDPs) offer a conservative approach to replacing missing teeth.
• Retention and debonding issues persist with RBFDPs, especially in posterior applications.
• Evaluating retainer design's impact on RBFDP bond strength is crucial for clinical success.

Purpose of the Study:

• To assess the influence of different retainer designs on the shear bond strength (SBS) of monolithic zirconia RBFDPs.
• To compare the performance of conventional overlay (OVL), modified overlay (MOVL), and full-coverage crown (FCC) retained FPDs.
• To analyze failure modes associated with each retainer design.

Main Methods:

• Fifteen monolithic zirconia FPDs were fabricated and divided into OVL, MOVL, and FCC groups (n=5 each).
• Restorations were cemented onto epoxy resin dies using dual-cure resin cement.
• Shear bond strength was measured using a universal testing machine, followed by stereomicroscopic failure analysis.

Main Results:

• The FCC group exhibited the highest mean SBS (1492.70 N), followed by MOVL (1201.60 N), and OVL (469.40 N).
• Statistically significant differences in SBS were found among the groups (p < 0.001).
• Adhesive failures were predominant in the OVL group, while mixed failures occurred more frequently in MOVL and FCC groups.

Conclusions:

• The modified overlay-retained FPD demonstrated significantly higher SBS than the conventional overlay design.
• The MOVL design showed comparable performance to the conventional FCC retained prosthesis.
• The modified overlay design presents a potentially conservative and clinically acceptable alternative for posterior RBFDPs.