Effect of Pontic Span Length on Fiber-reinforced Acrylic Provisional FPDs

Objectives: To evaluate the clinical performance of long span fiber-reinforced acrylic provisional fixed partial dentures (FPDs) with various pontic span lengths.
Methods: This prospective single-blind study included volunteers who needed fabricated long span provisional FPDs to replace more than two posterior teeth. The provisional FPDs (auto-polymerized PMMA resin, Tempron®) were randomly divided into test group (consisted of one bundle glass fiber (Fibrekor®) in the tension side according to their different pontic span length) and control group (unreinforced). Clinical performance of the provisional FPDs was recorded every month to detect any occurrence of fractures/cracks. Statistically analysis used Kaplan-Meier survival analysis to compare the survival curves, and Cox proportional hazards model to calculate odds ratio. Finally, ROC curve was conducted to find the ideal pontic span length for glass fiber reinforcement.
Results: Forty-five provisional FPDs were made for 33 participants (male=13, female=20) from September 2011 to December 2012. One participant was lost, therefore the dropout rate is 3% (1/33). The test (n=21) and control (n=23) groups were further divided into pontic span length<17mm, 17~20mm and >20mm subgroups. The 180-days survival-rate of three test subgroups were 100%, 100%, 42.9%. And control subgroups were 81.8%, 62.5%, 25.0%, respectively. Odds-ratio of fracture for pontic span length >20mm subgroup was 10.52 times higher (p<0.05) than that of <17mm subgroup. These results indicate a strong association between the pontic span length and clinical fracture rate. Unreinforced provisional FPDs can easily fracture with a pontic span length >16.9mm. For reinforced provisional FPDs, fractures may occurs when pontic span length is >21.4mm.
Conclusions: The clinical fracture rate of provisional FPDs is correlated with pontic span length. When pontic span length is between 17 and 21mm, glass fiber-reinforced PMMA resin can effectively prevent fracture. Fiber-reinforcement is not effectual for acrylic provisional FPDs with pontic span length >21mm.