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Effect of Dowel Material and Design on the Fracture Resistance of Premolars

Nadia Z. Fahmy*

Statement of problem: A dowel is essential to retain the core in case of severe tooth destruction. However, the placement of a dowel and core may actually weaken teeth and affect their failure pattern depending on their material properties and stress transfer.
Purpose: The present study compared the fracture resistance and failure pattern of endodontically treated premolars with different amounts of tooth destruction restored with dowels of different materials: a heat pressable ceramic (IPS e.max) and glass fiber reinforced dowels with 3 dowel space designs.
Materials and methods: Ninety single rooted premolars of similar dimensions were selected and divided at random into 9 groups (n=10) Group 1: Sound teeth (Control group), Group 2: Reduced sound teeth with 60 taper and a 1 mm shoulder FL. Groups (3-9) were endodontically treated and divided as follows: Group 3: Restored teeth with minimal endodontic access. Groups 4, 5 and 6 restored using a pressable ceramic dowel and core while groups 7, 8 and 9 were restored using fiber dowels and composite cores. The samples were loaded to fracture and the mode of fracture for each group was examined. The recorded values were tabulated and statistically analyzed.
Results: Group 5 (tapered ceramic) showed the highest fracture mean values followed by group 6 (parallel ceramic). Group 4 (parallel tapered ceramic) showed statistically similar values to group 1 (sound teeth).Group 2 (Reduced sound teeth) registered 20% reduction in fracture resistance when compared to group 1 (sound teeth). Group 3 (minimal endodontic access) showed statistically similar values to group 2. Fiber groups 7, 8 and 9 displayed statistically similar mean fracture resistance values, which were 30% lower than those of groups 2 and 3.
Conclusions: Reduction of sound teeth resulted in 20% decrease in their fracture resistance. Endodontically treated premolars with minimal access, restored with composite, maintained the same values as sound reduced teeth. Pressed ceramic bonded dowel and cores with three dowel designs displayed higher resistance means than sound reduced teeth; however, most failures were unfavorable. Fiber dowels and composite core groups registered approximately 70% of the values of sound reduced teeth but all failure patterns were favorable.