Purpose: An increase in instrument taper decreases the amount of residual radicular dentin thickness (RRDT), thus increasing the fracture strength of teeth. The aim of this study was to determine the residual dentin thickness and evaluate the fracture strength and mode of fracture of endodontically treated bifurcated maxillary premolars with different tapered file systems.
Methods: Fifty bifurcated maxillary first premolars were randomly divided into five groups. Group 1, consisting of 10 intact teeth, served as control. The 40 remaining teeth were divided into four groups consisting of 10 specimens per group. Group 2: 30.02% K file, group 3: 30.04% K3 system, group 4: 30.06% Mtwo system, and group 5: 30.09% ProTaper Universal System. Chemomechanical preparation was done up to apical preparation ISO 30. Assessment of RRDT was performed using the pre- and post-instrumentation cone -beam computed tomography scans. The obturated specimens were then subjected to static loading in a universal testing machine until fracture, and fracture strength & and mode of fracture were evaluated using scanning electron microscopy analysis. Data were analyzed using ANOVA, Tukeys HSD for multiple comparisons, with a significance level set at p< 0.05.
Results: The mean of difference in RRDT at 3 mm and 6 mm and the mean of maximum fracture loads were greatest for group 5: 30–9% ProTaper Universal System, while Group 2: 30-2% K file exhibited the least values among the experimental groups. There was a statistically significant difference in vertical and oblique loading between the experimental groups (p< 0.05). The most common mode of fracture was the crown-initiated vertical fractures in the root.
Conclusion: The findings showed that an increase in taper decreased the amount of residual dentin thickness, consequently increasing the fracture strength of maxillary premolars.