Effects of different apical preparation sizes and root canal sealers on the fracture resistance of roots aged for 12 months in endodontically retreated mandibular premolars

Objective This study evaluated the effect of different apical preparation sizes and root canal sealers on fracture resistance.Materials and methods In total, 100 mandibular premolars were collected; 90 were prepared with the VDW R25 file, obturated with AH Plus a single gutta-percha cone and stored for one month, after which ProTaper Universal Retreatment System instruments were used to remove the root canal filling materials. The K3XF rotary nickel-titanium files (25/0.04, 30/0.04, 35/0.04, 40/0.04, respectively, according to the experimental groups) were used to complete retreatment and obturated with root canal sealer and a single gutta-percha cone per the experimental groups. The root segments were randomly divided into ten experimental groups (n = 10 roots/group) as follows: Negative Control Group 1 (intact tooth group); Positive Control Group 2 (25/0.04 preparation, without obturation); Positive Control Group 3 (30/0.04 preparation, without obturation), Positive Control Group 4 (40/0.04 preparation, without obturation); Group 5A (30/0.04, AH Plus); Group 5B (40/0.04, AH Plus); Group 6A (30/0.04, NeoSealer Flo); Group 6B (40/0.04, NeoSealer Flo); Group 7A (30/0.04, MTA Bioseal); and Group 7B (40/0.04, MTA Bioseal). All the experimental groups were incubated at 37 °C for 12 months in 100% humidity. A universal testing machine measured the fracture resistance of each segment and the results were recorded in Newtons.Results There were no significant differences between the sealers and apical preparation sizes. The root segments obturated with AH-Plus, NeoSealer Flo and MTA Bioseal yield values significantly higher than those in the negative control groups.Conclusions All types of sealer (AH Plus, NeoSealer Flo and MTA Bioseal) exhibited nearly the same fracture resistance in retreated root segments aged 12 months.