Purpose: To assess the effect of three different drills used for post space preparation on fiber post retention after Reciproc endodontic treatment.
Methods: 30 human upper incisors were endodontically treated using Reciproc and warm vertical gutta-percha compaction. Teeth were sealed coronally using Fuji VII, then stored in 0.5% T chloramine solution at 4 degrees C. After 1 week, teeth were randomly assigned to three groups (n = 10) that differed for the drill type used for post space preparation: Group 1: Calibrated drill; Group 2: Largo drill; Group 3: MTwo drill. Illusion posts were luted into the root canals using Gradia Core. After 24 hours, posted roots were transversally cut into 1 mm-thick slices for thin-slice post push-out testing. Two slices per apical, middle, and coronal thirds were obtained, resulting in a total of 6 slices per tooth. Thin-slice push-out test was conducted using a universal testing machine. Post push-out strength was measured in MPa. For the fracture analysis, the specimens were observed using a stereomicroscope at x40 magnification and classified as adhesive [between post-cement (P-C) or dentin-cement (D-C) interface], cohesive (within the post or adhesive cement) and mixed (adhesive and cohesive fractures occurred simultaneously). Between-group differences in post retentive strength were statistically analyzed (Kruskal-Wallis ANOVA, Dunn's Multiple Range test, P > 0.05). Differences in push-out strength among root levels within each group (one-way ANOVA or Kruskal-Wallis ANOVA, depending on the normality of data distribution, P> 0.05) and in failure mode distribution were also statistically evaluated (Fisher's Exact Test, P > 0.05).
Results: For each group the mean of MPa values was: (1) 10.41 ± 3.56, (2) 10.98 ± 3.96, and (3) 12.11 ± 1.65. Failure mode was distributed as follows: Adhesive: (1) P-C - 23.3%, D-C - 21.7%; (2) P-C - 20%, D-C - 10%; (3) PrC - 46.7%, D-C - 13.3%; Cohesive: (1) 0.0%, (2) 3.3%; (3) 0.0%; Mixed: (1) 55.0%; (2) 66.7%; (3) 40.0%. The statistical analysis revealed the existence of significant between-group differences (P= 0.002). Group 3 measured significantly higher push-out strengths than Groups 1 and 2, which were comparable. Statistically significant between-group differences emerged also in failure mode distribution (P= 0.004). In Group 3 post-cement adhesive failures were significantly more frequent and mixed failures were significantly less frequent than in Group 2. No statistically significant differences emerged among the different root levels of the tested groups (P > 0.05).