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Purpose The aim of this study was to compare the influence of the number of coronal walls and post-endodontic restorations on the mechanical strength of 165 recently extracted endodontically treated maxillary premolars. Methods The teeth were divided into 3 control (no post) and 3 test groups according to the number of residual walls. Each test group was divided into subgroups according to the type of post-endodontic restoration (single, oval, and multi-post techniques). Samples were prepared conforming to the assigned subgroup. A universal loading machine applied a load parallel to the longitudinal axis of the teeth, thus simulating physiological occlusion. ANOVA and the Kruskal Wallis test were used for comparisons (P ≤ 0.05), and Tukey's test for multiple comparisons. Results For intact teeth, significant differences were found among all 3 subgroups, with single post showing the highest values. For 3 residual walls, oval post resulted in significantly lower values than single and multi-post systems. For 2 residual walls, the multi-post technique showed almost twice the resistance of oval post restorations. Conclusion In oval canals the use of a single or multi-post technique increased post-and-core resistance even in intact teeth, whereas oval fiber posts showed no improvements. Multi-post design improved fracture resistance mostly in maxillary premolars lacking both marginal ridges.

The purpose of this study was to evaluate the reinforcing effect of fibre-reinforced composites (FRC) applied in premolar teeth with different techniques and minimally invasive post space preparation. Fifty extracted and endodontically treated premolar teeth were used. The teeth were divided into five groups (n = 10) depending on the restorative technique (Groups 1-5). Group 1: one single conventional post, Group 2: one main conventional and one collateral post, Group 3: one elastic post, Group 4: one main elastic and one collateral post, and Group 5: individual post formed of elastic posts. After cementation and core build-up, the specimens were submitted to static fracture resistance test. Fracture thresholds and fracture patterns were measured and evaluated. Group 4 showed the highest average fracture resistance among the tested groups. The multi-post techniques (group 2 and 4) exhibited statistically higher fracture resistance compared to group 1. Regarding fracture patterns, there was no statistically significant difference between the tested groups. Within the limitations of this study, the application of multiple elastic or conventional FRC posts or a single elastic post in the same root canal is beneficial in terms of fracture resistance compared to a single conventional FRC post. The elasticity or the number of posts did not influence the fracture patterns.