Does selective root canal retreatment preserve the tooth’s fracture resistance? An ex-vivo study

OBJECTIVES: To assess the tooth's fracture resistance when submitted to a selective root canal retreatment compared to the conventional approach. METHODS: 33 intact permanent mandibular first molars were selected according to specific criteria. After teeth mounting, the primary root canal treatment was conducted and followed by thermo-mechanical aging procedures to mimic a few clinical conditions. The specimens were randomly divided into three groups (n = 11); a control group in which intact teeth were used and two experimental groups according to the retreatment approach: conventional non-surgical retreatment (Conventional-NSR), and selective non-surgical retreatment (Selective-NSR). Later, the teeth were submitted to a final thermo-mechanical aging procedure and tested regarding their fracture resistance (static fracture test). The maximum load to fracture was recorded as were the types of failure modes (repairable or non-repairable fracture). A proper statistical analysis was conducted, considering a significance level of 5%. RESULTS: The Conventional-NSR group showed a mean failure load of 867.7 ± 108.9 N while the Selective-NSR group had 1106.8 ± 159.8 N (P = 0.012). Both retreatment groups showed significantly lower results when compared to the control group. Additionally, the Conventional-NSR group showed higher proportions of non-repairable fractures (54.5%) when compared to both the Selective-NSR (36.4%) and control (18.2%) groups. CONCLUSIONS: Selective root canal retreatment preserved the tooth's fracture resistance compared to the conventional retreatment approach. CLINICAL TRIAL NUMBER: Non-applicable. Conducting the current experiment was limited to obtaining approval from the local Research Ethics Committee at the Faculty of Dentistry, Minia University (Committee No. 105, Registration No. 902, Date: 26/3/2024).