Investigations of Effects of Radiotherapy, Sonic Activation and Root Canal Treatment on Fracture Resistance of Mandibular Anterior Teeth: An In Vitro Study

<b>Background and objectives</b>: Head and neck cancer patients frequently undergo radiotherapy, which can affect the properties of dental hard tissues. This study aimed to evaluate the effects of root canal treatment, radiotherapy, and sonic activation during irrigation on the fracture resistance of mandibular anterior teeth. <b>Methods</b>: 80 extracted mandibular anterior teeth were randomly divided into five groups: untreated control (Group I); root canal treatment without radiotherapy or sonic activation (Group II); root canal treatment without radiotherapy but with sonic activation (Group III); root canal treatment with 70 Gray (Gy) radiotherapy and sonic activation (Group IV); and root canal treatment with radiotherapy but without sonic activation (Group V). Radiotherapy was administered in fractionated doses (2 Gy/day, 5 days/week) over 7 weeks. Following instrumentation, root canal obturation was performed accordingly. Fracture resistance was measured using a universal testing apparatus with vertical loading until fracture. Statistical analyses included Shapiro-Wilk normality testing followed by appropriate non-parametric Kruskal-Wallis test followed by Dunn's post hoc test with Bonferroni correction for multiple comparisons. <b>Results</b>: All root canal-treated groups exhibited significantly lower fracture resistance compared to the untreated control group [1572.3 (1217.0-1841.2) N, <i>p</i> < 0.05]. No statistically significant differences were observed between irradiated and non-irradiated groups (<i>p</i> > 0.05). Similarly, sonic activation during irrigation did not significantly affect the fracture resistance values (<i>p</i> > 0.05). <b>Conclusions</b>: Under the specific conditions of this in vitro protocol, fractionated radiotherapy and sonic activation did not demonstrate statistically significant effects on fracture resistance in mandibular anterior teeth, while endodontic procedures reduced fracture resistance.