Background <p>To investigate the influence of endodontic access cavity designs and root canal sealers on extracted mandibular incisors’ fracture resistance (FR) after 6 months of ageing.</p> Methods <p>Fifty mandibular incisors with similar dimensions and root lengths were collected and randomly divided into five groups (<i>n</i> = 10) based on endodontic access cavity: traditional access cavity (TAC) or minimally invasive access cavity (MIAC) and root canal sealers (AH Plus or NeoSealer Flo) with an intact tooth as control group. The teeth underwent FR testing after root canal filling and composite resin restoration. Statistical analysis was performed using the Shapiro-Wilk, one-way ANOVA, and post hoc Tukey tests with the significance level set at 0.05.</p> Results <p>The control group exhibited the highest FR (434.60 ± 80.65&#xa0;N). Significant differences were observed between the control and all experimental groups (<i>p</i> &lt; 0.001 for TAC/AH Plus, and TAC/NeoSealer Flo, <i>p</i> = 0.002 for MIAC/AH Plus, and <i>p</i> = 0.001 for MIAC/NeoSealer Flo). The mean values for the experimental groups were 309.62 ± 82.51&#xa0;N (TAC/AH Plus), 281.75 ± 50.79&#xa0;N (TAC/NeoSealer Flo), 320.85 ± 40.77&#xa0;N (MIAC/AH Plus), and 313.91 ± 42.44&#xa0;N (MIAC/NeoSealer Flo), with no significant differences among them (<i>p</i> &gt; 0.05).</p> Conclusions <p>Neither the shape of the endodontic access cavity nor the type of sealer affected the FR of extracted mandibular incisors after 6 months of ageing.</p>