To assess whether access cavity design influences the fracture strength of endodontically treated and restored molars. Fifty human lower molars with standard crown dimensions were selected and assigned to the following groups: S – positive control (healthy tooth), ET – negative control (conventional endodontic access (CEA) and no restoration), NI – negative control (minimally invasive endodontic access (MEA) and no restoration), ETR (CEA + restoration with Bulkfill flow) and NIR (MEA + restoration with Bulkfill flow). The specimens were subjected to a compression test. The teeth were inspected for the site of fracture: either pulp floor or cusp. ANOVA, followed by Tukey’s multiple comparison test (α = 5%), was used for statistical analysis. The type of access cavity preparation did not increase the fracture strength of endodontically treated teeth. Even with the restoration, all teeth with endodontic access performed had a higher incidence of fractures at the pulp chamber floor level.