Influence of access cavity design on the structural integrity of endodontically treated permanent mandibular 1^st...

Endodontically treated teeth are increasingly prone to fracture over time, and their resistance to fracture is closely related to the amount of coronal tooth structure removed during access cavity preparation. Preservation of sound tooth structure through appropriate access cavity design is therefore essential for maintaining long-term tooth strength and clinical performance. Accordingly, this study evaluated the influence of traditional and conservative access cavity designs on the fracture resistance of endodontically treated mandibular first molars.

Forty recently obtained human permanent mandibular first molars were arbitrarily allocated into four groups, each comprising ten teeth: traditional access cavity (TradAC), contracted access cavity (ConsAC), truss access cavity (TrussAC), and intact teeth (control). The experimental groups underwent root canal treatment, and the access cavities were subsequently restored with composite resin to standardize coronal reinforcement prior to fracture testing. Fracture resistance was evaluated using a universal testing machine, and fracture patterns were analyzed under a stereomicroscope for fracture type classification. Statistical comparisons among groups were accomplished using one-way ANOVA, tracked by Tukey post hoc tests at p < 0.05.

Through this experiment, teeth prepared with TradAC exhibited significantly lesser fracture resistance compared with TrussAC and intact teeth (p < 0.05), while no substantial differences were observed between TrussAC and ConsAC or between TradAC and ConsAC (p > 0.05). Unrestorable fractures were more common in the TradAC, ConsAC, and TrussAC groups compared with the control group, although this difference was not statistically significant (p > 0.05). Based on these findings, truss access cavity design demonstrated higher fracture resistance than traditional access cavity design in endodontically treated teeth, and unrestorable fractures were more common than restorable fractures in teeth with access cavity preparations.

These findings highlight that adopting conservative access cavity designs, particularly truss access cavities, may improve the structural durability of endodontically treated teeth and support more predictable long-term clinical outcomes.