Biomechanical influence of residual lateral wall thickness and resin reinforcement on the performance of endocrowns in premolars.

BACKGROUND

Restoring endodontically treated premolars (ETPMs) with mesio-occluso-distal (MOD) cavities poses clinical challenges due to reduced coronal thickness and heightened fracture risk. Despite advances in adhesive dentistry, the biomechanical effects of residual lateral wall (RLW) thickness and composite resin reinforcement on the performance of ceramic endocrowns in ETPMs remain underdefined. This study aims to evaluate how RLW thickness and resin reinforcement influence fracture resistance, stress distribution, and failure modes in ETPMs restored with ceramic endocrowns.

METHODS

Forty-two human maxillary premolars underwent endodontic treatment and MOD cavity preparation, followed by randomization into 2 groups. Group A (control) included teeth preserved at specific RLW thicknesses of 2.5 mm, 2.0 mm, 1.5 mm, and 1.0 mm. Group B (test) comprised specimens with an initial 1.0 mm RLW, which were reinforced with 0.5 mm, 1.0 mm, and 1.5 mm composite resin to form subgroups B-1.5, B-2.0, and B-2.5 (corresponding to total RLW thicknesses of 1.5 mm, 2.0 mm, and 2.5 mm, respectively). All specimens were restored with CAD/CAM ceramic endocrowns, subjected to thermocycling, and underwent load-to-failure testing. Fractographic analysis was performed on fractured specimens to characterize failure modes. 3D FEA was conducted to evaluate stress distribution and tooth deformation under occlusal loading, while Weibull analysis was incorporated with FEA data to predict long-term failure probabilities. Data were analyzed using a one-way ANOVA with Tukey post hoc tests (α = 0.05).

RESULTS

In Group A, fracture load varied significantly with RLW thickness (P < 0.05), with 2.5 mm RLWs showing the highest resistance and 1.0 mm the lowest. FEA confirmed that Group A-1.0 mm displayed the most pronounced stress concentration and the highest failure probability. Among subgroups with equivalent total wall thickness across Groups A and B, Group B showed higher fracture loads than Group A (except Group B-2.5 mm), though no statistical significance (P > 0.05); stress values and distribution patterns were comparable between corresponding subgroups. Within Group B, subgroup B-2.0 displayed the highest fracture resistance, followed by B-1.5, while B-2.5 was 24 % lower than B-2.0 mm. Notably, Group B-2.5 mm exhibited the highest maximum principal stress. Failure mode analysis indicated that Type III failure was predominant across most experimental groups. Fractographic analysis showed that specimens in Group B had a greater number of cracks in the tooth tissue above the cementoenamel junction, particularly adjacent to the composite resin, compared to Group A.

CONCLUSIONS

RLW thickness influences endocrown fracture resistance and stress distribution in ETPMs. Composite reinforcement effectively enhances the biomechanical performance for thin RLWs. These findings guide clinical strategies balancing tooth structure preservation and mechanical reinforcement in endocrown design for compromised premolars.