Should adhesive debonding be simulated for intra-radicular post stress analyses?

Objective: Elucidate the influence of debonding on stress distribution and maximum stresses for intra-radicular restorations.

Methods: Five intra-radicular restorations were analyzed by finite element analysis (FEA): MP=metallic cast post core; GP=glass fiber post core; PP=pre-fabricated metallic post core; RE=resin endocrowns; CE=single piece ceramic endocrown. Two cervical preparations were considered: no ferule (f₀) and 2mm ferule (f₁). The simulation was conducted in three steps: (1) intact bonds at all contacts; (2) bond failure between crown and tooth; (3) bond failure among tooth, post and crown interfaces. Contact friction and separation between interfaces was modeled where bond failure occurred. Mohr-Coulomb stress ratios (σ_{MC ratio}) and fatigue safety factors (SF) for dentin structure were compared with published strength values, fatigue life, and fracture patterns of teeth with intra-radicular restorations.

Results: The σ_{MC ratio} showed no differences among models at first step. The second step increased σ_{MC ratio} at the ferule compared to step 1. At the third step, the σ_{MC ratio} and SF for f₀ models were highly influenced by post material. CE and RE models had the highest values for σ_{MC ratio} and lower SF. MP had the lowest σ_{MC ratio} and higher SF. The f₁ models showed no relevant differences among them at the third step.

Significance: FEA most closely predicted failure performance of intra-radicular posts when frictional contact was modeled. Results of analyses where all interfaces are assumed to be perfectly bonded should be considered with caution.