Influence of endocrown-retained fixed dental prosthesis design on marginal integrity and fracture resistance.

PURPOSE: To investigate the effect of zirconia endocrown-retained fixed dental prosthesis (FDP) designs on marginal integrity and fracture resistance after thermomechanical aging, compared with full-coverage-retained FDPs.

MATERIALS AND

METHODS

Three extracted mandibular second premolars and second molars were randomly assigned to three abutment designs: full-coverage retainers (A), butt-joint endocrowns (B), and endocrowns with shoulder finish line and ferrule-like extensions (C). All teeth were prepared as abutments for three-unit zirconia FDPs replacing a missing mandibular first molar, and each FDP was duplicated into 12 epoxy resin models. High translucent zirconia FDPs were fabricated using Computer-Aided Design-Computer-Aided Manufacturing (CAD-CAM) and cemented using self-adhesive resin cement. Marginal gaps were measured under a stereomicroscope (× 35) before and after thermomechanical aging (1.2 × 105 cycles, 49 N, 5 - 55℃). Fracture resistance was assessed after aging under compressive loading until failure, and failure mode was recorded. Data were analyzed using one-way ANOVA with post hoc tests (α = 0.05).

RESULTS

All groups showed a significant increase in marginal gap after aging (P < .05). Group B had the smallest mean marginal gap before and after aging (P < .001). Group A exhibited the highest fracture resistance, significantly exceeding Groups B and C, with Group B showing the lowest values (P < .001). Failure mode analysis indicated that fractures were confined to the connector regions, mainly the distal connectors, with occlusal extension observed in Groups B and C.

CONCLUSION

Abutment design significantly affected the zirconia endocrown-retained FDPs performance. Marginal gaps increased after thermomechanical aging, but remained within clinically acceptable limits. The butt-joint design demonstrated superior marginal adaptation, while the full-coverage design exhibited the highest fracture resistance, exceeding physiologic posterior masticatory forces.