Biomechanical Evaluation of a Novel Chambered Overlay Design in Endodontically Treated Mandibular Molars
DOI:
https://doi.org/10.15218/edj.2026.2Keywords:
Overlay, Biomimetic design, Lithium Disilicate, Adhesive Restoration, Hozan’s Chambered OverlayAbstract
Background and objectives: Endodontically treated teeth (ETT) are structurally weakened because of extensive loss of internal dentin architecture. Although adhesive overlays have been introduced as a conservative restorative approach, limited evidence exists regarding the influence of internal design modifications on fracture resistance. This study evaluated the effect of a novel biomimetic overlay design, termed the Embedded Chamber Overlay (ECO), also known as Hozan’s Chambered Overlay, on the fracture resistance of lithium disilicate restorations in endodontically treated mandibular first molars.
Methods: Sixteen extracted human mandibular first molars underwent endodontic treatment and decoronation at the cementoenamel junction level. Specimens were randomly allocated into two groups (n = 8) according to overlay design: conventional lithium disilicate overlays or ECO lithium disilicate overlays. All restorations were fabricated and adhesively cemented using standardized protocols. Fracture resistance was evaluated under axial compressive loading using a universal testing machine. Failure modes were assessed under magnification. Data were analyzed using independent samples t-tests with statistical significance set at α = 0.05.
Results: The ECO lithium disilicate overlay group demonstrated significantly higher fracture resistance (3971 ± 20 N) than the conventional overlay group (2641 ± 20 N) (p < 0.001). Cohen’s d analysis revealed an extremely large effect size (d = 66.1). All specimens exhibited catastrophic Class IV fractures involving root-level structural separation.
Conclusion: Within the limitations of this in vitro study, ECO significantly enhanced the fracture resistance of lithium disilicate restorations in endodontically treated mandibular molars, suggesting improved biomechanical performance in structurally compromised posterior teeth.
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