Mechanical behavior of endodontically treated molars restored using two restorative approaches and two CAD/CAM materials: an in-vitro study

Background Restoration of endodontically treated teeth (ETT) with significant coronal loss poses a challenge in clinical dentistry. Advances in CAD/CAM technology and biomimetic materials have introduced minimally invasive approaches, such as endocrowns and overlays, which can replace traditional post-core and crown approach. Aim The aim of this in-vitro study was to comparatively assess the mechanical behaviour of two restorative designs (endocrowns and overlays) fabricated from two CAD/CAM materials in endodontically treated mandibular molars. Materials and methods Thirty-six endodontically treated lower molars ( n = 36) were split into two main groups based on restoration type ( n = 18): endocrowns and overlays. Each group was further subdivided into two subgroups based on the CAD/CAM material ( n = 9): lithium disilicate (Tessera) and indirect composite (Crios). Restorations were fabricated and bonded to their respective specimens following a strict bonding protocol with an adhesive resin cement (Bisco self-adhesive). Thermo-mechanical aging (Chewing Simulator CS-4, SD Mechatronic) was conducted to simulate oral conditions, followed by a universal testing machine's evaluation of fracture resistance. The test was stopped after fracture. Fractured parts were analysed to determine mode of failure. Data were analyzed using two-way ANOVA followed by Tukey’s honestly significant difference (HSD) test for pairwise comparisons (α = 0.05). Results All specimens survived the 5,000 chewing cycles, simulating early intraoral service. Fracture resistance test showed significantly higher fracture resistance for overlays (2048.46 ± 664.63 N) than endocrowns (1234.54 ± 338.50 N) ( p = 0.002). Crios overlays exhibited the highest fracture resistance (2384.60 ± 631.10 N), significantly outperforming Tessera overlays (1712.33 ± 559.59 N) ( p = 0.043) and endocrowns (1354.20 ± 346.88 N) ( p = 0.004). No substantial material change was seen in endocrown restorations ( p = 0.445). Conclusion Overlay restorations and indirect composite material (Crios) provide superior resistance to fracture compared to lithium disilicate overlays and endocrowns and may represent a reliable restorative option for endodontically treated molars.