article · BMC Oral Health
Restoring teeth after root canal treatment poses mechanical challenges when extensive tooth structure is lost. This laboratory study evaluated two computer-aided design and manufacturing restoration designs, specifically endocrowns and overlays, using two distinct materials: lithium disilicate ceramic and an indirect composite. Thirty-six endodontically treated lower molars were prepared, restored, and bonded using an adhesive resin cement. The restored teeth underwent simulated oral aging through thermo-mechanical chewing cycles before being tested for fracture resistance. All specimens successfully endured five thousand chewing cycles. Testing revealed that overlay restorations exhibited significantly higher resistance to fracture compared with endocrown designs. Among the tested combinations, indirect composite overlays demonstrated the greatest fracture resistance, outperforming lithium disilicate overlays and both types of endocrown restorations. The findings indicate that composite overlays offer superior mechanical performance for restoring root-treated molars.
Teeth that undergo root canal therapy often suffer from severe structural weakness, making them prone to fracture under normal biting forces. By showing that minimally invasive overlays, particularly those made from indirect composites, withstand greater loads than traditional endocrown designs, this work helps dental practitioners select more durable restorative strategies and materials that preserve natural tooth structure while lowering failure risks.
This research informs clinical decision-making for dental practitioners and dental laboratories utilising digital milling systems. The work represents applied laboratory research evaluating commercially available computer-aided restorative materials and adhesive systems. While the materials tested are already on the market, direct translation to routine practice relies on confirming these in-vitro mechanical findings through long-term clinical trials in patients.
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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.
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DOI: 10.1186/s12903-026-07835-4
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