New material perspective for endocrown restorations: effects on mechanical performance and fracture behavior

Abstract The aim of this study was to investigate the mechanical performance and the fracture behavior of endocrown restorations prepared using distinct restorative materials. A total of 42 sound molars with similar crown size and shape were cut at 2 mm above the cementoenamel junction and endodontically treated. They were categorized according to the restorative material used to fabricate endocrown restorations (n=7), namely, conventional composite (Filtek™ Z350 XT), bulk fill composite (Filtek™ Bulk Fill), conventional composite modeled using resin adhesives (SBMP: Scotchbond™ Multipurpose Adhesive; or SBU: Scotchbond™ Universal Adhesive), and IPS e.max lithium disilicate (Ivoclar Vivadent; positive control). Unprepared sound teeth were used as negative control. All endocrowns were bonded using a self-adhesive cement (Rely-X™ U200). The teeth were submitted to fatigue (Byocycle) and fracture (EMIC DL500) testing. Load-to-fracture (in N) and work-of-fracture (Wf, in J/m2) values were analyzed by ANOVA (p < 0.05). The endocrowns did not fracture or de-bond upon fatigue, showing similar load-to-fracture and work-of-fracture values, regardless of the restorative material (p > 0.05). The endocrowns fabricated by combining Z350 and SBMP had the least harsh fractures, in contrast to endocrowns prepared using Z350 only, which exhibited an equilibrium between repairable and irrepairable fractures. The e.max endocrowns exhibited more aggressive failures (root fracture) than other groups, resulting in higher rates of irrepairable fractures. In conclusion, dental practitioners may satisfactorily restore severely damaged nonvital teeth using the endocrown technique. Composite endocrowns prepared using resin adhesive as modeler liquid or using bulk fill material may result in less aggressive failures, thus providing a new material perspective for endocrown restorations.

摘要 本研究旨在探讨采用不同修复材料制备的髓腔固位高嵌体（endocrown）修复体的力学性能与断裂行为。研究共纳入42颗冠部尺寸与形态相近的完整恒牙磨牙，于釉牙骨质界（cementoenamel junction）上方2mm处截冠并行根管治疗。根据制备髓腔固位高嵌体所用修复材料进行分组（每组n=7），所涉材料包括：传统复合树脂（Filtek™ Z350 XT）、大块充填复合树脂（Filtek™ Bulk Fill）、采用树脂粘接剂改性的传统复合树脂（SBMP：Scotchbond™ 多功能粘接剂（Scotchbond™ Multipurpose Adhesive）；或SBU：Scotchbond™ 通用粘接剂（Scotchbond™ Universal Adhesive）），以及IPS e.max二硅酸锂玻璃陶瓷（义获嘉伟瓦登特（Ivoclar Vivadent）公司产品，阳性对照）。以未预备的完整天然牙作为阴性对照。所有髓腔固位高嵌体均采用自粘接树脂水门汀（Rely-X™ U200）粘接固位。对所有样本开展疲劳（Byocycle试验机）与断裂（EMIC DL500试验机）测试。采用方差分析（ANOVA）对断裂载荷（单位：N）与断裂功（Wf，单位：J/m²）数据进行统计分析，检验水准设为P<0.05。结果显示：经疲劳测试后，所有髓腔固位高嵌体均未发生断裂或脱粘，且无论采用何种修复材料，其断裂载荷与断裂功值均无显著差异（P>0.05）。联合使用Z350与SBMP制备的高嵌体，其断裂模式最为温和；与之相对，仅使用Z350制备的高嵌体，其可修复与不可修复性断裂的占比趋于均衡。IPS e.max高嵌体的断裂模式较其余各组更具破坏性，表现为牙根折裂，不可修复性断裂的发生率更高。综上，临床医师可采用髓腔固位高嵌体技术，成功修复重度缺损的无髓牙。采用树脂粘接剂改性或大块充填复合树脂制备的复合树脂高嵌体，其断裂模式相对温和，可为髓腔固位高嵌体修复提供新的材料选择思路。