Postgraduate student, Department of Restorative Dentistry, Center for Dentistry and Oral Hygiene, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands.
Associate Professor, School of Dentistry, Evangelical University of Goias (UniEVANGÉLICA), Anapolis, Brazil.
J Prosthet Dent. 2024 Jun;131(6):1150-1158. doi: 10.1016/j.prosdent.2024.03.039. Epub 2024 Apr 26.
More data are needed on the influence of preparation design on the fracture strength, failure type, repairability, and polymerization-induced cracks of molar teeth restored with direct composite resin restorations.
This in vitro and finite element analysis study investigated the effect of different preparation designs on fracture strength, failure type, repairability, tooth deformation, and the formation of polymerization-induced cracks of compromised molars restored with direct composite resin restorations.
Human molars (n=64) were randomly assigned to 4 different preparation designs: undermined inlay (UI), extended inlay (EI), restricted overlay (RO), and extended overlay (EO). The teeth were restored using direct composite resin and subjected to artificial thermomechanical aging in a mastication simulator, followed by load-to-failure testing. Three-dimensional (3D) finite element analysis was conducted to assess tooth deformation. Polymerization-induced cracks were evaluated using optical microscopy and transillumination. The fracture strength data were analyzed using a Kruskal-Wallis test, while the failure mode, repairability, and polymerization cracks were analyzed using the Fisher exact test (α=.05).
All specimens withstood thermomechanical aging, and no statistically significant difference in fracture strength was observed among the 4 preparation designs (P>.05). The finite element analysis showed differences in tooth deformation, but no correlation was observed with in vitro fracture resistance. The RO and EO groups presented significantly more destructive failures compared with the UI and EI groups (P<.01). The RO group had significantly fewer repairable failures than the UI and EI groups (P=.024). A correlation was found between higher frequencies of repairability and higher tooth deformation. A significant correlation between the increase in microfractures and preparation design was observed (P<.01), with the UI group exhibiting a higher increase in microfracture size compared with the EO group (P<.05).
No influence of preparation design on the fracture strength of compromised molars restored with direct composite resin restorations was evident in this study, but the failure mode of cusp coverage restorations was more destructive and often less repairable. The finite element analysis showed more tooth deformation in inlay preparations, with lower stresses within the root, leading to more reparable fractures. Since cusp coverage direct composite resin restorations fractured in a more destructive manner, this study suggests that even a tooth with undermined cusps should be restored without cusp coverage.
需要更多数据来研究预备设计对磨牙的断裂强度、失效类型、可修复性、聚合诱导裂纹的影响，这些磨牙通过直接复合树脂修复体进行修复。
本体外和有限元分析研究调查了不同预备设计对断裂强度、失效类型、可修复性、牙齿变形和聚合诱导裂纹形成的影响，这些影响涉及用直接复合树脂修复体修复的受损磨牙。
将 64 个人类磨牙随机分配到 4 种不同的预备设计组：牙内固位嵌体（UI）、扩展嵌体（EI）、限制覆盖（RO）和扩展覆盖（EO）。使用直接复合树脂对牙齿进行修复，并在咀嚼模拟器中进行人工热机械老化，然后进行加载至失效测试。通过三维（3D）有限元分析评估牙齿变形。使用光学显微镜和透光法评估聚合诱导裂纹。使用 Kruskal-Wallis 检验分析断裂强度数据，而使用 Fisher 确切检验（α=.05）分析失效模式、可修复性和聚合裂纹。
所有标本均能承受热机械老化，4 种预备设计之间的断裂强度无统计学差异（P>.05）。有限元分析显示牙齿变形存在差异，但与体外抗断裂强度无相关性。RO 和 EO 组与 UI 和 EI 组相比，破坏性失效明显更多（P<.01）。RO 组可修复失败的比例明显低于 UI 和 EI 组（P=.024）。可修复性的频率与牙齿变形的频率之间存在相关性。还发现微裂纹的增加与预备设计之间存在显著相关性（P<.01），与 EO 组相比，UI 组的微裂纹尺寸增加更高（P<.05）。
本研究未发现预备设计对用直接复合树脂修复体修复的受损磨牙的断裂强度有影响，但尖牙覆盖修复体的失效模式更具破坏性，且往往更不易修复。有限元分析显示牙内固位嵌体的牙齿变形更大，根部的应力更低，导致可修复性骨折更多。由于尖牙覆盖的直接复合树脂修复体以更具破坏性的方式断裂，因此本研究表明，即使是有牙尖下切迹的牙齿也应该不进行尖牙覆盖修复。
