Vasudeva Gaurav, Bogra Poonam, Nikhil Vineeta, Singh Vijay
Department of Conservative Dentistry and Endodontics, B.R.S Dental College and Hospital, Panchkula, India.
Indian J Dent Res. 2011 Mar-Apr;22(2):295-302. doi: 10.4103/0970-9290.84308.
Causes of failures in class V restorations have always been controversial until now, since the biomechanical aspects of these restorations have been understood.
This study was aimed to verify the hypothesis that eccentric forces are the cause of cuspal flexure, which lead to excessive stresses at the periphery of a class V restoration, further it identifies the amount of the stress and the flexure increase in the presence of an occlusal restoration using different restorative materials to restore (both cervical and occlusal) along with their comparison with respect to amount of stresses around the cervical restorations.
The study was done by modeling a mandibular first premolar which was sectioned bucco-lingually, in the NISA, EMRC II finite element software. A 100N eccentric load was applied on the tooth structure and stresses were observed at the peripheries of the class V restoration when it was restored with composite and with glass ionomer cement. The stresses were further analyzed in the presence of occlusal restorations with different materials and configurations.
It was seen that the stresses at the gingival wall interface in case of class V glass ionomer cement was more than that for composite. In the presence of an occlusal amalgam restoration, the cuspal flexure was more than that of occlusal composite and the stresses at the class V peripheries were also statistically significant.
It was suggested that lower modulus composites can flex with the tooth structure decreasing the bond failure and that the stresses are much lesser when there is absence of an occlusal restoration. Occlusal composite restorations reinforce the tooth structure and reduce the cuspal flexure as compared to silver amalgam.
直到现在，V类洞修复失败的原因一直存在争议，因为这些修复体的生物力学方面已经得到了解。
本研究旨在验证以下假设，即偏心载荷是牙尖弯曲的原因，牙尖弯曲会导致V类洞修复体边缘产生过大应力；此外，本研究还确定了使用不同修复材料修复（颈部和咬合面）时应力的大小以及咬合修复体存在时弯曲的增加情况，并比较了颈部修复体周围应力的大小。
本研究通过在NISA、EMRC II有限元软件中对下颌第一前磨牙进行颊舌向切片建模来完成。在牙齿结构上施加100N的偏心载荷，当用复合树脂和玻璃离子水门汀修复V类洞时，观察修复体边缘的应力。在存在不同材料和构型的咬合修复体的情况下，进一步分析应力。
可以看出，V类玻璃离子水门汀修复时牙龈壁界面的应力大于复合树脂修复时的应力。在存在咬合银汞合金修复体的情况下，牙尖弯曲大于咬合复合树脂修复体，V类洞边缘的应力在统计学上也有显著差异。
有人提出，较低模量的复合树脂可以与牙齿结构一起弯曲，减少粘结失败，并且在没有咬合修复体时应力要小得多。与银汞合金相比，咬合复合树脂修复体增强了牙齿结构并减少了牙尖弯曲。
