Dejak Beata, Młotkowski Andrzej
Department of Prosthetic Dentistry, Medical University of Łódź, Łódź, Poland.
Department of Strength of Materials and Structures, Technical University of Łódź, Łódź, Poland.
Dent Mater. 2015 Mar;31(3):e77-87. doi: 10.1016/j.dental.2014.11.016. Epub 2014 Dec 24.
Polymerization shrinkage of composites is one of the main causes of leakage around dental restorations. Despite the large numbers of studies there is no consensus, what kind of teeth reconstruction--direct or indirect composite restorations are the most beneficial and the most durable.
The aim was to compare equivalent stresses and contact adhesive stresses in molar teeth with class II MOD cavities, which were restored with inlays and direct restorations (taking into account polymerization shrinkage of composite resin) during simulated mastication.
The study was conducted using the finite elements method with the application of contact elements. Three 3D models of first molars were created: model A was an intact tooth; model B--a tooth with a composite inlay, and model C--a tooth with a direct composite restoration. Polymerization linear shrinkage 0.7% of a direct composite restoration and resin luting cement was simulated (load 1). A computer simulation of mastication was performed (load 2). In these 2 situations, equivalent stresses according to the modified von Mises criterion (mvM) in the materials of mandibular first molar models with different restorations were calculated and compared. Contact stresses in the luting cement-tooth tissue adhesive interface around the restorations were also assessed and analyzed.
Equivalent stresses in a tooth with a direct composite restoration (the entire volume of which was affected by polymerization shrinkage) were many times higher than in the tooth restored with a composite inlay (where shrinkage was present only in a thin layer of the luting cement). In dentin and enamel the stress values were 8-14 times higher, and were 13 times higher in the direct restoration than in the inlay. Likewise, contact stresses in the adhesive bond around the direct restoration were 6.5-7.7 times higher compared to an extraorally cured restoration. In the masticatory simulation, shear contact stresses in the adhesive bond around the direct composite restoration reached the highest values 32.8 MPa and significantly exceeded the shear strength of the connection between the resin luting cement and the tooth structure.
Equivalent stresses in the tooth structures restored with inlays and in the restoration material itself and contact stresses at the tooth-luting cement adhesive interface are many times lower compared to teeth with direct composite restorations. Teeth with indirect restorations are potentially less susceptible to damage compared to those with direct restorations. Composite inlays also ensure a better seal compared to direct restorations. Polymerization shrinkage determines stress levels in teeth with direct restorations, while its impact on adhesion in indirectly restored teeth is insignificant.
复合树脂的聚合收缩是牙修复体周围渗漏的主要原因之一。尽管有大量研究，但对于哪种牙齿修复方式——直接或间接复合树脂修复是最有益且最持久的，尚无定论。
旨在比较在模拟咀嚼过程中，用嵌体和直接修复体修复的II类MOD洞型磨牙中的等效应力和接触粘结应力（考虑复合树脂的聚合收缩）。
采用有限元法并应用接触单元进行研究。创建了三个第一磨牙的三维模型：模型A为完整牙齿；模型B为有复合树脂嵌体的牙齿；模型C为有直接复合树脂修复体的牙齿。模拟了直接复合树脂修复体和树脂粘结水门汀0.7%的聚合线性收缩（载荷1）。进行了咀嚼的计算机模拟（载荷2）。在这两种情况下，计算并比较了不同修复体的下颌第一磨牙模型材料中根据修正的冯·米塞斯准则（mvM）得出的等效应力。还评估并分析了修复体周围粘结水门汀与牙齿组织粘结界面的接触应力。
有直接复合树脂修复体的牙齿（其整个体积受聚合收缩影响）中的等效应力比有复合树脂嵌体修复的牙齿（收缩仅存在于粘结水门汀的薄层中）高很多倍。在牙本质和牙釉质中，直接修复体中的应力值比嵌体中的高8 - 14倍，且高13倍。同样，直接修复体周围粘结界面的接触应力比口外固化修复体高6.5 - 7.7倍。在咀嚼模拟中，直接复合树脂修复体周围粘结界面的剪切接触应力达到最高值32.8 MPa，显著超过树脂粘结水门汀与牙齿结构之间连接的剪切强度。
与有直接复合树脂修复体的牙齿相比，用嵌体修复的牙齿结构以及修复材料本身中的等效应力和牙齿 - 粘结水门汀粘结界面的接触应力要低很多倍。与直接修复体相比，间接修复体的牙齿潜在受损可能性更小。与直接修复体相比，复合树脂嵌体也能确保更好的密封性。聚合收缩决定了直接修复体牙齿中的应力水平，而其对间接修复体牙齿粘结的影响微不足道。
