Effect of bonding resin strength on contraction gap formation

对于聚合收缩间隙的形成，光固化后粘合树脂的机械性能似乎很重要。本研究的目的是在光固化5分钟后，在三种自蚀刻体系中评估键合树脂的纳米硬度(H)、弹性模量(E)和微拉伸强度（MTS）。用纳米压痕仪测量了粘接树脂辐照10秒后5分钟和24小时（作为对照）的H和E值。同时测定了材料在5分钟和24小时的mts。双向方差分析证实，与5分钟相比，24小时时所有三个力学性能均显著增加（p<0.05）。就材料而言，不同材料的力学性能值也不同。不同材料力学性能的差异可以用单体体系、引发剂体系、稳定剂、填料和偶联剂的不同来解释。同一种材料，在5分钟和24小时的力学性能之间的差异可能是由于一定程度的转换。在光固化修复剂之前，粘合树脂的抗拉强度可能需要足够大，以与聚合收缩应力相竞争。另一方面，考虑到粘接层作为应力破坏者的作用，粘接树脂的弹性模量不应太大。由于底漆、牙本质上的水等混合会影响粘接树脂的力学性能，因此进一步研究粘接体系的粘接性能与树脂-牙本质界面粘接层力学性能之间的关系是今后研究的重点。

Regarding with polymerizing contraction gap formation, mechanical properties of bonding resins immediately after light-curing seems to be important. The purpose of this study was to evaluate nano-hardness(H), elastic modulus(E) and microtensile strength(MTS) of bonding resins in three self-etching systems at 5minutes after light-curing the materials.The values of H and E at 5 minutes and 24 hours (as a control) after the 10 second irradiation for bonding resins were measured using a nano-indentation tester. MTSs of the materials at 5 minutes and 24 hours were also measured.Two-way ANOVA confirmed a significant increase in all the three mechanical properties at 24 hours compared with those at 5 minutes (p<0.05). As for the materials, the values of the mechanical properties were also varied among the materials.The variation of the mechanical properties observed in the different materials might be explained by differences in their monomer system, initiator system, stabilizer, filler and coupling agent. Within the same material, the difference between the mechanical properties at 5 minutes and at 24 hours might be due to a degree of conversion. It may be desirable that the tensile strengths of the bonding resins just before light-curing restoratives are large enough to compete with polymerizing contraction stresses. On the other hand, the elastic modulus of the bonding resins should not be so large considering the function of the adhesive layer as a stress breaker.As the mechanical properties of the bonding resins might be affected by mixture of primer, water on dentin and so on, further studies should focus on a relationship between bonding performance of the adhesive systems and the mechanical properties of adhesive layers at the resin-dentin interface.