Effect of bonding resin strength on contraction gap formation

关于聚合收缩间隙的形成，在光固化后立即粘合树脂的机械性能似乎是重要的。本研究的目的是评价三种自酸蚀体系中粘接树脂在光固化后5 min的纳米硬度（H）、弹性模量（E）和微拉伸强度（MTS），并利用纳米压痕仪测量粘接树脂在光固化后5 min和24 h（作为对照）的H和E值。还测量了材料在5分钟和24小时的MTSs 13 Two-way ANOVA证实了与5分钟相比，24小时的所有三个机械性能均显著增加（p<0.05）。不同材料的力学性能也存在差异，不同材料的力学性能差异可能与其单体体系、引发剂体系、稳定剂、填料和偶联剂的不同有关。在相同的材料中，5分钟和24小时的机械性能之间的差异可能是由于转化程度。可能希望粘合树脂在光固化固化剂之前的拉伸强度足够大以与聚合收缩应力竞争。另一方面，考虑到粘结层的应力破坏作用，粘结树脂的弹性模量不宜过大，粘结树脂的力学性能可能受到底漆混合物、牙本质上的水等因素的影响，因此，进一步的研究应着重于粘结系统的粘结性能与树脂-牙本质界面粘结层力学性能之间的关系。

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.