Nano-aggregates Improve Contraction Stress & Toughness in Dental Composite Resins

描述(申请人提供)：商用牙科复合树脂在聚合过程中存在2-5%的体积收缩的固有问题。这种聚合会在复合修复体中产生收缩应力，从而破坏复合修复体和牙齿结构之间的边缘密封。尽管有新的牙本质粘结剂的开发，但由于不可避免的聚合收缩应力，目前还没有一个系统能够承受牙齿/修复体界面处间隙的形成。此外，现有的复合树脂韧性较低，导致复合修复体的边缘断裂和块状断裂。 在这里，我们描述了一种降低收缩应力并提高复合树脂韧性的新方法，该方法只需对现有技术进行两次修改。在第一种方法中，一种柔顺的相材料，如聚丁二烯，以气相二氧化硅的集合体形式取代增强填料。这些均匀分散的顺应性集合体在聚合过程中产生的静水拉应力状态下屈服，并允许集合体的膨胀或顺应性，从而抵消固化收缩并降低粘合界面的应力。 第二种改性是在基质单体中引入少量增塑剂。增塑剂降低了固化过程中的玻璃化转变温度(Tg)，使得在交联链和扩链反应过程中，链的迁移率在更长的时间内保持较高的水平，从而在单体向聚合物转化的过程中，可以更顺应地抵消固化收缩和降低收缩应力。 我们发现，微米级柔顺聚集体的存在会导致弯曲弹性模量、弯曲强度和断裂能增加，而微米级聚集体与增塑剂结合会降低聚合收缩应力。此外，我们还表明，纳米聚集体对树脂基质具有非常大的柔顺表面积，从而导致聚合收缩应力的比例增加。 总体而言，顺应性聚集体有可能绕过当今美容树脂和后牙树脂的两个主要问题，即有问题的收缩应力和低韧性。作为对市售复合树脂的一种改进，顺应性聚集体有可能提供一种优异的复合修复系统。

DESCRIPTION (provided by applicant): Commercially available dental composite resins exhibit the inherent problem of 2-5% volumetric shrinkage during the polymerization process. This polymerization creates contraction stress in the composite restoration, which can disrupt the marginal seal between the composite and the tooth structure. Despite the development of new dentin bonding agents, no system is able to currently withstand the formation of gaps at the tooth/restoration interface, due to unavoidable polymerization contraction stress. In addition, available composite resins suffer from low toughness, which results in marginal and bulk fracture of composite restorations. We describe here a novel means of reducing contraction stress as well as improving toughness in composite resins that entails only two modifications of existing technology. In the first, a compliant phase material, such as polybutadiene, in aggregate form with fumed silica, replaces the reinforcing filler. These homogeneously dispersed, compliant aggregates yield under the hydrostatic tensile stress state generated during polymerization and allow expansion, or compliance, of the aggregates, thereby offsetting cure shrinkage and reducing stress at the bonded interfaces. The second modification is the introduction of a small amount of plasticizer into the matrix monomer. Plasticizers reduce the glass transition temperature (Tg) during curing such that chain mobility remains high for a longer time during the course of the crosslinking and chain extension reaction, and thereby allows greater compliant offset of cure shrinkage and reduction of contraction stress as monomer conversion to polymer progresses. We show that the presence of micrometer-sized compliant aggregates results in increased flexural modulus, flexural strength and energy to break, and that micrometer-sized aggregates in combination with plasticizer result in reduced polymerization contraction stress. In addition, we show that nanometer-sized aggregates, which present a very large compliant surface area to the resin matrix, result in a proportionately increased reduction in polymerization contraction stress. Overall, compliant aggregates have the potential to circumvent two of the major problems of today's esthetic and posterior resins, problematic contraction stress and low toughness. As a modification to commercially available composite resins, compliant aggregates have the potential to provide a superior composite restorative system.