Thiourethanes as low-stress modifiers in dental composites

描述(申请人提供)：患者和牙医对美观牙科修复体的需求不断增长，刺激了树脂复合材料的改进，如今，这种材料适用于每年提供的绝大多数直接的椅子边治疗。然而，由有机基质聚合产生的固有应力仍然对牙齿和修复体之间的粘结界面构成挑战，这降低了此类处理的寿命和可靠性。这项研究提出了一种相对简单的方法，在不改变操作技术的情况下，解决聚合应力，同时提高转化率和韧性。硫代低聚物添加剂将被设计成加入到树脂基质中，目的是延迟胶凝的开始，这将为粘性流动提供更多的机会，最终导致更高的转化率和显著减少应力发展。该添加剂还将提供更均匀的网络、更高的韧性和更大的折射率，以便更好地与无机组分匹配，从而改善固化深度。提出了两个目标：1)合成硫代乙烷齐聚物，将硫醇固定在其骨架上。硫醇和异氰酸酯的起始材料将被明智地选择，以产生广泛的主干灵活性。以硫代烯基和氨基甲酸酯类低聚物为对照，探讨硫代氨基甲酸酯的增韧机理。甲基丙烯酸酯网络结构和应力发展将作为硫代乙烷柔性、添加剂浓度和二次单体基质(包括牙科修复材料中常用的单体)的函数进行检查。弯曲力学性能、转化率和反应动力学将被用作筛选工具，以确定在延迟凝胶化和提高转化率/机械性能(特别是韧性)之间提供最佳折衷的低聚物。在选定的情况下，聚合应力将与转化率一起评估，从而提供大多数应力(玻璃化开始)开始发展的聚合程度的直接证明。2)由于有机部分仅占复合材料总体积的30%-40%，因此根据目标1确定的最佳材料也将作为填充成分进行测试，以确保对非填充树脂获得的改进适用于复合材料。这一目标还将包括合成一种新的含有硫氧乙烷键和系留硫醇的硅烷偶联剂。这将利用填料的大表面积作为增韧和链转移位置来放大应力降低和力学性能的提高。由于其固有的较高折射率，硫代乙烷低聚物将提高最终复合材料的光学清晰度，增加材料的透光率，并导致固化深度增加。该项目的预期结果是大幅降低聚合收缩应力，同时提高转化率和机械性能，最终克服目前直接聚合修复剂的主要缺点。

DESCRIPTION (provided by applicant): The ever increasing demand for esthetic dental restorations, both by patients and dentists, has stimulated the improvement of resin composites and, nowadays, this material responds for the vast majority of direct, chair- side treatments delivered each year. However, the stress that inherently develops from the polymerization of the organic matrix still poses a challenge to the bonded interface between the tooth and the restoration, which reduces the life-time and reliability of such treatments. This study proposes a relatively simple approach that will tackle polymerization stress while increasing conversion and toughness with no changes in the operatory technique. Thiourethane oligomeric additives will be designed to be incorporated into the resin matrix with the objective of delaying the onset of gelation, which will provide extended opportunity for viscous flow, ultimately leading to increased conversion and significantly reduced stress development. The additive will also provide more homogeneous networks, increased toughness and greater refractive index for better match with the inorganic fraction, in turn improving depth of cure. Two aims are proposed: 1) Thiourethane oligomeric species will be synthesized, comprising tethered thiols into their backbones. Thiol and isocyanate starting materials will be judiciously chosen to produce a wide array of backbone flexibilities. Analog oligomers based on thiolenes and urethanes will be used as controls, as well as to probe the mechanism of toughening by thiourethanes. Methacrylate network structure and stress development will be examined as a function of thiourethane flexibility, additive concentration and secondary monomer matrix (including monomers commonly used in dental restorative materials). Mechanical properties in flexure, degree of conversion and reaction kinetics will be used as screening tools to identify the oligomer providing the best compromise between delayed gelation and increased conversion/mechanical properties (especially toughness). In selected cases, polymerization stress will be evaluated concomitantly with conversion, providing a direct demonstration of the extent of polymerization at which the majority of stress (onset of vitrification) starts to develop. 2) Since the organic portion corresponds to only 30-40 % of the total composite volume, the best materials identified under aim 1 will also be tested as filled compositions to ensure that the improvements obtained for unfilled resins hold for composites. This aim will also include the synthesis of a new silane coupling agent containing thiourethane bonds and tethered thiols. This will take advantage of the large surface area of the fillers as toughening and chain-transfer sites to amplify the stress reduction and the gain in mechanical properties. Due to their inherently higher refractive index, thiourethane oligomers will improve the optical clarity of the final composite, increase light transmission through the material and lead to augmented depth of cure. The expected outcome of this project is to substantially reduce polymerization shrinkage stress, while increasing conversion and mechanical properties, ultimately overcoming the major drawbacks of current direct polymeric restoratives.