Interactions Between Oral Biofilms and Dental Resin Composites

描述（由申请人提供）：本项目的长期目标是通过对继发性龋齿的发展有基本的了解来延长牙科树脂复合材料的使用寿命。我们更直接的目标是检验口腔生物膜促进边缘降解，导致更频繁的继发性龋齿的假设。这可能是因为复合材料在边缘选择了更易致龋的植物群，或者是因为细菌代谢的产物有助于复合材料本身的分解。两种机制都不是相互排斥的，因此每个问题都将在补充的临床和实验室研究中解决，如具体目的：1.）比较银汞合金、复合材料、早期继发龋和单纯继发龋牙釉质界面生物膜的细菌种类组成。人类口腔微生物鉴定微阵列将用于提供包含272个物种的生物膜概况。我们将测试的假设，复合釉质界面的殖民地由独特的细菌物种，汞齐釉质界面相比。这样的生态选择可以解释在牙齿复合材料界面的生物膜的毒力增加。近红外光学计算机断层扫描（OCT）将被用作我们的临床龋齿诊断的重要辅助手段，通过检测龋齿早于传统方法，并确认声音接口。2.）通过优化生物膜反应器系统，使我们的临床研究和实验室研究相结合，该系统用于在放置在拔牙中并涂有唾液的牙釉质的复合物-釉质界面处生长多物种口腔生物膜微观世界。该系统将为检验细菌代谢产物有助于复合物分解的假设提供基础。来自临床研究的牙菌斑样本将用于建立对应于无龋、早期龋或明显龋的复合牙釉质界面的微观世界。HOMIM系统将用于监测微观世界的物种组成，并确定从患者样本中重现生物膜的主要物种概况所需的条件。3.）第三章使用明尼苏达人工口将负荷循环纳入生物膜反应器模型。放置在拔除的牙齿中的复合材料将经受唾液涂覆、反应器中的生物膜生长和人工口腔中的加载的重复循环。用产生不同水平收缩应力的复合材料修复的牙齿将暴露于不同类型的微观世界，并且还暴露于单独的无菌唾液介质，有或没有负载。OCT和micro-CT成像将用于监测牙齿组织中矿物质的损失，而显微硬度测试和傅里叶变换红外光谱法将用于评估复合材料的变化。该体外模型系统将用于测试以下假设：定义的细菌微观世界和机械载荷对复合材料牙列的材料性质、牙齿修复边缘的降解和修复失败的时间产生单独和组合的影响。 公共卫生相关性：更换失败的牙科修复需要牙医70%的努力，并为美国的医疗保健成本贡献了50亿美元。在不同类型的牙列充填中，复合牙列充填的失败率高于汞合金牙列充填，失败的主要原因是继发性或复发性龋。从这个和未来的项目中获得的知识将有助于指导下一代牙科复合材料的设计，这可能需要降低收缩应力，提高粘结强度，以及抗菌和防龋能力。

DESCRIPTION (provided by applicant): The long-term goal of this project is to increase the service life of dental resin composite restorations by obtaining a fundamental understanding of the development of secondary caries. Our more immediate goal is to test the hypothesis that oral biofilms contribute to the degradation of the margin, leading to more frequent instances of secondary caries. That might occur because composite materials select for a more cariogenic flora at the margin, or because products of bacterial metabolism contribute to the breakdown of the composite itself. Neither mechanism is mutually exclusive, so each question will be addressed in complementary clinical and laboratory studies, as described in the Specific Aims: 1.) Compare the bacterial species composition of biofilms collected from the enamel interface of sound amalgam restorations, sound composite restorations, composites with early secondary caries, and composites with frank secondary caries. Human Oral Microbe Identification Microarrays will be used to provide biofilm profiles incorporating 272 species. We will be testing the hypothesis that composite-enamel interfaces are colonized by distinctive bacterial species, compared to amalgam-enamel interfaces. Such ecological selection could account for an increase in virulence of the biofilm at the tooth-composite interface. Near-infrared optical computed tomography (OCT) will be used as an important adjunct to our clinical caries diagnosis, by detecting caries earlier than conventional methods, and confirming sound interfaces. 2.) Bridge our clinical and laboratory studies by optimizing a biofilm reactor system for growing multi-species oral biofilm microcosms at the composite-enamel interface of restorations placed in extracted teeth and coated with saliva. This system will provide the basis for testing the hypothesis that products of bacterial metabolism contribute to composite breakdown. Plaque samples from the clinical study will be used to establish microcosms corresponding to composite-enamel interfaces with no caries, early caries, or frank caries. The HOMIM system will be used to monitor the species composition of microcosms, and determine the conditions needed to reproduce the major species profiles of biofilms from patient samples. 3.) Use the Minnesota Artificial Mouth to incorporate load cycling into the biofilm reactor model. Composite restorations placed in extracted teeth will be subjected to repeated cycles of saliva coating, biofilm growth in the reactor, and loading in the artificial mouth. Teeth restored with composites that generate different levels of shrinkage stress will be exposed to the different types of microcosm, and also to sterile saliva medium alone, with or without loading. Both OCT and micro-CT imaging will be used to monitor the loss of minerals in the tooth tissues, while microhardness testing and Fourier-transform infrared spectrometry will be performed to assess changes in the composites. This in vitro model system will be used to test the hypothesis that defined bacterial microcosms and mechanical loading exert individual and combined effects on the material properties of composite restorations, degradation of the tooth-restoration margin and the time to restoration failure. PUBLIC HEALTH RELEVANCE: Replacing failed dental restorations takes up 70% of a dentist's effort and contributes $5 billion to health care costs in the US. Among the different types of restorations, composite restorations have been shown to have a higher failure rate than amalgam restorations, with the main cause of failure being secondary or recurrent caries. The knowledge gained from this and future projects will help guide the design of the next generation of dental composite materials, which are likely to require reduced shrinkage stress, improved bond strengths, as well as antibacterial and cariostatic capabilities.