Interactions Between Oral Biofilms and Dental Resin Composites

描述(申请人提供)：该项目的长期目标是通过对继发性龋齿的发展有一个基本的了解来提高牙科树脂复合修复体的使用寿命。我们更直接的目标是检验这一假设，即口腔生物膜有助于边缘的退化，导致更频繁的继发性龋齿。这可能是因为复合材料选择了边缘更容易龋齿的菌群，或者是因为细菌新陈代谢的产物导致了复合材料本身的分解。这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得到解决，具体目标如下：比较完好银汞合金修复体、完好复合体修复体、早期继发性龋病复合体和单纯继发性龋病复合体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种生物膜的概况。我们将检验这样一种假设，即与银汞合金-牙釉质界面相比，复合牙釉质界面会被不同的细菌种类定植。这种生态选择可以解释牙齿-复合体界面生物膜毒力增加的原因。近红外光学计算机断层成像(OCT)将作为临床龋病诊断的重要辅助手段，它可以比传统方法更早地发现龋病，并确认良好的界面。2.)通过优化生物膜反应器系统，在放置在拔除的牙齿中并涂有唾液的修复体的复合-釉质界面上生长多物种口腔生物膜微宇宙，架起了我们的临床和实验室研究的桥梁。这一系统将为检验细菌代谢产物导致复合分解的假说提供基础。临床研究的菌斑样本将被用来建立与没有龋齿、早期龋齿或普通龋齿的复合牙釉质界面相对应的微观世界。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复制主要生物膜物种图谱所需的条件。3.)使用明尼苏达州的人工嘴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修复体将经历反复的唾液涂层、反应器中的生物膜生长和人工口腔中的加载。使用产生不同程度收缩应力的复合材料修复的牙齿将暴露在不同类型的微观世界中，也将单独暴露在无菌唾液介质中，无论是否加载。OCT和Micro-CT成像将被用来监测牙齿组织中矿物质的损失，而显微硬度测试和傅立叶变换红外光谱将被用来评估复合材料的变化。这个体外模型系统将被用来检验这样的假设，即定义的细菌微观世界和机械载荷对复合修复体的材料性能、牙齿修复边缘的退化和修复失败的时间产生单独和联合的影响。 与公共健康相关：在美国，更换失败的牙科修复占牙医工作的70%，并为医疗保健成本贡献了50亿美元。在不同类型的修复体中，复合修复体的失败率高于银汞合金修复体，失败的主要原因是继发性或复发性龋齿。从这个项目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，这些材料可能需要减少收缩应力，提高粘结强度，以及抗菌和防腐能力。

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.