Dynamic monitoring of refractive index change through light-activated dental fillings

大多数牙科患者更喜欢与他们天然牙齿的美观相匹配的填充材料。然而，大型“白色”填充物（树脂基复合材料；红细胞）的耐用性通常被认为不如非美观的“银色”填充物（牙科汞合金）。除了红细胞固有的材料缺陷外，这可能与技术敏感应用步骤的数量增加有关。现代RBC填充材料以糊状形式提供。它们由牙医直接在牙腔中塑形，随后在高强度蓝光下“按指令”设置为刚性材料。然而，RBC填充材料的治愈深度有限（约2mm），因此牙医必须使用多层（增量）来填充大的腔体，而不像使用牙科汞合金那样可以大量填充腔体，从而降低了技术敏感性、手术时间和成本。因此，开发具有更高治愈深度的红细胞是非常可取的，这可能会改善这些材料的缺点，并最终提高其临床成功率，从而使患者群体受益。关于RBC填充材料在强光下硬化时光学特性的变化，仍有许多未解之谜，这可能会对固化反应提供更深入的了解，最终提高固化深度。通过改变RBC的成分，其中包括充满增强陶瓷颗粒的树脂基体，可以改变固化光通过材料传输的程度。这一独特的提议首次提供了利用光学相干断层扫描（OCT）测量RBC材料在整个硬化反应过程中光学性质变化的能力。随着RBC变硬，树脂成分变得更加致密和收缩。因此树脂成分的折射率增加（一种改变光通过材料的速度的特性）。当树脂的折射率接近增强填料颗粒的折射率（在整个硬化过程中保持不变）时，光散射的量将减少。本提案中OCT设备的设计将测量材料硬化时折射率的变化，并建立折射率变化与体积收缩之间的关系。光散射的总量还取决于填充颗粒的大小和形状以及树脂中负责硬化材料的化学成分的吸收。因此，通过对已知成分（模型配方）的红细胞进行测试，更好地了解折射率变化对硬化的影响，将为提高固化深度和潜在的白填充材料的临床耐久性提供一个平台。本提案旨在验证一种新型OCT技术的使用，以确定红细胞硬化时光学性质的变化。随后，可以建立材料组分（树脂类型和填料粒度和形状）对RBC试样体积三维折射率变化的影响。这将有助于更好地了解环境特征，最终有可能推动光活化红细胞的发展。

The majority of dental patients prefer filling materials that match the aesthetics of their natural teeth. However, the durability of large 'white'-fillings (resin-based composites; RBCs) is generally considered to be inferior to the non-aesthetic 'silver'-filling types (dental amalgams). This may relate to the increased number of technique-sensitive application steps in addition to any inherent material shortcomings of RBCs.Modern RBC filling materials are supplied in a paste form. They are moulded directly by the dentist in the tooth cavity and subsequently set to a rigid material 'on command' with a high-intensity blue light. However, the RBC filling material has a limited depth of cure (approximately 2mm) and therefore the dentist must use multiple (incremental) layers to fill large cavities, unlike the use of dental amalgam whereby the cavity can be filled in bulk, reducing technique sensitivity, procedure time and cost. Consequently, the development of RBCs with improved depth of cure is highly desirable which may improve the shortcomings of such materials and ultimately improve its clinical success in order to benefit the patient community.There remain many unanswered questions relating to the change in optical properties of RBC filling materials as they harden under high-intensity light, which may provide a greater insight into the setting reaction to ultimately improve the depth of cure. By altering the components of the RBC, which include a resin matrix filled with reinforcing ceramic particles, it is possible to change the extent with which the curing light is transmitted through the material. This unique proposal offers, for the first time, the capacity to measure the change in optical properties throughout the hardening reaction of RBC materials, using optical coherence tomography (OCT). As the RBC hardens, the resin component becomes more dense and shrinks. Consequently the refractive index of the resin component increases (a property which changes the speed of light through the material). As the refractive index of the resin approaches that of the reinforcing filler particles (which remain constant throughout hardening) the amount of light scattering will decrease. The design of the OCT equipment in this proposal will measure the change in refractive index as the material hardens and will establish the relationship between refractive index change and volumetric shrinkage. The total amount of light scatter is also dependent on the size and shape of the filler particles and the absorption of chemical components within the resin responsible for hardening the material. Therefore, by testing RBCs with known composition (model formulations) a greater comprehension of the effect of refractive index change on hardening will provide a platform with which to improve the depth of cure and potentially the clinical durability of white-filling materials.This proposal aims to validate the use of a novel OCT technique to determine the change in optical properties of RBCs as they harden. Subsequently, the effect of material components (resin type and filler particle size and shape) on the change in refractive index in three-dimensions through the bulk of the RBC specimen can be established. This will facilitate a greater understanding of the setting characteristics, which ultimately has the potential to drive forward the development of light-activated RBCs.