Dental materials with antibiofilm properties

Objectives

Oral bacteria have evolved to form biofilms on hard tooth surfaces and dental materials. The antibiofilm effect of materials used for the restoration of oral function affects oral health. In this review we describe the features involved in the formation of oral biofilms on different surfaces in the oral cavity and the antibiofilm properties of dental materials.

Methods

An electronic search of scientific papers from 1987 to 2013 was performed with PubMed, ScienceDirect and Google search engines using the following search terms: antibiofilm, dental material, dental hard tissue, endodontic material, implant material, oral biofilm, and restorative material.

Results

Selected inclusion criteria resulted in 179 citations from the scientific, peer-reviewed literature. Oral biofilms form not only on dental hard tissue, but also on a wide range of dental materials used in cariology, endodontics, restorative dentistry and periodontology, resulting in destruction of dental hard tissue and even infection. Therefore, there has been a continuous effort to develop the antibiofilm properties of dental materials used for different purposes. Specific antimicrobial design in the composition and application of new materials (e.g. bioceramic sealer, resin composite, implant coating) demonstrates an improvement of the antibiofilm properties of these materials compared to earlier generations.

Significance

A significant number of dental materials have been shown to affect biofilm growth by inhibiting the adhesion of bacteria, limiting their growth or killing microbes in the biofilms formed in vitro. Incorporation of an appropriate amount of antibacterial agent could provide dental materials with antibiofilm activity without significantly influencing their mechanical properties. However, more randomized and double-blind clinical studies of sufficient length with these materials are needed to confirm long term success following their use in the dental clinic.     

Confirmation of theoretical colour predictions for layering dental composite materials

Objective

The aim of this study is to confirm the theoretical colour predictions for single and double layers of dental composite materials on an opaque backing.

Methods

Single and double layers of composite resins were fabricated, placed in optical contact with a grey backing and measured for spectral radiance. The spectral reflectance and colour were directly determined. Absorption and scattering coefficients as previously reported, the measured thickness of the single layers and the effective reflectance of the grey backing were utilized to theoretically predict the reflectance of the single layer using corrected Kubelka–Munk reflectance theory. For double layers the predicted effective reflectance of the single layer was used as the reflectance of the backing of the second layer and the thickness of the second layer was used to predict the reflectance of the double layer. Colour differences, using both the CIELAB and CIEDE2000 formulae, measured the discrepancy between each directly determined colour and its corresponding theoretical colour.

Results

The colour difference discrepancies generally ranged around the perceptibility threshold but were consistently below the respective acceptability threshold.

Conclusion

This theory can predict the colour of layers of composite resin within acceptability limits and generally also within perceptibility limits.

Clinical significance

This theory could therefore be incorporated into computer-based optical measuring instruments that can automate the shade selections for layers of a more opaque first layer under a more translucent second layer for those clinical situations where an underlying background colour and a desirable final colour can be measured.     

In vitro resistance of titanium and resorbable (poly l-co-dl lactic acid) osteosynthesis in mandibular body fracture

This study was a comparative evaluation of the bending resistance of metallic and resorbable plates and screws in a mandibular body fracture model. Forty polyurethane synthetic hemimandibles were used; a vertical linear cut was made between the second and first premolars. These 40 hemimandibles were divided into four groups of 10 and were fixed with titanium plates and screws or resorbable plates and screws, with monocortical screws in the upper sector and bicortical screws in the lower sector. Bending resistance tests were done on a universal testing machine with a linear displacement speed of 1 mm/min, a cell load of 500 N, and a load cell on the lower central incisor or on the lower second premolar. Results were analyzed using the Student's t-test, with the significance level set at 5%. No statistically significant differences were observed between the groups studied, either in the analysis of the osteosynthesis materials or related to the load-bearing points. The variables of displacement and peak load did not present any significant differences. In this in vitro model of a mandibular body fracture, the mechanical behaviour of a resorbable osteosynthesis was similar to that of a titanium osteosynthesis.     

两种不同藻酸盐印模消毒效果对比研究

目的：比较两种不同藻酸盐印模消毒的效果。方法：使用不同的调拌方法制取3组藻酸盐印模样本各30个,共计90个（前两组用蒸馏水调拌,第3组用0．1％的洗必泰溶液调拌）。印模凝固后将3种不同菌液均匀涂布于印模表面。第1组为空白对照组,不做处理：第2组使用照射强度为100μW的紫外线照射5min;第3组用洗必泰溶液调拌,在空气中放置30min。3组印模洗脱表面残留的细菌进行培养,根据培养的细菌数量进行消毒效果的判定,并进行统计学分析（方差分析）。结果：与空白对照组相比,紫外线照射消毒与洗必泰消毒后印模表面细菌数量明显减少;用紫外线照射后的印模表面的细菌数少于用洗必泰调和消毒的印模,两者存在显著性差异。结论：紫外线照射的消毒效果优于洗必泰。     

“劲润”牙本质保护膜的牙本质粘结性能探讨

目的：探讨“劲润”牙本质保护膜（Hybrid Coat,HyC）的牙本质粘结性能。方法：选取A组（HyC）和其他3组不同类型的牙本质粘结剂：B组（G-Bond）、C组（MegaBond）和D组（single Bond）,比较其对牛牙牙本质的剪切粘结强度,并用实体显微镜观察粘结界面断裂模式。各组试料数分别为n=10,结果通过Tukey-Kramer（P〈0．05）进行统计学分析。结果：B、C、D组均显示了较大的粘结强度,3组之间无统计学差异。A组（HyC）显示了较低的粘结强度,约10．08MPa,与其他3组之间存在显著性差异。断裂模式显示,A组（HyC）以界面破坏为主,而其他3组以凝集破坏和混合破坏为主。结论：本研究结果提示,“劲润”牙本质保护膜（HyC）的粘结强度弱于其他3组牙本质粘结剂。为了保证HyC长期稳定的防过敏效果及粘结性能,在今后的研究中有必要进一步探讨如何提高HyC的牙本质粘结性能。     

软体机器人在医学领域的应用

软体机器人具有自由度高、适应性强、安全性高等优点,已成为机器人领域的研究热点;且因其采用软材料制成,与人体相容性较好,在医学领域中也具有广泛应用前景。本研究对软体机器人的驱动方式、建模控制、制造方法、变刚度方法等关键技术作了总结与分析;对软体机器人在医学领域如外科手术、康复治疗、药物输送、心脏设备等的典型应用及发展现状进行综述。针对现有医疗软体机器人存在的缺陷,总结出其面临的挑战,并提出对医疗软体机器人的展望。     

基于可降解磁性生物支架的离体三维心肌补片构建及其生物学特性分析

目的：合成可降解磁性氧化铁-壳聚糖-芦荟胶多孔支架，构建新型离体三维心肌补片，并探索其生物学特性。 方法：配置不同质量分数的磁性氧化铁纳米颗粒-壳聚糖-芦荟胶的混合溶液，通过低温梯度冷冻干燥技术制备出三维多孔支架，并通过扫描电子显微镜，动态热机械分析，孔隙率测试和体外降解实验等对其物理、生物特性进行表征。将幼稚心肌细胞消化后接种至支架混合培养一周。用荧光定量PCR技术检测离体心肌补片中，心肌细胞特异性基因及细胞凋亡基因的mRNA水平表达量。 结果：0.1% 磁性氧化铁纳米颗粒-1%壳聚糖-0.2%芦荟胶多孔支架的表面孔洞均一，孔隙率=0.93±0.017；机械拉伸强度=0.33±0.06mPa，弹性极限应变约0.12±0.01，且随支架中芦荟胶含量增加而减小（p<0.001）；体外生理条件下，7天降解率82.9±2.4%，且降解过程可被核磁共振监测。支架可促进大鼠心肌细胞（H9C2）生长增殖，无细胞毒性。复合培养形成的离体心肌补片，可在外加电场下收缩-舒张，且补片中的心肌细胞成熟相关基因表达升高（p<0.05）, 凋亡抑制（p<0.01）。 结论：可降解磁性氧化铁-壳聚糖-芦荟胶多孔支架的适合心肌组织工程应用；其构建的离体三维心肌补片可促心肌细胞成熟，具有植入心脏治疗心梗后心肌损伤的潜能。     

心肌组织工程细胞外基质的研究进展

心肌组织工程技术的问世良好地解决了心肌梗死后组织细胞移植过程中出现的一系列问题,同时也建立为选择更好材料及更好移植手段的技术平台。但无论是动物实验研究还是最近的临床试验都表明,目前细胞移植手段仍存在不少缺陷,主要在于优良种子细胞的缺乏以及移植后细胞的低生存率和低分化率。在这种背景下,作为心肌组织工程支架材料的细胞外基质(extracellular matrix,ECM)越来越受到人们的关注和重视,成为近些年来医学研究的前沿和热点。而ECM也不再仅仅被理解为一种支架材料或是一种组织,而是能为细胞提供必要信号、影响细胞内增殖、分化和代谢重要途径的关键角色。ECM相关模型大致可分为以下几类:天然生物支架材料、人工合成高分子支架材料以及物理和生物学特性更加平衡的复合支架材料。我们对近几年心肌组织工程领域ECM方面的研究进展及ECM的材料进行综述。     

口腔材料固化过程检测仪器的设计开发与实现

口腔材料在固化过程中温度会发生变化,通过检测材料的温度变化可以实时跟踪固化过程。本文依据相关口腔材料检测标准,构建了一个新型的自动化检测系统,检测口腔材料工作时间、固化时间。经过初步的试验结果表明,该检测系统能有效采集口腔材料固化过程中温度信号,跟踪温度变化,连续检测固化过程,绘制温度曲线,并能够依据标准要求自动处理曲线,从而得到口腔材料固化过程中高精度的工作时间、固化时间。