An Electron Microscopic Study on the Process of Acid Demineralization of Cortical Bone

Demineralization has been shown to foster osteoinductive properties of cortical bone grafts, yet little is known about the process of demineralization and how to control it. The purpose of this study was to investigate the process of cortical bone demineralization by using scanning electron microscopy to evaluate how hydrochloric acid demineralizes cortical bone. Results showed that in the demineralization of diaphyseal cortical bone specimens using hydrochloric acid, a uniformly thick circumferential band of demineralized bone matrix surrounds an inner undecalcified bone core as the process of demineralization occurs. The interface between the demineralized and mineralized section of the bone specimens was extremely sharp. This interface between demineralized and undemineralized bone was noted to advance as a reaction front with increasing demineralization which resulted in continuous shrinkage of the inner cortical bone core. This study suggests that cortical bone demineralization can be best described using an advancing reaction front theory, and this explanation can be used for implementation of the concept of controlled demineralization. Received: 19 December 1996 / Accepted: 25 April 1997     

Sodium trimetaphosphate enhances the effect of 250 p.p.m. fluoride toothpaste against enamel demineralization in vitro

This in vitro study investigated the effect of sodium trimetaphosphate (TMP), added to toothpaste containing 250 p.p.m. fluoride, on enamel demineralization. Bovine enamel blocks (n = 96) were subjected to five pH cycles over a 7‐d period and treatment with suspensions of toothpastes containing 0, 250, 500, and 1,100 p.p.m. fluoride (as sodium fluoride), as well as with 250 p.p.m. fluoride containing TMP at 0.25, 0.5, 1.0, and 3.0%. Treatment with toothpaste suspensions was performed under agitation twice a day, for 1 min. Surface and cross‐sectional hardness, and fluoride firmly bound to enamel, were quantified. Data were subjected to one‐way anova , followed by Tukey's test. Low‐fluoride toothpastes containing TMP at 0.25–1.0% resulted in enamel mineral loss similar to that seen for the toothpaste containing 1,100 p.p.m. fluoride. Also, the addition of TMP to the toothpaste containing 250 p.p.m. fluoride promoted enamel fluoride concentrations similar to those obtained for the 500 p.p.m. fluoride group. The toothpaste containing 250 p.p.m. fluoride and 0.25% TMP led to the lowest mineral loss among all groups. It was concluded that the addition of as little as 0.25% TMP to a toothpaste containing 250 p.p.m. fluoride can reduce enamel demineralization to levels similar to those seen for a conventional toothpaste containing 1,100 p.p.m. fluoride, in vitro.     

Ionic liquid as antibacterial agent for an experimental orthodontic adhesive

ObjectiveThe aim of this study was to formulate and evaluate experimental orthodontic adhesives with different concentrations of 1-n-butyl-3-methylimidazoilium bis(trifluoromethanesulfonyl)imide (BMIM.NTf₂).MethodsThe experimental orthodontic adhesives were formulated with methacrylate monomers, photoinitiators and silica colloidal. The ionic liquid BMIM.NTf₂ was synthesized and characterized. BMIM.NTf₂ was added at 5 (G_5%), 10 (G_10%) and 15 (G_15%) wt.%. One group contained no BMIM.NTf₂ to function as control (G_Ctrl). The adhesives were evaluated for polymerization kinetics, degree of conversion (DC), Knoop hardness and softening in solvent, ultimate tensile strength (UTS), shear bond strength (SBS), thermogravimetric analysis (TGA), antibacterial activity and cytotoxicity.ResultsBMI.NTf₂ showed the characteristic chemical peaks. The polymerization kinetics were different among the groups. G_10% and G_15% showed higher DC (p < 0.05). G_5% and G_Ctrl had no differences for softening in solvent (p > 0.05). There were no differences for UTS (p > 0.05) and SBS (p > 0.05). TGA showed one different peak for G_15%. All groups with BMIM.NTf₂ showed antibacterial activity compared to G_Ctrl (p < 0.05) without cytotoxicity (p > 0.05).SignificanceTo reduce biofilm formation around brackets and to prevent demineralization at susceptible sites, materials have been developed with antibacterial properties. In this study, a new experimental orthodontic adhesive was formulated with an imidazolium ionic liquid (BMIM.NTf₂) as antibacterial agent. The incorporation of 5 wt.% of ionic liquid decreased biofilm formation without affecting the physico-chemical properties and cytotoxicity of an experimental orthodontic resin.     

Inhibition of enamel demineralization and bond‐strength properties of bioactive glass containing 4‐META/MMA‐TBB‐based resin adhesive

We investigated the enamel demineralization‐prevention ability and shear bond strength (SBS) properties of 4‐methacryloxyethyl trimellitic anhydride/methyl methacrylate‐tri‐n‐butyl borane (4‐META/MMA‐TBB)‐based resin containing various amounts (0–50%) of bioactive glass (BG). Disk‐shaped specimens were immersed in distilled water and ions released were analysed by inductively coupled plasma atomic‐emission spectroscopy. Samples were also immersed in lactic acid solution (pH 4.6) to estimate acid‐neutralizing ability. Brackets were bonded to human premolars with BG‐containing resins and the bonded teeth were alternately immersed in demineralizing (pH 4.55) and remineralizing (pH 6.8) solutions for 14 d. The enamel hardness was determined by nanoindentation testing at twenty equidistant distances from the external surface. The SBS for each sample was examined. The amounts of ions released [calcium (Ca), sodium (Na), silicon (Si), and boron (B)] and the acid‐neutralizing ability increased with increasing BG content. After alternating immersion, the specimens bonded with the BG‐containing resin with high BG content were harder than those in the other groups in some locations 1–18.5 μm from the enamel surface. Bioactive glass‐containing (10–40%) resin had bond strength equivalent to the control specimen. Thus, the SBS obtained for BG‐containing resin (6.5–9.2 MPa) was clinically acceptable, suggesting that this material has the ability to prevent enamel demineralization.     

表没食子儿茶素没食子酸酯预防正畸固定矫治者的牙釉质白斑

文题释义： 龋白斑：很多接受正畸固定矫治的患者其牙面上会呈现白垩色的点或斑块，临床上表现为龋白斑(white spot lesions，WSL)，即釉质脱矿，如病变进一步发展甚至会形成龋洞。 表没食子儿茶素没食子酸酯(Epigallocatechin gallate，EGCG)：是茶多酚中最有效的活性成分，属于儿茶素。EGCG具有抗菌、抗病毒、抗氧化、抗动脉硬化、抗血栓形成、抗血管增生、抗炎以及抗肿瘤作用。绿茶里有EGCG，但红茶里没有，因为红茶里的EGCG被转化成了茶玉红精。EGCG在医药保健上具有防治癌症等多种疾病和增强免疫力等功能。 背景：目前已有大量研究证实表没食子儿茶素没食子酸酯(Epigallocatechin gallate，EGCG)可应用于牙科治疗中，但目前尚未有临床研究讨论EGCG用于托槽的釉质粘接是否可以减少临床上正畸术后白斑的发生率。目的：探讨EGCG应用于预防正畸固定矫治患者牙釉质白斑发生的价值。方法：选择接受正畸固定矫治治疗的50例符合纳入排除标准的患者，采用自身对照法，右侧使用添加有1 g/L EGCG的粘接剂(EGCG组)，左侧使用不含EGCG的粘接剂(对照组)，其余治疗步骤和材料均相同。于治疗开始后3，6和12个月检测目标牙位(16，11，46，26，31，36)牙釉质脱矿指数(EDI)和釉质白斑的发生率，并统计托槽脱落情况。研究方案的实施符合柳州市人民医院对研究的相关伦理要求，患者及监护人对试验过程完全知情同意。结果与结论：①EGCG组和对照组在试验期间托槽脱落率差异无显著性意义(P > 0.05)；②在治疗开始后3个月，2组白斑发生率和牙釉质脱矿指数值差异无显著性意义(P > 0.05)，治疗6，12个月，EGCG组白斑发生率和牙釉质脱矿指数值均较对照组显著降低(P < 0.05)；③结果说明，添加有1 g/L EGCG的粘接剂可以在不影响托槽粘接强度的情况下，起到预防正畸固定矫治患者牙釉质脱矿和白斑发生作用，且能长期维持。 ORCID: 0000-0002-5325-5037(杨柳青) 中国组织工程研究杂志出版内容重点：组织构建；骨细胞；软骨细胞；细胞培养；成纤维细胞；血管内皮细胞；骨质疏松；组织工程     

Inhibition of enamel demineralization by buffering effect of S‐PRG filler‐containing dental sealant

The buffering capacity and inhibitory effects on enamel demineralization of two commercially available dental sealants were evaluated in this study. The effects of filler particles were also examined. Disks of enamel and cured sealant materials of BeautiSealant (silica or S‐PRG filler) or Teethmate F‐1 were incubated in lactic acid solutions (pH 4.0) for 1–6 d. The pH changes and amounts of ions released in the solutions were assessed, and enamel surfaces were observed using a scanning electron microscope. The pH of the solution with BeautiSealant (S‐PRG filler) was neutralized from pH 4.0 to pH 6.1 (after incubation for 1 d) and from pH 4.0 to pH 6.7 (after incubation for 6 d). In addition, no release of calcium ions was detected and the enamel surface was morphologically intact in scanning electron microscopy images. However, the pH of the solution with Teethmate F‐1 remained below pH 4.0 during incubation from days 1 to 6. Calcium release was increased in solutions up to and after 6 d of incubation. Scanning electron microscopy images showed that the structures of hydroxyapatite rods were exposed at the specimen surfaces as a result of demineralization. Ions released from S‐PRG filler‐containing dental sealant rapidly buffered the lactic acid solution and inhibited enamel demineralization.     

酪蛋白磷酸多肽-无定形磷酸钙对固定正畸所致牙釉质脱矿的影响

研究酪蛋白磷酸多肽-无定形磷酸钙（商品名GC护牙素）对固定正畸所致牙釉质脱矿的影响。选择固定正畸治疗患者40例,经签字同意进入实验。以随机数字表法随机分为对照组、实验组各20例。对照组在口腔卫生宣教的基础上采用单纯口腔卫生措施,实验组在对照组的基础上使用GC护牙素。2组患者从治疗开始,进行连续13个月的牙〖XCz1.tif,JZ〗照片观察。观测指标为牙面是否有新出现的的白垩色斑片或龋洞,统计并计算牙釉质脱矿率及脱矿指数（EDI）。（1）对照组、实验组的牙釉质脱矿率均随着时间的增加而增高;（2）对照组EDI高于实验组。在口腔卫生措施的基础上使用GC护牙素预防固定正畸所致牙釉质脱矿是一种安全有效的措施。     

Kinetics of amorphous silica dissolution and the paradox of the silica polymorphs

The mechanisms by which amorphous silica dissolves have proven elusive because noncrystalline materials lack the structural order that allows them to be studied by the classical terrace, ledge, kink-based models applied to crystals. This would seem to imply amorphous phases have surfaces that are disordered at an atomic scale so that the transfer of SiO(4) tetrahedra to solution always leaves the surface free energy of the solid unchanged. As a consequence, dissolution rates of amorphous phases should simply scale linearly with increasing driving force (undersaturation) through the higher probability of detaching silica tetrahedra. By examining rate measurements for two amorphous SiO(2) glasses we find, instead, a paradox. In electrolyte solutions, these silicas show the same exponential dependence on driving force as their crystalline counterpart, quartz. We analyze this enigma by considering that amorphous silicas present two predominant types of surface-coordinated silica tetrahedra to solution. Electrolytes overcome the energy barrier to nucleated detachment of higher coordinated species to create a periphery of reactive, lesser coordinated groups that increase surface energy. The result is a plausible mechanism-based model that is formally identical with the classical polynuclear theory developed for crystal growth. The model also accounts for reported demineralization rates of natural biogenic and synthetic colloidal silicas. In principle, these insights should be applicable to materials with a wide variety of compositions and structural order when the reacting units are defined by the energies of their constituent species.     

四种正畸粘接剂对金属托槽粘接效果的评价

目的比较4种正畸粘接剂对金属托槽的粘接效果。方法选择正畸临床44例患者,792颗牙,随机分为4组,常规牙面处理,分别按照说明书要求用京津釉质粘接剂、GC树脂改良型玻璃离子粘接剂、3M化学固化型树脂粘接剂和3M光固化树脂粘接剂粘接金属托槽,然后使用MBT矫治技术进行综合性正畸治疗,记录托槽脱落情况。12个月后,评估每组牙的牙釉质脱矿情况,并对所有数据进行统计学分析。结果 3M光固化型树脂粘接剂组托槽的脱落率低于京津釉质粘接剂组,差异有显著性(P<0.05),而其余各组间托槽脱落率的比较差异均无统计学意义(P>0.05)。京津釉质粘接剂组造成釉质脱矿程度在4组中最高,而GC树脂改良型玻璃离子粘接剂的釉质脱矿程度最低,其差异均有统计学意义(P<0.05)。结论京津釉质粘接剂相对远期粘接效果较差;GC树脂改良型玻璃离子粘接剂能够通过释放氟离子有效降低釉质脱矿的发生,是正畸治疗中较为理想的粘接材料,具有良好的临床应用前景。