The mechanism of topical applied ion supplemented acidulated phosphate fluoride gel effects on dental enamel demineralization: an in vitro study]

The present study was carried out on dental enamel to describe surface changes in the scanning electron microscope and crystallites changes in the high-resolution transmitted electron microscope as related to treatments of topical applied ion supplemented acidulated phosphate fluoride (APFI) gel and artificial caries agent demineralization in vitro, which imitated in vivo with pH- cycling condition. Our data suggest that topical application of APFI gel produce some CaF2 spheres on the surface of enamel and some fluoride-containing apatites in dental enamel. The latter are considered as result of F- and CaHPO4 or hydroxyapatites. The essence of chemical reactions are discussed. The results confirm that enamel treated with APFI gel becomes more resistant to artificial caries agent and electron radiation damage.     

人氟斑牙早期龋再矿化的初步研究

目的研究离体氟斑牙早期龋模型经再矿化处理后,釉质表面显微硬度及微观形貌的变化。方法应用离体氟斑牙制备釉质样本40个,经酸蚀凝胶人工龋实验脱矿后,1.0%酪蛋白磷酸肽-磷酸钙（CPP-CP）再矿化液再矿化。采用显微硬度计测定各样本脱矿前后及再矿化后的显微硬度值。采用体视显微镜、偏光显微镜、透射显微镜以及扫描电镜观察釉质表面微观形貌。结果脱矿前,釉质表面显微硬度值为（241.53±21.31）kHV;脱矿后,表面显微硬度下降到（175.76±24.99）kHV（P＜0.05）。其表面硬度损失百分比（%SMHD）为（27.23±4.79）％,表现为类似早期龋的表层下脱矿;再矿化后,表面显微硬度提高到（210.17±21.48）kHV（P＜0.05）,其表面显微硬度恢复的百分比（%SMHR）为（52.32±4.23）％,主要表现为表层下再矿化。结论再矿化处理对治疗氟斑牙早期龋有较好的临床效果。     

Study of the initial enamel injuries in vitro

The purpose of the study was production under laboratory conditions of enamel changes corresponding to early caries. The study was carried out on 20 healthy human teeth in vitro, in two phases differing in the conditions of the experiment. Carietic changes were produced with lactate buffer (in concentrations from 0.025 to 1.0 M) as fluid without added inhibitor of the solubility of the superficial layer. The assessment of the degree of enamel demineralization was based on images obtained in JSM 50A scanning microscope. In the first stage of the experiment a minimal demineralization of the subsuperficial layer of the enamel was obtained. In the second stage besides damage to the subsuperficial layer enamel erosion was noted. In this connection further studies are necessary for determining of the proper conditions for obtaining initial enamel damage.     

电化学人工釉质龋和早期光滑面釉质龋组织病理学比较

为进一步研究电化学人工龋模型和龋病的关系，我们采用生物显微镜和扫描电子显微镜等手段，对体外形成的电化学人工釉和早期光滑面釉质龄的组织病理学进行了对比观察。结果表明电化学人工釉质龋在生物显微镜下和早期光滑面釉质龋一样形成以表层下脱矿为主要特征的病理改变，电化学人工釉质龋在扫描电子显微镜下主要表现为釉柱的釉柱的核心脱矿溶解，这亦和早期光滑面釉质龋相似。因此本研究结果提示二者有着十分相似的病理特点和病变     

Enamel of primary teeth--morphological and chemical aspects

Enamel is one of the most important structures of the tooth, both from a functional and esthetic point of view. Primary enamel carries registered information regarding metabolic and physiological events that occurred during the period around birth and the first year of life. Detailed knowledge of normal development and the structure of enamel is important for the assessment of mineralization defects. The aim of the thesis is to add more detailed information regarding the structure of primary enamel. The structural appearance of the neonatal line and the quantitative developmental enamel defect, enamel hypoplasia, was thoroughly investigated with a polarized light microscope, microradiography and scanning electron microscope. X-ray microanalysis of some elements was also performed across the enamel and the neonatal line. Postnatal mineralization of enamel at different ages and from different individuals was studied regarding the chemical content, by using secondary ion mass spectrometry. The enamel's response to demineralization was investigated in relation to the individual chemical content and the degree of mineralization of the enamel, by using polarized light microscope, microradiography, scanning electron microscope and X-ray microanalysis. The neonatal line is a hypomineralized structure seen as a step-like rupture in the enamel matrix. The neonatal line is due to disturbances in the enamel secretion stage. The enamel prisms in the postnatal enamel appeared to be smaller than the prenatal prisms. The hypoplasias showed a rough surface at the base and no aprismatic surface layer was seen in the defect. The enamel of the rounded border of hypoplasia appeared to be hypomineralized, with the bent prisms not being densely packed. Mineralization of enamel is a gradual process, still continuous at 6 months postnatally in the primary mandibular incisors. The thickness of the buccal enamel is reached at 3-4 months of age. Demineralization of enamel depends on the degree of mineralization and the chemical content of the enamel exposed. In a more porous enamel, deeper lesions will develop. The posteruptive maturation has a beneficial effect on the enamel's resistance to demineralization.     

The effect of 2 bleaching agents on the enamel surface. An in-vitro study]

We present a study "in vitro" of the effect of bleaching agents on dental surfaces using the "Walking bleaching technique". We found that hydrogen peroxide bleached more quickly than carbamide although, after a period of six weeks, the results were the same as far as whitening was concerned. In the scanning electron microscope we observed significantly different changes in each case. Carbamide caused a regular and uniform opening of the enamel prisms of the surface while hydrogen peroxide produced more severe superficial destruction with the appearance of patterning similar to the acid etching, and the presence of some crystalline areas emerging from the body of the prisms.     

镧、钙、氟对釉质脱矿的影响——显微硬度测定

目的 :比较镧、钙、氟对人牙釉质酸蚀脱矿影响 ,为镧的应用研究提供实验依据。方法 :酸性凝胶化学致龋 ,测定釉质脱矿区剖面显微硬度 ,逐点单因素方差分析其显微硬度值。结果 :釉质表层下 2 5～ 15 0 μm范围内 ,镧处理组、氟处理组的硬度值高于对照组 ;2 5～ 75 μm范围内 ,镧处理组的硬度值高于钙处理组 ;5 0～ 15 0 μm范围内 ,钙处理组的硬度值高于对照组 ,氟处理组的硬度值高于镧处理组。结论 :脱矿凝胶中加入 1g/L的Ca2 +、La3 +、F-均阻止釉质硬度的下降 ,氟的作用最强 ,钙的作用最弱 ,镧的作用界于氟和钙之间。     

酪蛋白磷酸肽-无定形磷酸钙促进牙再矿化的机制

牙体在正常生理状态下处于脱矿和再矿化的动力平衡之中,当环境改变后,平衡被打破,脱矿和再矿化会向某一方向持续进行.脱矿不仅导致牙体形态学发生改变,也是龋病的开端,所以应该采取有力措施阻断这一过程,使其平衡向再矿化方向发展.以往以氟化物防龋并取得了较好的效果,却因不良反应使其应用受到了一定的限制.研究显示,牛奶和奶酪等奶制...     

氟涂料预防正畸治疗中釉质脱矿的实验研究

目的　明确氟涂料对釉质脱矿进程的抑制效果。方法　研究分两组 ,实验组釉质表面覆盖氟涂料 ,对照组釉质表面暴露。经短期人工龋后 ,用偏振光显微镜观察托槽周围釉质脱矿病损的分布并测量病损体部深度。结果　对照组全部样本均出现较明显的釉质脱矿 ,病损体部的平均深度为 4 8.8± 15 .1微米 ,实验组中只有少数样本出现孤立的脱矿病损 ,其余样本没有发生明显的脱矿。结论　氟涂料对短期釉质脱矿的抑制作用较明显 ,可以成为正畸治疗中釉质脱矿的预防手段之一。     

护牙素在正畸治疗中对减少牙齿脱矿及促进再矿化的功效研究

目的评价Tooth Mousse护牙素对减少离体牛牙粘接托槽周围的釉质脱矿及促进再矿化的功效。方法将60颗粘接托槽的离体牛牙随机分成实验组、阳性对照组和阴性对照组,分别在牙面上涂擦Tooth Mousse护牙素、Duraphat氟保护漆和蒸馏水。将3组样本轮流放置入人工致龋液和人工唾液中浸泡,然后使用偏光显微镜、扫描电镜、电子探针检测。结果偏光显微镜下观察,实验组釉质表面完整,主要表现为以脱矿为主的正性双折射区明显减少;扫描电镜观察实验组釉质表面有大量的矿物质沉积,填补釉质表面局限性的小凹陷;电子探针检测结果显示,实验组釉质表面钙、磷含量明显高于阴性对照组（P<0.05）,与阳性对照组之间无统计学差异（P>0.05）。结论Tooth Mousse护牙素在体外实验模型中能使牛釉质在人工致龋环境中减少脱矿和促进再矿化。     

Electron microscopy of fissure caries in man

This transmission electron microscopical study of the early stages of fissure caries shows the similarity of these lesions with approximal caries. Typical areas of calculus coexisted in the fissure dental plaque with carious destruction of enamel apatite crystals. In the surface layer of fissure enamel, a diffuse destruction of apatite crystals as well as small and deep defects, filled with a consolidated organic stroma, were observed. In the deeper layers, the carious process consisted in a broadening of the prism sheath, followed by a preferential apatite crystal destruction along the prisms. At this stage, however, individual apatite crystal dissolutions were already noted in the interprismatic substance but at a lesser degree.     

氟对脱矿和再矿化牙釉质表面的影响

目的研究氟对脱矿和再矿化牙釉质表面的影响,探讨氟防龋的作用机理。方法将牛牙釉质标本分为空白对照组（A组）、非氟化组（B组）、低氟化组（C组）和高氟化组（D组）4组,其中低氟化组和高氟化组依次进行氟化实验、脱矿实验和pH循环再矿化实验,非氟化组只进行脱矿实验和pH循环再矿化实验,空白对照组不做处理。在体视显微镜、显微硬度计和扫描电镜下观察各组釉质表面的形态变化,同时测量分析釉质表面显微硬度。结果氟化牙釉质的表面微观形态显著不同,其脱矿损害具有相对完整的表层;氟化组在氟化、脱矿和再矿化后与非氟化组相比,表面显微硬度均有统计学差异（P<0.05）。结论氟化牙釉质可增强牙釉质的抗龋能力和再矿化效能。     

Electron microscopy of human carious dental enamel

Several stages in the progression of incipient caries in human enamel were examined, by combined scanning and transmission electron microscopy, to observe ultrastructural changes that occur during carious attack. Prism interstices and striae of Retzius were found to be sites of initial attack, and a relatively sound surface layer appeared to persist through this demineralization process. Also, in approximately 70 per cent of the specimens a “prismless” surface layer was found.     

Caries susceptibility of human fluorosed enamel and dentine

OBJECTIVE: Objective of our laboratory study was to determine the impact of dental fluorosis severity on the formation of caries in the human enamel and dentine. MATERIALS AND METHODS: Thirty-three human molars were grouped according to modified Thylstrup-Fejerskov index (TFI) into normal (N, TFI 0), mild fluorosis (ML, TFI 1-3) and moderate fluorosis (MD, TFI 4-6). Three mesio-distal sections were made in corono-apical axis of the tooth, giving enamel and dentine samples. They were embedded in an epoxy resin, and polished. Half of the polished surface was covered with an acid resistant varnish and immersed in standard acidified buffer solution (pH 4.5) for 48 h to create artificial caries lesions. They were treated with 5% NaOCl for 45 min and sectioned longitudinally along the center into two halves. Cut surfaces were polished and observed under a confocal laser scanning microscope for depth of demineralization. Morphology of the demineralized zones was observed under a field emission scanning electron microscope (FE-SEM). Data were analyzed using one-way ANOVA and Sheffe test (p=0.05). RESULTS: Statistically significant difference in depth of demineralization was found between N and MD groups (p=0.046) in the enamel, and between N and ML (p=0.002), N and MD (p<0.001), ML and MD (p=0.029) in dentine. FE-SEM observation of the normal enamel showed direct dissolution with large fissures. Spongy appearance of intertubular dentine gradually disappeared from N to MD. CONCLUSIONS: Moderately fluorosed enamel showed a significant caries resistance. In contrast, mild and moderately fluorosed dentine was significantly caries susceptible in vitro.     

Ultrastructural changes in the translucent and dark zones of early enamel caries

Abstract Selected areas of early enamel caries (‘White spot’ lesion) in human teeth were argon-ion-beam thinned and examined by transmission electron microscopy. A systematic examination of areas which were histologically defined as the translucent zone and the dark zone showed that the pattern of early caries was consistent with that of demineralization of the tissue commencing with a widening of the micropores and of the inter-rod spaces and gradually progressing to a severe destruction of the original enamel crystals, with possibly some remineralization. Observations indicate that the intercrystalline micropores and inter-rod spaces are the pathways by which acidic agents reach the crystals causing carious dissolution.     

Electron probe micro-analysis for subsurface demineralization and remineralization of dental enamel

A quantitative study of fluoride distribution profile changes in dental enamel was conducted by means of electron probe micro-analysis (EPMA). Fluoride-deposited hydroxyapatite powders were chosen as fluoride standards, and analytical conditions were optimized. The lower limit of detection for fluoride was estimated to be 270 ppm, with an accelerating voltage of 5 kV, a specimen current of 40 nA, and a counting time of 40 seconds. Fluoride profiles in fluoride-treated dental enamel, which exhibited intact surface layers and subsurface demineralization, were determined. The results were also compared with those of an acid-abrasion method, and reasonable consistency was found between these two methods, although the acid-abrasion procedure yielded a slightly lower fluoride content in the initial layers, followed by a higher content of fluoride in the deeper layers. The precision of fluoride profile data obtained from EPMA permits further studies to be conducted on the kinetics of subsurface demineralization and intact surface layer formation ("white spot" formation) which is observed during the acid challenge of dental enamel.     

釉质早期龋的光学相干断层成像与定量研究

目的 探讨光学相干断层成像技术（OCT）对釉质早期龋的成像和量化评估效能,为其在早期龋临床诊断中的应用提供实验依据。方法 采用OCT扫描牛牙光滑面早期人工龋模型和脱矿模型,获取釉质图像和光学信息,并与偏振光显微镜图像和原子吸收光谱测得的矿质损失量进行对比,采用SPSS软件包配对t检验和Pearson相关性分析进行数据分析。结果 早期龋及脱矿釉质OCT图像与偏光显微镜图像基本相符;OCT测得的早期龋组釉质的总反射率改变量低于脱矿组（P<0.05）,脱矿深度在两组间无统计学差异（P>0.05）。釉质总反射率改变量与矿质损失量呈正相关（P<0.05）。结论 OCT能够无创地、较准确地显示釉质早期龋的矿质改变,量化其病变范围和程度,在早期龋的临床诊断方面具有广阔的应用前景。     

The effect of sealing white spot lesions on lesion progression in vitro

The resistance of white spot lesions to acid demineralization when etched with phosphoric acid and sealed with a resin material was studied. Artificially created white spot lesions were sealed and re-exposed to an artificial caries medium along with unprotected white spot lesions. Examination with polarized light microscopy revealed continued progression of the unprotected white spot lesions, whereas no lesion progression was evident under the resin sealant. New lesions formed on unprotected sound enamel adjacent to the margin of the resin sealant over sound enamel tangent to the white spot lesions. The sealed sound enamel adjacent to the white spot lesions did not undergo demineralization indicating protection by the resin tags. Sealing white spot lesions following etching with a 37% phosphoric acid may be beneficial in inhibiting lesion progression.     

Sequence of ultrastructural changes of enamel crystals and Streptococcus mutans biofilm in early enamel caries in vitro

Undecalcified mature enamel sections were used to observe the sequence of ultrastructural changes of enamel crystals and Streptococcus mutans biofilm in the early stages of caries. Human enamel blocks were incubated from 1 to 7 days with S. mutans suspension, and the pH of biofilm was measured. They were processed for light microscopic and transmission electron microscopy observations, and the number of bacteria located in the area adjacent to enamel surface counted. It was observed that the pH of the biofilm dropped to 4, after 1-day of incubation and the S. mutans number increased until 4-day. Round shaped enamel crystals were observed in the 2-day specimens and from the 4-day, images of crystals showing defects and perforations were visualized, becoming more defective along the incubation days. The length of time that the enamel was exposed to biofilm was the main factor for enamel crystals demineralization. Current in vitro caries induction system could standardize time-related changes of the property of Streptococcus mutans biofilm and its relation to enamel crystals demineralization at the ultrastructural level, and thus provide a useful model for the evaluation of the effects of various anti-cariogenic agents.     

柚皮苷对早期釉质龋再矿化的影响

目的 研究不同浓度的柚皮苷溶液对早期釉质龋再矿化的作用。方法 通过体外脱矿方法建立人前磨牙早期釉质龋模型,利用不同浓度的柚皮苷溶液作为实验药物,氟化钠（NaF）和去离子水（DW）分别为阳性对照和阴性对照,对样本进行再矿化处理。用电子探针观察和分析釉质表面脱矿前、后的图像变化及钙磷比值。结果 电子探针结果显示,去离子水组釉质表面呈典型的脱矿表现,为蜂窝状疏松结构;NaF组可形成均匀球形沉积区;不同浓度柚皮苷溶液组可见不规则沉积物覆盖于脱矿后釉质的蜂窝状表面,并且随着浓度的升高,沉积物由疏松逐渐变为致密。实验组钙磷比值低于NaF组（P＜0.05)。1、10、20和50 mg/mL柚皮苷溶液组的钙磷比与DW组相似,差异无统计学意义;而100 mg/mL柚皮苷溶液组与1 mg/mL柚皮苷溶液组、10 mg/mL柚皮苷溶液组、和DW组相比有统计学意义（P＜0.05)。结论 不同浓度的柚皮苷溶液可促进早期釉质龋的再矿化,其作用效果随着浓度的升高而增强。