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

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.     

Ultrastructural pattern of enamel in initial caries

In beginning caries of particular interest are destructive changes in the enamel layers just below the surface. The studied material comprised about twenty enamel blocks obtained from 10 teeth with carietic spots removed for orthodontic reasons in children aged 12-14 years. The aim of the study was assessment of the initial enamel damage under electron microscope. In all electronograms of the enamel involved by the carietic spot various grades of demineralization of the enamel below its surface were seen. The changes in initial caries seemed well delineated from the remaining healthy enamel, although within the carietic focus demineralization was observed from very slight widening of the area around the prisms to massive destruction of prism structure. The changes in the carietic spot under electron microscope showed a wide variety of patterns of destruction of enamel prisms, although clinically the surface of the enamel involved by beginning caries was small and not damaged.     

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.     

The nature of early caries lesions in enamel

Since 1935, various mechanisms have been suggested for the formation of subsurface lesions and, in particular, the surface layer covering enamel lesions. The relatively intact mineral-rich and porous surface layer is most likely caused by kinetic events. The suggested mineral-rich outer layer in sound enamel, the organic matrix, the pellicle, or a non-uniform ion distribution have all been shown to be non-essential for surface layer formation; they may, however, influence the rate of surface layer formation. Models based on outer surface protection by adsorbed agents, the dissolution-precipitation mechanism, and combinations of these two models, as well as models based on porosity or solubility gradients, are discussed in this paper together with their advantages and disadvantages. Most models have not explained some important recent experimental observations on initial in vivo caries lesion formation: e.g., initial enamel lesions formed in vivo do not have a surface layer initially but develop this mineral-rich layer later on; and the fact that the F- level in the solid sound enamel is not determining the subsurface lesion formation. Furthermore, the observations that in vitro fluoride ions in the liquid at very low levels (approximately equal to 0.02 ppm) determine surface layer formation are difficult to explain. A new kinetic model for subsurface lesion formation is described, in which inhibitors such as F- or proteins play an important role. The model predicts that if lesions depth and demineralization period are denoted by df and t, lesion progress can be described by: dfp = alpha t + c, where alpha and c are constants with 1 less than or equal to p less than or equal to 3, depending on the lesion formation conditions. If lesion progress is entirely diffusion-controlled, p = 3, corresponding to low inhibitor concentrations; if the inhibitor content is so high that the progress is controlled by processes at the crystallite surface, p = 1. A kinetic mechanism for surface layer formation in vivo is proposed, based on the assumption that F- is a main inhibitor in the plaque-covered acidic in vivo situation. The inhibiting fluoride, adsorbed onto the crystallite surfaces at OH- vacancies, originates from the so-called fluoride in the liquid phase (FL) between the enamel crystallites. Under acidic conditions (plaque), we have, due to an influx of fluoride from the saliva or plaque as FL, an aqueous phase in the enamel supersaturated with respect to the mineral for a small distance (x*) only.(ABSTRACT TRUNCATED AT 400 WORDS)     

Organic material and the optical properties of the dark zone in caries lesions of enamel

Sections of uncavitated natural caries lesions of human enamel were extracted with various solvents and examined by polarizing microscopy. After lipid extraction, the dark zone enlarged by 19-162% and its birefringence increased, while after protein extraction it shrank by 37-92% and became less birefringent. It is concluded that occlusion of submicroscopic pores by organic material largely accounts for the optical properties of the dark zone. The results are not consistent with occlusion of pores by reprecipitation of mineral. On the basis of previous work, organic material in this location could influence demineralization and remineralization.     

早期龋再矿化的口内研究

目的：通过使用泡腾颗粒低氟矿化剂对牛牙人工龋标本在体内的再矿化作用进行观察。方法：受试者２０人采用金属丝结扎式口内装置法。实验结束后，取出釉质块，采用体外偏光显微镜，显微Ｘ线，显微硬度及扫描电镜等手段检查。结果：矿化组显示早期龋釉面硬度值升高，与对照组有明显差异。病变深层负光性增强，密度加大，而表层未见明显增厚。扫描电镜显示矿化组釉面病损区有矿物质沉积及釉面孔隙变小。结论：“泡腾”矿化剂在体内对早期龋有明显的再矿化作用     

奥乐V护牙剂对早期釉质龋再矿化作用的研究

目的 观察奥乐V护牙剂对早期釉质龋的再矿化作用。方法 将50个牛牙釉质块建立人工龋模型后随机分为5组：奥乐V护牙剂组、GC护牙素组、氟化钠（NaF）组、奥乐V护牙剂+NaF组、去离子水（DDW）组,分别进入 pH循环模型。采用显微硬度计测定各组标本脱矿前和pH循环后的釉质表面硬度值,扫描电镜观察各组再矿化后釉 质表面形态结构的改变。结果 各实验组经再矿化处理后其表面显微硬度均明显提高（P<0.001）,奥乐V护牙剂组再矿化后其表面显微硬度低于NaF组（P<0.001）,但与GC护牙素组间差异无统计学意义（P>0.05）;再矿化后奥乐V护牙剂组釉质表面有较大颗粒沉积。结论 奥乐V护牙剂具有促早期人工釉质龋再矿化的作用。     

早期釉质龋表层形成的化学机制

早期釉质龋表层相对完善，表层脱矿比表层下轻是其典型的病理特征，也是龋损机制的难点和关键。本文介绍了对早期釉质龋表层形成机制的研究历程，各种学说及氟等抑龋因子在早期龋表层形成中所发挥的作用。     

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。     

Impact of enamel defects on early caries development in preschool children

Quantitative defects of the enamel are considered risk factors for caries development at the cavitated level. Since caries risk assessment and control should be implemented as early as possible in order to prevent operative treatment, it seemed interesting to investigate the relationship between enamel defects and caries development in the stages of progression that precede cavitation. The impact of enamel defects and selected child-mother indicators on early caries development was investigated in a cohort of Brazilian preschool children. The null hypothesis that developmental defects of the enamel and dental caries are independent and that an association between them occurs by chance was tested. The sample (n = 1,718) was made up of 2- to 5-year-olds. Developmental defects of enamel and caries on buccal surfaces were identified in 48 and 26% of the children, respectively. Bivariate analyses at the surface level showed neither an association between demarcated/diffuse opacity and caries experience (p ≥ 0.64, GLM), nor between the presence of hypoplastic surfaces and non-cavitated lesions (p = 0.29, GLM). The multivariate analyses indicated that in the mouths of individual children, hypoplastic surfaces were more likely to present filled surfaces and non-cavitated/cavitated lesions than non-hypoplastic surfaces (within-child p = 0.03, GEE). However, children having teeth with hypoplastic surfaces were not at higher caries risk than those children who did not present hypoplastic surfaces (between-child p = 0.23, GEE). The null hypothesis could not be accepted for quantitative defects such as hypoplasia, since they had a significant impact on the within-child prevalence of filled surfaces and non-cavitated/cavitated lesions.     

Investigations of the optical properties of enamel and dentin for early caries detection

Introduction

The aim of this study was to experimentally investigate the potential of different light wavelengths to distinguish between healthy and carious tissue using a two-circle goniometer.

Materials and methods

Tooth slices were prepared from extracted human teeth that were caries free (n = 15) or had occlusal caries lesions (n = 10). The tooth slices were irradiated with diode laser modules of different wavelengths (532, 650, 780 nm). The transmitted and scattered laser light was spatially measured with a detector rotating on a two-circle goniometer. The anisotropy factor and attenuation coefficients were calculated.

Results

Enamel was more transparent than dentin and showed wavelength-dependent attenuation. Healthy dentin showed strong light scattering at all wavelengths, independent of the tested wavelength. The calculated attenuation coefficients of carious and healthy tooth tissue differed significantly (p < 0.05; t test). In contrast to healthy enamel, carious enamel showed lower light transmission and an increase in scattering. Differences in the light attenuation of carious versus healthy dentin were less pronounced than those for enamel. Carious dentin was slightly more transparent than healthy dentin. The light of longer wavelengths showed a better penetration of all tooth structures compared with shorter wavelengths.

Conclusion

Healthy and carious dentin and enamel exhibited distinct optical properties using laser light at different wavelengths. In dentin, changes in the optical properties caused by caries are significantly less pronounced.

Clinical relevance

The clear distinction between healthy and carious enamel makes optical caries diagnostic systems ideal tools for early caries detection.

     

釉质发育缺陷与低龄儿童龋病之间关系的研究进展

釉质发育缺陷是牙齿发育初期牙体组织受到干扰而导致的釉质结构异常。低龄儿童龋是影响儿童口腔健康的主要疾病,因其发展迅速,危害严重而受到广泛关注。近年来越来越多的研究认为釉质发育缺陷与低龄儿童龋的发生有着密切的联系,本文就近几十年来关于釉质发育缺陷与低龄儿童龋之间关系的流行病学调查作一综述。     

Crystallographic changes in human tooth enamel during in-vitro caries simulation.

Subsurface demineralization of human dental enamel similar to natural caries was produced by the use of lactate buffers containing diphosphonate (MHDP) as a surface dissolution inhibitor. X-ray diffraction was used to follow crystallographic changes in the surface layer to a depth of 40 μm during artificial carious lesion formation. The various lesion zones were dissected and submitted to X-ray diffraction. It was concluded that: the intact surface layer is formed from the original enamel, after partial demineralization, by deposition of calcium and phosphate, dissolved from underlying enamel, into defects of existing crystals; dicalcium phosphate CaHPO₄ is formed in the inner lesion (translucent) zone; carbonate-containing apatite is progressively lost during lesion formation; and that well-formed hydroxyapatite is left during subsurface dissolution.