The enamel substrate-characteristics of the enamel surface.

The outer enamel surface is of considerable interest in dentistry as it is the substrate for the acquired pellicle; the pellicle itself is the plaque carrier. In this paper the interface between outer enamel and pellicle is discussed with special emphasis on the outer enamel from a structural and chemical point of view. The outer enamel layer (less than 1 micron from the anatomical surface) is most likely a non-sto?chiometric apatite. The chemical composition is obviously strongly different from the composition of bulk enamel. A model for the structure and atomic composition of surface enamel is presented. The available experimental evidence indicates that at an atomic scale, enamel crystallites have mainly phosphate groups (HPO42-groups) on the solid surface; the liquid adhering Stern layer contains most likely large amounts of calcium ions.     

Ectopic tooth enamel. An SEM study of the structure of enamel in enamel pearls

Eighteen human molars with enamel pearls ranging in diameter from 0.8 to 2.7 mm were sectioned, acid-etched, and processed for SEM observation. In addition to pearl enamel, the specimens contained crown enamel for comparison. All pearls were of the composite type. The enamel layer reached maximal thicknesses of between 0.3 and 0.7 mm opposite the tip of the dentinal cone. The enamel structure was normal, but more variable and irregular than crown enamel. The prism course was often irregular throughout the whole thickness of enamel. Distinct Hunter-Schreger bands were absent. Prisms and interprism were occasionally difficult to identify as separate entities. The packing of crystals seemed to be less tight in pearl enamel. The scarcity of Retzius lines was attributed to the method of preparation. Prism cross-striations with a periodicity ranging between 1.3 and 4.5 microns were frequently encountered. A superficial prism-free zone with a regular 1.7-2.5-microns striation was present in localized regions of many pearls. The formation time of a medium-sized pearl was calculated to be about 11.5 months. A variety of cross-cut prism configurations was observed. Occasional hypoplastic lesions and hypomineralized areas were encountered. In conclusion, pearl enamel possesses most of the structural attributes of crown enamel, but in general its organization seems to be less orderly. Enamel pearls represent developmental disturbances in position and timing more than in structure.     

Quantifying enamel luster

OBJECTIVE: When the pH of the oral cavity drops below 5.5, the hydroxyapatite crystalline lattice is damaged and the tooth surface becomes rough. Consequently, specular reflection is decreased and results, clinically, in a loss of tooth luster. The aim of this study was to develop a digital image capture and processing algorithm to quantify enamel luster. METHODOLOGY: Extracted human teeth (n = 25) containing no restorations and with no clinical evidence of caries were used in this study. The teeth were sectioned longitudinally in a mesial-to-distal orientation to provide experimental and control groups. The experimental group was treated with six consecutive 60-minute exposures to an acidic soft drink, separated by tap water rinses; the control group was similarly treated with just the tap water. Standardized photographs were made before and after application of the treatment or control conditions. Images were converted to eight-bit monochrome digital format. The clinical crown was identified using a standard digital masking technique. Luster in the crown was quantified by determining pixels with luminescence values that were 65% above background. RESULTS: Overall, there was an average 53.6% change in luster in the experimental group, and a nominal 2.10% change in luster in the control group. Analysis of variance revealed a significant loss in luster as measured by this algorithm in the experimental group (p < 0.001), while no significant change in luster was found in the control group. The method reliably identified luster with a repeatability coefficient of 0.992. CONCLUSION: Our digital processing algorithm consistently quantified loss of enamel luster associated with exposure to an acidic beverage. This digit photographic technique may be valuable for evaluating changes in the esthetic chacteristics of teeth when they are exposed to a variety of adverse environments.     

Dissolution of enamel

abstract — Each of six premolars were exposed to 8 ml of a buffer, pH 5.0. The ionic activity products for FA, HA, CaHPO₄, CaF₂ and Ca₄H(PO₄)₃ were determined. It was found that the liquid phase initially was unsaturated with respect to all solid phases and that FA and HA were dissolving from the enamel. Four hours after initiation of the experiments the liquid phase was supersaturated with respect to FA while still unsaturated with respect to HA, which resulted in a precipitation of FA in the enamel and a dissolution of HA from the enamel. Teeth which had been exposed to a buffer unsaturated with respect to both FA and HA exhibited the signs of a natural erosion, while teeth exposed to a buffer supersaturated with respect to FA and unsaturated with respect to HA showed the characteristics of a caries lesion. It was found by analyzing various acidic beverages that these were unsaturated with respect to both FA and HA. By calculation it was found that saliva was unsaturated with respect to HA and supersaturated with respect to FA at a pH of between 5.5 and 4.5. It was concluded that the erosive lesion can be described as the result of a demineralization caused by a liquid phase unsaturated with respect to both HA and FA and the carious injury by a liquid phase unsaturated with respect to HA and supersaturated with respect to FA.     

An in-vitro study of enamel protein degradation in developing bovine enamel

An immature enamel fraction, as far as possible without cells, was prepared from fetal bovine molars, using aqueous-density fractionation. Portions were incubated at 37 degrees C with or without protease inhibitors. Amelogenins and enamelins were then examined for their molecular weight using HPLC-gel permeation. Degradation of amelogenins occurred rapidly and appeared to be related to proteolytic activity, probably localized extra-cellularly. Enamelins remained almost stable over the time intervals used.     

Morphology of dental enamel and dentine–enamel junction in osteogenesis imperfecta

Objectives . The aim of this study was to examine the morphology of primary and permanent human enamel, and the dentine–enamel junction, in individuals with osteogenesis imperfecta (OI) type I, III and IV in undecalcified sections using polarized light microscopy, microradiography and scanning electron microscopy (SEM), and to relate the findings to the type of OI.
Sample and methods . Extracted or exfoliated teeth from 15 patients representing the OI types I, III and IV (12 primary teeth from seven patients, and 11 permanent teeth from eight patients). Ten primary and nine permanent teeth from normal healthy patients served as controls. The teeth were serially cut longitudinally in a bucco-lingual direction and contact microradiographs were made. The sections were examined in polarized light. Sections of primary and permanent teeth were examined by means of SEM.
Results . This study shows that the permanent enamel from patients with OI exhibits few structural changes. No relationships were found between enamel morphology and the types of OI (I, III, IV). Primary enamel appeared to be slightly more irregularly mineralized, especially in cases with the additional diagnosis dentinogenesis imperfecta. The major findings were deviations in association with the dentine–enamel junction, and locally a lower degree of mineralization.
Conclusions . The mesodermal disease OI might also be manifested in ectodermal enamel, probably because of suboptimal mesenchymal–ectodermal interactions during amelogenesis.     

不同抛光方法对邻面去釉后牙釉质的影响

目的:研究不同抛光方法对离体牙邻面去釉区域釉质脱矿程度的影响.方法:选择20颗离体前磨牙作为实验对象,随机将牙的一个邻面作为对照组,另一邻面作为实验组.对照组邻面去釉后进行物理抛光,实验组邻面去釉后进行化学抛光.所有样本进行体外pH循环60d后,利用激光荧光诊断仪对样本实验区釉质脱矿程度进行定量测定,所得数据采用SPSS10.0软件包进行配对t检验.另选取试样通过扫描电镜观察釉质表面形态结构.结果:对照组釉质脱矿程度较实验组更重,两者差异有高度统计学意义(P＜0.01).扫描电镜观察发现,化学抛光后的釉质表面较物理抛光后更平滑.结论:对邻面去釉后的釉质进行化学抛光较物理抛光可提高釉质表面的光滑程度,降低釉质脱矿的风险.     

A study of enamel adhesives The physical relationship between enamel and adhesive

The physical relationship between several adhesive materials and treated enamel surfaces was investigated at the microscopic and ultramicroscopic level. Filamentous, “tag-like” extensions were noted at the interface between the materials and the enamel following demineralization of the latter. The origin of the extensions was attributed to the liquid monomer which had penetrated into the boundaries and cores of the prisms and polymerized therein. Such penetration can encapsulate the crystallite components of the enamel providing an effective and permanent mechanical bond and protect the outermost enamel from dissolution.     

An electron microscopic study of tetracycline-induced enamel defects in rat incisor enamel

abstract – The structure of incremental bands and gross hypoplastic lesions in rat incisor enamel which resulted from single or multiple injections with tetracycline hydrochloride was studied in the electron microscope. Both types of lesions which were investigated previously using microradiography and fluorescence microscopy exhibited many unusual structural features which are discussed in relation to current concepts of normal enamel formation. Disturbances in packing and organization were common to all the lesions indicating a primary interference with the first phase of enamel formation, i.e. matrix formation and initial mineralization. These changes were the main cause of the various mineralization disturbances seen in the microradiograms. Temporary and permanent interference with the second or maturation phase, i.e. crystal growth, was also evident but only as a corollary to the principal disturbance. This, and other evidence, suggests that tetracycline as well as many other chemical agents achieve their principal effects on enamel formation by injuring pre-secretory or secretory ameloblasts. Thus it appears that most developmental mineralization disturbances are symptomatic of hypoplastic lesions or are a sequela to the cell injury which also causes the hypoplastic lesions. Because of that it is suggested · that commonly used division between hypoplastic and hypomineralized defects be abandoned.     

Analysis of human enamel genes: insights into genetic disorders of enamel

A number of inherited craniofacial diseases are known to be associated with gene mutations. Inherited genetic disorders of enamel formation called amelogenesis imperfecta (AI) affect the human population with a prevalence of 1 in 14,000 in the United States. Amelogenins, the major proteins in developing enamel matrix of mammalian teeth, have been suggested to participate in normal enamel matrix biomineralization, as well as with abnormal biomineralization such as seen in AI. The complementary DNA for mouse amelogenin gene (AMEL) has been cloned, characterized, and used as a probe to establish the chromosomal locations of AMEL for mouse and man. The human AMEL gene sequences have been located to the distal short arm p22.1----p22.3 region of the X chromosome, and the pericentromeric region of the Y chromosome. An assignment of human AMEL gene to the X chromosome p22 region together with a recent assignment of the X-linked AI disease locus to the Xp22.2 region support the association of the AMEL-X gene with AI. This also leads us to propose that a mutated AMEL-X gene produces altered amelogenin polypeptide, which is defective in its ability to participate in mineralization of enamel matrix, thus giving rise to the X-linked phenotypes of AI.