Structure Of Dental Enamel Research Articles

Energy-dispersive Laue diffraction analysis of the influence of statherin and histatin on the crystallographic texture during human dental enamel demineralization.

Energy-dispersive Laue diffraction (EDLD) is a powerful method to obtain position-resolved texture information in inhomogeneous biological samples without the need for sample rotation. This study employs EDLD texture scanning to investigate the impact of two salivary peptides, statherin (STN) and histatin-1 (HTN) 21 N-terminal peptides (STN21 and HTN21), on the crystallographic structure of dental enamel. These proteins are known to play crucial roles in dental caries progression. Three healthy incisors were randomly assigned to three groups: artificially demineralized, demineralized after HTN21 peptide pre-treatment and demineralized after STN21 peptide pre-treatment. To understand the micro-scale structure of the enamel, each specimen was scanned from the enamel surface to a depth of 250 µm using microbeam EDLD. Via the use of a white beam and a pixelated detector, where each pixel functions as a spectrometer, pole figures were obtained in a single exposure at each measurement point. The results revealed distinct orientations of hydroxyapatite crystallites and notable texture variation in the peptide-treated demineralized samples compared with the demineralized control. Specifically, the peptide-treated demineralized samples exhibited up to three orientation populations, in contrast to the demineralized control which displayed only a single orientation population. The texture index of the demineralized control (2.00 ± 0.21) was found to be lower than that of either the STN21 (2.32 ± 0.20) or the HTN21 (2.90 ± 0.46) treated samples. Hence, texture scanning with EDLD gives new insights into dental enamel crystallite orientation and links the present understanding of enamel demineralization to the underlying crystalline texture. For the first time, the feasibility of EDLD texture measurements for quantitative texture evaluation in demineralized dental enamel samples is demonstrated.

Evaluation of Ilex guayusa and Piper marginatum Extract Cytotoxicity on Human Dental Pulp Mesenchymal Stem Cells.

Amelogenesis imperfecta is a hereditary disorder affecting dental enamel. Among its phenotypes, hypocalcified AI is characterized by mineral deficiency, leading to tissue wear and, consequently, dental sensitivity. Excessive fluoride intake (through drinking water, fluoride supplements, toothpaste, or by ingesting products such as pesticides or insecticides) can lead to a condition known as dental fluorosis, which manifests as stains and teeth discoloration affecting their structure. Our recent studies have shown that extracts from Colombian native plants, Ilex guayusa and Piper marginatum, deposit mineral ions such as phosphate and orthophosphate into the dental enamel structure; however, it is unknown whether these extracts produce toxic effects on the dental pulp. To assess cytotoxicity effects on human dental pulp stem cells (hDPSCs) exposed to extracts isolated from I. guayusa and P. marginatum and, hence, their safety for clinical use. Raman spectroscopy, fluorescence microscopy, and flow cytometry techniques were employed. For Raman spectroscopy, hDPSCs were seeded onto nanobiochips designed to provide surface-enhanced Raman spectroscopy (SERS effect), which enhances their Raman signal by several orders of magnitude. After eight days in culture, I. guayusa and P. marginatum extracts at different concentrations (10, 50, and 100 ppm) were added. Raman measurements were performed at 0, 12, and 24 h following extract application. Fluorescence microscopy was conducted using an OLIMPUS fv1000 microscope, a live-dead assay was performed using a kit employing a BD FACS Canto TM II flow cytometer, and data analysis was determined using a FlowJo program. The Raman spectroscopy results showed spectra consistent with viable cells. These findings were corroborated using fluorescence microscopy and flow cytometry techniques, confirming high cellular viability. The analyzed extracts exhibited low cytotoxicity, suggesting that they could be safely applied on enamel for remineralization purposes. The use of nanobiochips for SERS effect improved the cell viability assessment.

Crystalline analysis of dental enamel by X-Ray diffraction on pediatric patients with chronic kidney disease.

This study aimed to analyze the crystalline structure of dental enamel in pediatric patients with chronic kidney disease (CKD) by X-ray diffraction (XRD). The six tested samples had a mineral composition similar to hydroxyapatite, according to sheet JCPDS(Joint Committee on Powder Diffraction Standards) card #09-0432, which is normally found in dentine, and presented a lower amount of whitlockites (Ca, Mg)3(PO4)2. Pattern phases showed an increase in organic matter and a decrease in inorganic matter. At an interval of approximately 2θ = 15.7° to 27.2°, amorphous organic matter corresponding to hydrated glucose was found. The hydroxyapatite patterns in this study differed from that of dental enamel found on permanent teeth.

MICROABRASÃO DO ESMALTE

Enamel defects are described as changes in its structure characterized by local decrease or loss of its translucency from fluorosis, hypocalcifications, hypoplasias and inactive carious lesions with superficial and medium depth. The microabrasion of enamel selectively promotes the removal of its surface layer that presents color or structure modification through a mixture of abrasive and erosive agents mechanically. The association of these agents exposes a sub-layer of enamel with normal characteristics. This procedure can be used alone or associated with one or more aesthetic treatments, such as tooth whitening and composite resin restorations. Objective: to approach the microabrasion technique applied in dental enamel with changes in color and structure. Methodology: a non-systematic review of the scientific literature, published from 2009 to 2019, was carried out in the Virtual Health Library and in the academic Google. The inclusion criteria were articles in Portuguese and English, published in the last 10 years, that addressed the proposed theme. Conclusion: Dental microabrasion is a good alternative for aesthetic treatment for changes in the superficial structure of dental enamel, fluorosis and hypoplasia, because it wears little dental structure, restores aesthetics, does not cause damage to the pulp or periodontal tissues, requires little treatment time, does not require cavitary preparation, nor restorative material and is low cost. Aesthetic dissatisfaction is a concern of patients of all ages and the diagnosis of dental fluorosis should be the result of careful anamnesis and it should be taken into account that the etiology may be of various origins.

Enamel Surface Damage following Debonding of Ceramic Brackets: A Hospital-Based Study.

Methods The current study includes 80 extracted premolars of human from the patient visiting for orthodontic treatment of Coorg Institute of Dental Sciences, Karnataka, India. The brackets were debonded using four different methods. The enamel surface damage after the procedure was assessed with the Enamel Surface Index (ESI); similarly, the Adhesive Remnant Index (ARI) score was used to determine the adhesive residual deposit. Scanning electron microscopy (SEM) was used to visualize better microporosities and micromechanical retention of adhesive remnants on the enamel surface. The normality of the data was tested using the Kolmogorov–Smirnov test. Depending upon the normality test result, the one-way ANOVA test or Kruskal–Wallis test was used to test the mean ESI and mean ARI differences among different debonding methods along with the appropriate post hoc tests. The necessary ethical clearance was obtained from the Ethics Committee of the institute. Results The ultrasonic scaler (US) technique led to more significant enamel surface damage, with 13 (65%) samples in the ESI scores III and IV against the satisfactory surface in 2 (10%) samples with the ligature cutter (LC) technique (ESI-I) reflecting LC as a better technique. The ESI scores (III and IV) for debonding plier (DP) and thermal method (TM) reflected a higher value in 12 (60%) and 10 (50%) samples and caused more damage to the enamel surface as compared to the LC technique. The ARI score was highest (ARI-1 = 40%) with the LC technique, followed by the US (ARI-1 = 20%), TM (ARI-1 = 15%), and DP (ARI-1 = 5%) methods. We have observed a significant association (p value <0.05) of the ARI score among four different debonding ways in terms of each tooth's residual adhesive after the bracket removal. Conclusion The result establishes the LC technique as a more acceptable one as it causes minimal harm to the debonded surface. The adhesive left on the debonded area is also minimum as compared to the other three methods tested. Therefore, it can be suggested as an ideal method.

Dental enamel structure in long-nosed armadillos (Xenarthra:Dasypus) and its evolutionary implications

AbstractMost xenarthrans have a reduced and simplified dentition that lacks enamel. However, the presence of prismatic enamel has been recorded in the Eocene armadillos Utaetus buccatus (Euphractinae) and Astegotherium dichotomus (Astegotheriini). Among extant xenarthrans, the occurrence of enamel has been recognized only in the long-nosed armadillo, Dasypus novemcinctus (Dasypodinae), but its microstructure has never been described. In this contribution, we analyse the enamel microstructure in deciduous and permanent teeth of four Dasypus species. In deciduous molariform teeth of some species, we identify an apical cap of vestigial enamel (without crystalline structure), interpreted as an amorphous ameloblastic secretion. In permanent teeth, a thin layer of true enamel is found in the apical portion of unworn molariforms. The enamel is prismatic in D. novemcinctus, but in Dasypus hybridus, Dasypus sabanicola and Dasypus punctatus it is prismless. Taking into account the Eocene species of armadillos, the ancestral condition of enamel in cingulates could have been more complex (as in other placentals) and undergone progressive reduction, as shown in the Dasypus lineage. In light of previous genetic and developmental studies, we review and briefly discuss the processes that can account for the reduction/loss of enamel in extant and extinct armadillos. The retention of enamel and the fact that this genus is the only living xenarthran with two functional generations of teeth support the early divergence of the Dasypus lineage among living cingulates. This is in agreement with morphological and molecular analyses.

Magnesium incorporation into primary dental enamel and its effect on mechanical properties

Cross-sectional study of sound primary dental enamel revealed hardness zonation and, in parallel, significant change in the Mg content below the prismless layer. Mg content is known to play an important role in enamel apatite biomineralization, therefore, Mg ion exchange experiments were carried out on the outer surface of sound primary molars and on reference abiogenic Ca-phosphates using MgCl2 solution. Effects of Mg incorporation on crystal/particle size, ionic ratio and morphology were compared and the observed changes were explained by parallel diffusion and dissolution/reprecipitation processes.Based on depth profile analysis and high resolution electron microscopy of the Mg-exchanged dental enamel, a poorly ordered surface layer of approximately 10–15 nanometer thickness was identified. This thin layer is strongly enriched in Mg and has non-apatitic structure. Below the surface layer, the Mg content increased only moderately (up to ~3 at%) and the apatite crystal structure of enamel was preserved. As a common effect of the Mg exchanged volume, primary dental enamel exhibited about 20% increase of nanohardness, which is intrepreted by strengthening of both the thin surface layer and the region below due to the decreased crystallite size and the effect of incorporated Mg, respectively. Statement of SignificanceDental enamel is the most durable mineralized tissue in the human body, which, in spite to be exposed to extreme conditions like mastication and acidic dissolution, is able to fulfill its biological function during lifetime. In this study we show that minor component magnesium can affect hardness properties of human primary dental enamel. Then, through Mg incorporation experiments we provide an additional proof for the poorly ordered Mg-containing intergranular phase which has been recently observed. Also, we report that the hardness of dental enamel can be increased by ca. 20% by Mg incorporation. These results contribute to a deeper understanding of sound primary dental enamel structure and may inspire new pathways for assisted remineralization of enamel and regenerative dentistry.

The geometrical structure of interfaces in dental enamel: A FIB-STEM investigation

In this study a high resolution structural analysis revealed that enamel prisms are surrounded by an interface that is discontinuous with frequent mineral to mineral contact separated by gaps. This contact manifests either by crystallites bridging the boundary between prismatic and interprismatic enamel or continuous crystallites curving and bridging the interprismatic enamel to the prisms. The geometrical resolution of this TEM investigation of the interfaces is ≤2 nm as a basis for micromechanical models. Within this resolution, contrary to existing structural descriptions of dental enamel structure in materials science literature, here the crystallites themselves are shown to be either in direct contact with each other, sometimes even fusing together, or are separated by gaps. Image analysis revealed that on average only 57 ± 15% of the interface consists of points of no contact between crystallites. This work reveals structural features of dental enamel that contribute important understanding to both the architecture and mechanical properties of this biological material. A new structural model is proposed and the implications for the mechanical properties of dental enamel are discussed. Statement of significanceIn this study a high resolution structural analysis, employing focused ion beam and transmission electron microscopy revealed that enamel prisms are surrounded by interfaces that are discontinuous with frequent mineral to mineral contact separated by gaps. Although the interfaces in enamel have been investigated previously, existing studies are lacking in detail considering the geometry and morphology of the interfaces. We think that this result is of great importance when it comes to the understanding of the mechanical properties. In our opinion the concept of soft sheaths is no longer feasible. The resulting observations are included in a new structural model which provides new qualitative insights into the mechanical behavior. Existing analytical models were applied to simulate the new geometrical structure.

On the method of revealing enamel structure by acid etching. Aspects of optimization and interpretation.

The study aimed at finding an optimal combination of acid concentration and etching time when nitric acid is used as etchant for the study of the finer details of human dental enamel structure. Four hundred 2-3-mm-thick segments of facio-lingually sectioned human third molar crowns were assigned to 20 groups with 20 specimens in each group, each group differing with respect to acid concentration (0.1, 1, 2.5, and 5%) and etching time (15, 30, 45, 90, and 180 s). After etching and preparation, specimens were observed in the scanning electron microscope (SEM). Surface roughness/topography increased with increasing acid concentration and increasing etching time, but not in a linear fashion; generally, prisms tended to go from flat-surfaced to cone-shaped and prism sheaths from fissure-like to wedge-shaped. Intragroup variations and intergroup similarities were considerable. The two major enamel factors determining the etch effect are crystal orientation and prism sheath properties. Other factors, such as distribution of porosities and crystal quality, also contribute probably. Slight to moderate topography is best for observing the finer enamel structure, for example, etching with concentrations in the range 0.1-1% and with etching times in the range 15-90 s, the stronger the acid, the shorter the time. The depth effect of nitric acid is judged to be relatively small. Considerable variations in expression of prism cross-striations were observed. SEM observations of acid-etched enamel in carefully selected planes are a powerful method for the study of enamel structure, bearing in mind the artifactual aspects of the observed surface.

Scanning Electron Microscopy (SEM) Methods for Dental Enamel.

Scanning electron microscopy (SEM) is exceptionally well suited for the study of the structure of dental enamel, due to its ability to create high-resolution images of hard surfaces. Continuous attention on how to arrive at the observation stage with a clean and dry specimen is one main aspect of specimen preparation. Other main aspects are choice of whether the specimen should be embedded or not, choice of plane of section, and choice of acid-etching regime. Special attention is given to the preparation of small specimens and how to prepare and observe more than one plane or aspect in the same specimen.

FT-Raman spectroscopic characterization of enamel surfaces irradiated with Nd:YAG and Er:YAG lasers.

Background. Despite recent advances in dental caries prevention, caries is common and remains a serious health problem. Laser irradiation is one of the most common methods in preventive measures in recent years. Raman spectroscopy technique is utilized to study the microcrystalline structure of dental enamel. In this study, FT-Raman spectroscopy was used to evaluate chemical changes in enamel structure irradiated with Nd:YAG and Er:YAG lasers. Methods. We used 15 freshly-extracted, non-carious, human molars that were treated as follows: No treatment was carried out in group A (control group); Group B was irradiated with Er:YAG laser for 10 seconds under air and water spray; and Group C was irradiated with Nd:YAG laser for 10 seconds under air and water spray. After treatment, the samples were analyzed by FT-Raman spectroscopy. Results. The carbonate content evaluation with regard to the integrated area under the curve (1065/960 cm–1) exhibited a significant reduction in its ratio in groups B and C. The organic content (2935/960 cm-1) area exhibited a significant decrease after laser irradiation in group B and C. Conclusion. The results showed that the mineral and organic matrices of enamel structure were affected by laser irradiation; therefore, it might be a suitable method for caries prevention.

Evaluation of enamel surface after bracket debonding and polishing

INTRODUCTION: Preserving the dental enamel structure during removal of orthodontic accessories is a clinician's obligation. Hence the search for an evidence based debonding protocol. OBJECTIVE: to evaluate and compare, by means of scanning electron microscopy (SEM), the effects of four different protocols of bracket debonding and subsequent polishing on enamel surface, and to propose a protocol that minimizes damage to enamel surface. METHODS: Twelve bovine permanent incisors were divided into four groups according to the instrument used for debonding and removal of the adhesive remnant. In groups 1 and 2, brackets were debonded with a straight debonding plier (Ormco Corp., Glendora, California, USA), and in groups 3 and 4, debonding was performed with the instrument Lift-Off (3M Unitek, Monrovia, California, USA). In groups 1 and 3, the adhesive remnant was removed using a long adhesive removing plier (Ormco Corp., Glendora, California, USA) and in groups 2 and 4, residual adhesive was removed with a tungsten carbide bur (Beavers Dental) at high-speed. After each stage of debonding and polishing, enamel surfaces were replicated and electron micrographs were obtained with 50 and 200X magnification. RESULTS: All four protocols of debonding and polishing caused enamel irregularities. CONCLUSION: Debonding brackets with straight debonding plier, removal of adhesive remnant with a tungsten carbide bur and polishing with pumice and rubber cup was found to be the protocol that caused less damage to enamel surface, therefore this protocol is suggested for debonding brackets.

Dental Enamel Structure Is Altered by Expression of Dominant Negative RhoA in Ameloblasts

Using in vitrotooth germ cultures and analysis by confocal microscopy, ameloblasts treated with sodium fluoride were found to have elevated amounts of filamentous actin. Because this response is reduced by inhibitors of the Rho/ROCK signaling pathway, we generated mice that express dominant negative RhoA (RhoA^DN) in ameloblasts for in vivo analysis. Expression of the EGFP-RhoA^DN fusion protein was evaluated by RT-PCR and immunohistochemistry, and teeth were analyzed by scanning electron microscopy. The 3 strains expressed at either low (TgEGFP-RhoA^DN-8), intermediate (TgEGFP-RhoA^DN-2), or high (TgEGFP-RhoA^DN-13) levels, and the molar teeth from the 3 strains had enamel hypoplasia and surface defects. We conclude that RhoA^DN expressed in ameloblasts interferes with normal enamel development through the pathway that is induced by sodium fluoride.

Gene expression and dental enamel structure in developing mouse incisor

At the mouse incisor tip the initially differentiated ameloblasts produce a thin, prism-free enamel, while further apically, in the immediate adjacent segment, the enamel thickness increases and the four-layered enamel of mouse incisor is formed. Comparative gene-expression profiling was carried out on RNA isolated from these two segments of incisor tooth germs at embryonic day (E)17.5 and at postnatal days (P)0, 1, 2, and 10 using microarrays to measure messenger RNA (mRNA) and microRNA (miRNA) species present in the segments. Validation of expression data was achieved using real-time reverse transcription-polymerase chain reaction (RT-PCR) and western blotting. Bioinformatic data suggested enhanced cellular apoptosis in the incisal tip segment, which, together with diminished expression of the Amelx and Enam genes, may contribute to the production of the thin enamel seen in this tooth segment. For genes exhibiting higher levels of expression in the adjacent segment where complex enamel is being formed, bioinformatic analysis suggested significant associations with cellular functions involving the actin cytoskeleton, cellular development, morphology, and movement. This is suggested to reflect that ameloblasts with Tomes' process are being organized in transverse rows, facilitating the transverse movement that results in prism decussation in the inner enamel of the adjacent segment. Bioinformatic analysis of miRNA expression data lends support to these suggestions.

Formation and Structure of Dental Enamel

European Journal of Oral SciencesVolume 114, Issue s1 p. 349-350 Formation and Structure of Dental Enamel Ziedonis Skobe, Ziedonis SkobeSearch for more papers by this author Ziedonis Skobe, Ziedonis SkobeSearch for more papers by this author First published: 02 May 2006 https://doi.org/10.1111/j.1600-0722.2006.00374.xCitations: 3Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume114, Issues1May 2006Pages 349-350 RelatedInformation

Distribution and structure of dental enamel in incisors of Tabby mice

In Tabby mice, the Ta (EDA) gene is mutated. The resulting syndrome is homologous to hypohidrotic ectodermal dysplasia in humans. The Tabby phenotype is characterized by developmental defects of ectodermally derived structures. The teeth show aberrations in number, size and morphology. Dental enamel is a product of specialized epithelial cells, the ameloblasts. It was the aim of the present study to investigate the dental enamel phenotype in Tabby incisors, with emphasis on its distribution and structure. The incisors from five female Tabby and three female wild-type mice were sectioned and ground transversely, etched for 45s with 0.1% nitric acid, sputter-coated with gold-palladium, and observed in SEM. All measured dimensions were more variable in Tabby mice, as was the outline of the enamel-dentin junction. Maxillary incisors were wider in Tabby mice, while mandibular incisors were wider in wild-type mice. No significant difference in enamel thickness was observed. The enamel on the mesial aspect tended to extend further lingually in Tabby incisors in both jaws. On the lateral aspect, this tendency was only significant in mandibular incisors. The enamel-dentin junction often lacked the mesial concavity. Instances of hypoplastic enamel were observed. The complex mouse enamel structure was generally well preserved in Tabby mice, only few instances of aberrant structure were observed. It is suggested that the reciprocal expression pattern of Ta and Edar (the Ta ligand receptor gene) in outer and inner enamel epithelium, respectively, may influence the position of the enamel-cementum junction.

Inherited Risks for Susceptibility to Dental Caries

Dental caries incidence is affected by host factors that may be related to the structure of dental enamel, immunologic response to cariogenic bacteria, or the composition of saliva. Genetic variation of the host factors may contribute to increased risks for dental caries. This systematic review examined the literature to address the question, "Is the risk for dental decay related to patterns of genetic inheritance?" Numerous reports have described a potential genetic contribution to the risk for dental caries. Studies on twins have provided strong evidence for the role of inheritance. Establishing a basis for a genetic contribution to dental caries will provide a foundation for future studies utilizing the human genome sequence to improve understanding of the disease process. Inherited disorders of tooth development with altered enamel structure increase the incidence of dental caries. Specific genetic linkage has not been determined for all of the syndromes of altered tooth development. Consequently, genetic screens of large populations for genes or mutations associated with increased caries susceptibility have not been done. Altered immune response to the cariogenic bacteria may also increase the incidence of caries. Association between specific patterns of HLA genetic inheritance and dental caries risk is weak and does not provide a predictable basis for predicting future decay rates. The evidence supporting an inherited susceptibility to dental caries is limited. Genetic linkage approaches on well-characterized populations with clearly defined dental caries incidence will be required to further analyze the relationship between inheritance and dental caries.

Application of Laser on Dental Treatment (Part 3) : Chemical Composition and Crystalline Structure of Dental Enamel Fused by Laser Irradiation

Application of Laser on Dental Treatment (Part 3) : Chemical Composition and Crystalline Structure of Dental Enamel Fused by Laser Irradiation

Diffusion of 45Ca in bovine enamel.

The penetration of 45Ca ions into whole bovine enamel from an aqueous solution was studied as a function of the Ca content in the solution. A sectioning technique was employed to measure the penetration of 45Ca into the enamel. Probably only Ca ions occupying surface positions in the hydroxyapatite crystallites participate in the exchange process at the solution-enamel interface. The fraction of Ca ions participating in the exchange was 2% of the total number of Ca ions. Two different diffusion processes occur; firstly, a process governed by a diffusion coefficient, D1 ranging from about 5 x 10(-14) to 2 x 10(-12) cm2/s and strongly dependent on the calcium concentration in the solutions; and secondly a process with a concentration-independent diffusion coefficient, D2, with a value of 2.8 x 10(-12) cm2/s. It is assumed that the 2 diffusion types correspond to intra- and interprismatic transport, respectively. A model based on the pore structure of dental enamel and on surface charges on hydroxyapatite crystallites is discussed.

Composition and structure of dental enamel: Elemental composition and crystalline structure of dental enamel as they relate to its solubility

The same elements, 21 in number, were found in both acid-resistant and acid-susceptible enamel specimens by ion microprobe analyses. However, there were differences in the concentrations of 14 elements between groups. Of the 16 trace elements found in enamel, the concentrations of K, F, and Na in parts per million were the greatest. Enamel surface analyses showed V and Zn were more concentrated in acid-resistant specimens by factors of 7.4 and 6.1 respectively, followed by nine other elements, the last molybdenum, that were just slightly more prevalent in acid-resistant enamel. Four elements were equally concentrated in both groups of samples, and only one trace element, B, was more abundant in the acid-susceptible samples by a factor of ten. Ca and P were predominantly more abundant in acid-resistant speciems, and C, H, and O were more concentrated in acid-susceptible samples. The enamel substance in acid-resistant and acid-susceptible groups was found to be similar by these methods. --Ion microprobe: the same elements were detected in both groups. Four trace elements (titanium, lead, Cl, and lithium) were equally abundant in the two groups. --Electron diffraction: the crystal structure type was the same in both groups of samples. --Infrared absorption: the crystalline substance showed the same spectra in both groups. The enamel substance in the two groups of specimens was found to be dissimilar by these methods. --Ion microprobe: the concentrations of 11 trace elements as well as Ca and P were greater in acid-resistant enamel. The concentrations of C, H, O, and B were greater in acid-susceptible enamel. --X-ray diffraction: crystallites in the acid-resistant specimens were larger by a factor of more than two. Enamel solubility appears not to be related to atomic species but associated with one, some, or all elements quantitatively and also with its physical form (crystallite size and probably density).