Enamel Maturation Research Articles

Enamel maturation: a brief background with implications for some enamel dysplasias.

The maturation stage of enamel development begins once the final tissue thickness has been laid down. Maturation includes an initial transitional pre-stage during which morphology and function of the enamel organ cells change. When this is complete, maturation proper begins. Fully functional maturation stage cells are concerned with final proteolytic degradation and removal of secretory matrix components which are replaced by tissue fluid. Crystals, initiated during the secretory stage, then grow replacing the tissue fluid. Crystals grow in both width and thickness until crystals abut each other occupying most of the tissue volume i.e. full maturation. If this is not complete at eruption, a further post eruptive maturation can occur via mineral ions from the saliva. During maturation calcium and phosphate enter the tissue to facilitate crystal growth. Whether transport is entirely active or not is unclear. Ion transport is also not unidirectional and phosphate, for example, can diffuse out again especially during transition and early maturation. Fluoride and magnesium, selectively taken up at this stage can also diffuse both in an out of the tissue. Crystal growth can be compromised by excessive fluoride and by ingress of other exogenous molecules such as albumin and tetracycline. This may be exacerbated by the relatively long duration of this stage, 10 days or so in a rat incisor and up to several years in human teeth rendering this stage particularly vulnerable to ingress of foreign materials, incompletely mature enamel being the result.

Maturation and beyond: proteins in the developmental continuum from enamel epithelium to junctional epithelium

Enamel, covering the surface of teeth, is the hardest substance in mammals. It is designed to last a lifetime in spite of severe environmental challenges. Enamel is formed in a biomineralization process that is essentially divided into secretory and maturation stages. While the molecular events of enamel formation during the secretory stage have been elucidated to some extent, the mechanisms of enamel maturation are less defined, and little is known about the molecules present beyond the maturation stage. Several genes, all located within the secreted calcium-binding phosphoprotein (SCPP) gene cluster, were recently shown to be expressed during the developmental continuum from maturation stage ameloblasts to junctional epithelium (JE). This review introduces four such genes and their protein products, and presents our current state of knowledge on their roles, primarily in enamel formation and JE biology. The discovery of these proteins, and a more detailed analysis of their biological functions, will likely contribute to a more thorough understanding of the molecular mechanisms of enamel maturation and dentogingival attachment.

Comparative studies between mice molars and incisors are required to draw an overview of enamel structural complexity.

In the field of dentistry, the murine incisor has long been considered as an outstanding model to study amelogenesis. However, it clearly appears that enamel from wild type mouse incisors and molars presents several structural differences. In incisor, exclusively radial enamel is observed. In molars, enamel displays a high level of complexity since the inner part is lamellar whereas the outer enamel shows radial and tangential structures. Recently, the serotonin 2B receptor (5-HT2BR) was shown to be involved in ameloblast function and enamel mineralization. The incisors from 5HT2BR knockout (KO) mice exhibit mineralization defects mostly in the outer maturation zone and porous matrix network in the inner zone. In the molars, the mutation affects both secretory and maturation stages of amelogenesis since pronounced alterations concern overall enamel structures. Molars from 5HT2BR KO mice display reduction in enamel thickness, alterations of inner enamel architecture including defects in Hunter-Schreger Bands arrangements, and altered maturation of the outer radial enamel. Differences of enamel structure were also observed between incisor and molar from other KO mice depleted for genes encoding enamel extracellular matrix proteins. Thus, upon mutation, enamel analysis based exclusively on incisor defects would be biased. In view of the functional relationship between enamel structure and tooth morphogenesis, identification of molecular actors involved in amelogenesis requires comparative studies between mice molars and incisors.

Analysis of enamel development using murine model systems: approaches and limitations.

A primary goal of enamel research is to understand and potentially treat or prevent enamel defects related to amelogenesis imperfecta (AI). Rodents are ideal models to assist our understanding of how enamel is formed because they are easily genetically modified, and their continuously erupting incisors display all stages of enamel development and mineralization. While numerous methods have been developed to generate and analyze genetically modified rodent enamel, it is crucial to understand the limitations and challenges associated with these methods in order to draw appropriate conclusions that can be applied translationally, to AI patient care. We have highlighted methods involved in generating and analyzing rodent enamel and potential approaches to overcoming limitations of these methods: (1) generating transgenic, knockout, and knockin mouse models, and (2) analyzing rodent enamel mineral density and functional properties (structure and mechanics) of mature enamel. There is a need for a standardized workflow to analyze enamel phenotypes in rodent models so that investigators can compare data from different studies. These methods include analyses of gene and protein expression, developing enamel histology, enamel pigment, degree of mineralization, enamel structure, and mechanical properties. Standardization of these methods with regard to stage of enamel development and sample preparation is crucial, and ideally investigators can use correlative and complementary techniques with the understanding that developing mouse enamel is dynamic and complex.

Enamel organic matrix: potential structural role in enamel and relationship to residual basement membrane constituents at the dentin enamel junction

Although mature enamel is predominantly composed of mineral, a previously uncharacterized organic matrix layer remains in the post-eruptive tissue that begins at the dentin enamel junction and extends 200–300 μm towards the outer tooth surface. Identification of the composition of this layer has been hampered by its insolubility; however, we have developed a single step method to isolate the organic enamel matrix relatively intact. After dissociative dissolution of the matrix with SDS and urea, initial characterization by Western blotting and gel zymography indicates the presence of type IV and type VII basement membrane collagens and active matrix metalloproteinase-20. When combined with data from transgenic knockout mice and from human mutations, these data suggest that the enamel organic matrix (EOM) and dentin enamel junction may have a structural and functional relationship with basement membranes, e.g. skin. To clarify this relationship, we hypothesize a “foundation” model which proposes that components of the EOM form a support structure that stabilizes the crystalline enamel layer, and bonds it to the underlying dentin along the dentin enamel junction. Since we have also co-localized an active matrix metalloproteinase to this layer, our hypothesis suggests that, under pathologic conditions, MMP-mediated degradation of the EOM could destabilize the enamel–dentin interface.

Evolution of Klk4 and enamel maturation in eutherians.

Kallikrein-related peptidase 4 (KLK4) is a secreted serine protease that degrades residual enamel proteins to facilitate their removal by ameloblasts, which increases mineralization and hardens the enamel. Mutations in human KLK4 cause hypomaturation amelogenesis imperfecta. Enamel formed by Klk4 null mice is normal in thickness and prism structure, but the enamel layer retains proteins, is hypomineralized, and undergoes rapid attrition following tooth eruption. We searched multiple databases, retrieved Klk4 and Klk5 from various mammalian genomes, and identified Klk4 in 46 boreoeutherian genomes. In non-Boreoeutheria, Klk4 was detected in only one afrotherian genome (as a pseudogene), and not in the other six afrotherian, two xenarthran, or three marsupial genomes. In contrast, Klk5 was detected in both marsupial and eutherian mammals. Our phylogenetic and mutation rate analyses support the hypothesis that Klk4 arose from Klk5 by gene duplication near the divergence of Afrotheria, Xenarthra and Boreoeutheria, and that functionally-differentiated Klk4 survived only in Boreoeutheria. Afrotherian mammals share the feature of delayed dental eruption relative to boreoeutherian mammals. KLK4 shortens the time required for enamel maturation and could have alleviated negative selection following mutations that resulted in thicker enamel or earlier tooth eruption, without reducing enamel hardness or causing dental attrition.

Itm2a expression in the developing mouse first lower molar, and the subcellular localization of Itm2a in mouse dental epithelial cells.

Itm2a is a type II transmembrane protein with a BRICHOS domain. We investigated the temporospatial mRNA and protein expression patterns of Itm2a in the developing lower first molar, and examined the subcellular localization of Itm2a in murine dental epithelial (mDE6) cells. From the initiation to the bud stage, the in situ and protein signals of Itm2a were not detected in either the dental epithelial or mesenchymal cells surrounding the tooth bud. However, at the bell stage, these signals of Itm2a were primarily observed in the inner enamel epithelium of the enamel organ. After the initiation of the matrix formation, strong signals were detected in ameloblasts and odontoblasts. Itm2a showed a punctate pattern in the cytoplasm of the mDE6 cells. The perinuclear-localized Itm2a displayed a frequent overlap with the Golgi apparatus marker, GM130. A tiny amount of Itm2a was colocalized with lysosomes and endoplasmic reticulum. Minimal or no overlap between the Itm2a-EGFP signals with the other organelle markers for endoplasmic reticulum, lysosome and mitochondria used in this study noted in the cytoplasm. These findings suggest that Itm2a may play a role in cell differentiation during odontogenesis, rather than during the initiation of tooth germ formation, and may be related to the targeting of proteins associated with enamel and dentin matrices in the secretory pathway.

EMMPRIN/CD147 deficiency disturbs ameloblast–odontoblast cross-talk and delays enamel mineralization

Tooth development is regulated by a series of reciprocal inductive signaling between the dental epithelium and mesenchyme, which culminates with the formation of dentin and enamel. EMMPRIN/CD147 is an Extracellular Matrix MetalloPRoteinase (MMP) INducer that mediates epithelial–mesenchymal interactions in cancer and other pathological processes and is expressed in developing teeth. Here we used EMMPRIN knockout (KO) mice to determine the functional role of EMMPRIN on dental tissue formation. We report a delay in enamel deposition and formation that is clearly distinguishable in the growing incisor and associated with a significant reduction of MMP-3 and MMP-20 expression in tooth germs of KO mice. Insufficient basement membrane degradation is evidenced by a persistent laminin immunostaining, resulting in a delay of both odontoblast and ameloblast differentiation. Consequently, enamel volume and thickness are decreased in adult mutant teeth but enamel maturation and tooth morphology are normal, as shown by micro-computed tomographic (micro-CT), nanoindentation, and scanning electron microscope analyses. In addition, the dentino-enamel junction appears as a rough calcified layer of approximately 10±5μm thick (mean±SD) in both molars and growing incisors of KO adult mice. These results indicate that EMMPRIN is involved in the epithelial-mesenchymal cross-talk during tooth development by regulating the expression of MMPs. The mild tooth phenotype observed in EMMPRIN KO mice suggests that the direct effect of EMMPRIN may be limited to a short time window, comprised between basement membrane degradation allowing direct cell contact and calcified matrix deposition.

Ionizing radiation effects on the secretory-stage ameloblasts and enamel organic extracellular matrix

This study assessed the effects of high doses of ionizing radiation on eruption rate, odontogenic region morphology, secretory-stage ameloblasts, and enamel organic extracellular matrix (EOECM) of rat maxillary incisors. For the study, 30 male rats were divided into three experimental groups: control (non-irradiated), irradiated by 15Gy, and irradiated by 25Gy. Irradiated groups received a single dose of 15 or 25Gy of X-rays in the head and neck region. The maxillary incisor eruption rate was measured. Sections of 5-µm thickness of the maxillary incisor odontogenic regions were evaluated using bright field light microscopy. Ultrathin sections of secretory ameloblasts and their EOECM were analyzed by transmission electron microscopy (TEM). Irradiated groups showed significantly diminished eruption rate values at the 4th and at the 6th day after irradiation. Reduced optical retardation values were observed in the irradiated groups. The odontogenic region of maxillary incisors from irradiated rats exhibited altered and poorly organized preameloblasts. TEM showed degeneration areas in the secretory-stage EOECM and several autophagosomes in the secretory ameloblasts from irradiated animals. In conclusion, high radiation doses delay eruption and induce disturbances in secretory ameloblasts and EOECM of rat maxillary incisors. These findings may be associated with structural defects of mature enamel.

Y‐chromosome amelogenin isoform peptides found in mature dental enamel (918.1)

The dental enamel is the hardest and most calcified tissue in the human body, and most of its structure is unaltered during the time the teeth stay in mouth. The best known enamel specific structural proteins are amelogenin, ameloblastin and enamelin. The ability to recover proteins has enormous value in many fields where the study of proteins preserved from the past could give specific information on diet, life style, and even of biochemical evolution of the proteins themselves, since such information is not encoded in the DNA. So far, only X‐chromosome amelogenin peptides (AMELX) were recovered from mature enamel. Since amelogenin is encoded in the X and Y chromosomes in humans, peptides specific for the Y chromosome might exist in the mature enamel, but they have never been found. In this study we aimed at recovering peptides from male and female teeth, with the objectives of 1) finding Y‐encoded amelogenin peptides (if expressed at all, which is not known at the protein level) and 2) describing the aminoacid sequences of mature dental enamel peptides. Results showed that the Y‐specific amelgonenin (AMELY) sequence WYQSMIRPPY is found in male teeth and that with the enamel etch technique used here followed by nLC/MS/MS, dozens of peptides that are specific for enamel proteins were found (3 AMELX isoforms, 1 AMELY isoform, ameloblastin and enamelin).This report opens a myriad of possibilities for studying both present and long‐gone species, since dental enamel is a well preserved repository where such peptides can be detected.Grant Funding Source: Supported by FAPESP (Brazil)

Fluctuations in surface pH of maturing rat incisor enamel are a result of cycles of H+‐secretion by ameloblasts and variations in enamel buffer characteristics (1098.1)

The large hydroxyapatite (HA) crystals in dental enamel results from a long lasting process called enamel maturation, which follows a stage of enamel matrix secretion. Thus, after the full thickness of enamel is reached, the enamel still requires about 60‐70 % mineral to be deposited by HA‐crystals growing in width and thickness. This is facilitated by the ameloblasts, which during maturation change morphology every 6‐8th hour. This study aims to test the role of the ameloblasts in maintaining enamel pH in the maturation zone in order to elucidate the role of the cyclic changes in ameloblast morphology for HA‐crystal growth.Colorimetric pH‐indicators and ratiometric fluorometry were used to measure surface pH in maturation zone enamel of rat incisors. Alternating acidic (down to pH 6.24±0.06) and alkaline zones (up to pH 7.34±0.08) corresponding to ruffled‐ended and smooth‐ended ameloblasts, respectively, were found along the tooth thus coinciding with ameloblast morphological cycles. Underlying the cyclic pattern, a gradual decrease in pH towards the incisal edge was seen. Vinblastine or FR167356 (H+‐ATPase‐inhibitor) disturbed ameloblast acid‐secretion, especially in the early parts of acidic zones.At the pH‐values observed, PO43‐ would be protonated (pKa >12) and HA dissolved. However, by molecular dynamics simulations we estimate the pKa of HPO42‐ at an ideal HA surface to be 4.3. The acidic pH measured at the enamel surface may thus only dissolve non‐perfect domains of HA crystals in which HPO42‐ is less electrostatically shielded. As a result of the repeated alkaline/acidic cycles induced by ameloblasts, near‐perfect domains will therefore gradually replace less perfect domains and large near‐perfect HA crystals will be produced.In conclusion, fluctuations in surface pH of maturing rat incisor enamel are a result of cycles of H+‐secretion by ameloblasts and variations in enamel buffer characteristics.

Mature dental enamel: a diverse repository of past and present information (918.2)

Dental enamel is the hardest, densest, and most mineralized tissue in vertebrates. It achieved its very high crystallinity with evolution of enamel specific proteins for more than 500 million years. During enamel formation (still inside the jaw bones), the proteins are degraded by the enamel‐resident proteinases and eventually “mature” enamel contains less than 0.1% of proteins 96% of minerals. This pre‐fossilized rocky tissue is essential for proper nutrition and survival, even today.The past century witnessed the characterization of 3 enamel structural proteins and 2 enamel proteinases, achieved by cumbersome work with samples of thousands of developing teeth to obtain micrograms of protein for mass spectrometry analyses and Edman degradation. Newer equipments enable today that hundreds of different peptides from all 3 enamel proteins can be obtained from enamel acid extracts, obtained with a much less invasive procedure compared to the ones used before. Mammal´s mature enamel harbors Y‐chromosome amelogenin specific peptides that allow the determination of sex, which we show at the EB2014 for the first time in humans samples. Enamel is also a good biomarker for toxic metals like lead and cadmium. Superficial enamel etch (for 2 minutes) was sufficient to obtain enamel specific peptides from shed primary teeth. Thus, dental enamel is an immense and diverse repository with relevant information for paleontology, archaeology, forensics, toxicology, medicine and developmental biology.Grant Funding Source: Supported by FAPESP (Brazil)

Bacterial Profile of Dentine Caries and the Impact of pH on Bacterial Population Diversity

Dental caries is caused by the release of organic acids from fermentative bacteria, which results in the dissolution of hydroxyapatite matrices of enamel and dentine. While low environmental pH is proposed to cause a shift in the consortium of oral bacteria, favouring the development of caries, the impact of this variable has been overlooked in microbial population studies. This study aimed to detail the zonal composition of the microbiota associated with carious dentine lesions with reference to pH. We used 454 sequencing of the 16S rRNA gene (V3–V4 region) to compare microbial communities in layers ranging in pH from 4.5–7.8 from 25 teeth with advanced dentine caries. Pyrosequencing of the amplicons yielded 449,762 sequences. Nine phyla, 97 genera and 409 species were identified from the quality-filtered, de-noised and chimera-free sequences. Among the microbiota associated with dentinal caries, the most abundant taxa included Lactobacillus sp., Prevotella sp., Atopobium sp., Olsenella sp. and Actinomyces sp. We found a disparity between microbial communities localised at acidic versus neutral pH strata. Acidic conditions were associated with low diversity microbial populations, with Lactobacillus species including L. fermentum, L. rhamnosus and L. crispatus, being prominent. In comparison, the distinctive species of a more diverse flora associated with neutral pH regions of carious lesions included Alloprevotella tanerrae, Leptothrix sp., Sphingomonas sp. and Streptococcus anginosus. While certain bacteria were affected by the pH gradient, we also found that ∼60% of the taxa associated with caries were present across the investigated pH range, representing a substantial core. We demonstrated that some bacterial species implicated in caries progression show selective clustering with respect to pH gradient, providing a basis for specific therapeutic strategies.

STIM1 and SLC24A4 Are Critical for Enamel Maturation

Dental enamel formation depends upon the transcellular transport of Ca2+ by ameloblasts, but little is known about the molecular mechanism, or even if the same process is operative during the secretory and maturation stages of amelogenesis. Identifying mutations in genes involved in Ca2+ homeostasis that cause inherited enamel defects can provide insights into the molecular participants and potential mechanisms of Ca2+ handling by ameloblasts. Stromal Interaction Molecule 1 (STIM1) is an ER transmembrane protein that activates membrane-specific Ca2+ influx in response to the depletion of ER Ca2+ stores. Solute carrier family 24, member 4 (SLC24A4), is a Na+/K+/Ca2+ transporter that exchanges intracellular Ca2+ and K+ for extracellular Na+. We identified a proband with syndromic hypomaturation enamel defects caused by a homozygous C to T transition (g.232598C>T c.1276C>T p.Arg426Cys) in STIM1, and a proband with isolated hypomaturation enamel defects caused by a homozygous C to T transition (g.124552C>T; c.437C>T; p.Ala146Val) in SLC24A4. Immunohistochemistry of developing mouse molars and incisors showed positive STIM1 and SLC24A4 signal specifically in maturation-stage ameloblasts. We conclude that enamel maturation is dependent upon STIM1 and SLC24A4 function, and that there are important differences in the Ca2+ transcellular transport systems used by secretory- and maturation-stage ameloblasts.

New insights into the functions of enamel matrices in calcified tissues

Ameloblasts secrete enamel matrix proteins, including amelogenin, ameloblastin, enamelin, amelotin, and Apin/odontogenic ameloblast-associated protein (Apin/ODAM). Amelogenin is the major protein component of the enamel matrix. Amelogenin, ameloblastin, and enamelin are expressed during the secretory stage of ameloblast, while amelotin and Apin/ODAM are expressed during the maturation. Amelogenin and ameloblastin are also expressed in osteoblasts, and they regulate bone formation. In addition, recent studies show the importance of protein–protein interactions between enamel matrix components for enamel formation. In a mouse model mimicking a mutation of the amelogenin gene in amelogenesis imperfect (AI) in humans, the mutated amelogenin forms a complex with ameloblastin, which accumulates in the endoplasmic reticulum/Golgi apparatus and causes ameloblast dysfunction resulting in AI phenotypes. Ameloblastin is a cell adhesion molecule that regulates cell proliferation. It inhibits odontogenic tumor formation and regulates osteoblast differentiation through binding to CD63. Amelotin interacts with Apin/ODAM, but not ameloblastin, while Apin/ODAM binds to ameloblastin. These interactions may be important for enamel mineralization during amelogenesis. The enamel matrix genes are clustered on human chromosome 4 except for the amelogenin genes located on the sex chromosomes. Genes for these enamel matrix proteins evolved from a common ancestral gene encoding secretory calcium-binding phosphoprotein.

Oral Problems And Treatment Needs of Adults and Children With Sickle Cell Anemia

The oral problems and treatment needs of adults and children with sickle cell anemia were investigated. Study Design: This cross-sectional study was approved by the research ethics committee of the University Center Cesmac and conducted at the Public Blood Center of Alagoas/Brazil. A questionnaire was administered and examinations were performed. Oral conditions were recorded in accordance with the World Health Organization (WHO) evaluation form. Results: A total of 34 children and 12 adults, all of little education and low socioeconomic class, were examined. All of the patients had pallor of the oral mucosa. In 10 children enamel maturation defects were observed. Although malocclusion has been found, the major problems for these patients remain periodontal diseases and dental caries. Dental restoration is the major treatment need. Conclusions: It is important maintain oral health in order to reduce the risks of dental problems when treating these patients.

Estimating Mineral Changes in Enamel Formation by Ashing/BSE and MicroCT

Enamel formation produces the most highly mineralized tissue in the human body. The growth of enamel crystallites is assisted by enamel proteins and proteinases. As enamel formation progresses from secretory to maturation stages, the composition of the matrix with its mineral and non-mineral components dynamically changes in an inverse fashion. We hypothesized that appropriately calibrated micro-computed tomography (µCT) technology is suitable to estimate the mineral content (weight and/or density) and volume comparable in accuracy with that for directly weighed and sectioned enamel. Different sets of mouse mandibular incisors of C57BL/6 mice were used for dissections and µCT reconstructions. Calibration phantoms corresponding to the range of enamel mineral densities were used. Secretory-stage enamel contained little mineral and was consequently too poor in contrast for enamel volumes to be accurately estimated by µCT. Maturation-stage enamel, however, showed remarkable correspondence for total mineral content per volume where comparisons were possible between and among the different analytical techniques used. The main advantages of the µCT approach are that it is non-destructive, time-efficient, and can monitor changes in mineral content of the most mature enamel, which is too physically hard to dissect away from the tooth.

Genome-wide analysis of miRNA and mRNA transcriptomes during amelogenesis.

BackgroundIn the rodent incisor during amelogenesis, as ameloblast cells transition from secretory stage to maturation stage, their morphology and transcriptome profiles change dramatically. Prior whole genome transcriptome analysis has given a broad picture of the molecular activities dominating both stages of amelogenesis, but this type of analysis has not included miRNA transcript profiling. In this study, we set out to document which miRNAs and corresponding target genes change significantly as ameloblasts transition from secretory- to maturation-stage amelogenesis.ResultsTotal RNA samples from both secretory- and maturation-stage rat enamel organs were subjected to genome-wide miRNA and mRNA transcript profiling. We identified 59 miRNAs that were differentially expressed at the maturation stage relative to the secretory stage of enamel development (False Discovery Rate (FDR) < 0.05, fold change (FC) ≥ 1.8). In parallel, transcriptome profiling experiments identified 1,729 mRNA transcripts that were differentially expressed in the maturation stage compared to the secretory stage (FDR < 0.05, FC ≥1.8). Based on bioinformatics analyses, 5.8% (629 total) of these differentially expressed genes (DEGS) were highlighted as being the potential targets of 59 miRNAs that were differentially expressed in the opposite direction, in the same tissue samples. Although the number of predicted target DEGs was not higher than baseline expectations generated by examination of stably expressed miRNAs, Gene Ontology (GO) analysis showed that these 629 DEGS were enriched for ion transport, pH regulation, calcium handling, endocytotic, and apoptotic activities. Seven differentially expressed miRNAs (miR-21, miR-31, miR-488, miR-153, miR-135b, miR-135a and miR298) in secretory- and/or maturation-stage enamel organs were confirmed by in situ hybridization. Further, we used luciferase reporter assays to provide evidence that two of these differentially expressed miRNAs, miR-153 and miR-31, are potential regulators for their predicated target mRNAs, Lamp1 (miR-153) and Tfrc (miR-31).ConclusionsIn conclusion, these data indicate that miRNAs exhibit a dynamic expression pattern during the transition from secretory-stage to maturation-stage tooth enamel formation. Although they represent only one of numerous mechanisms influencing gene activities, miRNAs specific to the maturation stage could be involved in regulating several key processes of enamel maturation by influencing mRNA stability and translation.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-998) contains supplementary material, which is available to authorized users.

A rare case of bilateral complex odontomas: Clinical, radiological and histopathological findings

Odontoma is the most common odontogenic tumor that is radiographically and histologically characterized by the production of mature enamel, dentin, cementum and pulp tissue. It grows slowly and has nonaggressive behavior. This case report presents clinical, radiological and pathological findings of bilateral complex odontoma that is rarely in literature in a 30-year-old female patient.

Fluctuations in surface pH of maturing rat incisor enamel are a result of cycles of H+-secretion by ameloblasts and variations in enamel buffer characteristics

It is disputed if ameloblasts in the maturation zone of the enamel organ mainly buffer protons released by hydroxyapatite (HA) crystal growth or if they periodically secrete protons to create alternating acidic and alkaline conditions. The latter hypothesis predicts alternating pH regimes in maturing enamel, which would be affected by pharmacological interference with ameloblast H+-secretion. This study tests these predictions.Colorimetric pH-indicators and ratiometric fluorometry were used to measure surface pH in maturation zone enamel of rat incisors. Alternating acidic (down to pH6.24±0.06) and alkaline zones (up to pH7.34±0.08) were found along the tooth coinciding with ameloblast morphological cycles. Underlying the cyclic pattern, a gradual decrease in pH towards the incisal edge was seen. Vinblastine or FR167356 (H+-ATPase-inhibitor) disturbed ameloblast acid-secretion, especially in the early parts of acidic zones.Enamel surface pH reflects the titration state of surface PO43−-ions. At the pH-values observed, PO43− would be protonated (pKa>12) and HA dissolved. However, by molecular dynamics simulations we estimate the pKa of HPO42− at an ideal HA surface to be 4.3. The acidic pH measured at the enamel surface may thus only dissolve non-perfect domains of HA crystals in which PO43− is less electrostatically shielded. During repeated alkaline/acidic cycles, near-perfect HA-domains may therefore gradually replace less perfect HA-domains resulting in near-perfect HA-crystals.In conclusion, cyclic changes in ameloblast H+-secretion and the degree of enamel maturation determine enamel surface pH. This is in accordance with a hypothesis implicating H+-ATPase mediated acid-secretion by ameloblasts.