Defective Enamel Formation Research Articles

Comprehensive Interdisciplinary Approach to Restorative Dentistry for Patients under 18 with Amelogenesis Imperfecta

Amelogenesis imperfecta (AI) is a genetically inherited disorder characterized by defective enamel formation, posing a significant challenge in esthetic treatment for clinicians. The choice of an appropriate treatment modality is largely dictated by the specific type of AI. This paper aims to elaborate on therapeutic options available for patients under 18 with amelogenesis imperfecta, emphasizing a multidisciplinary treatment approach.

The management of patients with amelogenesis imperfecta

Amelogenesis imperfecta (AI) refers to a genetically based hereditary disorder characterized by defective enamel formation. Esthetic treatment of patients with AI presents a challenge in clinical practice. the practitioner should select the appropriate treatment modality, which is determined mostly by the type of AI. In this paper we will detail the therapeutic options for patients with amelogenesis imperfecta depending on the type of damage.

Adam10-dependent Notch signaling establishes dental epithelial cell boundaries required for enamel formation

SummaryThe disintegrin and metalloproteinase Adam10 is a membrane-bound sheddase that regulates Notch signaling and ensures epidermal integrity. To address the function of Adam10 in the continuously growing incisors, we used Keratin14Cre/+;Adam10fl/fl transgenic mice, in which Adam10 is conditionally deleted in the dental epithelium. Keratin14Cre/+;Adam10fl/fl mice exhibited severe abnormalities, including defective enamel formation reminiscent of human enamel pathologies. Histological analyses of mutant incisors revealed absence of stratum intermedium, and severe disorganization of enamel-secreting ameloblasts. In situ hybridization and immunostaining analyses in the Keratin14Cre/+;Adam10fl/fl incisors showed strong Notch1 downregulation in dental epithelium and ectopic distribution of enamel-specific molecules, including ameloblastin and amelogenin. Lineage tracing studies using Notch1CreERT2;R26mT/mG mice demonstrated that loss of the stratum intermedium cells was due to their fate switch toward the ameloblast lineage. Overall, our data reveal that in the continuously growing incisors the Adam10/Notch axis controls dental epithelial cell boundaries, cell fate switch and proper enamel formation.

Dental enamel defects predict adolescent health indicators: A cohort study among the Tsimane' of Bolivia.

Bioarchaeological findings have linked defective enamel formation in preadulthood with adult mortality. We investigated how defective enamel formation in infancy and childhood is associated with risk factors for adult morbidity and mortality in adolescents. This cohort study of 349 Amerindian adolescents (10-17 years of age) related extent of enamel defects on the central maxillary incisors (none, less than 1/3, 1/3 to 2/3, more than 2/3) to adolescent anthropometrics (height, weight) and biomarkers (hemoglobin, glycated hemoglobin, white blood cell count, and blood pressure). Risk differences and 95% confidence intervals were estimated using multiple linear regression. Enamel defects and stunted growth were compared in their ability to predict adolescent health indicators using log-binomial regression and receiver operating characteristics (ROCs). Greater extent of defective enamel formation on the tooth surface was associated with shorter height (-1.35 cm, 95% CI: -2.17, -0.53), lower weight (-0.98 kg, 95% CI: -1.70, -0.26), lower hemoglobin (-0.36 g/dL, 95% CI: -0.59, -0.13), lower glycated hemoglobin (-0.04 %A1c , 95% CI: -0.08, -0.00008), and higher white blood cell count (0.74 109 /L, 95% CI: 0.35, 1.14) in adolescence. Extent of enamel defects and stunted growth independently performed similarly as risk factors for adverse adolescent outcomes, including anemia, prediabetes/type II diabetes, elevated WBC count, prehypertension/hypertension, and metabolic health. Defective enamel formation in infancy and childhood predicted adolescent health outcomes and may be primarily associated with infection. Extent of enamel defects and stunted growth may be equally predictive of adverse adolescent health outcomes.

Impacto emocional y en calidad de vida de individuos afectados por amelogénesis imperfecta

“Amelogenesis imperfecta” (AI) (prevalence up to 1 in 700) describes largely Mendelian enamel defects arising from gene mutations that present as structural abnormalities of the temporary and permanent teeth as a result of defective enamel formation. AI has a wide range of clinical presentations and phenotypes and affects both sexes. Despite increasing knowledge of the genetic mutations underlying AI there has been little research focussing on the effect of AI on the quality of life of AI patients. This study aimed to investigate the effects of AI on patient quality of life in a Costa Rican AI cohort. Affected family members were interviewed and their experiences used to develop an instrument (questionnaire) that was subsequently used to evaluate the impact of AI on their quality of life. 18 AI patients from 17 families were included in the study. Our findings showed that 100% had been teased and had suffered social rejection; 77.8% were concerned about their children´s inheritance and 66.7 % were concerned by the cost of treatment; 89% placed a high importance on their teeth. Results were not statistically significant when sorted by sex (p = 0.732). The results of this study indicate that dental professionals need to understand AI not only as defective tooth enamel structure demanding specialist clinical management but also the negative impacts of the condition on the lives of their patients. This should be taken in to account when communicating with those affected.

A solution NMR investigation into the impaired self-assembly properties of two murine amelogenins containing the point mutations T21→I or P41→T

Amelogenesis imperfecta describes a group of inherited disorders that results in defective tooth enamel. Two disorders associated with human amelogenesis imperfecta are the point mutations T21→I or P40→T in amelogenin, the dominant protein present during the early stages of enamel biomineralization. The biophysical properties of wildtype murine amelogenin (M180) and two proteins containing the equivalent mutations in murine amelogenin, T21→I (M180-I) and P41→T (M180-T), were probed by NMR spectroscopy. At low protein concentration (0.1mM), M180, M180-I, and M180-T are predominately monomeric at pH 3.0 in 2% acetic acid and neither mutation produces a major structural change. Chemical shift perturbation studies as a function of protein (0.1–1.8mM) or NaCl (0–400mM) concentrations show that the mutations affect the self-association properties by causing self-assembly at lower protein or salt concentrations, relative to wildtype amelogenin, with the largest effect observed for M180-I. Under both conditions, the premature self-assembly is initiated near the N-terminus, providing further evidence for the importance of this region in the self-assembly process. The self-association of M180-I and M180-T at lower protein concentrations and lower ionic strengths than wildtype M180 may account for the clinical phenotypes of these mutations, defective enamel formation.

Amelogenesis imperfecta: A clinician′s challenge

Defective enamel formation can be explained as defects occurring at the stages of enamel formation. Quantitative defects in matrix formation leads to hypoplastic form of amelogenesis imperfecta. Inadequate mineralization of matrix leads to hypocalcification and hypomaturation variants. The demarcation of matrix formation and mineralization is not so distinct. This paper describes a case of a 7-year-old boy with amelogenesis imperfecta - Type IA i.e., hypoplastic pitted autosomal dominant.

Perturbed Amelogenin Secondary Structure Leads to Uncontrolled Aggregation in Amelogenesis Imperfecta Mutant Proteins

Mutations in amelogenin sequence result in defective enamel, and the diverse group of genetically altered conditions is collectively known as amelogenesis imperfecta (AI). Despite numerous studies, the detailed molecular mechanism of defective enamel formation is still unknown. In this study, we have examined the biophysical properties of a recombinant murine amelogenin (rM180) and two point mutations identified from human DNA sequences in two cases of AI (T21I and P41T). At pH 5.8 and 25 °C, wild type (WT) rM180 and mutant P41T existed as monomers, and mutant T21I formed lower order oligomers. CD, dynamic light scattering, and fluorescence studies indicated that rM180 and P41T can be classified as a premolten globule-like subclass protein at 25 °C. Thermal denaturation and refolding monitored by CD ellipticity at 224 nm indicated the presence of a strong hysteresis in mutants compared with WT. Variable temperature tryptophan fluorescence and dynamic light scattering studies showed that WT transformed to a partially folded conformation upon heating and remained stable. The partially folded conformation formed by P41T, however, readily converted into a heterogeneous population of aggregates. T21I existed in an oligomeric state at room temperature and, upon heating, rapidly formed large aggregates over a very narrow temperature range. Thermal denaturation and refolding studies indicated that the mutants are less stable and exhibit poor refolding ability compared with WT rM180. Our results suggest that alterations in self-assembly of amelogenin are a consequence of destabilization of the intrinsic disorder. Therefore, we propose that, like a number of other human diseases, AI appears to be due to the destabilization of the secondary structure as a result of amelogenin mutations.

Oral health in Autoimmune Polyendocrinopathy Candidiasis Ectodermal Dystrophy (APECED)

APECED (Autoimmune Polyendocrinopathy Candidiasis Ectodermal Dystrophy) is a rare autosomal recessive disease characterised primarily by sequential immune-mediated destruction of endocrine tissues, chronic oral or mucocutaneous candidiasis and ectodermal disorders, including hypoplasia of dental enamel. This was to investigate the oral health and presence of enamel defects in a cohort of patients with APECED. 16 patients with APECED (mean age of 13.9 years) were matched for age and gender with healthy controls. A comprehensive medical, dental and drug history was recorded, followed by a clinical assessment of oral health which was determined by assessing periodontal treatment needs, prevalence of dental caries, erosion, fluorosis and enamel defects. The estimated time of the development of the enamel defects and the contemporaneous medical diagnosis were recorded. Oral health of patients with APECED was poor compared with controls, with a higher prevalence of periodontal disease, caries and erosion. There was a significantly (P < 0.05) higher prevalence of enamel defects in the study group. The enamel defects were mostly hypoplastic in the form of pits, missing enamel and grooves. The enamel defects occurred in a chronological pattern. There was a strong association between the estimated time of defective enamel formation and a history of hypoparathyroidism. Gastrointestinal dysfunction and a history of chronic mucocutaneous candidiasis were also associated with the presence of enamel defects. The oral health of individuals with APECED was poor compared with controls with a higher prevalence of periodontal disease, caries, erosion and enamel defects. The enamel defects in the study population occurred in a chronological pattern and some were associated with a history of systemic disease during the period of tooth development.

The cell adhesion molecule nectin-1 is critical for normal enamel formation in mice

Nectin-1 is a member of a sub-family of immunoglobulin-like adhesion molecules and a component of adherens junctions. In the current study, we have shown that mice lacking nectin-1 exhibit defective enamel formation in their incisor teeth. Although the incisors of nectin-1-null mice were hypomineralized, the protein composition of the enamel matrix was unaltered. While strong immunostaining for nectin-1 was observed at the interface between the maturation-stage ameloblasts and the underlying cells of the stratum intermedium (SI), its absence in nectin-1-null mice correlated with separation of the cell layers at this interface. Numerous, large desmosomes were present at this interface in wild-type mice; however, where adhesion persisted in the mutant mice, the desmosomes were smaller and less numerous. Nectins have been shown to regulate tight junction formation; however, this is the first report showing that they may also participate in the regulation of desmosome assembly. Importantly, our results show that integrity of the SI–ameloblast interface is essential for normal enamel mineralization.

Perturbed Amelogenin Protein Self-assembly Alters Nanosphere Properties Resulting in Defective Enamel Formation

AbstractDental enamel is a unique composite bioceramic material that is the hardest tissue in the vertebrate body, containing long-, thin-crystallites of substituted hydroxyapatite. Enamel functions under immense loads in a bacterial-laden environment, and generally without catastrophic failure over a lifetime for the organism. Unlike all other biogenerated hard tissues of mesodermal origin, such as bone and dentin, enamel is produced by ectoderm-derived cells called ameloblasts. Recent investigations on the formation of enamel using cell and molecular approaches have been coupled to biomechanical investigations at the nanoscale and mesoscale levels. For amelogenin, the principle protein of forming enamel, two domains have been identified that are required for the proper assembly of multimeric units of amelogenin to form nanospheres. One domain is at the amino-terminus and the other domain in the carboxyl-terminal region. Amelogenin nanospheres are believed to influence the hydroxyapatite crystal habit. Both the yeast two-hybrid assay and surface plasmon resonance have been used to examine the assembly properties of engineered amelogenin proteins. Amelogenin protein was engineered using recombinant DNA techniques to contain deletions to either of the two self-assembly domains. Amelogenin protein was also engineered to contain single amino-acid mutations/substitutions in the amino-terminal self-assembly domain; and these amino-acid changes are based upon point mutations observed in humans affected with a hereditary disturbance of enamel formation. All of these alterations reveal significant defects in amelogenin self-assembly into nanospheres in vitro. Transgenic animals containing these same amelogenin deletions illustrate the importance of a physiologically correct bio-fabrication of the enamel protein extracellular matrix to allow for the organization of the enamel prismatic structure.

Analysis of self-assembly and apatite binding properties of amelogenin proteins lacking the hydrophilic C-terminal.

Amelogenins, the major protein component of the mineralizing enamel extracellular matrix, are critical for normal enamel formation as documented in the linkage studies of a group of inherited disorders, with defective enamel formation, called Amelogenesis imperfecta. Recent cases of Amelogenesis imperfecta include mutations that resulted in truncated amelogenin protein lacking the hydrophilic C-terminal amino acids. Current advances in knowledge on amelogenin structure, nanospheres assembly and their effects on crystal growth have supported the hypothesis that amelogenin nanospheres provide the organized microstructure for the initiation and modulated growth of enamel apatite crystals. In order to evaluate the function of the conserved hydrophilic C-terminal telopeptide during enamel biomineralization, the present study was designed to analyze the self-assembly and apatite binding behavior of amelogenin proteins and their isoforms lacking the hydrophilic C-terminal. We applied dynamic light scattering to investigate the size distribution of amelogenin nanospheres formed by a series of native and recombinant proteins. In addition, the apatite binding properties of these amelogenins were examined using commercially available hydroxyapatite crystals. Amelogenins lacking the carboxy-terminal (native P161 and recombinant rM166) formed larger nanospheres than those formed by their full-length precursors: native P173 and recombinant rM179. These data suggest that after removal of the hydrophilic carboxy-terminal segment further association of the nanospheres takes place through hydrophobic interactions. The affinity of amelogenins lacking the carboxy-terminal regions to apatite crystals was significantly lower than their parent amelogenins. These structure-functional analyses suggest that the hydrophilic carboxy-terminal plays critical functional roles in mineralization of enamel and that the lack of this segment causes abnormal mineralization.

Dental disease of sheep

Extract Dental abnormalities of sheep are common and in many parts of the world are the main reason for culling otherwise-healthy breeding ewes before the end of their natural reproductive life, leading to increased flock replacement costs. Excessive incisor-tooth wear and periodontal disease are considered the two most important syndromes affecting sheep's teeth and their supporting structures; less commonly, problems of occlusion or bite, defective enamel formation, caries, fluorosis, and odontogenic cysts also occur (West and Spence 2000).

Detection of a novel mutation in X-linked amelogenesis imperfecta.

Amelogenesis imperfecta (AI) is a heterogeneous group of inherited disorders of defective enamel formation. The major protein involved in enamel formation, amelogenin, is encoded by a gene located at Xp22.1-Xp22.3. This study investigated the molecular defect producing a combined phenotype of hypoplasia and hypomineralization in a family with the clinical features and inheritance pattern of X-linked amelogenesis imperfecta (XAI). Genomic DNA was prepared from buccal cells sampled from family members. The DNA was subjected to the polymerase chain-reaction (PCR) in the presence of a series of oligonucleotide primers designed to amplify all 7 exons of the amelogenin gene. Cloning and sequencing of the purified amplification products identified a cytosine deletion in exon VI at codon 119. The deletion resulted in a frameshift mutation, introducing a premature stop signal at codon 126, producing a truncated protein lacking the terminal 18 amino acids. Identifying mutations assists our understanding of the important functional domains within the gene, and finding another novel mutation emphasizes the need for family-specific diagnosis of amelogenesis imperfecta.

Localised enamel hypoplasia of human deciduous canines: genotype or environment?

A discrete area of defective enamel formation that appears on the labial surface of the crowns of deciduous canine teeth has been described in both recent and prehistoric human populations, with reported frequencies varying from 1 to 45 per cent. Suggestions about the aetiology of this localized hypoplasia range from genotypic factors to environmental conditions and systemic effects. The major aims of this study were to describe the frequency of occurrence and pattern of expression of the lesion in Australian Aboriginal and Caucasian ethnic groups, and to clarify the role of genetic factors by examining a sample of twins. The study sample consisted of dental casts of 181 pairs of Australian Caucasian twins, 215 Aborigines and 122 Caucasian singletons, together with 253 extracted deciduous canines. Examination of dental casts and extracted teeth was undertaken under 2x magnification with emphasis being placed upon location and expression of the lesion. The defect was observed in 49 per cent of twins and 44 per cent of Aborigines, but only 36 per cent of singletons. The percentages of affected teeth in each group were: 18 per cent in twins, 17 per cent in Aborigines and 13 per cent in Caucasians. A significant proportion of the defects occurred on the mesial aspect of the labial surface, in the middle area incisocervically, with the majority in the lower jaw. A number of significant differences in frequency were observed between groups, sexes, arches and sides. The results confirm some of the findings of previous studies, but also suggest that none of environmental, genetic or systemic factors can be ruled out as being involved in aetiology of the defect. The higher incidence of the lesion occurring on the mesial aspect of the labial surface is suggestive of physical trauma. Also, the vulnerability of the prominent developing mandibular canine, with its thin or missing labial covering of bone, would be expected to lead to higher prevalence of the lesion in the lower jaw. Although not definitive, the results of concordance analyses in twins were suggestive of a possible genetic predisposition in the formation of the lesion. Further research with a greater clinical orientation and emphasis on determining specific aetiological factors within any given environment in different ethnic groups may provide better insight into the ambiguous aetiology of the hypoplastic enamel defect.

PENATALAKSANAAN GIGI HIPOPLASIA EMAIL

Enamel hypoplasia is a defect in the formation of the enamel matrix, cause enamel surface defects and irregularities. The defective enamel formation may be caused by systemic or local factors. The clinical features of enamel hypoplasia may be thin enamel groove or pit of surface enamel. The conditions of the primary or permanent dentition considerably disturb for the tooth function, tooth sensitivity and poor esthetics. For the pediatric dentist, the long term aim of treatment is to maintain the maximum amount of hard dental tissue possible until the patient reaches an age at which advanced restorative techniques can be employed to rehabilitate the dentition. However, in the short term, it is frequently necessary to intervene to relieve the patient's symptoms o sensitivity, to improve esthetics, and to prevent the loss of vertical dimension.

Multisystem disorder of Punjabi children exhibiting spontaneous dermal and submucosal granulation tissue formation

We describe a multisystem disease that affects children of Muslim families originating in the Punjab region of Pakistan and India. An altered cry due to vocal cord thickening, skin ulceration, nail abnormalities, and conjunctival scarring appear in the first few months of life. Progression and spread of the disease in these sites may be accompanied by involvement of other epithelial surfaces. The teeth may exhibit defective enamel formation. Histology reveals the formation of simple granulation tissue arising in the dermis and submucosa which become massively thickened and ulcerated. There is good evidence for an autosomal recessive gene defect, but the actual mechanism of the disease is not known. Medical and surgical therapy have been ineffective in altering the course of this devastating and usually fatal condition. We suggest the term LOGIC (laryngeal and ocular granulation tissue in children from the Indian subcontinent) for this newly established disease.

Tetracyclines stain children’s teeth

It has been known for over ten years that tetracyclines can stain children’s teeth.1 More recently defective enamel formation has also been reported in children.2 3 Should this affect the use of tetracyclines in pregnant women and in children?