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Dental enamel formation and its impact on clinical dentistry.

The nature of tooth enamel is of inherent interest to dental professionals. The current-day clinical practice of dentistry involves the prevention of enamel demineralization, the promotion of enamel remineralization, the restoration of cavitated enamel where demineralization has become irreversible, the vital bleaching of dental enamel that has become discolored, and the diagnosis and treatment of developmental enamel malformations, which can be caused by environmental or genetic factors. On a daily basis, dental health providers make diagnostic and treatment decisions that are influenced by their understanding of tooth formation. A systemic condition during tooth development, such as high fever, can produce a pattern of enamel defects in the dentition. Knowing the timing of tooth development permits estimates about the timing of the disturbance. The process of enamel maturation continues following tooth eruption, so that erupted teeth can become less susceptible to decay over time. Mutations in the genes encoding enamel proteins lead to amelogenesis imperfecta, a collection of inherited diseases having enamel malformations as the predominant phenotype. Defects in the amelogenin gene cause X-linked amelogenesis imperfecta, and genes encoding other enamel proteins are candidates for autosomal forms. Here we review our current understanding of dental enamel formation, and relate this information to clinical circumstances where this understanding may be particularly relevant.

Amelogenesis↗

Association of Streptococcus mutans infection and oral developmental nodules in pre-dentate infants.

Since dental caries may present soon after tooth eruption, we hypothesized that colonization of Streptococcus mutans can occur in the predentate stages. In this study, we examined S. mutans colonization and its association with oral developmental nodules (Bohn's nodules) in 60 pre-term and 128 full-term, three-month-old infants. Overall, S. mutans was cultured from 30% (56/188) of the infants, and oral developmental nodules were noted in 55% (103/188). Compared with the pre-term, full-term infants showed a higher prevalence of S. mutans (34% vs. 20%, p < 0.02) as well as developmental nodules (61% vs. 42%, p < 0.05). In both groups, S. mutans was positively associated with numbers of developmental nodules in a dose-response relationship (p < 0.001), and with maternal salivary levels of the bacteria (p = 0.03). The permanence of S. mutans infection was confirmed by repeat saliva sampling at 6 months of age. Our results thus showed that many infants have already acquired S. mutans at 3 months of age, prior to tooth eruption.

Alveolar Process↗

Evaluation of oral and systemic manifestations in an amelogenesis imperfecta population.

OBJECTIVES: The aim of this investigation was to describe the dental and craniofacial characteristics of patients with amelogenesis imperfecta (AI). METHODS: The study group included 43 patients(33 female and 10 male) with a mean age of 11.4+/-2.6 years. A panoramic and a cephalometric radiograph were obtained from each of these patients. Clinically AI cases were divided into four main groups according to Witkop. All patients were evaluated for chronological, bone and dental age. The patients who had severe retarded bone age were evaluated for plasma growth hormone(GH) concentrations. RESULTS: Dental and bone ages were retarded with respect to chronological age in five patients. Dental maturity and tooth eruption were not age- appropriate in some of our patients. In type III AI patients a delay in skeletal age was observed. Severe late eruption was seen in 3 patients, severe delay in dental maturity was noted in patients with type IV AI. Dental age was clinically lower in GH-deficient subjects, and skeletal age was consistently more retarded than dental age when compared to chronological age. Anterior open bite was present in both primary and permanent dentitions of 50% of the patients with type I AI, 30.8% of the patients with type II AI, and 60% of type III AI. CONCLUSION: It is concluded that the primary structure for the classification of AI be based on the mode of inheritance, with the clinical and radiographic appearances (and any other features such as systemic findings) being the secondary discriminators.

Age Determination by Skeleton↗

Growth and development considerations in the diagnosis of gingivitis and periodontitis in children.

Increasing information emphasize the relevance of the prevention, early diagnosis and early treatment of periodontal diseases in children. In order to avoid erroneous diagnosis and unnecessary treatments, the pediatric dentist is required to differentiate between pathologic processes and normal changes that take place in the periodontum with age. The present review outlines structural and functional changes of the periodontal structures, the establishment and maturation of the oral microflora and immune defense reactions to periodontal pathogens in children and adolescents. The age-related tendency to develop gingivitis, that is evident in children and adolescents, may be related to changes in the bacterial composition of the dental plaque, the inflammatory cell response, hormonal changes, morphological differences, tooth eruption and shedding. The hormonal influence on the gingival tissues and the composition of the dental plaque are of particular relevance during puberty. Large ranges for the prevalence of attachment loss, periodontitis or destructive periodontal disease in children and adolescents have been reported. The variance in values may be related to population characteristics, method of examination or diagnostic criteria that may include measurements of attachment loss and distances from the cementoenamel junction to the alveolar bone crest, both of which may be either physiological or pathological. The pediatric dentist should be able to diagnose gingival inflammation, attachment loss or distances from the cementoenamel junction to the alveolar crest which are out of proportion to the child's age and the amount of dental plaque. These may be indicative of a high susceptibility to periodontal diseases or reflect systemic conditions that affect the periodontum.

Adolescent↗

Autotransplantation of human premolars. A clinical and radiographic study of 100 teeth.

The purpose of the present study was to identify factors which might influence the success of autotransplantation, such as root development, root resorption, pulp condition and tooth eruption. The material consisted of 100 human premolars transplanted in 87 patients. The observation period ranged from 3-18 years, with a mean value 6.3 years. Clinical and radiographic examinations were performed. The transplanted premolars were divided into 7 stages of root development. At the final control, 93 teeth remained and 7 teeth were extracted. Periodontal healing without root resorption was related to stage of root development. It decreased from 93% in teeth with 3/4 root development to 37% in teeth with fully developed roots. Inflammatory root resorption was seen in 7 cases and replacement root resorption in 12 cases. Pulp revascularization was observed in 100% in stages with initial root development to 1/2 root development and decreased to 0% for teeth with fully developed roots. Pulp obliteration was observed in all cases with revascularized pulp tissue. The gingival condition was similar to contralateral, not transplanted premolars or adjacent teeth. Root growth increased with the stage of root development at the time of transplantation. It is concluded that transplantation of premolars with 1/2-3/4 root development provides a good chance of pulp survival, limited risk of root resorption and ensures sufficient final root length, and is thus recommended.

Adolescent↗

Metabolism and effects of epidermal growth factor and related growth factors in mammals.

The initial observations of Stanley Cohen in the 1960s established that EGF induced in vivo effects such as precocious eyelid opening and tooth eruption. Subsequently the actions of EGF have been extensively explored in cell culture systems. The receptor for EGF was characterized as a prototype model for other growth factors and the now extensive in vitro data indicate multiple functions for EGF. Moreover, EGF and EGF receptors have been characterized in many tissues, and EGF has been identified in most body fluids of several mammalian species. Interestingly, neither EGF antibody administration to newborn animals nor passive immunization of pregnant rodents against EGF has caused major deleterious effects (except the delay in epidermal maturation events), as might be expected from the in vitro studies. This is in contrast to the effects of nerve growth factor antiserum in developing rodents. Also, to date, no pathological EGF deficiency disorder has been characterized. However, the EGF family of growth factors appears to be important in mammalian development and function, although the precise roles and significance are not yet clear. Members of the family may have a role in embryogenesis and fetal growth since receptors have been identified in fetal tissues. Available evidence suggests that TGF alpha subserves the growth factor family roles in fetal development. In the developing postnatal animal pro-EGF mRNA, immunoreactive EGF, immunoreactive TGF alpha, and EGF receptors are present in many tissues. EGF also is produced and secreted by the maternal mammary gland, and mammary derived EGF appears to be important in gut development in the neonatal rodent. There is now extensive data to indicate important hormone-EGF interactions. In the postnatal period, thyroid and steroid hormones including retinoic acid have been shown to modulate EGF and/or EGF receptors in several tissues. GH increases EGF binding in liver and increases urine EGF concentrations. Moreover, EGF stimulates secretion of several hypothalamic and pituitary hormones, increases placental production of hCG and human chorionic somatomammotropin, increases adrenal cortisol production, and inhibits testicular, ovarian, and thyroid hormone secretions. As summarized in this review EGF has been implicated in a number of developmental events including palate and skin differentiation, growth of hair follicles, eye opening and tooth eruption, lung maturation, gut and liver growth, and differentiation of neurons. These EGF actions probably are mediated via autocrine, paracrine, and endocrine routes. A role for salivary and urine EGF in the maintenance of adult stomal, gut, and urinary epithelial surface integrity seems likely, although not yet proven.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗

Extracellular matrix-mediated tissue remodeling following axial movement of teeth.

Tooth eruption is a multifactorial process involving movement of existing tissues and formation of new tissues coordinated by a complex set of genetic events. We have used the model of the unopposed rodent molar to study morphological and genetic mechanisms involved in axial movement of teeth. Following extraction of opposing upper molars, lower molars supererupted by 0.13 mm. Labeled tissue sections revealed significant amounts of new bone and cementum apposition at the root apex of the unopposed side following supereruption for 12 days. Newly apposited cementum and alveolar bone layers were approximately 3-fold thicker in the experimental vs the control group, whereas periodontal ligament width was maintained. Tartrate-resistant acid phosphatase staining indicated bone resorption at the mesial alveolar walls of unopposed molars and provided in tandem with new bone formation at the distal alveolar walls an explanation for the distal drift of molars in this model. Microarray analysis and semiquantitative RT-PCR demonstrated a significant increase in collagen I, integrin beta5, and SPARC gene expression as revealed by comparison between the unopposed molar group and the control group. Immunohistochemical verification revealed increased levels of integrin beta5 and SPARC labeling in the periodontal ligament of the unopposed molar. Together our findings suggest that posteruptive axial movement of teeth was accomplished by significant formation of new root cementum and alveolar bone at the root apex in tandem with upregulation of collagen I, integrin beta5, and SPARC gene expression.

Acid Phosphatase↗

Endodontic therapy averting major surgery and avoiding keloid formation.

Keloids and mandibular unfavorable fractures are reviewed. A case report of a patient with keloid diathesis, who had a mandibular unfavorable fracture, is presented. A grossly carious, abscessed first molar was in the line of fracture. This tooth was the only erupted tooth present in the proximal fragment. Endodontic therapy and restoration of normal contour enabled the surgeons to treat the fractured mandible by means of simple closed reduction. The endodontic treatment pre-empted a major surgical procedure under general anesthesia and also averted a skin incision which would have subsequently formed a disfiguring keloid.

Abscess↗

The effect of adriamycin on dentinogenesis and 3H-thymidine incorporation into the enamel organ of the rat incisor.

The effect of adriamycin (5 mg/kg) on 3H-thymidine incorporation and on dentin formation was studied in rat incisors. Male Sprague Dawley rats received an intravenous injection of adriamycin. Some of these also received a subcutaneous injection of 3H-thymidine at a dose of 2 mCi/kg one day later. One group of control animals received an intravenous injection of a volume of physiological saline equal to that of the adriamycin dose. Another group received physiological saline, and one hour later was given an additional injection of 3H-thymidine at a similar dose as above. All the animals were killed by perfusion with 2.5% phosphate buffered glutaraldehyde 1 h, 1 d, 4 d, 8 d, 16 d, 28 d, and 32 d after 3H-thymidine treatment. Light microscopy revealed irregular dentin deposits between the mantle and circumpulpal layer of the labial dentin at 16 d. Within these deposits were trapped cells. The latter, through radioautographic labelling, appeared to be cells from the odontoblast layer. Also, the labelling pattern of the enamel organ in both the control and experimental groups indicated that the eruption rate of the tooth was not affected. Serial sectioning and examination of the lingual portion of the incisors at 28 d revealed a lack of dentin formation and a failure in the closure of the apical foramen. Electron microscopic observations showed an irregular and random arrangement of collagen fibers within the deposits of irregular dentin, and the presence of twisted odontoblastic processes. Examination of the lingual surface showed the presence of fibroblasts and collagen fibers bridging the gap that resulted from the failure in dentin formation. These cells, which were similar to periodontal ligament cells, appeared to have arisen from that area. These results indicate that adriamycin has no effect on tooth eruption, but has a reversible effect on the function of secretory odontoblasts, which manifested itself as a periodic deposition of irregular dentin on the labial surface, and on dentin formation on the lingual surface which manifested itself as a failure in dentin formation, and consequently, the closure of the apical foramen.

Animals↗