Tooth Development

Dental fluorosis is a developmental disturbance of dental enamel, caused by successive exposures to high concentrations of fluoride during tooth development, leading to enamel with lower mineral content and increased porosity. The severity of dental fluorosis depends on when and for how long the overexposure to fluoride occurs, the individual response, weight, degree of physical activity, nutritional factors and bone growth. The risk period for esthetic changes in permanent teeth is between 20 and 30 months of age. The recommended level for daily fluoride intake is 0.05 - 0.07 mg F/Kg/day, which is considered of great help in preventing dental caries, acting in remineralization. A daily intake above this safe level leads to an increased risk of dental fluorosis. Currently recommended procedures for diagnosis of fluorosis should discriminate between symmetrical and asymmetrical and/or discrete patterns of opaque defects. Fluorosis can be prevented by having an adequate knowledge of t...

This study investigates differences in the δ13Ccol, δ15N, δ13Csc, δ18Osc, Sr/Ca, and Ba/Ca values of juvenile and adult woolly mammoths (Mammuthus primigenius) from Old Crow, Yukon, Canada. The data indicate that nursing in woolly mammoths lasted at least three years, and was associated with minimal decreases in δ13Ccol (~0.2‰), large decreases in δ13Csc (~1.5‰), and large increases in δ15N (~2‰) and δ18Osc (~2‰) values. Sr/Ca and Ba/Ca ratios suggest that woolly mammoth juveniles began consuming plant foods between 2 and 3 “African Elephant Years” of age, much later than the initiation of weaning in modern elephants. We hypothesize that delayed weaning was an adaptation to increased predation risk and decreased food quality/quantity during the extended hours of darkness that occur in winter at high latitudes. Prolonged nursing and delayed weaning may have made mammoths particularly vulnerable to climatic stressors or human hunting.

Age at menarche is a frequently used indicator to study growth and development. The development of hand and wrist indicates the peak height velocity which appears about two years before menarche. Bone development is linked with dental mineralization but the relationship between tooth maturation and sexual maturity has not been demonstrated yet (Lewis & Garn 1960, Garn et al. 1965, Demirjian 1985). Proving that a link exists between these indicators would be interesting to study trends of development rhythm from menarche: easy to collect and to encode, panoramic radiographs could be a new way to know menarche status in large samples.
Our sample consists in 176 panoramic radiographs of French girls from 7 to 17 years old, with known menarche status. Dental mineralization was encoded with Demirjian et al. 1973 and Moorrees et al. 1963 methods.
Despite previous studies results, statistical tools (correlation ratios, regression and classification trees, Bayes’ theorem) show that premolars mineralization is correlated with menarche. We have created computer programs based on the implementation bayesian inference results with premolars: (1) to estimate mean age of menarche in a population sample; (2) to assign menarche status (ante or post). Mean age of menarche estimation is based on seven mandibular tooth stages: program calculates mean dental age of girls selected to be peri-menarche thanks to their premolars tooth stages. Menarche status assignation requires premolars tooth stages only.
Further studies are planned to get the accuracy needed in clinical studies and to test our computer programs in a meta-population sample.

Dental fluorosis is a developmental disturbance of dental enamel, caused by successive exposures to high concentrations of fluoride during tooth development, leading to enamel with lower mineral content and increased porosity. The severity of dental fluorosis depends on when and for how long the overexposure to fluoride occurs, the individual response, weight, degree of physical activity, nutritional factors and bone growth. The risk period for esthetic changes in permanent teeth is between 20 and 30 months of age. The recommended level for daily fluoride intake is 0.05 - 0.07 mg F/Kg/day, which is considered of great help in preventing dental caries, acting in remineralization. A daily intake above this safe level leads to an increased risk of dental fluorosis. Currently recommended procedures for diagnosis of fluorosis should discriminate between symmetrical and asymmetrical and/or discrete patterns of opaque defects. Fluorosis can be prevented by having an adequate knowledge of t...

Tooth development results from sequential and reciprocal interactions between the oral epithelium and the underlying neural crest-derived mesenchyme. The generation of dental structures and/or entire teeth in the laboratory depends upon the manipulation of stem cells and requires a synergy of all cellular and molecular events that finally lead to the formation of tooth-specific hard tissues, dentin and enamel. Although

Teeth are the most durable structures in the human body. The timing and sequence of their development, as contained in dental development charts, have been used as valid criteria for age determination. The third molars however are the last teeth to erupt and are regarded as the most variable in the dentition. Age estimation in a legal context, using developing third molars must be carefully applied otherwise justice may miscarry. A case of wrongful use of the technique is presented here.

Epithelial-mesenchymal interactions guide tooth development through its early stages and establish the morphology of the dentin surface upon which enamel will be deposited. Starting with the onset of amelogenesis beneath the future cusp tips, the shape of the enamel layer covering the crown is determined by five growth parameters: the (1) appositional growth rate, (2) duration of appositional growth (at the cusp tip), (3) ameloblast extension rate, (4) duration of ameloblast extension, and (5) spreading rate of appositional termination. Appositional growth occurs at a mineralization front along the ameloblast distal membrane in which amorphous calcium phosphate (ACP) ribbons form and lengthen. The ACP ribbons convert into hydroxyapatite crystallites as the ribbons elongate. Appositional growth involves a secretory cycle that is reflected in a series of incremental lines. A potentially important function of enamel proteins is to ensure alignment of successive mineral increments on th...

The interference with tooth development by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was studied in dioxin-resistant Han/Wistar rats. Lactating dams were given a single dose of 50 or 1000 microg TCDD/kg body wt 1 day after delivery and the pup heads were analyzed radiographically or histologically at postnatal days 9 and/or 22. Of 19 animals studied histologically, 10 lacked one or more third molars, which were at the bud stage at the start of the experiment. A higher proportion of pups exposed to the higher dose (9/13) lacked third molars than those exposed to the lower dose (1/6) (27/52 and 2/24 teeth missing, respectively). Missing upper third molars (19/38) were more frequent than were lower (10/38). The development of the third molars present was retarded. The root tips of the more advanced first and second molars were prematurely closed and root formation was arrested, but eruption was not affected. Dentinogenesis of the continuously erupting lower incisor teeth was preerupti...