Effects of orthodontic force on enamel formation in normal and hypocalcemic rats

Environmental causes of enamel defects

A large number of causes of enamel defects, both environmental and genetic, have been described. However, many of these are derived from case histories and studies of individual conditions. What is needed now is a systematic investigation of the problem. The first requirement in exploring the aetiology further is the standardization of both the clinical diagnosis and the descriptive terminology. This has been provided by the Fédération Dentaire Internationale Developmental Defects of Enamel Index. Comparing studies using standardized methods, including this index, has highlighted areas for closer investigation. The total prevalence of enamel defects in a population needs to be established as a baseline for studies on aetiology. Sixty-eight per cent of 1518 school children in London have enamel defects in the permanent dentition, with 10.5% having 10 or more teeth affected and 14.6% having hypoplasia, i.e. missing enamel. These findings are in contrast to the 37% with hypoplasia found in a group of third to fifth century Romano-Britons from Dorset, England, suggesting further consideration of possible environmental and genetic differences between the two populations. An overall long-term study of dental development in low birth weight children has shown significantly more (P < 0.001) enamel defects related to major health problems during the neonatal period. By using standardized, reproducible criteria in prevalence studies to gain an overview of the problem and then studying specific groups or conditions, it is possible to identify general and specific factors in the aetiology of enamel defects and investigate further the varying role of genetic and environmental effects.

Intubation and mineralization disturbances in the enamel of primary teeth

This study was undertaken to examine the effects of intubation on the enamel development of primary teeth in children intubated during the first 3 months of life. The teeth of 35 children were examined clinically for signs of defects. Dental enamel defects were seen in 26 (74%) patients; enamel hypoplasia was seen in 15 and enamel hypomineralization in 19 cases. In eight patients both enamel hypoplasia and hypomineralization were found. There was a preponderance of enamel defects in the right maxilla, which supports the hypothesis that an early trauma to mineralizing primary teeth caused by laryngoscope may lead to dental enamel hypoplasia.

Long-term effects of orthodontic forces on the morphology of the rat-incisor socket and its location in the mandible

The effect of orthodontic force application on the rat-incisor socket and mandible was studied on roentgenograms. A mean linguo-intrusive force of 19 +/- 0.6 g was applied continuously to the shortened left lower incisor for a period of two (group A) and four weeks (group B). A third group of rats, subjected to shortening of the left mandibular incisor only, served as a hypofunctional control (group C). A fourth group of normal rats constituted the intact control (group D). After a recovery period of three months, the animals were killed, and standardized roentgenograms of the cleaned mandibles were taken. Socket and mandibular dimensions were measured on magnified tracings of the roentgenograms. Comparison of groups A and B with the control groups, on the one hand, and of group C with group D, on the other, facilitated isolation of the hypofunctional factor. In groups A and B, the orthodontic forces caused changes in the parameters affected (i.e., socket area, alveolar bone thickness, mandibular dimensions) and not affected by hypofunction (i.e., socket angulation and location, anterior-socket length). The former findings implies modification of the adaptive capability of dental structures to functional demands. It is concluded that mechanical loading of the incisor for two to four weeks causes long-lasting changes in the socket and its surrounding bone.

Tetracycline as a marker in hard tissue research: effects on enamel formation in rat maxillary incisors

Tetracycline in low dose is often used as a marker in hard tissue research. A low dose effect on enamel formation has never been proven despite well known toxic reactions in enamel after higher doses. The purpose of the investigation was to evaluate enamel formation in maxillary incisors of rats given a single low dose of a tetracycline with low toxicity, commonly used in research. Eight young rats received an intraperitoneal injection of 2 mg oxytetracycline per 100 g. The rats were terminated after periods between 1 h until 5 days. Undemineralized ground sections were prepared and studied under fluorescence microscopy. Microradiograms were taken to study the degree of mineralization. A diffuse uptake was seen within enamel in areas corresponding to late secretory stage and incisally in maturing enamel with a low mineralization degree. Tendencies of enamel aberrations were seen in all rats. These appeared as splittings within the formed enamel. In conclusion, low toxicity tetracycline disturbs normal amelogenesis, even if administered in low doses. It should therefore be avoided in hard tissue research where enamel formation is studied.

Social and biological correlates of localized enamel hypoplasia of the human deciduous canine tooth

Recent studies of teeth from prehistoric children have reported a localized, roughly circular patch of deficient enamel on the labial aspect of the primary canine, which reaches its highest prevalence in the Upper Paleolithic of Europe. This study reports social and biological correlates of 33 affected kindergarten-aged children from Vancouver, Canada (2.4% of 1,350 examined). Affected children can be characterized as coming from low-income families often of East Asian or Chinese origin in which there is a degree of milk avoidance and reduced breastfeeding. The defect appears to be due to minor physical trauma to the face approximately 6 months after birth occasioned by normal motor development, involving handling and mouthing objects, which damages the developing tooth crown through deficient cortical bone over the canine crypt. Reduced cortical bone in the face of the infant is attributed to nutritional factors, involving calcium deficiency, of the mother and/or developing infant.