Changes in molar position associated with missing opposed and/or adjacent tooth: a 12-year study in women.

The aim of this study was to radiographically analyse long-term changes in (i) overeruption of unopposed molars and (ii) tipping of molars with a mesial edentulous space, and whether there is an interaction between the two events. A further aim was to analyse if loss of alveolar bone height might influence overeruption and tipping. The sample consisted of panoramic radiographs taken at an interval of 12 years of 292 subjects from a prospective population study of women. The panoramic radiographs were scanned and analysed. Changes in tipping, overeruption and alveolar bone height of molars and control teeth were measured. The results showed that unopposed molars were more commonly found in the upper jaw and that unopposed molars showed 4·9 times higher risk of overeruption of ≥2 mm (95% CI 1·5-15·3) than opposed molars during the 12-year observation period. The average overeruption for the unopposed molars was 4·5% (s.d. 7·6), which corresponds to approximately 0·9 mm. The degree of overeruption increased with decreased bone support. Molars with a mesial edentulous space were most prevalent in the lower jaw, but neither an edentulous space nor alveolar bone level/bone level change were found to have a significant effect on tipping of the molars. The average mesial tipping was 0·8° (s.d. 5·6). In conclusion, unopposed molars showed a significantly increased risk for overeruption. Molars facing a mesial edentulous space showed a low risk for mesial tipping, but a significant interaction between overeruption and tipping was identified.

Craniofacial bone remodeling in growing rats fed a low-calcium and vitamin-D-deficient diet and the influence of masticatory muscle function.

Fifty-two male growing rats were randomly divided into three groups. The first group (n = 18) received a hard deficient diet, and the second (n = 18) a soft deficient diet. The control group (n = 16) was fed the normal hard diet. At the beginning and in the middle of the 28-day experimental period oxytetracycline was injected. Two representative coronal sections of the snout and the corresponding contact microradiographs were analyzed. The bone mass of the premaxillary and nasal bones seemed to be less in the two deficient diet groups than in the normal one, due to an increased endosteal bone resorption and decreased bone formation. No difference in the bone apposition rate and pattern could be seen between the deficient hard and soft diet groups, except in the dorsal part of the premaxilla, where the bone formed in the first half of the experiment was markedly more resorbed in the deficient soft diet group during the remaining period than in the deficient hard diet group. The morphology of the sutures was influenced by the altered function, since the sutural space became narrower, and premature obliterations of the internasal suture were observed in the deficient soft diet group. In conclusion, poor bone quality was observed in the skull of rats fed a low-calcium and vitamin-D-deficient diet, with less bone mass than in normal conditions. Masticatory function was a significant factor influencing bone remodeling and sutural growth even in situations in which a metabolic bone disturbance exists.

Orthodontic tooth movement into edentulous areas with reduced bone height. An experimental study in the dog.

The present study was performed in order to test the hypothesis that the height of supporting bone and connective tissue attachment will be maintained around teeth bodily moved into areas of reduced bone height. During a pre-experimental period, areas with markedly reduced bone height were produced in the mandible of 4 beagle dogs through extraction of the 4th premolars and subsequent surgical reduction of the bone height in the extracted sites to a level corresponding to half the root length of the 3rd premolar. Following healing, one of the third premolars was bodily moved in a distal direction into the area of reduced bone height, while the contralateral premolar served as a non-moved control. After 6 months of active tooth movement, the teeth were retained in their new position for a further 2 months before biopsies of test and control tooth sites were sampled. Radiographic evaluation showed that a bodily movement had been achieved with no or only minimal vertical displacement of the teeth. The histological analysis revealed that none of the teeth, orthodontically moved or not, had experienced loss of connective tissue attachment. Although a greater distance between the cemento-enamel junction and the bone crest was found on the pressure side of the orthodontically moved test teeth in comparison to the contralateral, non-moved control teeth, the bone level at all test teeth was more coronally positioned than the original, reduced bone level in the area into which the test teeth had been moved. Hence, these findings indicate that a tooth with a normal height of periodontal support can be orthodontically moved into an area of markedly reduced bone height with maintained height of the supporting apparatus.