Root resorption and tooth movement in orthodontically treated, calcium-deficient, and lactating rats

[Follow-up study of the reaction of the marginal and apical periodontium under the continuous application of force]

Radiological findings and clinical data from existing treatment records have been examined using X2-test for clarification of possible relationships between pathological reaction of the periodontal ligament to continuous application of force and different patient-specific and therapeutic factors. It was shown that 70% of the total group have pathological changes following fixed appliance therapy. Apical root resorption usually could be diagnosed five times more frequently than marginal bone loss. No age-specific relationship was noted. The findings confirmed that active intrusion, extensive tooth movement, interruption of treatment, and in particular the anatomical configuration of the roots codetermine the quality of the periodontal reaction.

A study of the relationship between incisor intrusion and root shortening

Apical root shortening is one of the most common complications of orthodontic treatment. Force magnitude has been suggested as an important factor. Studies on the occurrence of root resorption show equivocal results. The aim of the present study was to evaluate the relationship between intrusion with low forces (25 gm) using utility arches in the bioprogressive technique and root shortening. Age, sex, facial type, treatment time, extraction versus nonextraction therapy, width of the symphysis, and the angle of the incisors to skeletal reference planes also were studied for their relationship to intrusion and root shortening. Root shortening was found to average 1.84 mm for maxillary incisors and 0.61 mm for mandibular incisors subjected to intrusive force. Intrusion of incisors in a population exhibiting growth was found to be one of "holding against growth" and in the upper arch to a change in angulation of the maxillary incisors. Furthermore, when extraction was a part of the orthodontic treatment, it was related to intrusion of maxillary incisors but not to intrusion of mandibular incisors. No relationship was found between the amount of root shortening and degree of intrusion achieved. However, a long treatment time was significantly correlated to root shortening. None of the other characteristics studied were related to either intrusion or root shortening. In the present study, it was found that intrusion with the utility arch type of technique is not related to amount of root shortening. The degree of root shortening was markedly higher in the maxilla than the mandible. In general, treatment time was the most significant factor for occurrence of root shortening.(ABSTRACT TRUNCATED AT 250 WORDS)

[Periodontal reactions to orthodontic forces in the diabetic metabolic state]

The reaction of the periodontium to orthodontic tooth movement was studied in rats with streptozotocin diabetes. Forces employed to initiate mesial movement of first molar were 10 N 20 N 30 N and the duration of application was three, six, ten and 14 days. The 14-day rats were treated with fluorochrome sequential labelling according to Rahn. Diabetes mellitus in rats is accompanied by characteristic changes: The most important findings were: 1. a slow osseous regeneration, as could be shown by fluorescence microscopy, 2. the new bone ist unable to pick up the labellings in a sequential manner, 3. a weakening of the periodontal ligamentum, 4. microangiopathies in the gingiva area. the specific diabetic changes are more pronounced following orthodontic tooth movement.

[Apical root resorption during orthodontic treatment]

Pre- and posttreatment radiographs of 2050 orthodontically treated patients were examined and apical root resorptions of more than 2 mm were identified. 30 patients (211 teeth) were affected. Treatment characteristics and objectives of this group (with severe apical root resorption) were compared to a treated group of 30 patients (with no resorption) to determine clinical risk factors. Extrusion, but especially jiggling and a long treatment period were found to be significantly more frequent in the group exhibiting resorption than in the control group. Pathogenesis of treatment-induced root resorption is discussed in respect to histological results.

Leukotrienes in orthodontic tooth movement

Prostaglandins (PGs) and leukotrienes (LTs) are products of arachidonic acid conversion. PGs have an established role in mediating orthodontic tooth movement. The role of LTs in modulating or mediating orthodontic tooth movement was investigated in this study. One hundred thirty-two Sprague-Dawley rats were used; the animals weighed 300 to 400 gm with equal numbers of male and female rats. They were divided into five main groups of 24 animals each and a sham group of 12 animals. An orthodontic appliance was placed and activated on all the animals except the sham group; in this group the appliances were not active. Each main group was given one of the following treatments daily: distilled water, 5% gum arabic solution, PG synthesis inhibitor indomethacin, LT synthesis inhibitor AA861, and a combination of both drugs. Each group was divided into six subgroups of four animals; the animals were killed at either 1, 3, 5, 7, 10, or 14 days, and tooth movement measured. The three sham subgroups received distilled water and were killed at 1, 7, or 10 days. The first maxillary molar (the moved tooth) and surrounding tissues were removed from all animals in the sham group and the subgroups killed at 1, 7, and 10 days in the gum arabic solution group and the LT synthesis inhibitor group. Prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) were extracted, measured with radioimmunoassay (RIA), and standardized per milligram of protein in the sample. A significant inhibition of tooth movement occurred beginning on day 7 in the indomethacin, AA861, and combination groups; there was no significant difference among these groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of orthodontic force on periodontal tissue metabolism. A histologic and biochemical study in normal and hypocalcemic young rats

The relationship between force and degradation activity after application of orthodontic force is still obscure. Of particular clinical interest are the etiologic factors behind excessive root resorptions appearing in connection with orthodontic movement of teeth that has been proposed to be influenced by systemic factors regulating the tissue-degrading activity in periodontal tissues. Thus, the aim was, by histologic and new biochemical methods, to investigate the effect of orthodontic forces on the periodontal tissues in the normal and the hypocalcemic situation with secondary hyperparathyroidism. Root resorptions were induced in upper incisors of normal and hypocalcemic rats by subjecting the teeth to a moderate orthodontic force. In both groups the resorption of the roots occurred consistently in the vicinity of reorganizing areas of the periodontal ligament (PDL) with ongoing degradative activities and alveolar bone resorption. Furthermore, specific cell metabolic changes in alveolar bone and PDL in tension and pressure zones were detected and quantified by biochemical determination of alkaline phosphatase activity. This biochemical quantification of the metabolic changes together with the morphologic observations gave the clinically valuable information that the observed increase in occurrence and severity of root resorptions in moderate hypocalcemia was related to an increase in alveolar bone turnover. This study has shown that root resorptions were clearly related to the degradation process occurring in the vicinity of the hyaline zone and that in the hypocalcemic situation, the increase in root resorptions was related to an enhanced alveolar bone resorption. Thus, factors that minimize the time for resorptive/degradative activity should be discussed in this context rather than force per se.

The effect of load duration on long-term recovery of the eruptive function in the rat incisor

The purpose of this study was to determine the long-term recovery of the normal rate of eruption of the rat incisor following application of loads of similar magnitude but of varying duration. The daily rate of eruption of the continuously growing tooth served as indicator of the functional recovery of its periodontium. The left mandibular incisor was shortened out of occlusion in 34 experimental and 16 control rats. The experimental animals were divided into groups A, B, and C, and continuous loads (19.47 g +/- 0.42 g) were applied to the shortened incisors by means of closed-coil springs for 5, 14, and 28 days, respectively. Following removal of the springs, the daily rate of eruption was measured and calculated in all 50 animals for a period of 10 weeks. The extended impairment of eruption in the experimental animals was directly proportional to the duration of loading: at 10 weeks postloading, it was present in 18%, 67%, and 100% of the rats in groups A, B, and C, respectively. The intragroup variations in the rate of eruption of individual teeth were more pronounced following short-term loading than after prolonged load application. Short-term loading proved to be least harmful regarding recovery of eruptive function.

The effect of age on tooth movement and mineral density in the alveolar tissues of the rat

A comparison of tooth movement cycles and changes in alveolar tissue mineral densities was made between young (21 to 28 days old) and adult (90 to 100 days old) rats. An initial 60-g mesial tipping force was applied to the maxillary first molars; tooth movement was estimated by measuring the opening between first and second molars, and tissue mineral density by sample ash weight per cubic centimeter. A characteristic three-part tooth movement cycle was found in both groups of rats. This cycle consists of an early "instantaneous" movement that is a function of the viscoelastic properties of the tissues, a delay period during which little tooth movement occurs due to hyalinization and undermining resorption, and a late period during which bone remodeling and tooth movement occur. Compared with the adult group, the amount of "instantaneous" movement in the young rats was greater (P less than 0.001), the delay period was shorter, and the rate of late tooth movement was faster (P less than 0.001). The young rats had significantly lower (P less than 0.05) mineral densities before orthodontic treatment. Both groups experienced a slight but insignificant increase in density followed by rapid declines to a nadir that was not different between the groups. The young rats reached this point by day 5 and the adults by day 7. The point of lowest mineral density occurred in the treated alveolar tissues toward the end of the delay period for each group and was followed by a return to control values at rates that were not significantly different between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)