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Experimental evidence suggests that cellular changes and tissue turnover occurs in the periapical tissue during tooth movement. The possible role of apoptosis in tooth movement has never been investigated. The purpose of this study was to show whether apoptosis plays any role in orthodontic tooth movement. A sample of 21 adult male Sprague-Dawley rats was divided into 4 groups. Orthodontic appliances were attached to the rats for various times-to group I (n = 6) for 3 days, to group II (n = 6) for 1 week, and to group III (n = 6) for 2 weeks. Rats in group IV (n = 3) had appliances but no force and served as the control group. At the end of the observation period, the animals were killed and tissue blocks of involved teeth were processed and prepared for TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) reaction. TUNEL-positive cells from selected areas on each slide were counted and compared by means of an analysis of variance. Group I demonstrated a significantly higher (P <.05) number of positive cells. This suggests that the maximum apoptosis occurs approximately 3 days after the application of the appliance.

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Literature on apical root shortening published in the 1990s is reviewed. Three categories were assigned: sample-based clinical studies, clinical case reports, and animal model studies. Great variability for root shortening was reported, including resorption experienced by individuals who had never undergone orthodontic treatment. Some studies attempted to predict severe resorption whereas others compared different types of treatment. Included are several histological studies of teeth that were moved in humans. Very few of the sample-based clinical studies were prospective, randomized clinical trials. Data from a study that the author was involved in was used to estimate the percentage of patients who would experience different amounts of apical root shortening. It was estimated that 5% of the patients treated would experience more than 5 mm of root shortening.

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Longitudinal growth changes were investigated cephalometrically for sixty-one Japanese girls who had anterior crossbite at the initial visit (ages 3 years and 11 months on an average). Cephalograms were taken annually from the initial visit to the end of the observation period (ages 7 years 6 months on an average). Eleven of them (Group N1) showed self-correction of anterior crossbite during the primary dentition; ten (Group N2) showed self-correction when the permanent incisors erupted and forty (Group R) did not show self-correction. There was no statistical skeletal difference between Groups N1 and N2 during the observation period. Groups N1 and N2 were larger, however, than Group R in A'-Ptm'/Pog'-Go (p < 0.05) and Group N1 was smaller than Group R in Pog'-Go/N-S (p < 0.01) at the end of the observation period. In summary, favorable growth of the maxilla relative to the mandible leads to self-correction of primary crossbite and when mandible size relative to the cranial base is large, primary crossbite does not show self-correction.

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The purpose of the present study was to determine whether pretreatment measures of facial and dentoalveolar structure can be used to predict apical root shortening liability. Four hundred patients were randomly selected from the files of the Orthodontic Clinic at the Saint Louis University Health Sciences Center. Pretreatment and posttreatment periapical radiographs of maxillary central incisors and pretreatment lateral cephalometric radiographs were traced and measured. A large amount of apical root shortening was found in 2% of the sample. A relationship that was weak but highly significant statistically (r = 0.335; p < 0.01) was found between the amount of apical root shortening and the duration of active treatment. Several measures of dentoalveolar structure were also statistically significant. However, these measures did not account for enough of the observed variability to be clinically useful as a predictor. In the absence of a history of trauma or pretreatment signs of root resorption, pretreatment facial and dentoalveolar structure cannot be used to accurately identify persons who will experience a large amount of apical root shortening during the course of comprehensive orthodontic treatment with a fixed appliance.

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It has been shown that a release of periosteal tension may augment the growth of a long bone; however, similar experiments in the mandible have produced equivocal results. For further definition of the role of periosteal tension in the growth of the mandibular condyle, 80 young female Sprague-Dawley rats were randomly assigned to four equal groups: (1) sham, (2) condylotomy, (3) narrow periostomy, and (4) wide periostomy. All procedures were performed unilaterally. Lateral cephalograms, transcranial condylar radiographs, and metallic implants made possible the measurement of the actual increment of condylar growth over three post-operative periods: 0 to 14 days, 14 to 28 days, and 0 to 28 days. Analysis of covariance was performed (weight gain as the covariate) and, where overall significance was found, Turkey's HSD test was used for determination of individual group differences. Conservative, circumferential periostomy of the condylar neck as well as condylotomy failed to alter the condylar growth rate, whereas removal of a wide band of periosteum led to a small decrease. These findings suggest that, at least in the rat, periosteal tension plays only a minor role-if any-in the control of condylar/mandibular growth. Furthermore, a subsequent increase or decrease in condylar growth, in experiments that use a condylotomy model, cannot be attributed solely to a disturbance in periosteal integrity caused by the condylotomy.

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A technique for using implants to superimpose oriented transcranial and cephalometric images for the study of mandibular growth in the rat.

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It has been suggested that, by changing the orientation (and hence the function) of the condyle/ascending ramus segment, surgical control of mandibular growth rotation is possible in growing children. To test one aspect of this hypothesis--the effect of changes in condylar orientation--one condyle in each of thirty-five young male rats was rotated surgically, either clockwise or counterclockwise, and then wired to the ramus to preserve the new orientation. Amalgam implants and lateral cephalograms were used to measure the subsequent pattern of mandibular growth. The findings revealed that surgical rotation of the condyle and the subsequent pattern of mandibular displacement are poorly correlated (r = 0.1-0.3). It was concluded, therefore, that changes in the pattern of mandibular rotation that may follow early mandibular advancement are the result of factors other than the orientation of the condyle following surgery.

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This study was designed to assess the gingival tissue resistance to remodeling in determining the rate of orthodontic tooth movement. Closed coil spring orthodontic appliances were stretched bilaterally between the first molars and incisors in the maxillary arches of 18 adult rats. The resistance of gingival tissues was eliminated around the randomly chosen first molars by a circumferential fiberotomy procedure. Movements of teeth were measured on submental vertex radiographs against the metallic implants that were placed in zygomatic processes. The data were analyzed by randomized block design analysis of variance. During the 30-day experimental period, the teeth that underwent the fiberotomy procedure moved faster (0.63 mm versus 0.51 mm, P less than 0.05), indicating that the resistance of gingival tissues may be a rate-limiting factor in orthodontic tooth movement.

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