This article reviews the current knowledge of the biological aspects of dental tissue changes incident to orthodontic tooth movement. The inflammatory nature of these tissue changes was first recognized in the early 1970s, and since then a number of morphological and quantitative investigations have been published in support of this view. The studies dealing with vascular and cellular dental tissue changes, as well as those concerned with inflammatory mediators present at sites of orthodontic tooth movement are systematized and presented accordingly. Special emphasis is placed upon the role of the sensory nerve fibres and their neuropeptides in the control, and development of an inflammatory process, i.e. their role in tooth movement.
In Norway, bonded retainers alone were reported to be most commonly used in the mandible, while bonded retainers used in combination with a removable retainer appear to be the most commonly used appliances in the maxilla. This is similar to the most frequently used retainers in other countries, but there are disparities in duration and follow-up protocols. Most female orthodontists desire common retention guidelines.
Relapse after orthodontic tooth movement (OTM) is an undesirable outcome that involves a number of factors. This study investigated the remodelling of the alveolar bone and related periodontal structures during orthodontic relapse in rat molars. The maxillary right first molars of 35 Wistar rats were moved mesially by a fixed orthodontic appliance for 10 days and the contralateral molars served as controls. The appliances were removed and six animals killed. The molars were allowed to relapse, and the remaining animals were sacrificed at 1, 3, 5, 7, 14, and 21 days. The jaws were sectioned and stained with haematoxylin and eosin and tartrate-resistant acid phosphatase (TRAP). One day after appliance removal, the molars relapsed to a mean 62.5 per cent of the achieved OTM and then steadily relapsed to 86.1 per cent at 21 days. The number of osteoclasts situated along the alveolar bone of the first molars was highest at the end of active treatment and significantly decreased during the relapse period. In the OTM group, osteoclasts were most numerous in the pressure side of the periodontal ligament (PDL). As the molars relapsed over time, the osteoclast distribution shifted, and after 7 days of relapse, TRAP-positive cells were registered in previous pressure and tension sides of the first molars. After 21 days, these cells were concentrated in the distal parts of the PDL of all three maxillary right molars. These results indicate that orthodontic relapse in the rat model occurs rapidly and remodelling of the alveolar bone and PDL plays a central role in the relapse processes of both actively moved and adjacent teeth.
Fluorescent microspheres (FM) were used to semi-quantify the effect of orthodontic forces on blood flow in oral tissues in young rats. Forty-five animals had an orthodontic appliance inserted on the first maxillary molar on one side exerting a mesial force of approximately 50 g. Ten animals served as unoperated controls. On days 1, 3, 7, 14, and 21 after the start of the experiment, FM were injected into the left ventricle through an abdominal approach in the experimental and control animals. FM were counted in serial sections from the jaws in the periodontal ligament, pulp, and alveolar bone in a fluorescent microscope. The number of FM per tissue volume and/or tissue weight was taken as a measure of blood flow. The experimental side had significantly lower numbers of FM/mm3 in the periodontal ligament of the first and the second molar on the first day, compared with the contralateral side. However, a steady, significant increase in the number of FM/mm3 in the periodontal and pulpal tissues, and FM/mg in the alveolar bone could be observed on the third and seventh days on the experimental side of the first, second, and third molars compared with the contralateral side, while in the later stages the values of the two sides approached each other. The results of this study indicate that a localized experimental tooth movement initiates a more generalized blood flow response in the periodontal ligament, dental pulp and alveolar bone.
Objective: To assess the prevalence and severity of vestibular gingival recession of mandibular incisors after orthodontic treatment and to evaluate possible contributing factors. Materials and Methods: From the record pool of patients who completed orthodontic treatment from 1999-2006 at the Department of Orthodontics, University of Oslo, Norway, 588 patients fulfilled the inclusion criteria. Intraoral color slides were used for the evaluation of gingival recessions (based on Miller classification), presence of visible plaque, and gingival inflammation. Cephalometric radiographs were used to assess the sagittal intermaxillary relation, mandibular and intermaxillary angles, and the position of the lower incisors. A control group was drawn from the same pool of 588 patients. All statistical analyses were performed using SPSS. Results: The prevalence of gingival recessions after orthodontic treatment was 10.3%. Most (8.6%) were classified as Miller Class I, and 1.7% were classified as Miller Class II. Gingival recession was predominantly found on central incisors. Reduction of the sagittal intermaxillary angle and retroclination of the lower incisors was correlated with the development of a more severe gingival recession. Conclusions: The present study indicates that vestibular gingival recession of mandibular incisors after orthodontic treatment is of minor prevalence and severity. The presence of gingival recession or retroclination of the incisors with mesial basal relations increases the risk of more severe gingival recession. (Angle Orthod. 2012;82:42-47.)
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