American journal of orthodontics最新文献

Aberrant functional patterns of the masticatory musculature have been alleged as a factor influencing the morphogenesis of mandibular dysplasias. These include such expressions as the hyperdivergent skeletal open bite and its counterpart, the hypodivergent skeletal deep bite. A lack of anatomic data dealing with the actual musculoskeletal orientations of these types has resulted in speculative reports on divergent anatomy and its purported effects. In this study anatomic dissections of a hyperdivergent and a hypodivergent human cadaver illustrated that skeletally dysmorphic types possess different spatial orientations of the masticatory adductors in relation to dentofacial structures. A two-dimensional analysis of static equilibrium using computer-aided modeling demonstrated that these two types produce biomechanically distinct modes of muscle action. Temporalis activity must be 40% higher in the hyperdivergent model as compared with its counterpart to produce a biting force of 500 N (112 lb). The data suggest a rationale for the weak biting forces previously reported in long-faced persons when compared with horizontally developed subjects. The direction of condylar reaction force was also found to vary from a vertical orientation in the hyperdivergent model to oblique in the hypodivergent model. “Physis-like” behavior of the condyle, which can orient axially toward loading forces, may present an explanation for the reported differences in the direction of condylar growth in dysmorphic persons. A finite element analysis pictured distinct regions of deformation and compression in a novel perspective to help evaluate the currency of accepted hypotheses of stress-induced osteogenesis. The data support previous work reporting a latent geometric interdependency existing between muscle orientation and mandibular morphology.

This article describes the Active Vertical Corrector (AVC), which is a simple removable or fixed orthodontic appliance that intrudes the posterior teeth in both the maxilla and mandible by reciprocal forces. By the use of effective posterior intrusion of teeth, the mandible is allowed to rotate in upward and forward directions. The uniqueness of this appliance is that it allows the clinician to correct anterior open bite problems by actually reducing anterior facial height. This treatment approaches the problem at its cause (overeruption of posterior teeth) and provides better facial balance and esthetics than most conventional orthodontic treatment procedures. Problems formerly thought to require orthognathic surgery can now be treated successfully with the AVC.

Elastic bending (flexure) theory, although apparently extendable to the arch wire, incorporates assumptions that are violated in orthodontic application, and neglects several influences confined to the clinical arena. The standard elastic-bending test for orthodontic wires uses a passively straight segment of wire, and a rotational bending stiffness rather than the force-deflection ratio akin to the transverse deformation of a leveling wire is determined. In this study the transverse flexural stiffnesses of five preformed arch wires were quantified in each of three activation directions at five separate sites on simulated dental arches to which appliances were affixed. The influences of elastic moduli, numbers of strands, and interbracket distances were found to be less substantial than theory suggests. Other parameters, including wire curvature at the activation site, malalignment direction relative to that curvature, bracket-wire friction, and preactivation fit of the preformed arch to the dentition, also affected the localized, transverse, flexural stiffnesses.

The aims of this study were to determine the effects of surgical and conventional orthodontics on patients' body image and self-esteem and the association between personality characteristics and postoperative reports of pain, paresthesia, swelling, and satisfaction among 90 patients who underwent surgical orthodontics. Patients who underwent surgery completed questionnaires before their operations and up to 6 months after surgery. Self-esteem and body image were compared longitudinally between these patients and 33 persons who were undergoing orthodontic treatment only and 33 persons who had decided against treatment. Results suggest that patients' self-esteem, body image, and degree of extroversion are unrelated to postsurgical satisfaction and discomfort. Neuroticism was correlated with satisfaction, so that patients who scored in the higher range on a scale of neuroticism were less satisfied immediately after surgery and at removal of fixation wires. Neurotic patients also were more likely to complain of pain and swelling 6 months after surgery. Surgical patients held a more negative facial image and were more introverted than those in the other two groups but were similar in other personality traits before surgery. Both surgical and orthodontic patients improved significantly in body image over time, with the greatest increase among the former. Similar shifts in self-esteem occurred for the three groups, suggesting that surgery per se may not be the major determinant of longitudinal changes in self-esteem. Notably, the positive effect of surgery and orthodontic treatment on body image is an important motive for many persons seeking treatment. Results of this study provide important insights into how to prepare and counsel patients undergoing orthodontic treatment with and without surgery.

The lower border of the mandible in mandibulofacial dysostosis is characteristic of the syndrome. Evaluation of the cephalograms by means of the medial axis analysis and inflectional tangents captures the shape deformity. Morphometric data from lateral cephalograms on seven patients, ages 3 through 20 years, are reported: a total of 22 observations on three males and four females. These forms were compared to normal mandibular forms from the University of Michigan University School Study. The curvature of the gonial angle in the study population is not distinguishable from the normal curvature. Relative to this apparently normal region, there is a marked downward displacement of the symphysis that results in the curvature typical of the lower mandibular border in this syndrome. These findings are not consistent with earlier reports.

Cephalometric and clinical examination data from a group of 62 subjects with documented structural and functional changes in the temporomandibular joint were compared with that of a group of 102 subjects from a normative sample. The purpose of the study was twofold: (1) to provide a description of a sample of subjects with documented TMJ alterations and (2) to make cephalometric comparisons between this sample and a sample of control subjects from the general population. Results indicated an increased proportion of subjects with “high plane” characteristics and a decreased proportion of subjects with “low plane” characteristics in the experimental sample, but little or no differences in dental and occlusal parameters were found. There were no differences in the proportions or characteristics of subjects in any Angle classification group. There was a tendency, based solely on descriptive statistics, for the group of experimental subjects with negative trauma histories to exhibit an increased proportion of “division 2” incisal relationships.