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Abstract

Delineating the limits of orthodontic treatment in nongrowing individuals is important when making treatment decisions, especially in borderline orthodontic-surgical cases. The labial and lingual cortical plates at the level of the incisor apex may represent the anatomic limits of tooth movement. Cephalometric films of 107 adults were measured to determine the width of alveolar bone anterior and posterior to the incisor apex in each arch. Thin alveolar widths were found both labial and lingual to the mandibular incisors in groups of Class I, II, and III individuals with high SN-MP angle and in a group of Class III average SN-MP individuals. Thin alveolar widths were also found lingual to the maxillary incisors in a Class II high angle group.

Clinical cases are presented showing that orthodontic tooth movement may be limited in patients with narrow alveolar bone widths and that these patients are likely to experience increased iatrogenic sequelae.

Abstract

Using roentgenographic cephalograms from a sample of subjects with metallic implants, appropriately superimposed tracings were used to distinguish developmental and treatment-associated displacements of the maxillary central incisor and first molar associated with “local” changes within the periodontium from “secondary” changes which reflect sutural and appositional growth at more distant osseous loci.

Tracings were superimposed on anterior cranial base (ACB), on the maxillary implants only (IMP_MAX), and according to the best fit of maxillary anatomic structures without reference to the implants (A_MAX). Using the IMP_MAX superimposition, one could measure total local displacement at any landmark taking into consideration the effects of all appositional and resorptive changes on the superior and anterior surfaces of the palate, whereas using the A_MAX superimposition one could measure local displacement without consideration of surface appositional and resorptive changes. If the second of these measurements were subtracted from the first, the result would be a direct measurement of the effects of surface appositional and resorptive changes as they are expressed at that particular landmark.

This strategy has enabled us to quantify and report the amount of accommodation which occurs at the location of each dental landmark in association with the resorptive and appositional changes which occur through time on the superior and anterior surfaces of the hard palate.

Abstract

This study was designed to investigate biomechanical responses of the sutures in the nasomaxillary complex to orthopedic headgear forces applied in various directions. A three-dimensional analytic model of the craniofacial complex was used for finite element analysis. A posteriorly-directed force of 1.0 Kgf was applied to the maxillary first molars in 30° inferior, parallel, and 30°, 52.4° and 60° superior directions to the functional occlusal plane. Mean principal and shear stresses were evaluated at the sphenozygomatic, temporozygomatic, sphenomaxillary, frontomaxillary and frontozygomatic sutures and lamina cribrosa. As the force direction passed closer to the center of resistance (CRe) of the complex (52.4° superior direction), normal stresses approached a certain level of uniform compressive stress (−2.5 gf/mm²) with gradual decrease in shear stresses, whereas variation in these stresses produced by the forces applied in other horizontal and inferior directions was greater. It is shown that stresses in the nasomaxillary sutures are varied by the direction of headgear force. Directing the line of force closer to the CRe may produce the most optimal sutural modification effective for controlling forward and downward maxillary growth.

Abstract

The purpose of this study was to assess postretention stability of maxillary midline diastema closure, to search for predictors of relapse, and to test for associations between relapse and other postretention changes. The sample consisted of 35 patients with pretreatment diastemas ranging from 0.9 mm to 3.0 mm (mean 1.4, SD = 0.5) following eruption of the maxillary canines. Data were gathered from treatment charts, study models, periapical radiographs, and cephalograms taken pretreatment, posttreatment, and 1 to 26 years postretention (mean 11.4, SD = 6.4). Measurable diastema relapse was observed in only 12 cases. The majority of the relapse was 0.6 mm or less, and maximum relapse was 3.0 mm. Abnormal frenums and/or intermaxillary osseous clefts did not appear to be risk factors for relapse, and no pretreatment predictors of relapse could be established. The only posttreatment change associated with diastema relapse was proclination of the maxillary incisors (p<0.01).

Abstract

Twenty-four Japanese girls with anterior crossbite (Class III malocclusion) were selected for this study of the stability of changes associated with chin cup therapy. Pretreatment cephalometric measurements of the study sample were compared with those in a normal group. In addition, angular and linear measurements were also compared to assess the effectiveness of chin cup therapy in improving Class III skeletal components during the postretention period. The subjects showed characteristic values found in Class III malocclusion for SNB, ANB, and NPg to FH, and these values were significantly different from those in the normal group. The subjects who were past puberty showed more severe Class III skeletal patterns for ANB compared with the prepubertal subjects, and their initial Class III skeletal components showed more satisfactory improvement, including 2.0° increase of SNA and 1.8° increase of ANB during the postretention period.

Abstract

Twenty-one cases of transposition are presented showing a crude prevalence of 0.47%. A high rate of bilateral occurrence was seen. A significant number of cases were associated with other dental anomalies, such as peg-shaped lateral incisors and overretained deciduous teeth. Genetic etiology has been stressed and various other theories discussed.

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