Thomas E. Southard

Cervical vertebrae maturation method: poor reproducibility.

INTRODUCTION The cervical vertebrae maturation (CVM) method has been advocated as a predictor of peak mandibular growth. This method relies on the clinicians ability to determine the stage of maturation of the vertebrae. Careful examination of reports of this technique shows methodologic flaws that can lead to inflated levels of reproducibility. The purpose of this study was to evaluate the reproducibility of CVM stage determination by using a more stringent methodology. METHODS Ten practicing orthodontists, trained in the CVM method, evaluated 30 individual and 30 pairs of cephalometric radiographs in 2 sessions to determine the CVM stage. Interobserver and intraobserver reliability was determined by using the Kendall coefficient of concordance and the weighted kappa statistic. RESULTS All degrees of interobserver and intraobserver agreement were moderate (Kendalls W, 0.4-0.8). Interobserver agreement levels for CVM staging of the 10 orthodontists at both times were below 50%. Agreement improved marginally with the use of 2 longitudinal radiographs. Intraobserver agreement was only slightly better; on average, clinicians agreed with their own staging only 62% of the time. CONCLUSIONS Based on these results, we cannot recommend the CVM method as a strict clinical guideline for the timing of orthodontic treatment.

The anterior component of occlusal force: Part 2. Relationship with dental malalignment

The objective of this study was to determine the relationship between the anterior component of occlusal force and malalignment of the mandibular anterior teeth. The anterior component of occlusal force that resulted from axially loading the second molars was measured in 15 subjects with varying degrees of mandibular anterior dental malalignment. Malalignment of the mandibular anterior teeth was found to be related to the magnitude of the anterior component of occlusal force and to the tightness of interproximal contacts in the mandibular posterior segments.

Intrusion anchorage potential of teeth versus rigid endosseous implants: A clinical and radiographic evaluation

The purpose of this study was to compare the intrusion anchorage potential of teeth to osseointegrated titanium implants. Titanium implants were surgically placed unilaterally in a healed mandibular fourth premolar extraction site in eight adult mongrel dogs. The implants were surgically uncovered 3 months later and second stage abutments with soldered edgewise brackets secured. Edgewise brackets were also placed on the ipsilateral third premolars and on the contralateral third and fourth premolars. Segmental edgewise arch wires were placed between the implant and the third premolar and between the contralateral third and fourth premolars. Intrusion arch wire bends (v-bends) just mesial to the implant and the fourth premolar brackets were adjusted to apply a 50 to 60 gm intrusive force to the third premolars, bilaterally. Seven weeks later this force was increased to approximately 100 gm. Force levels were monitored biweekly for a total period of 16 weeks. Superimposition of initial and final periapical radiographs with bone markers demonstrated that for each dog the implant remained immobile and the third premolar on the implant anchor side was intruded in a curved path. On the contralateral side of the arch the dental anchor (fourth premolar) underwent an adverse reactive tip-back movement, and the third premolar was not intruded. We conclude that rigid endosseous implants are superior to dental anchorage for orthodontic intrusion of teeth and offer a potential means to intrude anterior teeth in adult patients with missing posterior teeth.

Fractal dimension in radiographic analysis of alveolar process bone

OBJECTIVES This in vitro study examined radiographic fractal dimension changes in alveolar process bone during simulated osteoporosis. STUDY DESIGN Ten specimens of human maxillary alveolar process bone were progressively decalcified, and the percentage of calcium lost at each decalcification stage was quantified. Four radiographs of each specimen, together with an aluminum step-wedge, were exposed at 70 kVp at each stage. The test set of 560 radiographs was digitized, identical bony regions of interest were selected from the density-corrected images of each specimen, the regions were digitally filtered to reduce film-grain noise, and fractal dimension was computed on a line-to-line basis. Correlation analysis quantified the relationship between calcium loss and fractal dimension change. Analysis of variance and Duncans multiple range test determined whether a difference existed in fractal dimension computed from images at x-ray beam angulations of -5, 0, and +5 degrees. RESULTS A strong correlation (average r = -0.94, p < or = 0.0037) was found between generalized demineralization and decreasing fractal dimension. In every bone sample fractal dimension changed significantly (p < or = 0.0189) with angular change. CONCLUSIONS Radiographic fractal dimension holds promise for detecting simulated osteoporosis in the maxilla under ideal conditions, but the sensitivity of fractal dimension to small x-ray beam angular change renders its clinical application questionable.

Bicortical vs monocortical orthodontic skeletal anchorage

INTRODUCTION Case reports have documented the use of titanium miniscrews in providing skeletal anchorage for orthodontic tooth movement. Success rates as low as 50% have been reported for screw retention in either the facial or the lingual cortical plates (monocortical placement). The purpose of this in-vitro study was to test the hypothesis that bicortical miniscrew placement (across the entire width of the alveolus) gives the orthodontist superior force resistance and stability (anchorage) compared with monocortical placement. METHODS Forty-four titanium alloy screws, 1.5 x 15.0 mm, were placed in 22 hemi-sected maxillae and mandibular specimens between the first and second premolars. Half were placed monocortically, half were placed bicortically, and all were subjected to tangential force loading perpendicular to the miniscrew through a lateral displacement of 1.5 mm. Bone samples were sectioned and bone thickness at the screw sites measured. Statistical analyses, consisting of paired samples t tests, 2-samples t tests, Spearman rank correlation tests, and Fisher exact tests, were used to compare monocortical with bicortical screw force-deflection characteristics and stability. Additionally, 2-dimensional plane-stress finite-element models of bicortical and monocortical screw placement subjected to similar loading were analyzed. RESULTS As hypothesized, deflection force values were significantly greater for bicortical screws than for monocortical screws placed in both the maxilla and the mandible (P <0.01 in each instance). Furthermore, force values at mandibular sites were significantly greater than those at maxillary sites for both types of screws. No significant differences in deflection force values were found between the right and left sides of the jaws, or between coronal and apical alveolar-process screw positions. A significant increasing relationship was found between mandibular buccal bone thickness and deflection force for monocortical screws only, and no relationship was found between maxillary bone thickness and deflection force for monocortical or bicortical screws. Monocortical screws were significantly more mobile after force application than bicortical screws. Finite-element analysis indicated lower cortical bone stresses with bicortical placement than with monocortical placement, and these results were consistent with in-vitro experimental findings. CONCLUSIONS Bicortical miniscrews provide the orthodontist superior anchorage resistance, reduced cortical bone stress, and superior stability compared with monocortical screws.

Evaluation of profile esthetic change with mandibular advancement surgery.

Our purpose was to investigate the impact of mandibular advancement surgery on profile esthetics and to attempt to define guidelines that could be of value to the clinician in predicting profile esthetic change. The sample consisted of 34 patients who had been treated with a combination of orthodontics and mandibular advancement surgery without genioplasty. Initial (pretreatment) and final (posttreatment) cephalometric radiographs of each patient were used to produce silhouette images and to quantify skeletal changes that occurred with surgery. The images were displayed randomly to lay persons and orthodontic residents who were asked to score the esthetics of each profile. On average, after mandibular advancement surgery, B point moved forward 5.0 mm (SD = 2.6 mm) and downward 4.7 mm (SD = 3.1 mm), and the ANB angle decreased 3.0 degrees (SD = 1.6 degrees ) Graphical analysis and results of paired t tests revealed that for patients with an initial ANB angle >/= 6 degrees, a consistent improvement in profile esthetics was seen following surgery (P </=.001). This represented, on average, about a 45% improvement in esthetics. For patients with an initial ANB angle < 6 degrees, an improvement in profile esthetics after surgery was seen about half the time but poorer esthetics were equally likely. These results underscore the importance of using the ANB angle as a skeletal guideline when deciding whether to treat patients with mandibular advancement surgery. If improved profile esthetics are a desired outcome, an initial ANB angle of at least 6 degrees is recommended.

Periodontal force: a potential cause of relapse.

Relapse of aligned mandibular anterior teeth and the progressive collapse of the mandibular arch is a significant problem for orthodontists. However, identification of a specific cause of such relapse has proved elusive. The transseptal fiber system is thought to stabilize teeth against separating forces. It is hypothesized that this fiber system may actually maintain the contacts of approximating teeth in a state of compression, the long-term result of which could be contact slippage and collapse of the arch. The interproximal force (IPF) at the mandibular first molar-second premolar contact was investigated on the basis of previous studies with this representative contact. The IPF was measured in 10 subjects at six different widths of contact separation. By means of graphic plotting techniques, the IPF at zero separation was calculated to estimate the contact force when the molar and premolar were actually touching. The mean IPF at zero separation was found to be 36.7g (SE = 6.6g), and a t test confirmed the hypothesis that a state of compression between contacts exists (p less than 0.0001). After chewing, the mean IPF at zero separation was 57.2g (SE = 9.1g), and a paired t test revealed an increase in contact compression had resulted (p less than 0.01). It was concluded that the periodontium exerts a continuous force on the mandibular dentition and that this force acts to maintain the contacts of approximating teeth in a state of compression. This force is increased after occlusal loading and may help to explain long-term crowding of the mandibular anterior teeth, physiologic drifting of teeth, and maintenance of posterior dental contacts after interproximal wear.

Development of the curve of Spee

INTRODUCTION Ferdinand Graf von Spee is credited with characterizing human occlusal curvature viewed in the sagittal plane. This naturally occurring phenomenon has clinical importance in orthodontics and restorative dentistry, yet we have little understanding of when, how, or why it develops. The purpose of this study was to expand our understanding by examining the development of the curve of Spee longitudinally in a sample of untreated subjects with normal occlusion from the deciduous dentition to adulthood. METHODS Records of 16 male and 17 female subjects from the Iowa Facial Growth Study were selected and examined. The depth of the curve of Spee was measured on their study models at 7 time points from ages 4 (deciduous dentition) to 26 (adult dentition) years. The Wilcoxon signed rank test was used to compare changes in the curve of Spee depth between time points. For each subject, the relative eruption of the mandibular teeth was measured from corresponding cephalometric radiographs, and its contribution to the developing curve of Spee was ascertained. RESULTS In the deciduous dentition, the curve of Spee is minimal. At mean ages of 4.05 and 5.27 years, the average curve of Spee depths are 0.24 and 0.25 mm, respectively. With change to the transitional dentition, corresponding to the eruption of the mandibular permanent first molars and central incisors (mean age, 6.91 years), the curve of Spee depth increases significantly (P < 0.0001) to a mean maximum depth of 1.32 mm. The curve of Spee then remains essentially unchanged until eruption of the second molars (mean age, 12.38 years), when the depth increases (P < 0.0001) to a mean maximum depth of 2.17 mm. In the adolescent dentition (mean age, 16.21 years), the depth decreases slightly (P = 0.0009) to a mean maximum depth of 1.98 mm, and, in the adult dentition (mean age 26.98 years), the curve remains unchanged (P = 0.66), with a mean maximum depth of 2.02 mm. No significant differences in curve of Spee development were found between either the right and left sides of the mandibular arch or the sexes. Radiographic measurements of tooth eruption confirm that the greatest increases in the curve of Spee occur as the mandibular permanent incisors, first molars, or second molars erupt above the pre-existing occlusal plane. CONCLUSIONS On average, the curve of Spee initially develops as a result of mandibular permanent first molar and incisor eruption. The curve of Spee maintains this depth until the mandibular permanent second molars erupt above the occlusal plane, when it again deepens. During the adolescent dentition stage, the curve depth decreases slightly and then remains relatively stable into early adulthood.

Application of the Millon Adolescent Personality Inventory in evaluating orthodontic compliance.

Lack of adolescent patient compliance is a significant problem in orthodontics. The purpose of this study was to examine the feasibility of using a commercially available adolescent personality test to predict the behavior of adolescent patients in an orthodontic practice. Specifically, this study tested (1) the use of the Millon Adolescent Personality Inventory (MAPI) as an appropriate instrument for an adolescent orthodontic population and (2) the correlation between MAPI test results and orthodontic compliance. The MAPI was administered to 104 13- to 18-year-old orthodontic patients who were blindly evaluated for orthodontic compliance after 2 years of treatment. Twenty modified MAPI scales with high internal consistencies (coefficient alpha = 0.66 to 0.87) were developed. Factor analytic results demonstrated that the modified scales had a dimensionality that was similar to that of the original test. Seven of 20 test scales and gender were found to be significantly correlated with orthodontic compliance. These eight variables contribute to a predictive model that accounts for 24% of the variance in assessing orthodontic compliance. We conclude that the MAPI has potential as a useful instrument in assisting the management of adolescent patient behavior in an orthodontic practice.

Mesial force from unerupted third molars

Erupting mandibular third molars are implicated as a cause of anterior crowding of mandibular teeth. The goal of this two-part investigation was to measure the mesial force exerted by unerupted mandibular third molars. We hypothesized that such a force increases the tightness of all proximal posterior tooth contacts mesial to the mandibular second molar, and that surgical removal of third molars relieves the tightness by eliminating this force. The contact tightness between mandibular posterior teeth was measured bilaterally in 20 patients with bilateral unerupted mandibular third molars, immediately before and after unilateral removal of a third molar. We found unexpectedly that mean proximal tightness decreased bilaterally in all contacts that were measured after unilateral removal of a third molar, and we did not detect a mesial force exerted by unerupted third molars. We suspected that this bilateral relief of contact tightness resulted from placing the patients in a supine position for surgery. The second part of the experiment was conducted to determine the effects of postural change on proximal contact tightness where no surgery had been performed. For ten subjects we discovered a mean decrease in the tightness of all mandibular posterior contacts 2 hours after the patient had been moved from an upright to a supine position. The greatest mean decrease (-32%, p less than 0.0001) was found at the most posterior tooth contact. We conclude that surgical removal of unerupted mandibular third molars does not significantly reduce proximal contact tightness, but that simple movement from an upright to a supine position relieves such tightness dramatically.(ABSTRACT TRUNCATED AT 250 WORDS)