Karin A. Southard

The effect of corticosteroid-induced osteoporosis on orthodontic tooth movement.

The purpose of this research was to study the effect of corticosteroid-induced osteoporosis on orthodontic tooth movement and relapse. Sixteen 3-month-old New Zealand white rabbits were divided into four equal groups, two treatment and two control. All treatment rabbits were administered daily injections of 15 mg/kg cortisone acetate for 4 days before and during the experimental period. An orthodontic appliance delivering a mesial force of 4 ounces was placed on the maxillary left first molar of all animals. For all groups, measurements of active tooth movement were made after 4, 7, 11, and 14 days. For two of the groups, appliances were removed on day 14, and additional measurements of relapse were made through day 21. With the use of radiodensitometric readings of the humerus bone and histology of the maxilla, osteoporosis was demonstrated in the treatment animals. Mean incremental and cumulative active tooth movement was three to four times greater (p < 0.0001) in the treatment rabbits than in the controls. The treatment group in which relapse was measured demonstrated 100% relapse on day 18, whereas the control group relapsed at a much lesser rate through day 21 and never achieved 100% relapse. Histologic findings appeared to support tooth movement results. In conclusion, the results of this study indicate that rabbits subjected to corticosteroid-induced osteoporosis undergo significantly more rapid orthodontic tooth movement and subsequent relapse than control animals.

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.

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.

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)

Effect of screw diameter on orthodontic skeletal anchorage

INTRODUCTION Many case reports have documented the successful use of titanium miniscrews for orthodontic anchorage. However, the literature lacks a well-controlled study examining the effect of miniscrew diameter on anchorage force resistance. The purpose of this in-vitro study was to compare the force resistance of larger-diameter monocortical miniscrews to smaller-diameter monocortical miniscrews; and to compare the force resistance of larger-diameter monocortical miniscrews to smaller-diameter bicortical miniscrews. METHODS Ninety-six titanium alloy screws were placed into 24 hemisected maxillary and 24 hemisected mandibular specimens between the first and second premolars. Specimens were randomly and evenly divided into 2 groups. In the first group, 24 large-diameter screws (2.5 x 17 mm) and with 24 small-diameter screws (1.5 x 15 mm) were placed monocortically. In the second group, 24 large-diameter screws (2.5 x 17 mm) were placed monocortically and 24 small-diameter screws (1.5 x 15 mm) were placed bicortically. All screws were subjected to tangential force loading perpendicular to the miniscrew with lateral displacement of 0.6 mm. Statistical analyses, including the paired-samples t test and the 2-samples t test, were used to quantify screw force-deflection characteristics. One-way analysis of variance (ANOVA) with the post-hoc Tukey studentized range test was used to determine any significant differences, and the order of those differences, in force anchorage values among the 3 screw types at maxillary and mandibular sites. RESULTS Mean mandibular and maxillary anchorage force values of the 2.5-mm monocortical screws were significantly greater than those of the 1.5-mm monocortical screws (P <0.01). No statistically significant differences in mean mandibular anchorage force values were found between the 2.5-mm monocortical screws and the 1.5-mm bicortical screws. However, mean maxillary anchorage force values of the 1.5-mm bicortical screws were significantly greater than those of the 2.5-mm monocortical screws (P <0.01). Data analyzed with 1-way ANOVA with the post-hoc Tukey studentized range tests indicated that the mean mandibular and maxillary force values of the 2.5-mm monocortical screws and the 1.5-mm bicortical screws were significantly greater than those of the 1.5-mm monocortical screws (P <0.01). Based on the 2-samples t test, mean anchorage force values at mandibular sites were significantly greater than at maxillary sites for the 2.5-mm monocortical screws and the 1.5-mm monocortical screws. There were no statistically significant differences in mean anchorage force values between maxillary and mandibular sites for the 1.5-mm bicortical screws. CONCLUSIONS In vitro, larger-diameter (2.5 mm) monocortical screws provide greater anchorage force resistance than do smaller-diameter (1.5 mm) monocortical screws in both the mandible and the maxilla. Smaller-diameter (1.5 mm) bicortical screws provide anchorage force resistance at least equal to larger-diameter (2.5 mm) monocortical screws. An alternative to placing a larger-diameter miniscrew for additional anchorage is a narrower bicortical screw.

Comparison of digitized radiographic alveolar features between 20- and 70-year-old women : a preliminary study

The purpose of this investigation was to determine whether a difference exists in four digital image features, extracted from standardized periapical radiographs of the maxillary alveolar bone, between younger and older women. These features included mean pixel intensity, I(x); pixel intensity variance, var I(x); mean absolute Fourier transform coefficient, magnitude of F(u); and mean spatial first moment of the absolute Fourier coefficients, M1. The interproximal bone between the maxillary canine and lateral incisor was analyzed in two groups of 10 younger and older women with mean ages of 24 and 74 years, respectively. I(x) was significantly less in the 70-year-old group than in the 20-year-old group (p = 0.01), as were magnitude of F(u) (p less than 0.05) and M1 (p less than 0.01). Var I(x) tended to be significantly less in the 70-year-old group (p = 0.06). We conclude that in women a measurable diminution in the magnitude of these four bony features comes with age.