Distal molar movement with Kloehn headgear: is it stable?

Headgear therapy in children with Class II malocclusion and the role of compliance on treatment outcome: A nine-month randomized controlled trial

OBJECTIVES

To evaluate three-dimensional movements of maxillary teeth during headgear treatment in Class II growing children, using digital analytical tools, and to determine the effects of compliance on these movements.

MATERIALS AND METHODS

A 9-month parallel-group randomized controlled trial was carried out on 40 children with Class II malocclusion, aged 8-12 years, half assigned to receive a cervical headgear and half to a no-treatment group, using block randomization. Subjects in the treatment group were instructed to wear the headgear for 12 hours daily and monitored using an electronic module. After 9 months, the following dental outcomes were measured: first maxillary molar distalisation, rotation, tip and torque, arch depth, and interpremolar and intermolar distances. Caregivers and participants were not blinded to group assignments, but those assessing outcomes were. Linear regression models were used to detect differences between groups and correlation coefficients to find correlations between compliance and dental outcomes.

RESULTS

All 40 included patients were analysed. A significant difference in molar distalisation was observed between the treatment (1.2 mm) and control groups (-0.2 mm). Arch depth change was also increased to a larger extent in the treatment groups (1.3 mm vs 0.1 mm), as was the interpremolar distance (1.9 mm vs 0.4 mm). In contrast, no significant differences in molar rotation or torque change were observed. With regard to compliance, average compliance was 55%. A significant correlation was found between molar distalisation and compliance in the treatment group.

CONCLUSIONS

Headgear therapy has significant effects on molar distalisation, arch depth, and arch width. Compliance has a significant positive effect on molar distalisation.

The impact of force magnitude on the first and second maxillary molars in cervical headgear therapy

AIM

To study the effect of force magnitude on the maxillary first and second molars in cervical headgear (CHG) therapy.

MATERIAL AND METHODS

In this controlled clinical trial, patients (n = 40) were treated with CHG with a light (L, 300 g, n = 22) or a heavy force (H, 500 g, n = 18) magnitude. The subjects were asked to wear CHG for 10 hours a day for 10 months. The outer bow of the CHG facebow was lifted up for 10-20 degrees and the inner bow was expanded 3-4 mm. Adherence to instructions and force magnitude were monitored using an electronic module (Smartgear, Swissorthodontics, Switzerland). Panoramic and lateral radiographs before (T1) and after treatment (T2) were analysed using a Romexis Cephalometric module (Planmeca, Finland) focussing on the angular, sagittal, and vertical positions of the permanent first and second molars.

RESULTS

According to the cephalometric analysis of the maxillary first and second molars, distal tipping occurred during T1-T2 in the H group (P = 0.010 and 0.000, respectively), and the change was greater in the H group compared to the L group (P = 0.045 and 0.019, respectively). Based on the panoramic analysis, tipping occurred in the distal direction during therapy in the H group in the second molars compared to the midline or condylar line (P = 0.001 and 0.001; P = 0.008 and 0.003 on the right and left, respectively).

CONCLUSION

With heavy force magnitude, the maxillary first and second molars can tilt more easily in the distal direction even if the CHG was used less. Distal tipping of the molar can be considered to be a side effect of CHG therapy.

Total maxillary arch distalization with modified C-palatal plates in adolescents: A long-term study using cone-beam computed tomography

INTRODUCTION

The aims of this study were to evaluate the long-term skeletodental effects, the volume of maxillary tuberosity, and airway space changes after maxillary molar distalization using modified C-palatal plate (MCPP) in adolescents with Class II malocclusion.

METHODS

The sample consisted of 20 adolescent patients (MCPP group; mean age, 12.9 ± 1.0 year) who underwent bilateral distalization of their maxillary dentition and 20 subjects as a control group. In the MCPP group, cone-beam computed tomography images were taken before distalization, at the end of the treatment, and during retention with a minimum of a 3-year posttreatment follow up period. Repeated measures ANOVA followed by post-hoc analysis with the Bonferroni test were used to identify significant differences between time points.

RESULTS

After the long-term observation period, sagittal skeletal and dental relationships were maintained (there were no significant changes in ANB, occlusal plane angle, and overjet postretention). The vertical skeletal dimension did not change during treatment and was stable at the long-term follow-up (the mandibular plane angle and ANS-Me were relatively well maintained). The volume of the maxillary tuberosity showed no significant change during long-term retention. However, the volume was significantly smaller in the treatment group than in the control group (P <0.0001). There were no significant airway space changes after distalization and the postretention period. In addition, there was no significant difference between the MCPP and control groups.

CONCLUSIONS

Improved sagittal skeletal and dental relationships because of treatment were maintained in the long-term evaluation. There was no negative long-term effect on airway space associated with the maxillary arch distalization. Therefore, these findings might be beneficial for clinicians in diagnosis and treatment planning for Class II malocclusion in adolescents.

Effects of the cervical headgear in growing Angle Class II malocclusion patients: a prospective study

Objective:

Evaluate dental and skeletal changes resulting from the exclusive use of the cervical headgear for 15 ± 4 months in the treatment of patients with Class II division 1 malocclusion.

Methods:

Differences between the beginning (T₁) and immediately after the end of the therapy (T₂) with the cervical headgear in growing patients (Experimental Group, EG, n = 23) were examined and compared, during compatible periods, with those presented by a group of untreated individuals (Control Group, CG, n =22) with similar malocclusions and chronological age. The cephalometric variables evaluated were: ANB, GoGn.SN, AO-BO, S'-ANS, S'-A, S'-B, S'-Pog and S'-U6 (maxillary first molar). The Shapiro-Wilk and Levene tests were used to evaluate the results.

Results:

Significant differences were found relative to the ANB, S'-U6, AO-BO, S'-ANS, S'-A, S'-B and S'-Pog variables between T₁ and T₂ when comparing both groups. No statistically significant variation was found regarding the GoGn.SN angle.

Conclusions:

The use of cervical headgear promoted distal movement of the maxillary first molars and restricted the anterior displacement of the maxilla, without significantly affecting the GoGn.SN angle.

Long-term skeletal effects of high-pull headgear followed by fixed appliances for the treatment of Class II malocclusions

OBJECTIVES

The long-term skeletal effects of Class II treatment in growing individuals using high-pull facebow headgear and fixed edgewise appliances have not been reported. The purpose of this study was to evaluate the long-term skeletal effects of treatment using high-pull headgear followed by fixed orthodontic appliances compared to an untreated control group.

MATERIALS AND METHODS

Changes in anteroposterior and vertical cephalometric measurements of 42 Class II subjects (n = 21, mean age = 10.7 years) before treatment, after headgear correction to Class I molar relationship, after treatment with fixed appliances, and after long-term retention (mean 4.1 years), were compared to similar changes in a matched control group (n = 21, mean age = 10.9 years) by multivariable linear regression models.

RESULTS

Compared to control, the study group displayed significant long-term horizontal restriction of A-point (SNA = -1.925°, P < .0001; FH-NA = -3.042°, P < .0001; linear measurement A-point to Vertical Reference = -3.859 mm, P < .0001) and reduction of the ANB angle (-1.767°, P < .0001), with no effect on mandibular horizontal growth or maxillary and mandibular vertical skeletal changes. A-point horizontal restriction and forward mandibular horizontal growth accompanied the study group correction to Class I molar, and these changes were stable long term.

CONCLUSIONS

One phase treatment for Class II malocclusion with high-pull headgear followed by fixed orthodontic appliances resulted in correction to Class I molar through restriction of horizontal maxillary growth with continued horizontal mandibular growth and vertical skeletal changes unaffected. The anteroposterior molar correction and skeletal effects of this treatment were stable long term.

Extra-oral Appliances in Orthodontic Treatment

Extra-oral appliances are used in orthodontics to apply forces to the jaws, dentition or both and the popularity of these appliances is cyclical. Although the use of retraction headgear for the management of Class II malocclusion has declined over the last 20 years with the refinement of non-compliance approaches, including temporary anchorage devices, headgear still has a useful role in orthodontics. The use of protraction headgear has increased as more evidence of its effectiveness for the treatment of Class lIl malocclusion has become available. This paper describes the mechanics and contemporary uses of headgear in orthodontics for primary care dentists and specialist orthodontists. CPD/CLINICAL RELEVANCE: Extra-oral appliances have specific uses in orthodontic biomechanics. Clinicians using retraction headgear and protraction headgear should be familiar with their clinical indications, the potential problems and how these can be avoided.

Evaluation of long-term stability of mesiodistal axial inclinations of maxillary molars through panoramic radiographs in subjects treated with Pendulum appliance

OBJECTIVE

To evaluate the stability of mesiodistal inclination of maxillary molars produced by a pendulum appliance, five years after completion of orthodontic treatment. Angulation changes were compared to an untreated sample.

METHODS

The sample consisted of 20 patients (14 females and 6 males) with Class II, Division 1 malocclusion that was treated through molar distalization with a pendulum appliance followed by cervical headgear and full fixed appliances. Maxillary molar inclination was evaluated through panoramic radiograph. The mean age at pretreatment was 14.3 ± 1.6 years, whereas at immediate post-treatment it was 18.6 ± 1.8 years, and at long-term post-treatment it was 23.8 ± 2.0 years. A control group of 16 untreated individuals with untreated normocclusion ranging in age from 12 to 17 years old were used as comparison group. Data were statistically analyzed with independent t-tests and ANOVA test followed by Tukey post-hoc tests.

RESULTS

Statistically significant differences were found between T1(94.50) and T2 (98.80) as well as between T2 and T3 (94.70) for maxillary first molars. Maxillary second molars did not show any statistically significant positional changes during the evaluated time periods T1 (107.50), T2 (109.30) and T3 (106.90).

CONCLUSION

Although maxillary first molars underwent distal crown inclination immediately after treatment, approximately five years thereafter their roots tended to upright close to the pretreatment positions.

Maxillary molar distalization therapy in adult patients: a multicentre study

OBJECTIVES

To evaluate dento-skeletal changes following conventional anchorage molar distalization therapy in adult patients.

SETTING AND SAMPLE POPULATION

Thirty-three patients (25 women, mean age 23 years 1 months ± 3 months; 8 men, mean age 28 years 3 months ± 7 months) were recruited from 4 Board Certified specialists. All subjects underwent molar distalization therapy using intra-oral distalizing appliances.

SUBJECTS AND METHODS

Cephalometric headfilms were available for all subjects before (T1) and at the end of comprehensive treatment (T2). The initial and final measurements and treatment changes were compared by means of a paired t-test.

RESULTS

Mean total treatment time was 3 years 2 months ± 6 months. Maxillary first molar distalized 2.9 ± 0.6 mm contributing 64.4% to Class II molar correction, whereas mandibular first molar showed a concomitant mesial movement of 1.6 ± 0.5 mm. Maxillary incisors retroclined an average of 5.8° ± 3.9°, lower incisors proclined 4.1° ± 1.1° and the occlusal plane rotated downwards and backwards 1.8° ± 2.1°. Clockwise rotation of the mandible (1.7° ± 0.5°) and increase in lower facial height (2.5 ± 1.5 mm) were also observed.

CONCLUSIONS

Maxillary molar distalization therapy can be successfully performed in adult patients despite a slight increase in vertical facial dimension should be considered.

Treating Class II malocclusion in children. Vertical skeletal effects of high-pull or low-pull headgear during comprehensive orthodontic treatment and retention

OBJECTIVES

To evaluate, in Class II malocclusion children, vertical skeletal changes occurring with high- and low-pull headgear during non-extraction comprehensive orthodontic treatment, and retention.

SETTING AND SAMPLE POPULATION

Two groups of thirty Class II malocclusion children (mean age 10.8 years) who had undergone non-extraction comprehensive orthodontic treatment with either high- or low-pull headgear and fixed appliances.

MATERIAL AND METHODS

Retrospective longitudinal study, where pre-treatment, post-treatment and at least 2 year post-retention lateral cephalometric radiographs were analyzed. Comparisons were made concerning changes during treatment and retention in high- or low-pull headgear-treated children. Correlation analyses were carried out investigating changes in vertical cephalometric parameters and pre-treatment vertical facial pattern or type of headgear used.

RESULTS

During treatment, sagittal relationships improved in all children and remained stable during retention. Vertically, in both high- and low-pull headgear groups, the intermaxillary angle as well as the maxillary and mandibular plane angles did not show statistically significant changes during treatment or retention, and large variation was seen between patients. When pooling the whole patient sample, change in the vertical facial pattern was independent of the pre-treatment vertical facial pattern or type of headgear used.

CONCLUSION

When treating Class II malocclusion children non-extraction with high- or low-pull headgear and fixed appliances, changes in vertical skeletal relationships demonstrate wide variation, both during treatment and retention. Dentoalveolar changes brought about by these appliances may not be able to make a predictable difference in vertical skeletal patterns of growing patients.

[Not Available]

Dr Birte Melsen est née à Aabenraa, au Danemark, le 9 Juin 1939.

Elle fait ses études dentaires au Royal Dental College à Aarhus, Danemark (1964).

Elle est professeur et chef du Département d’Orthodontie à l’Université dentaire, à Aarhus, depuis 1975 et traite exclusivement des adultes en pratique privée à Lübeck, en Allemagne (temps partiel depuis 1986).

Birte Melsen est l’auteur de plus de 350 articles et publications, dans des domaines aussi variés que la croissance et le développement cranio-facial (recherches sur cadavres humains), la biologie osseuse et les réactions tissulaires, la distraction osseuse, les implants dentaires, les traitements adultes, les asymétries, la stabilité à long terme, sans oublier les mini-vis orthodontiques d’ancrage temporaire, les attaches auto-ligaturantes et l’imagerie.

Dentoskeletal effects of the fast-back molar distalizer followed by fixed appliances

INTRODUCTION

The purpose of this study was to analyze the skeletal and dentoalveolar changes induced by the Fast-Back appliance followed by fixed appliances when compared with untreated Class II controls.

MATERIALS AND METHODS

The treated and untreated samples consisted of 27 subjects each (16 girls and 11 boys in the Fast-Back Group, FBG; 15 girls and 12 boys in the control Group, CG) with mean ages at the start of treatment of 13 years 3 months in the FBG and 13 years 2 months in the CG. Subjects of the FBG were treated during either the pubertal or postpubertal periods. Lateral cephalograms were analyzed at 2 observation periods: before distalization (T1) and after comprehensive orthodontic treatment appliance (T2). The T1-T2 changes in the FBG were contrasted with those in the CG by means of Mann-Whitney U test (p<0.05).

RESULTS

Treatment induced an average correction of molar relationship of 2.4mm. The significant correction of the overjet (2.1mm) was associated with a significant amount of lower incisor proclination (3.8 degrees). A significant extrusion of lower molars (1.8mm) was recorded in the FBG. The FBG showed also a significant increase in total mandibular length (Co-Gn, 2.6mm), a counterclockwise rotation of the palatal plane (1.4 degrees), an increase in anterior facial height (N-Me, 2.7 mm), and in mandibular ramus height (Co-Go, 2.6mm).

CONCLUSIONS

The Fast-Back is an effective appliance for Class II correction during the pubertal or postpubertal periods.

Long-term evaluation of the molar movements following Pendulum and fixed appliances

OBJECTIVE

To describe the molar movements and skeletal changes associated with Pendulum-fixed appliance treatment and the long-term postretention period.

SUBJECTS AND METHODS

The treatment sample consisted of 76 Class II patients, 35 males and 41 females. Lateral cephalograms were obtained at the start of treatment (T1); the end of distalization (T2); the end of orthodontic fixed appliance therapy (T3); and long-term observation (7 years 2 months later; T4). Mean age was 12 years 11 months at T1, 13 years 8 months at T2, 15 years 4 months at T3, and 22 years 5 months at T4. The average amount of Class II molar relationship was 3.1 mm, with a mean overjet of 5.9 mm at the beginning of treatment. A paired t-test was used to identify significant between-group differences between T2-T4 and T3-T4.

RESULTS

Distal molar movement was obtained during the distalization phase (T2), and more than half of the distalizing effect was maintained at the end of maxillary growth (T4). Most of the relapse occurred during fixed appliance therapy (T3), whereas no significant change was detected in the postretention period (T4). The molar relationship did not show any significant difference between T2 and T4. The vertical facial dimension increased during the distalization phase (T2) and fixed appliance therapy (T3) but returned to the initial values during the postretention period (T4).

CONCLUSIONS

The Pendulum appliance induces significant dentoalveolar effects, which can be partially maintained during the long-term period. The Class I molar relationship does not change during completion of individual growth. Increase in vertical facial dimension represents a temporary effect.

Stability and relapse of maxillary anterior crowding treatment in class I and class II Division 1 malocclusions

INTRODUCTION

The maxillary anterior teeth are the most important to facial esthetics because they are the first to show on a smile. Therefore, stability of the maxillary anterior teeth alignment is an important issue. The objective of this study was to compare the stability of maxillary anterior tooth alignment in Class I and Class II Division 1 malocclusions.

METHODS

The sample comprised dental casts of 70 patients with Class I and Class II Division 1 malocclusions and a minimum of 3 mm of maxillary anterior crowding measured by an irregularity index. The patients were treated with extractions and evaluated at pretreatment and posttreatment and at least 5 years after treatment. The sample was divided into 3 groups: group 1, Class I malocclusion treated with 4 first premolar extractions comprising 30 subjects, with an initial age of 13.16 years and 8.59 mm of initial maxillary irregularity; group 2, Class II malocclusion treated with 4 first premolar extractions comprising 20 subjects, with an initial age of 12.95 years and 11.10 mm of maxillary irregularity; and group 3, Class II malocclusion treated with 2 first maxillary premolar extractions comprising 20 subjects, with an initial age of 13.09 years and 9.68 mm of maxillary irregularity.

RESULTS

The decrease in the maxillary irregularity index was significantly greater in group 2 than in group 1 during treatment. The stability of maxillary anterior alignment was 88.12% over the long term; 77% of the linear displacement of the anatomic contact points tended to return to their original positions.

CONCLUSIONS

Stability of maxillary anterior alignment between the 3 groups was similar. The stability of maxillary anterior alignment was high over the long term, but a high percentage of teeth tended to return to their original positions.

Análise do movimento inicial de molares superiores submetidos a forças extrabucais: estudo 3D

OBJETIVO: analisar pelo método dos elementos finitos o deslocamento dos molares superiores frente a três diferentes inclinações do arco externo do aparelho extrabucal na tração do tipo cervical. MÉTODOS: maxila, dentes montados em má oclusão de Classe II e aparelho foram modelados através de formulação variacional e seus valores reproduzidos em coordenadas X, Y e Z. Foram realizadas simulações em microcomputador tipo PC, utilizando o programa ANSYS versão 8.1. Cada modelo de arco externo reproduziu linhas de força que passaram (1) acima (AcCR), (2) abaixo (AbCR) e (3) no centro de resistência (CR) do molar permanente superior de um mesmo modelo portador de má oclusão de Classe II. A avaliação restringiu-se ao movimento inicial dos molares frente à força extrabucal de 4 Newtons. RESULTADOS: o movimento distal inicial dos molares, tendo como ponto de referência a mesial do tubo, foi maior na coroa do modelo AbCR (0,47x10-6), e maior na raiz do modelo AcCR (0,32x10-6), provocando inclinações da coroa para distal e mesial, respectivamente. No modelo CR, os pontos na coroa (0,15x10-6) e raiz (0,12x10-6) deslocaram-se para distal equilibradamente, resultando em movimento de translação. Em todos os modelos, numa vista oclusal, houve tendência de rotação distal inicial da coroa, porém no modelo CR esse movimento foi muito pequeno. No sentido vertical (Z), todos os modelos revelaram movimento extrusivo (AbCR= 0,18x10-6; CR= 0,62x10-6; AcCR= 0,72x10-6). CONCLUSÃO: a simulação computacional do uso de aparelho extrabucal com tração cervical revelou a ocorrência de movimento extrusivo e distal, podendo ser por inclinação distal de coroa, de raiz ou movimento de translação.

[Are extraoral forces justified in the early treatment of Class II malocclusions?]

First phase class II early treatments are able to restore a correct growth. DAC (Distal Active Concept) is an early fixed treatment using class II elastics, coils and springs. The aim of this retrospective study was to evaluate short and long term dental and skeletal effects of head-gear applied on upper first molars associated to class II elastics and to compare our results to a sample treated with early DAC. Headgear group included 37 subjects. DAC group included 100 subjects. Cephalometric values came from Pancherz's and Tweed's analysis. Lateral head-films were analysed at t1 (before early active treatment), at t1' (after early active treatment) and at t2 (before second stage in permanent dentition). T-tests were performed to compare the groups. Results were quite similar for these two types of treatment showing nevertheless greater mandibular answer in DAC group. Only a prospective randomised study would be able to precise these observations.

Sutural strain in orthopedic headgear therapy: a finite element analysis

INTRODUCTION

The goal of this study was to analyze the strains induced in the sutures of the midface and the cranial base by headgear therapy involving orthopedic forces. Does the mechanical signal induced in the sutures sufficiently account for a growth-influencing effect?

METHODS

A finite element model of the viscerocranium and the neurocranium was used. It consisted of 53,555 tetrahedral elements and 97,550 nodes. The strain induced in the sutures of the cranial base and the midface when applying orthopedic headgear forces of 5 and 10 N was computed and recorded with an interactive measurement tool.

RESULTS

The magnitude and the distribution of the measured strains depended on the level and the direction of the acting force. Overall, the strain values measured at the sutures of the midface and the cranial base were moderate. The measured peak values at a load of 5 N per side were usually just below 20 microstrain irrespective of the force direction. A characteristic distribution of strain values appeared on the anatomical structures of the midface and the cranial base for each vector direction. The measurements based on the finite element method provided a good overview of the approximate magnitudes of sutural strains with orthopedic headgear therapy. The signal arriving in the sutures is apparently well below threshold, since the maximum measured strains in most sutures were about 100 fold lower than the minimal effective strain. A skeletal effect of the orthopedic headgear due to a mechanical effect on sutural growth cannot be confirmed from these results.

CONCLUSIONS

The good clinical efficacy of headgear therapy with orthopedic forces is apparently based mainly on dentoalveolar effects, whereas the skeletal effect due to inhibition of sutural growth is somewhat questionable.

Treatment and posttreatment changes with combined headgear therapy

OBJECTIVE

To determine the effects of combined headgear treatment in high-angle patients and to evaluate the differences 2 years after treatment.

MATERIALS AND METHODS

The study material consisted of lateral cephalograms of 21 patients (13 girls and eight boys; mean age 10 years 3 months) with Class II dental relationship. Only extraoral combined traction that was applied to maxillary first molars was used in the treatment of all patients. The patients were instructed to wear the appliance 20 hours per day until the molar relationship was corrected. The treatment time was approximately 5 months. At the beginning (T0), at the end (T1), and approximately 2 years after (T2) combined headgear treatment, lateral cephalometric radiographs were obtained.

RESULTS

SNA and ANB angles and convexity decreased significantly during treatment (T0-T1; P<.05 and P<.01, respectively), and the net changes (T0-T2) in ANB angle and convexity were also found to be statistically significant (P<.01). During treatment, significant distal movement was found in the upper first molar, and the second premolar and molar were also distalized significantly (P<.001). At the end of 2 years, there was a significant mesial migration of the upper molars and the second premolar during the posttreatment period, but all of them were positioned more distally compared to the beginning of treatment (P<.001). The decrease in molar relation was statistically significant during the T0-T1 and T0-T2 periods (P<.001).

Long-term stability of orthodontic treatment and patient satisfaction. A systematic review

OBJECTIVE

To evaluate morphologic stability and patient satisfaction at least 5 years after orthodontic treatment.

MATERIALS AND METHODS

Published literature was searched through the PubMed and Cochrane Library electronic databases from 1966 to January 2005. The search was performed by an information specialist at the Swedish Council on Technology Assessment in Health Care. The inclusion criteria consisted of a follow-up period of at least 5 years postretention; randomized clinical trials, prospective or retrospective clinical controlled studies, and cohort studies; and orthodontic treatment including fixed or removable appliances, selective grinding, or extractions. Two reviewers extracted the data independently and also assessed the quality of the studies.

RESULTS

The search strategy resulted in 1004 abstracts or full-text articles, of which 38 met the inclusion criteria. Treatment of crowding resulted in successful dental alignment. However, the mandibular arch length and width gradually decreased, and crowding of the lower anterior teeth reoccurred postretention. This condition was unpredictable at the individual level (limited evidence). Treatment of Angle Class II division 1 malocclusion with Herbst appliance normalized the occlusion. Relapse occurred but could not be predicted at the individual level (limited evidence). The scientific evidence was insufficient for conclusions on treatment of cross-bite, Angle Class III, open bite, and various other malocclusions as well as on patient satisfaction in a long-term perspective.

CONCLUSIONS

This review has exposed the difficulties in drawing meaningful evidence-based conclusions often because of the inherent problems of retrospective and uncontrolled study design.

Applicability of mathematical curve-fitting procedures to late mixed dentition patients with crowding: A clinical-experimental evaluation

INTRODUCTION

This study aimed at investigating the applicability of a polynomial function laterally, combined with a parabola or hyperbolic cosine function in the front, for mandibular curve-fitting purposes in late mixed dentition patients with crowding. The possible advantages of using a bilateral center of gravity for curve construction were examined.

METHODS

After digitizing 30 mandibular casts (14 boys, 16 girls), 14 coordinates per model were used to fit a hyperbolic cosine function or a parabola in the anterior segment and a third-degree polynomial function bilaterally, by using the method of least squares. The lateral functions were fitted by using a mirrored center of gravity for the premolar/molar area. To assess curve fit and enable comparison with other studies, Pearson correlation coefficients, residuals, mean square error, root mean square values, and average perpendicular distance of the points to the constructed curve were calculated.

RESULTS AND CONCLUSIONS

High correlation coefficients were found (mean, 0.994; SD, 0.004). The mean square error (1.80 mm2, SD, 1.12 mm2) and the average root mean square value (1.28 mm, SD, 0.42 mm) appears to be comparable with other studies. Combined with the relatively low average perpendicular distance of the points to the curve (mean, 0.47 mm; SD, 0.16 mm), it seems that this method is successful in describing mandibular arch forms of mixed dentition patients with crowding, and it could be a useful tool in treatment planning.

A comparison of two intraoral molar distalization appliances: Distal jet versus pendulum

INTRODUCTION

This study compared the dentoalveolar and skeletal effects on Class II malocclusions of the distal jet with concurrent full fixed appliances and the pendulum appliance both followed by fixed appliances.

METHODS

The 2 samples each consisted of 32 subjects (19 girls and 13 boys) with mean ages at the start of treatment of 12 years 3 months in the distal jet group and 12 years 6 months in the pendulum group. The durations of the distalization phase of treatment were 10 months in the distal jet group and 7 months in the pendulum group, and the durations of the second phase of treatment with fixed appliances were 18 months in the distal jet group and 24 months in the pendulum group. Lateral cephalograms were analyzed at 3 observation times: before treatment, after distalization, and after orthodontic treatment.

RESULTS

During molar distalization, the pendulum subjects showed significantly more distal molar movement and significantly less anchorage loss at both the premolars and the maxillary incisors than the distal jet subjects. The distal jet used simultaneously with fixed appliances and the pendulum were equal in their ability to move the molars bodily. Very little change occurred in the inclination of the mandibular plane at the end of the 2-phase treatment (less than 1 degrees ) in both groups. At the end of comprehensive treatment, the maxillary first molars were 0.6 mm mesial to their original positions in the distal jet group and 0.5 mm distal in the pendulum group. Nevertheless, total molar correction was identical in the 2 groups (3.0 mm), and both appliances were equally effective in achieving a Class I molar relationship. Simultaneous edgewise orthodontic treatment during molar distalization in the distal jet group shortened the overall treatment time but produced significant flaring of both maxillary and mandibular incisors at the end of treatment. The impact on the soft tissue profile was minimal with both appliances.

Assessment of mandibular growth and response to orthopedic treatment with 3-dimensional magnetic resonance images

INTRODUCTION

Three-dimensional (3D) craniofacial images are commonly used in clinical studies in orthodontics to study developmental and morphologic relationships.

METHODS

We used 3D magnetic resonance imaging to study relationships among craniofacial components during the pubertal growth spurt and in response to Fränkel appliance therapy. The sample for this prospective study was 156 high-resolution magnetic resonance images with 1 mm isotropic voxel resolution of 78 subjects taken initially (T1) and 18 +/- 1 months (T2) after treatment or an observation period. The subjects were Brazilian children; 28 were treated and 25 were untreated for Class II malocclusion, and 25 were untreated with normal occlusions. A Procrustes geometric transformation of 3D skeletal landmarks was used to assess growth or treatment alterations from T1 to T2. The landmarks were located on the mandibular rami and the other craniofacial parts specifically related to the mandibular growth (the middle cranial fossae and the posterior part of the bilateral nasomaxilla). This allowed visualization of the entire volumetric dataset with an interactive 3D display.

RESULTS

Statistically significant differences were found in the relative 3D skeletal growth directions from T1 to T2 for treated vs untreated Class II children (Bonferroni-adjusted P < .001) and for treated Class II vs normal-occlusion subjects ( P < .001). The major differences in the treated group were increased mandibular rami vertical dimensions and more forward rami relative to the posterior nasomaxilla and the middle cranial fossae. Principal component analysis made it possible to show individual variability and group differences in the principal dimensions of skeletal change.

CONCLUSIONS

These methods are generalizable to other imaging techniques and 3D samples, and significantly enhance the potential of systematically controlled data collection and analysis of bony structures in 3 dimensions for quantitative assessment of patient parameters in craniofacial biology.

Comparison of relative mandibular growth vectors with high-resolution 3-dimensional imaging

INTRODUCTION

The mandibular rami and their endochondrally growing condyles develop in many directions relative to the variable anatomic patterns of the nasomaxilla and middle cranial fossae during growth and response to orthopedic treatment.

METHODS

High-resolution magnetic resonance images were used to compare 3-dimensional (3D) growth vectors of skeletal displacement and bone remodeling in 25 untreated subjects with Class II malocclusions, 28 subjects with Class II malocclusions who were treated with Fränkel appliance therapy, and 25 subjects with normal occlusions. Marked differences were noted over an 18-month observation period. The 3D coordinates of anatomic landmarks were registered by Procrustes fit to control for rotation, translation, and scale differences.

RESULTS

Compared with untreated Class II and normal-occlusion subjects, the treated group showed highly significant differences in the 3D displacement/remodeling vectors of gonion and pterygomaxillary fissure relative to condylion and middle cranial fossae bilateral skeletal landmarks, by using both permutation tests ( P < .001) and a general linear multivariate model ( P < .0001).

CONCLUSIONS

In a prospective and systematically controlled study, we quantitatively described significant 3D rami skeletal compensations in the structural assembly of facial morphogenesis at the beginning of the adolescent growth spurt using novel modeling techniques. These techniques have facilitated quantification of relative 3D growth vectors to illustrate skeletal changes with Fränkel appliance therapy. Future studies are required to assess the long-term clinical significance of our findings.

The transfer of occlusal forces through the maxillary molars: a finite element study

The morphology of the skeleton is known to reflect functional demand. A change in the intramaxillary position of molars can be expected to influence the transfer of occlusal forces to the facial skeleton. A finite element analysis allows us to simulate the displacement of a molar in relation to the well-defined morphology of the maxilla. Three 3-dimensional unilateral models of a maxilla from a skull with skeletal Class I and neutral molar relationships were produced based on CT-scan data. The maxillary first molar was localized so that the contour of the mesial root continued into the infrazygomatic crest. When the molar was loaded with occlusal forces, the stresses were transferred predominantly through the infrazygomatic crest. This changed when mesial and distal displacements of the molars were simulated. In the model with mesial molar displacement, a larger part of the bite forces were transferred through the anterior part of the maxilla, resulting in the buccal bone being loaded in compression. In the model with distal molar displacement, the posterior part of the maxilla was deformed through compression; this resulted in higher compensatory tensile stresses in the anterior part of the maxilla and at the zygomatic arch. This distribution of the occlusal forces might contribute to the posterior rotation often described as the orthopedic effect of extraoral traction.