Long-term skeletal effects of high-pull headgear ... - Angle Orthodontist

Original Article

Long-term skeletal effects of high-pull headgear followed by fixed appliances for the treatment of Class II malocclusions E. Erin Bilboa; Steven D. Marshallb; Karin A. Southardc; Verrasathpurush Allareddyd; Nathan Holtone; Allyn M. Thamesf; Marlene S. Otsbyg; Thomas E. Southardh ABSTRACT Objectives: The long-term skeletal effects of Class II treatment in growing individuals using highpull 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 ¼ 21, mean age ¼ 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 ¼ 21, mean age ¼ 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 ¼1.9258, P , .0001; FH-NA ¼3.0428, P , .0001; linear measurement A-point to Vertical Reference ¼3.859 mm, P , .0001) and reduction of the ANB angle (1.7678, 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. (Angle Orthod. 2018;88:530–537.) KEY WORDS: Class II malocclusion; Headgear; Long-term stability; Orthopedics

INTRODUCTION

or in conjunction with, fixed edgewise appliances, have been widely reported for cervical-pull headgear but not

The long-term effects on maxillary position and maxillary dentoalveolar changes resulting from one phase treatment using extra-oral traction followed by,

for high-pull headgear. Wieslander1 demonstrated that maxillary growth inhibition (reduction of SNA) and

Private Practice, Birmingham, AL, USA. Visiting Professor, Department of Orthodontics, College of Dentistry and Dental Clinics, The University of Iowa, Iowa City, IA, USA. c Professor Emeritus, Department of Orthodontics, College of Dentistry and Dental Clinics, The University of Iowa, Iowa City, IA, USA. d Associate Professor, Department of Orthodontics; and Collegiate Director of Clinical Research, College of Dentistry and Dental Clinics, The University of Iowa, Iowa City, IA, USA. e Assistant Professor, Department of Orthodontics, College of Dentistry and Dental Clinics, The University of Iowa, Iowa City, IA, USA. f Private Practice, Auburn, AL, USA. g Private Practice, Billings, MT, USA. h Professor and Head, Department of Orthodontics, College of Dentistry and Dental Clinics, The University of Iowa, Iowa City, IA, USA. Corresponding author: Dr Steven Marshall, Department of Orthodontics, College of Dentistry and Dental Clinics, S220 DSB, 801 Newton Rd., Iowa City, IA 52246, USA (e-mail: [email protected]) a b

Accepted: February 2018. Submitted: September 2017. Published Online: April 18, 2018 Ó 2018 by The EH Angle Education and Research Foundation, Inc. Angle Orthodontist, Vol 88, No 5, 2018

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DOI: 10.2319/091517-620.1

LONG-TERM SKELETAL EFFECTS OF HIGH-PULL HEADGEAR

maxillary molar distalization to achieve Class I molar relationship using cervical-pull headgear was stable when measured 6 years post-treatment relative to controls. Melsen, using metallic implants to record jaw and tooth movements in 20 subjects treated with cervical-pull headgear followed by fixed-edgewise treatment, demonstrated a temporary effect on the maxilla as her subjects exhibited, on average, normal downward, and forward maxillary and mandibular growth after being ‘‘released’’ from maxillary corpus horizontal restriction and clockwise rotation produced by cervical traction.2 Evaluated 7 years after headgear treatment, Melsen’s subjects maintained class I molar relationship attained by cervical headgear treatment during downward and forward maxillary corpus growth similar to that of untreated controls over the same period.3 Melsen did not quantify long-term horizontal maxillary restriction compared to controls. Additional studies on the long-term effects of cervical traction come from non-randomized retrospective observational studies evaluating the use of cervicalpull headgear before or during edgewise treatment, with follow-up measurements after a minimum postretention period of 2 years.4–11 Although the vast majority of these studies did not include comparison to matched controls, by and large they showed that reduction of SNA by cervical-pull face bow traction to the maxilla is maintained throughout edgewise treatment, retention, and post-retention. After restriction of forward maxillary growth with cervical headgear, during continued edgewise treatment and growth, measurable changes in SNA reverted to an expected pattern of continued forward growth. In contrast, the SNB and SN–MP angles showed little alteration during cervical headgear treatment, edgewise treatment, and continued growth compared to that anticipated in the growth of untreated individuals.12 The long-term effects of high-pull headgear used in conjunction with fixed edgewise appliances in the treatment of Class II malocclusion compared to untreated controls has not been reported. Phan et al. reported on the long-term skeletal effects of headgear treatment on Class II malocclusion, but only five of the 30 subjects studied were treated with high-pull headgear and data for these individuals was pooled with subjects treated with cervical headgear and/or intermaxillary elastics.9 Given the lack of published reports on long-term assessment of patients treated with high-pull headgear, the purpose of the present study was to evaluate the long-term effects of Class II treatment applied as one phase treatment, using only high-pull headgear followed by fixed orthodontic appliances. This study tests the hypothesis that use of high-pull headgear followed by fixed orthodontic

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appliances is associated with longitudinal changes in angular and linear cephalometric outcomes. MATERIALS AND METHODS Study Design and Participants This study received Institutional Review Board Approval (IRB #201509793) by the Office of Human Subjects Protection of the University of Iowa. For this retrospective study, records were obtained from consecutively treated cases in the University of Iowa College of Dentistry and Dental Clinics, Department of Orthodontics. Inclusion criteria were: (1) Class II molar relationship, (2) Late mixed dentition stage of tooth development, (3) SN-MP angle . 288, (4) One phase of orthodontic treatment beginning with high-pull headgear alone and directly followed by treatment with a complete fixed edgewise appliance, (5) Treatment with high-pull headgear until Class I molar was achieved, and (6) Availability of complete records at four timepoints: prior to any treatment (T1), prior to beginning fixed edgewise appliance therapy (T2), at retention (T3), and at a minimum of 24 months post retention (T4). Patients with craniofacial anomalies or syndromes were not included in the study. For all study group subjects, high-pull facebow headgear engaging the maxillary first molars was used as the primary means of anteroposterior dental and skeletal correction. Twelve patients wore Class II elastics at the end of fixed edgewise treatment, but only for a very short time: an average time period of 2.95 months between T3 and T4. The control sample was chosen from the historical records of two growth studies. The subjects chosen for the control sample were matched as closely as possible by the gender, initial age, age at the three subsequent time points, initial cephalometric characteristics, and initial molar relationship of the study sample. The study group consisted of nine females and 12 males. The control group consisted of 11 females and 10 males. Ages and initial characteristics of the study group and control group are displayed in Table 1. Sample Size Estimation The sample size estimation for this study was based on one observational study and two randomized controlled trials, where measurements of SNA were compared between a headgear-treated group and a control group.5,13,14 Data from these studies were used to arrive at a pooled standard deviation for calculation of a sample size estimate. Based on these data, sufficient statistical power (80% power, 0.05 level of Angle Orthodontist, Vol 88, No 5, 2018

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BILBO, MARSHALL, SOUTHARD, ALLAREDDY, HOLTON, THAMES, OTSBY, SOUTHARD

Table 1. Comparison of Descriptive Statistics for Study Group and Control Group Study Group Characteristic Age T1 (months) T2 (months) T3 (months) T4 (months) Initial measurements SNA (8) SNB (8) ANB (8) FH-NA (8) FH-NPog (8) SN-MP (8) FMA (8) ACB (mm) A-point Horizontal (mm) B-point Horizontal (mm) Pog Horizontal (mm) ANS Vertical (mm) PNS Vertical (mm) Me Vertical (mm)

Control Group

Mean

Median

S. D.

Mean

Median

SD

P Value

127.0 145.9 173.3 231.4

126.0 147.0 175.0 220.0

12.5 14.6 17.5 33.9

131.3 147.5 171.1 245.7

132.0 144.0 168.0 229.0

6.0 6.8 8.4 47.7

.248 .630 .614 .281

81.1 76.1 5.0 88.4 83.7 36.6 29.3 67.6 65.8 57.6 56.6 38.7 38.3 95.1

81.2 75.7 5.2 89.1 84.2 36.2 29.5 67.3 66.0 57.4 56.6 39.2 38.6 94.9

3.1 2.8 1.4 3.6 3.3 4.9 4.7 3.3 4.6 6.2 7.3 2.2 2.3 3.8

80.0 75.9 4.1 88.5 85.0 35.9 27.4 66.2 63.3 55.6 55.1 38.8 37.7 93.8

79.3 75.6 4.5 88.9 83.5 36.2 27.4 66.0 62.7 54.8 54.0 39.3 37.6 94.0

3.9 3.6 1.8 3.5 4.1 4.5 5.8 2.7 3.4 5.0 6.6 2.5 2.3 4.5

.131 .765 .097 .894 .282 .587 .293 .188 .081 .184 .407 .919 .395 .280

significance, and two-sided tests) to detect an outcome variation (effect size) in SNA angle of 1.08 required a sample size of 20 subjects for each group. As it was deemed skeletal changes in the SNA angle . 18 to be clinically significant, the sample size had sufficient power to detect meaningful skeletal change at A-point. Key Study Variables A list of cephalometric landmarks, lines, and angles used for measurement are shown in Table 2 and displayed in Figure 1. Linear measurements were taken relative to constructed horizontal and vertical reference axes that intersected at the cephalometric landmark Sella. The vertical axis (y-axis) passed through Sella and was perpendicular to the horizontal axis (x-axis) defined as a line 78 below the Sella– Nasion line following Hack et al.15 The midpoint between bilateral landmark projections was recorded when appropriate. All linear measurements were taken to the nearest 0.1 mm. Angular measurements were taken to the nearest 0.18. Most of the linear measurements in this study were to cephalometric landmarks in the mid-sagittal plane. For landmarks not in the midsagittal plane, the average distance between left and right landmark was used. All linear measures were corrected for magnification prior to statistical analysis. Corrected linear measurements were obtained as the product of the equation multiplying each linear measurement value to the following quotients:16 (1) distance from x-ray source to subject’s mid-sagittal plane, and (2) distance from x-ray source to subject’s radiograph film. Angle Orthodontist, Vol 88, No 5, 2018

Outcomes Evaluated Outcomes gathered in this study were lateral cephalometric outcomes (changes in angles SNA, SNB, ANB, FH-NA, FH-NPog, SN-MP, FMA, and linear changes in ACB, A-point Horizontal, B-point Horizontal, Pogonion Horizontal, ANS-Vertical, PNSVertical, Menton-Vertical). First molar relationship was recorded for each study and control participant. Independent variables in this study were: treatment (treatment vs no treatment), initial cephalometric values, initial first molar relationships, starting age of treatment, and gender. Examiner Reliability To evaluate measurement reliability, twenty cephalograms representing five subjects and five controls were randomly selected and remeasured for selected linear and angular measurements. The investigator was blind to any previous measurements. To test measurement reliability, the precision of measurement and re-measurement of 12 linear and angular measures was estimated using the intraclass correlation coefficient (ICC) and Dahlberg’s formula (Table 3). Statistical Analysis Outcomes (changes in SNA, SNB, ANB, SN-MP, FMA, ACB, A-point Horizontal, B-point Horizontal, Pogonion Horizontal, ANS Vertical, PNS Vertical, Menton Vertical, FH-NA, FH-NPog, and FMA) across different time points (T2 to T1, T3 to T1, and T4 to T1) were compared between the study and control groups

LONG-TERM SKELETAL EFFECTS OF HIGH-PULL HEADGEAR Table 2. List of Cephalometric Landmarks, Lines and Angles Used for Measurement Landmark Sella Nasion A-point B-point Pogonion Menton Gonion Anterior nasal spine Posterior nasal spine Linear measures (Figure 1) ACB A-point Horizontal B-point Horizontal ANS Vertical PNS Vertical Menton Vertical

Angular measures SNA SNB ANB FH–NA angle FH–NPog angle SN–MP FMA

Abbreviation S N A B Pog Me Go ANS PNS Definition Horizontal distance from the vertical reference axis to Nasion Horizontal distance from the vertical reference axis to A-point Horizontal distance from the vertical reference axis to B-point Vertical distance from the horizontal reference axis to ANS Vertical distance from the horizontal reference axis to PNS Vertical distance from the horizontal reference axis to Menton Definition Angle formed at the intersection S–N and N–A lines Angle formed at the intersection S–N and N–B lines Angle formed at the intersection N–A and N–B lines Angle formed at the intersection FH plane and N–A line Angle formed at the intersection FH plane and N–Pog line Angle formed at the intersection S–N line and Go–Me plane Angle formed at the intersection FH and Go–Me planes

of of of of of of of

by multivariable linear regression models. In these models, the potential confounding effects of gender, age at T1, and duration (eg, time difference between T2 to T1, T3 to T1, or T4 to T1) were adjusted. All regression models were fit using the ordinary least squares approach. Parameter estimates of changes in outcomes and associated 95% confidence intervals were computed. All statistical tests were two-sided and a P value of ,.05 was deemed to be statistically significant. Statistical analyses were conducted using SPSS Version 24.0 software (IBM Corp, Armonk, NY).

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ship at all time points T1-T4. The results of the multivariable linear regression models, following adjustment for the effects of gender, age at T1, and difference in duration between time points, are summarized in Table 4. Those in the study group had negative changes (reduction) in the SNA angle from T2 to T1 (parameter estimate ¼ 1.387, P , .001), T3 to T1 (parameter estimate ¼2.373, P , .001), and T4 to T1 (parameter estimate ¼1.925, P , .001), in the FHNA angle from T2 to T1 (parameter estimate ¼1.578, P ¼ .02), T3 to T1 (parameter estimate ¼ 2.875, P , .001), and T4 to T1 (parameter estimate ¼ 3.042, P ¼ .001), and in A-point horizontal from T2 to T1 (parameter estimate ¼ 1.248, P ¼ .04), T3 to T1 (parameter estimate ¼ 2.687, P , .001) and T4 to T1 (parameter estimate ¼ 3.859, P , .001) when compared to controls. This was accompanied by those in the study group showing negative changes in ANB from T2 to T1 (parameter estimate ¼0.884, P , .001), T3 to T1 (parameter estimate ¼1.501, P , .001), and from T4 to T1 (parameter estimate ¼1.767, P , .001) when compared to controls. There was no significant difference in SNB changes between the study and control groups. There were no significant horizontal changes in B-point or Pogonion, nor were there significant changes in the angle FH– NPog between the study and control groups with the exception of the time period T3 to T1. Those in the study group had negative changes in B-point horizontal, in Pogonion Horizontal, and in angle FH–NPog from T3 to T1 (parameter estimate ¼ 2.279, P ¼ .02; parameter estimate ¼ 2.279, P ¼ .02; parameter estimate ¼ 1.401, P ¼ .03, respectively) when compared to controls. Long term (T4–T1) there were no significant differences in changes of these mandibular measurements between study and control groups. There were no significant changes in SN–MP angle or the FMA between the study and control groups with the exception of the time period T3 to T1. The study group had positive difference in SN–MP and FMA, from T3 to T1 (parameter estimate ¼ 1.338, P ¼ .04), and (parameter estimate ¼ 2.067, P ¼ .02), respectively, when compared to controls. There were no significant differences in changes of ACB between the study and control groups across different time points. There were no significant differences in vertical changes of ANS and PNS between study and controls. Those in the study group had positive vertical changes in Menton from T3 to T1 (parameter estimate ¼ 2.199, P ¼ .04) when compared to controls.

RESULTS All study group participants achieved Class I first molar relationship at T3 that was maintained at T4. All control group participants had Class II molar relation-

DISCUSSION This study focused on assessing the long-term skeletal effect of treatment using high-pull headgear Angle Orthodontist, Vol 88, No 5, 2018

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Figure 1. Linear measurements. Horizontal measurements (left) were taken from a constructed vertical axis through sella. Vertical measurements (right) were taken from a constructed horizontal axis 78 below the Nasion–Sella line and perpendicular to the vertical axis.

immediately prior to, or immediately prior to and during, fixed edgewise appliances (one continuous treatment phase) for correction of Class II malocclusion. The principal finding was that the skeletal effects of highpull headgear, restriction of maxillary growth combined with continued normal mandibular forward growth, were stable long term. The data indicated that the study group experienced significant decreases in SNA angle, FH–NA angle, and horizontal growth at A-point compared to controls. This represents restraint of forward maxillary growth in the study group due to the effect of the high-pull headgear (T2 to T1) that was maintained during subsequent edgewise treatment (T3 to T1) and the retention period (T4 to T1). In contrast,

the data suggests treatment with high-pull headgear and fixed edgewise appliances had no significant longterm effect on the position of B-point. Compared to the control group, the significant treatment effect on Apoint and the nominal treatment effect on B-point resulted in a long-term mean reduction in ANB (1.778, Table 4). The findings for the short-term effect (T2 to T1) of high-pull headgear on the horizontal growth of the maxilla and mandible compare favorably with the results of randomized controlled trials reporting that use of headgear (cervical-pull or straight-pull) or headgear with a maxillary flat-plane bite plate (cervical-pull if SN–MP , 408; high-pull if SN–MP . 408)

Table 3. Measurement Error Estimation for Different Cephalometric Measurements Measurement Linear measurements (mm) A-point H B-point H Pog H ANS V PNS V Me V Angular measurements (degrees) SNA SNB MP-SN FH-Na FH-NPg FMA

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Intrarater ICC

Dahlberg Error

Relative Dahlberg Error

0.9999 0.9991 0.9998 0.9993 0.9984 0.9993

0.205 0.173 0.093 0.076 0.081 0.099

0.32% 0.31% 0.17% 0.20% 0.22% 0.11%

0.9992 0.9993 0.9992 0.9965 0.9990 0.9986

0.102 0.116 0.105 0.235 0.107 0.132

0.13% 0.15% 0.29% 0.27% 0.13% 0.44%


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Table 4. Effect of Treatment on Changes in Outcomes Across Different Time Points (Summary of Estimates from Multivariable Linear Regression Models) Treatment Group Compared to Control Group* Outcome SNA

SNB

ANB

FH-NA angle

FH-NPog angle

SN-MP angle

FMA

ACB

A-point Horizontal

B-point Horizontal

Pogonion Horizontal

ANS Vertical

PNS Vertical

Menton Vertical

Time Points T2 T3 T4 T2 T3 T4 T2 T3 T4 T2 T3 T4 T2 T3 T4 T2 T3 T4 T2 T3 T4 T2 T3 T4 T2 T3 T4 T2 T3 T4 T2 T3 T4 T2 T3 T4 T2 T3 T4 T2 T3 T4

to to to to to to to to to to to to to to to to to to to to to to to to to to to to to to to to to to to to to to to to to to

Parameter Estimate

95% CI

P Value

1.387 2.373 1.925 0.504 0.858 0.134 0.884 1.501 1.767 1.578 2.875 3.042 0.326 1.401 0.548 0.607 1.338 0.800 0.961 2.242 2.070 0.432 0.115 0.240 1.248 2.771 3.859 1.126 2.778 1.859 0.553 2.279 0.755 0.882 1.365 0.160 0.842 1.625 0.250 1.152 2.199 1.312

2.1 to 0.675 3.502 to 1.244 3.019 to 0.831 1.272 to 0.264 2.039 to 0.323 1.384 to 1.116 1.351 to 0.418 2.085 to 0.917 2.403 to 1.132 2.897 to 0.260 4.162 to 0.604 4.734 to 1.351 1.517 to 0.865 2.649 to 0.153 2.129 to 1.032 0.233 to 1.446 0.062 to 2.614 0.911 to 2.510 0.462 to 2.384 0.469 to 4.015 0.137 to 4.277 0.653 to 1.516 1.220 to 0.991 1.552 to 1.072 2.421 to 0.075 4.092 to 1.449 6.572 to 2.758 2.849 to 0.597 4.832 to 0.723 4.179 to 0.460 1.883 to 0.778 4.185 to 0.373 3.164 to 1.655 0.289 to 2.053 0.640 to 3.369 1.025 to 1.345 1.916 to 0.232 1.577 to 4.827 1.567 to 1.068 1.285 to 3.590 0.118 to 4.279 1.053 to 3.678

,.001 ,.001 .001 .19 .15 .83 ,.001 ,.001 ,.001 .02 ,.001 .001 .58 .03 .49 .15 .04 .35 .18 .01 .06 .42 .83 .71 .04 ,.001 ,.001 .19 .009 .11 .40 .02 .53 .13 .18 .78 .12 .31 .70 .34 .04 .27

T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1

* Estimates adjusted for the confounding effects of gender, age at start of treatment, and duration between different time points. Bold type indicates significant P value.

restrained forward growth of the maxilla (decreases in SNA) when used in a phase of treatment prior to, and separate from, edgewise therapy.13,14,17–22 The use of headgear alone (cervical-pull or straight-pull) restricted maxillary forward growth slightly (SNA decreases 18–38), with no change in B-point (and SNB angle) compared to controls.13,14,17,18 This resulted in a mean reduction in ANB angle of about 18.14,17,18 The use of high-pull or cervical-pull headgear, in conjunction with a maxillary bite plate, restricted maxillary forward growth slightly (0.58–18),21,22 reducing ANB by approximately 18 compared to controls.19–22 The mandibular

effects ranged from no significant difference in length or SNB angle change compared to controls,22 to enhanced mandibular growth greater than controls and comparable to that of a Bionator.19,20 Vertical changes from the use of headgear have been reported as non-significant changes in LAFH and SN–MP,20 slight increases in LAFH (0.1 mm),13 and slight increases in SN–MP (18–1.38).14,21 During treatment with fixed edgewise appliances (T3 to T1), the study group displayed a significant restriction of forward growth at B-point and Pogonion, and significant increase in the vertical dimension of the Angle Orthodontist, Vol 88, No 5, 2018

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anterior face (Table 4, SNB, FH-NPog, SN-MP, Pogonion-Horizontal, Menton-Vertical). These significant differences in mandibular position seen at T3 became non-significant long-term. The T3 to T1 findings in this study are in agreement with reports showing small but significant short-term (immediate post-treatment) effects of high-pull or cervical headgear and edgewise appliances on vertical dimension. 4,5,9,10,23–27 However, the results are not in agreement with studies where short-term effects on vertical skeletal relationships were not detected.28–31 The findings for the vertical growth of the maxilla and the inferior point of the chin indicate that, over the long term, high-pull headgear treatment followed by fixed edgewise appliances did not affect vertical development of the face. Both the study group and untreated control group exhibited significant increases in the vertical growth of PNS, ANS, and Menton that were not dissimilar over the long-term (Table 4). This finding of no significant differences for maxillary and mandibular vertical dimension change long-term (T4 to T1) between high-pull headgear treated and untreated groups is the first report of a long-term analysis of the skeletal response to the use of high-pull headgear followed immediately by fixed edgewise appliance treatment. The long-term (post-retention) effects of high-pull headgear have not been studied with randomized trials, but have only been reported in observational studies (controlled and uncontrolled). Long-term observational studies using cervical headgear, just prior to or in conjunction with fixed edgewise appliances (one phase of treatment), have reported that SNA decreases compared to SNB in the short term, and these changes remain stable throughout edgewise treatment and retention.4–12 The long-term (post-retention) findings for the effects of high-pull headgear in the current study are in agreement with these studies using cervical-pull headgear. The study findings should be interpreted keeping the limitations in perspective. Retrospective observational studies suffer from selection bias. Subjects were included for which successful Class II treatment with high-pull headgear was attained, thus excluding outcomes from individuals demonstrating poor compliance, poor response to treatment, or both. The study subjects were drawn from a single center. Therefore, the results are not generalizable to all prospective patients with Class II malocclusion. Also, retrospective studies cannot eliminate biases due to differences in distribution of covariates between study and control groups. There was an attempt to minimize these biases using multivariable linear regression models where the potential confounders were adjusted. Simply put, studies using a matched control group suffer from an Angle Orthodontist, Vol 88, No 5, 2018

uncertainty of alignment of all pertinent descriptive factors between the groups. Notwithstanding these limitations, the results of this study suggest that, with good patient compliance and response, the use of a high-pull facebow headgear, as part of a continuous phase of treatment including fixed edgewise appliances, can provide an effective means of correcting a Class II malocclusion in growing patients that appears to be stable long term. CONCLUSIONS

Class II correction using high-pull headgear followed by fixed edgewise appliance results in restriction of maxillary horizontal growth during treatment that remains stable long term (average retention: 4.08 years). ANB angle reduction with this treatment is achieved through a restriction of A-point forward growth and continued forward growth of the mandible. ANB angle continues to decrease during retention via continued mandibular growth. Treatment with high-pull headgear had no effect on vertical skeletal changes.

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Angle Orthodontist, Vol 88, No 5, 2018