Treatment effects of the light-force chincup

Introduction

The objective of this study was to evaluate the effectiveness of the light-force chincup appliance in correcting the skeletal and dentoalveolar components of Class III malocclusion compared with an untreated Class III control group.

Methods

The treatment sample consisted of 26 patients (11 boys, 15 girls) treated with the light-force chincup (125-250 g). The mean age at the start of treatment in the chincup group was 8.5 years, with posttreatment cephalograms taken on average 2.6 years later. The control group consisted of 20 subjects. The mean age at the start of observation for the control group (6 boys, 14 girls) was 7.3 years, and the mean time of observation was 2.4 years. Lateral cephalograms were analyzed with a specific tracing regimen at the 2 time points for both groups. Treatment outcome were determined. The treatment group subsequently was subdivided into those treated simultaneously with a quad-helix appliance and those with the chincup only. Mann-Whitney U tests for independent samples were performed to evaluate the differences between the treated and untreated groups at both time points, the changes between the 2 time points, and the differences between the groups treated with the quad-helix and chincup, and the chincup only.

Results

The chincup sample showed no significant skeletal changes in the mandible in either the vertical or horizontal direction, except for a slight decrease in SNB angle and an increase in ANB angle. There were significant dentoalveolar changes, particularly uprighting of the mandibular incisors. Significant positive Class III treatment outcomes were recorded in the quad-helix group, including a decrease in mandibular length of 1.9 mm compared with the chincup group.

Conclusions

Fewer than 50% of the subjects treated with the chincup had favorable clinical outcomes. Correction of the initial Class III malocclusion occurred through significant dentoalveolar changes. The light-force chincup did not produce orthopedic changes in the mandible. Maxillary expansion with a quad-helix might aid in the correction of the Class III malocclusion in conjunction with the chincup.

The effects of the chincup on dentofacial growth have been investigated in both animal experiments and cephalometric analyses. The animal experiments on monkeys, rabbits, and rats all demonstrated retardation of ramal growth, closure of the gonial angle, decrease in the prechondroblastic layer of the condylar cartilage, and overall growth retardation of the mandible. Cephalometric studies on humans, however, did not show such consistent results. Several studies reported decreases in mandibular length due to chincup wear. However, most cephalometric studies showed no reduction in mandibular length but demonstrated orthopedic changes, including redirection of mandibular growth with downward and backward repositioning of the mandible and remodeling of the mandibular shape.

In an overview of the chincup literature ( Table I ), we found that treatment protocols used forces between 200 and 900 g. Graber proposed that the use of force levels similar to that of the Milwaukee brace in the range of at least 2 pounds (900 g) per side would obtain orthopedic changes. No studies in the literature attempted to identify the minimum amount of force or the minimum threshold of force needed to obtain an orthopedic change. Thilander, Allen et al, Sugawara and Mitani, and Deguchi et al described contrasting results from the use of chincups that delivered 200 to 300 g of force (light-force chincup). However, these investigations (similar to most chincup studies) had some methodologic drawbacks (lack of adequate untreated Class III controls) or clinical inconsistencies (long duration of chincup wear).

Table I
Chincup studies in the literature with forces measured at the center of the chincup
Author Sample size (n) Sample ethnicity Mean age at T1 or age range Treatment time Force level (g) Untreated controls
Thilander (1963) 60 White 5-16 y 12 mo 200-350 Self-control
(1 y before treatment)
Cleall (1974) 2 White 9.5 y 3 y 900 None
Irie and Nakamura (1975) 29 Japanese Not stated Not stated Not known None
Vego (1976) 5 White 4-9 y 2-9 mo 300-600 Class III (gorecast tracing)
Graber (1977) 30 White 6 y 3 y 900 Class III
Sakamoto (1981) 26 Japanese 7.2 y 2 y 9 mo 500-600 Class III
Mitani and Sakamoto (1984) 3 Japanese 4-8 y 2.5-6 y 500-600 None
Wendell et al (1985) 10 Japanese 5-15 y 3 y 1 mo 500-600 Class III
Ritucci and Nanda (1986) 10 Japanese 7.6 y Not known 500 Class III
Mitani and Fukazawa (1986) 26 Japanese 6-10 y 4-6 y 500-600 Class I
Sugawara et al (1990) 63 Japanese 7, 9, 11 y 4.5 y 500-600 Class III
Allen et al (1993) 23 White 8.2 y 1.4 y 200-450 Class I
Lu et al (1993) 30 Japanese 9 y 5 y 1 mo Not known Class I
Uner et al (1995) 27 Turkish 9 y 3 mo 12 mo 600 Class I treated
Deguchi and Kitsugi (1996) 24 Japanese 8-10 y 3-5 y 500-600 Class I
Mimura and Deguchi (1996) 19 Japanese 10 y 2 mo 5 mo-6 y 500-600 Class I
Basdra et al (1997) 29 White 8-9 y 5 y Not known Class I
Sugawara and Mitani (1997) 63 Japanese 7, 9, 11 y 4-5 y 500-600 Class III
Deguchi et al (1999) 36 Japanese 8 y 4 mo 7 y 250-300 Class III
Deguchi and McNamara (1999) 22 Japanese 9 y 4 mo 1 y 9 mo 400-500 Class III
Abu Alhaija and Richardson (1999) 23 White 8.11 y 3 y 200-450 Class III
Deguchi et al (2002) 56 Japanese 8 y 4 mo 2 y 7 mo
7 y 2 mo
500
250-300
Class III

The primary purpose of this study was to investigate the short-term modifications in craniofacial structures produced by the light-force chincup appliance in a white population with Class III tendencies compared with a control group of untreated Class III subjects. The results also were analyzed in an attempt to identify factors that could allow a greater probability of success with chincup treatment, with special regard to the use of a quad-helix combined with the chincup.

Material and methods

This investigation of consecutively treated patients was designed to evaluate cephalometrically the skeletal and dentoalveolar changes produced by the light-force chincup appliance in patients with Class III malocclusion compared with Class III untreated controls. The treatment sample consisted of the cephalometric radiographs of 26 patients treated with the chincup. All subjects had occlusal signs of Class III malocclusion with a Wits appraisal of –2 mm or more. In addition, 12 of the 26 patients were treated with a quad-helix appliance for maxillary expansion. All patients were treated with the same protocol by the same group of private practitioners.

The chincups and elastic straps were obtained from Summit Orthodontics (Munroe Falls, Ohio). The traction bands were obtained from Orthoband Company (Imperial, Mo). The chincup was fitted on each patient with about 1 in of slack, which resulted in force generation of approximately 150 to 250 g, as measured by a Correx force gauge (Haag-Streit, Koeniz, Switzerland) at the center of the chincup.

The subjects in this study were instructed to wear the chincup at night only for at least 1 year. After 1 year, they were evaluated for Class III correction. If Class III correction had been achieved after a year (determined by lack of anterior crossbite and Class I molar and canine relationship), then the chincup was discontinued. If Class III correction was not achieved, chincup wear continued until Class III correction was achieved or the need for surgical intervention was determined. The mean age at the start of treatment of the chincup group was 8.5 years (T1), with the duration of treatment (T2) 2.6 years for boys and 2.4 years for girls ( Table II ). If a quad-helix was used, the device was placed either before or during chincup treatment and removed immediately after adequate expansion.

Table II
Demographics of observation times
T1 age (y) T2 age (y) T2-T1 (y)
Group Mean SD Mean SD Mean SD
Chincup (11 boys, 15 girls) 8.5 1.4 11.1 1.4 2.6 1.3
Control (6 boys, 14 girls) 7.3 0.7 9.7 0.6 2.4 0.8

The Class III untreated control group consisted of 20 subjects. The cephalograms of the untreated patients were obtained from the University of Florence from clinic patients who initially refused treatment and subsequently returned seeking intervention and from the University of Michigan Growth Study. The mean age at the start of observation (T1) for the Class III control group was 7.3 years, and the mean time of observation (T2) was 2.4 years. Significant effort was directed to matching the control and treatment subjects as closely as possible with respect to sex distribution, age at T1, occlusal Class III characteristics, duration of observation, and prepubertal skeletal maturity as measured by the stage of cervical vertebral maturation at both time points (stage 1 or 2 at T1, and stage 2 or 3 at T2).

All lateral cephalograms used in this study were hand traced on 0.003-in matte acetate paper by using a sharp 2H lead drafting pencil. Each of the 2 films for every patient was hand traced in 1 sitting and in exactly the same way by the primary investigator (A.A.F.B.), and landmark location and the accuracy of the anatomic outlines and contours were verified by a second investigator (J.A.M.). The functional occlusal plane was included on each tracing.

Regional superimpositions were done by hand, as described by Ricketts and McNamara. Cranial base superimpositions showed changes in maxillary and mandibular skeletal positions. Films were oriented along the basion-nasion line and registered at the most posterosuperior aspect of the pterygomaxillary fissure, with the contour of the skull immediately posterior to the foramen magnum used to verify the accuracy of the superimposition.

Maxillary regional superimpositions identified movements of the maxillary dentition relative to the maxillary basal bone. The maxilla was superimposed along the palatal plane by registering on bony internal details of the maxilla superior to the incisors and the superior and inferior surfaces of the hard palate. Mandibular regional superimpositions characterized movements of the mandibular dentition relative to the mandibular basal bone. Mandibular superimpositions were performed posteriorly on the outline of the inferior alveolar nerve canal and any tooth germs (before root formation) and anteriorly on the anterior contour of the bony chin and the internal structures of the mandibular symphysis.

Lateral cephalograms for each patient at T1 and T2 were digitized by using a customized digitization regimen (version 2.5, Dentofacial Planner, Toronto, Ontario, Canada) that included 78 landmarks and 4 fiducial markers. Any magnification differences were adjusted before digitization by using the magnification factor in the software. This program analyzed the cephalometric data and superimpositions of the serial cephalograms to meet the needs of this study.

After digitization, a custom cephalometric analysis was performed. Thirty-three variables were generated for each tracing. Then all linear measurements were standardized to an enlargement of 8%.

The overall treatment outcomes in the chincup patients were assessed from the T2 films. Treatment outcomes were divided into 3 categories: positive, negative, or neutral. The criteria for a positive outcome were positive overjet, Class I (or super Class I) molar relationship, and improvement in the facial profile. An outcome was considered neutral when there was no noticeable improvement in these characteristics, and the patient appeared similar to the T1 film. A negative outcome was noted when overjet and all other Class III features were worse in the T2 film than in the T1 film.

After treatment outcome assessment, it became evident that many subjects with positive treatment outcomes were those who had received a quad-helix in addition to chincup treatment. Because of this finding, the treated sample subsequently was subdivided into 2 groups: those treated with the quad-helix and the chincup (n = 12), and those treated with the chincup only (n = 14). The cephalometric outcomes of these 2 subgroups after treatment were compared to evaluate the possible effectiveness of the quad-helix.

Statistical analysis

Means and standard deviations were calculated for age, duration of treatment, and changes between T1 and T2 of all cephalometric measurements for the treatment and control groups. The data were analyzed with a Windows-based statistical software package (version 16.0, SPSS, Chicago, Ill). Statistical significance was tested at P <0.05, P <0.01, and P <0.001.

Lack of normal distribution for the examined variables was shown by the Shapiro-Wilks test. Mann-Whitney U tests for independent samples were performed to evaluate the differences between the treated and untreated groups at both time points and the changes between time points. Because of the number of subjects examined and the standard deviations of the variables investigated, the power of the study exceeded 0.85 at α = 0.05. Mann-Whitney U tests for independent samples were used to compare the changes in the quad-helix and chincup group vs the chincup-only group. The same nonparametric test didd not find a significant difference between the 2 subgroups at T1.

On the basis of repeated cephalometric measurements, errors were smaller than 1° and 1 mm for all angular and linear measurements, thus confirming previous reports on the error of a comparable cephalometric analysis.

Results

Descriptive data and statistical comparisons for starting forms and cephalometric changes in both groups from T1 to T2 are given in Tables III and IV , respectively.

Table III
Comparison of starting forms between the treated and untreated groups
Chincup group n = 26 Control group (CG) n = 20 Chincup vs CG
Cephalometric measurement Mean SD Mean SD Mean difference P value
Cranial base
Ba-S-N (°) 126.6 4.2 128.7 5.5 −2.1 0.150 NS
Maxillary A-P skeletal
SNA (°) 79.4 4.2 79.9 4.7 −0.6 0.666 NS
Pt A-Na perp (mm) −2.2 3.2 −1.0 3.3 −1.2 0.210 NS
Co-Pt A (mm) 81.5 5.1 79.3 4.4 2.2 0.136 NS
Mandibular A-P skeletal
SNB (°) 80.0 3.7 79.4 4.4 0.6 0.598 NS
Pg-Na perp (mm) −2.6 5.2 −2.7 7.5 0.3 0.875 NS
Co-Gn (mm) 107.4 6.0 104.7 5.3 2.7 0.113 NS
Co-Go (mm) 49.6 2.9 48.9 3.6 0.6 0.509 NS
Intermaxillary
ANB (°) −0.7 2.3 0.5 3.1 −1.2 0.142 NS
Wits (mm) −5.4 1.7 −6.8 4.0 1.4 0.119 NS
Mx/mn diff (mm) 25.9 2.6 25.3 4.3 0.6 0.575 NS
Vertical skeletal
FH-FOP (°) 9.8 3.5 11.9 4.3 −2.0 0.080 NS
FH-PP (°) 1.1 2.4 −0.4 3.2 1.5 0.071 NS
FMA (°) 25.1 5.6 27.7 6.6 −2.5 0.171 NS
Gonial angle (°) 126.7 8.0 130.8 6.3 −4.1 0.063 NS
UFH (mm) 46.9 3.4 46.6 2.8 0.3 0.755 NS
LAFH (mm) 60.1 5.2 59.6 4.2 0.5 0.738 NS
Interdental
OJ (mm) −0.9 1.3 −1.7 3.3 0.8 0.270 NS
OB (mm) 0.7 1.7 0.5 2.2 0.2 0.736 NS
I/I (°) 134.3 14.1 137.3 11.4 −3.0 0.449 NS
6/6 (mm) 3.6 1.9 4.3 2.1 −0.8 0.207 NS
Maxillary dentoalveolar
U1-FH (°) 110.5 6.2 106.9 5.8 3.6 0.107 NS
U1-Pt A vert (mm) 2.7 1.4 2.1 1.9 0.6 0.210 NS
Mandibular dentoalveolar
IMPA (°) 90.1 5.6 88.3 4.7 1.8 0.458 NS
L1-APg (mm) 3.8 2.6 3.9 2.1 −0.1 0.896 NS
Soft tissue
UL to E plane (mm) −4.4 2.5 −4.7 3.4 0.3 0.722 NS
LL to E plane (mm) −0.8 2.7 −0.2 3.1 −0.6 0.492 NS
Nasolabial angle (°) 108.0 14.3 108.3 11.6 −0.3 0.944 NS
NS , Not significant.

Independent sample Student t test.

Table IV
Comparison of changes during time of observation
Chincup group n = 26 Control group (CG) n = 20 Chincup vs CG
Cephalometric measurement Mean SD Mean SD Mean difference P value §
Cranial base
Ba-S-N (°) 0.2 1.5 −0.2 1.8 0.4 0.371 NS
Maxillary A-P skeletal
SNA (°) −0.9 2.1 −0.6 1.5 −0.4 0.486 NS
Pt A-Na perp (mm) −1.1 1.7 −0.9 1.2 −0.1 0.780 NS
Co-Pt A (mm) 2.8 3.1 2.5 1.0 0.3 0.684 NS
Mandibular A-P skeletal
SNB (°) −1.3 2.2 0.2 1.3 −1.5 0.010
Pg-Na perp (mm) −1.6 3.1 0.1 2.4 −1.7 0.045
Co-Gn (mm) 4.7 4.4 5.8 2.0 −0.9 0.391 NS
Co-Go (mm) 2.4 2.9 2.8 1.9 −0.4 0.614 NS
Intermaxillary
ANB (°) 0.3 1.7 −0.7 1.1 1.1 0.016
Wits (mm) 1.5 2.5 −0.1 4.3 1.7 0.102 NS
Mx/mn diff (mm) 2.1 2.7 3.3 1.6 −1.2 0.079 NS
Vertical skeletal
FH-FOP (°) −1.2 2.8 −1.5 2.1 0.4 0.638 NS
FH-PP (°) −1.0 2.3 0.6 1.8 −1.6 0.014
FMA (°) 0.2 2.1 0.4 2.1 −0.2 0.698 NS
Gonial angle (°) −2.3 2.7 −1.2 2.8 −1.1 0.191 NS
UFH (mm) 3.6 3.0 3.5 1.4 0.2 0.822 NS
LAFH (mm) 3.1 3.0 2.8 2.4 0.3 0.741 NS
Interdental
OJ (mm) 3.2 1.7 0.6 1.3 2.6 0.000
OB (mm) 1.0 1.7 1.2 1.9 −0.2 0.678 NS
I/I (°) −1.3 11.1 −7.1 7.8 5.8 0.053 NS
6/6 (mm) −0.4 1.5 0.4 1.4 −0.8 0.080 NS
Maxillary dentoalveolar
U1-FH (°) 6.2 2.7 6.8 2.5 −0.6 0.754 NS
U1-Pt A vert (mm) 1.8 1.4 1.8 1.4 0.1 0.869 NS
U1H (mm) 1.9 1.6 2.3 1.4 −0.5 0.301 NS
U1V (mm) 1.0 1.8 1.3 1.4 −0.3 0.587 NS
U6H (mm) 1.3 1.5 1.4 1.0 −0.1 0.794 NS
U6V (mm) 0.7 1.7 1.6 7.0 −0.8 0.555 NS
Mandibular dentoalveolar
IMPA (°) −4.5 3.4 −0.3 3.5 −4.2 0.001
L1-APg (mm) −1.0 1.4 0.8 1.1 −1.8 0.000
L1H (mm) −0.8 1.1 0.2 1.1 −1.0 0.004
L1V (mm) 2.3 1.9 2.2 1.2 0.2 0.724 NS
L6H (mm) 1.3 1.6 0.4 0.7 0.9 0.062 NS
L6V (mm) 2.2 2.2 1.6 1.5 0.6 0.265 NS
Soft tissue
UL to E plane (mm) −0.2 1.9 −0.2 2.4 −0.1 0.910 NS
LL to E plane (mm) −1.5 1.6 0.0 1.6 −1.5 0.003
Nasolabial angle (°) 0.7 9.2 −4.9 11.6 5.6 0.049
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Apr 13, 2017 | Posted by in Orthodontics | Comments Off on Treatment effects of the light-force chincup
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