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.
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.
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.
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).
|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
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.
|T1 age (y)||T2 age (y)||T2-T1 (y)|
|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.
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.
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.
|Chincup group n = 26||Control group (CG) n = 20||Chincup vs CG|
|Cephalometric measurement||Mean||SD||Mean||SD||Mean difference||P value ∗|
|Maxillary A-P skeletal|
|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|
|Pg-Na perp (mm)||−2.6||5.2||−2.7||7.5||0.3||0.875||NS|
|Mx/mn diff (mm)||25.9||2.6||25.3||4.3||0.6||0.575||NS|
|Gonial angle (°)||126.7||8.0||130.8||6.3||−4.1||0.063||NS|
|U1-Pt A vert (mm)||2.7||1.4||2.1||1.9||0.6||0.210||NS|
|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|
|Chincup group n = 26||Control group (CG) n = 20||Chincup vs CG|
|Cephalometric measurement||Mean||SD||Mean||SD||Mean difference||P value §|
|Maxillary A-P skeletal|
|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|
|Pg-Na perp (mm)||−1.6||3.1||0.1||2.4||−1.7||0.045||∗|
|Mx/mn diff (mm)||2.1||2.7||3.3||1.6||−1.2||0.079||NS|
|Gonial angle (°)||−2.3||2.7||−1.2||2.8||−1.1||0.191||NS|
|U1-Pt A vert (mm)||1.8||1.4||1.8||1.4||0.1||0.869||NS|
|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||∗|