The purpose of this research was to compare dentoskeletal changes produced by Herbst and Xbow appliances in late mixed/early permanent dentition patients with Class II Division 1 malocclusion to an untreated control group.
The retrospective cohort consisted of 41 patients treated with the Herbst appliance on average for 14 months (mean age of 11.3 years), 41 patients treated with Xbow appliance on average for 14 months (mean age of 11.11 years), and an untreated control sample of 25 patients followed on average for 21 months (mean age of 11.9 years). All patients had Class II Division 1 malocclusion characteristics. Lateral cephalometric radiographs were taken before and after phase 1 treatment/follow-up. Data were analyzed by an analysis of variance followed by Tukey post-hoc tests.
Although there was a high equivalence among the groups in the pretreatment cephalometric values, 4 variables showed differences (U6-FHp, L6-FHp, LAFH, and PP-U1). When comparing the mean changes (before and after phase 1 treatment/follow-up), incisor mandibular plane angle (IMPA), Wits appraisal, L6-FHp, Co-Pog, and PP-U1 measurements showed statistically significant differences. In addition, more relative mesial movement of the mandibular molars (an additional 2.4 mm) and a larger increase in mandibular length (an additional 3.2 mm) was noted for the Herbst group.
Class II correction using Herbst and Xbow occurred in both groups through improvement in the maxillomandibular relationship and labial inclination of the mandibular incisors, as well as a relatively increased mesialization of the mandibular molars. Although both appliances improve occlusal features, the portrayed changes were not always similar. Herbst seems to produce more mandibular size increase over a similar treatment period.
Herbst and Xbow produced dental and skeletal changes favorable to Class II correction.
Differences between treatment effects of 2 appliances were subtle.
Herbst appliance might produce a greater mandibular size increase.
Xbow might favor dentoalveolar effects.
Several orthopedic appliance types have been used for the correction of Class II malocclusion, aiming to possibly improve functional, muscular, skeletal, and dental disharmonies. A wide array of related published articles have been summarized through several systematic reviews with or without meta-analysis.
The Herbst appliance is widely known for its relative effectiveness in correcting Class II malocclusions. It is most commonly used as a fixed device that repositions the jaw to a more anterior and downward position displacing the condyles away from the articular eminence. This is thought to facilitate condylar bone apposition; hence, increasing overall mandibular size dimensions. Several papers have considered the efficiency of the Herbst appliance in the Class II correction during early permanent dentition. But only one study evaluated changes produced by the Herbst appliance in mixed dentition patients, and it concluded that the effects of the Herbst appliance were mainly dentoalveolar. Several different designs of the Herbst appliance have been reported in the literature.
The Xbow appliance is a fixed Class II corrector, with only a few published studies reporting its effectiveness and mechanism of Class II malocclusion correction. A recent study reported that the immediate changes in patients treated with the Xbow appliance were associated with more dental than skeletal changes.
Only 1 previous study directly compared the Xbow appliance to another form of Class II correction. Ehsani et al investigated skeletal and dental differences after orthodontic treatment in which the Xbow and Twin-block appliance among patients with Class II malocclusion and concluded that the Class II correction using an Xbow or Twin-block followed by fixed devices occurred by means of a relatively similar combination of dental and skeletal effects. Nevertheless, they noted that the magnitude of mandibular skeletal increase when using the Twin-block was more significant (around 3 mm more).
To date, no study has directly compared the treatment results of Class II malocclusion treatment between Herbst and Xbow fixed Class II appliances. Therefore, the objective of this retrospective clinical research is to evaluate the dental and skeletal cephalometric effects produced by these appliances in young patients with Class II Division 1 malocclusion during late mixed dentition or early permanent dentition and to compare those change with an untreated Class II malocclusion control group.
Material and methods
This retrospective study was approved by the Ethics Committee of the Faculty of Dentistry of Bauru, University of São Paulo, Brazil (protocol no. 82197317.1.0000.5417).
The sample size was calculated by assuming an alpha of 5%, a beta of 20%, and a mean clinically meaningful difference of 3.6 mm with a standard deviation of 3.8 mm for Co-Pog. On the basis of these parameters, a minimal sample size of 36 patients was needed per group. An effect size of 0.5 would be discernable with this sample size.
The Herbst group comprised 41 patients (20 males and 21 females), with an initial mean age of 11 years 3 months and final mean age of 12 years 6 months, who were treated with the modified Herbst appliance ( Fig 1 ) for approximatively 14 months. All patients were treated by a single clinician (M.R.A.) at the Orthodontics Clinic of the Faculty of Dentistry of Bauru. Initial cephalogram (T1) was obtained 2 weeks before the appliance was installed and the final cephalogram (T2) approximately 4 weeks after removal of the Herbst appliance to potentially eliminate any mandibular postural advancement caused by the appliance. Fixed orthodontic appliances were placed around 4 weeks after Herbst therapy to let the occlusion settled. The initial characteristics of this group can be seen in Table I .
|Variable||Mean values||P value|
|Age at T1 (y)||11.90||11.31||11.11||0.673|
|Age at T2 (y)||13.70 a||12.59 b||12.39 b||0.000 ∗|
|Treatment/observation||1.82 a||1.28 b||1.28 b||0.001 ∗|
The Xbow group consisted of 41 patients (21 males and 20 females), with a mean initial age of 11 years 11 months and final mean age of 12 years and 3 months, treated for an average of 14 months ( Fig 2 ). The sample obtained was treated by a different single clinician in the private clinic of the inventor of the Xbow appliance (Duncan W. Higgins). Initial cephalogram (T1) was obtained between 2 and 4 weeks before the appliance was installed and the final cephalogram (T2) approximately 4 months after the removal of the Xbow appliance to eliminate any mandibular postural advancement and/or the dentoalveolar compensation caused by the appliance. Fixed orthodontic appliances were placed around 4 months after Xbow therapy. The initial characteristics of this group can be seen in Table I .
The control group included 25 patients (16 males and 9 females), with an initial mean age of 11 years 9 months and final mean age of 13 years 7 months, who were followed up for 1 year 8 months. This group was selected from the longitudinal growth study sample from the University of Toronto Burlington Growth Study (Department of Orthodontics, University of Toronto, Toronto, Ontario, Canada).
The samples were selected according to the following inclusion criteria: (1) Class II Division 1 (greater than one-half cusp Class II molar on both sides); (2) ANB angle, ≥4.5°; (3) overjet, >4 mm; (4) absence of agenesis or loss of permanent teeth; (5) absence of supernumerary teeth; and (6) dental arches with no to mild crowding.
Patients requiring teeth extraction and/or orthognathic surgery or syndromic patients were excluded.
For a direct comparison among the groups, the measurements of the control group were annualized and adjusted to an average time frame of 1 year and 2 months follow-up to be compared with the treated groups (average available time frame of 1 year 2 months).
Cephalograms of each patient were obtained in pretreatment (T1) and posttreatment (T2). They were digitized and had their marks identified by a single operator (R.R.A.P) in the Dolphin Imaging software (version 11.5; Dolphin Imaging and Management Solutions, Chatsworth, Calif), which also corrected the magnification factors of the different radiographic machines in which the lateral cephalograms were taken. All patients per group were imaged by the same radiographic machine, but those machines were different between groups. Cephalometric variables can be observed in Table II . Posttreatment changes were calculated from T2 − T1. The reference lines and planes used in this study are shown in Table III and Figures 3 and 4 .
|Cephalometric measurements||Control (n = 25)||Herbst (n = 41)||Xbow (n = 41)||P value|
|A-Na Perp (mm)||2.32||3.26||3.28||2.88||2.60||2.65||0.223|
|Pg-Na Perp (mm)||−4.50||5.38||−3.50||4.61||−3.72||5.74||0.117|
|Wits appraisal (mm)||3.10||2.53||4.11||2.42||4.14||2.33||0.300|
|Frankfort-mandibular plane angle (°)||23.54||3.70||24.23||4.78||23.53||5.25||0.761|
|LAFH (mm)||57.83 a||3.23||63.67 b||4.88||60.16 a||5.27||<0.001 ∗|
|PP-U1 (°)||107.49 a||6.13||116.65 b||5.57||110.09 b||9.00||<0.001 ∗|
|Incisor mandibular plane angle (°)||98.68||5.81||99.23||5.56||97.71||6.06||0.493|
|U6-FHp (mm)||56.28 a||4.25||55.84 a||4.54||51.87 b||3.81||<0.001 ∗|
|L6-FHp (mm)||55.75 a||4.25||54.21 a||4.71||50.97 b||4.07||<0.001 ∗|