During recent years, some articles have been published on Herbst appliance treatment in adult patients, an approach that has been shown to be most effective in Class II treatment in both early and late adulthood. However, no results on stability have yet been published. Our objective was to analyze the short-term occlusal stability of Herbst therapy in adults with Class II Division 1 malocclusions.
The subjects comprised 26 adults with Class II Division 1 malocclusions exhibiting a Class II molar relationship ≥0.5 cusp bilaterally or ≥1.0 cusp unilaterally and an overjet of ≥4.0 mm. The average treatment time was 8.8 months (Herbst phase) plus 14.7 months (subsequent multi-bracket phase). Study casts from before and after treatment and after an average retention period of 32 months were analyzed.
After retention, molar relationships were stable in 77.6% and canine relationships in 71.2% of the teeth. True relapses were found in 8.2% (molar relationships) and 1.9% (canine relationships) of the teeth. Overjet was stable in 92.3% and overbite in 96.0% of the patients; true relapse did not occur.
Herbst treatment showed good occlusal stability 2.5 years after treatment in adults with Class II Division 1 malocclusions.
Class II malocclusions in adults are usually treated by either orthognathic surgery or camouflage treatment, depending on the severity of the skeletal discrepancy. However, recently, some articles have been published on Herbst appliance treatment in adult patients. This method has been shown to be most effective in Class II treatment in both early and late adulthood.
A prospective cephalometric study by Ruf and Pancherz demonstrated a favorable effect of Herbst treatment on all mandibular parameters, and also the hard- and soft-tissue profile convexities were reduced. Furthermore, magnetic resonance imaging studies have proven that adult Herbst treatment stimulates condylar growth as well as modeling of the glenoid fossa similarly as in adolescents. These findings are also supported by histologic data collected from adult rhesus monkeys and rats, confirming that even the adult temporomandibular joint can adapt to mandibular protrusion.
Comparing the effects of adult Herbst treatment and mandibular sagittal split osteotomy on Class II molar and overjet correction, it was shown that more dental changes occurred in the Herbst patients. Therefore, adult Herbst treatment has been recommended for adult Class II Division 1 surgical borderline treatment. This recommendation agrees with that of Cassidy et al, who concluded that orthodontic treatment would be a better choice for the borderline Class II adults, whereas surgery would be appropriate for more severely affected patients.
Looking at long-term stability of adult Class II treatment, Mihalik et al compared the outcomes of orthodontic camouflage treatment with orthognathic surgery and found that overbite was equally stable in both groups, but overjet relapsed twice as often in surgery patients. Furthermore, the camouflage patients reported fewer functional and temporomandibular joint problems than did the surgery patients, and had similar reports of overall satisfaction with treatment.
Concerning adult Herbst treatment, no results on the stability have yet been published. Therefore, it was our aim in this retrospective study to analyze the short-term occlusal stability of Herbst treatment in young adult Class II Division 1 patients during the retention period.
Material and methods
The records of all 350 Class II Division 1 patients who were treated with a Herbst appliance at the orthodontic department at the University of Giessen in Germany until 2006 were examined for the following inclusion criteria: Class II molar relationship of at least half a cusp bilaterally or a full cusp unilaterally, overjet of at least 4 mm, and minimal or no remaining growth. To assume the latter, the patients had to have an incomplete or a complete junction of the radial epiphysis. Correspondingly, hand-wrist radiographs were evaluated according to the method of Hägg and Taranger and screened for the appropriate stages (R-IJ and R-J).
Thirty-one patients fulfilled these inclusion criteria, but, because of incomplete records, 5 of them were excluded.
The final sample included 26 subjects (22 female, 4 male) with a mean age of 21.1 years (SD, 7.7; range, 15.1-44.4 years) before treatment fulfilling all inclusion criteria. Eight subjects had an incomplete radial epiphysis skeletal maturity stage, and 18 had a complete radial epiphysis stage. The pretreatment average Class II molar relationship was three quarters of a cusp, and the mean overjet was 6.8 mm.
All subjects were exclusively treated with a Herbst multi-bracket (Herbst-MB) appliance. The treatment was performed by either the head of department, senior residents, or postgraduate students (under senior supervision). The average treatment length was 8.8 months for the Herbst and 14.7 months for the multi-bracket appliance phase.
The average retention time was 32 months (SD, 12.0 months). Retention after active treatment was performed with a removable appliance (6 Activators, 17 Hawleys) combined with a fixed mandibular canine-to-canine retainer in 23 of the 26 subjects. Three subjects were retained with fixed maxillary and mandibular canine-to-canine retainers only. At the time of this investigation, the fixed retainers were still in place in all patients, and the removable appliances were still used occasionally by most of them.
Study casts from before Herbst treatment (T1), after Herbst-MB (T2), and after retention (T3) were analyzed. The following variables were used for the assessment of the treatment (T2-T1) and posttreatment changes (T3-T2): MR and ML, sagittal molar relationships, right and left; CR and CL, sagittal canine relationships, right and left; OJ, overjet, mean right and left; and OB, overbite, mean right and left.
For the assessment of occlusal stability, the occlusion at T3 was compared with that at T2. The molar and canine relationships were considered stable if there was a normal or overcompensated Class I relationship at T3, or if the occlusion had not changed after T2. A change of ≤0.25 cusp width (CW) was considered an insignificant relapse, and a change >0.25 CW was considered a true relapse.
For OJ and OB, the values measured at T3 were compared with those at T2. OJ and OB were considered stable with final values up to 3 mm at T3, an increase <1.5 mm during T3-T2, or if the value did not change after T2. Final values >3 mm were defined as insignificant relapse for an increase of 1.5 to 2.5 mm during T3-T2 and as true relapse for an increase of >2.5 mm during that period.
Ratings of the occlusion were made to the nearest 0.25 CW. Linear measurements were made to the nearest 0.5 mm with a manual caliper. To minimize the method error, all assessments were done twice, at least 2 weeks apart. The mean value of the 2 assessments was used in the final evaluation. The arithmetic mean and standard deviation were calculated for each variable. The Wilcoxon test was used to evaluate the changes in the variables during the examination periods. The following levels of significance were used: P <0.001, P <0.01, and P <0.05. P >0.05 was considered statistically not significant.
The method error of the double ratings and all measurements were calculated with Dahlberg’s formula :
where d is the difference between 2 registrations and n is the sample size (n = 26). Method errors did not exceed 0.1 for the ratings and 0.4 for the measurements.
The results of the T1 analysis of the study casts are shown in Table I and the treatment (T2-T1) and posttreatment changes (T3-T2) are shown in Table II . Three subjects received prosthetic therapy on molars during the retention period; thus, in these patients, only canine stability was evaluated. One subject was excluded from the evaluation of the OB changes because she had an anterior OB before treatment, and a relapse of this OB during retention would have influenced the results in a wrong, positive way, since Class II Division 1 patients usually have an increased OB as relapse.
|Adult Herbst sample
(n = 26)