Former Graduate Student, Dental School, The University of Western Australia.
Program Director, Orthodontics, Dental School, The University of Western Australia.
Senior Lecturer, Orthodontic, Dental School, The University of Western Australia.
Objective: To investigate the impact of simultaneous maxillary expansion on the therapeutic effects of the Herbst appliance.
Materials and Methods: Pre-treatment and post-treatment lateral cephalograms of 28 growing patients who were treated with the Herbst appliance with simultaneous rapid maxillary expansion (Herbst/RME), (mean age 12.50 years, range 10.89 years, 14.13 years) and 19 growing patients treated with the Herbst appliance without expansion (mean age 12.85 years, range 10.42 years, 15.12 years) were analyzed using the method of Pancherz.
Results: In the maxilla, A-point came forward 0.62mm in the Herbst/RME, but was almost stationary for the Herbst (forward 0.13mm). In the mandible, pogonion came forward 3.70mm for the Herbst/RME and 1.18mm for the Herbst. Molar correction was 6.28mm for the Herbst/RME and 4.7mm for the Herbst appliance. Overjet correction was 6.72mm for the Herbst/RME and 4.67mm for the Herbst appliance. The relative contribution to overjet and molar correction was predominantly dental for the Herbst appliance and approximately equally dental and skeletal for the Herbst/RME.
Conclusion: Whilst the use of rapid maxillary expansion has long been demonstrated to be useful to address a transverse discrepancy, this study does not demonstrate an enhanced headgear effect for the correction of a Class II malocclusion when rapid maxillary expansion is undertaken simultaneously with the Herbst appliance.
The Herbst appliance is a well-recognised and accepted treatment for the correction of Class II malocclusion in growing patients, 1-6 and even contentiously suggested to treat adults in borderline surgical skeletal Class II malocclusions effecting skeletal change.7 Variations in appliance design have been noted, and specifically little research has been undertaken to investigate the impact of simultaneous expansion on treatment effects.
Typically, Herbst appliance therapy achieves effects through a combination of dental and skeletal changes. Favourable outcomes have been demonstrated after removing the effect of normal growth when comparing subjects with age- and sex-matched European norms.2 Changes include an increase in mandibular length but the specific effects on the temporomandibular joint morphology to altered functional loading (condyle position) remains unknown.8 Typical effects include mesial movement of the mandibular molars and incisors, minor distal movement of the maxillary incisors and the following, which have been coined the “headgear effect” of the appliance: maintenance of the sagittal maxillary jaw position, distalization and intrusion of the upper molars, and the opening of the maxillary occlusal plane.
The treatment of the Class II malocclusion often involves addressing any transverse discrepancy, and the effects of expansion have been reported extensively in animal and human studies.9-14 Simultaneous RME with headgear in tantalum implanted monkeys demonstrated increased cellular activity in the sutures and less bony deposition, reduction in vertical and horizontal movement and even superior movement of the maxilla.14 Additionally, simultaneous RME with reverse headgear is commonly suggested to enhance Class III orthopaedic correction although the effectiveness has been questioned.15-17
Rapid maxillary expansion has been incorporated into the Herbst appliance itself in order that the antero-posterior and transverse discrepancies be addressed simultaneously. It is proposed that concurrent RME might also stimulate advantageous changes in the orthopaedic correction of the Class II malocclusion by changes in the maxilla.
It is therefore feasible to consider that in Class II correction with expansion there might be some therapeutic effects on the simultaneously expanded maxilla as a consequence of the purported headgear effects of the Herbst appliance. The objective of this study therefore was to investigate if simultaneous maxillary expansion enhanced the Class II correction of the Herbst appliance.
The retrospective sample of 47 patients was selected from a specialist private orthodontic practice and the Orthodontic Department of the Oral Health Centre of Western Australia. Ethical approval for the study was granted by the Human Research Ethics Committee, the University of Western Australia. Twenty eight (mean age 12.50 years, range 10.89 years, 14.13 years) were treated with the Herbst-RME and 19 (mean age 12.85 years, range 10.42 years, 15.12 years) were treated with the Herbst appliance without expansion.
The two groups were tested for similarity according to the following pre-treatment factors: age less than 15 years 6 months, at the time of the pre-treatment radiograph, post-treatment radiographs were taken less than 14 months apart and post-treatment radiograph was taken within 60 days of appliance removal.
A number subjects had simultaneous fixed appliances so the sample was further subdivided into four subgroups representing this detail.
The pre-treatment (T1) and post-treatment (T2) lateral cephalogram radiographs of each patient were scanned, digitized, (Fig 1a) superimposed utilising “cranial base best fit” and analyzed according to the method of Pancherz3 (Fig 1b) and four standard cephalometric variables: SNA, SNB, ANB, SNPg with Viewbox™ (Viewbox 3.01 dHAL, Kissia, Greece) software.
Fig 2: Pre-treatment (T1) and post-treatment (T2) cephalometric values for Herbst and Herbst/RME (H/RME) groups, by variable. Outliers are individually represented as flat horizontal lines.
Differences for the 18 variables were assessed between two groups (Herbst/RME and Herbst) and further broken down to analyze the four groups based on the presence/absence of simultaneous fixed appliances.
The total change was measured by the change of the position of the incisor tips and mesial contacts of the first molars for overjet and molar correction respectively. The skeletal change was measured by the change of A-point (for the maxilla) and Pg (for the mandible). The dental change was the difference between the total and skeletal changes.
There were only minor statistical differences in cephalometric variables between the Herbst and Herbst/RME groups both pre-treatment and post-treatment (Fig 2). At pre-treatment (T1), there were no statistically-significant (p<0.05) differences between the Herbst/RME and Herbst groups for 16 of the 18 variables analyzed: (Table 2). The pre-treatment SNB was smaller for the Herbst/RME group compared to the Herbst group. The pre-treatment overjet was larger for the Herbst/RME group compared with the Herbst group. This indicates that the Herbst/RME group had a slightly greater Class II malocclusion pre-treatment.
Post-treatment (T2), there were no statistically-significant (p<0.05) differences between the Herbst and Herbst/RME groups for any of the 18 variables with the exception of molar relation. This was smaller for the Herbst/RME group compared to the Herbst group indicating that the Herbst group had a slightly greater Class II malocclusion tendency post-treatment.
As would be expected, statistically-significant treatment changes (T1–T2) were noted for both the Herbst and Herbst/RME groups (Table 3). For both groups there were statistically-significant treatment changes (p<0.001) for ANB, overjet, molar relation, lower incisor position, lower molar position, lower incisor horizontal mandibular base and lower molar horizontal mandibular base. The Herbst group also demonstrated statistically significant treatment changes for SNA (p<0.01) and maxillary molar horizontal maxillary base (p<0.001). The Herbst/RME group also demonstrated statistically-significant treatment changes (p<0.001) for SNB, SNPg, mandibular base, mandibular length and maxillary incisor horizontal maxillary base; (p<0.01) for maxillary molar horizontal maxillary base; and (p<0.05) for maxillary base. The ANB correction was slightly greater for the Herbst/RME group (1.75mm) compared with the Herbst group (1.47mm), as was the overjet correction (Herbst 4.67mm, Herbst/RME 6.72mm) and molar correction (Herbst 4.70mm, Herbst/RME 6.28mm). No significant treatment changes were noted for condylar position.
Both appliances were successful in Class II correction as measured by improvements in ANB, overjet and molar relation. A-point came forward slightly (0.62mm) in the Herbst/RME group, but was almost stationary for the Herbst group (moving back 0.13mm). Pogonion came forward more in the Herbst/RME group (3.70mm) than the Herbst group (1.18mm).
The Herbst/RME group had more improvement of the Class II malocclusion in terms of the incisal and molar relationship. (Herbst/RME overjet improvement of 6.72mm, molar relation improvement 6.28mm; Herbst overjet improvement of 4.67mm, molar relation improvement 4.70mm).
Since it was found that there were minor differences between the two groups before treatment, a linear regression model was used to investigate differences between the two groups at T2 when T1 differences were accounted for (Table 3): there were differences (p<0.01) for molar relation, mandibular base, mandibular length and mandibular molar horizontal; and (p<0.05) for mandibular incisor horizontal (Table 4). Thus, using this model, the Herbst group at T2 were more Class II molar, had a more retrognathic mandible, a smaller mandible, more retrusive lower molars (p<0.01) and more retrusive lower incisors (p<0.05).
The overall relative skeletal contribution to correction of overjet and molar relationship change was found to be greater with the Herbst/RME than the Herbst appliance (Fig 3). Conversely, the overall relative dental contribution to correction of overjet and molar relationship change was found to be greater with the Herbst appliance than the Herbst/RME.
Pair-wise comparisons of Herbst Fixed and No Fixed and Herbst/RME fixed and No Fixed groups found no significant treatment effect differences when full fixed appliances were added. Thus it was considered valid to combine the data of fixed and no fixed subjects for the 2-group analysis.
It must be noted however that given that the 47 subjects were divided into four small groups for the 4-group analysis, sample size was too small to be able to find strong statistical differences between the four groups that could not be due to chance.
A measurement of method error was undertaken according to the Dahlberg analysis.18 The pre-treatment and post-treatment radiographs of five subjects who were randomly selected from the pool of 47 subjects were redigitized and re-superimposed at least four weeks after initial digitisation to assess the accuracy of data collected. From this, the combined method error for linear measures was ±1.46mm and for angular measures was ±0.83º.
The anticipated “headgear effect” in the Herbst-RME group produced by the combination of concurrent rapid maxillary expansion and the Herbst appliance was not demonstrated in what minor differences were seen. On the contrary, in the Herbst-RME group, the maxilla (Point A) came forward but remained relatively stable in the Herbst group. Though greater skeletal change was found in the Herbst/RME group, this was seen in the mandible rather than the maxilla.
Overall changes in ANB were more modest in magnitude and speed than that reported by Pancherz with the Herbst appliance. In the correction of molar relationship and overjet, this study found that the Herbst-RME produced proportionally more skeletal effect than the Herbst appliance, with skeletal changes equalling dental changes, whereas the Herbst appliance alone produced predominantly dental changes. In contrast, Pancherz found equal skeletal and dental changes with the Herbst appliance.
The mean age of both treatment groups is considerably higher than in three major prospective randomized clinical trials involving removable functional appliance therapy19-21 and therefore direct comparison in terms of treatment effect is difficult. However, broadly speaking, the overall effects were similar, in that correction of the Class II molar relationship and overjet were achieved through a combination of skeletal and dental changes. It has also been proposed that step-by-step advancement with the Herbst appliance is more effective than conventional maximal jumping of the mandible but this strategy was not used in this study.
When measuring growth and treatment changes, there is large variation between patients and mean changes usually observed are small.26 Given the relatively small sample size, a problem which was further compounded in the 4-group analysis, the minor statistical differences in cephalometric variables between the Herbst and Herbst/RME groups both pre-treatment and post-treatment might have been due to chance.
Whilst the use of rapid maxillary expansion has long been demonstrated to be useful to address a transverse discrepancy, this study does not demonstrate an enhanced headgear effect for the correction of a Class II malocclusion when rapid maxillary expansion is undertaken simultaneously with the Herbst appliance.
1. Pancherz H. Treatment of class II malocclusions by jumping the bite with the Herbst appliance. A cephalometric investigation. Am J Orthod 1979;76:423-442.
2. Manfredi C, Cimino R, Trani A, Pancherz H. Skeletal changes of Herbst appliance therapy investigated with more conventional cephalometrics and European norms. Angle Orthod 2001;71:170-176.
3. Pancherz H. The mechanism of Class II correction in Herbst appliance treatment. A cephalometric investigation. Am J Orthod 1982;82:104-113.
4. Pancherz H. The Herbst appliance–its biologic effects and clinical use. Am J Orthod 1985;87:1-20.
5. Pancherz H, Anehus-Pancherz M. The headgear effect of the Herbst appliance: a cephalometric long-term study. Am J Orthod Dentofacial Orthop 1993;103:510-520.
6. Du X, Hagg U, Rabie AB. Effects of headgear Herbst and mandibular step-by-step advancement versus conventional Herbst appliance and maximal jumping of the mandible. Eur J Orthod 2002;24:167-174.
7. Ruf S, Pancherz H. Temporomandibular joint remodeling in adolescents and young adults during Herbst treatment: A prospective longitudinal magnetic resonance imaging and cephalometric radiographic investigation. Am J Orthod Dentofacial Orthop 1999;115:607-618.
8. Popowich K, Nebbe B, Major PW. Effect of Herbst treatment on temporomandibular joint morphology: a systematic literature review. Am J Orthod Dentofacial Orthop 2003;123:388-394.
9. Haas AJ. Rapid Expansion of the Maxillary Dental Arch and Nasal Cavity by Opening The Midpalatal Suture. Angle Orthod 1961;31:73-90.
10. Wertz RA. Skeletal and dental changes accompanying rapid midpalatal suture opening. Am J Orthod 1970;58:41-66.
11. Haas AJ. The Treatment of Maxillary Deficiency by Opening the Midpalatal Suture. Angle Orthod 1965;35:200-217.
12. Haas AJ. Palatal expansion: just the beginning of dentofacial orthopedics. Am J Orthod 1970;57:219-255.
13. Timms DJ. A study of basal movement with rapid maxillary expansion. Am J Orthod 1980;77:500-507.
14. Thompson RW. Extraoral high-pull forces with rapid palatal expansion in the Macaca mulatta. Am J Orthod 1974;66:302-317.
15. Ngan P, Hagg U, Yiu C, Merwin D, Wei SH. Soft tissue and dentoskeletal profile changes associated with maxillary expansion and protraction headgear treatment. Am J Orthod Dentofacial Orthop 1996;109:38-49.
16. Nartallo-Turley PE, Turley PK. Cephalometric effects of combined palatal expansion and facemask therapy on Class III malocclusion. Angle Orthod 1998;68:217-224.
17. Williams MD, Sarver DM, Sadowsky PL, Bradley E. Combined rapid maxillary expansion and protraction facemask in the treatment of Class III malocclusions in growing children: a prospective long-term study. Semin Orthod 1997;3:265-274.
18. Dahlberg G. Statistical Methods for Medical and Biological Students. London: George Allen & Unwin Ltd; 1940.
19. Tulloch JF, Phillips C, Koch G, Proffit WR. The effect of early intervention on skeletal pattern in Class II malocclusion: a randomized clinical trial. Am J Orthod Dentofacial Orthop 1997;111:391-400.
20. Keeling SD, Wheeler TT, King GJ, Garvan CW, Cohen DA, Cabassa S et al. Anteroposterior skeletal and dental changes after early Class II treatment with bionators and headgear. Am J Orthod Dentofacial Orthop 1998;113:40-50.
21. Ghafari J, Shofer FS, Jacobsson-Hunt U, Markowitz DL, Laster LL. Headgear versus function regulator in the early treatment of Class II, division 1 malocclusion: a randomized clinical trial. Am J Orthod Dentofacial Orthop 1998;113:51-61.
22. Gianelly AA. One-phase versus two-phase treatment. Am J Orthod Dentofacial Orthop 1995;108:556-559.
23. Tulloch JF, Proffit WR, Phillips C. Outcomes in a 2-phase randomized clinical trial of early Class II treatment. Am J Orthod Dentofacial Orthop 2004;125:657-667.
24. Livieratos FA, Johnston LE, Jr. A comparison of one-stage and two-stage nonextraction alternatives in matched Class II samples. Am J Orthod Dentofacial Orthop 1995;108:118-131.
25. von Bremen J, Pancherz H. Efficiency of early and late Class II Division 1 treatment. Am J Orthod Dentofacial Orthop 2002;121:31-37.
26. Tulloch JF, Medland W, Tuncay OC. Methods used to evaluate growth modification in Class II malocclusion. Am J Orthod Dentofacial Orthop 1990;98:340-347.