Stepwise Advancement Herbst Appliance versus Mandibular Sagittal Split Osteotomy

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1 Original Article Stepwise Advancement Herbst Appliance versus Mandibular Sagittal Split Osteotomy Treatment Effects and Long-term Stability of Adult Class II Patients A. Chaiyongsirisern a ; A. Bakr Rabie b ; Ricky W. K. Wong c ABSTRACT Objective: To compare the treatment effects and long-term stability of the stepwise Herbst appliance and mandibular sagittal split osteotomy in skeletal Class II adult patients. Materials and Methods: Subjects comprised 16 patients in the Herbst group and another 16 patients in the surgery (mandibular sagittal split osteotomy) group. Lateral head films were taken before treatment (T0), after removal of the Herbst appliance/surgery (T1), after the fixed appliance treatment (T2), and 3 years after treatment (T3). All films were analyzed by standard cephalometrics and SO-analysis (analysis of changes in sagittal occlusion). Results: All Herbst and surgery patients were treated successfully to Class I occlusal relationships with normal overjet and overbite. Both groups showed a significant change in mandibular base advancement (SNB, SNPg, Pg/OLp), which resulted in a decrease in the ANB angle, the Wits appraisal, and facial convexity. However, the surgery group showed larger changes in the parameters mentioned above. In terms of long-term stability, both groups achieved stable results, and no significant difference occurred over time. Conclusion: Stepwise advancement Herbst appliance therapy can be used to treat borderline skeletal Class II adult patients with long-term stability. (Angle Orthod. 2009;79: ) KEY WORDS: Herbst appliance; Osteotomy INTRODUCTION Two treatment options are available for adult patients with skeletal Class II malocclusion caused by mandibular deficiency. The first option is combined surgical and orthodontic treatment, which lengthens the mandible anteriorly through mandibular sagittal split osteotomy; this, in turn, can correct the skeletal and soft tissue relationship. 1 3 The second option is Herbst appliance therapy, which reactivates condylar growth to correct mandibular deficiency Previous researchers looked into the possibility of a Postgraduate student, Department of Orthodontics, Faculty of Dentistry, Hong Kong. b Professor, Department of Orthodontics, Faculty of Dentistry, Hong Kong. c Associate Professor, Department of Orthodontics, Faculty of Dentistry, Hong Kong. Corresponding author: Dr A. Bakr Rabie, Professor, Department of Orthodontics, Faculty of Dentistry, Prince Philip Dental Hospital, 34 Hospital Road, Hong Kong ( rabie@hkusua.hku.hk) Accepted: January Submitted: November by The EH Angle Education and Research Foundation, Inc. stimulating growth of the condyle in adults. Among them, Xiong et al showed that forward mandibular positioning affected the biophysical environment of the temporomandibular joint (TMJ), and this induced recruitment of mesenchymal cells. These cells underwent endochondral ossification, which resulted in new bone formation in adult rats. A recent clinical study demonstrated the formation of new cartilage and bone in the condylar areas of adult patients, along with a concomitant reduction in facial convexity, following stepwise Herbst appliance therapy. 10 The studies mentioned earlier suggest that there exists a possible nonsurgical treatment modality for skeletal Class II malocclusion in adults, especially among borderline cases. It is therefore important to study the treatment effects and stability of the stepwise advancement adult Herbst appliance in adult patients, compared with patients who have undergone mandibular surgery. The aim of this study was to compare the treatment effects and stability of two groups of adult skeletal Class II patients with use of the Herbst appliance with stepwise mandibular advancement or bilateral sagittal split osteotomy DOI: /

2 HERBST APPLIANCE AND SAGITTAL SPLIT OSTEOTOMY 1085 Figure 1. References points and lines used in the standard cephalometric analysis. MATERIALS AND METHODS Figure 2. SO-analysis. The OL/OLp reference grid and the measuring landmarks are shown. 16 A group of subjects, which comprised 16 adults (12 females, 4 males), were treated with a cast splint Herbst appliance with stepwise advancement (Herbst group) at the Orthodontic Department of The University of Hong Kong. Another 16 adults (11 females, 5 males) were treated with orthognathic surgery (surgery group). All patients had Class II malocclusion with mandibular deficiency. At the end of treatment, all patients had achieved Class I occlusion with normal overjet and overbite. The mean treatment age was 22 years ( years) for the Herbst group and 24 years ( years) for the surgery group. The mean pretreatment overjet was 8.0 mm (standard deviation [] 2.07) and 9.9 mm ( 2.60) for the Herbst group and the surgery group, respectively. Maturity status was determined by hand-wrist radiographs. Individuals were considered mature if handwrist radiograph stage R-IJ or R-J 15 had been reached. All subjects in the Herbst group reached R-IJ (3 subjects) and R-J (13 subjects) before treatment. Subjects in the surgery group reached stage R-J before the surgical procedure. The 16 subjects in the Herbst group were treated with the silver-casted splint Herbst appliance with stepwise advancement rather than one-step bite jumping. At the time when the Herbst appliance was fitted, the mandible was advanced by 5 mm. Subsequent advancement(s) eliminated any remaining overjet, and all subjects received fixed appliances after they had been given the Herbst appliance for an average of 14.3 months. In the surgery group, all 16 subjects were treated with mandibular advancement with bilateral sagittal split osteotomy. The surgery group was stabilized with internal rigid fixation, and all subjects received fixed appliances after surgery for an average of 10.2 months. Subjects in both groups had lingual fixed retainers after treatment. Materials for both groups included retrospective serial lateral head radiographs in centric occlusion. The following radiographs of adult Herbst patients were taken: pretreatment (T0), after Herbst appliance (T1), after fixed appliance treatment (T2), and 3 years after treatment (T3). For surgery patients, the following radiographs were taken: pretreatment (T0), after surgical procedure (T1), after fixed appliance treatment (T2), and 3 years after treatment (T3). To minimize method error, all four cephalometric tracings for each subject were completed in the same session and were compared, so that cephalometric landmark locations were consistent. The four lateral head radiographs for each patient then were traced again at an interval of at least 2 weeks between the first and second sessions of tracing. values of the registrations were calculated. All linear and angular measurements were rounded to the nearest 0.5 mm and 0.5 degree, respectively. No correction was made for linear magnification, which was approximately 6% to 8% for all samples. Standard cephalometrics (Figure 1) and the sagittal-occlusal analysis of Pancherz 16 (Figure 2) were used for analyses of skeletal and dental changes. Statistical Methods and standard deviations were calculated for all linear and cephalometric variables. Method error was calculated with the use of Dahlberg s formula (ie, 2 ME d /2n ). 17 Method error did not exceed 0.7

3 1086 CHAIYONGSIRISERN, RABIE, WONG Table 1. Standard Cephalometric Records of 16 Adult Herbst Subjects and 16 Surgical Subjects a Variables Before Treatment (T0) After Herbst (T1) Herbst Group After Treatment (T2) After Follow-up (T3) Sagittal jaw relationship SNA SNB SnPg ANB ANPg Wits, mm Vertical jaw relationship ML/NSL NL/NSL ML/NL Incisor relationship Overbite, mm Facial height Spa-Gn* 100/N-Gn, index Spp-Go* 100/S-Go, index Profile convexity NAPg NS/Sn/PgS NS/No/Pgs Lip position UL-E-Line, mm LL-E-Line, mm a T0, before treatment; T1, after Herbst/surgical; T2, after the fixed appliance; T3, 3 years after treatment. Asterisks represent multiplication symbol. mm for linear variables, 1.0 degree for angular measurements, and 1.2 for index variables. Unpaired t-tests were undertaken to assess differences between the Herbst and surgery groups in terms of magnitude of change between the two groups. Paired t-tests were conducted to assess treatment changes within the group. The level of statistical significance was set at P.05. RESULTS Standard Cephalometric Analysis Treatment effects in the Herbst and surgery groups are shown in Table 1 Herbst/Surgical Treatment Period (T1-T0) The Herbst group showed significant increases in SNB (1.41 degrees), SNPg (1.13 degrees), ML/NSL (0.64 degree), anterior facial height (0.68 degree), NAPg (3.22 degree), NS/Sn/PgS (3.06 degrees), NS/ No/PgS (2.28 degrees), and LL-E-Line (1.31 mm). It also showed significant reductions in ANB (1.61 degrees), ANPg (1.33 degrees), Wits appraisal (3.93 mm), overbite (4.19 mm), and UL-E-Line (1.7 mm) (Table 2). The surgery group showed significant increases in SNB (3.34 degrees), SNPg (2.63 degrees), ML/NSL (2.25 degrees), ML/NL (2.99 degrees), anterior facial height (1.50 degrees), NAPg (5.10 degrees), NS/Sn/ PgS (4.47 degrees), and NS/No/PgS (4.41 degrees). It also showed significant reductions in ANB (3.29 degrees), ANPg (2.58 degrees), Wits appraisal (4.62 mm), overbite (3.47 mm), posterior facial height (2.00 mm), and UL-E-Line (2.41 mm) (Table 2). Group comparison. The Herbst group showed significantly less change in SNB (1.93 degrees), SNPg (1.50 degrees), ANB (1.68 degrees), ANPg (1.25 degrees), ML/NSL (1.61 degrees), anterior facial height (0.82 mm), posterior facial height (2.22 mm), NAPg (1.88 degrees), and NS/No/PgS (2.13 degrees) than did the surgery group (Table 2). Fixed Appliance Treatment Period (T2-T1) Group comparison. The Herbst group showed a significantly greater increase in overbite (1.03 mm) than did the surgery group (Table 2).

4 HERBST APPLIANCE AND SAGITTAL SPLIT OSTEOTOMY 1087 Table 1. Extended Before Treatment (T0) Surgery Group After Surgery (T1) After Treatment (T2) After Follow-up (T3) Herbst/Surgical Plus Fixed Appliance Treatment Period (T2-T0) The Herbst group showed significant increases in SNB (0.99 degree), SNPg (0.66 degree), NAPg (2.47 degree), NS/Sn/PgS (2.40 degree), and NS/No/PgS (1.87 degrees). It also showed significant reductions in ANB (1.20 degrees), ANPg (0.86 degree), Wits appraisal (3.40 mm), overbite (2.85 mm), and UL-E-Line (1.49 mm) (Table 2). The surgery group showed significant increases in SNB (2.68 degrees), SNPg (2.08 degrees), ML/NSL (1.56 degrees), ML/NL (2.53 degrees), anterior facial height (1.09 mm), NAPg (4.88 degrees), NS/Sn/PgS (4.09 degrees), and NS/No/PgS (4.16 degrees). It also showed significant reductions in ANB (2.78 degrees), ANPg (2.17 degrees), Wits appraisal (3.99 mm), overbite (3.16 mm), posterior facial height (2.08 mm) and UL-E-Line (2.54 mm) (Table 2). Group comparison. The Herbst group showed significantly less change in SNB (1.69 degrees), SNPg (1.42 degrees), ANB (1.58 degrees), ANPg (1.31 degrees), anterior facial height (0.97 mm), NAPg (2.41 degrees), and NS/No/PgS (2.29 degrees) than did the surgery group (Table 2). Post-Treatment Period (T3-T2) Group comparison. No significant difference was noted between the Herbst and surgery groups (Table 2). SO-Analysis Treatment effects in the Herbst and surgery groups are shown in Table 3. Herbst/Surgical Treatment Period (T1-T0) The Herbst group showed a significant overjet reduction of 8.3 mm, and a molar relation correction of 6.3 mm. Pogonion and lower incisors moved anteriorly 2.3 mm and 5.0 mm, respectively, whereas upper molars moved to the distal 1.8 mm and lower molars moved to the mesial 2.4 mm (Table 4). The surgery group showed a significant overjet reduction of 8.4 mm and a molar relation correction of 6.9 mm. Pogonion and lower incisors moved anteriorly by 5.7 mm and 2.0 mm, respectively, whereas lower molars moved to the mesial by 2.0 mm (Table 4). Group comparison. The Herbst group showed significantly less forward movement of the Pogonion than did the surgery group (a difference of 3.4 mm), but it

5 1088 CHAIYONGSIRISERN, RABIE, WONG Table 2. Standard Cephalometrics: Changes (D) During Treatment (T1-T0, T2-T1, T2-T0) and Post Treatment (T3-T2) in 16 Adult Herbst and 16 Surgery Subjects a Herbst Group Surgery Group Group Difference (Herbst Surgery) Sagittal jaw relationship SNA T1-T ns ns ns T2-T ns ns ns T2-T ns ns ns T3-T ns ns ns SNB T1-T *** *** *** T2-T * *** ns T2-T *** *** *** T3-T ns ns ns SNPg T1-T *** *** *** T2-T * ** ns T2-T ** *** *** T3-T ns ns ns ANB T1-T *** *** *** T2-T ns ** ns T2-T *** *** *** T3-T ns ns ns ANPg T1-T *** *** *** T2-T ns ns ns T2-T ** *** ** T3-T ns ns ns Wits, mm T1-T *** *** ns T2-T ns ns ns T2-T *** *** ns T3-T ns ns ns Vertical jaw relationship ML/NSL T1-T *** ** * T2-T ns ** ns T2-T ns * ns T3-T ns ns ns NL/NSL T1-T ns ns ns T2-T ns ns ns T2-T ns ns ns T3-T ns ns ns ML/NL T1-T ns *** ns T2-T ns ns ns T2-T ns ** ns T3-T ns ns ns Incisor relationship Overbite, mm T1-T *** *** ns T2-T *** ns ** T2-T *** *** ns T3-T ns * ns Facial height Spa-GN*100/N-Gn T1-T ** *** * (anterior facial height) T2-T ** ns ns T2-T ns ** ** T3-T ns ns ns Spp-GO*100/N-Gn T1-T ns *** * (posterior facial height) T2-T ns ns ns T2-T ns *** *** T3-T ns ns ns Profile convexity NAPg T1-T *** *** * T2-T *** ns ns T2-T ** *** * T3-T ns ns ns

6 HERBST APPLIANCE AND SAGITTAL SPLIT OSTEOTOMY 1089 Table 2. Continued Herbst Group Surgery Group Group Difference (Herbst Surgery) NS/Sn/Pgs T1-T *** ** ns T2-T ** * ns T2-T *** ** ns T3-T ns ns ns NS/No/Pgs T1-T *** *** * T2-T * ns ns T2-T *** *** ** T3-T ns ns ns Lip position UL-E-Line, mm T1-T ** *** ns T2-T ns ns ns T2-T ** *** ns T3-T ns ns ns LL-E-Line, mm T1-T ** ns ns T2-T ** ns ns T2-T ns ns ns T3-T ns ns ns a T0, before treatment; T1, after Herbst/surgical; T2, after the fixed appliance; T3, 3 years after treatment. * P.05; ** P.01; *** P.001; ns P.05. showed significantly greater forward movement of the lower incisors (3.0 mm) and distal movement of the upper molars (2.4 mm) than did the surgery group (Table 4). The mechanism of overjet and molar relation correction results are shown in Figures 3 through 6. Fixed Appliance Treatment Period (T2-T1) Group comparison. The Herbst group showed a significantly greater increase in overjet (by 1.9 mm), in relapse of molar relation correction (by 1.5 mm), and in backward movement of lower incisors (by 1.4 mm) than did the surgery group (Table 4). Mechanisms of overjet and molar relation relapse results are shown in Figures 3 through 6. Herbst/Surgical Plus Fixed Appliance Treatment Period (T2-T0) The Herbst group showed significant overjet reduction (5.3 mm), molar relation correction (3.7 mm), Pogonion and lower incisor anterior movement (1.5 mm and 3.4 mm, respectively), and lower molar mesial movement (1.8 mm) (Table 4). The surgery group showed significant overjet reduction (7.3 mm), molar relation correction (5.8 mm), and Pogonion and lower incisor anterior movement (4.7 mm and 1.8 mm, respectively). Upper and lower molars moved to the mesial 1.1 mm and 2.4 mm, respectively (Table 4). Group comparison. The Herbst group showed significantly less overjet reduction and molar relation cor- Table 3. SO-Analysis: Record of 16 Adult Herbst and 16 Surgery Subjects a,b Herbst Group Surgery Group Variable, mm T0 () T1 () T2 () T3 () T0 () T1 () T2 () T3 () Overjet Is/OLp minus 8.0 (2.07) 0.3 (2.22) 2.7 (1.21) 3.4 (0.99) 9.9 (2.62) 1.5 (0.90) 2.6 (0.97) 3.0 (1.04) ii/olp Molar relation ms/olp minus 0.7 (1.41) 5.6 (2.26) 3.0 (2.70) 2.4 (3.59) 1.7 (1.63) 5.2 (1.94) 4.1 (1.72) 3.7 (1.72) mi/olp Maxillary base A/OLp 78.6 (4.54) 78.8 (4.31) 78.9 (4.24) 78.9 (4.42) 79.7 (4.12) 79.9 (4.07) 79.9 (4.08) 79.9 (4.06) Mandibular base Pg/OLp 79.4 (8.45) 81.7 (7.93) 80.9 (7.95) 80.7 (7.96) 79.9 (6.83) 85.6 (6.05) 84.6 (6.22) 84.3 (6.24) Maxillary incisor is/olp 90.0 (3.97) 89.0 (4.35) 89.6 (4.71) 89.7 (4.69) 90.5 (6.53) 89.8 (6.28) 89.7 (5.95) 90.3 (6.24) Mandibular incisor ii/olp 82.0 (4.84) 89.3 (5.46) 86.9 (5.24) 86.3 (4.80) 80.6 (6.07) 88.3 (6.42) 87.1 (6.11) 87.3 (6.45) Maxillary molar ms/olp 58.8 (5.90) 57.2 (5.67) 58.4 (5.24) 58.8 (5.02) 58.1 (5.36) 58.9 (5.51) 59.4 (5.41) 59.7 (5.44) Mandibular molar mi/olp 58.1 (6.22) 62.8 (6.22) 61.4 (5.90) 61.2 (6.03) 56.4 (5.46) 64.1 (6.41) 63.5 (6.09) 63.4 (5.56) a T0, before treatment; T1, after Herbst/surgical; T2, after the fixed appliance; T3, 3 years after treatment. b Plus ( ) indicates a distal molar relation; minus ( ) indicates a neutral or mesial molar relation.

7 1090 CHAIYONGSIRISERN, RABIE, WONG Figure 3. SO-analysis: Skeletal and dental components contributing to overjet changes in the Herbst group. Plus ( ) means favorable changes aimed at overjet correction; minus ( ) means unfavorable changes aimed at overjet correction. T0 is before Herbst treatment; T1 is after Herbst treatment; T2 is after the fixed appliance; and T3 is 3 years after treatment. rection (a difference of 2 mm and 2.1 mm, respectively). Its Pogonion anterior movement is 3.2 mm less than that of the surgery group (Table 4). Mechanisms of overjet and molar relation correction results are shown in Figures 3 through 6. Post-Treatment Period (T3-T2) Group comparison. No significant difference was noted between the Herbst and surgery groups (Table 4). Figure 4. SO-analysis: Skeletal and dental components contributing to overjet changes in the surgery group. Plus ( ) means favorable changes aimed at overjet correction; minus ( ) means unfavorable changes aimed at overjet correction. T0 is before treatment; T1 is after surgery; T2 is after the fixed appliance; and T3 is 3 years after treatment.

8 HERBST APPLIANCE AND SAGITTAL SPLIT OSTEOTOMY 1091 Figure 5. SO-analysis: Skeletal and dental components contributing to molar relation changes in the Herbst group. Plus ( ) means favorable changes aimed at Class II molar correction; minus ( ) means unfavorable changes aimed at Class II molar correction. T0 is before Herbst treatment; T1 is after Herbst treatment; T2 is after the fixed appliance; and T3 is 3 years after treatment. DISCUSSION This study was designed to compare treatment effects and long-term stability of stepwise advancement Herbst appliance therapy vs surgical mandibular advancement. Women in both groups were overrepresented in this study. The reason for this might be associated with the fact that women generally showed a greater interest in improving their dental and facial ap- Figure 6. SO-analysis: Skeletal and dental components contributing to molar relation changes in the surgery group. Plus ( ) means favorable changes aimed at Class II molar correction; minus ( ) means unfavorable changes aimed at Class II molar correction. T0 is before treatment; T1 is after surgery; T2 is after the fixed appliance; and T3 is 3 years after treatment.

9 1092 CHAIYONGSIRISERN, RABIE, WONG Table 4. SO-Analysis: Changes (D) During Treatment (T1-T0, T2-T1, T2-T0) and Post-Treatment (T3-T2) Periods in 16 Adult Herbst and 16 Surgery Subjects a,b Variable, mm Herbst Group Surgery Group Group Difference (Herbst Surgery) Overjet Is/OLp minus T1-T *** *** ns ii/olp T2-T *** *** ** T2-T *** *** * T3-T ns ns ns Molar relation ms/olp minus T1-T *** *** ns mi/olp T2-T *** * * T2-T *** *** * T3-T ns ns ns Maxillary base A/OLp T1-T ns ns ns T2-T ns ns ns T2-T ns ns ns T3-T ns ns ns Mandibular base Pg/OLp T1-T *** *** *** T2-T *** ** ns T2-T ** *** *** T3-T ns ns ns Maxillary incisor is/olp (D) minus T1-T ns ns ns A/Olp (D) T2-T ns ns ns T2-T ns ns ns T3-T ns * ns Mandibular incisor ii/olp (D) minus T1-T *** * ** Pg/Olp (D) T2-T *** ns ** T2-T *** * ns T3-T ns ns ns Maxillary molar ms/olp (D) minus T1-T ** ns *** A/Olp (D) T2-T ** * ns T2-T ns ** ** T3-T ns ns ns Mandibular molar mi/olp (D) minus T1-T ** * ns Pg/Olp (D) T2-T ns ns * T2-T * ** ns T3-T ns ns ns a T0, before treatment; T1, after Herbst/surgical; T2, after the fixed appliance; T3, 3 years after treatment. b *P.05; ** P.01; *** P.001; ns P.05. pearance. 18 We demonstrated that after removal of the Herbst appliance (T2-T1), subjects in the Herbst group who were overcorrected at least into edge-to-edge bite had a relapse in overbite, overjet, and molar relationship through backward movement of the mandible and lower incisors and mesial movement of the maxillary molars. This movement was due to both persistent liptongue dysfunction habits and unstable cuspal interdigitation following treatment. 7 On the other hand, the main cause of relapse in the surgery group was the backward and downward movement of the mandible, probably because surgery stretched the masseteric, pterygoid, and temporal muscles. 19 Both Herbst and surgery groups achieved a Class I occlusal relationship and a reduction in the convexity of both hard and soft tissues during the treatment period (T2-T0). However, the surgery group showed more skeletal contribution and reduction of soft tissue convexity than did the Herbst group. In other words, the adult Herbst reduced hard and soft tissue convexity (NAPg and NS/Sn/PgS) by 50% and 58%, respectively, compared with the surgery group (Table 2). In the surgery group, greater upper lip retrusion occurred, most likely because of the larger mandibular base advancement. Hence, the esthetic line moved anteriorly automatically, resulting in upper lip retrusion. This finding agrees with that of a previous study that compared treatment changes of orthodontic and orthognathic surgery. 4 With respect to long-term stability after treatment (T3-T2), no significant relapse was seen within the Herbst group, or compared with the surgery group. Long-term stability in the skeletal and facial profiles of the Herbst group was demonstrated to be comparable with that of the surgery group. This study indicates a new alternative treatment modality for skeletal Class II correction in adult patients who are considered to be nongrowing. Reactivation of

10 HERBST APPLIANCE AND SAGITTAL SPLIT OSTEOTOMY condylar growth helps to correct skeletal Class II malocclusion and reduction in facial convexity. Key factors in the long-term success of the Herbst appliance are based on the clinical integration of basic scientific research. These factors include (1) stepwise advancement, (2) a 6-month duration for each instance of advancement, and (3) initial advancement of at least 5 mm. One magnetic resonance imaging (MRI) study showed that functional appliances lead to remodeling of the glenoid fossa. 8 Experiments that compared step-by-step and maximum jumping procedures in rats showed that stepwise advancement resulted in 100% and 50% more bone formation in the glenoid fossa and condyle, respectively. 20 Furthermore, a clinical study that compared stepwise and single-step advancement with the Herbst appliance in adult patients showed that the amount of correction resulting from skeletal changes was greater in the stepwise group. 10 The study in rats also showed that duration of advancement is a critical factor in the maturation of newly formed bone and in the stability of results. 21 Late removal of the appliance prevented subnormal growth and enhanced the maturity of the matrix of newly formed bone to the same degree as bone formed during development and bone repair. Previous studies 21 showed that it took 6 months for newly formed bone (which was type III collagenous matrix) to mature to the more stable type I collagenous matrix. Therefore, it is necessary to advance the mandible and hold it in the advanced position for at least 6 months. The amount of initial advancement is also important. A minimum threshold of strain must be exceeded to solicit a response. 22 Therefore, initial advancement was set at a minimum of 4 mm to obtain the optimum response in the Herbst group. The choice of treatment for adult patients who have a moderate skeletal Class II malocclusion depends on the attitude of the patients. The surgical method showed larger reduction of facial convexity than did the Herbst appliance, but some patients may choose to avoid surgery. Both treatment options have associated complications. The most common complication of surgery is neurosensory disturbance of the lower lip. 23 Mandibular advancement also risks condylar resorption, 24,25 which causes severe relapse in some surgical patients. In orthodontic treatment, the main complication is root resorption. The amount of root resorption is correlated with the amount of overjet reduction and horizontal tooth movement. 26 Hence, the best treatment for the borderline skeletal Class II adult depends on the demands of the patient. If the patient wants to achieve greater improvement in 1093 facial profile convexity and is willing to accept the risks of complications from surgery, then this method may be the best option. On the other hand, if facial profile improvement is not the most important issue, the Herbst appliance with stepwise advancement is a sensible alternative. CONCLUSIONS The Herbst appliance with stepwise advancement is an available option for correcting borderline skeletal Class II malocclusion in adult patients. The surgical procedure reduces facial convexity to a larger degree and provides significant improvement in the soft tissue profile. The stability of the Herbst treatment is as great as that of orthognathic surgery over the long term. ACKNOWLEDGMENT This study was supported by the RGC CERG grant awarded to Professor Rabie, We thank Mr. Shadow Yeung for his kind assistance with the statistical analysis. REFERENCES 1. Obwegeser HL. The indication for surgical correction of mandibular by sagittal splitting technique. Br J Oral Surg. 1964;1: Dal Pont G. Retromolar osteotomy for the correction of prognathism. J Oral Surg. 1961;19: Schendel SA, Epker N. Result after mandibular advancement surgery and analysis of 87 cases. J Oral Surg. 1980; 38: Ruf S, Pancherz H. Orthognathic surgery and dentofacial orthopedics in adult Class II Division 1 treatment: mandibular sagittal split osteotomy versus Herbst appliance. Am J Orthod Dentofacial Orthop. 2004;126: Pancherz H, Ruf S. The Herbst appliance: research-based updated clinical possibilities. World J Orthod. 2000;1: Pancherz H. Dentofacial orthopedics or orthognathic surgery: is it a matter of age? Am J Orthod Dentofacial Orthop. 2000;117: Hansen K, Pancherz H, Hägg U. Long-term effects of the Herbst appliance in relation to the treatment growth period: cephalometric study. Eur J Orthod. 1991;13: 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: Ruf S, Pancherz H. Dentoskeletal effects and facial profile changes in young adults treated with the Herbst appliance. 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11 1094 CHAIYONGSIRISERN, RABIE, WONG 12. Xiong H, Rabie AB, Hägg U. Mechanical strain leads to condylar growth in adult rats. Front Biosci. 2005;10: Xiong H, Rabie AB, Hägg U. Neovascularization and mandibular condylar bone remodeling in adult rats under mechanical strain. Front Biosci. 2005;10: Rabie AB, Xiong H, Hägg U. Forward mandibular positioning enhances condylar adaptation in adult rats. Eur J Orthod. 2006;26: Hägg U, Taranger J. Skeletal stages of the hand and wrist as indicators of the pubertal growth spurt. Acta Odontol Scand. 1980;38: Pancherz H. The mechanism of Class II correction in Herbst appliance treatment. Am J Orthod. 1982;82: Dahlberg G. Statistical Methods for Medical and Biological Students. New York: InterScience Publications; Hoppenreijs TJ, Hakman EC, van t Hof MA, Stoelinga PJ, Tuinizing DB, Freihofer HP. Psychologic implication of surgical orthodontic treatment in patients with anterior open bite. Int J Adult Orthod Orthognath Surg. 1999;14: Eggensperger N, Wenko S, Akram R, Iizuka T. Skeletal relapse after mandibular advancement and setback in single jaw surgery. J Oral Maxillofac Surg. 2004;62: Rabie AB, Chayanupatkul A, Hägg U. Stepwise advancement using fixed functional appliances: experimental perspectives. Semin Orthod. 2003;9: Chayanupatkul A, Rabie AB, Hägg U. Temporomandibular response to early and late removal of bite-jumping devices. Eur J Orthod. 2003;25: Rabie AB, Al-Kalaly A. Does the degree of advancement during functional appliance matter? Eur J Orthod. 2008;30: Kiyak HA, Bell R. Psychosocial consideration in surgery and orthodontics. In: Proffit WR, White RP ed. Surgical-Orthodontic Treatment. St. Louis: Mosby; 1990: Cassidy DW, Herbosa EG, Rotskoff KS, Johnston LE. A comparison of surgery and orthodontics in borderline adults with Class II division I malocclusions. Am J Orthod Dentofacial Orthop. 1993;104: Schellhas KP, Piper MA, Bessette RW, Wilkes CH. Mandibular retrusion, temporomandibular joint derangement, and orthognathic surgery planning. Plast Reconstr Surg. 1992; 90: Sameshima GT, Sinclair PM. Predicting and preventing root resorption: I. Diagnosis factor. Am J Orthod Dentofacial Orthop. 2001;119: