Material and methods

After obtaining ethical approval from the Institutional Review Board of West Virginia University (protocol number 1405291690) and approval from 2 authors (M.R. and L.A.) for the use of orthodontic records from their office, the records of 100 Class II patients successfully treated with the reinforced Herbst appliance from 2005 to 2012 were retrospectively examined with the following inclusion criteria: convex facial profile, Class II malocclusion with at least a half-step Class II molar relationship, late mixed dentition to early permanent dentition (age, 10-16 years) at the start of treatment, nonextraction treatment, no previous orthodontic treatment, and availability of pretreatment, posttreatment, and final records taken within 12 months after removal of fixed appliances. The exclusion criteria included patients in the primary or early mixed dentition, with craniofacial syndromes or severe facial asymmetry, or with a history of periodontal disease. A total of 30 treated subjects (16 boys, 14 girls) fulfilled these criteria. The average age at the start of treatment was 12.3 ± 2.5 years (range, 10-15 years). The average treatment time with the Herbst appliance was 1.5 ± 0.7 years, and the average treatment time with the fixed appliance was 1.8 ± 0.5 years. The control sample, obtained from the Bolton-Brush study, was matched closely for age, sex, and craniofacial morphology with the experimental sample. No significant differences in craniofacial morphology were found between the 2 groups ( Table I ).

Separators were placed 5 to 7 days before the fitting appointment. At the next appointment, maxillary and mandibular molar bands with facial and lingual cleats prewelded as guides for accurate positioning in an alginate impression were fitted. An alginate impression was taken, and the bands were transferred from the patient, glued in the impression (Great Lakes Adhesive, Tonawanda, NY), and poured up as soon as possible. A wax bite registration was not necessary because the amount of advancement and the midline position were noted on the laboratory prescription. A skeletal midline discrepancy was corrected during Herbst treatment. If there was a dental midline discrepancy, the correction was made after the Herbst was removed and full brackets were placed. The initial advancement was usually 1 to 2 mm short of the edge-to-edge position, and then the mandible was advanced in gradual increments (1 or 2 mm every 8 weeks) until an edge-to-edge or an anterior crossbite position was achieved. A laboratory prescription was completed including any special features requested by the clinician in the Herbst construction. Also, at the fitting appointment, brackets were bonded to the maxillary incisors, and a sectional wire was placed to align those teeth before the Herbst was delivered at the next appointment. This is particularly helpful in patients with a Class II Division 2 malocclusion whose incisors need alignment and advancement. Separators were placed about a week before delivery of the appliance to provide adequate band space. The Herbst appliance was modified by an investigator (M.R.; Fig 1 ). The transpalatal arch was eliminated for added comfort. For stability, buccal archwire tubes were incorporated on the maxillary molar bands, and a larger 0.051-in lingual arch was used on the mandibular arch. Although the thicker 0.010-in bands were less likely to break than conventional bands, 0.051-in reinforcing wires were soldered to the distal occlusal margins of the maxillary and mandibular bands to give them even more bulk and strength. In addition, 0.025-in wires were soldered to the mesial occlusal margins of the mandibular and maxillary bands. Finally, the universal nut and a 0.022 × 0.028-in archwire tube were welded on a 0.020-in unibody plate (Specialty Appliances, Cumming, Ga) and brazed to the mesial area of the maxillary bands, permitting the archwires to be used for alignment and control of the maxillary anterior segment. This design does not require occlusal rests on the second molars because the support wire soldered to the distal surfaces of the maxillary and mandibular bands prevents overeruption of the second molars. Although clinicians have tried to use a cantilever Herbst design with bands, they have reported excessive breakage.

Reinforced banded Herbst appliance: A, occlusal view of the appliance showing the molar bands reinforced with soldered 0.051-in stainless steel wires; B, buccal view of the appliance showing the telescopes incorporated into the design to eliminate some of the old problems with rods and tubes coming apart and the rods impinging on the ascending ramus.

At the insertion appointment, the appliance was tried in the mouth before cementation, with the telescope inspected and shims added if necessary to make sure that the midlines matched the prescription (centered for a skeletal problem or off center for a dental discrepancy). The use of the M-4 telescopes developed by Specialty Appliances eliminated some of the old problems with rods and tubes coming apart and rods impinging on the ascending ramus. The 0.051-in mandibular lingual arch should lie no more than 0.5 mm from the mandibular incisors. If the wire is slightly off the incisors, it will settle against them in several days. Once the fit was satisfactory, the appliance was removed and dried. The maxillary telescopes were secured to the maxillary pivots in the laboratory before trying on the Herbst by placing Ceka Bond (Specialty Appliances) on the screw threads. The mandibular telescopes were secured after cementation. Ceka Bond ensures that the threads will not back out during treatment. Before cementation, the molars were pumiced and cleaned and etched on the buccal aspect only with GC Ortho Conditioner (GC America, Alsip, Ill), a 10% polyacrylic acid solution. Using Fuji I (GC America) band cement, the maxillary molar bands were cemented. A laboratory soldered the upper pivots as far mesially as feasible so that they would not impinge on the ascending ramus. Immediately after the bands were firmly seated, the excess cement was removed with a cotton roll. This saved considerable cleanup time and was more comfortable for the patient.

When arch development is needed, maxillary or mandibular rapid palatal expanders can be added to the Herbst appliance. The maxillary rapid palatal expander should be turned once a day until the desired expansion is achieved; the mandibular screw should be turned once every 4 days. Thumb cribs or tongue prongs for habit control could also be easily incorporated into this Herbst design. The mandible was initially advanced 1 to 2 mm short of the edge-to-edge position and reactivated by adding shims 1 to 2 mm every 8 weeks until an overcorrected Class III canine relationship was achieved. An advantage of the Herbst is that patients and parents can immediately see improvement in the facial profile; this boosts their enthusiasm and cooperation. One great advantage with this design, however, is its ease of removal when the Herbst phase of treatment is finished. The mandibular screws were removed, and the maxillary telescopes were left attached during removal. The mandibular arch and bands were then taken out with a band-removing plier. The maxillary anterior brackets, archwires, telescopes, and bands were removed as a unit, reducing the risk of a patient’s swallowing a band or a compontent.

Lateral cephalograms were taken before treatment (T1), immediately after removal of the Herbst appliance (T2), and at completion of fixed appliance therapy (T3). Figure 2 shows the skeletal and dental changes of a typical subject in the study. The radiographs in digital format were uploaded into the software (Dolphin Imaging and Management Solutions, Chatsworth, Calif) and traced digitally to ensure a 1:1 conversion. The lateral cephalometric images were then printed out on a printer (C510; Lexmark International, Lexington, Ky) using photographic paper. The digital lateral cephalometric radiographs for the control subjects were obtained from the Bolton-Brush study and matched closely for age, sex, and craniofacial morphology with the experimental subjects. The images were scanned at 12-bit gray scale resolution with a spatial resolution of 0.1 mm per pixel and stored in uncompressed TIFF format. The images were converted to JPEG format with the IrfanView software (version 4.0; IrfanView, Jajce, Bosnia) and loaded into Photoshop (version 6.0; Adobe Systems, San Jose, Calif) for size analysis. All original radiographs from the Bolton-Brush study were indexed with 4 corner fiduciary points using a template according to the method described by Baumrind and Miller. In Photoshop, the resolutions of the images were verified (600 dpi), and the images were resized to the original dimensions of the unscanned radiographs. Printouts were then made on the C510 printer, and the fiduciary points were measured with an electronic digital caliper to ensure a 1:1 conversion with no distortion from the original radiographs.

Lateral cephalogram of a typical patient treated with the Herbst and fixed appliance therapy: A, pretreatment; B, immediately after removal of the Herbst appliance; C, after treatment with fixed appliance therapy.

Tracings were made on printouts obtained from the digitized cephalograms by an operator (T.T.) using a number 2 HB mechanical lead pencil (0.5 mm; Pentel, Torrance, Calif), an orthodontic protractor, and 0.003-in matte cephalometric acetate tracing film (3M Unitek, Monrovia, Calif). A custom cephalometric analysis was performed using landmarks correlating with the cephalometric systems described by Bjork, Pancherz, VanLaecken et al, and Wigal et al. The data were normalized to account for magnification differences between the cephalometric machine used for the Bolton-Brush study (5.6%) and the cephalometric machine used for the experimental subjects. All linear measurements were made with a digital caliper (accurate to 0.01 mm) and reported to the nearest 0.1 mm. Analyses of the sagittal skeletal and dental changes were recorded along the occlusal plane (OLs) and to the occlusal plane perpendicular (OLp) from the first cephalogram; this formed the reference grid. The grid was then transferred to subsequent cephalograms by superimposing the tracing on the midsagittal cranial structures. The changes in overjet and molar relationships were calculated using the formula in Table II . The measurement for each angular variable was performed with a cephalometric protractor and evaluated to the nearest 0.5°. The measurement for each sagittal and vertical measurement was performed with an electronic digital caliper and evaluated to the nearest 0.01 mm. The caliper was calibrated to 0.0 mm before each measurement. Because lateral cephalograms often show landmarks with right and left images, the midpoint bisecting the 2 images was used.

Results

Table III shows the treatment effects with the Herbst appliance for the time period T2 to T1. A total of 18 of 23 variables investigated showed significant differences after 1.5 years of treatment with the Herbst appliance. For the sagittal measurements, no significant change in condylar position was noted. The maxilla moved forward 0.34 mm (Olp–A-pt). The maxillary molars and incisors moved backward 1.46 and 2.02 mm, respectively (Olp-Ms, Olp-Mi). The mandible moved forward 3.7 mm (Olp-Pg). The mandibular molars moved forward 5.5 mm, and the mandibular incisors moved forward 5 mm (Olp-Is, Olp-Ii). For the vertical variables, the maxilla moved downward 2.2 mm (OLs-Apt). Overbite decreased by 3.3 mm. The maxillary molars intruded by 0.8 mm (Msc-NL), and the mandibular molars intruded by 0.6 mm (Mic-ML). The mandibular incisors intruded by 0.9 mm (Ii-ML). For the angular variables, SNA decreased by an average of 0.6°, SNB increased by 4.0°, and ANB decreased by 4.6°. The Wits appraisal decreased by 4.4 mm. The palatal plane (SNL-NL) increased by 2.6°, and the occlusal plane (SNL-OLs) was 2.5° steeper. The maxillary incisors were retracted by 5.5°, and the mandibular incisors were proclined by 8.8°.

Table III

Changes in treatment group for the time periods T2-T1 and T3-T1

Variable	T2-T1				T3-T1
	Mean	SD	P value	Sig	Mean	SD	P value	Sig
Sagittal (mm)
Olp-Co	0.34	2.14	0.3907	NS	2.09	2.43	0.0001	‡
Olp-A-pt	0.34	2.35	0.0037	†	1.87	2.87	0.1311	NS
Olp-Ms	−1.46	2.50	0.0032	†	0.71	3.05	0.0437	∗
Olp-Mi	5.53	2.58	0.0001	‡	7.0	3.45	0.0001	‡
Olp-ls	−2.02	3.64	0.0021	†	−0.39	3.84	0.5813	NS
Olp-li	5.04	3.75	0.0001	‡	7.2	4.47	0.0001	‡
Olp-Pg	3.7	3.18	0.0001	‡	5.5	4.68	0.0069	†
Wits	−4.39	2.40	0.0001	‡	−2.32	2.37	0.0048	†
Vertical (mm)
OLs-A-pt	2.19	1.41	0.0001	‡	4.51	2.23	0.0001	‡
ANS-Me	2.19	6.09	0.3085	NS	4.65	3.49	0.0001	‡
Is-NL	0.16	1.46	0.5647	NS	0.7	2.34	0.1152	NS
Ii-ML	−0.87	1.59	0.0055	†	0.71	2.17	0.0857	NS
Overbite	−3.25	1.35	0.0001	‡	−3.64	1.50	0.0001	‡
Msc-NL	−0.81	1.14	0.0014	†	0.89	1.77	0.0026	†
Mic-ML	−0.6	1.33	0.0022	†	1.38	1.84	0.0001	‡
Angular (°)
SNA	−0.58	1.67	0.1169	NS	0.37	2.32	0.1479	NS
SNB	4.03	1.61	0.0022	†	3.15	2.09	0.0012	†
ANB	−4.61	1.68	0.0001	‡	−2.78	1.61	0.0002	‡
SNL-NL	2.55	2.61	0.0025	†	1.6	2.87	0.0466	∗
SNL-ML	−0.56	2.29	0.1917	NS	−1.23	3.15	0.0401	∗
SNL-OLs	4.47	2.87	0.0001	‡	1.8	3.65	0.0026	†
Is/NL	−5.52	7.77	0.0019	†	−4.32	8.18	0.0045	†
Ii/ML	8.82	5.69	0.0001	‡	5.24	9.8	0.0065	†

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