Material and methods

The subjects in this study were derived from a well-defined sample of 22 consecutive patients with Class II Division 1 malocclusions (bilateral Class II molar and canine occlusion, large overjet, and deep overbite) treated with the Herbst appliance at the University of Malmö in Sweden in 1977 and 1978. The subjects were originally presented in 2 articles from 1982.

In 2011 and 2012, 30 to 33 years after Herbst therapy, these 22 subjects were recalled to the orthodontic department in Malmö, Sweden, for a follow-up investigation. At this time, they were 42 to 48 years old. Two persons were deceased, and 6 did not appear for several reasons. Thus, the final follow-up sample comprised 14 subjects (12 men, 2 women), shown in detail in Table I . The patients’ ages were, on average, 12 years at the start of treatment and 14 years after treatment. The patients were reexamined 6 years (age 20) and 32 years (age 46) after treatment.

All subjects were treated by an author (H.P.) using a banded type of Herbst appliance with a simple anchorage system that did not include brackets on any teeth. Since the treatment of the original 22-subject sample was designed as a clinical experimental study, no further fixed appliance treatment phase after the Herbst phase was planned. However, because of major tooth irregularities after Herbst therapy, extractions of 4 premolars were performed in 2 subjects (patients 1X and 8X), and maxillary and mandibular fixed multibracket appliances were placed for about 1 year. Furthermore, for tooth alignment in 1 nonextraction patient (12), a maxillary multibracket appliance treatment phase was instituted for 6 months after the Herbst phase. In these 3 patients, multibracket treatment after the Herbst phase aimed to align the teeth after the Class I dental arch and overjet corrections were achieved by the Herbst appliance.

Retention after Herbst treatment, performed in 10 of the 14 patients, was inconsistent and of short duration (2-4 years). No retainers were used in 4 subjects ( Table I ).

Lateral head films were analyzed at 4 times: T1, before Herbst treatment; T2, after treatment (12 months after the Herbst appliance was removed and the occlusion had settled); for the 2 extraction patients (1X and 8X), T2 implied that analyses were done after removal of the multibracket appliance; T3, 6 years after treatment at an average age of 20 years when the radius epiphysis/diaphysis plate was closed (hand-wrist stage R-J, according to Hägg and Taranger ); and T4, 32 years after treatment at an average age of 46 years.

The treatment and posttreatment changes of different variables were analyzed during the following observation periods: T1-T2, treatment changes; T2-T3, early posttreatment changes; T3-T4, late posttreatment changes; and T2-T4, total posttreatment changes.

All cephalometric roentgenograms were taken at the Department of Oral Radiology, Faculty of Dentistry, Malmö University, Malmö, Sweden. The lateral head films at T1, T2, and T3 were taken by the analog technique and the films at T4 by the digital technique. For each technique, the radiographic records were obtained using a standardized procedure with a fixed-focus midsagittal film distance. For accomplishing the same magnification of all head films, the printouts of the T4 images were reduced in size by 14% to match the T1, T2, and T3 images (7%). With the help of 1-mm metal indicators placed at intervals of 5 mm in the center of the cephalostat’s forehead rest, the final radiographic magnification could be checked.

The measurements from the roentgenograms were performed on matte acetate tracing film, on which the reference points were marked with a sharp pencil. The angular measurements were made to the nearest 0.5°, and the linear measurements to the nearest 0.5 mm. These values were not corrected for linear enlargement (7%) in the median plane.

The reference points and lines used in the cephalometric analysis were those defined by Björk and Pancherz.

To minimize the tracing and landmark identification errors in the analysis of the serial head films, the tracings of the 4 head films from each patient were done in a simultaneous parallel way at the same occasion.

The head film evaluations comprised a standard analysis and an analysis of the sagittal changes in the occlusion (SO).

The head film analysis comprised 7 angular measurements (variables 1-7) and 2 linear measurements, the latter of which were made on dental casts (variables 8 and 9).

• 1.

  SNA, sagittal maxillary position to the cranial base.

• 2.

  SNB, sagittal mandibular position to the cranial base.

• 3.

  ANB, sagittal maxillomandibular relationship.

• 4.

  ML/NSL, vertical mandibular position to the cranial base (mandibular plane angle).

• 5.

  ILs/NSL, maxillary incisor inclination to the cranial base.

• 6.

  ILi/ML, mandibular incisor inclination to the mandibular plane.

• 7.

  ILs/ILi, interincisal inclination.

• 8.

  Overjet, the horizontal distance between the incisal edge of the most prominent maxillary central incisor and the labial surface of the corresponding mandibular incisor parallel to the occlusal plane.

• 9.

  Overbite, the vertical distance between the incisal edges of the maxillary central and mandibular central incisors.

The SO analysis has been described extensively in a previous article. The SO analysis allows a quantitative assessment of skeletal and dental changes in the maxilla and mandible that contribute to changes in the sagittal molar relationship and overjet.

The reference points and lines used are shown in Figure 1 . The occlusal line (OL) is defined by the incisal tip of the most prominent maxillary central incisor and the mesiobuccal cusp tip of the first maxillary molar. The OLp is a line perpendicular to OL through the tangent point of the anterior wall of sella turcica. The OL and the OLp from the first head film were used as a reference grid. The grid was transferred from the T1 tracing to the following tracings (T2, T3, and T4) by superimposition of the radiographs, using the stable skull structures in the anterior cranial base for orientation. The objective was to obtain the closest coincidence for the maximum number of the following structures: (1) the anterior wall of sella turcica, (2) the cribriform plate, (3) the trabecular pattern of the superior portion of the ethmoid bone, (4) the medial border of the orbital roof, (5) the anterior walls of the median cranial fossae, and (6) the anterior contours of the pterygopalatine fossae.

Measuring points and lines used in the SO analysis. The reference grid (OL and OLp) is shown.

Perpendicular to the OLp line, the following changes in linear measurements ( Fig 1 ) were assessed (variables 1-8): (1) ms minus mi, molar relationship; (2) is minus ii, overjet; (3) ss, maxillary base position; (4) pg, mandibular base position; (5) ms minus ss, maxillary molar position; (6) mi minus pg, mandibular molar position; (7) is minus ss, maxillary incisor position; and (8) ii minus pg, mandibular incisor position.

To visualize the dentoskeletal growth changes during the different observation periods, the radiographs from T1, T2, T3, and T4 of each subject were superimposed using the stable anterior cranial base structures for orientation.

Results

All head film registrations from the 14 subjects were performed twice. The precision of the double registrations was tested with Dahlberg’s formula with a 2-week interval. For the angular measurements, the method error varied between 0.6° (SNA, SNB) and 1.1° (ILs/NSL). For the linear measurements, the error ranged between 0.2 mm (pg-OLp) and 0.5 mm (mi-OLp).

The final results were based on the first series of head film measurements.

For the standard cephalometric evaluation for each variable, the arithmetic mean and standard deviation at each examination as well as the statistical evaluation of changes during the different examination periods are given in Table II .

Table II

Standard analysis: lateral head film measurements of 14 subjects with Class II Division 1 malocclusions treated with the Herbst appliance and followed for 32 years after therapy

Variable	T1		T2		T3		T4		T1-T2		T2-T3		T3-T4		T2-T4
	Mean	SD	Mean	SD	Mean	SD	Mean	SD	t ∗	P	t ∗	P	t ∗	P	t ∗	P
SN-maxillary position (°)	82.8	4.15	82.2	4.56	82.3	4.58	81.5	5.25	0.97	NS	−0.29	NS	1.15	NS	0.90	NS
SNB-mandibular position (°)	77.0	3.61	76.9	4.02	77.9	3.52	77.4	4.72	0.08	NS	−3.61	<0.01	0.87	NS	−0.79	NS
ANB-maxillomandibular relationship (°)	5.9	2.02	5.3	1.85	4.4	2.39	4.4	1.86	2.18	<0.05	3.10	<0.01	0.00	NS	1.94	NS
ML/NSL-mandibular plane angle (°)	30.1	5.72	30.5	6.71	28.0	6.53	28.0	7.23	−0.53	NS	6.15	<0.001	0.06	NS	3.93	<0.01
ILs/NSL-maxillary incisor inclination (°)	101.9	4.73	96.5	7.94	98.0	6.81	97.8	6.76	3.36	<0.01	−1.21	NS	0.22	NS	−0.83	NS
ILi/ML-mandibular incisor inclination (°)	100.1	6.25	104.2	5.33	101.1	4.59	101.7	6.29	−4.59	<0.001	4.07	<0.001	−0.54	NS	1.98	NS
ILs/Ili-interincisor inclination (°)	128.0	8.13	131.1	7.15	133.3	9.72	132.9	9.40	−1.88	NS	−1.06	NS	0.20	NS	−0.79	NS
Overjet (mm) †	8.1	1.62	3.9	0.89	4.0	1.13	4.2	1.67	7.23	<0.001	−0.31	NS	−0.72	NS	−0.67	NS
Overbite (mm) †	5.0	1.23	3.5	1.06	3.8	0.78	3.8	0.83	3.20	<0.01	−0.74	NS	−1.00	NS	−0.36	NS

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