The aim of this study was a retrospective analysis of posterior teeth in 20 adolescents and young adults with Angle Class II Division 1 malocclusion treated with a banded Herbst appliance to check for inhibited root development and apical root resorption.
Panoramic radiographs were taken of every patient at the beginning and after the completion of functional orthopedic treatment. The magnification of the area of the posterior teeth was determined individually for every radiograph. Then the vestibular lengths of the molars and premolars were assessed metrically. To assess root-length changes, the difference between the lengths of the teeth before and after treatment was calculated.
After treatment with a banded Herbst appliance, tooth length generally increased in the area of the anchorage. But there was a tendency toward root-length decrease in teeth immediately adjacent to the Herbst fittings in the vestibular roots of both the maxillary first molars (distovestibular, –0.02 ± 2.31 mm; mesiovestibular, –0.06 ± 2.05 mm) and the mandibular first premolars (–0.46 ± 3.53 mm).
The banded Herbst appliance might deliver unphysiologic forces to immediate anchor teeth, thereby exposing these to a higher risk of root resorption than in other teeth incorporated into the anchorage either directly via bands or indirectly via occlusal or approximal contacts. Looking at uncompromised root morphology in the area of the anchorage, we believe that early treatment with fixed functional appliances can be predicted to yield better outcomes than late treatment because of the higher biologic tolerance expressed by teeth with an apical latency.
Fixed functional orthopedic appliances, such as the Herbst appliance (Dentaurum, Ispringen, Germany), allow achieving neutral or overcompensated neutral occlusion in the treatment of Class II malocclusion. The occlusal changes derive from a combination of skeletal and dental effects. The treatment stimulates mandibular growth and causes length increases in the mandible. Treatment with a Herbst appliance is indicated particularly when only a little residual growth can be expected or the pubertal growth peak is already over. The appliance is also used when the patient’s compliance is not sufficient to correct the distoclusion with a removable functional appliance.
Both telescoping fixtures of the Herbst appliance feature a guide tube and a sliding pin fitted to the maxillary first molar and the mandibular first premolar with cast splints or prefabricated bands or crowns. In this study, the Herbst variant with prefabricated orthodontic bands on the first premolars and the first molars (banded Herbst appliance) was used. In terms of laboratory technique, it was constructed by soldering the Herbst fixtures to the vestibular side of the bands placed on the anchorage teeth (maxillary first molars and mandibular first premolars). Palatal and lingual archwires were fitted for connection to other anchorage teeth wearing bands and for transverse reinforcement.
During treatment with fixed functional orthopedic appliances, the occlusal changes stretch both the mastication musculature and the soft tissues. This exposes the patient’s teeth to a highly complex force system. The forces are intermittent, and their strength and duration vary according to the function (swallowing, opening, closing, or resting). If sustained forces are too strong or last too long, there is always the possibility that resorption in the apical area or, if root growth is incomplete, an inhibiting effect on root development will occur.
It must be asked whether root-growth disorders or the development of apical root resorption in the anchorage teeth will result specifically from treatment with a Herbst appliance fitted to prefabricated bands. Therefore, the aim of this study was to compare the root lengths of the posterior dentition before and after functional orthopedic treatment.
We assessed whether (1) apical root resorption in the area of the posterior teeth develops as an effect of functional orthopedic treatment with the banded Herbst appliance and (2) particular teeth or tooth groups of the posterior dentition are exposed more clearly to resorption than others.
Material and methods
Twenty patients (9 male, 11 female) with Class II Division 1 malocclusion were treated with a functional orthopedic approach to achieve distal bite correction with a banded Herbst appliance. Treatment progress was documented by using dental plaster casts and 2 panoramic radiographs (start of treatment, T1; completion of functional orthopedic treatment, T2) for every patient. Pantomograms were the radiographic technique of choice, since they are routinely taken during orthodontic treatment. For reasons of radiation exposure management, no additional dental films were taken. The patients’ mean age at the time of Herbst appliance placement was 13.5 years (range, 8.9-22.3 years), and the mean treatment duration was 12 months.
The pantomograms were visually inspected to verify whether root development in the anchorage teeth was completed. Root formation was found to be incomplete in 61.25% of the premolars (60% of the maxillary first premolars, 60% of the maxillary second premolars, 55% of the mandibular first premolars, and 70% of the mandibular second premolars).
Depending on the stage of root formation in the mandibular first premolars—ie, the teeth immediately exposed to the Herbst appliance anchorage—the patients were divided into 2 groups (PG 1, root growth not completed, n =11, mean age 11.7 years; PG 2, root growth completed, n = 9, mean age 15.7 years).
Radiographic images were digitized on a transmitted-light scanner (Epson Scan, Seico Epson, Tokyo, Japan) set to 800 dpi and then processed for analysis with Adobe Photoshop CS (version 8.0, Adobe Systems Software, Dublin, Republic of Ireland). The analysis of the panoramic tomograms was conducted by using the computer program AutoCAD 2005 (Autodesk, Munich, Germany). A scale factor of 0.1 was inserted into the radiographic images. With this program, the mesiodistal diameter of each maxillary first molar was traced first. Then the tooth lengths of the first and the second premolars and the first molars in both jaws were determined by registering the distance from the vestibular cusp to the apex of the root. When the apical foramen was still open, the reference point chosen was the midpoint of the distance between both canal walls. The palatal roots of the maxillary teeth were not assessed because the imaging technique does not display them sharply, and tracings can be distorted as a result. In addition to the determination of the mesiodistal diameter of the maxillary first molars based on the radiographic image, their widths were measured on the cast with a digital caliper. This enabled calculating the magnification of the pantomogram, which is not directly measurable, before proceeding to statistical analysis. This was achieved by defining the mesiodistal diameter of the first molar (M1) in the first and second quadrants from every cast in each patient as the reference for the calculation of magnification at T1 and T2. The factors of magnification at T1 and T2 were calculated as follows.
Magnification factor MF T1 = width (tooth M1) panto T1 : width (tooth M1) cast.
Magnification factor MF T2 = width (tooth M1) panto T2 : width (tooth M1) cast.
By using this magnification factor, the actual tooth lengths could then be computed individually (premolars and molars) as follows.
Actual length (tooth) T1 = length (tooth) T1 : MF T1.
Actual length (tooth) T2 = length (tooth) T1 : MF T2.
To achieve sound statements about root-length development, the difference between the computed actual tooth lengths (T2-T1) was calculated. The clinical crown height was presupposed to remain constant. When a numeric result had a positive sign, length had increased; when the number was negative, length had decreased.
Statistical analysis was performed with a computer program (version 220.127.116.11, MedCalc Software, Mariakerke, Belgium); tests were performed with paired t tests for intragroup comparisons and with unpaired t tests for intergroup assessments. The level of significance was defined as P ≤0.05.
Considering all teeth as 1 study group, tooth length increased by 0.22 ± 2.98 mm ( P = 0.2263). In the subsamples, PG 1 showed a significant increase (0.84 ± 2.53 mm, P = 0.0004), and PG 2 exhibited a trend for tooth-length decrease (–0.28 ± 3.23 mm, P = 0.2920). When we assessed the jaws individually, tooth-length increase could be observed in both jaws (0.34 ± 2.88 mm in the maxilla; 0.11 ± 3.09 mm in the mandible). The changes were not significant in either jaw. In the subsamples, the treatment outcomes were significant length increases in both jaws in PG 1 (0.92 ± 2.27 mm, P = 0.0030 in the maxilla; 0.77 ± 2.78 mm, P = 0.0366 in the mandible) and slight tooth-length reductions in PG 2 that were not significant ( Table I ).
|T1 mean and SD||T2 mean and SD||T2-T1 mean and SD||P value|
|Overall||23.23 ± 5.82||23.45 ± 5.48||0.22 ± 2.98||0.2263|
|PG 1||22.24 ± 4.30||23.08 ± 5.72||0.84 ± 2.53||0.0004 ∗|
|PG 2||24.18 ± 6.11||23.90 ± 5.79||−0.28 ± 3.23||0.2920|
|Overall maxilla||22.95 ± 5.60||23.29 ± 6.05||0.34 ± 2.88||0.1771|
|PG 1 maxilla||22.20 ± 4.57||23.12 ± 6.03||0.92 ± 2.27||0.0030 ∗|
|PG 2 maxilla||23.61 ± 5.74||23.49 ± 6.10||−0.12 ± 3.23||0.7446|
|Overall mandible||23.51 ± 6.02||23.62 ± 5.46||0.11 ± 3.09||0.6937|
|PG 1 mandible||22.27 ± 4.07||23.04 ± 5.42||0.77 ± 2.78||0.0366 ∗|
|PG 2 mandible||24.74 ± 6.45||24.30 ± 5.47||−0.44 ± 3.24||0.2484|
For the assessments with the paired t test, the teeth of the respective jaws (ie, their roots) were defined as tooth groups. These groups were composed of the distovestibular (dv) and distal (d) roots of the maxillary and mandibular first molars (UP 6 dv, LO 6 d), the mesiovestibular (mv) and mesial (m) roots of the maxillary and mandibular first molars (UP 6 mv, LO 6 m), and the maxillary and mandibular first and second premolars (UP and LO 5, UP and LO 4), respectively. Although, in the total patient sample no statistically significant changes occurred, there was a tendency for root-length decreases in both vestibular roots of the maxillary first molars (UP 6 dv, –0.02 ± 2.31 mm; UP 6 mv, –0.06 ± 2.05 mm) and the mandibular first premolars (–0.46 ± 3.53 mm). In all other tooth groups, however, root-length increases were detected (maxillary first premolars, 0.88 ± 3.59 mm; maxillary second premolars, 1.04 ± 3.87 mm; mandibular second premolars, 0.11 ± 3.38 mm; distal roots of the mandibular first molars, 0.53 ± 2.82 mm; mesial roots of the mandibular first molars, 0.06 ± 2.87 mm). In the subsamples, PG 1 exhibited length increases in all tooth groups. In PG 2, trends for tooth-length decreases were observed in particular in the maxillary first molars and the mandibular first premolars, which were the anchorage teeth immediately exposed to fitting the Herbst appliance (UP 6 dv, –0.60 ± 2.09 mm, P = 0.2407; UP 6 mv, –1.01 ± 2.19 mm, P = 0.0424; mandibular first premolars, –1.22 ± 3.58 mm, P = 0.1663). Comparison of tooth groups between both patient subsamples showed a significant difference in tooth-length changes only in the mesiovestibular roots of the maxillary first molars (PG 1, 0.72 ± 1.57 mm; PG 2, –1.01 ± 2.19 mm; intergroup significance, P = 0.0059) ( Table II ).
|T1 mean and SD||T2 mean and SD||T2-T1
mean and SD
PG 1 vs PG 2
|UP 6 dv|
|Overall||18.08 ± 2.12||18.06 ± 2.03||−0.02 ± 2.31||0.9586|
|PG 1||17.46 ± 1.57||17.91 ± 2.05||0.45 ± 2.43||0.3883|
|PG 2||18.85 ± 2.48||18.25 ± 2.05||−0.60 ± 2.09||0.2407||0.1541|
|UP 6 mv|
|Overall||18.14 ± 2.52||18.08 ± 1.87||−0.06 ± 2.05||0.8591|
|PG 1||17.19 ± 1.54||17.91 ± 1.76||0.72 ± 1.57||0.0661|
|PG 2||19.30 ± 3.01||18.29 ± 2.01||−1.01 ± 2.19||0.0424 ∗||0.0059 ∗|
|Overall||28.14 ± 4.79||29.18 ± 4.15||1.04 ± 3.87||0.2108|
|PG 1||26.14 ± 4.76||28.39 ± 3.74||2.25 ± 3.13||0.1836|
|PG 2||28.84 ± 4.68||29.54 ± 4.48||0.70 ± 4.07||0.4724||0.4420|
|Overall||27.42 ± 3.12||28.30 ± 3.23||0.88 ± 3.59||0.2165|
|PG 1||27.29 ± 2.61||28.47 ± 3.34||1.18 ± 2.68||0.0771|
|PG 2||27.49 ± 3.42||27.90 ± 3.13||0.41 ± 3.96||0.6662||0.3506|
|LO 6 d|
|Overall||18.59 ± 3.48||19.12 ± 1.77||0.53 ± 2.82||0.2414|
|PG 1||17.90 ± 2.57||18.35 ± 1.37||0.45 ± 2.42||0.3958|
|PG 2||19.43 ± 4.27||20.06 ± 1.77||0.63 ± 3.32||0.4298||0.8403|
|LO 6 m|
|Overall||18.95 ± 3.68||19.01 ± 1.84||0.06 ± 2.87||0.8953|
|PG 1||17.96 ± 2.68||18.49 ± 1.31||0.53 ± 2.46||0.3270|
|PG 2||20.17 ± 4.39||19.66 ± 2.21||−0.51 ± 3.29||0.5198||0.2617|
|Overall||28.56 ± 4.44||28.67 ± 3.73||0.11 ± 3.38||0.8774|
|PG 1||26.55 ± 4.72||28.67 ± 3.39||2.12 ± 4.29||0.2390|
|PG 2||29.36 ± 3.42||28.68 ± 4.13||−0.68 ± 2.69||0.2989||0.0606|
|Overall||28.37 ± 4.45||27.91 ± 3.69||−0.46 ± 3.53||0.5093|
|PG 1||26.61 ± 1.57||27.68 ± 2.92||1.07 ± 3.07||0.3256|
|PG 2||30.01 ± 4.54||28.79 ± 4.08||−1.22 ± 3.58||0.1663||0.1135|