INTRODUCTION

The Class II, division 2 malocclusion is characterized by retroclined upper front teeth (at least the 2 central incisors), a deep overbite, and a Class II molar relationship.1,2 The perioral soft tissue features of the malocclusion such as the hyperactive mentalis muscle and the high lip line (defined as the lower lip covering the upper incisors)3–11 are said to be the cause of the steep upper incisor position2,3,9,12–19 as well as of the relapse frequently seen after treatment.

A Herbst/multibracket appliance combination has been shown to be most effective in the therapy of Class II, division 2 malocclusions. Class II molar and overjet/overbite corrections are accomplished by both skeletal and dental changes.20 The influence of this treatment on the soft tissues, especially on the vertical position of the lower lip in relation to the upper incisors, however, to this date has received no attention.

Thus, the aim of the present cephalometric roentgenographic investigation was to assess the effect of Herbst/multibracket appliance treatment on the upper incisor–lower lip relationship in the management of Class II, division 2 malocclusions.

MATERIALS AND METHODS

Subjects

The patient sample consisted of 19 Class II, division 2 malocclusions (8 females, 11 males) treated for an average period of 1 year and 10 months with the banded (n = 5) or the cast splint (n = 14) Herbst appliance followed by a multibracket appliance. The average pretreatment age of the subjects was 13 years, and each patient had a bilateral Class II molar relationship, retroclined upper incisors, and a deep overbite. After treatment, all subjects exhibited Class I dental arch relationships with a normal overjet and overbite. In 12 subjects, posttreatment retention was performed with a lower cuspid-to-cuspid retainer and an upper Hawley plate. The remaining 7 subjects were retained with an activator or a positioner.

The lateral head films of all subjects were analyzed on 3 occasions: before (T1) and after (T2) Herbst/multibracket appliance treatment and 1-year posttreatment (T3). The reference points and lines used are shown in Figure 1. The measured variables are seen in Figure 2a,b.

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Method error

The total method error for double registrations of each variable was calculated. The error comprised the identification of the reference points and lines, the tracing procedure, and the measurements of angles and distances. In the method error (ME) calculations, the following formula of Dahlberg21 was used:

where d is the difference between 2 registrations of a pair and n is the number of the double registrations (n = 19). The results of the calculations are seen in Table 1.

TABLE 1. Method Error Evaluation Upon Double Registrations in 19 Class II, Division 2 Subjects Treated With Herbst/Multibracket Appliance (T1, Before Treatment; T2, After Treatment; T3, 1 Year After Treatment)

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RESULTS

The cephalometric records from before, after, and 1 year after Herbst treatment are presented in Table 2. The treatment and posttreatment changes are shown in Table 3. The individual changes in lower lip position are given in Figure 3, and the mean changes of selected variables are given in Figures 4 through 8.

TABLE 2. Cephalometric Records (Mean, SD) in 19 Class II, Division 2 Malocclusions Treated With the Herbst/Multibracket Appliance (T1, Before Treatment; T2, After Treatment; T3, 1 Year After Treatment)

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TABLE 3. Change of Cephalometric Records in 19 Class II, Division 2 Malocclusions Treated With the Herbst/Multibracket Appliance (T1, Before Treatment; T2, After Treatment; T3, 1 Year After Treatment)

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DISCUSSION

Long-term stability of treated Class II, division 2 malocclusions is, among other things, said to be related to a relative decrease of the lower lip cover on the upper incisors.2,4,5,7,13,16–19,22–24 Upon Herbst/multibracket appliance treatment of the present Class II, division 2 subjects, the lower lip overlap on the upper incisors was reduced by 29% (from 5.9 mm to 4.2 mm). During the 1-year posttreatment period, this lip position remained stable. In another Class II, division 2 investigation, using exclusively a multibracket appliance approach, the lower lip overlap was reduced from 4.6 mm to 2.8 mm and then relapsed 1.0 mm during a 1-year posttreatment period.25 The net improvement in the lip position was thus only 17%. The differences in stability found in the two studies may be explained by the various retention regimes performed. In the present study, all subjects had posttreatment retainers, while no retention was performed in Fuhrmann's25 subjects. Furthermore, in regular multibracket appliance treatment, as in Fuhrmann's patients, overbite is reduced by active intrusion of the incisors and extrusion of the molars. The tendency toward overbite relapse is, however, great when incisors are intruded.26

In a long-term cephalometric evaluation of treated Class II, division 2 malocclusions, Binda et al27 found that the lower lip line was lowered during treatment (1.2 mm) and relapsed 0.2 mm during the first 2 years of postretention but did not change afterward. Furthermore, in untreated subjects with normal occlusion, Vig and Cohen28 found that the most marked changes in the relationship of the lower lip to the upper incisors occurred between 9 years and 13 years. After the 13th year, the lower lip overlap on the upper incisors is nearly constant. This would be in agreement with the present findings since the average pretreatment age of the Class II, division 2 cases was 13 years.

Mills16 as well as van der Linden and Boersma19 found a significant correlation between the lower lip overlap on the upper incisor position, the interincisal angle, and the overbite. It can, therefore, be assumed that the high positioned lip retroclines the upper and lower incisors. The resulting large interincisal angle then causes the deep overbite due to the missing incisal support allowing the front teeth to erupt freely.

In the present investigation, the overbite was reduced on average from 7.3 mm to 1.7 mm but then relapsed to 2.9 mm. The net overbite reduction was thus 59%, which is relatively high in comparison with other studies.25,29,30 The overbite reduction was mainly accomplished by proclination of the maxillary and mandibular incisors,21,31,32 extrusion of the lower molars,32 and downward tilt of the mandibular occlusal plane.32 While proclination of the lower incisors usually is undesirable in orthodontics, it is an advantage in the correction of the deep bite in Class II, division 2 malocclusions since the teeth are in a retroclined position to begin with.

In the treatment of the present 19 cases, the upper incisors were, in most cases, proclined with a multibracket appliance before the Herbst appliance was placed. This decompensation of upper incisor position allowed free lower incisor proclination during the mandibular advancement procedure with the Herbst telescope mechanism.

Relapse in overbite has been found to be significantly correlated with relapse of the interincisal angle.13,26,29,33,34 Exaggerated proclination of the lower incisors in Class II, division 2 patients would therefore result in a reduction of the interincisal angle, which will contribute to posttreatment overbite stability.26,29 Berg30 considered an interincisal angle of less than 140° after treatment to be favorable for long-term stability. In the present sample, the interincisal angle was reduced from 150° to 125° during treatment and increased only 4° after treatment.

Long-term posttreatment stability of the occlusion is certainly also dependent on balanced muscle forces acting on the teeth. A lower lip coverage will challenge this balance.18 Therefore, in the correction of Class II, division 2 cases, it is necessary to retain the treatment result over a longer period of time to get a soft tissue adaptation.

Selwyn-Barnett24 recommends that the lower arch be retained permanently when any tendency to an increase in the interincisal angle is anticipated. A fixed cuspid-to-cuspid lingual retainer behind the lower front teeth ensures a stable antero-posterior and transverse position of the lower labial segment, which is the foundation of the correct incisor relationship. Crowding of the lower labial segment with concomitant reduction of the intercanine width would lessen the transverse support for the upper arch. This effect is potentially more serious in patients with tight perioral musculature, as seen in Class II, division 2 malocclusions.35 In spite of the lower cuspid-to-cuspid retainer in the present study, the inclination of the lower incisors recovered by an average of 2.3° during the follow-up period. This change in incisor position was certainly the cause of the posttreatment increase in the interincisal angle and in the small overbite relapse seen.36

CONCLUSION

In conclusion, it was found that in Class II, division 2 malocclusions, the upper incisor–lower lip relationship was improved by Herbst/multibracket appliance treatment and remained stable during a 1-year posttreatment period in spite of minor relapses of incisor tooth position and relationships. Postretention follow-up studies are, however, necessary to assess the long-term effect of the Herbst/multibracket appliance approach on the incisor–lower lip relationship.