INTRODUCTION

In Class II treatment the main goal is an increase in mandibular prognathism. This can be accomplished by (1) three components of temporomandibular joint (TMJ) changes (each component separately or all three in combination): condylar modeling, glenoid fossa modeling, and anterior condylar displacement in the fossa and by (2) an anterior rotation of the mandible causing the chin to come forward. The single components of the TMJ changes are difficult to assess as appropriate TMJ landmarks are difficult to define on lateral head films.1 However, with the method of Creekmore2 using an arbitrary condylar point, condylar modeling, glenoid fossa modeling, and condylar displacement can easily be measured as the sum of changes, ie, “effective” TMJ changes.

In previous studies, the “effective” TMJ changes and their effect on the position of the chin have been analyzed in Class II, division 1 patients treated with two functional appliances: the fixed Herbst3–7 and the removable Activator.8–11 For both appliances favorable “effective” TMJ as well as associated chin changes have been shown. Furthermore, magnetic resonance imaging (MRI) of the TMJ performed in Herbst treated patients disclosed condylar and glenoid fossa modeling promoting a Class II correction.671213

When using multibracket appliances with Class II elastics, the general opinion is that Class II correction is accomplished by dentoalveolar changes and not by mandibular (TMJ) growth stimulation. Experimental studies in monkeys1415 and in rats,16 however, have shown that condylar and glenoid fossa modeling could be accomplished by Class II elastics. In man, on the other hand, this has never been verified.

Therefore, the aim of the present investigation was to assess and compare the “effective” TMJ changes and corresponding chin changes in Class II, division 1 patients treated with either an orthodontic approach using a multibracket appliance with Class II elastics (Tip-Edge) or an orthopedic approach using a fixed functional appliance (Herbst). Furthermore, the study addressed the question of whether Class II elastics had any orthopedic effects.

MATERIALS AND METHODS

The following two groups of successfully treated Class II division 1 subjects were evaluated:

• Twenty-four patients (9 male, 15 female) treated with a Tip-Edge multibracket appliance in the maxilla and mandible together with Class II elastics.17–22 The force of the elastics was approximately 2.5 ounces corresponding to 70 cN. The patients were selected from the total pool of Class II division 1 patients treated with Tip-Edge appliances at the Department of Orthodontics, University of Giessen (Germany) 1996–2005. The mean age of the subjects before treatment was 12.3 years (SD ± 3.1 years). The average examination period (treatment period) was 2.6 years.

• Forty patients (20 male, 20 female) treated with a Herbst appliance.2324 The patients were selected randomly from the total pool of 118 Class II division 1 patients treated with the banded type of Herbst appliance, at the Department of Orthodontics, University of Malmö (Sweden). The mean age of the subjects before treatment was 12.4 years (SD ± 1.3 years). The average examination period was 2.6 years (a 0.6-year treatment period with the Herbst appliance plus posttreatment period of 2.0 years with a multibracket appliance in both arches for occlusal refinement).

The following criteria had to be fulfilled for patient selection: (1) a Class II molar relationship of at least one-half cusp width if the second deciduous molars were lost or at least three-fourths cusp width if the second deciduous molars were still in place; (2) no extractions of permanent teeth; and (3) no syndromes.

As a control group the Bolton Standards25 were used. The Standards are composed of composite lateral head film tracing from 32 untreated subjects (16 boys and 16 girls) with ideal occlusion followed annually from 6 years to 18 years of age. The Tip-Edge and the Herbst subjects were compared with the 12 years and 15 years Bolton Standards, thus covering an observation period of 3 years.

In all three examination groups lateral head film tracings in habitual occlusion from before and after the examination period were evaluated by one of the authors. A linear roentgenographic enlargement of 7% in the Tip-Edge and Herbst groups was not corrected. The enlargement of 5.5%–5.8% in the Bolton group was adjusted to that of the two treatment groups. Linear and angular measurements were performed to the nearest 0.5 mm and 0.5°, respectively. In order to reduce the method error, all registrations were done twice and the mean value of the duplicate registrations was used in the final evaluation.

The methods for the assessment of “effective TMJ changes” (the sum of condylar modeling, fossa modeling, and condylar position changes within the fossa), chin position changes, and mandibular growth rotation are summarized in Figure 1A through D.

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The following variables were considered:

• Co/RLp The horizontal distance of the arbitrary condylar point (Co) to the RLp reference line

• Co/RL The vertical distance of the arbitrary condylar point (Co) to the RL reference line

• Pg/RLp The horizontal distance of the chin point pogonion (Pg) to the RLp reference line

• Pg/RL The vertical distance of the chin point pogonion (Pg) to the RL reference line

• RL The line from the incisal edge of the lower central incisor to the distobuccal cusp of the first upper molar. This line could be considered as an artificial implant line26 due to the mandibular superimposition procedure used (see Figure 1D).27

Method Error Evaluation

The size of the combined method error (ME) in locating the reference points, superimposing the roentgenograms, and measuring the variables was assessed upon double registrations of all 24 Tip-Edge subjects using the formula of Dahlberg28:

where d is the difference between two registrations of a pair and n is the number of double registrations. For the different variables the method error varied between 0.60 mm and 1.07 mm for the linear measurements and was 0.65° for the angular measurement. The errors corresponded to those in previous investigations using the same cephalometric method.389

RESULTS

At the end of the examination period of 2.6 years all Tip-Edge and Herbst subjects had a Class I occlusion with a normal overjet and overbite. Because no statistically significant gender differences existed for the cephalometric variables, the male and female subjects were pooled in the presentation of the results.

The changes of the different variables during the examination period of 2.6 years in the two appliance groups and the control group are presented in Table 1. Figure 2 shows the “effective” TMJ changes and chin position changes. Additionally, for the Herbst group the active treatment changes during the 0.6-year period are depicted graphically in Figure 2. Furthermore, to make group comparisons possible for this shorter period, a 0.6-year period was also marked on the graph for the Tip-Edge and control groups by data interpolation.

Table 1.  Variable Changes in the Tip-Edge (n = 24), Herbst (n = 40), and Bolton (n = 32) Samples During 2.6 years (Bolton 3 years) of Examination. The Statistical Significance (Sign) of Changes and Group Differences are Given^a

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DISCUSSION

To distinguish between treatment effects and normal growth, the Bolton Standard control sample was used for comparison. This is not an ideal reference group and it would have been better to use a group of untreated Class II, division 1 subjects, but no such sample exists that covers a period of about 3 years, from the age of 12 to 15 years.

The method of Creekmore for the assessment of “effective” TMJ changes has the following advantages: (1) an arbitrary condylar point (Co) is used which implies no difficulties in the identification of an anatomic reference point; (2) all TMJ changes (condylar modeling, glenoid fossa modeling, and condylar position changes) are assessed simultaneously as a sum of changes; and (3) using a common reference grid (RL/ RLp) for before and after examination period measurements, a quantitative evaluation of both the amount and direction of changes can be performed.

CONCLUSIONS

• The present results indicate that Class II elastics in connection with multibracket appliances (orthodontic treatment approach) have no favorable sagittal orthopedic effect on the mandible.

• Jumping the bite with the Herbst appliance (orthopedic treatment approach) has a favorable sagittal orthopedic effect on the mandible on a short-time, but not on a long-time basis.