A cephalometric evaluation of hard and soft tissue changes during class III traction European Journal of Orthodontics 7 (1985) 201-204 1985 European Orthodontic Society Abstract Summary. In this retrospective cephalometric study, the lateral skull radiographs of 12 children with Class III malocclusions of skeletal origin were examined. An analysis ofthe changes produced during treatment revealed that whilst changes in apical base relationship were small, and were mainly limited to a reduction in angle SNB, the effects on the soft tissue profile were surprisingly effective. Introduction
Anterior cross-bite may originate from
either dental or skeletal causes. It is well known that cross-bite of dental origin can be treated, whilst the prognosis of skeletal Class III cases is often considered to be more doubtful. In this study, Class III traction was used in the treatment of skel-etal III cases with favourable results.
The purpose of the present study was to evaluate cephalometrically the facial appearance of patients with anterior cross-bites of skeletal origin before and after treatment, and to examine the effect of Class III traction on the profile.
Subjects and methods
The sample studied consisted of 6 boys and 6 girls with anterior cross-bites, in the age range of 11 to 14 years (mean age, 11.8).These patients attended the Orthodontic Department at the Stomatological Hospital,Beijing Medical College. Lateral cepha-lometric films of all the cases were taken before and after treatment.
The criteria for selection of the cases for this study were:
1) Full Class III molar relationship
2) Skeletal Class III pattern (ANB<-2 degrees)
3) Severe reverse or negative overjet, ranging from -2.5 to -4.5 mm (mean, -3.5 mm)
4) Lack of initial incisor contact followed by mandibular displacement 5) An obvious inability to relieve the cross-bite simply by the use of an upper removable appliance.
Upper removable and simplified lower fixed appliances were used (Fig. 1).
1) .Palatal springs (0.022") were used to procline the upper incisors. Hooks for Class III traction were soldered on to Adams Cribs\(0.032")on each side and to the lower labial bow for Class III traction.
Of the 12 cases, there were 4 whose first premolars were extracted for relief of labial segment crowding. The other cases,whose dental alignments were nearly acceptable, had a lower central incisor extracted.
The appliances were worn 24 hours per day and the elastics were replaced every 3-4days. The Class Ill traction force was 300-400 gm. The average period of treat-ment was 12.5 months, and after treatment,a stable overbite and overjet were established.
The cephalometric measurements are shown in Figures 2 and 3. The significance of pre- and post treatment differences was tested by Student's t test. 
Results
Comparisons between pre- and post-treatment measurements are shown in Table 1.
Hard Tissue Changes
During treatment the increase in the aver-age value of angle SNA did not reach the significant level of p<0.05, whereas the decrease of angle SNB was significant and angle ANB increased from -3.79 degrees to -2.33 degrees during treatment. This suggests that the anteroposterior relationship between maxillary and mandibular apical bases (points A and B) had been improved.
The increase of the skeletal convexity angle from -8.50 degrees before treatment to -5.42 degrees after treatment also showed this. As a result of the increase of angle UI-SN, indicating proclination of upper incisors, and the decrease of angle LI-MP indicating retroclination of lower incisors,the changes of angle UI-LI did not reach the significant level of p<0.05. Significant changes were not found in the mandibular plane angle or the gonial angle.
Soft Tissue Changes The increase in angle S'-N'-Sn during treatment was significant and this demonstrated forward movement of the upper labial base (point Sn). The decrease of angle S'-N'-Si was also significant, indicating a backward shift of point Si. Consequently,the mean angle Sn'-N'-Si increased signifi-cantly from -0.58 degrees before treatment to 2.63 degrees after treatment. This indi-cated improvement in the anteroposterior relationship of points Sn and Si. The increase of angle N'-Sn-Po' from -0.33degrees before treatment to 5.13 degrees after treatment indicated that facial convex-ity of soft tissue had improved. The markedincrease of the distance Esth./Plane UL and the significant decrease of the distance Esth./Plane LL indicated the forward move-ment of the upper lip and the backward movement of the lower lip respectively during treatment. As a result, the rela-tionship between upper and lower lip
obviously improved.
Treatment
The appliances used with Class III traction had a definite effect on anterior cross-bite in the early stage of the perma-nent dentition. The correction of the cross-bite depended not only on proclination of upper anterior teeth and retroclination of lower anterior teeth, but also on a decreased angle SNB, hence an increased angle ANB,and angle of skeletal convexity.
However, it is to be noted that duringtreatment the angle MP-SN, and gonial angle hardly altered and after treatment the means of angle ANB and angle N-A-Po were still negative, i.e. -2.33 degrees and -5.42 degrees respectively. This suggests that the effect of Class III traction on skeletal components such as maxillary or mandibular apical bases was limited so that although the overbite and overjet after treatment were within the normal range, a Class III skeletal profile was still present to some extent (Fig. 4).
In some cases, the soft tissue changes were in accord with those of the correspond-ing hard tissues. For instance, as angle UI-SN increased, so did the distance UL,and the lower lip retrusion varied, corres-pondingly with lower incisor retroclination.This also applied to the reduction of bothangle SNB and angle S'-N'Si. How
ever, it is worth noting that some soft tissue changes did not accord with the corresponding hard tissue changes. Despite the stability of the hard tissue angle SNA, the soft tissue angle S'-N'-Sn increased significantly during treatment. On the other hand, though the angle ANB and the skeletal convexity angle showed a considerable reduction during treatment, their post-treatment means remained negative, and the skeletal profile was still Class III or concave. The changes of the corresponding soft tissues were different. Angle Sn-N'-Si and the facial soft tissue angle increased so markedly that both their means became positive after treatment. Finally, the soft tissue profile became acceptable (Fig. 5). 
It is generally believed that even fixed appliances are of limited effect in dealing with skeletal III problems. However, the findings of this investigation demonstrate that some orthodontic treatments may be of greater influence in improvingsoft tissue profile than hard tissue discrepancy.
Thus, it is possible for some patients with malocclusions of skeletal origin to obtain a normal,or at least a more satisfactory soft tissue profile than their skeletal pattern would appear to permit. Thus, effectiveness of the appliances used with Class III traction lies not just in the improving of anterior cross-bite, but also in soft tissue profile improvement (Fig.6). 
|
