Oct. 9 (Tue.), 2001

9. Differential diagnosis of Class III malocclusions 2

Method of the study 1

In each patient with a diagnosis of crossbite in the early mixed dentition, the rapid maxillary expander and protractor were placed to correct the crossbite, followed by observation until dental age IIIB. Dental casts, occlusal radiographs and charts recording hours of appliance wear were taken at three time points for comparison; at the initial examination (at initial examination), immediately after appliance removal (at appliance removal) and 1 to 2 years after treatment when the occlusion appeared to be stable (at occlusal stability).
The following results were obtained.

@Results 1

1. A mean lateral expansion of 3.19mm was achieved in 3 to 4 weeks with the rapid maxillary expander.
2. The subjects wore the protractor for an average of 5.71 months, slightly short of the target of 6 months.
3. The subjects were asked to record the time of appliance wear each day, which was targeted at 10 to 12 hours. For those who had a complete record of appliance wear, an average time of appliance wear was 10.51 hours per day.
4. Results of the interceptive treatment for crossbite correction could be divided into the following 4 categories:
(i) A crossbite of the upper permanent incisors was successfully corrected.
(ii) An unstable, edge-to-edge relationship of the incisors was obtained.
(iii) Incisor relationship was once corrected but relapsed back to a crossbite.
(iv) A normal incisor relationship was never obtained during treatment.

Changes in cephalometric parameters were also studied.

Method of the study 2

The cephalograms taken at the three time points were analyzed. The subjects were divided into two groups, Group N and Group R consisting of patients who had a normal incisor relationship at occlusal stability and those who had an anterior crossbite at occlusal stability, respectively. Linear and angular cephalometric measurements were compared between the two groups.
The [Versa-stat] software (Yasunaga Computer, Inc.) was used for statistical analysis.
The figure shows a case from Group N with a normal incisor relationship at occlusal stability in the late mixed dentition.

The figure shows a case from Group R with an anterior crossbite in the same time period.

AO-BO and APDI values were analyzed in relation to incisor relationship at occlusal stability.

The larger the AO-BO value and the smaller (closer to the norm) the APDI value, the higher the likelihood of maintaining a normal incisor relationship and thus being classified into Group N (green circles). Many of the subjects in Group R showed a tendency of deterioration (reaction) after appliance removal.
Incisor relationship did not improve with the rapid maxillary expander and facial mask in patients indicated by yellow circles. The lack of improvement was due to an extremely limited use of the appliances. These patients were therefore excluded from the study.

Longitudinal cephalometric study -2 ODI and APDI values were also investigated.

ODI and APDI closely represent vertical and sagittal facial dimensions, respectively. Thus, they were expected to distribute in such a way as to indicate some trend, but showed great individual variations.