Abstract
We studied 12 children in the mixed dentition period who were diagnosed as having an open bite or an open bite tendency with tongue thrusting who were treated with two types of removable habit breakers, a Hawley's type retainer with incorporated tongue cribs (the Plate group) and a bionater for open bite (the Bionator group). We compared their lateral cephalograms at both the time of examination and the time of removal of the appliances (around 1 year later) with the standard values of the cephalograms of groups of the same age.
The results were as follows.
1. At the time of the examination, besides significantly smaller over-bites in both groups than those of the standard value, the distance between the Prosthion and the Infradentale in the Plate group was significantly longer and the angle of the upper central incisor to the SN plane in the Bionator group was significantly higher than those of the standard value.
2. At the time of removal, the over-bites had changed to the range of from 1.0 mm to 0.2 mm in the Plate group, and from 1.5 mm to 0.2 mm in the Bionator group.
3. At the time of removal in the Plate group, the lower central incisor angle to the mandibular plane became significantly smaller, and the upper central incisor angles had become nearer to the standard values on the whole. The distance between the Prosthion and the Infradentale was no more significant compared with the standard value. There were more changes of the linear measurements, however, than those of the standard values between the same age groups.
4. At the time of removal in the Bionator group, the lower central incisor angle to the mandibular plane also became significantly smaller. The reduction of the labial inclination of the central incisors to some extent, with the significant labial movement of the point A, seemed to be brought about from the myoplate added to the bionator. The changes of the linear measurements were roughly equal to those of the standard values between the same age groups.
5. To reduce the excessive lingual inclination of the lower central incisors, it seemed necessary that the design of the tongue crib should be changed in the Plate and the adjustment methods should be improved in the Bionator.
