PubMed · 282817
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H Pancherz. 1977. [My dissertation].. https://pubmed.ncbi.nlm.nih.gov/282817/
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In laboratory experiments, progressive transversal jaw expansion with screw plates was simulated and the resulting increase in labial archwire force and deflection (autoactivation) was analysed. The results showed that progressive activation of a screw plate caused an initial increase in labial archwire force, which was subsequently followed by a minor reduction, and which stabilised after 90 seconds. Archwire force increases with the diameter of the wire, spring-hard wires developing higher forces than hard wires, and deflection decrease progressively with increasing size of the single activation step, as well as with increasing total activation. These results may have the following practical implications: on adjustment of the screw of the plate, the labial archwire is automatically activated to a reasonable degree for retroclination of the front teeth in screw plate treatment. This is particularly true when an 0.8 mm spring-hard wire is used. More constant archwire force is obtained by applying frequent small activations of the screw rather than a few large ones. To maintain the labial archwire force at a useful level, throughout treatment, fabrication of a new plate is recommended before the full range of screw adjustment is exhausted.
The theoretically favourable aspects of orthodontic space closure with segmented arch technique and the T-loop type A are clinically reproducible. In our study of eleven patients we found for the isolated canine retraction, as well as for the en masse retraction, controlled types of movement for the active units and maximum anchorage situations for the passive units produced by the torquing force. Because of these good anchorage conditions space closure could be done without headgear. The level of the anchorage segments was negligibly influenced but in the anterior segments a marked tilting was found in several cases. Besides other factors the intrusive force of the T-loops type A must be considered. As a rule the positioning of the T-loop between central and lateral incisor is to be recommended.
The effect of the treatment of Angle Class II, Division 2 malocclusion was studied in 22 children by x-ray cephalometry and by recording the relation between the retruded and the intercuspal mandibular positions. The treatment was performed in three phases. In the first phase the upper incisors were proclined, and the deep bite was corrected with an upper removable plate. In the second phase the distal occlusion was corrected with an activator. The result was retained in the third phase with a second activator designed for retention. The relation between the retruded (RCP) and the intercuspal (ICP) mandibular positions was recorded with wax bites and dental casts mounted in a modified gnathothesiometer. The anteroposterior distance between RCP and ICP was large before the start of the treatment. The distance was unchanged after proclination of the upper incisors and correction of the deep bite but decreased after correction of the distal occlusion and increased again somewhat during the retention phase. The proclination of the upper incisors and the correction of the deep bite (phase one of the treatment) did not result in mandibular anterior positioning. This fact and the results of the recordings of the relation between RCP and ICP were interpreted as evidence that the mandible is not posteriorly displaced in Class II, Division 2 malocclusion.