Effects of two different functional appliances on root development of posterior teeth: activator vs. bite-jumping...

The aim of this study was to investigate retrospectively the incidence of inhibited root development by metric analysis of orthopantomograms, based on examination of the posterior teeth of 40 children and adolescents with Angle Class II, Division 1 malocclusion who received two different removable functional appliances to treat the distal intermaxillary relationship.

The patients were divided into two groups of equal size according to the appliance they wore for treatment (activator, bite-jumping appliance). Orthopantomograms for each patient were available from the start (time point T1) and after completion of the functional treatment (time point T2). Each radiograph's enlargement factor in the posterior region was ascertained. The vestibular tooth lengths of the molars and premolars were then measured. To assess root length development, we determined the differences between tooth lengths at the start and after the end of the treatment.

Functional treatment generally led to an increase in tooth lengths in the anchorage region. Direct comparison of the two removable appliances revealed significant differences (p = 0.0478) in how much longer the maxillary first premolars became: following treatment with the activator, the teeth lengths increased by a mean of 2.64 mm +/- 5.12 mm, whereas the mean increase in length after bite-jumping appliance therapy was 0.59 mm +/- 3.40 mm.

As a result of treatment with removable functional appliances, we observed locally different trends in root length increase in the posterior region in late-mixed and young adult dentitions, hence at a stage when root development had not concluded. The roots became longer during treatment with both the activator and bite-jumping appliance, but the maxillary first premolars' root development varied widely. This may be because the bite-jumping appliance's anchorage is right on the dentition, and the forces thus exert an immediate effect on the anchorage unit, particularly in the immediate vicinity of the protrusive bars in the maxilla. This led to certain groups of teeth to fail to achieve their entire potential length.