Comparison of the initial orthodontic force systems produced by a new lingual bracket system and a straight-wire...

Over the last few years, lingual appliances have become an established orthodontic treatment technique. Many studies have concentrated on various esthetic aspects, on laboratory and clinical procedures, and on patient comfort and compliance. The orthodontic force systems of these appliances, however, have not yet been investigated. The aim of this study was thus to determine the forces and moments produced by a new lingual bracket system during the leveling phase of orthodontic treatment and to compare those with the corresponding force system of a labial straight-wire appliance.

The intra-oral situation of ten patients undergoing orthodontic treatment was replicated in measurement casts fitted with lingual and labial brackets. Special care was taken to precisely reproduce each patient's interbracket geometry. We measured each tooth's force systems as generated by a leveling arch inserted into the lingual and labial brackets.

The resulting force systems of both appliances were found to be quite similar with regard to the magnitude of most force and moment components. Only the first molars were subjected to considerably greater single forces with the lingual appliance. Tipping moments were found to be significantly smaller with the lingual technique, whereas the rotational moments were significantly smaller with the labial appliance. All in all we noted significant differences between the two techniques only in certain areas which upon closer examination were distributed over only a few tooth types.

The initial force systems produced by the new lingual bracket system proved to be comparable with those delivered by a conventional straight-wire appliance. The actual levels of forces and moments, however, were found in certain cases to be too heavy with both techniques. We therefore recommend the development of leveling wires producing considerably lighter forces and moments.