A number of laboratory studies have shown very low levels of archwire friction for self-ligating brackets when compared to conventional ligation methods. However, justifiable reservations have been expressed as to the in vivo relevance of these findings. This study was designed to compare treatment efficiency with conventional fully programmed brackets and Damon SL self-ligating brackets. Thirty consecutively finished cases treated by the author with Damon SL brackets were compared with 30 matched cases treated by the author with conventional brackets. Parallel studies quantified the incidence of technical problems with Damon SL brackets and with conventional ligatures and also the chairside time required for ligation/slide closure and ligature removal/slide opening with these two bracket types. The Damon SL cases required an average of four fewer months and four fewer visits to be treated to an equivalent level of occlusal regularity as measured by the PAR scores.
The current situation regarding self-ligating brackets is reviewed. Recent developments, clinical advantages, and remaining imperfections are described. The question of active versus passive ligation is scrutinized. The evidence regarding treatment efficiency is reviewed. Suggested clinical tips and changes of treatment mechanics are summarized and illustrated. Self-ligating brackets have reached a stage of design and production control, where the advantages are significantly greater than the remaining imperfections.
The problem of late mandibular incisor crowding is a well established phenomenon, the cause of which has been the substance of considerable debate over the years. A central issue is the possible role of the third molars though no definitive conclusions have been consistently drawn. This prospective study was designed to investigate the effects of randomly assigned early extraction of third molars on late crowding of the mandibular incisors. One-hundred-and-sixty-four patients entered the study from 1984 following completion of retention after orthodontic treatment. Seventy-seven patients (47%) returned for records up to a mean of 66 months later, and their start and finish study casts were digitized on a reflex microscope to determine Little's index of irregularity, intercanine width and arch length. Forty-four of the patients had been randomized to have third molars removed. There was no evidence of responder bias. Where third molars were extracted the mean increase in lower labial segment irregularity was reduced by 1.1 mm from a mean of 2.1 mm for the group where third molars were retained (P = 0.15, not statistically significant). This difference was also not considered to be clinically significant. The principal conclusion drawn from this randomized prospective study is that the removal of third molars to reduce or prevent late incisor crowding cannot be justified.
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