The effect of different extraction sites upon incisor retraction.

1. From this study, it was found that in cases treated by the Begg technique one can anticipate greater retraction of the anterior dental units in nonextraction (see article) cases, in both types of premolar extraction cases, and in cases, involving extraction of first molars plus first premolars than would be expected on the basis of root surface area resistance values. 2. There is a likely explanation for this. Molars were maintained upright and allowed to move bodily only while incisors were not only moved bodily but often partially tipped as well. 3. The actual mean anterior retraction in first molar extraction cases exhibited a close approximation to the expected mean anterior retraction values in relation to root surface resistance values. 4. Second premolar extraction is one answer to overretraction and has the added edge of creating even less incisor retraction than second premolar extraction. 5. It was also found that the extraction of premolars alone did not result (see article) in a significant change in the increased eruption of the third molars into functional occlusion. A very significant improvement in the rate of sucessful third molar eruption was found in first molar extraction cases and in cases involving extraction of first molars plus first premolars. 6. The mean ages of the patients in the various treatment categories at the start of treatment were similar enough to each other to suggest that age at the start of treatment had no bearing on the success rate of third molar erup tion. Extraction-site selection seemed to be the dominating factor in successful third molar eruption. 7. It was found that the group of cases that exhibited the least amount of anterior retraction also inhibited the least amount of anterior relapse and, conversely, the group of cases exhibiting the greatest amount of anterior retraction also exhibited the greatest amount of anterior relapse. (see article) 8. The nonextraction cases, with no extraction space to close, were treated in the shortest mean time, while the eight-tooth (first molar plus first premolar) extraction cases having the greatest amount of extraction space required the greatest amount of mean treatment time.9. In conclusion, it can be said that changing the location of the extraction site resulted in a change in relative root surface areas of the opposing anchor units in the anterior and posterior segments. There was a definite and predictable change in the amount of anterior retraction achieved by varying the location of the extraction site. This should be considered in the diagnosis, so that a desired treatment goal for the final position of the incisors within the facial profile can be achieved.