Serial extraction revisited: 30 years in retrospect

One of the most common problems in orthodontics is tooth size-arch length discrepancy (TSALD). The controversy over whether to resolve this discrepancy by increasing the size of the dental arch or by reducing the amount of tooth structure persists to this day. Because virtually any approach to resolving TSALD can align the teeth, the long-term stability of competing approaches is of paramount importance. The effect on the face is also a major consideration. Of the various aspects of occlusion such as molar relationship, overbite, and overjet, mandibular anterior alignment is the area of relapse most noted by patients. Therefore, it has been the focus of many stability studies. The most common unit of measurement for mandibular anterior tooth alignment is the irregularity index as suggested by Little in 1975. The irregularity index is defined as the sum of the distance between the contact points of the 6 permanent anterior teeth. It is not the same as TSALD. An irregularity index of less than 3.5 mm is judged to be minimal and thus clinically satisfactory. An irregularity index score greater than 6.5 mm indicates severe irregularity. There are few reports in the literature on long-term postretention stability of TSALD patients treated in the mixed dentition. Four studies at the University of Washington reported on both approaches—increasing arch length and extracting premolars. The study of resolving the TSALD in the mixed dentition by increasing arch length (expansion) was especially discouraging. Seven and a half years postretention, 89% of the patients studied had unsatisfactory results, with a mean irregularity index score of 6.06 mm. The 3 studies in which premolars were extracted in the mixed dentition found an irregularity index 10 years postretention of 4.39, 3.15, and 3.09 mm, respectively. Foster and Wiley found that extraction of deciduous canines had no detrimental effect on the eventual width of the permanent canines. Numerous studies have documented that mandibular incisors tip lingually as a result of serial extraction, but not excessively. So, is extracting in the mixed dentition, followed by multibanded treatment in the permanent dentition and a retention phase of approximately 3 years, a better choice in the long term? In one study, researchers examined a subsample of 30 serial extraction patients from the 114 studied by Scott Franklin in his 1995 “AAO Award of Merit” thesis. The subsample included 8 males and 22 females with a mean T1 age of 10.44 years and a mean postretention (T3) age of 30.3 years. T2 records were collected shortly after the end of active treatment. Long-term postretention crowding in these serial extraction patients was minimal. The mean T3 irregularity index of 2.7 mm was below the cut-off level of 3.5 mm considered to be satisfactory. The range was 0.31 to 5.9 mm, and 70% of the patients were in the minimally irregular category, and none was in the severe category (over 6.5 mm). Evaluation of the facial profiles at the end of treatment and 15 years later by using the Holdaway line showed that profiles were within the normal range at both periods. Numerous studies have found that premolar extractions do not produce poor facial balance. In her thesis at the University of Toronto, Julianne Peterson found similar results. She examined 20 serial extraction patients (3 males and 17 females) with a mean T1 age of 10.5 years and a mean postretention age of 30.8 years. Nearly 16 years posttreatment, the mean T3 irregularity index score was 2.4 mm (range, 0.5 to 4.95 mm). Seventy-five percent of the patients fell into the minimal category, and none was severe. In these stable cases, the mandibular intercanine expansion was minimal (1.2 mm), and the mandibular Associate professor, Baylor College of Dentistry, Texas AM Phoenix, Ariz. Am J Orthod Dentofacial Orthop 2002;121:575-7 Copyright © 2002 by the American Association of Orthodontists. 0889-5406/2002/$35.00 0 8/1/124685 doi:10.1067/mod.2002.124685