Controversies in orthodontics.

Three controversial interrelated aspects of orthodontics have been reviewed: retention, the effect of third molars on lower anterior crowding, and extraction and nonextraction orthodontic treatment. Recent studies have shown that unacceptable lower anterior crowding occurs in 90 per cent of well-treated extraction cases. The implication is that nonextraction cases should be 90 per cent or higher. In view of our present general inability to identify the 10 per cent that will remain acceptable, some form of indefinite retention is advised. A literature review of the effect of third molars on lower anterior crowding finds strong opinions on both sides of the issue. Similar studies often show dissimilar conclusions, particularly when observing cases of third molar extraction or agenesis. Certainly the problem is multifactorial; however, the vast bulk of the evidence indicates that the third molars play an insignificant role in lower anterior crowding. Extraction of teeth for orthodontic treatment prior to 1900 was prevalent and indiscriminate. From the turn of the century to the mid-thirties Angle moved the specialty away from extractions to a relatively rigid nonextraction treatment philosophy. Dissatisified with relapsing Class II cases, recurrence and aggravation of crowding, and what he felt were bimaxillary full faces, Tweed and others, circa 1935, redirected the profession back to extractions with a more disciplined approach to treatment by the removal of four first premolars. Fifty years later we have found that extraction treatment and uprighting lower incisors does not prevent long-term postretention crowding and that flattened profiles are not always esthetically desirable. Earlier treatment of maxillomandibular basal discrepancies by old and new treatment philosophies and mechanics have produced more stable nonextraction corrections. Better control of leeway space and a reduction in caries has helped reduce the amount of lower anterior flaring that was seen in the nonextraction cases in the first third of the century. These reasons have moved the specialty of orthodontics to a mixed but more nonextraction-oriented approach to treatment.