The spontaneous effects of lower first premolar extraction on the mesio-distal angulation of adjacent teeth and the relationship of this to extraction space closure in the long term.

This study was undertaken to examine the short- and long-term effects of uncontrolled extraction space closure on the angulation of buccal teeth in the lower arch following the extraction of all first premolars. The sample consisted of 20 subjects (12 males, 8 females). Impressions for study models were taken before premolar extraction (mean age 13 years), at monthly intervals during the first year thereafter, and at long-term follow-up (mean 13 years post-extraction). Measurements were made using the Reflex Microscope. Angulations of teeth (canines, second premolars, and first molars) were measured relative to the occlusal plane and to each other. The findings showed that although teeth tended to tip towards the extraction space, the amount of tipping was small (not exceeding 15 degrees in the majority of cases). The tipping was found to be greatest during the first 6 months following premolar extraction. In the long-term, as spaces continued to close, some uprighting was noted especially in the canine angulation. It is concluded that excessive tipping appears to be the exception rather than the rule in lower first premolar extraction cases.