Aim: To review and discuss the dental and lateral profile soft tissue effects of orthodontic treatment involving three different premolar extraction patterns (4/4, 4/5, 5/5).
Method: The results of three previously reported studies were compared and discussed.
Results: Wide ranges of individual variation were found for the amounts of forward molar movement and incisor retraction, and for changes in the depths of upper and lower lip curves within all three premolar extraction pattern groups. The amount of pretreatment crowding and the residual space following initial alignment were the two factors most likely to influence changes in tooth positions during treatment. Treatment changes in the curvature of the lips were influenced by the pretreatment thickness of the lips at the vermilion level.
Conclusion: Factors other than simply the choice of premolar extraction pattern influence positional changes in the molars, incisors and lips during orthodontic treatment.
