The article aims to clarify wether the interlabial gap (shown as number 2 on the tracing to the left) reduction over time can be associated with the treatment therapy that was chosen.
62 Class I and Class II patients (with lip incompetence) were treated with or without extractions, and the gap was measured before, after and at the long term follow up.
What was found is that the interlabial gap decreases significantly more at the extraction therapy group compared to the non-extraction one. This happens during treatment.
During retention however, non-extraction group has a greater decrease of the gap, when compared to the extraction therapy group.
Also the authors show that variables such as lip length are associated with the amount of interlabial gap but NOT the decrease during treatment and over-time. The later has to do with the treatment chosen, and of course normal aging.
In plain words the decrease of interlabial gap during treatment at the extraction therapy group happens faster, and that is why during retention there is a smaller decrease when compared to the non-extraction therapy. "Aging faster?!"
The article can be found here: http://www.jwfo.org/article/S2212-4438(13)00056-8/abstract