Labial changes following extraction of first premolars for orthodontic treatment in patients with malocclusion class II Div I

Introduction
In orthodontic treatment, extraction of teeth is usual especially for first premolars.
After observing lip prominence improvement in the lower third of the face in girls with concave or long faces following orthodontic treatment and extraction of the upper and lower first premolars, we decided to carry out this research.  The aim of this research was to study anterior and posterior changes of upper and lower lips following retraction of upper and lower incisors in patients with extracted upper and lower four first premolars.
Materials and Methods
Because this research process started on specific patients at one cut of paint of time, is cross sectional and because the cases in this investigation long time have been treated, can be considered longitudinal. In this research twenty patients with Class II Div I malocclusion were selected. Lateral cephalometry before and after treatment was the technique through which the data were collected. The average age at the start of the treatment in males was 12.2 and in females 11.8 years, and the average duration of treatment was 2.9 years.  All patients were treated by the standard edgewise method and overjet was decreased 5mm in average.  In all of these patients the upper and lower first premolars were extracted for treatment.  We used SPSS statistical software to analyze the data T-test, paired t-test and correlation coefficient test were used.
Results
Without omission of growth rate
1. In females, for 3.39mm retraction of upper incisors, lips protruded 0.32 mm indicative of a reverse and weak relationship between them.
2. In males, the ratio between retraction of upper incisors and upper lip was 4.4:1 It means that for 8.83mm retraction of upper incisors, upper lip retrusion was 2mm.
3.  In boys and girls for 5.02 mm retraction of upper incisors, the upper lip retruded 0.37 mm indicative of a direct but weak relationship.
girls for 0.1 mm retraction of lower incisors, lower lip had 0.7mm protrusion in contrast
5. In boys, for 5.75 mm retraction of lower incisors, lower lip retruded 5.16 mm and the ratio was 101:1.
6. With omission of growth rate, the retrusion rate of upper lip had a direct relationship with upper incisors in girls and the ratio between them was 3.3:1 that means 3.3 of incisors became retracted, the upper lip retruded 1 mm. The ratio considering boys and girls was 3:1 and 2.7:1 just in boys. 
7. In girls and boys, lower lip, following retraction of upper anterior teeth, had retrusion. The correlation coefficient was r = 97.5 and the ratio between them was 2:1.
8. Lower incisors retraction had a direct relationship with lower lip retrusion (correlation coefficient was r=82.1). The ratio in boys and girls was 1:1 and 1:1 respectively.
Conclusion
In this study we concluded that the rate of soft and hard tissue changes were different.  In other words, soft tissue did not move alongside hard tissue.  Changes in boys and girls were different from each other.  Rate of overjet, thickness of lips and upper lip connection to nose columella play probably some role in retrusion rate. Lower lip retrusion was more than upper lip. Growth had its own influence on retrusion.  In girls less than in boys, lips were influenced by incisor retraction.