The relationship between first premolar extraction and third molar angulation in orthodontic treatment

Extraction of first premolars and their influence on the third molar's eruption and impaction has been of concern to dental profession. The aim of this study, was to determine the relation between the changes of third molar angulation and the first premolar extraction in orthodontic treatment. This analytical study was carried out on a total 90 subjects selected from two orthodontic clinics. Forty five subjects (14 males and 31 females) 14.46±1.64 years old treated with extraction of four first premolars (extraction group) and the other 45 subjects (13 males, 32 females) 13.9±1.99 years old treated by non-extraction were studied. Lateral cephalometric and panoramic films were examined before and after treatment. Eight angles in panoramic, four angles and 4 linear variables on the lateral cephalometric films were measured. Age, gender, amount of crowding in both dental arches and treatment duration were matched in the two groups. Student t and chi square tests were used to analyze the data. The upper eruption space (UES) and the lower eruption space (LES) (R), (xi) were more in extraction group and the difference was significant (P=0.02, P=0.004, P<0.001). The changes of third molar angulation was not significant between the two groups. Eruption rate of the third molars in both arches were more in extraction group and the difference was significant (P<0.001). Extraction of the first premolars did not influence the changes in the third molar angulation, while it affected the third molar eruption by space creation. It seems that extraction of the first premolars is not a way for secure eruption of the third molar.