title: [Effects of the first premolar extraction on the third molar angulation].
abstract: OBJECTIVE
  To analyze the effects about inclinations of the second and the third molars in patients treated with or without premolar extractions.
  
  
  METHODS
  Fifty-six adolescents were chosen and divided into the first premolar extraction and non-extraction groups, 30 and 26 patients respectively. The pre-treatment and post-treatment panoramic radiographs were made. Angles between long axis of the third molar and the occlusal plane (the second molar alike), and long axis of the second and the third molar were measured and evaluated.
  
  
  RESULTS
  The maxillary and mandibular third molar angulations were all improved after treatment in two groups. Compared with non-extraction group, the average changes of angle between long axis of the third molar and the occlusal plane increased significantly in maxilla and mandible (P < 0.05). Average changes of angles between long axis of the second and the third molar decreased and had statistically significant difference (P < 0.05). The change of angle between long axis of mandibular second molar and the occlusal plane had statistically significant difference (P < 0.05), but there was no statistically significant difference in maxillary second molar (P > 0.05).
  
  
  CONCLUSIONS
  The first premolar extraction in orthodontic treatment could improve the third molar angulations and it would promote the eruption of the third molar.
authors.affiliation: Dept. of Stomatology, General Hospital of Jinan Military Area, Jinan 250031, China.
authors.forename: Yu-hong
authors.initials: YH
authors.lastname: He
authors.forename: Yin-zhong
authors.initials: YZ
authors.lastname: Duan
authors.forename: Ji-jun
authors.initials: JJ
authors.lastname: Pan
authors.forename: Lan-lan
authors.initials: LL
authors.lastname: Xi
mesh_terms: D000293:Adolescent; D001641:Bicuspid; D003766:Dental Occlusion; D005260:Female; D006801:Humans; D008297:Male; D008334:Mandible; D008437:Maxilla; D008963:Molar; D008964:Molar, Third; D011862:Radiography, Panoramic; D014078:Tooth Eruption; D014081:Tooth Extraction