title: [Morphological characteristics of the mandibular first premolars in people from Pearl River Delta region in Guangdong province].
abstract: OBJECTIVE
  To investigate the morphological characteristics of the mandibular first premolars in people from Pearl River Delta region in Guangdong province using three techniques, including periapical radiographs, the radiographs with files inserted the canals and the clearing technique.
  
  
  METHODS
  A total of 363 extracted mandibular first premolars were collected and numbered. Two preoperative radiographs were taken in buccolingual and mesiodistal directions respectively. After access opening, the files were placed in the canals and two other radiographs were taken. The mandibular first premolars with multi-canal system were selected and observed under dental operating microscope (DOM). The mandibular first premolars were made transparent and were categorized using the Vertucci's classification.
  
  
  RESULTS
  There were different results among the three approaches. Periapical radiographs could be used to distinguish only between one and multiple canals systems. The incidence of multiple canals was 33.33% from the radiographs with file. The mandibular first premolars had a high frequency (34.44%) of multi-canal system by clearing method. The root canal morphology of the mandibular first premolars showed great variance. The canal orifices of the mandibular first premolars with one or two canal distributed in a buccolingual line. The floor of pulp chamber of the mandibular first premolars with three or four canals was a plat form.
  
  
  CONCLUSIONS
  The mandibular first premolars have a high frequency multi-canal system and could be classified in many categories. Using DOM and radiographs with file is a useful way in judging the canal numbers and categories.
authors.affiliation: Dept. of Conservative Dentistry and Endodontics, Guanghua College of Stomatology, Sun Yat-Sen University, Guangzhou, China.
authors.forename: Zheng-mei
authors.initials: ZM
authors.lastname: Lin
authors.forename: Yi-yun
authors.initials: YY
authors.lastname: Fang
authors.forename: Jun-qi
authors.initials: JQ
authors.lastname: Ling
mesh_terms: D001641:Bicuspid; D003786:Dental Pulp Cavity; D006801:Humans; D008334:Mandible; D045483:Rivers; D012390:Root Canal Therapy; D014092:Tooth Root