title: A cone-beam computed tomographic study of root canal systems in mandibular premolars in a Turkish population: Theoretical model for determining orifice shape.
abstract: OBJECTIVE
  The purposes of this retrospective study were to represent a newly designed theoretical model for determining orifice shape and morphologic properties of mandibular premolars and to correlate these findings with each other.
  
  
  METHODS
  A total of 287 mandibular premolar images obtained from 88 patients by cone-beam computed tomography were included in this study. The measurements were performed below the cementoenamel junction, and different orifice configurations were defined in accordance with various ratios. The age and gender of the patient, the tooth type and position, the number of roots, orifice configuration, root canal configuration, presence of C-shaped canal, and the presence of radicular groove were recorded. It was also recorded whether the root canal becomes round or not and if any, length of the root canal from the orifice to the section in which it becomes round. Furthermore, the theoretical model for determining orifice shape was defined after measurements. The orifice shape was determined as round, oval, flat, keyhole-shaped, and T-shaped, and orifices with short, normal length, and long isthmus. Statistical analyses were performed using Chi-square and Spearman's rank correlation tests (P = 0.05).
  
  
  RESULTS
  Orifice configurations were, usually, flat (37%), or keyhole-shaped (23%). The prevalence of T-shaped was found to be 3.8%. The prevalence of C-shaped canals was found to be 2.1%. The percentage of root canals that became round in the middle or apical thirds was 95.1%. Radicular grooves were detected in 37 (24%) of first premolars and six (4.5%) of second premolars. Statistical analysis revealed that the mean length of distance until the canal reached a round shape varied according to age group (r = -0.270; P < 0.001). There was a statistically significant difference between radicular groove and tooth type (P < 0.001).
  
  
  CONCLUSIONS
  The mean length of distance until the canal reached a round shape correlated with the patient's age. The new theoretical model could be beneficial to determine orifice configurations.
authors.affiliation: Department of Endodontics, Faculty of Dentistry, Ataturk University, Erzurum, Turkiye.
authors.forename: Hakan
authors.initials: H
authors.lastname: Arslan
authors.affiliation: Department of Endodontics, Faculty of Dentistry, Izmir Katip Celebi University, Izmir, Turkiye.
authors.forename: Ismail Davut
authors.initials: ID
authors.lastname: Capar
authors.affiliation: Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Izmir Katip Celebi University, Izmir, Turkiye.
authors.forename: Elif Tarim
authors.initials: ET
authors.lastname: Ertas
authors.affiliation: Department of Endodontics, Faculty of Dentistry, Izmir Katip Celebi University, Izmir, Turkiye.
authors.forename: Huseyin
authors.initials: H
authors.lastname: Ertas
authors.affiliation: Department of Pedodontics, Faculty of Dentistry, Izmir Katip Celebi University, Izmir, Turkiye.
authors.forename: Merve
authors.initials: M
authors.lastname: Akcay
keywords: Cone-beam computed tomography; Turkish; isthmus; mandibular premolars; orifice; theoretical modeling