title: Prevalence and Characteristics of the Maxillary C-shaped Molar.
abstract: BACKGROUND
  The anatomy of the maxillary C-shaped molar has been the subject of several case reports although no true prevalence research has ever been conducted. The aim of this observational study was to evaluate and characterize the incidence of these morphologies using cone-beam computed tomographic (CBCT) technology.
  
  
  METHODS
  Patients having presurgical CBCT examination were selected. CBCT analysis was performed at 5 different axial levels, and the teeth were classified as maxillary molar C shapes according to the inclusion criteria for the present investigation. The prevalence of C-shaped anatomy was calculated. The z test for proportions in independent groups was used to analyze the differences between proportions. Intrarater reliability was also tested.
  
  
  RESULTS
  A total of 2227 teeth (928 upper first molars and 1299 upper second molars) from 895 patients were included in this research. Five different types of C-shaped molars were found, which included fusion between mesiobuccal and palatal roots (type A), mesiobuccal and distobuccal roots (type B), distobuccal and palatal roots (type C), 2 possible palatal roots (type D), and mesiobuccal and palatal roots connecting with an independent distobuccal root canal at apical or between distobuccal and palatal roots connecting with an independent mesiobuccal root canal at apical (type E). The global prevalence was 1.1% for first molars and 3.8% for second molars. Differences were observed between sex, teeth, and some types of C shapes at P < .05.
  
  
  CONCLUSIONS
  Maxillary C-shaped molars have low prevalence but high anatomic complexity. An understanding of their anatomic configuration and variations is important in ensuring that they are treated properly. Distinct differences exist between C-shaped configurations of upper and lower molars.
authors.affiliation: Department of School of Dental Medicine, Biomedical and Oral Sciences Research Unit (FCT Unit 4062), Evidence Based Dentistry Center, Lisbon University, Lisbon, Portugal; Private Practice, Lisbon, Portugal. Electronic address: jnr_martins@yahoo.com.br.
authors.forename: Jorge N R
authors.initials: JN
authors.lastname: Martins
authors.affiliation: Department of Biology, New York University, New York, New York; Department of Oral Biology, Biomedical and Oral Sciences Research Unit (FCT Unit 4062), Evidence Based Dentistry Center, Lisbon University, Lisbon, Portugal; Department of Oral Biology and Biochemistry Group, Biomedical and Oral Sciences Research Unit (FCT Unit 4062), Evidence Based Dentistry Center, Lisbon University, Lisbon, Portugal.
authors.forename: António
authors.initials: A
authors.lastname: Mata
authors.affiliation: Department of Anatomy and Physiology, Biomedical and Oral Sciences Research Unit (FCT Unit 4062), Evidence Based Dentistry Center, Lisbon University, Lisbon, Portugal; Department of Oral Biology and Biochemistry Group, Biomedical and Oral Sciences Research Unit (FCT Unit 4062), Evidence Based Dentistry Center, Lisbon University, Lisbon, Portugal.
authors.forename: Duarte
authors.initials: D
authors.lastname: Marques
authors.affiliation: Private Practice, Biloxi, Mississippi.
authors.forename: Craig
authors.initials: C
authors.lastname: Anderson
authors.affiliation: Department of Implantology, Biomedical and Oral Sciences Research Unit (FCT Unit 4062), Evidence Based Dentistry Center, Lisbon University, Lisbon, Portugal.
authors.forename: João
authors.initials: J
authors.lastname: Caramês
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000379:methods; D003786:Dental Pulp Cavity / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D005260:Female; D005671:Fused Teeth / Q000000981:diagnostic imaging; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008297:Male; D008437:Maxilla / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D008875:Middle Aged; D008963:Molar / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D015995:Prevalence; D014092:Tooth Root / Q000033:anatomy & histology / Q000000981:diagnostic imaging
keywords: C-shaped root canal; Cone-beam computed tomography; dental morphology; maxillary molars