title: Submorphotypes of the maxillary first molar and their effects on alignment and rotation.
abstract: BACKGROUND
  The aim of this study was to explore the shape differences in maxillary first molars with orthographic measurements using 3-dimensional virtual models to assess whether there is variability in morphology that could affect the alignment results when treated by straight-wire appliance systems.
  
  
  METHODS
  A total of 175 maxillary first molars with 4 cusps were selected for classification. With 3-dimensional laser scanning and reconstruction software, virtual casts were constructed. After performing several linear and angular measurements on the virtual occlusal plane, the teeth were clustered into 2 groups by the method of partitioning around medoids. To visualize the 2 groups, occlusal polygons were constructed using the average data of these groups.
  
  
  RESULTS
  The resultant 2 clusters showed statistically significant differences in the measurements describing the cusp locations and the buccal and lingual outlines. The rotation along the centers made the 2 cluster polygons look similar, but there was a difference in the direction of the midsagittal lines.
  
  
  CONCLUSIONS
  There was considerable variability in morphology according to 2 clusters in the population of this study. The occlusal polygons showed that the outlines of the 2 clusters were similar, but the midsagittal line directions and inner geometries were different. The difference between the morphologies of the 2 clusters could result in occlusal contact differences, which might be considered for better alignment of the maxillary posterior segment.
authors.affiliation: Postgraduate student, Department of Oral Anatomy, Dental Research Institute, School of Dentistry, Seoul National University, Seoul, Korea.
authors.forename: Hong-Kyun
authors.initials: HK
authors.lastname: Kim
authors.affiliation: Associate professor, Department of Prosthodontics, Dental Research Institute, School of Dentistry, Seoul National University, Seoul, Korea.
authors.forename: Ho Beom
authors.initials: HB
authors.lastname: Kwon
authors.affiliation: Associate professor, Department of Pediatric Dentistry, Dental Research Institute, School of Dentistry, Seoul National University, Seoul, Korea.
authors.forename: Hong-Keun
authors.initials: HK
authors.lastname: Hyun
authors.affiliation: Adjunct associate professor, Department of Orthodontics, Dental Research Institute, School of Dentistry, Seoul National University, Seoul, Korea.
authors.forename: Min-Ho
authors.initials: MH
authors.lastname: Jung
authors.affiliation: Postgraduate student, Department of Oral Anatomy; assistant professor, Division of Orthodontics, Department of Dentistry, St Vincent's Hospital, Catholic University of Korea, Suwon, Korea.
authors.forename: Seong Ho
authors.initials: SH
authors.lastname: Han
authors.affiliation: Associate professor, Department of Oral Anatomy, Dental Research Institute, School of Dentistry, Seoul National University, Seoul, Korea. Electronic address: ayoayo7@snu.ac.kr.
authors.forename: Young-Seok
authors.initials: YS
authors.lastname: Park
mesh_terms: D059925:Anatomic Landmarks / Q000473:pathology; D002648:Child; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D007834:Lasers; D008297:Male; D008310:Malocclusion / Q000473:pathology* / Q000628:therapy; D008437:Maxilla; D008963:Molar / Q000473:pathology*; D009811:Odontometry / Q000379:methods; D061848:Optical Imaging / Q000379:methods; D009969:Orthodontic Wires; D025341:Principal Component Analysis; D012399:Rotation; D019228:Tooth Crown / Q000473:pathology; D014087:Tooth Movement Techniques / Q000295:instrumentation; D014584:User-Computer Interface