title: Defining new dental phenotypes using 3-D image analysis to enhance discrimination and insights into biological processes.
abstract: OBJECTIVE
  In studying aetiological interactions of genetic, epigenetic and environmental factors in normal and abnormal developments of the dentition, methods of measurement have often been limited to maximum mesio-distal and bucco-lingual crown diameters, obtained with hand-held calipers. While this approach has led to many important findings, there are potentially many other informative measurements that can be made to describe dental crown morphology. Advances in digital imaging and computer technology now offer the opportunity to define and measure new dental phenotypes in 3-D that have the potential to provide better anatomical discrimination and clearer insights into the underlying biological processes in dental development. Over recent years, image analysis in 2-D has proved to be a valuable addition to hand-measurement methods but a reliable and rapid 3-D method would increase greatly the morphological information obtainable from natural teeth and dental models. Additional measurements such as crown heights, surface contours, actual surface perimeters and areas, and tooth volumes would maximise our ability to discriminate between samples and to explore more deeply genetic and environmental contributions to observed variation. The research objectives were to investigate the limitations of existing methodologies and to develop and validate new methods for obtaining true 3-D measurements, including curvatures and volumes, in order to enhance discrimination to allow increased differentiation in studies of dental morphology and development. The validity of a new methodology for the 3-D measurement of teeth is compared against an established 2-D system. The intra- and inter-observer reliability of some additional measurements, made possible with a 3-D approach, are also tested.
  
  
  RESULTS
  From each of 20 study models, the permanent upper right lateral and upper left central incisors were separated and imaged independently by two operators using 2-D image analysis and a 3-D image analysis system. The mesio-distal (MD), labio-lingual (LL) and inciso-gingival (IG) dimensions were recorded using our 2-D system and the same projected variables were also recorded using a newly developed 3-D system for comparison. Values of Pearson's correlation coefficient between measurements obtained using the two techniques were significant at the 0.01 probability level for variables mesio-distal and incisal-gingival with labio-lingual significant at the 0.05 level for the upper left side only, confirming their comparability. For both 2-D and 3-D systems the intra- and inter-operator reliability was substantial or excellent for variables mesio-distal, labio-lingual, incisal-gingival actual and projected and actual surface area. The reliability was good for inter-operator reliability measurement of the labio-lingual dimension using 3-D.
  
  
  CONCLUSIONS
  We have developed a new 3-D laser scanning system that enables additional dental phenotypes to be defined. It has been validated against an established 2-D system and shown to provide measurements with excellent reliability, both within and between operators. This new approach provides exciting possibilities for exploring normal and abnormal variations in dental morphology and development applicable to research on genetic and environmental factors.
authors.affiliation: University of Liverpool, Department of Clinical Dental Sciences, Edwards Building, Pembroke Place, Liverpool L69 3GN, UK. r.n.smith@liverpool.ac.uk
authors.forename: Richard
authors.initials: R
authors.lastname: Smith
authors.forename: Halla
authors.initials: H
authors.lastname: Zaitoun
authors.forename: Tom
authors.initials: T
authors.lastname: Coxon
authors.forename: Mayada
authors.initials: M
authors.lastname: Karmo
authors.forename: Gurpreet
authors.initials: G
authors.lastname: Kaur
authors.forename: Grant
authors.initials: G
authors.lastname: Townsend
authors.forename: Edward F
authors.initials: EF
authors.lastname: Harris
authors.forename: Alan
authors.initials: A
authors.lastname: Brook
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation*; D021621:Imaging, Three-Dimensional / Q000295:instrumentation*; D007180:Incisor / Q000033:anatomy & histology*; D007834:Lasers; D003765:Models, Dental; D009811:Odontometry / Q000295:instrumentation*; D010641:Phenotype; D015203:Reproducibility of Results; D014584:User-Computer Interface; D055815:Young Adult