title: Mineral density of hypomineralised enamel.
abstract: OBJECTIVE
  To characterize molar-incisor hypomineralisation (MIH) defects of different severities quantitatively and qualitatively using X-ray microtomography (XMT) and to measure the range of reduction in mineral density (MD) of MIH enamel compared with the normal range.
  
  
  METHODS
  Ten sound teeth and ten MIH teeth were scanned using a commercial XMT system. Four hydroxyapatite phantoms of different densities were used as calibration standards with each scan. A calibration equation derived from the phantoms with each tooth was used for MD calibration. MD was traced from the cementum-enamel junction (CEJ) to the cusp tip and from the dentine-enamel junction (DEJ) to the outer enamel surface.
  
  
  RESULTS
  In sound teeth, MD increased from CEJ to cusp/incisal tip, while in MIH teeth MD dropped from the CEJ to the occlusal region, then increased again at the cusp tip. MD was highest midway between DEJ and outer enamel in sound teeth. In MIH, enamel showed normal thickness and MD was highest near the DEJ and then decreased towards the outer enamel. MD of MIH enamel was on average about 19% lower than sound enamel. The MIH defects seemed to follow the incremental lines of enamel formation.
  
  
  CONCLUSIONS
  MIH defects are hypomineralised defects of different severities that follow the natural incremental lines of enamel formation. Cuspal areas are usually only mildly affected and cervical enamel always appears to be sound.
authors.affiliation: Dept of Oral Sciences, Faculty of Dentistry, University of Otago, Dunedin, Otago, New Zealand. farra304@student.otago.ac.nz
authors.forename: R A
authors.initials: RA
authors.lastname: Farah
authors.forename: M V
authors.initials: MV
authors.lastname: Swain
authors.forename: B K
authors.initials: BK
authors.lastname: Drummond
authors.forename: R
authors.initials: R
authors.lastname: Cook
authors.forename: M
authors.initials: M
authors.lastname: Atieh
mesh_terms: D019412:Anatomy, Cross-Sectional; D003743:Dental Enamel / Q000737:chemistry* / Q000473:pathology; D003804:Dentin / Q000737:chemistry / Q000473:pathology; D017886:Durapatite / Q000737:chemistry; D006801:Humans; D008903:Minerals / Q000032:analysis*; D008963:Molar / Q000737:chemistry / Q000473:pathology; D019047:Phantoms, Imaging; D019237:Tooth Cervix / Q000737:chemistry / Q000473:pathology; D019228:Tooth Crown / Q000737:chemistry / Q000473:pathology; D017001:Tooth Demineralization / Q000378:metabolism* / Q000473:pathology; D055114:X-Ray Microtomography
chemical_list: D008903:Minerals; D017886:Durapatite