title: Characterisation of developmentally hypomineralised human enamel.
abstract: OBJECTIVE
  To investigate and clarify physical and chemical properties of enamel affected by molar incisor hypomineralisation (MIH).
  
  
  METHODS
  A series of in vitro studies were performed on extracted molars affected by MIH and sound teeth for controls. Tooth sections underwent Vickers microhardness testing before lapping and subsequent transverse microradiographic analysis and examination under polarised light microscopy. Carbonate content was determined by CO2 release from acid digestion. Unprepared and fractured surfaces were examined under scanning electron microscopy.
  
  
  RESULTS
  MIH-affected molars demonstrated a severe degree of hypomineralisation with an average mineral content of only 58.8%vol% mineral. Vickers microhardness was significantly reduced in MIH compared with controls (1.8±1.1 v 4.4±1.0 GPa, p<0.05) and polarised light microscopy revealed the bulk of MIH lesions had a porosity of ≤5% but also substantial areas of ≥10% and smaller areas exceeding 25% porosity. A surface layer was frequently observed on both intact and broken-down lesions and cervical regions of MIH teeth were typically spared. Carbonate content of MIH enamel was higher than control samples (6.6±2.1 v 4.4±1.1 wt%, p<0.05). Scanning electron microscopy showed that both the enamel rod and surface ultrastructure were defective. Clinical characteristics did not consistently correlate with all properties.
  
  
  CONCLUSIONS
  The properties of MIH-affected enamel significantly differ from those of normal enamel and were highly variable, however some common characteristics were observed. Implications for aetiology and clinical management are discussed.
authors.affiliation: Oral Health Cooperative Research Centre, Melbourne Dental School, Bio21 Institute, The University of Melbourne, Australia.
authors.forename: Felicity A
authors.initials: FA
authors.lastname: Crombie
authors.forename: David J
authors.initials: DJ
authors.lastname: Manton
authors.forename: Joseph E A
authors.initials: JE
authors.lastname: Palamara
authors.forename: Ilya
authors.initials: I
authors.lastname: Zalizniak
authors.forename: Nathan J
authors.initials: NJ
authors.lastname: Cochrane
authors.forename: Eric C
authors.initials: EC
authors.lastname: Reynolds
mesh_terms: D002254:Carbonates / Q000032:analysis; D055598:Chemical Phenomena; D003743:Dental Enamel / Q000737:chemistry / Q000648:ultrastructure*; D003744:Dental Enamel Hypoplasia / Q000378:metabolism / Q000473:pathology*; D006244:Hardness; D006801:Humans; D008852:Microradiography; D008855:Microscopy, Electron, Scanning; D008859:Microscopy, Polarization; D008903:Minerals / Q000032:analysis; D008963:Molar / Q000737:chemistry / Q000473:pathology; D016062:Porosity
chemical_list: D002254:Carbonates; D008903:Minerals