title: Degraded prism sheaths in the transition region of hypomineralized teeth.
abstract: OBJECTIVE
  Failure of the enamel adjacent to the defects in teeth with molar incisor hypomineralization (MIH) limits the success rate of the restorations placed in these teeth and this frequently leads to their ultimate extraction. To understand the cause, a state-of-the-art combination of focused ion beam (FIB) and nanoindentation techniques was used to evaluate the fracture properties and microstructure of enamel from specific regions of two MIH teeth.
  
  
  METHODS
  Nanoindentation, bend tests on micro-cantilevers and transmission electron microscopy (TEM) were employed to compare the microstructure and mechanical properties of the unaffected, opaque and transitional region in two MIH teeth. Special attention was paid to the transitional region in all the experiments in an attempt to identify its role in affecting the overall integrity of the MIH teeth.
  
  
  RESULTS
  The enamel in the transitional region, despite its translucent appearance under the naked eye, was found, under TEM, to have prism sheaths that were significantly less mineralized than unaffected enamel and were proved to be weaker in holding the prisms together when measured using bend tests on micro-cantilever samples machined from the region.
  
  
  CONCLUSIONS
  The enamel in the transitional region adjacent to the demarcated defects in MIH has notable alterations in their prism sheaths which likely contribute to their lowered mechanical properties.
authors: Department of Mechanical Engineering, Faculty of Engineering, University of Hong Kong, Pokfulam Road, Hong Kong. roycyl@graduate.hku.hk
authors: Y L
authors: YL
authors: Chan
authors: A H W
authors: AH
authors: Ngan
authors: N M
authors: NM
authors: King
mesh_terms: D003743:Dental Enamel / Q000473:pathology* / Q000648:ultrastructure; D003744:Dental Enamel Hypoplasia / Q000473:pathology*; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D006244:Hardness; D006801:Humans; D007180:Incisor / Q000473:pathology; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D008963:Molar / Q000473:pathology; D018583:Pliability