title: Effect of Er:YAG laser and organic matrix on porosity changes in human enamel.
abstract: OBJECTIVE
  Cariostatic effects of lasers have been well documented in the past few decades; however, the mechanisms remain unclear. Our previous study revealed the statistically significant effect of organic matrix (OM) in the laser-induced caries prevention. The aim of the present study is to further investigate the role of organic matters in the laser-induced porosity changes.
  
  
  METHODS
  Enamel powder from five sound molars was randomly divided into two samples. One sample was treated with approximately 10% NaClO solution to remove OM and the other was left untreated. Both groups were then subjected to irradiation by an Er:YAG laser. The samples were characterized by thermogravimetric analysis (TGA) and N(2) physico-adsorption.
  
  
  RESULTS
  TGA results confirmed that the NaClO treatment had at least partially removed the OM in enamel powder. The surface area and pore volume of normal enamel powder decreased significantly after laser treatment. In contrast, in the NaClO-treated enamel powder, laser treatment did not significantly decrease the surface area and the pore volume remained almost unchanged. The substantial difference between the normal enamel powder and the NaClO-treated enamel powder after laser treatment confirmed the laser-induced blocking of OM in the micro-diffusion pathway in enamel.
  
  
  CONCLUSIONS
  The findings in this study seemed to substantiate the "organic blocking theory" as one of the mechanisms in the laser-induced caries prevention.
authors.affiliation: Department of Preventive Dentistry, Faculty of Dentistry, National University of Singapore, 5 Lower Kent Ridge Road, 119074 Singapore, Republic of Singapore.
authors.forename: Deng
authors.initials: D
authors.lastname: Ying
authors.forename: G K
authors.initials: GK
authors.lastname: Chuah
authors.forename: Chin-Ying S
authors.initials: CY
authors.lastname: Hsu
mesh_terms: D003743:Dental Enamel / Q000737:chemistry* / Q000187:drug effects; D004058:Diffusion; D004871:Erbium; D006358:Hot Temperature; D006801:Humans; D006838:Hydrocarbons; D053685:Laser Therapy; D028022:Low-Level Light Therapy; D016062:Porosity; D012973:Sodium Hypochlorite / Q000494:pharmacology; D013818:Thermogravimetry; D017001:Tooth Demineralization / Q000628:therapy*
chemical_list: D006838:Hydrocarbons; D004871:Erbium; D012973:Sodium Hypochlorite