title: A comparative study on compositional changes and Knoop hardness measurement of the cavity floor prepared by Er:YAG laser irradiation and mechanical bur cavity.
abstract: OBJECTIVE
  This present study was performed to compare the compositional changes of human dentin and, Knoop hardness of the cavity floor prepared by Er:YAG laser irradiation with that of the conventional bur cavity.
  
  
  BACKGROUND
  There are still no reports on the compositional changes of dental hard tissues and microhardness of the cavity floor prepared by Er:YAG laser irradiation.
  
  
  METHODS
  Fifteen laser and 15 bur cavities were cross-sectioned, and subjected to atomic analysis by SEM-EDX and Knoop hardness testing. Statistical analyses were performed using the Mann-Whitney U test; a value of p < 0.01 was considered significant. Cross sections of the remaining five laser and five bur cavities were examined by light microscopy and then by SEM.
  
  
  RESULTS
  The results showed that the quantities of Ca (Ca weight %) and P (P weight %) were increased significantly in the laser cavities, but no significant differences were found between the Ca/P ratio and Knoop hardness number of laser and bur cavities. The results of SEM observation revealed that the lased cavity surface was irregular, and there was also the absence of a smear layer; the orifice of dentinal tubules was exposed.
  
  
  CONCLUSIONS
  Er:YAG laser device produces minimal thermal induced changes of dental hard tissue compositions; Ca/P ratio and Knoop hardness of the lased cavity floor was almost similar to the bur cavities.
authors.affiliation: Department of Endodontics, Showa University School of Dentistry, 2-1-1 Kitasenzoku, Ohta-ku, Tokyo 145-8515, Japan.
authors.forename: Mozammal
authors.initials: M
authors.lastname: Hossain
authors.forename: Yukio
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Murakami
authors.forename: Yoshishige
authors.initials: Y
authors.lastname: Yamada
authors.forename: Koukichi
authors.initials: K
authors.lastname: Matsumoto
mesh_terms: D002118:Calcium / Q000032:analysis; D003737:Dental Cavity Preparation / Q000295:instrumentation; D003804:Dentin / Q000528:radiation effects; D004871:Erbium; D006244:Hardness; D006801:Humans; D066298:In Vitro Techniques; D007834:Lasers; D010758:Phosphorus / Q000032:analysis; D014070:Tooth / Q000737:chemistry* / Q000528:radiation effects / Q000648:ultrastructure
chemical_list: D010758:Phosphorus; D004871:Erbium; D002118:Calcium