title: Ultra-structural changes at the apical stop irradiated with CO2 laser.
abstract: OBJECTIVE
  This study evaluated ultra-structural dentine changes at the apical stop after CO(2) laser irradiation used during biomechanical preparation.
  
  
  BACKGROUND
  Most studies evaluating the sealing efficiency of CO(2) lasers have been carried out after apical root canal resections and retro-filling procedures.
  
  
  METHODS
  Sixty human canines were prepared with #1 to #6 Largo burs. The apical stops were established at 1 mm (n = 30) and 2 mm (n = 30) from the apex. Final irrigation was performed with 1% NaOCl and 15% EDTA followed by 20 ml of distilled and deionized water. Specimens were subdivided into three subgroups (n = 10 for each stop distance): GI- no radiation (n = 20); GII- 3W potency (n = 20), GIII- 5W potency (n = 20). After preparation, specimens were evaluated by scanning electron microscopy, with ultra-structural changes classified according to a scoring system based on six qualitatively different outcomes.
  
  
  RESULTS
  Statistical analysis using the Mann-Whitney test confirmed more intense results for the specimens irradiated at 5 W potency than at 3 W (p < 0.0001). The Kruskal-Wallis test indicated that when using the same potencies (3 or 5 W) at 1 and 2 mm from the apex, there were no statistically significant differences in ultra-structural changes.
  
  
  CONCLUSIONS
  Our results showed that ultra-structural changes ranged from smear layer removal to dentine fusion. As laser potency was increased from 3 to 5 W, ultra-structural changes included extensive fused lava-like areas sealing the apical foramen.
authors.affiliation: Department of Endodontics, University of Ribeirão Preto (UNAERP), Ribeirão Preto, SP, Brazil.
authors.forename: João
authors.initials: J
authors.lastname: Gonçalves
authors.forename: Melissa Andréia
authors.initials: MA
authors.lastname: Marchesan
authors.forename: Aline Evangelista
authors.initials: AE
authors.lastname: Souza-Gabriel
authors.forename: Luis Pascoal
authors.initials: LP
authors.lastname: Vansan
authors.forename: Manoel D
authors.initials: MD
authors.lastname: Sousa-Neto
authors.forename: Yara T C
authors.initials: YT
authors.lastname: Silva-Sousa
mesh_terms: D002245:Carbon Dioxide; D003804:Dentin / Q000528:radiation effects* / Q000648:ultrastructure*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D007834:Lasers; D008855:Microscopy, Electron, Scanning; D012388:Root Canal Irrigants / Q000494:pharmacology; D018915:Root Canal Preparation / Q000379:methods*; D016369:Smear Layer; D014092:Tooth Root / Q000528:radiation effects
chemical_list: D012388:Root Canal Irrigants; D002245:Carbon Dioxide