title: The influence of dentin demineralization on morphological features of cavities using Er:YAG laser.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the influence of erbium-doped: yttrium-aluminum-garnet (Er:YAG) laser parameters and different degrees of demineralization on morphological features, diameter, and depth of prepared cavities.
  
  
  BACKGROUND
  Minimally invasive dentin caries removal has been recommended. Ablation of deep caries lesions using Er:YAG laser should preserve remaining demineralized dentin; however, the influence of the degree of mineralization of this substrate had not been entirely described.
  
  
  METHODS
  A randomized, factorial design was used to study the effects of two factors. Laser parameter was tested at two levels (250 mJ/4 Hz vs. 200 mJ/2 Hz) and degree of demineralization was tested at four levels (control, two-four-eight cycles). Twelve slabs of human dentin were divided into four groups according to the number of cycles induced by pH-cycling: G1, zero cycles; G2, two cycles, G3, four cycles, and G4, eight cycles. An Er:YAG laser was used at an output energy of 250 mJ/4 Hz and 200 mJ/2 Hz for all groups, for 10 sec at 12 mm distance focus/object. Circumference and depth of the cavities were measured on scanning electron microscopy (SEM) images using image analysis software. The mean values were subjected to two way analysis of variance (ANOVA) and Tukey tests.
  
  
  RESULTS
  When using 250 mJ/4 Hz, the mean values of circumferential area increased significantly in relation to control (503.54 μm(2)) with increasing demineralization level (eight cycles) (555.45 μm(2)). Regardless of the demineralization level, there was also significant statistical difference in the studied measurements of the cavities when 250 mJ/4 Hz and 200 mJ/2 Hz were used. SEM also showed that laser cavity preparations left no smear layer, and the dentinal tubules were clear.
  
  
  CONCLUSIONS
  The circumferential area and depth measurements were affected by laser parameter and demineralization level (eight cycles). Energy level output represents a relevant factor for increased circumferential area and depth measurements. High demineralized artificially caries-affected dentin may also imply higher ablation. Appropriated parameter of laser pulse frequency/power density for demineralized dentin should be used for effective less-invasive caries treatment.
authors.affiliation: 1 Department of Endodontics, Prosthodontics, and Operative Dentistry, University of Maryland Dental School , Baltimore, Maryland.
authors.forename: Mary A S
authors.initials: MA
authors.lastname: Melo
authors.forename: Juliana P M
authors.initials: JP
authors.lastname: Lima
authors.forename: Vanara F
authors.initials: VF
authors.lastname: Passos
authors.forename: Lidiany K A
authors.initials: LK
authors.lastname: Rodrigues
mesh_terms: D003731:Dental Caries / Q000601:surgery*; D003804:Dentin / Q000473:pathology*; D006244:Hardness; D006801:Humans; D066298:In Vitro Techniques; D053844:Lasers, Solid-State / Q000627:therapeutic use*; D008855:Microscopy, Electron, Scanning; D011897:Random Allocation; D013499:Surface Properties; D017001:Tooth Demineralization