title: Surface degradation of glass ceramics after exposure to acidulated phosphate fluoride.
abstract: OBJECTIVE
  This study evaluated the surface degradation effect of acidulated phosphate fluoride (APF) gel exposure on the glassy matrix ceramics as a function of time.
  
  
  METHODS
  Disc-shaped ceramic specimens (N = 120, 10/per ceramic material) were prepared in stainless steel molds (inner diameter: 5 mm, height: 2 mm) using 6 dental ceramics: 3 indicated for ceramic-fused-to-metal (Vita Omega 900, Carmen and Vita Titankeramik), 2 for all-ceramic (Vitadur Alpha and Finesse Low Fusing) and 1 for both types of restorations (IPS d.SIGN). The specimens were wet ground finished, ultrasonically cleaned and auto-glazed. All specimens were subjected to calculation of percentage of mass loss, surface roughness analysis and topographical description by scanning electron microscopy (SEM) before (0 min) and after exposure to 1.23 % APF gel for 4 min and 60 min representing short- and long-term etching effect, respectively. The data were analyzed using two-way ANOVA with repeated measures and Tukey's test (a=0.05).
  
  
  RESULTS
  Significant effect of the type of the ceramics (p=0.0000, p=0.0031) and exposure time (p=0.0000) was observed in both surface roughness and percentage of mass loss values, respectively. The interaction factor between both parameters was also significant for both parameters (p=0.0904, p=0.0258). Both 4 min (0.44+/-0.1 - 0.81+/-0.2 microm) and 60 min (0.66+/-0.1 - 1.04+/-0.3 microm) APF gel exposure created significantly more surface roughness for all groups when compared to the control groups (0.33+/-0.2 - 0.68+/-0.2 microm) (p<0.05). There were no significant differences in percentage of mass loss between the ceramics at 4 min (p>0.05) but at 60 min exposure, IPS d.SIGN showed the highest percentage of mass loss (0.1151+/-0.11). The mean surface roughness for Vita Titankeramik (0.84+/-0.2 microm) and Finesse Low Fusing (0.74.+/-0.2 microm) was significantly higher than those of the other ceramics (0.59+/-0.1 microm - 0.49+/-0.1 microm) and Vita Titankeramik (p<0.05) regardless of the exposure time. A positive correlation was found between surface roughness and percentage of mass loss for all ceramic materials [(r=0.518 (Vitadur Alpha), r=0.405 (Vita Omega 900), r=0.580 (Carmen), r=0.687 (IPS d.SIGN), r=0.442 (Finesse Low Fusing), r=0.572 (Vita Titankeramik), Pearson's correlation coefficient)]. The qualitative SEM analysis showed evidence of corrosive attack on all of ceramics at varying degrees.
  
  
  CONCLUSIONS
  The ceramics indicated for either metal-ceramic or all-ceramic restorations were all vulnerable to surface texture changes and mass loss after short-term and long-term APF gel exposure.
authors.affiliation: São José dos Campos Dental School, Department of Dental Materials and Prosthodontics, São Paulo State University, São José dos Campos, Brazil.
authors.forename: Vanessa Zulema S
authors.initials: VZ
authors.lastname: Ccahuana
authors.forename: Mutlu
authors.initials: M
authors.lastname: Ozcan
authors.forename: Alfredo Mikail Melo
authors.initials: AM
authors.lastname: Mesquita
authors.forename: Renato Sussumo
authors.initials: RS
authors.lastname: Nishioka
authors.forename: Estevão Tomomitsu
authors.initials: ET
authors.lastname: Kimpara
authors.forename: Marco Antonio
authors.initials: MA
authors.lastname: Bottino
mesh_terms: D000149:Acidulated Phosphate Fluoride; D000538:Aluminum Silicates; D000704:Analysis of Variance; D002327:Cariostatic Agents; D002516:Ceramics; D003343:Corrosion; D045662:Dental Etching; D003776:Dental Porcelain / Q000737:chemistry; D005782:Gels; D006358:Hot Temperature; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D017680:Potassium Compounds; D018709:Statistics, Nonparametric; D013499:Surface Properties; D013997:Time Factors
chemical_list: D000538:Aluminum Silicates; D002327:Cariostatic Agents; D005782:Gels; D017680:Potassium Compounds; D003776:Dental Porcelain; C016447:feldspar; D000149:Acidulated Phosphate Fluoride; C023506:Glass ceramics