Surface degradation of glass ceramics after exposure to acidulated phosphate fluoride

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. material and 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 mm) and 60 min (0.66±0.1 - 1.04±0.3 mm) 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 mm) (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 mm) and finesse？ low fusing (0.74.±0.2 mm) was significantly higher than those of the other ceramics (0.59±0.1 mm - 0.49±0.1 mm) and vita titankeramik (p<0.05) regardless of the exposure tim