OBJECTIVES: The aim of this in-vitro study was to assess the long-term effects of hydrochloric acid on the surface roughness of three all-ceramic restorative materials CEREC VITABLOC® Mark II CAD, IPS Empress CAD® and IPS e.max CAD®. MATERIALS AND METHODS: Six cylindrical specimens (10mm diameter, 3mm height) of each material type were prepared, using the CEREC CAD/CAM machine. The unpolished samples were immersed in 15ml hydrochloric acid (pH 2) at 370C. Before immersion (baseline) and at periods of 7.5 hours, 45 hours and 91 hours, the specimens were removed from the acid and two randomised areas (10μm X 10μm) were selected and tested on each. The atomic force microscope (Bruker Dimension icon) was used to assess surface roughness and surface area at baseline and after each exposure time. The materials were compared over time with respect to surface roughness and surface area (baseline, 1 month, 6 months, 1 year) in a repeated measures analysis of variance (ANOVA). RESULTS: Sample groups differed significantly for roughness (p<0.0001) and surface area (p<0.0001). For both parameters a significant interaction also existed between material and time (surface roughness: p=0.0085; surface area: p=0.0014). CEREC VITABLOC® Mark II CAD and IPS Empress CAD® had substantially higher levels of roughness and surface area than IPS e.max CAD®, which was also affected to a lesser extent over time. CONCLUSION: The results showed that IPS e.max CAD was least affected by long-term exposure to hydrochloric acid. CLINICAL SIGNIFICANCE: These results can aid the clinician in choosing the appropriate materials for patients who are bulimic or who suffer from gastro oesophageal reflux.