Purpose: To investigate the growth of primary human gingival epithelial (HGE) cells on polymer-infiltrated ceramic network (PICN) material (Vita Enamic) with different surface roughnesses. Materials and Methods: PICN material specimens were polished with either silica carbide paper (grit-polished) or the manufacturer's polishing wheels (wheel-polished), and the surface roughness (R a ) measured. HGE cells were seeded and grown for 1, 3, or 6 days. Growth on tissue culture plastic was used as a control. Non-linear regression analysis was used to examine the effect of surface roughness on cell growth. Results: HGE cell growth on tissue culture plastic fitted an exponential growth model over the 6-day experimental period (R 2 = 0.966). Through day 6, cell density on PICN decreased with increasing surface roughness, with a fit to an exponential decay model (R 2 = 0.666). A threshold R a value of 0.254 µm (95% CI 0.177-0.332) was determined as an upper limit for exponential growth. Cell growth was greatest on the group of specimens with R a value below 0.127µm. Specimens polished by the manufacturer's method produced surface roughness of 0.118 µm and below. Conclusions: PICN material polished to a smooth surface (R a < 0.254 µm) resulted in exponential growth of HGE cell growth compared to rough surfaces. Polishing PICN material as smooth as possible (below a R a of 0.127 µm) was found to maximize epithelial cell growth on the PICN material surface. The manufacturer's polishing method achieved a sufficiently smooth surface. These results are contrary to previous research regarding surface roughness of transgingival implant restoration components. The study results suggest that smoother restorative material surfaces could improve peri-implant soft tissue health.