Statement of Problem. Soft tissue health around an implant restoration is important in preventing infection of peri-implant tissues. There has been little investigation of the effect of surface roughness of implant restorations on gingival cell growth. 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. Material and Methods. PICN material samples were polished with either silica carbide paper(grit-polished) or the manufacturers polishing wheels (wheel polished), and the surface roughness (Ra) 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 six day experimental period (r2 = 0.966). Through Day 6, cell density on PICN decreased with increasing surface roughness, with a fit to an exponential decay model (r2 = 0.666). A threshold Ra value of 0.254 micrometers (95% CI 0.177-0.332) was determined as an upper limit for exponential growth. Samples polished by the manufacturers method produced surface roughness below 0.245 micrometers.