INTRODUCTION:The production of numerous types of materials for diverse uses in dentistry is a rapidly growing and researchintensive field. Although 3D printed resins are among the many materials utilized in prosthetic appliances today, research on their biocompatibility in long-term dental applications is limited. OBJECTIVE: Evaluation of cellular behavior of human gingival fibroblasts "HGFs" when put in contact with 3D photoinitiated printed resins and heat polymerized acrylic resin. METHODOLOGY: HGFs were isolated from attached keratinized gingival tissues from healthy patients who had crown lengthening procedures, cellular viability using MTT assay in response to 3D printed resin Dental LT Clear (FORM LABS), compared to Heatpolymerized acrylic resin (Acrostone)which was assessed throughout four-time intervals (24, 48, 72 and 168 hours). RESULTS: All groups' cell viability decreased over time, although with favorable cell viability of more than 90% and non-cytotoxicity. It was found to be significant among Heat polymerized acrylic resin (RG), while among Dental LT Clear (TG) the decrease in cell viability were statistically insignificant. The highest cell viability was found after 24 hours among all groups; however, the least viability was found after 48 hours among RG, and among TG after 72 hours. There was a non-statistical significant difference in cell viability after 168 hours. CONCLUSION: Throughout time intervals and for long term use, it was found that photoinitiated resin were less cytotoxic than heat polymerized acrylic resin but with no statistically significant difference.