The in-vitro tests to assess the biocompatibility of materials used in humans, giving a quantifiable effect of approximation of the materials onto human tissues. The cytotoxicity of Filtek™ Z-350 over human gingival fibroblasts was evaluated, by a colorimetric analysis to determine cell lysis by the activity of lactate dehydrogenase and cell proliferation via XTT kit, assay was performed using as a benchmark the Triton X-100 which is a toxic agent. Analysis at 6 and 24 hours showed only 0.36% of the cells in contact with the resin had lysis, letting us to conclude, it is not cytotoxic, then is sure to be used in patients.