Methyl methacrylate (MMA) is used widely for basic material in dental clinics. One of them is cold curing resins acrylic for orthodontics removable appliance. MMA is potentially to have the character to irritate and give an allergic reaction to oral mucous. Previous study showed that MMA have an effect on mitochondrial dehydrogenase epithelial cells by loosing its hydrogen and tight on this enzyme. The influence of cold curing resins acrylic on DNA synthesis of oral mucous epithelial is not known until at present. The purpose of this in-vitro study is to examine the DNA synthesis of fibroblast cells BHK-21 induced MMA. The result of this study is to increase the DNA synthesis from the cell culture induced MMA monomer at an incubation time of 12 and 18 hours. Toxicity of MMA was proved to increase DNA synthesis because DNA has a more sensitive effect as a toxic material may cause a deviation of oral mucous.