In the dental pulp extracellular matrix, the main macromolecules are collagenous proteins, non-collagenous proteins and proteoglycans. Regulated synthesis of the interstitial collagens, in particular, type I collagen, is important during development and wound healing but also in a number of pathological conditions. Tenascin is also a matrix protein highly expressed during development while it decreases in mature organs. Under pathological conditions such as infections and inflammation, during tumorigenesis and mechanical stress applied to cells in culture or tissue in vivo, the expression of tenascin is increased. In this study, HEMA, widely used in dentistry, ophthalmology and drug delivery, has been used to study its influence on the expression of procollagen alpha1 type I and tenascin proteins in the primary cultures of human pulp fibroblasts. Different concentrations of the resin monomer and different times of exposition were tested. The influence of HEMA on the cell viability was evaluated by means of an MTT assay while immunofluorescence and western blotting analysis were performed to detect possible interference with the presence and the synthesis of these proteins. We observed a strong reduction in cell viability in specimens treated for 96 h and 168 h, especially at concentrations of 1 and 3 mmol/L HEMA. Both immunofluorescence and western blotting analysis demonstrated a reduction of procollagen alpha1 type I protein and an overexpression of tenascin protein. Our results showed that long-term exposure and low concentrations of HEMA influence normal cell activity, such as the synthesis of some of the dental pulp extracellular matrix proteins.