Universal adhesives are simplified systems that can be used both in etch-and-rinse or self-etching approaches. Due to the presence of functional monomers, usually 10-MDP, universal adhesives chemically bond to dental substrates [1]. This makes them an interesting alternative for use in deep cavities with a self-etching mode [2], [3], [4] because of their reduced etching potential and lower monomer diffusion into the pulp chamber compared to the etch-and-rinse strategy, triggering an inflammatory process [2], [4].

The toxicity of dental adhesives is influenced by several factors such as solvent type and content, monomer composition, and degree of conversion [5], [6], [7]. In this regard, the toxicity of universal adhesives was evaluated in previous studies, demonstrating contrasting results, with cell toxicity of some materials and reduced influence of others [7], [8]. Previous studies focused primarily on adhesive toxicity on gingival fibroblasts [8], mouse dental cells [9], mouse fibroblasts [10], and monocytes [11], [12]. However, to the best of our knowledge, there is no study evaluating the toxicity of adhesives on human dental pulp stem cells (hDPCs).

Considering that adhesive degree of conversion plays a crucial role in the evaluation of resin dental material properties [13], [14], [15], [16], including its cytotoxicity [17], this study provides insights about the toxicity of universal adhesives to the HDPSCs. Since the cited cells can be affected by the diffusion of adhesive components through the substrate, and consequently be involved in the host response to the adhesives, this study evaluated the toxicity and inflammatory profile of the hDPCs to universal adhesives. Additionally, the degree of conversion of the adhesives obtained with two different light-emitting diode (LED) curing units (one single-peak and one polywave) was determined, to verify the effect of degree of conversion on cell toxicity.