I read with great interest the article by Nascimento et al in the May 2017 issue on the effects of adding an ammonium-based methacrylate to an experimental dental adhesive for bonding metal brackets. I appreciate the authors’ goal of preventing white spot lesions by the use of quaternary ammonium monomer. But an issue concerns me. Quaternary ammonium monomers are mainly used as wood preservatives, pesticides, and fungicides, since they exhibit a broad range of antimicrobial activity. The release of free ammonia from quaternary ammonium compounds happens in mixed aerobic cultures. Although the authors have regarded ammonium chloride from the monomer as a potential cause for the decreased bond strength, they did not address the percentage of release and its potential consequences. The toxicity of free ammonia in the oral cavity is well established. Moreover, the concentration of the monomer used in this study was higher compared with similar monomers used in previous studies, which the authors themselves noted. It will be greatly appreciated if the authors could throw some light on this potential hazard.