Delgado, E. (2009) “Tooth-whitening efficacy of custom tray-delivered 9% hydrogen peroxide and 20% carbamide peroxide during daytime use: A 14-day clinical trial”, Puerto Rico Health Sciences Journal, 26(4). Available at: https://prhsj.rcm.upr.edu/index.php/prhsj/article/view/225 (Accessed: 19 December 2025).