https://scholar.google.com/scholar_lookup?title=Effect+of+Bleaching+Agents+on+Hardness,+Surface+Roughness+and+Color+Parameters+of+Dental+Enamel&author=de+Carvalho,+A.-C.-G.&author=de+Souza,+T.-F.&author=Liporoni,+P.-C.-S.&author=Pizi,+E.-C.-G.&author=Matuda,+L.-S.A.&author=Catelan,+A.&publication_year=2020&journal=J.+Clin.+Exp.+Dent.&volume=12&pages=e670–e675&doi=10.4317/jced.56913