Hey Bellebebe!
I just had my fourth Coppola treatment about a month ago (had four in the year + between Feb 2010 and April 2011) and would def recommend using additional protein in between treatments. I didn't do ANYTHING protein related to my hair between the first and third treatment which left it sorta mushy and made my ends snap like crazy. I did a hard protein between the third and fourth which I believe helped me retain length and strength a lil better. Just my .02
HTH n HHG