DNS Setup Question

DNS for my public hosts is done by my ISP. I have set up internal dns
using the same domain name as my public domain. The internal dns server
has just my internal host A records.

My question is:

Is it o.k. to let my internal dns server use the named.ca file to do name
lookups on the Internet Root Servers or should I forward public lookups to
my ISPs name server? My firewall allows my internal name server to do
lookups on the Internet Root Servers.

Thanks,

Tom Naves