Yes, they do need a proper UVB light or they can get MBD one day even as adults. I recommend taking the Tegu outside ( on a reptile leash ) in the summer time. Natural sunlight is the best for the Tegu. It's hard to sex a Tegu when it's still very small. But when it's about 6 months old or a bit older and it's a male you can feel some pumbs ( beads ) under the vent. One on each side ( at the end ) of the vent. The females don't have that. The females also have a bit of a longer nose and not as wide of a head as the males do. The females also grow a lot slower.

http://www.anapsid.org/mbd.html