Can you use a 9 / 10 speed chainring with an 8 speed chain?
Assuming you are talking about chainring (not sprocket), it should be fine. You should only be worry with an 8- or lower-speed chain on a 9- or more speed freehub.

http://en.wikibooks.org/wiki/Bicycles/Maintenance_and_Repair/Chains/Chain_sizes