As cyccommute said, it's probably not worn at all. The big ring is deliberately designed to have shorter teeth in some sections to facilitate easy shifting up from the small ring.

When I worked in bike stores, customers would come in to ask about/complain about the short teeth on the big ring at least a few times per week. We'd just walk them over to the display bikes and point out that the big rings on all the brand new bikes had teeth that looked exactly the same as their ring.