A note for other patients:
The doctor alerted me to the tooth wear caused by tennis balls (my dog's passion is chasing and chewing on tennis balls) and indicated that this wear was probably due to the grit the balls picked up. I looked into this with the following results:
1. I believe the wear is caused by the material a tennis ball is made of. It's essentially a fine grained scrub pad. Great for creating a durable tennis ball, but bad for dogs' teeth.
2. Chuck-it makes a durable, smooth rubber tennis ball - sized ball. It's a bit heavier than a tennis ball, but not much, and is flexible (hollow), so no risk of injuring the dog as a hard ball might do. They're available at pet stores and Target. They're expensive... around $10 for two... but worth it if it avoids wearing the dog's teeth down as a tennis ball does.
Many thanks for pointing this issue out before it became a significant health issue.