About a year ago my little buddy Ivan broke his larger premolar on his left side. I was shocked and very upset when I discovered it simply because of how much it must have been hurting him since it went right to the pulp chamber. I brought him to his Vet and within a week got him into surgery and had the remaining part of the tooth removed. My next thought though was how did this happen? Ivan is a very well behaved and laid back corgi who DOESN'T go around chewing on random objects in or out of the house. The only thing that he knows to chew on is his Nylabone (the hard ones, not the soft rubbery ones), but when I asked my Vet if this could have caused the fractured tooth she said "no".
For awhile I listened to my own gut and stopped giving him the bones, but Ivan seemed to miss chewing on them.
For a second time at a regular checkup I asked a different Vet if there was any link between the bone and his broken tooth and once again I got "no". Well yesterday when checking Ivan's teeth and about to give them some brushing I found that he broke the same premolar on the other side. Frankly, now I'm really pissed off at myself and my Vet. I can't help but feel like it was the Nylabone because I've never ever seen him chew on random objects like a chain-link fence, rocks, etc.

My question is has anyone else had a similar problem? is it common for the larger premolar to break? and could the Nylabone been hard enough for him to break a tooth on it?
Before anyone asks, Ivan's teeth were kept very clean for dog standards and had no buildup on either tooth before it broke. He was about 6 years old when he lost his first one and is now 7 years.

Thanks!