missing tooth

Question
Since the Australian Shepherd site is on vacation I hope I can ask this question on this site.  I have an 2 year old Aussie and a 2 year old Lab.  I discovered yesterday that the Aussie is missing one of her front bottom teeth.  She constantly pulls on the labs collar like she is playing tug-of-war.  Do you think a tooth can be pulled out doing that or do you think there is another problem.  Both are strong, healthy dogs.  They get feed well, etc.  There is no teeth decay or plaque.  Is there a chance that the teeth on each side of the missing tooth be in danger of getting loose because of the lack of the tooth?  Any help would be appreciated.  Thank you.

Answer
Sure, it's very possible the dog ripped a tooth out while tugging on the others collar.  I've had a dog break a healthy tooth on a rubber bumper.  They are SOFT!  Go figure.  

The other teeth should be fine.  

You MAY want to consider keeping collars off the dogs when they are home, as long as they play/run in a safe confined area.