Chew toys and bones are the reason I got into dentistry! My first adventure into the scary world of dentistry came as a result of a dog that had broken its major chewing tooth with a hard plastic bone. I had never extracted such a large tooth before but the owners could not afford to refer to a specialist so I read up on it, discussed it with a local specialist who was gracious enough to walk me through it.
Since then, many courses later, that tooth is still the one I see on a regular basis and the causes most commonly are plastic bones, elk antlers, pigs hooves and other small and tough chew toys. It seems that the smaller diameter objects get wedged in the dog's jaws and when forceful chewing action happens, the whole outside of the tooth fractures off, the term is a slab fracture.
Large chewed objects seem to be able to prevent the slab fractures but still can be associated with damage. The larger firm objects will chip or wear down the teeth leading to permanent damage to the tooth. If the fracture is deep enough, extraction will be needed. Some have advocated a root canal or filling for these broken teeth but I do not find it possible to teach a dog not to chew so aggressively in the future.
If small bones and large bones both cause broken teeth (for a gallery of broken teeth pictures click here), what is there to chew? The safest bet is to only offer soft rubbery toys or bones. There are some pressure compressed chews that claim to be safe, and they may be. As far as I am concerned, many "dangerous" treats can be tolerated by many dogs, but who can tell what kind of chewer your pet is? Once the tooth is broken, its too late. My recommendation is to avoid any hard chews, period. The argument I hear all the time is "what about the chewing action, doesn't it keep the teeth clean?" Yes, I respond, sustained chewing of 20 minutes or more can reduce the plaque accumulation but brushing the teeth is much better! Most dogs will "crunch" through a biscuit so quickly that there is no benefit to oral health!
Acceptable chews are soft, pliable and easily digested if swallowed whole. Be careful of "rawhide" chews as they may indeed be raw, bringing a health risk for pets and people. My preferred chew is a rubber bone. Be careful however, many companies also make the harder plastic bones that keep me in business... Best bet is to brush your dog's teeth and then give an edible product that will not break the teeth.
Below is an excerpt from a video on puppy teething issues. In this clip I am discussing what can happen with hard chew toys on baby teeth. The reality is that even adult teeth are vulnerable to breaking for some dogs. For the full video on teething for puppies, 
check it out on youtube.
A quick word about tennis balls. Dogs love to play with balls but you must take care to make sure that the ball is not doing damage! Tennis balls are notorious for acting like sand paper and filing down a dogs front teeth from carrying it around all the time. Soccer balls are so tough that I have seen the incisors wear away in as little as a few months. If you notice any kind of wear on your pet's teeth, be sure to have it assessed by a veterinarian with dental expertise and try to identify the object causing the damage.
