In time excess plaque and calculus build up on the broken tooth resulting in asymmetry from one side of the mouth to the other. This is almost pathognomonic for local oral pain. Obviously individual pain thresholds vary. Some animals appear stoic with massive injuries and others scream in pain at the thought of a toe nail trim. Masked pain is the type most deceiving to owners and veterinarians.
Dogs are pack animals.
It has always been in their best interest to hide pain in the pack for fear of displacement in their social standing. Today the family unit is the pack but the evolutionary behavior persists. Also, animals that exhibited pain were consumed by predators because of appearing disabled. Minor pain is easy for animals to mask and since they can't talk to us its easy to overlook this problem. The same principles apply to cats although the species behavior tends to be more territorial than pack.