Functional occlusion: I'm OK, but are your patients, really?

Functional occlusion: I'm OK, but are your patients, really?

Apr 01, 2007

I hung up the receiver after explaining to one of my clients why his "normally" undershot Shih Tzu's maxillary incisors needed be removed because they were penetrating the mandibular gingiva.

How could this perfectly "normal" dog be abnormal?

A book I read many years ago, titled "I'm OK, you're OK" (Thomas A. Harris, 1973) seemed to apply to breeds and the problems unique to each animal. Harris theorized there are four types of relationships between people or organizations:

  • I'm OK, you're OK. Both parties are normal and functioning well.
  • I'm OK, you're not OK. You or your organization is well but the opposite party is not. It will create problems that need attention.
  • I'm not OK, you're OK. You or the organization has the problem. The opposite side is fine and expected to stay that way.
  • I'm not OK, you're not OK. Both sides have significant problems that interfere with their relationship.

How does this apply to orthodontics?

As soon as you find an orthodontic abnormality, you first need to determine if it is a functional problem. Can the dog or cat expect to live a pain-free life if nothing is done to correct the problem? If the answer is yes, then the abnormality should be followed in the future to make sure it does not revert. If the answer is the condition is non-functional, then the tooth or teeth needs to be removed or repaired.

Let's apply some of these orthodontic conditions to the I'm OK, you're OK theory:

Fully functional

There are three types of head types: mesocephalic (also called mesaticephalic) typical of Beagles, terriers, German Shepherds, where the caudal surface of the maxillary incisors just touch the rostral surface of the mandibular incisors (Photos 1, 2 and 3), brachycephalic found in flat nose breeds (Bulldogs, Pugs, Persians) where the maxillary incisors are behind the mandibular incisors and do not touch them (Photos 4, 5 and 6); and the dolichocephalic or long- and narrow-faced breeds typified by the Greyhound, Saluki and Siamese, where there is a scissor bite and a longer muzzle compared to the mesocephalic breeds (Photos 7, 8 and 9). Even though brachycephalic mouths do not look normal, they are functional and if maintained properly will not cause the dog or cat pain or disease.

Normal for breed but not functional

In this situation, the dog or cat has a normal bite as called for in American Kennel Club breed standards ( But the occlusion creates a painful condition for the animal (Photos 10, 11, p. 18S). Unfortunately, the scenario is becoming more of an issue in companion-animal practice where breeders are mating two breeds that may look cute when combined have a non-functional occlusion. Case in point is the widely popular Puggle (Pug and Beagle cross) that combines two dogs with functional occlusion and creates one which often immediately needs multiple incisors extracted due to interference.

Functional; no therapy indicated

Here the dental or skeletal malocclusion is abnormal but there is no apparent cause for alarm because damage is not occurring or destined to occur. In most cases of mandibular brachygnathias (mandibular distoclusion, overbite, overjet) the mandibular canine penetrates into the maxillary gingiva necessitating intervention.