MALOCCLUSIONS – “IT DOESN’T BOTHER THE DOG!”
By Dr Wayne Fitzgerald- Dental surgeon
“But it isn’t worrying him.” … we hear these words all the time and what do you say when you know this just can’t be true?
Our patients are very good at masking pain, especially chronic pain. People generally can’t ignore their own pain, but can be pretty good at it if it isn’t theirs!
Dental malocclusions do cause discomfort, even significant pain, and generally result in some sort of pathology.
“In people, the main reason for treating malocclusion is cosmetic; in veterinary medicine however, the reason for performing orthodontic correction is to enhance function and prevent disease.” (Jan Bellows, 1999)
Affected animals often become defensive around their head making examination difficult; however, given time these may progress to hard or soft-tissue pathology and even loss of function. Malocclusions are most often hereditary but some such as a tipped tooth may be acquired. Trauma or illness (during a growth period of the jaw bones) may also alter these relationships by changing growth patterns producing a wry mouth or altered functions.
Humans introduced line- or in-breeding, later, these became established types and hence ‘breeds’. Malocclusions are primarily the result of inherited dento-facial proportions governed by breeding for a desired head shape.
Malocclusions may be produced by inheritance in 2 ways:
1. Inherited disproportion between the size of the teeth and the size of the jaws producing a crowded or abnormal spacing of the teeth, or
2. Inherited disproportion between the size or shape of the upper and lower jaws causing improper occlusal relationships.
Genetic isolation and uniformity as seen in wild dogs, rarely produce instances of malocclusion. When this group carries the same genetic information for tooth and jaw size, there is little possibility of individuals inheriting discordant characteristics. Genes that introduce disturbances into the jaws would tend to be eliminated from the population. The ‘typical” specimen has a normal scissor occlusion and tooth/jaw size discrepancies are infrequent as each tends to have the same jaw relationship.
When cross-breeding between distinct breeds occurs, malocclusions may develop. In 1941, this genetic problem was demonstrated by cross-breeding dogs and recording their body structure. It was believed that malocclusions occurred in cross-bred dogs more from jaw length or width discrepancies than from tooth/jaw size imbalances. However, the miniature dog breeds were examined where the latter is common. This research confirmed that “independent inheritance of facial characteristics is a major cause of malocclusion and the rapid increase in malocclusion accompanying urbanisation was probably the result of increased out-breeding.” That is, breeding between dissimilar dogs such as Basset Hounds and English Bulldogs, and we have seen the emergence of such ‘designer breeds in the last few decades.