VETERINARY ORTHODONTICS: KNOWING THE RIGHT BITE
Like most other disciplines within veterinary medicine, recognition of disease begins with familiarization of what normal looks like. Proper occlusion is important for several reasons in veterinary medicine for not only cosmetic reasons, but also for function and comfort. Probably the most important aspect of veterinary orthodontics and occlusion is functionality of a bite. If the bite is not functional, or is lacking, prehension of food and normal mastication may be altered. Comfort is also important in that our role, as veterinarians, is to help treat or prevent disease and ease suffering whenever possible. Some malocclusions may potentiate disease conditions such as periodontal disease, lead to chronic infections such as oro-nasal fistulas, or result in uncomfortable situations when chewing food or simply at rest. “Proper” occlusion depends on breed standards and what may be normal for one breed could be considered abnormal for another. For example the occlusion of a boxer can be considerably different than that allowed for a Doberman pincer.
WHAT IS NORMAL?
There are basically 6 points to evaluating the occlusion in most dogs:
1. The “scissor” incisor relationship
2. The canine interlock
3. The premolar interdigitation
4. Alignment of developmental grooves of the carnassial teeth
5. A consistent freeway space between arcades
6. Head symmetry
If you ask most people familiar with dog dentition what the proper occlusion for most breeds is, they typically will say a “scissor” occlusion. And, for the most part they are correct. What they mean is the incisor relationship should be in a scissor fashion. This means the six maxillary incisors should be slightly more forward and overlap the six mandibular incisors. In more specific terms, the cusp tips of the mandibular incisors should occlude or strike the cingulum or flat area on the backside (palatal side) of the maxillary incisors. Jaw length problems are usually most obvious here, and since jaw length is known to be a hereditary trait, this relationship is very important in those animals intended for breeding.
Proper canine interlock is very important in maintaining jaw length relationships. This is important from early in life with the deciduous (baby)teeth as the jaws are growing. The mandibular canine tooth should rest or occlude between the maxillary 3 rd incisor and the maxillary canine tooth. This creates an interlock situation that prevents one or the other jaw from overgrowing the other. Observant owners may recognize that around 4-5 months of age, a jaw length discrepancy develops shortly after the deciduous canines are shed, and before the permanent canines have time to erupt into full occlusion. Also, malocclusions such as base narrow mandibular canine teeth do not allow for a proper interlock, therefore releasing the jaws to grow at will. The ideal occlusion would be if there were equidistance between each of the teeth involved when held in occlusion.
One of the best indicators of jaw length relationship is the premolars. Both the interdigitation of the cusp tips of the premolars and the alignment of the developmental groove of the carnassial teeth show evidence of proper jaw length relationship. The cusp tips of the premolars should point to the interdental (diastema) space of the opposing premolars creating a “pinking shear” effect. If there is a shift in one or the other jaws, this effect will be altered. An even more precise measurement is the alignment of the developmental groove of the maxillary 4 th premolar with the same groove on the mandibular 1 st molar. Although not as sensitive an indicator to subtle jaw length discrepancies, this is a good visual tool to show differences in jaw lengths.
The last two points of evaluation are the space between the arches, and the symmetry of right and left sides. A consistent freeway space implies that the space between the upper and lower arch has a relatively even angle from caudal to rostral (back to front). This means there is no bowing of one or the other jaws. The head symmetry can best be evaluated from a rostral (front) perspective. The midline between the central incisors of the maxilla and mandible should line up and both left and right sides ideally should be mirror images of each other. Any alteration of these may indicate a wry occlusion.