ORTHODONTIC 101
Evaluating a Bite

©2001 Dr. Ira R. Luskin Diplomate AVDC
Bite evaluation starts before the mouth is even opened. The first step in this process is to observe the symmetry of the head, face, and dentition. An imaginary plane divides the head sagitally in order to evaluate right and left halves. The midpoints of the mandibular and maxillary dental arches should be centered over each other and should be in alignment with the midplane of the head. When viewed from the side, the muzzle of the Mesiocephalic (Shepherd Skull type) and Dolicocephalic (Collie skull type) has a slope of 75-80 degrees from maxilla to the mandible and should never approximate 90 degrees.

The next step is to count the teeth of the breed in question and compare it to the dental formula for the dog. There are 42 teeth in the mesiocephalic dog. Three incisors, 1 canine, 4 premolars, and 2 molars upper (3 molars lower) in each quadrant. Missing teeth or extra (supernumerary) are genetic faults! There are discrepancies between what the AKC breed standards think are acceptable versus a truly healthy bite.

The occlusal relationship of the incisors of a normal head type, like the mesiocephalic German shepherd dog, should be a smooth radius arc. View the maxillary incisors from below and the mandibular incisors from above, to determine if rotated or misplaced teeth versus a group of teeth are breaking this arc in an arch segment. In the second instance the dental malalignment is being caused by skeletal growth abnormalities (genetic bone growth disturbances). The normal incisor occlusion (when jaws closed) has the large cusps of the lower incisors occluding on or near the cingulum (enamel ridge on the lingual side of the upper incisors). The large cusps of the central incisors should be centered with each other. The second and third incisors lose their centered relationship and the large cusp of the third mandibular incisor should be in the interproximal space between the second and third maxillary incisors.
A seldom discussed, but a key factor in allowing the flap to heal, is the prevention of trauma by teeth from the opposing arch. This is of special importance when working with pedicle flaps to close anterior maxillary defects. The constant trauma of the lower canines can greatly influence the flaps healing. It is this author’s opinion that performing a crown reduction and vital pulpectomy of the mandibular canine teeth of the affected side will greatly enhance the flaps vitality. Although beyond the scope of this paper, the procedure is covered in depth in most small animal dental texts.

Incisal Tooth Relationship Canine Tooth Relationship
Premolar Relationship
The canine teeth relationship should be as follows: The mandibular canine tooth should occlude buccally to the gingiva of the maxilla and should be equidistant between the maxillary canine tooth and the maxillary third incisor. Remember that if you see already that the deciduous bite has the lower canines hitting palatally the adult mandibular canines will erupt more lingually (medially) to their deciduous counterparts and therefore create a worse “Base Narrow” condition. The most important criteria, in my opinion, for bite evaluation is the relationship of the premolars. The large cusp on the lower fourth premolar should equally divide the space between the upper third and fourth premolars. (Note, the large carnassial tooth in the maxilla is the 4th Premolar, the large carnassial tooth in the mandible is the 1st Molar) The lower Premolars should be directly in front of their maxillary counterparts. When viewed from the side, the interdigitating space of upper and lower premolars in occlusion should resemble a “Pinking Shear”.

Classes of Occlusion and their Sequella if Uncorrected:

Class I: Patients with class I occlusions have a normal occlusion in respect to both jaws being in proper length and premolar teeth in a normal mesiodistal location. Usually one or more anterior teeth out of alignment or rotated. The following are subcategories of the basic Class I:

  • Anterior Crossbite: One or more of the lower incisors occlude anterior to the upper incisors. Sequellae: abnormal wear, loss of periodontal support.
  • Posterior Crossbite: One or more lower premolars or molars occlude labially (toward the lip) to the upper premolars. Sequella abnormal chewing.
  • Base Narrow Canines: Lower canines hit the palate or other teeth. Sequellae: oro-nasal fistulization, periodontal abscess, dentigerous cyst formation secondary to incomplete dental eruption. Severe defect!!!
  • Rostroversion of Maxillary Canines: Upper canines are directed mesially (cranially) reducing the interdental space causing the lower canine to be traumatized and tipped labially. Sequellae: Upper lip trauma by the lower tipped canine and abnormal enamel attrition.

Class II: Synonyms for this condition are:Overshot (suffix “shot” always refers to the maxilla “bite” refers to the mandible) Underbite, Parrot Bite, Brachygnathism (mandibular) Prognathism (maxillary). This is a skeletal growth (genetic) disorder !! The animals have the lower premolars and molars positioned behind (distal) to the normal. Sequella: The lower canines cannot tip out and therefore will create holes in the palate similar to the “Base Narrow” condition.

Class III: Synonyms for this condition are: Undershot, Overbite, Mandibular Prognathism, Maxillary Brachygnathism, Level Bite!! ( Incisal cusps of the upper and lower meet tip to tip. This causes premature wear and a traumatic occlusion). Note that this condition is truly a genetic malocclusion irregardless of AKC acceptance. Once they allow this defect into a line the more extreme condition of reverse scissors, usually is difficult to breed out. Irregardless of whether the incisors are “scissor” if the lower canine sits on the lateral incisor of the maxilla and the lower premolars are more than one tooth width mesially to their maxillary counterpart, this is a class III malocclusion!!

Unclassified: Wry Bite An abnormal occlusion caused by a difference in length of the two maxillae and mandibles. This is considered to be a genetic jaw growth problem that can be associated with facial asymmetry. It can be also induced by facial trauma during the bone growth phase. When involving the maxillae it can be detected often by a deviation of all the incisors on the affected hemi jaw. Also a lack of continuity of the palatal rugae as they go from right to left sides.

As can be seen in this brief discussion of occlusion and malocclusion, the practitioner has within their powers of observation, the ability to diagnose and recommend treatment to their clients that can greatly impact the health of their pets. If this is not done, it can lead to subsequent costly therapeutic repairs. The most appropriate time for practitioner intervention is when these animals are in frequently for their general wellness exams and puppy vaccines. It is during the change from deciduous to adult teeth that oral examination is critical. Mal erupting or non erupting teeth can often be corrected efficiently through the appropriate interceptive orthodontic extraction techniques.