Several types of malocclusions exist, which are divided into four classes.
- Class 0 occlusions are normal. In most breeds, a class 0 occlusion is present when the maxillary incisors overlap the mandibular
incisors, and the incisal edges of the mandibular incisors rest on or near the cingulum of the maxillary incisors (scissor
bite).7 In addition, the mandibular cuspids should interdigitate between the maxillary cuspids and maxillary lateral incisors (Figure 6). However, brachycephalic breeds are considered class 0 with a mandible that is longer than the maxilla. This is also referred
to as a class 0, type III occlusion.8
- A class I malocclusion occurs when there is a normal jaw length but one or more teeth are out of alignment. Examples of class
I malocclusions include mesioclusion of a maxillary cuspid (lance effect) (Figure 7) and linguoversion of a mandibular cuspid (base narrow).
- A class II malocclusion, or overshot, exists when the maxilla is longer than the mandible (Figure 8).
- A class III malocclusion, or undershot, occurs when the mandible is longer than the maxilla (Figure 9). This occlusion is considered class 0, or normal, in brachycephalic breeds.
- A class IV malocclusion occurs when one mandible is longer and the other is shorter than the maxilla.7 Keep in mind that a wry bite, which is a jaw length discrepancy in which one of the mandibles is shorter than the other,
resulting in a shift of the mandibular midline (Figure 10), is typically a unilateral class II or III malocclusion.
Orthodontic problems arise from several different sources that can be genetic or nongenetic. In general, jaw length discrepancies
(class II, III, and IV) are considered genetic (unless there is obvious evidence of a local or systemic cause) and tooth discrepancies
(class I) are considered nongenetic. However, the increased incidence of lance effect in Shetland sheepdogs and base narrow
in standard poodles makes a genetic component likely in these cases.
Managing deciduous dentition malocclusions
Most malocclusions can be diagnosed early, since they are often present in the deciduous dentition. An oral examination will
reveal that the mandible and maxilla do not rest in the correct occlusion.
Depending on the class of malocclusion, palatine, gingival, or lip trauma may occur.5 The deciduous teeth (especially cuspids) are sharper than permanent teeth, so trauma and pain caused by deciduous teeth
are more intense and are more likely to be clinically evident than that caused by permanent teeth. Patients with malocclusions
often show no outward signs of distress. Regardless of the lack of clinical signs, if occlusal trauma is present, expedient
therapy is mandated.
In some cases, the patient may be genetically programmed for a normal bite and have only a temporary malocclusion. Temporary
malocclusions can occur since the maxilla and mandible may grow at varying rates during development because of an independent
mandible or maxilla growth surge.4
When the deciduous dentition is trapped by a tooth or the soft tissues on the opposite arcade, it may interfere with the jaw
movement and subsequent self-correction. This condition is called an adverse dental interlock (Figure 11).2
If occlusal trauma is present (Figure 12), extract the offending deciduous teeth expediently to minimize damage and discomfort.5 Even in the absence of occlusal trauma, extract the deciduous teeth to remove the adverse dental interlock and allow unrestricted
jaw movement. This technique is the most common interceptive orthodontic procedure and should be performed as soon as the
problem is noted (6 to 8 weeks of age) to allow the largest amount of normal jaw lengthening.5
Deciding which teeth to extract can be difficult. Obviously any tooth that is creating trauma should be extracted. When performing
pure interceptive orthodontics, extract the teeth of the jaw that needs to grow, but make sure to remove any hindrance to