Brook A. Niemiec, DVM, DAVDC, FAVD
There are four established classes of malocclusion. Class I malocclusions are defined as the patient having a normal maxillary/mandibular relationship; however, a tooth (or teeth) is out of alignment. Class II–IV malocclusions occur due to a discrepancy of the dentofacial proportions. Class II malocclusions are where the mandible is shorter than the maxilla and the mandibular canines are striking the palate. In class III malocclusions, the mandibular incisors and possibly canines are rostral to the maxillary incisors. A class IV malocclusion occurs when one mandible is longer than the maxilla and the other is shorter than the maxilla.
Class I malocclusions are typically considered nongenetic in origin. However, certain presentations are seen in specific breeds and therefore a genetic component is likely. Class II–IV malocclusions are considered genetic, especially class III.
Ethics of Treatment
The main goal of veterinary orthodontics is to provide the patient with a pain-free functional bite. However, it should be stressed that this does not necessarily mean a "perfect" bite. Orthodontia for purely cosmetic reasons is typically not recommended. This is for several reasons. First, orthodontic therapy generally requires several anesthesias, which is not in the patient's best interest. There is some discomfort associated with orthodontic movement. The possibility of iatrogenic complications is always present. And finally, camouflage orthodontics is unethical.
The jaw length discrepancies are most commonly seen in the deciduous dentition, whereas tooth alignment issues are usually normal in the deciduous and only present as a malocclusion in the permanent dentition.
In some cases, the patient may be genetically programmed for a normal bite and only temporarily maloccluded. In these cases, the alignment problem is typically mild. These temporary malocclusions occur when the jaws grow at varying rates during development. In many cases, the deciduous dentition is trapped by a tooth or the soft tissues on the opposite arcade, which interferes with programmed jaw growth and subsequent self-correction. This is called an adverse dental interlock.
Depending on the class of malocclusion, palatine/gingival/lip/tooth trauma may occur. One major difference between adult and deciduous malocclusions is the anatomy of the teeth involved. The deciduous teeth are much sharper than the corresponding permanent tooth. Therefore, trauma and pain are more intense initially so are more likely to be clinically evident early in the course of disease. This may result in pain or bleeding as the presenting complaint. However, patients will commonly show no outward signs of distress. Occlusal trauma is traumatic and painful, regardless of the lack of clinical signs; therefore, expedient therapy is mandated.
Dental radiographs of the surgical area are required prior to extraction. These radiographs will document the presence of the permanent dentition. The radiographs will also reveal the location and integrity of the permanent. Finally, the root structure of the deciduous will be elucidated.
If occlusal trauma is present, extraction of the offending deciduous teeth should be performed as quickly as possible to minimize the trauma and relieve the patient's discomfort. Even if there is no current occlusal trauma, selective extraction of the deciduous teeth should be performed to remove the adverse dental interlock and allow jaw movement. This is termed interceptive orthodontics.
Mesioversion of Maxillary Canines (Lance Effect)
Mesioversion of the maxillary canine is a malocclusion that occurs in a patient with normal jaw lengths, where one or both of the maxillary canines are tipped in the mesial direction. This is a class I malocclusion, typically considered nongenetic. However, the high incidence in certain breeds indicates a genetic predisposition. Shetland Sheepdogs and Persian cats are strongly overrepresented.
The patient's jaws are of the correct length, but the maxillary canine(s) are mesioversed. These canines are often infra-erupted, resulting in a pseudopocket, which may hasten the development of periodontal disease. In extreme cases, the tooth will contact the maxillary third incisor, worsening the periodontal disease in the area.
There are several options for treatment, including orthodontic movement of the tooth, coronal amputation and vital pulp therapy, or extraction.
Linguoversed (Base Narrow) Mandibular Canines
This is a class I malocclusion. In class I malocclusions, the patient has a normal maxillary/mandibular relationship; however, a tooth (or teeth) is out of alignment. In this case, the mandibular canines are linguoversed, resulting in palatine trauma.
This is classified as a class I malocclusion, and thus is classically considered nongenetic. However, due to the increased incidence in some breeds, the base narrow condition is often considered hereditary.
Another possible etiology is trauma (early in life) causing the tooth bud to be misaligned. A less common cause may be a cystic structure which has developed early in the patient's development. Finally, it has been reported that a malpositioned mandibular first premolar or lateral incisor can interfere with the normal eruption path. Patients with this condition generally do not show any clinical signs; however, oral pain and bleeding may be noted. The jaws are the correct length and in a scissors bite except for the canines being linguoversed. One or both mandibular canines will be out of alignment and causing palatine trauma. Regardless of the lack of clinical signs with base narrow canines, these patients are uncomfortable. Depending on the severity of misalignment, the malocclusion can result in severe palatine damage (on occasion causing an oronasal fistula) or periodontal damage to the maxillary canine.
There are numerous options for treatment of base narrow canines. These can be separated into two distinct categories: orthodontic movement of the tooth or removal of the source of trauma (via extraction or coronal amputation and vital pulp therapy).
If the malocclusion is minor and diagnosed early, a wedge of the maxillary gingiva can be removed to guide the tooth into the correct position. Orthodontic therapy has an excellent success rate for this condition. The most common means of achieving the desired movement is via an incline plane. If the owner desires a one-step therapy, it is best achieved via coronal amputation and vital pulp therapy. Alternatively, the tooth may be extracted, but due to the size of the tooth and the importance of the mandibular canines in tongue retention and aesthetics, this is generally not the treatment of choice.
Class II Malocclusions (Overjet)
These are considered a primarily genetic condition. Class II malocclusions occur due to a discrepancy of the dentofacial proportions. The mandible is shorter than the maxilla and the mandibular canines are striking the palate. Depending on the severity of the misalignment, a class II malocclusion can result in severe palatine damage (on occasion causing an oronasal fistula) or periodontal damage to the maxillary canine. The most common form of therapy is coronal amputation and vital pulp therapy of one or both of the mandibular canines. This is due to the fact that orthodontic correction is a challenge in these cases and is less traumatic than extraction.
Class III Malocclusion (Underjet)
Because this is a jaw length discrepancy, it is considered a genetic condition. In fact, this malocclusion is particularly genetic in nature in human beings, and is due to a discrepancy of the dentofacial proportions.
In most instances, this malocclusion is present in the deciduous dentition and occasionally interceptive orthodontics may have been attempted.
The patient will present with the mandibular incisors and possibly canines rostral to the maxillary incisors. This may cause tooth-to-tooth trauma resulting in attrition.
In most cases, there is no significant trauma associated with this malocclusion, and the problem is strictly cosmetic. When traumatic problems are seen with this malocclusion, they present as soft tissue trauma to the mandibular gingiva from the maxillary incisors. This often occurs distal to the teeth and causes transient pain. Over time, the body does appear to create a form of "callus" in the area. On occasion, however, contact may occur in the gingival sulcus and create periodontal inflammation and disease. In these cases, therapy is mandated. The most common reason for presentation results from the tooth-to-tooth contacts of the maxillary lateral incisors and mandibular canines. Depending on the severity of the discrepancy, this can result in significant attrition to the mandibular canines and may contribute to fracture of the tooth. Finally, in some cases this malocclusion may result in upper lip ulcers.
Many cases require no therapy, as there is minimal to no trauma present and no discomfort for the patient. If lip, tooth, or gingival trauma is present, then vital pulp therapy, extraction, or rarely orthodontic movement of the offending tooth or teeth should be performed.
Class IV Malocclusion (Wry Bite)
A wry bite is a jaw length discrepancy in which one of the mandibles is shorter than the other, resulting in a shift of the mandibular midline. A true class IV malocclusion occurs when one mandible is longer than the maxilla and the other is shorter than the maxilla. The remainder of wry bites are subsets of class II or III. Class IV malocclusions are jaw length discrepancies and therefore should be considered a primarily genetic condition.
Oral exam will reveal that the midline of the maxilla will not be even with the midline of the mandible. The uneven occlusion will result in one or both of the mandibular canines striking the soft tissue of the maxillary palate, gingiva, or lip.
The most common form of therapy is coronal amputation and vital pulp therapy of one or both of the mandibular canines. A second option for therapy if the malocclusion is mild is orthodontic therapy. The typical appliance created in these cases is an incline plane device. The final method of correction involves extraction of the tooth or teeth causing occlusal trauma. Due to the size of the tooth as well as the importance of the mandibular canines in tongue retention and aesthetics, this is generally not the treatment of choice.