Normal occlusion or malocclusion: that is the question (Proceedings)

Occlusion is a contact between the incising or masticating surfaces of the maxillary and mandibular teeth. Normal occlusion in the dog and cat is also known as a "scissors bite". The mandibular teeth should occlude lingual to the maxillary teeth. The mandibular incisor cusps should rest on the cingulum on the palatal side of the maxillary incisors. The mandibular canine crowns should lie equally between the maxillary third incisor and maxillary canine. The mandibular premolar crown tips should point to the interproximal spaces between the crowns of the maxillary premolars. Each mandibular premolar should be positioned rostral to the corresponding maxillary premolar.

Malocclusion is any deviation from normal occlusion which is not standard for that breed. Recognition of malocclusion is an important part of the oral exam. Patients with malocclusion may have difficulty chewing their food and/or significant oral pain from teeth impinging on soft tissue. The American Veterinary Dental College (AVDC) has categorized commonly found malocclusions. The goal of this lecture is a review of the signs and treatment options that are available to treat these malocclusions.

Types of malocclusion

Skeletal or jaw length malocclusion is found when the maxilla and mandible are abnormally positioned. The most common cause is hereditary due to line breeding to achieve a particular characteristic and the mating of parents with dissimilar jaw sizes and head shapes.

Dental or tooth malocclusion is found when you have normal relationship of the maxilla and mandible but the teeth are abnormally located.

     • Distoversion – when a tooth is in normal anatomical placement but angled distally

     • Mesioversion – when a tooth is in normal anatomical placement but angled mesially

     • Linguoversion – when a tooth is in normal anatomical placement but angled lingually

     • Labioversion – an incisor or canine tooth that is in normal anatomical placement but angled labially

     • Buccoversion – a premolar or molar tooth that is in normal anatomical placement but angled buccally

Other non-genetic causes of malocclusion are local disturbances such as trauma, early or delayed loss of primary teeth, cystic formation, bruxism or abnormal chewing. Systemic disturbances can also contribute, such as severe illness, nutritional or endocrine disorders.

Malocclusion of deciduous teeth

Some malocclusions involving deciduous teeth can be temporary or develop into a permanent problem. The most common malocclusion seen involving deciduous teeth is jaw length discrepancies. These patients are genetically programmed for a normal bite but are only temporarily maloccluded due to the fact that each mandible grows at a varying rate.

The most common malocclusion presentations seen in pediatric dentition is Class II – overshot, Class III – undershot, Base Narrow Mandibular Canines, Class II with Base Narrow Mandibular Canines. With these conditions the deciduous dentition can become trapped by a tooth or soft tissue on the opposite arcade which causes an adverse dental interlock. When dental interlock is present trauma to the soft tissues can occur causing pain and infection.

     • Standard treatment options for pediatric patients with malocclusion Is:

     • Extraction: if trauma is present to minimize the trauma.

     • Selective Extraction/Interceptive Orthodontics: If no trauma is present this is done to prevent adverse dental interlock to allow the mandible to grow freely. The extractions usually are done on the jaw that needs to grow. Extractions are ideally done at 4-8 weeks of age.

Classification of Malocclusion in the Dog

Class I – neutroclusion

On examination there is a normal maxillary/mandibular relationship, but one or more teeth is out of alignment. This condition is considered non-genetic although there are incidences of syndromes in certain breed such as mesiocclusion of the maxillary canines aka lance canines.

Class I malocclusion can be caused locally through lip, cheek or tongue pressure, cystic or neoplastic formation. Other causes could be systemic or endocrine disorders and lastly deciduous tooth retention. Deciduous tooth retention is caused by an improper eruption of the permanent tooth. This condition can cause trauma to the soft tissue and periodontal disease due to the crowding.

Common class I malocclusions

Lance effect canines/mesioversed maxillary canines

One or both maxillary canines are tipped in a mesial direction. This condition is considered non-genetic but certain breeds have shown predisposition such as Shetland Sheepdogs and Persians. Causes can be due to abnormal lip, cheek or tongue pressure or systemic or endocrine conditions. Rarely, there have been some cases where tugging on toys at a young age might be a cause.

This condition can be diagnosed as early as 6 months of age. A pseudopocket can form due to the crowding between the canine and the lateral incisor. On occasion occlusion with the maxillary canine may cause the mandibular canine to deflect buccally or labially. This can cause the upper lip to get caught and ulcers and pain could occur.

Treatment includes orthodontic movement of the maxillary canine into normal position. This treatment can take a long time and be costly. Coronal amputation involves lowering the height of the offending tooth and performing a vital pulpotomy procedure to protect the pulp. Lastly, the affected maxillary canine can be extracted. This could be beneficial to prevent periodontal disease in the area of lateral incisor.

Base narrow mandibular canines

One or both mandibular canines are tipped lingually. This condition causes the mandibular canines to occlude with the hard palate where trauma, oral pain and bleeding can occur. In some cases, an oronasal fistula can occur. This is a non-genetic condition but breed disposition has been seen in dolichocephalic breeds and Standard Poodles.

Improper eruption of the permanent canines has been found to be the cause along with a malpositioned first premolar or lateral incisor. This can be diagnosed as early as 6 months of age, but also can be seen in deciduous dentition.

Treatment includes many options. For a minor malocclusion, a small wedge of gingiva can be excised between the maxillary canine and third incisor to provide a guide for the mandibular canine to slide into proper position when the mouth is closed. Composite crown extensions can be placed on the mandibular canines to also help guide the tooth into place. Ball therapy is for those cases with a mild malocclusion. It works best on those patients who like to carry toys. A rubber ball that is just wide enough to sit on top of the lower canines is given to the patient to carry around. The downward pressure on the mandibular canines can help them move into proper position.

Orthodontic therapy involves placing an inclined plane attached to the upper canines and incisors made of dental acrylic or metal. A ramp for the mandibular canines is molded into the acrylic and when the patient bites down it guides the mandibular canine into place.

Coronal amputation of the mandibular canines with vital pulp therapy lowers the mandibular canines to a height that keeps it from occluding from the palate. These patients will need follow-up dental radiographs to make sure the teeth stay stable. Lastly, extraction of the mandibular canines is a treatment option.

Anterior cross bite

This condition occurs when one or more maxillary incisors are located rostral to the maxillary canines. The bite pressure may cause increased trauma to the misaligned teeth. Treatment can be extraction of the malpositioned teeth or the placement of an orthodontic device. The device is made up of an arch wire and elastics to pull the misaligned teeth into place.

Posterior cross bite

This condition occurs when one or more of the posterior mandibular premolars is located buccal to it's maxillary counterpart. This is a rare inherited condition found mostly in dolichocephalic breeds. This condition can cause trauma to the soft tissue or periodontal disease. Treatment includes extraction of the malpositioned teeth or crown amputation of the affected teeth with vital pulpotomy.

Class II – overshot, mandibular brachygnathism

This condition occurs due to a jaw length discrepancy. The mandible is abnormally short with the mandibular premolars distal to the maxillary premolars. It can be genetic disorder due to the variety of the size and structure of the maxilla and mandible and tooth sizes between the parents. Systemic infection, trauma at an early age and nutritional disorders can also play a role.

Linguoversion of the Mandibular Canines

Due to the shortness of the mandible, the mandibular canines sit medial to the maxillary canines. In this position the mandibular canines can strike the palate and cause trauma. This condition is commonly seen in Labradors and Rhodesian Ridgebacks. If this condition is found in the deciduous dentition the mandibular canines should be extracted. If this condition is found in the permanent dentition, coronal amputation with vital pulpotomy therapy is the most common. Extraction of the mandibular canines is also an option.

Class III – undershot, mandibular prognathism

This condition occurs due to a jaw length discrepancy in a non-brachycephalic breed. The mandible is longer than the maxilla. It can be a genetic disorder due to the variety of the size and structure of the maxilla and mandible and teeth between the parents. The degree of displacement can be mild or severe.

Level bite

This is seen when incisors meet edge to edge. This can cause significant wear to both the maxillary and mandibular incisors which can then lead to traumatic pulpitiis, trauma to the periodontal ligament, pulpal exposure, or early tooth loss. Orthodontic correction can be done to move the maxillary incisors forward.

Reverse scissor bite

The mandibular incisors occlude just in front of the maxillary incisors. Trauma can occur to the mandibular gingival from occlusion by the maxillary incisors. Calluses and ulcers can occur. No treatment is necessary if there is little to no trauma. If there is lip, tooth or gingival trauma, coronal amputation with vital pulpotomy can be performed. If the trauma is severe, orthodontic correction can be preformed to move the maxilla more rostrally and move the mandibular incisors distally.

Class IV – wry bite

This condition occurs due to a jaw length discrepancy involving the mandible. One of the mandibles is shorter than the other which causes a shift of the mandibular midline. This is considered a primarily genetic disorder, although trauma with bone scarring, severe infection and nutritional disorders can play a role. Clinical signs include trauma from the mandibular canines embedding into the lip, gingiva or palate.

If there is no soft tissue trauma, no treatment is necessary. If there is trauma, rule out the possibility of TMJ luxation or jaw fracture. Coronal amputation with a vital pulpotomy or extractions can be performed. If orthodontic correction is requested, genetic counseling is recommended. Orthodontic correction involves the use of an appliance to move the affected tooth into the right position.

Malocclusion in cats

While cats fall under the same classification description as dogs, there are some issues that are unique to the cat oral anatomy.

Cats are born with a mandibular mesioclusion which is closer to a level bite. This allows kittens to nurse. As kittens grow and start eating solid food, a maxillary growth spurt occurs which adjusts the occlusion to near normal.

Cat breeds that are mesocephalic or dolichocephalic do not have have problems accommodating all of their teeth. They have a "scissor" bite like their dog counterpart.

Class II – mandibular distoclusion

Mandibular arch occludes caudal to normal

Class III – mandibular mesioclusion

Mandibular arch occludes rostral to normal. This is often present in brachycephalic cats that have short, wide muzzles. This can cause trauma to the lips or gingival.

Ethics of performing veterinary orthodontics

The size and shape of the skull, the number of teeth and the position of teeth are genetically controlled.

The AKC does not allow a dog that has orthodontic care to compete in the show ring.

Patients that have pain or periodontal disease due to occlusal abnormalities deserve to have a bite that is more comfortable.

Clients that have agreed to orthodontic care must understand that there is potential injury to teeth and gingiva. Treatment can take months and the outcome of a functional bite is more common than a perfect bite.

Signed treatment releases must be signed.

Information about the normal occlusion of specific breeds can be found at the American Kennel Club website. www.akc.org/breeds/complete_breed_list.cfm

Bibliography

Bellows J. Oral pathology. In: Feline Dentistry: Oral Assessment, Treatment and Preventative Care. Wiley-Blackwell, Ames, 2010; 101-148.

Bellows J. Orthodontic equipment, materials, and techniques. In: Small Animal Dental Equipment, Materials and Technique: A Primer. Blackwell, Ames, 2004; 263-296.

Niemic BA. Pathology in the pediatric patient. In: Small Animal Dental, Oral and Maxillofacial Disease. Manson, London, 2010; 89-126.