Anesthesia | Periodontal Disease | Extractions
Endodontics | Orthodontics | Neoplasia
Trauma | Dysphagia | The Feline Oral Cavity
Growth and development of the oral cavity does not just happen. There are a series of events that must occur in proper sequence or long term complications will occur. Understanding basic growth patterns in the oral cavity will help the veterinarian to know when to intervene to prevent further developmental defects. The term used is "interceptive orthodontics". Preventing major problems with early intervention is in the animal's best interest.
Developmental defects can be divided into three major staging periods. Each stage has its own set of problems thus requiring close inspection by the veterinarian. Stage One is from zero to sixteen weeks of age, Stage Two is from sixteen weeks to seven months of age, and Stage Three is from seven months to one and a half years of age.
Both the feline and canine species are born with "overshot" maxilla's (brachygnathism). This configuration allows the neonatal animals to nurse. As the animal grows and the impending transition from the mother's milk to solid food occurs, the mandible goes through a growth spurt nearly catching up to its relative adult percentage of jaw length. If this spurt does not occur and the deciduous dentition erupts the mandibular canines will most likely be distal (behind) to the maxillary canines. This immediately creates a malocclusion with the potential for inhibiting any chance for the mandible to catch up and seek its proper length. If this occlusal pattern is noticed in a puppy or kitten the best therapy is to remove the mandibular canine teeth (cautiously so as not to damage the permanent tooth bud). If the mandibular incisors are excessive in length and occluded behind the dental papilla the mandibular incisors are extracted using the same care. As a result, the mandible will have the opportunity to catch up to its genetic potential thus averting problems with the permanent dentition. If the animal is genetically predetermined to have a significant overbite this therapy will not affect the outcome.
The other defect to watch for is an "underbite" (prognathism). This occurs when the mandible grows ahead of schedule and becomes too long for the maxilla. This condition becomes evident as early as eight weeks of age. It is characterized by the maxillary incisors occluding inside the mandibular incisors and the mandibular canines occluding up to or even mesial to the maxillary lateral incisors. The treatment of choice is to extract (with care) the maxillary central and middle incisors. As a rule the maxillary lateral incisors are preserved, especially if they are acting as a deterrent to growth to the mandible. The prognosis for the permanent dentition to be within normal limits is not as favorable as for brachygnathism. However, early intervention is the best hope for the animal. Other congenital and developmental problems that require intervention include polydontia (extract the extra teeth) or gross displacement of a deciduous tooth (extract the tooth if it is causing mechanical interference). Asymmetry of maxilla and or mandibular growth is dealt with by extracting the teeth on the affected (underdeveloped) side. Asymmetry problems usually carry a poor prognosis for correction but are dealt with to give the animal every opportunity for "self correction."
The hallmark of problems in this stage is the retention of deciduous teeth. The normal shedding process begins around fourteen weeks of age with the loss of the maxillary central incisors. Then for the next three months the deciduous teeth are replaced with permanent teeth plus additional permanents to complete the animal's dentition. If the deciduous teeth are not lost at the time of eruption of the counterpart permanent tooth, a malocclusion occurs. No two teeth can occupy the same alveolus at the same time so by definition the permanent tooth is always in malocclusion. Obviously the treatment of choice is to extract the deciduous tooth the minute retention becomes evident. Only in rare circumstances will an error be made by removing a deciduous tooth. The phrase "when in doubt whip it out" is a good rule of thumb.
Multiple Retained Deciduous Teeth
Other developmental defects that occur in this stage include lingualversion of the mandibular canine teeth, rostralversion of the maxillary canines, and brachygnathism. When the canine teeth have finished erupting a window of opportunity exists for simple orthodontic correction of lingual displacement of the mandibular canine teeth with a maxillary bite plate. Because the oral skeletal system is developing at a rapid rate at six to seven months of age orthodontic appliances can only be left in an animal's mouth for two to three weeks at a time. Thus, any therapy must be accomplished in this short period of time. Rostralversion of the maxillary canines typically occurs in the Sheltie breed of dogs, although it has been reported in many small breeds as well as cats. If orthodontics are to be attempted, it is best to wait for the animal to finish growing for as long as possible. The distal dentition does not mature until at least ten months of age so this is the minimum age for the beginning of orthodontic therapy. If attempted, buttons, brackets and masial chain are the materials of choice. And finally, brachygnathism is dealt with using temporary maxillary bite plates if the degree of brachygnathism is minimal. If the brachygnathism is severe (mandibular canine occluding on the palatal side of the maxillary canine) other options are considered, such as crown reduction of the mandibular canines or extraction of the maxillary canines.
The final stage of developmental occlusal defects occurs from seven months to eighteen months of age. Anterior crossbites (incisors in reverse scissors) and posterior crossbites (carnassial teeth in reverse position), crowding, tooth rotation along with the final expressions of prognathism and brachygnathism are evident. Anterior crossbites can be dealt with if the remaining dentition is within normal limits (most anterior crossbites are a result of prognathism) using maxillary expansion screw splints or other accepted orthodontic treatments. Posterior crossbites are best dealt with by extracting the maxillary fourth premolar. If othodontic treatment is attempted a very cooperative animal and owner are mandatory. Crowding of teeth (large teeth-small space) is resolved by extracting the offending teeth. Likewise, teeth that are rotated greater than forty five degrees (often found in brachycephalic breeds) are removed from the animal. If there is any doubt as to which teeth to remove, remember the phrase "establish normal anatomy" and few errors will be made.
In conclusion, orthodontic problems can be dealt with at a practical level by extracting unhealthy teeth. While many malocclusions are not unhealthy (i.e. simple anterior crossbites) thus being more of a concern for a "show dog" many unhealthy malocclusions can be solved with a set of elevators and high speed burs (rostralversion maxillary canines). In the final analysis, interceptive orthodontics is the best recommendation following the old adage that "an ounce of prevention is worth a pound of cure." For those animals with correctable defects, orthodontics is an option for many companion animal owners.
Displaced upper canine tooth
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