Diplomate, American Board of Veterinary Practitioners
All Pets Dental Clinic
Pembroke Pines, Florida 33024
Orthodontics is the science of monitoring and malocclusions (abnormal spatial relationships). Orthodontic care in veterinary dentistry is not used solely for cosmetics but rather to provide a functional and pain-free mouth.
There are three basic anatomic categories of muzzle structures in dogs. Some breeds (Collie, Greyhound, Borzoi, Saluki, Whippet) have elongated facial profiles and are called dolichocephalics. On the other end of the spectrum are the brachycephalics (Pug, Boxer, Bulldog), which have flat facial profiles. The mesocephalics (Golden Retriever, Labrador Retriever, German Shepherd, Beagle) have medium- sized facial profiles.
The canine jaw enlarges in spurts, and each quadrant (right and left uppers and lowers) develops independently. It is important to monitor each dog's growth individually because malocclusions can develop suddenly (within days) or may quickly correct without need for intervention.
TYPES OF MALOCCLUSION
Malocclusions can develop as soon as the teeth erupt (deciduous or puppy malocclusion), once all the adult teeth have erupted (permanent or adult malocclusion), or when there is a combination of deciduous and permanent teeth involved in an abnormal bite (mixed malocclusion). Two additional types of malocclusion are also described: Dental malocclusion exists when the jaw bones are normal in size and rela- tionship but the teeth are malpositioned; skeletal malocclusion exists when the teeth are normal but the jaw bones are unequal. Most dental malocclusions are developmental, whereas most skeletal malocclusions are genetic. Dental malocclusions are easier to treat than are skeletal ones.
Many terms are used to categorize malocclusions. The "Angle" (named after Dr. Angle) classification defines five main categories of dental relationships:
*Class 0 is considered normal (i.e., orthoclusion; Figures 1 and 2).
-Type 1: True normal
-Type 2: Variant normal
-Type 3: Normal class III (brachycephalic breeds)
Figure 1 A Figure I B
Figure 1. Scissors bite. Note how the upper incisors lie just in front of the lower incisors.
Figure 2. Normal interdigitation of premolars. Note the lower Figure 3. Crowded left mandibular second and third incisors.
premolar crown tips point to the interspace between the upper
Figure 4. Overjet (Class 11 malocclusion). Figure 5. Undershot occlusion with lower canine in front
of lateral upper incisor.
*Class I malocclusion, also called neutroclusion, occurs when there is neither an overbite nor an underbite but nevertheless some or all of the teeth are malpositioned. There is a normal premolar/molar relationship, although there may be a slight shift in premolar orientation, such as 1/3 to 1/2 a tooth being in front of or behind its normal position. The lower posterior (cheek) teeth are directed in front of their counterparts, while the cusp tips point to the center of the opposing interproximal spaces. This is the single most important malocclusion that serious breeders need to detect because it contains very subtle changes in the dental relationship (Figure 3).
-Type 1: Anterior crossbite
-Type 2: Posterior crossbite
-Type 3: Facial (wide) cuspids
-Type 4: Lingual (base narrow) cuspids
-Type 5: Crowded or rotated teeth
*Class II malocclusion, also termed distoclusion, brachygnathism, retrusive mandible, pig mouth, overjet, or overshot jaw, occurs when some or all of the upper jaw teeth are located markedly in front of their lower jaw counterparts (Figure 4). The upper first premolar often will oppose the first lower premolar.
-Type 1: Short mandible (also known as mandibular brachygnathism, mandibular retrognathism, mandibular retrusion, wry bite)
-Type 2: Long maxilla (maxillary protrusion, maxillary prognathism, wry bite)
*Class III malocclusion (mesioclusion, prognathism, protrusive mandible, or undershot jaw) occurs when some or all of the upper jaw teeth are markedly positioned behind the lower jaw counterparts (Figure 5). The upper premolars are often situated behind their normal position, while the upper first premolar may oppose the lower second premolar.
*Class IV occlusion occurs when part of the jaw is in front of and part in back of the opposing jaw.
There are six criteria commonly used for bite evaluation in mesocephalic or dolichocephalic breeds:
• Incisor relationship-The upper incisors should normally overlap the lower jaw incisors, and the inside surface of the upper incisors should barely touch the front surface of the lower incisors. A level bite is acceptable in some breeds.
• Canine relationship-The lower canines should interdigitate in the interproximal space between the upper lateral incisors and upper canine teeth. There should be no contact between the lower canine and either upper tooth.
• Premolar interdigitation-The cusps of the second lower premolars should point directly into the interproximal spaces between the first and second premolars. The third lower Premolars should point between the upper second and third premolars. The space between the upper and lower cusps should be level. The cusps of the upper fourth premolars should be lateral to the lower first molars.
Figure 6. Normal fourth premolar relationship. Figure 7. Anterior crossbite with the right upper central
incisor in reverse scissors bite.
Figure 8. Posterior crossbite in which the lower first Figure 9. Misdirected upper canine tooth.
Molar is abnormally located in the outside of the
upper forth premolar.
Figure 10. Level bite. Note abnormal wear pattern on Figure 11. Base narrow canines. Note the lower canine penetrating the opposing incisers. upper palate.
•Lower fourth premolar relationship-The cusp of the lower fourth premolar should be centered between the upper third and fourth premolars (Figure 6).
•Head symmetry-Perfect symmetry of the head, nasal cavity, and dentition is expected. A deviation in the growth to one side or the other is a sign of wry mouth.
•Temporal mandibular joint angle-The coronoid process and the lower jaw should form a right angle. If this angle is less than 90 degrees, there is a tendency for the jaw to be overshot; if the angle is greater than 90 degrees, there is a tendency for an undershot jaw.
The following terms and phrases are used to describe dental abnormalities:
*Anterior crossbite-A common malocclusion in which one or more of the upper incisors develop in a reverse scissors orientation. The premolar relationship should be normal. This condition can be caused by trauma from tug-of-war games, retained baby teeth, or impacted roots. It is not considered a genetic or inherited defect (Figure 7).
*Posterior crossbite-One or more of the maxillary premolars or molars occlude inside the mandibular premolars or molars rather than in the normal position on the outside (Figure 8).
*Displacement-A tooth's crown and root have moved in the same direction to lodge in an abnormal position in the mouth. Mesial displacement occurs when a tooth is displaced toward the midline of the arch and distal displacement when the tooth moves away from the midline of the arch. Lingual displacement occurs when tooth movement is directed towards the tongue. Facial displacement describes movement of a tooth away from the tongue (Figure 9).
*Level bite-incisor teeth meet edge to edge or premolars meet cusp to cusp. A level bite is actually an expression of a class III malocclusion. Even though this is an acceptable bite in some breeds, it can cause abnormal wear of the incisal (cutting) edge of opposing incisor teeth. The continual trauma that results from the incisal edges rubbing against each other can create inflammation around the tooth roots. Level bites can predispose a dog to periodontal disease and eventual tooth loss (Figure 10).
*Lingually displaced mandibular canine teeth (also called base narrow canines)-Usually occur when deciduous teeth are retained but can also develop when the lower jaw is shorter than the upper jaw. In this condition the lower canines frequently penetrate the upper palate. If left untreated, the condition can progress to form a permanent hole between the oral and nasal cavities (Figure 11).
*Open bite-An area in the mouth where a space is created by malocclusion. The teeth will not meet properly when the mouth is closed (Figures 12 to 14).
Figure 12. Open bite caused by undershot jaw. Figure 14. Extraction of upper incisor, leaving room for canine and therefore eliminating open bite.
Figure 13. Lower canine interfering with upper Figure 15. Underbite.
incisor, creating an open bite.
Figure 16. Wry bite. Note triangular defect in the incisor area.
•Overbite (vertical overlap)-The upper teeth vertically extend over the lower teeth. What is commonly referred to as an overbite is really an overjet.
•Overjet (horizontal overlap)-The upper teeth horizontally extend over the lower teeth. The upper premolars are displaced at least 25% further forward when com- pared with the lower premolars. An overjet malocclusion is never considered normal in any breed and is a genetic fault. The most commonly affected breeds are those with elongated muzzles (Collies, Shetland Sheepdogs, Dachshunds, and Borzoi).
•Rotated tooth-One or more teeth may rotate on their long axis toward or away from the tongue.
*Scissors bite (normal occlusion in doliochocephalic and mesocephalic skull breeds)-Typified by lower incisors resting on the inside surface of the upper incisors. There is a smooth curve from canine to canine without misplaced or rotated teeth. The lower canines should lie exactly between the upper lateral incisors and upper canines without touching either. Premolar crown tips should point to a space between the crowns of the opposing premolars. A reverse scissors bite exists when the lower incisors are located in front of the upper incisors. The lower canines and premolars will also be shifted forward.
• Shortened tooth-The biting edge of the tooth has not reached normal height. Partial impaction is a common cause.
• Underbite-Class III malocclusion. Some short-muzzled breeds (Boxer, Bulldog, Shih Tzu, Lhasa Apso) normally have an underbite; when it occurs in medium- or long-muzzled breeds, it is considered abnormal (Figure 15).
• Wry mouth or wry bite-One side of the jaw grows differently than the other. Wry bites appear as triangular defects in the incisor area. Some of the incisors will meet their opposing counterparts while others will not. Wry bite is a severe, inherited defect (Figure 16).
WHAT CAUSES MALOCCLUSIONS?
There are numerous genetic and nongenetic reasons for teeth to appear abnormally in the mouth. About half of the malocclusions are developmental rather than genetic.
Genetic defects cause skeletal length abnormalities (overbite, underbite, wry bite) and atypical tooth sizes. Various genes determine the shape, size, and exact location of each tooth as well as shape and size of the jaws. Defects affecting individual tooth direction may or may not be related to genetic inheritance. In the puppy the lower jaw grows forward faster than does the upper jaw. For a puppy to be mildly overshot at a young age is of minimal concern; in fact, it is preferable. By the time the dog reaches maturity, the bite will usually be normal.
It is believed that small animal genetic malocclusions are inherited as recessive traits with incomplete penetrance. This means that even animals that are homozygous for the recessive trait of malocclusion may not exhibit the defect and such deviations may not be seen in every generation. It takes at least five defect-free generations to ensure that a malocclusion has been eliminated from a certain line.
Congenital malocclusions can occur during pregnancy and the postnatal period. Causes of congenital malocclusions include traumatic whelping, infectious diseases, glandular abnormalities, suckling habits, and trauma.
Many nongenetic developmental defects are the result of retained puppy (deciduous) teeth. When a retained puppy tooth remains in the same socket as a permanent tooth, the permanent tooth is forced out of its normal position. This is a common but treatable problem. Examples of malocclusions caused by retained puppy teeth include lingually or rostrally deviated canines and anterior crossbites (Figure 17).
Humans with poor dental appearance due to irregular teeth or discrepancies of upper and lower jaw position will suffer from social prejudice. The primary reason for treating malocclusions in humans is therefore cosmetic, although straightening teeth will help prevent periodontal disease. In dogs and cats, however, orthodontic correction is performed to enhance function and prevent disease. Poorly aligned teeth can traumatically impinge on gum tissues, causing damage and discomfort. Crooked and crowded teeth accumulate debris, which increase the likelihood of periodontal disease.
Malocclusions can be corrected at any age, but, as a rule, the younger the patient, the faster the alteration will be completed. Malocclusion repair can be divided into three general categories: preventative, interceptive, and corrective.
Extraction of the baby canines and/or incisors before problems become apparent can aid in pre- venting malocclusion. This is especially true in toy breeds (Yorkshire, Maltese, etc.), which have an increased likelihood of problems due to retained puppy teeth.
Figure 17. Retained baby upper canine, causing Figure 18. Elastics placed around lower incisors and canines.
A common procedure performed by some breeders is to "trim" the puppy teeth in hopes that they will be shed early, thus preventing orthodontic problems. However, by cutting the tooth in half, nerve and blood supplies are exposed to the oral environment, which eventually causes infection and tooth loss. Additionally, this procedure is not recommended because it causes pain for the animal and, potential for infection that can affect adjoining adult teeth. To remove puppy teeth properly, the puppy is anesthetized and the entire tooth is carefully extracted under sterile conditions by a licensed veterinarian.
Interceptive orthodontics is employed when teeth begin erupting. Removal of baby incisors prior to their normal time of exfoliation may allow the permanent incisors to advance normally without interference from the baby teeth.
During development of the mouth, independent growth of both jaws may be affected by environmental or internal nongenetic factors. In breeds in which scissors bites are normal, the upper jaw may interlock if the upper incisors become trapped behind the lower ones. Since puppies sleep most of the time with the jaw closed at rest, the lower jaw, which continues to grow at the same rate as the upper jaw, prevents independent growth. Using interceptive orthodontics, the interfering front teeth (varying from 2 canines to all 16 teeth) are extracted as soon as the problem is detected or, ideally, before the dog is 4 months old.
Interceptive orthodontics does not stimulate jaw growth but rather removes interference, allowing previously interlocked growth to catch up. Unfortunately, it will not cure a preexisting genetic problem.
Corrective orthodontics refers to the controlled movement of malpositioned teeth and their attachment apparatus through bone. The best way to achieve this is through light, continuous force applied at least 6 hours daily. Corrective orthodontics has active and retention phases. The active phase uses devices (appliances) to move teeth. Once the active phase is completed, retention is usually achieved by opposing teeth; however, a retainer device is sometimes employed.
Orthodontic appliances can be attached to one or more teeth to direct them into functional occlusion. Some appliances function by pulling abnormal teeth into normal location with elastics, buttons, hooks, and brackets. With the use of such appliances, teeth can usually be saved and returned to their normal anatomy (as opposed to extraction or crown reduction).
Pet owners often apply elastic ligatures around the canines and incisors in hopes of moving teeth back into a normal occlusion. The uncontrolled, constant pressure of elastics around the gumline, however, may cause mobile teeth that move but usually will not remain in the desired location. Additionally, such teeth are often lost due to the resulting periodontal disease. Orthodontic care by a trained veterinarian spares the gingiva from direct ligature trauma (Figure 18).
Figure 19. Class III occlusion (undershot). Figure 20. Ulcers on lower jaw caused by undershot upper jaw.
Figure 21. Extraction of crowded lower incisors and crown Figure 22. Orthodontic stone model displaying anterior reduction of upper incisors to relieve trauma to lower jaw. crossbite.
Figure 23. Fixed orthodontic appliance used to pull teeth Figure 24. Corrected anterior crossbite after 3 months.
into normal occlusion.
Figure 25. Inclined plane to correct base narrow canines. Figure 26. Flostrally deviated canine tooth causing lateral displacement of lower ca- nines.
Figure 27. Corrected rostrally upper deviated canine after elastic application.
Repairing Specific Abnormalities
Skeletal malocclusions (overbite, underbite) are often treated by reducing the height of interfering teeth to decrease trauma to the gums. After reducing tooth height, protective medication is placed on the pulp and acrylic bonding is applied to seal and restore the tooth to normal function (Figures 19 to 21).
Anterior Crossbite and Level Bite
Anterior crossbites and level bites can be corrected with expansion de- vices placed on the palate behind the incisors or with a wire arch placed in front of the incisors with elastics to pull the affected incisor(s) into normal occlusion. Premolar relationship creating the malocclusion should be evaluated for genetic causes before therapy. If only the incisors are involved and all other occlusal parameters are normal, retained baby teeth or trauma are probable causes and therapy should be instituted (Figures 22 to 24).
Base Narrow Teeth
Base narrow deflection of the lower canine teeth can be repaired using inclined planes inserted on the hard palate between the upper canines. The deviated lower canine(s) moves slowly to a functional position after repeated contacts with the incline. The appliance should be made with a telescoping attachment to allow for the pup's skull growth (Figure 25).
Rostrally Displaced Canine Teeth
Rostrally displaced canine teeth are commonly corrected with power chains and direct bond brackets. To reposition teeth, removable lingual buttons are cemented to the canine, upper fourth premolar, and first molar. An elastic chain is placed between the buttons. In time the canine is pulled back to normal occlusion (Figures 26 and 27).
AMERICAN KENNEL CLUB STANDARDS RELATING TO DENTAL CORRECTIONS
A dog is considered "changed in appearance by artificial means" if it has been subjected to any type of procedure that has the effect of obscuring, disguising, or eliminating any congenital or hereditary abnormality or any undesirable characteristic or that does anything to improve a dog's natural appearance, temperament, bite, or gait.
Even procedures that are absolutely necessary to the health and comfort of a dog shall disqualify that dog from competition if the former had the incidental effect of changing or even improving the dog's appearance, bite, or gait. Other kennel club standards should be consulted for variations.
Breed Dental Specification Supplied by the American Kennel Cluba
Compiled by Jan Bellows, DVM
Affenpinscher-undershot bite with lower teeth closing closely in front of upper teeth. Level bite is acceptable if the monkey-like expression is maintained. Teeth and tongue should not show when the mouth is closed.
Lower jaw should be broad enough for the lower teeth to be straight and even
Afghan Hound-mouth should be level (i.e., the teeth from the upper jaw and lower jaw match evenly-, i.e. neither overshot nor undershot). This is a difficult mouth to breed. A scissors bite can be more easily bred into a dog than can a level mouth; a dog that has a scissors bite, where the lower teeth slip inside and rest against the teeth of the upper jaw, should not be penalized
Airedale Terrier-teeth should be white and free from discoloration or defect. Bite should be either level or vise- like. A slightly overlapping or scissors bite is permissible without preference
Akita-scissors bite preferred; level bite acceptable Alaskan Malamute-upper and lower jaws should be broad with large teeth, and incisors should meet with a scissors grip. Overshot or undershot is a fault
aInformation from the American Kennel Club Web site: www.akc.org.
American Cocker Spaniel-teeth should be sound and not too small and should meet in a scissors bite
American Eskimo Dog-scissors bite. Jaw should be strong with a full complement of close-fitting teeth American Foxhound-teeth must meet squarely. Overshot or undershot jaw is a disqualification
American Staffordshire Terrier-upper teeth should meet tightly outside lower teeth. Undershot and overshot mouths are faults
American Water Spaniel-scissors or level bite
Anatolian Shepherd-teeth and gums should be strong and healthy. Scissors bite preferred; level bite acceptable. Broken teeth are not to be faulted. Overshot, undershot, or wry bite are disqualifications
Australian Cattle Dog-teeth should be sound, strong, and regularly spaced and should grip with a scissors-like action. The lower incisors should be close behind and just touching the uppers. Should not be undershot or overshot
Australian Terrier-scissors bite with teeth of good size
Australian Shepherd-full complement of strong white teeth should meet in a scissors bite or may meet in a level bite. Disqualifications include undershot or overshot greater than 1/8 inch. Loss of contact caused by short center incisors in an otherwise correct bite shall not be judged undershot. Teeth broken or missing by accident shall not be penalized
Basenji-evenly aligned teeth in a scissors bite
Basset Hound-teeth should be large, sound, and regular and should meet in either a scissors or even bite. Overshot or undershot bite is a serious fault
Bearded Collie-teeth should be strong and white and should meet in a scissors bite. Full dentition is desirable
Bedlington Terrier-large, strong, and white teeth. Level or scissors bite. Lower canines should clasp the outer surface of the upper gum just in front of the upper canines. Upper premolars and molars should lie outside those of the lower jaw
Belgian Malinois-a full complement of strong, white teeth should be evenly set and should meet in a scissors or level bite. Overshot and undershot bites are a fault. An undershot bite in which two or more of the upper incisors lose contact with two or more of the lower incisors is a disqualification. One or more missing teeth is a serious fault
Belgian Sheepdog-full complement of strong, white teeth should be evenly set. Should not be overshot or undershot. Should have either an even bite or a scissors bite
Belgian Tervuren-full complement of strong white teeth, evenly set, meeting in a scissors or a level bite. Overshot and undershot teeth are a fault. Undershot teeth such that contact with the upper incisors is lost by two or more of the lower incisors is a disqualification. Loss of contact caused by short center incisors in an otherwise correct bite shall not be judged undershot. Broken or discolored teeth should not be penalized. Missing teeth are a fault
Bernese Mountain Dog-upper and lower jaws should be broad with large teeth. The incisors should meet with a scissors grip. Overshot or undershot is a fault
Bichon Frise-scissors bite. Undershot or overshot is severely penalized. A crooked or out-of-line tooth is permissible; missing teeth are severely faulted
Black and Tan Coonhound-teeth should fit evenly with scissors bite. Excessive deviation from scissors bite is penalized
Bloodhound-teeth should fit evenly with scissors bite. Excessive deviation from scissors bite is penalized
Border Collie-teeth and jaws should be strong and meet in a scissors bite
Border Terrier-scissors bite and strong teeth that are large in proportion to size of dog
brachygnathism-almormally short mandible
gnath(o)--combining form referring to the jaw
Lingual-pertaining to the tongue; the tooth surface facing the tongue
malocclusion-mimproper allgnment of the teeth mandible-lowerjaw
mesial-located nearer the center of the dental arch
occlusion-the way teeth align
prognathism-abnormal protrusion of one or both jaws; usually used to refer to a protruding lower jaw
retrognathism-an underdevelopment ofthe jaw in which the lower jaw is located posterior to its normal relationship with other facial structures
*Since malocclusions can develop suddenly, each dog's growth should be monitored to ensure early detection.
*Both genetic and nongenetic factors can affect the way the teeth appear in the jaw; about half of all malocclusions are developmental rather than genetic.
*Orthodontic correction is performed in dogs to enhance and restore function and prevent disease. Procedures should not be attempted by lay people but rather should be performed by a competent veterinary dentist.
Information on American Kennel Club dental specifications for approximately 150 dog breeds is listed beginning on p. 9.