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Canine MalocclusionMisalignment of Teeth |
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Occlusion is the way in which teeth align with each other. Normal occlusion in most medium and long muzzled breeds consists of the upper (maxillary) incisors that just overlap the lower (mandibular) incisors (scissors bite). The lower canine should be located equidistant between the corner (lateral) incisor and the upper canine tooth. Premolar tips of the lower jaw should point between the spaces of the upper jaw teeth. Occlusion is controlled by genetics, nutrition, environment, and by mechanical forces generated by the interlock of the upper and lower teeth.
Malocclusion refers to an abnormal tooth alignment. Any condition where the teeth are not normally positioned is called a malocclusion. Malocclusions are corrected only if there is a problem with mastication (chewing). Occasionally, a dog will not shed a deciduous tooth when a permanent tooth starts to come through the gums in the same location. These retained deciduous teeth , along with any extra teeth, should be removed because they will result in displacement of the permanent teeth.
Some abnormal bites (malocclusions) are genetically influenced, such as severe over or under bites and wry bites. Other bite abnormalities are known to be acquired (non-genetic). Acquired malocclusions can result from tug of war games played with towels or ropes that move teeth into an abnormal position. Traumatic birthing can also be responsible for some acquired abnormalities.
In most breeds of dog the bites are "set" by the time a puppy is ten months old. A malocclusion will rarely improve after the puppy reaches ten months. Within the standard for each breed is specifications as to what is the acceptable parameters for bite. For most breeds the scissors bite is ideal. Scissors bite is one in which the upper incisors just overlap and touch the lower incisors.
There are 7 primary types of malocclusion:
1.
Overshot Mouths (parrot mouth, over shot, class two,
over jet, mandibular brachygnathism)
Over bite occurs when the lower jaw is shorter than the upper and is similar to buck teeth in people. This deformity is also known as Parrot Mouth because the upper jaw extends beyond the lower jaw causing upper teeth to overlap the lower teeth. This prevents the teeth from aligning snugly as they would in a normally formed jaw. There may be a gap between the upper and lower incisors when the mouth is closed. The upper premolars are displaced at least 25% toward the front compared to the lower premolars. An over bite malocclusion is not considered normal in any breed and is a genetic fault. An overshot bite can create dificulties for the dog grasping with both jaws and in severe cases the growth of the adult teeth can cause significant injury to the soft tissues of the dog's mouth. For early detection of this problem a puppy should be examined for the condition at the age of about three weeks old. Remember, however, that a dogs jaw does not finish growing untill it's about ten months of age, and untill that time a mild overshot - or undershot - jaw should be left alone at it may correct itself. A severe bite structure problem is unlikely to correct itself and may need surgery. Some puppies with overshot bites will experience difficulties when their permanent teeth come in. Due to the increased size of the permanent teeth, as they come in they can damage the soft parts of the mouth. Overbites should be carefully watched, as sometimes extractions become necessary.
2. Undershot Mouths
In this condition an under bite (under shot, reverse scissors bite, prognathism, class III) occurs when the lower teeth protrude in front of the upper jaw teeth. Severe undershot jaws can cause lip trauma. Some short-muzzled breeds (Boxers, English Bull Dogs, Shih-Tzus, and Lhasa Apsos) normally have an under bite, but it is abnormal when it occurs in medium-muzzled breeds. With slightly undershot bites, the incisors may be the only teeth affected. In extreme cases, the difference in jaw length can result in problems eating, teeth that cannot be used, teeth that interfere with each other, improper wear, and damage to the soft tissues of the opposite jaw by the canines. Undershot bites tend to run in families and the mode of inheritance is likely to be polygenic. There is some speculation that selecting for shortened muzzles can lead to undershot bites.
Even or Level Bite
When the upper and lower incisor teeth meet each other edge to edge, the occlusion is considered an even or level bite. Constant contact between upper and lower incisors can cause uneven wear, periodontal disease, and early tooth loss. Level bite is considered normal in some breeds, although it is actually an expression of under bite. An Undershot jaw is seen on occasion, and is prevalent in small dogs and in breeds like Bulldogs, Shih Tzu's, and Lhasa apso's.
3. Anterior Cross Bite
Anterior cross bite is a common malocclusion. In this case both sides of the bite close normally, however one or more of the lower incisors are positioned in front of the upper incisors. It is not considered a genetic or inherited defect and is usually correctable.
4. Posterior cross bite
Posterior cross bite occurs when one or more of the premolar lower jaw teeth overlap the upper jaw teeth. This is a rare condition that occurs in the longer nosed dog breeds.
5. A Wry Mouth
Of the malocclusions this is the worst form. A dog with wry mouth has one side of the jaw that is longer than the other side. This problem can lead to difficulty in grasping and chewing food. A wry mouth or wry bite occurs when one side of the jaw grows more than the other. Wry bites show 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. Wry mouth appears to be hereditary and correction is difficult (if possible).
6. Base narrow canines
Base narrow canines occur when the lower canine teeth protrude inward, often producing damage to the upper palate. This condition is either due to retained deciduous teeth, or by an overly narrow mandible. Base narrow canines may be corrected through orthodontic devices that push the teeth into normal occlusion. An open bite occurs when some incisors are displaced vertically and do not touch. The tongue will often protrude.
7. Rostral cross bite
This deformity occurs when canine and premolar teeth on both sides of the mouth occlude normally, but one or more of the lower incisors are positioned in front of the upper incisors. This condition can be caused by tug-of-war games, retained primary teeth, or impacted roots.
Over bite occurs when the lower jaw is shorter than the upper and is similar to buck teeth in people. This deformity is also known as Parrot Mouth because the upper jaw extends beyond the lower jaw causing upper teeth to overlap the lower teeth. This prevents the teeth from aligning snugly as they would in a normally formed jaw. There may be a gap between the upper and lower incisors when the mouth is closed. The upper premolars are displaced at least 25% toward the front compared to the lower premolars. An over bite malocclusion is not considered normal in any breed and is a genetic fault. An overshot bite can create dificulties for the dog grasping with both jaws and in severe cases the growth of the adult teeth can cause significant injury to the soft tissues of the dog's mouth. For early detection of this problem a puppy should be examined for the condition at the age of about three weeks old. Remember, however, that a dogs jaw does not finish growing untill it's about ten months of age, and untill that time a mild overshot - or undershot - jaw should be left alone at it may correct itself. A severe bite structure problem is unlikely to correct itself and may need surgery. Some puppies with overshot bites will experience difficulties when their permanent teeth come in. Due to the increased size of the permanent teeth, as they come in they can damage the soft parts of the mouth. Overbites should be carefully watched, as sometimes extractions become necessary.
2. Undershot Mouths
In this condition an under bite (under shot, reverse scissors bite, prognathism, class III) occurs when the lower teeth protrude in front of the upper jaw teeth. Severe undershot jaws can cause lip trauma. Some short-muzzled breeds (Boxers, English Bull Dogs, Shih-Tzus, and Lhasa Apsos) normally have an under bite, but it is abnormal when it occurs in medium-muzzled breeds. With slightly undershot bites, the incisors may be the only teeth affected. In extreme cases, the difference in jaw length can result in problems eating, teeth that cannot be used, teeth that interfere with each other, improper wear, and damage to the soft tissues of the opposite jaw by the canines. Undershot bites tend to run in families and the mode of inheritance is likely to be polygenic. There is some speculation that selecting for shortened muzzles can lead to undershot bites.
Even or Level Bite
When the upper and lower incisor teeth meet each other edge to edge, the occlusion is considered an even or level bite. Constant contact between upper and lower incisors can cause uneven wear, periodontal disease, and early tooth loss. Level bite is considered normal in some breeds, although it is actually an expression of under bite. An Undershot jaw is seen on occasion, and is prevalent in small dogs and in breeds like Bulldogs, Shih Tzu's, and Lhasa apso's.
3. Anterior Cross Bite
Anterior cross bite is a common malocclusion. In this case both sides of the bite close normally, however one or more of the lower incisors are positioned in front of the upper incisors. It is not considered a genetic or inherited defect and is usually correctable.
4. Posterior cross bite
Posterior cross bite occurs when one or more of the premolar lower jaw teeth overlap the upper jaw teeth. This is a rare condition that occurs in the longer nosed dog breeds.
5. A Wry Mouth
Of the malocclusions this is the worst form. A dog with wry mouth has one side of the jaw that is longer than the other side. This problem can lead to difficulty in grasping and chewing food. A wry mouth or wry bite occurs when one side of the jaw grows more than the other. Wry bites show 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. Wry mouth appears to be hereditary and correction is difficult (if possible).
6. Base narrow canines
Base narrow canines occur when the lower canine teeth protrude inward, often producing damage to the upper palate. This condition is either due to retained deciduous teeth, or by an overly narrow mandible. Base narrow canines may be corrected through orthodontic devices that push the teeth into normal occlusion. An open bite occurs when some incisors are displaced vertically and do not touch. The tongue will often protrude.
7. Rostral cross bite
This deformity occurs when canine and premolar teeth on both sides of the mouth occlude normally, but one or more of the lower incisors are positioned in front of the upper incisors. This condition can be caused by tug-of-war games, retained primary teeth, or impacted roots.
Never
breed from a dog with these deformities for fear of passing them on to
another generation of pups.
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Malocclusion |