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The ABCs of veterinary dentistry: M is for malposition and malocclusion
In veterinary medicine, the goal of orthodontic correction isnt a pretty smile but pain-free, functional occlusion.
“Are those braces on dogs' teeth?”
This question, posed to me by a fellow passenger on my return flight from a veterinary conference, caused me to put my current task (subject-tagging images of dogs' and cats' mouths on my computer) on pause. I explained that in cats and dogs, the goal of orthodontic correction isn't a pretty smile but pain-free, functional occlusion.
What happens when you peek into the mouth of a patient and note that one or more teeth are out of place? Hopefully you don't quickly close the mouth, hoping that the pet owner didn't spot the problem. (Out of sight, out of mind.) It's much better to let your client know when something isn't right in their pet's mouth and explain what it will take to fix a poor or nonfunctional bite. But before you can recommend orthodontic care for your patients, you'll need to embrace the concepts of malposition and malocclusion.
Occlusion refers to the relationship between the maxillary and mandibular teeth when they approach each other, as occurs during chewing or rest. Normal occlusion exists when the maxillary incisors just overlap the mandibular incisors (Figure 1A), the mandibular canines are equidistant from the maxillary third incisors and the maxillary canine teeth, and the premolar crown tips of the lower jaw point between the spaces of the upper jaw teeth in a saw-toothed fashion (Figure 1B). Flat-faced breeds, such as boxers, shih tzus, Boston terriers, Lhasa apsos and Persian cats, have abnormal bites that are recognized as normal for their breed in which the mandibular jaw protrudes in front of the maxillary jaw, altering the above tooth-to-tooth relationship (Figures 2A and 2B).
Figure 1A. Normal maxillary incisor overlap. (All images courtesy of Dr. Jan Bellows)
Figure 1B. A dog's left buccal view; normal interdigitation of canines and premolars.
Figures 2A and 2B. Normal but painful nonfunctional rostral occlusion in a boxer. Note the maxillary incisors penetrating the mandible.
Malocclusion and malposition
Malocclusion refers to abnormal tooth alignment. Skeletal malocclusion occurs when jaw anomalies result in abnormal jaw alignment that causes the teeth to be out of normal orientation. Dental malposition occurs when jaw alignment is normal but one or more teeth are out of normal orientation.
When dental malposition or skeletal malocclusion causes trauma to other teeth or oral soft tissues, the condition is termed poorly functional or nonfunctional and treatment is indicated. Therapy options include moving or removing the offending or offended tooth or teeth, or surgically creating additional space for the malpositioned tooth to occupy without causing trauma.
Here are some of the common terms associated with abnormal jaw alignment:
Mandibular distoclusion (also called overbite, overjet, overshot, class 2, and mandibular brachygnathism) occurs when the lower jaw is shorter that the upper and there's a space between the upper and lower incisors when the mouth is closed. The upper premolars will be displaced rostrally (toward the nose) compared with the lower premolars. Mandibular distoclusion is never normal in any breed (Figures 3A and 3B).
Figure 3A. A cat's mandibular distocluson and asymmetry.
Figure 3B. A dog's mandibular distocluson.Mandibular mesioclusion (also called underbite, undershot, reverse scissor bite, prognathism, and class 3) occurs when the lower teeth protrude in front of the upper teeth. If the upper and lower incisor teeth meet each other edge to edge, the occlusion is an even or a level bite (Figure 4).
Figure 4. Mandibular mesioclusion in a dog.Maxillary mandibular asymmetry (also called wry bite, especially by breeders) is a skeletal malocclusion in which one side of the jaw grows differently from the other side (Figures 5A and 5B).
Figure 5A. Maxillary mandibular asymmetry in a dog.
Figure 5B. Maxillary mandibular asymmetry in a cat.
Abnormally placed teeth can result in the following conditions:
Rostral cross bite occurs when the canine and premolar teeth on both sides of the mouth are normally aligned but one or more of the lower incisors are positioned in front of the upper incisors (Figure 6).
Figure 6. Rostral cross bite.Mesioverted mandibular canines (also called lingually displaced canines or base narrow canines) occur when the lower canine teeth protrude inward, impinging on or penetrating the maxillary gingiva (Figure 7). Often this condition is due to retained deciduous teeth. The resulting trauma can be alleviated through tooth movement, crown reduction and restoration, or extraction.
Figure 7. Mesioverted left mandibular canine.Rostroverted maxillary canine (also called lance canines) may be inherited (Shetland sheepdogs are prone to this condition) or developmental secondary to retained deciduous teeth (Figure 8). Treatment includes moving the maxillary canine caudally with the help of orthodontic brackets and elastics, crown reduction and restoration, or extraction.
Figure 8. Rostroversion of the maxillary canine in a Shetland sheepdog.
Your patient has an abnormal bite. Now what?
When it's time to refer …
To find a boarded veterinary dentist in your area, visit avdc.org.
The challenge with examining every dog and cat that comes through your practice for evidence of malocclusion or malposition is that your exams will uncover many abnormalities. However, this also means you have many more opportunities to improve your patients' health. Consider these basic orthodontic concepts when tailoring a treatment plan for each patient with orthodontic anomalies.
Is the abnormality functional? If a tooth is out of place but isn't interfering with other teeth or with eating, and if it isn't penetrating the gingiva, a functional bite exists (Figure 9). To repair a functional bite for cosmetic or show purposes isn't necessary and is considered unethical.
Figure 9. The left mandibular canine tooth is malpositioned but functional. When abnormally positioned teeth interfere with other teeth or penetrate the gingiva, a poorly functional or nonfunctional bite exists, and something needs to be done.
Options for correction. Here are the techniques and procedures that can improve quality of life in an animal with malocclusion.
1. Extraction. Extraction of the offending or offended tooth (or teeth) usually results in immediate relief. Extraction of the canines can be challenging, so consider referring if you aren't comfortable with the procedure or the possible surgical consequences.
2. Tooth movement. Moving malpositioned teeth to functional positions can be both challenging and rewarding. Teeth are moved surgically or through the use of inclined planes, orthodontic brackets and elastics (Figures 10A-10H). Orthodontic movement is an advanced dental procedure that should be performed only by someone with a thorough understanding of dental anatomy, physiology and orthodontic principles.
Figures 10A and 10B. Right and left mandibular canines impinging on maxillary gingiva.
Figures 10C and 10D. Orthodontic brackets and elastics are used to move a maxillary canine caudally after extraction of the right and left maxillary first premolars.
Figures 10E and 10F. Laser gingivoplasty creates an inclined plane to push mandibular canines labially.
Figures 10G and 10H. Functional occlusion is created.
3. Crown reduction and restoration. Decreasing canine or incisor crown height will often resolve gingival impingement or penetration. This procedure preserves the vitality of the tooth through vital pulp or root canal therapy and restoration with light-cured composite (Figures 11A-11C). You can place a metallic crown for extra protection.
Figure 11A. Malpositioned left mandibular canine impinging on palatal gingiva.
Figure 11B. Left mandibular canine with reduced crown before restoration.
Figure 11C. Restored crown on reduced canine; impingement resolved.Understanding and embracing orthodontic correction will create smiles on your clients', patients' and team members' faces. Everyone wins.