pet orthodontics

12.05.2010, 19:32Pet Orthodontics

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Normal scissors bite, notice themidline of upper and lower jaws

are aligned

Normally, the lower canineshould intersect the upper

lateral incisor and upper canine

Pet OrthodonticsJust as one would seek to cure a painful skin condition, ortreat a sore joint in their pet, one should also considerrelieving pain brought on by orthodontic abnormalities.Poorly aligned teeth can lead to serious periodontal disease.In most breeds, teeth are arranged "shoulder to shoulder,"in an arch. A self cleaning mechanism occurs in the arch topush food away from the teeth and gums. If the teeth arenot aligned normally, food may be retained between theteeth causing inflammation and infection.

It is important to understand the head shape whendetermining normal bite relationships in various breeds.There are three basic head shapes for dogs. Those with longand narrow muzzles (Rough Collies, Borzoi, Doberman,Greyhound, Saluki); those with a short and wide muzzles(Bulldog, Pug, Pekingese, Boxer, Boston Terrier, Shih Tzu);and dogs with medium length and width muzzles (LabradorRetriever, German Shepherd Dog, most Spaniels, Terriers,and Hounds). Cats also have different head shapes whichvary from the short muzzled Persian to the longer muzzledSiamese.

The normal bite of dogs andcats with medium or longlength and width muzzles iscalled a scissors bite. Theupper incisors are located infront of the lower incisorswhen the mouth is closed,and there is a smooth curvefrom canine to canine withoutmisplaced or rotated teeth.The lower canines should lieexactly between the upperlateral incisors and uppercanines, yet touching neither.Premolar crown tips shouldpoint to a space between thecrowns of the opposingpremolars. In dogs that havea short, wide muzzle, areverse scissors bite is



lateral incisor and upper canine

Normal interdigitation of premolars

This is a genetic malocclusion becausethe premolars do not line up in a pinking

shear arrangement

considered normal where thelower incisors are in front ofthe upper incisors. The lower canines and premolars will alsobe shifted forward. While the reverse scissors bite is anacceptable breed standard, at times the upper incisors causetrauma and pain to lower jaw tissues.

Genetic or Not

Occlusion is controlledby genetics, nutrition,environment, and bymechanical forcesgenerated by theinterlock of the upperand lower teeth. Someabnormal bites(malocclusions) havebeen proven to begenetically influenced,such as severe over orunder bites, and wrybites. Other bite abnormalities are known to be acquired(non genetic). Acquired malocclusions can result from tug ofwar games played with towels or ropes which move teethinto abnormal position. Traumatic birthing can alsoresponsible for some acquired abnormalities.

To help define whetherthe malocclusion isgenetic in origin,interdigitation of thepremolars is studied. Inbreeds that havemedium and longmuzzles, the premolarsshould meet in a saw-toothed fashion. Forexample, the tip of thelower third premolarshould be positionedequally between thecrowns of the upperthird and fourth premolars. If the tip of one premolar pointsto the tip of another premolar, there may be a geneticallyinduced malocclusion. This only holds true in those breedsthat do not have shortened muzzles.



Retained upper caninetooth

Some genetic bite problems do not show up in each litterbecause they are recessively passed on. The goal ofselective breeding is to mate one animal to another that hassuperior occlusion.

Retained Deciduous Teeth

Normally the deciduous tooth's root isresorbed, making room for an adulttooth. Should this fail, the adult toothmay deviate from it's normal position,producing malocclusion. The resultingdouble set of teeth overcrowds thedental arch, causing food to becometrapped between the teeth, leading toearly periodontal disease. A doubleset of roots may also prevent normaldevelopment of the socket, and erodeperiodontal support around the adulttooth, resulting in early tooth loss. Aretained deciduous tooth should be extracted as soon as anadult tooth is noted in the same area as the baby tooth. Ifextraction is performed early, the abnormally positionedadult tooth usually moves to it's normal location.

A procedure performed by some breeders is to trim or cutdeciduous teeth in hopes that they will be shed earlypreventing orthodontic problems. By cutting the tooth inhalf, pulp is exposed to oral bacteria causing infection, pain,and tooth loss. Unfortunately, the remaining infected rootcan interfere with the emerging adult tooth, which may notcome in normally.

Dental Interlock

Jaws do not grow at equal rates. If deciduous teeth eruptduring an accelerated growth phase of one jaw, aninterlocking of both sets of primary teeth can maintain theabnormal bite relationship. Even genetically normal dogs canoccasionally develop abnormal bites due to the interlock ofprimary teeth. If an under bite is noted before thepermanent teeth erupt, treatment may be helpful. Removalof primary teeth from the shorter jaw that interfere withforward growth, if performed by ten weeks of age may allowthe upper jaw to lengthen unimpeded. This procedure calledinterceptive orthodontics will correct about 50% of minorjaw length malocclusions, by the time permanent teeth



Missing lower fourth premolar

8 upper baby incisor teeth in boxerpuppy (normally should have only 6)

erupt. Extraction does not stimulate jaw growth, it onlyremoves a mechanical barrier to genetic control of thegrowth process.

Teeth that are crowded, rotated, or tilted at abnormal anglescan result in:

Early onset and increased severity of oral infectionDamage to the soft tissues of the mouth, due to sharpteeth that penetrate the unprotected gum and mouthtissues. In addition, the lower canines can erodethrough the hard palate, causing food to enter thenasal cavityExcessive wear when abnormally aligned teeth grindagainst each other. Such abrasion frequently wearsthrough enamel, causing a weakened tooth to fractureand expose the root canal system.Pain in joints of the jaw

Breeders, show judges, veterinarians, and others who wishto describe specific dental conditions in dogs and cats needto use proper orthodontic terms. Over bite, open bite, overjet, level bite, overshot, under bite, anterior cross bite,posterior cross bite, wry bite, and base narrow canines areorthodontic terms that are at times confusing.

Missing or Extra Teeth

Dogs and cats may beborn without the propernumber of teeth. Extra(supernumerary) teeth cancause periodontal diseasefrom over crowding. TheAmerican Kennel Club setsstandards concerningminimum number of teethaccepted for each breed tobe considered for show.Dental x-rays can betaken as early as tenweeks of age to evaluateif the correct number ofteeth are present. X-raysare recommended as a part of the prepurchase examinationin certain breeds. Missing teeth (hypodontia) usually occursin the premolar area, but any tooth in the mouth may noterupt. Missing or extra teeth are considered genetic faults.



Rostrally deviated upper canine toothtreated by crown reduction or elastic to

pull back tooth into normal occlusion

Open bite - incisors do not meet

Collies and Doberman Pinchers are most commonly affected.Sometimes the missing tooth is trapped below the gum line.A dental x-ray can be taken to determine if an uneruptedtooth is present.

Misdirected Canine Syndrome

Misdirected caninesyndrome is a biteabnormality, in whichretention of thedeciduous tooth tiltsthe eruptingpermanent caninetooth into abnormallocation. The opposingcanines may not haveroom to occludeproperly, resulting inabnormal wear,periodontal disease, or early tooth loss.

Occlusion

The way which teeth align with each other is termedocclusion. Normal occlusion in most medium and longmuzzled breeds consists of the upper (maxillary) incisorsthat just overlap the lower (mandibular) incisors (scissorsbite). The lower canine should be located equidistantbetween the corner (lateral) incisor and the upper caninetooth. Premolar tips of the lower jaw should point betweenthe spaces of the upper jaw teeth.

Malocclusion

Malocclusion refers to anabnormal tooth alignment.Over bite (parrot mouth, overshot, class two, over jet,mandibular brachygnathism)occurs when the lower jaw isshorter than the upper. Theremay be a gap between theupper and lower incisorswhen the mouth is closed.The upper premolars aredisplaced at least twenty-fivepercent toward the front, compared to the lower premolars.



Base Narrow Canines

Underbite, undershot prognathic skelatalmalocclusion

An over bite malocclusion is never considered normal in anybreed and is a genetic fault. The most commonly affectedbreeds are those with elongated muzzles (Collies, Shelties,Dachshunds, and Russian Wolfhounds).

An under bite (undershot, reverse scissorsbite, prognathism,class 3) occurs whenthe lower teethprotrude in front of theupper jaw teeth. Someshort muzzled breeds(Boxers, English BullDogs, Shih-Tzus, andLhasa Apsos) normallyhave an under bite,but when it occurs inmedium muzzledbreeds it is abnormal.When the upper andlower incisor teeth meet each other edge to edge, theocclusion is considered an even or level bite. Constantcontact between upper and lower incisors can cause unevenwear, periodontal disease, and early tooth loss. Level bite isconsidered normal in some breeds, although it is actually anexpression of under bite.

Level Bite Anterior Crossbite Wry Bite

Anterior cross bite occurswhen canine and premolar teethon both sides of the mouthocclude normally but one ormore of the lower incisors arepositioned in front of the upperincisors. This condition can becaused by tug-of-war games,retained primary teeth, orimpacted roots. Anterior cross bite is a commonmalocclusion. It is not considered a genetic or inherited



Inclined Plane

defect. Posterior cross bite occurs when one or more ofthe premolar lower jaw teeth overlap the upper jaw teeth.This is a rare condition that occurs in the longer-nosed dogbreeds. A wry mouth or wry bite occurs when one side ofthe jaw grows more than the other. Wry bites show astriangular defects in the incisor area. Some of the incisorswill meet their opposing counterparts, while others will not.Wry bite is a severe inherited defect. Base canines occurwhen the lower canine teeth protrude inward oftenproducing damage to the upper palate. This condition iseither due to retained deciduous teeth, or an overly narrowmandible. Base narrow canines may be corrected throughorthodontic devices that push the teeth into normalocclusion. An open bite occurs when some incisors aredisplaced vertically and do not touch. Often, the tongue willprotrude. Rotated teeth, commonly affecting the upperthird premolar, occurs mostly in short muzzled breeds.

Selective breeding hascreated undersizedmouths that cannotaccommodate forty twoteeth in normalalignment. The rotatedtooth root closest to thepalate is prone toperiodontal disease.Strict tooth brushingmay be helpful insaving a rotated tooth, but, frequently, the tooth cannot besaved.

Orthodontic Care

Many abnormal bitescan be corrected.Orthodontic care shouldbe performed byveterinarians familiarwith tooth movementprinciples. Breeders attimes use rubber bandswhich may move teeth,but compromise thegum tissue aroundteeth leading toperiodontal disease, pain, and early tooth loss. Orthodonticcare should be reserved to ease pet discomfort, by



realigning teeth. Tooth movement is accomplished byemploying brackets, acrylic retainers, springs, and elastics.

Fortunately, in animals, orthodontic movement can usuallybe accomplished in months rather than years.

This page last updated on October 31, 2000Copyright 1997-2000, All Pets Dental ClinicNo portion of this site may be copied without authorization.If you have any questions about the site, or are referencing it in an article orother website, please notify the webmaster.Site hosted and maintained by acInternet.

Jan Bellows, DVMAll Pets Dental Clinic17100 Royal Palm Blvd.Weston, FL 33326(954) [email protected]

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