Dentition


Dentition & Anatomy | Normal Occlusion | Malocclusions | Other Dentition Disorders

 

Canine Dentition & Anatomy

In order to understand canine dentition faults, one must first recognize a correct bite or proper occlusion; that is, the alignment of teeth. In shelties, normal occlusion is when the superior dental arch is larger than the inferior, so that the teeth in the maxillae (upper jaw) slightly overlap those of the inferior maxillae (lower jaw) both in front and at the sides. Dogs normally have 28 deciduous (primary or puppy) teeth that erupt during the first six months of life, replaced by 42 permanent, adult teeth. There are four types of teeth, as illustrated below: Incisors, used for grasping food and help keep the tongue in the mouth; Canines (cuspids or fang teeth), used to grasp food; Premolars (bicuspids), for shearing or cutting food; and Molars, for grinding food.

Lateral Views


 

Maxillary View (upper jaw)

 

Mandibular Views (lower jaw)

 

Dental Formula

Deciduous

3 1 3
3 1 3

= 14

Permanent

3 1 4 2
3 1 4 3

= 21

Note: P 4 and M 1 are the carnassials or shearing teeth

A dog generally has full dentition by six to seven months of age. The teeth of large dogs, which have a shorter life span than smaller dogs, erupt earlier.

Development

Deciduous

Permanent

1-3 weeks No noticeable growth  
3-5 weeks Canines erupt  
4-6 weeks Incisors erupt  
5-6 weeks Premolars erupt (Dp2, 3)  
6-7 weeks Dp4 erupts  
8 weeks Dm1-3 erupt  
3-5 months   I1 & I2 erupts
4-5 months   I3, P1, P4 erupts
5-6 months   P2, P3, M1 & M2 erupts
507 months   Canines erupts
7 months   M3 erupts
1 year   Teeth white and clean
1-2 years   Teeth may appear dull with some tartar build-up on molars. Grade 1 gingivitis.
3-5 years   Teeth show more tartar build-up and some tooth wear. Grade 2 gingivitis.
5-10 years   Teeth show increased wear and disease. Grade 3 gingivitis.
10+ years   Teeth are worn and show heavy tartar build-up; some teeth may be missing. Grade 4 gingivitis.

Historically, the canine skull has been a contributing factor in identifying and classifying the evolution of the canid. Not only do ancient skulls identify various types, but so do modern skulls. The heads of varying breeds differ enormously in conformation exhibiting a greater range of size and shape than in any other mammal. The classification of canid skulls is based on the cephalic scale and is largely determined by skull shape, eye position and size, and form and carriage of the ears. Three classifications follow:

  1. Mesaticephalic - a head of 'medium' proportions, neither unusually long nor too short, not too wide or abnormally narrow, and found in a majority of breeds;
  2. Dolichocephalic - long and narrow and found in such breeds as greyhounds, collies, shelties and borzois;
  3. Brachycephalic - short and wide and found in such breeds as bulldogs, bostons and small spaniels.

While the shape of these three classifications are clear; there are slight differences between the skulls of different breeds belonging to the same group. Note the slight differences between the collie and sheltie skulls below, specifically the stop (a depression located centrally between the eyes, at the junction of the frontal bones of the skull with those of the upper jaw (maxilla) nose (nasal bones) in front. It is nearly undetectable in the collie.

 

[Sheltie Skull]

[Collie Skull]

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Dentition & Anatomy | Normal Occlusion | Malocclusions | Other Dentition Disorders

[Normal Occlusion]
["Pinking Shear Arrangement"]

The cusp of the mandibular fourth premolar points to the space between the maxillary third and fourth premolars.

[Scissor Bite]

The lower canine should be located equidistant between the last (lateral) incisor and the upper canine tooth.

 

Canine Dentition

by Margo B. Maloney, DVM
Versatile Hunting Dog Magazine, December 2001
Photographs provided by Dr. Jan Bellows, DVM

The teeth are highly specialized structures which serve as weapons of offense and defense, as well as for the procuring, cutting, and crushing of food. Each tooth is divided into three parts: the crown is the exposed part which protrudes above the gum line; the neck which the slightly constricted area just at the level of the gum; and the root which is usually embedded in sockets in the jawbone.

The teeth are arranged as upper and lower dental arches. Many teeth are so placed in the jaw that they fail to meet or else overlap or protrude between adjacent teeth laying opposite to them. The function of these nonocclusal or imperfectly occluding teeth is to grasp, puncture, or shear things like food or fore. In dogs, food is bolted rather than chewed, and a complete occlusal surface is not necessary.

The surface of the tooth which faces the lip or cheek is called the vestibular surface, formerly called the buccal surface. The surface which faces the tongue is called the lingual surface. The surface adjacent to the next tooth is called the contact surface. The tooth surface that faces the opposing tooth is the opposite dental arch is called the masticatory or occlusal surface.

The incisor teeth are the six small teeth located at the center of each dental arch. Next are the canine or "fang" teeth. All the teeth behind the canine teeth are referred to as cheek teeth. In the permanent dentition, there are four premolars on each side in each jaw. The upper fourth premolars are the largest cutting teeth of the upper jaw. They are referred to as carnassials teeth or "shearing" teeth. Finally, the molars are the large grinding teeth in the back of the mouth.

When examining a dog's dentition, be sure to clear the lips and cheek tissue clearly from the mouth or the teeth may be miscounted or misidentified. Be sure the dog is not nervous and setting its teeth in an abnormal position due to tenseness. Try to "soften" the jaw by relaxing the dog's head and neck position. Tooth placement is affected by genetics, jaw structure, lip structure, the tongue, other teeth - deciduous ("baby teeth") and/or permanent, as well as the habits of the dog such as carrying a training dummy, chewing on kennel fencing or crate wire, or continual rock fetching.

When evaluating dog's teeth, we need to look at the relationship of all the teeth to each other and the jaw. Ethical breeders do are about dentition and require knowledge about the whole mouth - not just the incisors. It is very easy to just count the number of teeth or evaluate the "bite" of the incisors, but it is only when we look at the overall picture that we can see how genetics is affecting the dentition. The breeder needs to know the number of teeth; the type of bite or how the incisors meet; the relationship of the canine teeth, the premolars, the molars, and the jaw curvature. If there are any genetic inconsistencies, this should be taken into consideration in the breeding program.

A very good reference source is the 1992 publication of Veterinary Dental Techniques by Drs. Holstrom, Frost, and Gammon. This book was released by W.B. Saunders Company and discusses how the understanding of the different types of occlusions can be "scored" to total up an estimate of genetic heritability.

Here is a step-by-step method of evaluating the teeth as described in the above publication (page 340):

Observe the symmetry of the head, face, and teeth.

Count the teeth. The teeth are divided into four quadrants. Upper and lower left; Upper and lower right. There are three upper left incisors; one upper left canine; four upper left premolars; two upper left molars. It is the same for the upper right teeth. There are three lower left incisors; one lower left canine; four lower left premolars; three lower left molars. It is the same for the lower right teeth. Total teeth in an adult canine should be 42.

Evaluate the incisors. The normal incisor occlusion has the large cusp (a pointed or rounded protuberance making up a divisional part of the chewing surface of a tooth) of the lower incisors occluding near the cingulum (the lingual lobe of an anterior tooth; lingual refers to the surface of the tooth facing the tongue) on the lingual side of the upper incisors. The large cusps of the central incisors should be centered with each other. The second and third incisors lose their centered orientation and the large cusp of the third incisor should be in the interproximal space (space between adjoining teeth) between the second and third maxillary with no rotation. Rotation would mean that the tooth is not seated properly on the jaw bone. The axis of the tooth should be parallel to the jaw.

Observe the relationship of the canine teeth. The mandibular canine or "fang" tooth should occlude buccal (toward the cheek tissue) to the gingiva of the maxilla and should divide the space between the maxillary canine tooth and the maxillary third incisor. This is the most reliable reference point in the mouth. Observe the relationship of the premolars. The large cusp on the lower fourth premolar should divide the space between the upper third and fourth premolars. Observe the occlusal plane of the upper and lower arches. The occlusal surface is the surface of the tooth that faces the opposite dental arches' chewing surface. The premolars should interdigitate from the second premolars back to the cusps of the upper fourth premolar with overlapping of the cusp tips. The molars should occlude to allow the cusps to function in crushing. The premolars and molars should be aligned mesial (toward the center line of the dental arch) to distal (position on the dental arch farther from the median line of the jaw) in a slightly curved line with none of the teeth rotated.

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Dentition & Anatomy | Normal Occlusion | Malocclusions | Other Dentition Disorders

After evaluating the teeth and their relationship to the jaw, the dentition can be categorized into the following types of malocclusions. The normal occlusion is a "scissor bite." This is the pattern in which the lower incisors occlude next to the cingulum (lingual lobe of an anterior tooth) on the lingual surface of the upper incisors.


[Anterior Crossbite]

Class 1: Dogs with a Class One occlusion have a normal occlusion with one or more teeth out of alignment or rotated.
The following bites are Class One:

1) The anterior crossbite where one or more of the lower incisors are anterior (situated in front of) to the upper incisors and the rest of the teeth occlude normally;

[A posterior crossbite 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 larger-nosed dog breeds.]


[Even or Level Bite]
[Pincer bite, vise bite]

2) The level bite where the upper and lower incisors occlude cusp-to-cusp ("butt bite"); and


[Base Narrow Canines]

3) The base narrow bite where the tips of the manibular canine teeth are displaced lingually (toward the tongue) and occlude on the hard palate.


[Overshot]
[Class two, parrot mouth, pig or swine jaw, shark mouth, over bite, overjet, retrusive mandible, manibular brachygnathism, distal mandibular excursion]

Class 2: Dogs with a Class Two occlusion have the lower premolars and molars positioned behind the normal relationship [displaced 25% toward the front when compared to the lower premolars]. This occlusion may also be termed brachygnathism, overshot, "parrot mouth," retrusive mandible, or distal mandibular excursion.


[Undershot]
[Class three, bulldog bite, under bite, reverse scissor bite, prognathism, protrusive mandible, mesial mandibular excursion]

Class 3: Dogs with a Class Three occlusion have the lower premolars and molars positioned ahead (anterior) of the normal relationship. This occlusion may also be termed prognathism, undershot, "Bulldog bite", protrusive mandible, or mesial mandibular excursion.


[Wry Bite]

An unclassified bite is the "wry bite." An abnormal occlusion caused by a difference in length of the two maxillae (upper jaw bones) and the mandibles (lower jaw bones). The abnormal occlusion results in a variety of different jaw relationships as one side of the jaw grows faster than the other and distorts or "twists" the mouth giving it a "wry" appearance. This condition is quite a handicap and leads to difficulty in grasping and chewing food as well as retrieving game.

It is only when we as dog handlers, breeders, and/or judges evaluate the dog's entire mouth that we can effectively understand how genetics and the environment are affecting the dog's dentition. Each dog should have a good oral exam to determine any health concerns or breeding considerations.

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Dentition & Anatomy | Normal Occlusion | Malocclusions | Other Dentition Disorders

Lance Canines or
Misdirected Canine Syndrome


[Unilateral Lance Canine]
(Disorder expressed on one side)

[correct scissor bite]

 


[Bilateral Lance Canine]
(Disorder expressed on both sides)

Retained Deciduous Canine

Normally deciduous canines erupt between three and five weeks of age and shed out between five to seven months of age. When the deciduous canine(s) are retained for a longer duration, the roots of the deciduous and permanent teeth interfere with the space.

The resulting double set of teeth that appear at this time (see above) overcrowds the dental arch, which ultimately forces a deviation of the permanent canines to cut distally forward from their normal position, either bilaterally or unilaterally or maxillary or mandibular (see left).

Thereafter, food is easily trapped between the teeth, leading to early periodontal disease. A double set of roots may also prevent normal development of the socket, and erode periodontal support around the adult tooth, resulting in early tooth loss.

A retained deciduous tooth should be extracted as soon as an adult tooth is noted in the same area as the baby tooth. If extraction is performed early, the abnormally positioned adult tooth usually moves to it's normal location.

Breeders that pull young canines encourage the canines to properly align, which not only greatly benefits the health of the dog but also discourages the canine to grow in a lanced position. Bracing techniques can also be used to correct this condition.

Although these methods correct the immediate problem, it does not fix the genetic component that produced it. With first-hand experience breeding through lance canines, we suspect the mode of inheritance to be a simple autosomal dominant trait.

Thus far, by not pulling affected teeth (breeding dogs only), we have been able to identify affected dogs and removed them from our gene pool. Effectively, we have (seemingly) eliminated the problem from our breeding program. Breeders that do not disclose information regarding the routine pulling of teeth or surgically correcting a misdirected canine are not only saturating the gene pool with this disorder, but are also perpetuating this condition in the breed, and to those unwary.


[Missing Premolar]

Dogs will lack one or more teeth, usually premolars. Sometimes there will be an extra premolar or molar.

 


[Open Bite "Mouse Mouth"]
(Pictured above also a wry bite)

Occurs when the upper and lower incisors do not overlap or even meet each other when the mouth is closed. Loose lip lines or lips that do not fit properly can also interfere with this disorder, lending to the "mouse mouth" appearance.


[Dropped Center Incisors]
(Pictured above also a wry bite)

The two centre lower incisors will be situated lower in the gum line than the other incisors. Sometimes these incisors will tip forward giving the illusion of a level or slightly undershot bite when viewed from the side.

 

Dentition & Anatomy | Normal Occlusion | Malocclusions | Other Dentition Disorders

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"Just because some people select and breed dogs now does not mean that the original dogs were created that way. Looking closely at the behavior of wolves, and understanding the biology of a wild animal, I don't think there is a ghost of a chance that people tamed and trained wild wolves and turned them into dogs. I think a population (at least one) of wolves domesticated themselves."

-Raymond Coppinger

 


 

Common breeding tests for the Shetland sheepdog include eye tests, hips/elbows/knees, thyroid panels and sometimes vWD certification.

The only breeding test that can 100% identify whether or not your puppy has any one of the genetic diseases listed above is the vWD-DNA test. However, this disease is very rare in shelties, affecting 1% of the breed's population.

 

Eye exams

Eye exams certified by the Canine Eye Registration Foundation (CERF), which reports any eye abnormalities in the breed due to hereditary disease. In Shetland sheepdogs, the two main concerns are Collie Eye Anomaly (CEA) and Progressive Retinal Atrophy (PRA).

 

Hips/Elbows/Knees

This is done through x-rays evaluated by three specialists at the Orthopedic Foundation for Animals (OFA) or PennHip (University of Pennsylvania) and is used to detect the presence of hip dysplasia. OFA will do preliminary evaluations on dogs under two years of age, but will only certify dogs over two years of age. Dogs that have preliminary certification done through OFA, should have x-rays resubmitted because they are not given a permanent rating and often times, the rating can change for better or worse.

 

Thyroid

This test is used to detect autoimmune thyroid disease. Autoimmune thyroiditis can be influenced by environmental changes, such as excessive heat; or hormonal changes, such as aging. A thyroid test is a blood test and should be a complete panel that includes Total T4, Free T4, Total T3, Free T3, T4 auto antibodies, T3 auto antibodies, TSH (thyroid stimulating hormone), and TgAA. A thyroid test is not always a conclusive diagnosis.

 

vonWillebrand's Disease

vWD, Factor III is a bleeding disorder in the Shetland sheepdog. The DNA test determines whether a dog is affected (two genes), a carrier (one gene), or clear of the disease. According to vetGen, affected shelties are very rare: (7% carrier-status; 1% affecteds as of January 26, 2005). Most breeders will not introduce the affected gene, but those that are breeding affected lines can easily & effectively manage its safe elimination through prudent vWD-DNA testing.

 

Control of Canine
Genetic Diseases
by George A. Padgett, DVM
ISBN 0-87605-004-6

Genetics of the Dog
by Malcolm B. Willis
ISBN 0-87605-551-X

Dog Owner's
Home Veterinary Handbook
by James M. Giffin, MD &
Liisa D. Carlson, DVM
ISBN 0-87605-201-4

Medical &
Genetic Aspects of
Purebred Dogs
Edited by Ross D. Clark, DVM &
Joan R. Stainer
ISBN 0-935078-24-X

Canine Inherited
Disorders Database (CIDD)
http://www.upei.ca/cidd/

Alice Crook, BSc, DVM
Brian Hill, DVM, MS, DACVIM
Sue Dawson, BA, PhD


Amatras are breeders dedicated to focusing on longevity, health, temperament, structure, brains and beauty. Dogs are added to the program with these qualities only and bred only to improve each trait through each successive generation.

 

 

 

© Amatras Shetland Sheepdogs

Englewood, Florida

Established 2000.