Understanding your pet's teeth, and how they work, will help you to provide a diet that can help prevent or reduce the problems that can arise causing discomfort.

Diet and lack of oral hygiene have become much more widely recognised by the veterinary profession as a contributing factor to early onset dental disease.

Dentition

There are four types of teeth and they are designed to perform a specific function.

• I or i - incisors. These are small teeth with a sharp cutting surface and are used for nibbling, grooming and to grasp and tear food

• C or c - canines. Ideal for piercing food and killing prey as they have pointed crowns.

• P or p - premolars. Used for crushing and cutting food.

• M or m - molars. Larger than premolars and used for crushing and grinding food.

The layout of the teeth in the mouth can be described by a standard formula. As the structure of a normal skull is symmetrical (the left hand side being mirrored by the right hand side), the formula describes only one side of the mouth with the maxillary teeth (those in the upper jaw) along the top line, and the mandibular (lower jaw) teeth on the bottom line. Capital letters are used to indicate permanent teeth, and lower case for deciduous¹ teeth.

For example, an adult human has a total of 32 permanent teeth.

The dental formula is written as follows:  
I ² ⁄ ₂  
C ¹ ⁄ ₁  
P ² ⁄ ₂  
M ³ ⁄ ₃

This means that humans have 2 upper and 2 lower incisors, 1 upper and 1 lower canine, 2 upper and 2 lower premolars and 3 upper and 3 lower molars on each side.

Differences in Jaw Structure

The composition of the mammalian jaw and the need for different types of teeth (a heterodont dentition) is determined by the animal's natural diet in the wild. The herbivore has more need for crushing and grinding teeth, a carnivore needs more cutting and tearing teeth whilst omnivores need a mixture of both, in order to maximise their ability to kill, tear or chew the food available.

The same variety in the type of teeth is present in domesticated animals now kept as pets.

Dogs and Cats

In dogs and cats, the permanent teeth start to erupt at around 3 months of age, pushing the deciduous teeth up, when they should start to fall out. Often the animal will simply swallow the teeth, so the only indication to the owner that this process is happening may be some bleeding and redness along the gumline.

Some dogs and cats that are bred for specific characteristics - such as Persian cats and Pekinese dogs for their flatter faces - can have problems with tooth eruption and have less teeth - or an imbalance in symmetry or alignment of the jaw.

Dentition of Dogs

Puppies have a total of 28 deciduous teeth consisting of:
3 upper and 3 lower incisors, 1 upper and 1 lower canine, 3 upper and 3 lower premolars on each side.

The dental formula is:  
i ³ ⁄ ₃   
c ¹ ⁄ ₁  
p ³ ⁄ ₃  
m ⁰ ⁄ ₀

As the dental formula shows, they have no temporary molars. At such an early age the puppies have little need for them - moving from their mothers milk through weaning (starting at about 3 weeks of age) onto soft food². The jawbone has not grown sufficiently in length at that age to to accommodate all the teeth types an adult dog requires.

Adult dogs have a total of 42 permanent teeth consisting of:
3 upper and 3 lower incisors, 1 upper and 1 lower canine, 4 upper and 4 lower premolars and 2 upper and 3 lower molars on each side.

The dental formula is:  
I ³ ⁄ ₃  
C ¹ ⁄ ₁  
P ⁴ ⁄ ₄  
M ² ⁄ ₃

Dentition of Cats

Kittens have a total of 26 deciduous teeth consisting of:
3 upper and 3 lower incisors, 1 upper and 1 lower canine, 3 upper and 2 lower premolars on each side.

The dental formula is:   
i ³ ⁄ ₃  
c ¹ ⁄ ₁  
p ³ ⁄ ₂  
m ⁰ ⁄ ₀

Kittens have no temporary molars for the same reasons a puppy does not.

Adult cats have a total of 30 permanent teeth consisting of:
3 upper and 3 lower incisors, 1 upper and 1 lower canine, 3 upper and 2 lower premolars and 1 upper and 1 lower molar on each side.

The dental formula is:  
I ³ ⁄ ₃  
C ¹ ⁄ ₁  
P ³ ⁄ ₂  
M ¹ ⁄ ₁

Rabbits, Guinea Pigs and Chinchillas

In smaller pets food type plays a major part in oral health.

These animals tend to suffer from a specific type of dental problem that is very different to that of dogs and cats.

Rabbits, Guinea pigs and Chinchillas have teeth that continually grow as they have an open root apex³. Unfortunately, if the teeth are not worn down by their diet, the crowns of the teeth grow unevenly and can cause cheek ulceration due to 'spikes'. Their teeth will then erupt in reverse fashion when the eruption path into the mouth is blocked by overgrowth of the crowns, causing blockage of the lachrymal and naso-lachrymal ducts⁴, leading to persistent conjunctivitis and abscesses. This is extremely painful for the animal and will result in anorexia and weight loss. Incisor overgrowth is much more noticeable and causes less internal damage, but is often an indication of further problems with the cheek teeth.

Dentition of Rabbits

Rabbits have a total of 28 teeth consisting of:
2 upper and 1 lower incisor(s), 3 upper and 2 lower premolars and 3 upper and 3 lower molars on each side.

The dental formula is:   
I ² ⁄ ₁  
C ⁰ ⁄ ₀  
P ³ ⁄ ₂  
M ³ ⁄ ₃

Dentition of Guinea Pigs and Chinchillas

Guinea pigs and Chinchillas have the same dentition, a total of 20 teeth consisting of:
1 upper and 1 lower incisor, 1 upper and 1 lower premolar, 3 upper and 3 lower molars on each side.

The dental formula is:   
I ¹ ⁄ ₁  
C ⁰ ⁄ ₀  
P ¹ ⁄ ₁  
M ³ ⁄ ₃

Diet

Rabbits eat grass in the wild, guinea pigs and chinchillas normally live at high altitude in the Andes and survive on tough, woody type plants, so the teeth are naturally being worn down.

If these animals are fed only unsuitable foods such as pellets, pet muesli, soft vegetables and hay, there is not adequate chewing to wear down the cheek teeth properly leading to painful dental conditions. Adding 'dried pet grass'⁵ and raw carrot and curly kale to the diet will help encourage the pets to use their cheek teeth, as well as their incisors, to chew food.

Another dietary problem with small mammals is 'selective' eating. This is where a commercial dry diet is fed. Nutritionally these are balanced and make an excellent pet food but the pet will choose the tastiest bits from the bowel, leaving the more fibrous and woody types of food at the bottom of the bowl. The food is changed or topped up and they continue to eat the tastier bits. This means that a balanced diet is not eaten and the rough, fibrous pellets are avoided, increasing the risk of overgrown teeth.

One way to avoid this is by feeding a 'complete' diet where the food is in an 'all pellet' form but contains all the nutrition required as well as containing enough fibrous material to help wear the teeth down.

Small Rodents

Although the incisors of these pets grow continuously during their lifetime, the molars do not. Nibbling and gnawing on commercial food and raw vegetables will wear down the incisors. As the molars are not continually growing, they do not suffer the same dental problems as rabbits, guinea pigs and chinchillas.

Dentition of Rats, Mice, Hamsters, and Gerbils

Rats, Mice, Hamsters, and Gerbils have a total of 16 teeth consisting of:
1 upper and 1 lower incisor, 3 upper and 3 lower molars on each side.

The dental formula is:  
I ¹ ⁄ ₁  
C ⁰ ⁄ ₀  
P ⁰ ⁄ ₀  
M ³ ⁄ ₃

Summary

It is worth noting that pets live longer than their wild predecessors and may encounter difficulties that they would not have experienced, or indeed been able to survive, in the wild. Recreating an animal's natural diet is not necessarily the ideal thing to do - modern diets have been well researched and offer the optimum balance of nutritional requirements for pets throughout each of their different life-stages.

However, being aware of specific dental needs of pets will enable you to reduce the risk of some problems and be prepared for others.

A twice yearly health examination by a vet is recommended and any suspected oral problems should always be referred to a veterinary surgeon.

References

• Norman Johnston BVM&S FAVD DipAVDC DipEVDC MRCVS
  RCVS, American and European specialist in Veterinary Dentistry

• British Veterinary Dental Association

Related BBC Links

• For useful information on all feathered, furry or scaly companions, head over to BBC Pets...