Adult dogs have a total of 42
permanent teeth, 20 in the upper jaw and 22 in the lower jaw. A dog is said to have 'Full Dentition' when it has the complete compliment of 42 teeth in place.

Puppies however, only have 28 teeth, 14 in the upper jaw and 14 in the lower jaw.   Puppies do not have any molars or premolar1 (refer to table below). The puppy teeth are known as
deciduous teeth (sometimes also called baby teeth or milk teeth). The deciduous teeth are lost and replaced with the permanent teeth when the pup is between 3 - 7 months old. A dog's jaws can also change in length and grow until the age of approximately 11 months.
diagram 1. Dentition chart for an adult dog, 42 permanent teeth               diagram 2.  Dentition chart for a puppy, 28 deciduous teeth
                                                              FUNCTIONS OF THE DIFFERENT TYPES OF TEETH
INCISORS: 12 in total, 6 in each jaw - used for cutting, nibbling, grooming and picking up objects. Incisors are found at the front of the mouth
CANINES: 4 in total, 2 in each jaw - used for holding and tearing, sometimes called the fangs. The canines sit just behind the incisors.
PRE-MOLARS: 16 in total, 8 in each jaw - used for cutting, holding, grinding and shearing off food, basically breaking the food into smaller pieces. Pre-molars are found down the sides of each jaw behind the canines.
MOLARS: 10 in total,  6 in the lower jaw and 4 in the upper jaw - used for grinding food into smaller pieces. Molars are situated at the back of the jaw behind the pre-molars. 
diagram3. Dentition chart showing the positioning of the teeth in the upper lower and upper jaws of an adult dog.
                                             THE BITE: CORRECT AND INCORRECT BITES
The term 'bite' refers to the positioning of the dog's teeth at the front of the jaw and is determined by the length of the top and bottom jaw in relation to each other. The normal bite for most dog breeds is the  'scissor bite'. This is when the incisors from the top jaw close just over and touching the incisors of the bottom jaw (like a pair of scissors). As in diagram 1 above.

Incorrect bites in all the Australian breeds are jaws that are overshot, undershot, wry or level (refer to diagram 4). Within these breeds such bites are regarded as a fault. Hence these dogs can not be shown and should not be bred from.
It must be noted that some of these bites are perfectly acceptable in the standards of other particular breeds. For example the bulldog must have an undershot bite, which in this breed is considered correct.
diagram 4: Incorrect bites for 'most' dog breeds.
OVERSHOT BITE: also referred to as overbite, parrot mouth and brachygnathism. In humans this condition is called 'bucktoothed'.
Overshot is when the upper jaw extends beyond the lower jaw, there is a distinct gap between the incisors of the top and bottom jaw.

A dog's bottom jaw will continue growing until the age of 10 - 12 months. Until this time a slight undershot will often correct itself naturally with ageing. A severe overshot is unlikely to correct itself but is not a significant health issue for the dog. Overshot dog's can still lead healthy lives as happy and loving pets regardless of this problem. Dog's with an overbite should not be shown or bred from.

UNDERSHOT BITE: also referred to as an underbite. This when the bottom jaw is longer than the top jaw and the incisors on the bottom jaw protrude past those of the top jaw. This type of bite is actually correct for breeds such as the bulldog. An underbite generally does not adversly effect the dog in anyway. These dogs still make loving and healthy pets but should not be shown or bred from.

LEVEL BITE: also called the pinscer bite. This is where both jaws are the same length and the incisors meet edge to edge. This bite does not affect the dog adversely in any way but can cause premature wearing of the incisor teeth. Often in a slightly older dog the bite can go from scissor to level with ageing.

WRY BITE: This is where the bottom jaw is twisted and the incisors do not meet in a correct straight scissor bite. This type of bite is not very common and generally the dog suffers no ill effects. A dog with a wry mouth should not be shown or bred from.

In most cases and overshot, undershot, level or wry bite is not a serious condition and should not discourage someone from purchasing such a pup unless their intentions are specifically to show or breed. In the wild a dog with an incorrect bite could have great difficulty hunting and killing prey. For the purposes of a pet an incorrect mouth is not a serious concern as modern prepared dog foods are in palatable sized portions. An incorrect bite would however exclude a dog from a working career where the dog was required to use it's mouth, for example, herding or police work.

The inheritance mode of a dog's bite is largely unknown and litters may present with confusing outcomes. However, because an incorrect bite can be determined by 12 months of age, a dog with such a fault can be excluded from a breeding programme.

Incorrect bites vary greatly with respect to severity and occurrence. Some breeds and lines within breeds appear to have a higher incidence of bite faults than others. It has also been found that dogs with undershot bites often result from parents with correct scissor bites. This would indicate that the fault is recessive but no conclusive proof is available.

Dogs who produce offspring with bite faults should not necessarily be exclude from a breeding programme because of this reason alone. There is a saying, "Don't throw out the baby with the bathwater."  Which basically means that a good example of the breed both in conformation and temperament should not be excluded solely because it has produced offspring with an incorrect bite. Other offspring from this dog may be perfectly correct in mouth. To exclude such a dog would mean eliminating valuable genetic material from the population unnecessarily. To breed from this dog would however mean that the fault can not be eliminated completely from future generations and as such the offspring would need to be checked for this fault.  Often a recessive fault can go unseen for several generations before it makes an appearance again.

It has also been suggested that the bite might not be entirely governed by genetics and that the size of the actual incisors can play a role in the bite. In our own breeding programme we have observed that dogs with larger incisors are less likely to have an even or overshot bite as an older dog.

Because the bottom jaw continues to grow until the dog reaches 12 months is has been observed that a puppy with a slight overshot bite has corrected. Hence it is sometimes worth retaining an otherwise promising puppy that may have a very slight gap in the jaws at a young age. Some people say that a matchstick gap is ideal. Puppies with smaller incisors and no gap can actually go even or undershot. Some breeders also believe that a slight overshot can be corrected by administering the puppy extra calcium supplements at a young age while the jaw is still growing.

A bite can stay the same throughout puppyhood or change greatly as the dog grows during the first year. There is no hard and fast rule. We have observed a particular puppy go from being overshot to scissor to even to undershot in the space of  several months while it's littermates held perfect scissor bites the whole time.

MISSING TEETH (incomplete dentition)
Another concern from a breeding perspective is dogs that have missing teeth. For most working and herding breeds the standard requires full dentition (42 teeth).

Once again the genetic mode of inheritance for missing teeth is unknown. Parents with full dentition can produce offspring with one or more missing teeth suggesting inheritance is recessive. This appears to be compounded by the fact that x-rays have shown that some dogs who were thought to have a missing tooth, actually possessed the tooth in question but it was below the gum-line and was therefore not visible.

Some breeders are overly pedantic about a dog having one missing tooth and will eliminate such a dog (and even sometimes it's parents) from their breeding programme. This action is unwarranted as the genetic material in an otherwise excellent specimen could be lost forever. This decision can be yet another example of  "Throwing out the baby with the bathwater." Particularly when the mode if inheritance is not understood.
An animal should be assessed in its entirety and it's value to the gene pool as a whole, never on one factor alone.

Although missing teeth are certainly not desirable in a show or breeding dog, there are very few standards that actually describe this as a serious or disqualifying fault (one of which is the German Shepherd Dog). The ANKC standards for the Australian breeds do not state that full dentition is required therefore although not desirable, a dog should not be penalised for having a missing tooth.

A puppy's teeth and bite should be regularly checked whilst they are growing. This is to ensure that the bite is correct but also to make sure that the deciduous teeth fall out correctly as the permanent teeth grow in. It is possible for a puppy to retain baby teeth particularly the canine teeth (this is quite common in smaller breeds). These teeth will need to be pulled or removed if they don't fall out naturally. Sometimes the tooth is already loosened by the permanent tooth and can just be wiggled and will come free. It the tooth is still deep rooted and not loose it may need to be removed by a veterinarian.

When puppies are teething their gums are often sore and swollen. It is of value to supply the puppy with something suitable and safe to chew which will both help relieve the discomfort and loosen the deciduous teeth. Brisket bones and rawhide chews are ideal.

Overall gum and tooth health requires the owner to periodically check the teeth for build up of tartar or any infections. A dog's teeth need to be checked just like humans do. It is also worth mentioning that a diet of only soft foods is not good for tooth health.