As breeders, the 2 most common issues we see with puppy teeth are retained puppy teeth and malocclusion (overbite/underbite). More often than not, they are mild forms and the only issue is that of appearance and there are no health problems associated with the issue.
Retained Puppy Teeth Retained baby teeth are a very common occurrence in puppies - especially toy breeds. Just as with people, puppies lose their baby teeth, or deciduous teeth, and then develop adult teeth. Puppies normally start to get their baby teeth around 4-6 weeks of age and have all 28 Baby (deciduous) teeth by the time they reach 8-10 weeks of age. The adult teeth start to come in between months 4-7 and by 8 months, all 42 adult teeth should be in. As soon as the permanent teeth start to form, the baby teeth weaken, loosen, and SHOULD fall out, but very commonly, one or more may remain.This is referred to as "retained deciduous/puppy teeth." Problems could result because the teeth can be crowded and/or crooked. If the problem is strictly cosmetic, meaning it does not cause the dog to be uncomfortable in any way, the teeth can be left alone. More often than anything, the retained teeth just crowd other teeth and cause a lot of plaque/tartar build up which could speed up tooth decay. Occasionally, retained teeth can cause an abnormal bite, meaning the upper and lower jaw do not line up, which may actually cause pain/discomfort and trouble chewing and therefore eating. The extra teeth can actually poke into the gums above/below it and be extremely irritating/painful and can cause infection. This would be a defect necessitating a quick solution. Unless there is a severe problem, baby teeth do not have to be dealt with immediately, and can be left until the pup is in for it's spay/neuter surgery. The extra teeth can be safely removed while the pup is already under anesthesia for these procedures.
Overbite / Underbite Mild over/underbites are normally harmless conformation flaws that do not cause any problems. Usually a breeder who recognizes a dog who produces a lot of pups with over/underbites would remove the dog from the breeding program. Even so, occasionally pups are still born with malocclusions.
Because a pup's top jaw and bottom jaw often grow at different speeds, there can often be a temporary misalignment of the teeth. A puppy's jaw finishes growing at approximately 10 months of age and until that time, a mild overshot/undershot jaw will commonly correct itself. Other times, the jaw will remain over/undershot which in a mild form, causes no problems.
Overbites (overshot jaw, parrot mouth or brachygnathism) occur when the upper jaw is longer than the lower jaw causing the upper teeth to overlap the lower.
Underbites (prognathism) occur when the lower jaw is longer than the upper jaw. It is interesting to note that an underbite is an expected part of a normal mouth in brachycephalic breeds such a Boxers, Shih Tzus, Bulldogs etc.
In some instances, more rapid tooth decay and/or eroding of the dental enamel could occur due to the rubbing of teeth on one another. In extremely severe cases of malocclusion, where the teeth from one jaw are actually irritating the soft tissue in the mouth, corrective dental surgery should be performed to improve the dog's comfort and chewing ability.