Canine deciduous teeth summary:

Puppies can start to teeth from three weeks of age and a total of 28 deciduous teeth erupt. 

This is also around this time that they start to wean onto solid food. 

From 3 months of age adult (permanent) adult teeth erupt and this teething is usually complete by 7 months of age where they will usually have 42 permanent teeth. 

Background:

How can I tell if my puppy is teething?

Some signs that may indicate that your puppy has entered the teething stage include: increased chewing, drooling, bad breath due to gum inflammation, mild bleeding from the gums (a little blood on a soft toy), reduced appetite and speed of eating or missing teeth.

Most of these symptoms should not be a cause for concern. However, you should still monitor your puppy. If your pet loses significant weight because of a lack of appetite, for example, it's a good idea to contact your vet. And while mild bleeding in the gums is normal, you should contact your veterinarian if there is excessive bleeding as this could be a sign of dental issues or other severe disease. Discomfort is usually mild and should resolve itself. For cases with obvious pain, make sure you contact your veterinarian. Never give your puppy medications formulated for older dogs or other pets! Always consult your vet before administering.

What can I do to make my teething puppy feel better?

Offer soft food; either a canned diet or kibble soaked in warm water.

Make sure your puppy gets plenty of interactive playtime with you.

Make ice cubes for your puppy. to play with and chew on. The ice will soothe irritated gums. This is an especially popular item during hot weather!

Provide soft or rope toys to chew on. Always supervise your pet when they are playing with toys.

Can I tell how old a puppy is by looking at the teeth?

If you have a new puppy but are not sure when they were born, you may want to know how to tell how old a puppy is by teeth. 

Since puppy teeth begin coming in at around 3 weeks, a very young puppy under that age will have no teeth at all. Once their tiny needle-like puppy teeth come in it can be challenging to tell how old the puppy is just from their teeth, but once they begin losing their puppy teeth you can assume that your puppy is about 3 months old.

At about 14 weeks your puppy's first middle incisors should begin to appear, followed closely by the second incisors at around15 weeks and the third incisors at around 16 weeks of age.

To more accurately estimate the age of your puppy it is important to consider other factors such as how open their eyes are, how much they weigh and whether your puppy has begun playing.

Your puppy's health and wellbeing are a priority and preventive care including early checkups is essential. If you have a young puppy and you aren't sure how old they are it's time to head to the vet. Your veterinarian will be able to give your puppy a thorough examination looking for signs of worms or other parasites that could affect their long-term health and be able to best advise you on when its vaccinations are due.