My dog has a black spot in mouth after dental surgery. Is it normal?

This could be normal pigmentation in the gums. You can keep an eye on it now that your are brushing Snoopy's teeth daily. If it begins to grow or change rapidly, then he should be seen by your veterinarian.

I would recommend getting your vet to check this closely, it appears in the pictures that the lower canine is making contact with the gum and chronic irritation can cause inflammation, scarring and occasionally tumour changes

This does not look concerning to me. I suspect it is just normal pigmentation in the skin (like freckle-- only obvious quite large!). If he is licking at it a lot, or if the associated skin seems warm or inflamed, have your vet take a look. Again, overall I don't think you need to worry. Thanks for asking Petco Pet Education Center, formerly Petcoach!

Hello and thank you for contacting Petco Pet Education Center, formerly Petcoach. It looks like normal pigmentation, which can appear suddenly on the skin or mucous membranes. Please, show it to your local vets the next time you take Rocky in to make sure there is nothing to worry about.

Hello and thank you for contacting Petco Pet Education Center, formerly Petcoach. It looks like local gum pigmentation or mild inflammation. I don't think there is anything to worry about, but please show it to your vet the next time you take Tiny for an appointment.

Both teeth look normal. The gums above the tooth are pigmented in the second picture, which can be normal. (like a freckle inside the mouth). There is mild tartar calculus on both teeth but the gums look healthy. Thank you for asking Petco Pet Education Center, formerly Petcoach! You are doing a good job with the brushing!

As long as its not raised, and its never been ulcerated/bleeding, and its not changing in size, I don't think you need to be concerned. Pigment of skin and mucous membranes (gums, tongue, etc) can change with age and it is not indicative of a problem. If it DOES seem to be changing, if it becomes ulcerated or raised, talk to your vet; if that occurs, then it needs to be biopsied. But as I said already, based on what your saying and on your photo, I'm not worried. This can be a normal change. No one knows exactly why it happens. Thanks for asking Petco Pet Education Center, formerly Petcoach!