Had an injection at dentist 2 months ago now have pins and needles feeling in im chin when touched also sometimes can't feel my salava run down my chin?

Trigeminal nerve: You could have had injury or irritation to the trigeminal nerve, which supplies sensation to the face.

Since dental visit?: Have you had the "pins and needles" since the dental visit? Or is this something that came up a while afterward? If since, this can be a mild form of paresthesia, where the nerve remains numb for some time. Talk to your dentist about it, but it should go away over time. It can be common after having wisdom teeth extracted, as the nerve sometimes runs along very close to the roots of the tooth.

Unusual but happens: This can happen, especially when working on a lower tooth. It almost always resolves by itself with time. It can take many months to completely go away. Talk to the dentist who did the treatment and see what he thinks.