Yes, that is possible. It can be caused by the needle breaking a blood vessle or by the novocain collecting in one spot. This can happen if you take aspirin or blood thinners.
Any shots can produce a discoloration of the skin or in this case the oral muscosa. The usual cause is nicking a small capillary, which then leaks a small amount of blood before it clots and is later repaired.
No, normally dental shots will not leave you with a bruise. They will be painful when the medication goes in, but your dentis will give you a topical numbing cream first. Your jaw may be slightly sore the rest of the day.
Yes, the inside of your mouth could have a bruise or feel like it. Whenever I go to the dentist I always can feel where he gave me a shot for a few days after.
