Smoking reduces blood flow and reduces the ability of your immune system to tackle infections.
Both of these important functions will be impaired if you are recovering from a dental surgical procedure (such as an extraction).
Smokers are at increased risk of developing a dry socket (Where a normal blood clot fails to form in the extraction socket, leading to superinfection of the exposed bone by oral bacteria. This is an extremely painful condition that takes a long time to heal.) take longer to heal, and are more prone to infections of the surgical site.
If a graft (bone or soft tissue) has been performed, the poor blood circulation in the area may cause the graft to fail. Dental implants are also more likely to fail in smokers.