The reason behind the sensitivity you feel to cold or hot while drinking or eating is the fact the the tooth has one or several nerves inside.
When a big cavity reaches the nerve, the only treatment is to remove the diseased tissue and clean the root, otherwise the tooth will be infected and might get severe pain and swelling.
At Akra Dental Clinics root canal therapy is performed by well experienced specialists following all the recent treatment protocols through a very meticulous and delicate procedures using up-to-date and high tech inurnments.