What are the causes of pain during and after root canal therapy?
Root canal procedure (RCT) is a common endodontic procedure in dentistry, done when the caries or the infection has reached the pulp. A tooth has two parts- crown and a root. Now going from outside to inside the crown portion has 3 layers- enamel, dentin and pulp. The root has 3 layers- cementum, dentin and pulp.( Wheeler's dental anatomy)
Now only the pulp tissue is vascular as well as innervated. Hence if the infection/caries is superficial then there is generally no pain however sensitivity to cold may be experienced. When the infection is superficial then simple removal or excavation followed by a proper shape and then that portion is restored.
However when the infection or the caries has involved pulp deeply or even made the pulp dead or necrosed, infecting tissues apical to the pulp then RCT is the preferred treatment of choice to conserve the tooth than a simple extraction of the tooth.
Now during RCT pain can be experienced due to- 1)Generally local anaesthesia is given prior to the procedure. However at times especially when lower back molar tooth is involved local anaesthesia fails. And during the procedure patient feels sharp and severe pain. This condition is known as hot tooth( Grossman's endodontic practice). In those cases a different technique of local anaesthesia is employed. 2) Pain is also experienced when the instrument goes beyond the apical foramen. Apical foramen is a hole at the apex of the root from which blood vessels and nerves enter and leaves the tooth. The pain in this case stops once the instrument is withdrawn. The dentist should make sure that this should not be repeated since the instrument can injure the tissues apical to the tooth. In rare cases, the dentist may inject the irrigant beyond the apical foramen. Irrigant usually used by the dentists is sodium hypochlorite. It kills the bacteria and debris. However it should not be extended beyond the tooth. In these cases patient experiences sharp pain, redness, swelling immediately lasting minutes but may continue upto days. The dentist should neutralize the irrigant and compress the area with cold compress and afterwards followed by warm compress. Antibiotics and painkillers should also be given.( Grossman's endodontic practice, Thomas Matthew 2015) These pains are experienced by the patient at the chair side.
3)If the RCT is carried out in multiple sittings the patient may experience endodontic flare up(Grossman's endodontic practice) as he/she goes back from the clinic. In this case patient may experience pain and swelling in the area. There can be many reasons for this including anxiety of the patient, procedural error on the side of dentist, etc. The patient should contact his/her dentist explaining about his/her problem. Now after RCT procedure patient may experience the pain. This pain generally is more significant during biting and chewing. Common reasons can be procedural error or a missed canal by the dentist.(Grossman's endodontic practice) At times the RCT treated tooth may fracture (known as vertical fracture) giving rise to dull, spontaneous pain, mobility. This may be due to a habit of grinding teeth by the patient (bruxism) or excessive load on that tooth, etc. In these cases the fractured tooth is extracted. ( Grossman's endodontic practice).
These were some of the reasons wherein the patient may experience the pain during/after RCT. It's important to note that these situations happen only in few cases, not always. RCT procedure is a very effective procedure to conserve the tooth. The anatomy and physiology of each individual varies. Hence, these conditions may or may not happen. The patient should trust the dentist and should discuss his/her problem openly.
I hope I have answered your question :). References have been given in the parentheses.