Root canal treatment is an effective treatment method for endodontic and periapical diseases and has been widely used in clinical practice. However, during and after the treatment, the patient may experience pain for various reasons, causing distress to the patient. Therefore, clarifying the causes, mechanisms and related factors of pain during root canal treatment will help clinicians to take corresponding effective measures and treatment methods to relieve the pain of patients.
The pulp is located in the pulp cavity composed of dentin and is connected to the periapical tissue through the apical foramen. The pulp also has the following characteristics: surrounded by unyielding dentin; the matrix is fibrous and viscous; no efficient blood collateral circulation. These characteristics make pulp damage generally difficult to recover and prone to pain.
The nerves of the dental pulp originate from the maxillary and mandibular branches of the trigeminal nerve, including Aδ and C fibers. Aδ fibers are distributed in the pulp-dentin junction area, and their stimulation threshold is low, usually sharp pain, which is related to dentin hypersensitivity; C fibers are unmyelinated nerve fibers that are located in the entire dental pulp. They have a high stimulation threshold and produce burning pain after stimulation, which is related to the pain of dental pulp diseases. C fibers are more resistant to hypoxic environment, and C fibers are still active when the pulp tissue is necrotic, so the affected tooth will still experience pain when the root canal of the dead pulp is prepared. In addition, there are no pressure and proprioceptors in the nerve endings in the pulp, so pulp pain is often not localized.
Clinically, pain during root canal treatment is mainly related to C fibers. The main causes of pain are:
(1) During inflammation, the tissue pressure in the medullary cavity increases, and C fibers are sensitive to pressure and produce pain;
(2) The periapical tissue activates and releases a variety of chemical substances, such as histamine, bradykinin, serotonin, prostaglandin and other inflammatory mediators that directly act on nerve endings, making pain receptors more sensitive to environmental changes.
(1) Age and gender
Although it is generally accepted that pain from root canal treatment is not related to gender, women tend to have higher rates of pain than men. The pain after root canal treatment is related to gender. Cortisol hormone can make it easier for people to resist pain, and male cortisol hormone secretes more than female, so the proportion of female pain after root canal treatment is higher. At the same time, women's hormone secretion levels fluctuate during menstruation or when taking oral contraceptives, serotonin and norepinephrine levels may change, and the incidence of pain increases.
Pain after root canal treatment often occurs in younger people (18-33 years). Because of the narrow diameter of the root canal, less debris pushing out of the apical foramen, and relatively less blood supply to the jaw, the elderly experience less post-treatment pain.
(2) Condition of the pulp and periapical tissue
Bone resorption in the apical region visible on X-ray is also a risk factor for emergencies during root canal treatment. Some scholars pointed out that the number of emergencies during root canal treatment in patients with bone resorption in the apical region was 9.64 times that in patients with no abnormality in the apical region. The probability of pain is significantly increased if the bone destruction in the apical region of the tooth is 5 mm in diameter or larger. Some scholars hold the opposite opinion, they believe that the tooth without bone destruction in the apical area has a higher probability of pain after treatment. The reason is considered to be that there is no bone destruction in the apical area, so there is not enough space to buffer the pressure of inflammation in the apical area.
(3) Tooth symptoms
It is generally believed that teeth with obvious pain and discomfort before root canal treatment are more prone to pain after treatment. Most patients with tooth pain symptoms before root canal treatment also experience pain after treatment. Pain makes the patient more nervous, and the body's immune system weakens, so the probability of emergencies during root canal treatment increases. Some scholars believe that patients with asymptomatic apical periodontitis may experience pain after treatment, and some scholars have suggested that the teeth with chronic pulpitis and apical periodontitis have "local adaptation syndrome", that is, chronic inflammation persists without obvious swelling of the teeth. During root canal treatment, the periapical tissue is exposed to physical and chemical stimuli, resulting in a strong response, the pressure in the apical area increases significantly, and pain and swelling occur.
(4) Tooth position
Molars, especially mandibular molars, are more painful after root canal treatment. Scholars such as Watkins found that compared with maxillary molars, mandibular molars had a higher incidence of pain after root canal treatment, and the incidence of posterior teeth was higher than that of anterior teeth. The probability of emergencies during root canal treatment in molars is 1.7 times higher than that in premolars and anterior teeth. The reason is that the number of root canals in the posterior teeth is large, the anatomical shape is complex, and the amount of debris pushing out of the apical foramen is more.