"Doctor, Why Does My Tooth Still Hurt"

"Doctor, Why Does My Tooth Still Hurt"

Alan S. Law, D.D.S., Ph.D.*, Emily Utoft Durand, RDH, RF**, D. Brad Rindal, D.D.S.†, and Donald R. Nixdorf, D.D.S., M.S.‡ for the DPBRN Group:

“Why does my tooth still hurt? I thought that a root canal would take the pain away.”

Out of all the questions patients ask, those involving persistent pain can be among the most challenging to answer.
Based upon what is known about the number of root canal treatments performed annually and research findings related to post-treatment pain, many patients and dentists will experience  significant frustration related to persistent pain.
It is estimated that approximately 16.4 million root canal treatments are performed annually in the United States.1 Most studies that examine pain after root canal treatment show that three to six percent of patients will experience severe pain in the days following treatment.2 A recent meta-analysis of the endodontic literature suggests that 5.3% of patients who received root canal  therapy report some form of pain six months or longer following treatment.3 Extrapolating from these numbers, approximately 800,000 U.S. patients will have severe, acute, post-operative (in the first 7-10 days after treatment) pain annually, and a similar number will be experiencing persistent (present at six months or longer after treatment) pain.
This article will review existing literature on acute and persistent endodontic pain, and will suggest how dentists in Minnesota can help to develop new knowledge related to the issue of post-treatment pain.

Acute Pain Following Root Canal Treatment
Significant tooth pain occurring within one week of root canal therapy, referred to as post-endodontic flare-up pain, has been reported to occur in 1.6% to 6.6% of all root canal procedures.4-11

This pain has been well described within the literature as severe pain (>_ 7 on a scale of 0-10) occurring in or around the location of a tooth that received root canal therapy within the prior  week. Post-endodontic flare-up pain is also associated with lost productivity for both patients and dentists due to a frequent need for emergent appointments for re-evaluation.10 Together these  issues are significant, since approximately 800,000 patients experience postendodontic flare-up pain each year.  These numbers are particularly important given that pain experienced during and  after root canal therapy is known to cause significant amounts of dental anxiety and fear,12 presents a major barrier to receiving dental care,13-17 and has other negative psychosocial  consequences.18

Acute post-endodontic pain is typically treated with various short-term prescription analgesic regimes taken orally when the pain becomes severe. This approach is very effective for the majority of patients,19 but does not address the analgesic needs of the approximately three percent of patients experiencing flare-up pain.20

Research has elucidated a number of risk factors associated with the development of postendodontic flare-up pain, but most are not modifiable (e.g., pretreatment pain, pretreatment  diagnosis).6,10 In non-dental surgeries, pre-existing pain has been found to relate to the development of severe short-term post-operative pain.21 This finding from outside dentistry suggests  that a more complete understanding of the factors related to the development of peri-operative pain may open up new avenues for more effective pre-emptive treatment strategies to reduce the  occurrence of postendodontic flare-up pain.

Persistent Pain Following Root Canal Treatment
Persistent tooth pain (i.e., present six months after root canal therapy) has been reported to occur in 3% to 12% of cases,22-24 but methodological issues have limited the ability to relate these  results to community dental practices. A recently completed systematic review of the endodontic literature and meta-analysis suggests a frequency of 5.3% (95% CI: 3.5-7.2%)3 with a best  estimate of 3.4% (95% CI: 1.4-5.5%) being of non-odontogenic origin (Nixdorf et al - unpublished). To extrapolate this to a conservative estimate for the United States population, approximately  870,000 new cases of persistent pain are thought to occur following a relatively common dental treatment, with 550,000 cases of such pain not having an identifiable local reason explaining why it is present.

It is unknown to what extent the population is burdened by this type of persistent pain. In previous reports of patients who have undergone general surgical operations, up to 30% developed  persistent pain. Moreover, of those who did develop persistent pain, up to one third experienced pain that was sufficiently burdensome to be considered disabling.21,25-27 The burden of  persistent pain has not been reported by any studies investigating dental procedures such as root canal therapy. But if the same 3:1 ratio applies to root canal therapy as to non-dental surgical  procedures, then overall we would expect three percent of patients to report persistent pain, and one percent of patients to report persistent pain that interferes substantially with activities of  daily life.

Possible mechanisms for persistent pain following root canal treatment are unknown, but some insight into this phenomenon may be gleaned from looking at findings from other pain models. Persistent pain after nerve sectioning is not a newly recognized phenomenon in health care; historic reports refer to it as “phantom limb pain”.25 In 1978, the term “phantom tooth pain” was  coined to describe pains after amputation of dental pulps via root canal therapy.28 Other terms have been used to describe similar tooth-related pain presentations, such as idiopathic  periodontalgia,29 idiopathic odontalgia,30 and atypical odontalgia.31 In this research protocol, the term “persistent pain” is used because it is generic, descriptive in nature, eliminates confusion  with previously used terminology that may be associated with specific pain mechanisms, and most notably, causation by the root canal therapy is not implied, since often pre-existing pain is present.

Adequate treatments are emerging for certain pain phenomena and appear to be more effective when patients are treated early in their course of pain.32 Early identification and treatment may  improve prognosis, but the first step is to determine how widespread the problem is and how severely it affects the individual, as discussed above. Following this, a critical next step toward  improving care would be to identify at-risk individuals before root canal therapy is performed and intervene to prevent development of persistent pain and disability. For this to occur, risk factors  involved in the development of persistent pain associated with root canal therapy need to be assessed before providing treatment. Potentially significant risk factors may be associated with the person (e.g., gender, tooth anatomy, psychosocial variables, other medical conditions, concomitant medication use), disease (i.e., pulp/peri-radicular diagnosis), and treatment rendered (e.g.,  instrumentation and procedural difficulties, type of root canal provided).24,26 With knowledge of these risk factors, dentists could reduce patients’ potential for developing persistent pain by  altering the course of treatment. Using them together, under the concept of multimodal approach to treatment, has been advocated to improve perioperative pain management, which includes  pre-operative pain, intraoperative pain, and post-operative pain.21 Examples include improving existing chronic pain conditions prior to elective surgery, establishing and maintaining local  anesthesia, and pre-emptive administrative of medications shown to reduce neuropathic pain (i.e., gabapentin, pregabalin, venlafaxine, ketamine),26 as well as adequately addressing post-operative pain with traditional analgesic medication.33

Other strategies might include pre-operatively addressing modifiable high-risk factors as well as preventive methods to neutralize non-modifiable risk factors. In this way, new knowledge will create a foundation for future clinical research that will further improve root canal therapy and potentially other dental and surgical procedures as well.

What Can You Do?
Dentists in Minnesota have a unique opportunity to participate in a research project that will address this important clinical issue. If you are interested in participating or learning more, please visit the website http://www.umn.edu/~nixdorf for more information. On that website is a link to a Study Timeline, which displays both the dentists’ and the patients’ activities.
To learn more about the Dental PBRN, visit our website at http://www.dentalpbrn.org. To enroll you need to complete the online enrollment form, complete Protection of Human Research Subjects  training (for which CE credit is given), and watch an orientation DVD.
If you would like more information about this study, please contact Emily Utoft Durand, DPBRN Regional Coordinator, at Emily.C.Durand@healthpartners.com or at (952) 967-7404.

This research has been supported by the National Institutes of Health (NIH) grants NIDCR, U01-DE016746, U01-DE016747, and NCRR, K12-RR023247.

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*Dr. Law is an endodontist in private practice with The Dental Specialists, Lake Elmo, Minnesota.
**Emily Utoft Durand is research coordinator, HealthPartners Research Foundation, Bloomington, Minnesota.
†D. Brad Rindal is a dental investigator, HealthPartners Research Foundation, Bloomington, Minnesota.
‡Donald R. Nixdorf is assistant professor, University of Minnesota, Minneapolis, Minnesota.