A First-of-its-Kind Study on Long-term Survival of Endodontic Teeth

The first-ever nationwide study sheds light on the long-term survival rate of endodontically treated teeth. 

By Dr. Mehmood Asghar

Root canal treatment is among the most commonly performed endodontic procedures worldwide. It has been estimated that over 15 million root canal treatment (RCT) procedures are performed annually. Regarded as a dentist’s last resort to save a critically damaged tooth, the longevity of RCT procedures is often questioned. A few studies have previously attempted to determine the clinical service life of endodontically treated teeth. However, most of these studies only collected data from either tertiary dental hospitals or dental practices that were visited by patients having dental insurance. Hence, a more generalized understanding of the longevity of RCT procedures has been lacking.

Recently, a team of US researchers performed a first-of-its-kind study (1) that provides unique and interesting insights into the longevity of RCT procedures. Unlike the previous studies, this research study (Thyvalikakath et al., 2022), which was published in the Journal of Dental Research (JDR), involved collecting electronic data records (EDR) of patients from general dentistry practices to obtain a generalized, comprehensive understanding of the success of endodontic treatment nationwide.

The Methodology

The EDR of patients undergoing endodontic treatment was collected from nationwide general dental practices associated with the National Dental Practice-Based Research Network (PBRN). For this purpose, two different EDR systems were utilized: Dentrix and EagleSoft.

Inclusion Criteria

Overall, 99 PRBN-associated dental practices were inducted in this study, which met the following criteria:

  • Must have used Dentrix or EagleSoft for at least 5 yrs.
  • Performed RCT on at least one tooth in at least 50 patients.
  • At least 2 years of follow-up data of the patients available for the patients.
  • EDR of permanent teeth was collected between January 1, 2000 – October 31, 2015.

For patients who had undergone only one RCT, the Kaplan-Meir estimator was used to ascertain the longevity of the endodontic treatment. For patients who had undergone more than one RCT procedure, the marginal Cox model was used for the clustered data. Finally, a multivariate comparison between different treatment variables such as age, gender, tooth type, insurance coverage, post-RCT filling or crown placement, and Network practice location was performed using the Cox proportional hazards model.

The Demographics

This nationwide study involved EDR data collected from 99 Network dental practices and 46,702 patients. Among the collected data, 14,410 (20%) teeth were anterior, 23,707 (33%) premolars, and 33,411 were molars (47%).

The Findings

The study revealed interesting findings. First, it was shown that the overall median survival rate for endodontically treated teeth was 11.1 years (10.7 – 11.5), with 21.6% of RCT expected to survive beyond 20 years. Interestingly, variables such as tooth type, insurance coverage, and post-RCT filling with or without crown placement were found to have a statistically significant effect on the survival rates of root canal-treated teeth (p < 0.0001).

Descriptive Analysis Results

Tooth Type

The results highlighted that the anterior teeth (12.4 years) had a higher median survival time than the premolars (10.3 years). In addition, patients having insurance coverage had 2 times higher instances of root canal treated teeth than those without insurance.

Post-RCT Filling or Crown Placement

It was shown that filling and crown placement increased the survival life of endodontically treated teeth. In addition, it was revealed that the median survival time of a tooth which received neither a filling nor a crown after RCT (6.5 years) increased to 11.2 years when only a filling was placed, to 11.4 years with only crown placement, and to 20.1 years when a tooth received both a filling and crown placement.  

Network Practice Location

Among the six regions studied, the highest median survival times were for the Northeast (20.5 years), followed by Midwest and Southwest (11.2 years), South Atlantic (9.1 years), South Central (9.0 years), and West regions (8.7 years), respectively.

Multivariate Analyses

  • Inter-tooth Comparison: The results showed that posterior teeth (premolars and molars) RCT procedures were 1.64 times more likely to fail than the anterior ones. However, there was no statistically significant difference between the median survival rates when premolars and molars were compared (p = 0.9989).

  • Gender: RCTs in male patients were 1.1 times more likely to fail than in female patients, showing a statistically significant difference (p < 0.006).

  • Insurance Coverage: RCT on patients without insurance coverage was likely to fail 1.2 times more than those with an insurance plan (p < 0.0001).

  • Network Practice Location: A statistically significant difference was observed between the median survival rates of RCTs in the South Atlantic versus the Northeast region (p < 0.0001). In contrast, no significant difference in survival rates was observed for the remaining areas (p = 0.9915). It was shown that an RCT in the South Atlantic region had a 2.0 times higher chance of failure than in the Northeast.

  • Post-RCT Filling or Crown Placement: The results highlighted those teeth that did not receive a filling or crown after RCT have a higher risk of failure. It was shown that teeth without any post-RCT filling or crown placement had a 2.94 times higher chance of failure than those restored with a filling before crown placement (p < 0.0001).

The Take-home Message

This is the first-ever study to provide comprehensive data about the long-term survival rates of root canal-treated teeth obtained from PBRN-associated dental practices worldwide. An important thing to note here is that this study showed slightly lower median survival rates (11.1 years) than previous studies. This may be because this study offers a greater diversity of patient data regarding location, insurance coverage, and inclusion of more dental codes than the previous studies. For example, large insurance claim data-based studies showed higher 5-year survival rates of 92% and 95% (Burry et al., 2016) than in community-based dental practices (Alley et al., 2004; Tilashalski et al., 2004).

Interestingly, a variation in the survival rates of RCT was observed for different regions. This might be due to the difference in treatment planning and decision-making process of dentists based on their location and training or level of specialization. Similarly, the clinical outcome of RCT was also significantly affected by whether a tooth was restored with a restoration or reinforced with a crown post-RCT.

Overall, this study paves the way for understanding various factors that affect the clinical outcome of RCT. However, there is still a long way to go. Future studies should focus on further understanding the factors that affect the survival rates of root canal treatment based on the dentist’s location, insurance coverage, and post-RCT tooth treatment.

Reference: (1) Regenstrief Institute. "U.S. study analyzing tooth survival after root canal in general population: Region, insurance status and other restorative dental treatments impact longevity of treated teeth." ScienceDaily. ScienceDaily, 17 May 2022. <www.sciencedaily.com/releases/2022/05/220517094850.htm&gt;.


Author: Dr. Mehmood Asghar is a dentist by profession and an Assistant Professor of Dental Biomaterials at the National University of Medical Sciences, Pakistan. Dr. Asghar received his undergraduate and postgraduate dental qualifications from the National University of Science and Technology (NUST). He is also currently pursuing a Ph.D. in Restorative Dentistry from Malaysia. Besides his hectic clinical and research activities, Dr. Asghar likes to write evidence-based, informative articles for dental professionals and patients. Dr. Asghar has published several articles in international, peer-reviewed journals.

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