Clinical takeaways
- Cracked teeth can often be preserved after root canal therapy. The study found an 82.9% success rate and an 89.7% overall survival rate, with an estimated 99.2% two-year and 78.6% five-year survival rate, suggesting extraction is not automatically necessary.
- Crack severity and periodontal involvement strongly influence outcomes. Teeth with deep radicular crack extensions and probing depths of ≥5 mm were significantly more likely to fail than less severe cases.
- Restorative and protective measures may improve longevity. Crowns were associated with better outcomes than onlays or composite restorations, and occlusal splints appeared to benefit patients with bruxism or heavy chewing habits.
A cracked tooth requiring root canal therapy poses concerns for clinicians, namely whether the tooth can be salvaged or if extraction is necessary. New research published in the Journal of Endodontics reports optimistic outcomes for many treated teeth, suggesting that extraction is not necessarily inevitable, according to a June 25 press release from the American Association of Endodontists.
In addition, seven factors, as well as specific treatment choices, predicted the long-term outcomes of endodontically treated teeth, according to the study’s authors.
"Nothing functions exactly like a natural tooth," said Dr. W. Craig Noblett, MS, president of the American Association of Endodontists, in the release. "One of the most important messages from this research is that patients should understand all of their options before deciding to remove a tooth. Endodontists specialize in saving teeth, and many teeth that appear compromised may still be treatable."
In the study, researchers evaluated the success and longevity of cracked posterior teeth that were endodontically treated and the factors that were associated with success or failure (J Endod, August 22, 2025, Vol. 52:1, P79-88).
Clinical data from two board-certified endodontists who treated 2,520 patients with root canal therapy (RCT) from July 2019 to March 2024 were collected. From that number, 263 teeth met the inclusion criteria, which were adults ages 18 to 80 with RCT on posterior molars because of cracks and at least one year of follow-up. Additionally, teeth were excluded if the cracks extended more than 5 mm below the orifice, cracks crossed more than one-third of the pulpal floor, or there was a root fracture or a condition rendering the tooth unrepairable.
The research team classified cracks confined to the pulp chamber as coronal (C) and those extending into the root canal as radicular (R). Using the Iowa index, researchers modified it to establish staging, which included I-C, I-R, II-C, II-R, III-C, III-R, IV-C, and IV-R.
Using the Kaplan-Meier method, researchers estimated the two- and five-year survival rates of RCT teeth, while both univariable and multivariable Cox regression identified factors linked to RCT failure. Of the 263 cracked teeth, 82.9% were classified as successful and 45 teeth as failures.
The success rates for stages I-C, I-R, II-C, II-R, III-C, III-R, IV-C, and IV-R were 98.3%, 88.9%, 92.6%, 88.6%, 83.9%, 78.9%, 75%, and 33.3%, respectively. The mean follow-up period was 40.3 months (range, 12 to 67 months; median, 38 months; standard deviation, 14.9 months). The overall survival rate was 89.7%, and the Kaplan-Meier survival curve estimated the five-year survival rate as 78.6%.
Seven factors predicted failure, including:
- Older age
- A periodontal probing depth of ≥5 mm along the crack
- A radicular extension of ≥3 mm
- The presence of a preoperative periapical lesion
- Multiple crack lines
- Lack of an occlusal splint in patients with heavy chewing and/or bruxism
- A restoration with an onlay or composite filling rather than a crown
Besides the factors above, using an intraorifice barrier with a flowable hybrid composite enhanced fracture resistance, particularly for radicular cracks, the research team noted.
Teeth with periodontal pockets <5 mm (stages I to III) fared well, with a 78.9% to 98.3% success rate, whereas teeth with a radicular crack and a deep periodontal pocket ≥5 mm) (which researchers classified as stage IV-R) did worse, with a 33.3% success rate and 63% survival.
The strongest risk multiplier was a radicular crack extending ≥3 mm followed closely by intermediate composite restorations and onlays. Older patients and those with multiple cracks had significantly worse outcomes, possibly reflecting cumulative “structural fatigue” in tooth tissue over time, the authors wrote.
“Cracked teeth requiring root canal treatment often present a dilemma for clinicians: whether to preserve or extract the tooth. The development of a prognostic evaluation index may assist clinicians in making more informed treatment decisions and enhance communication with patients regarding expected outcomes,” concluded the study's lead author, Dr. Tadkamol Krongbaramee, PhD, of the Chiang Mai University Division of Endodontics, which is based in Thailand.
