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Int Endod J. 2016 Jan;49(1):6-16. doi: 10.1111/iej.12429. Epub 2015 Feb 3.

The Tennessee study: factors affecting treatment outcome and healing time following nonsurgical root canal treatment.

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Department of Bioscience Research, College of Dentistry, University of Tennessee Health Science Center, Memphis, Tennessee.
Biomedical Materials Science, School of Dentistry, University of Mississippi Medical Center, Jackson, MS, USA.



To determine factors that may influence treatment outcome and healing time following root canal treatment.


Root filled and restored teeth by pre-doctoral students were included in this study. Teeth/roots were followed-up regularly, and treatment outcome was evaluated at every follow-up appointment (healed, healing, uncertain or unsatisfactory). Host (age, immune condition, pulp/periapical diagnosis, tooth/root type, location and anatomy) and treatment factors (master apical file size, apical extension, voids and density of root filling) were recorded from patient dental records. Univariate, bivariate and multivariate analyses were performed to determine the impact of the factors on treatment outcomes and healing times.


A total of 422 roots from 291 teeth met the inclusion criteria with a mean follow-up period of 2 years. The preoperative pulp condition, procedural errors during treatment, apical extension and density of root fillings significantly affected the treatment outcome. The average time required for a periapical lesion to heal was 11.78 months. The healing time increased in patients with compromised healing, patients older than 40 years, roots with Weine type II root canal systems, root canal systems prepared to a master apical file size <35, and roots with overextended fillings (P < 0.1).


Multiple host and treatment factors affected the healing time and outcome of root canal treatment. Follow-up protocols should consider these factors before concluding the treatment outcome: patient's age, immune condition, as well as roots with overextended fillings, root canal systems with smaller apical preparations (size <35) or roots with complex canal systems. Intervention may be recommended if the treatment quality was inadequate or if patients became symptomatic.


apical periodontitis; complex canal anatomy; compromised healing; endodontic healing time; endodontic outcome; master apical file size

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