Study designs of evaluations included in the review
Randomised controlled trials (RCTs) were eligible for inclusion. The sample sizes in the included studies ranged from 17 to 36 teeth per treatment group. The duration of follow-up ranged from 1 to 5 years.
Specific interventions included in the review
Studies that compared single-visit with multiple-visit nonsurgical root canal treatment were eligible for inclusion. All of the included studies appeared to use standard endodontic treatment with 1 to 2.5% sodium hypochlorite irrigant. Multiple-visit treatments included calcium hydroxide dressings for 1 to 4 weeks.
Participants included in the review
Studies of patients with no underlying medical condition, with previously untreated apical periodontitis in mature teeth with infected necrotic root canal and radiographic evidence of periapical bone loss, were eligible for inclusion. One of the included studies only included patients with a periapical index (PAI) of 3 or more (out of a possible 5 points).
Outcomes assessed in the review
Studies that assessed the number of teeth with radiographic evidence of healing were eligible for inclusion. The included studies measured healing using different time periods: one study classified healing as a decrease in PAI at 1 year, while another followed up most patients until complete healing occurred up to 5 years; methods used in the third study were not reported.
How were decisions on the relevance of primary studies made?
Two reviewers independently selected studies, but the methods used to resolve disagreements were not reported.