Sixteen studies were included for review (n= 5,081 teeth): six RCTs (n=1,048); seven prospective cohort studies (n=2,963); two retrospective cohort studies (n=683) and one cohort study where it was not possible to establish whether it was retrospective or prospective (n=387).
There was wide variation in results between included studies. In patients with apical periodontitis, one prospective cohort study found that a single-visit treatment was more likely to result in post-operative pain compared to multiple-visit treatment in patients with apical periodontitis ( n= 405, OR = 2.8, 95% confidence interval (CI): 1.7, 4.7, p<.0001). However, one retrospective cohort study found that multiple-visit treatment was more likely to result in post-operative flare ups (n=402, OR = 2.8, 95% CI:1.1, 7.1, p=.03). There was no significant difference in post-operative pain levels between single-visit treatment compared to multiple-visit treatments in patients with no acute periodontitis (three studies, n=428). In studies where there was mixed or unknown periapical status, eight out of 10 studies found no significant differences in pain or flare ups between single-visit or multiple-visit treatment in groups of patients with mixed or unknown periapical status (n=2,248 for studies finding no difference; n=1,371 for studies favouring a single visit). One RCT found that the risk of flare up was higher in patients undergoing re-treatment in a single visit compared to patients undergoing multiple visit treatments (n=227, OR=4.9, 95% CI: 1.1, 19 p=.05).