Abstract: Forty-five RCTs were identified and, from these, 26 trials including a total of 1217 participants and 2120 implants were included. Two trials were at low risk of bias, 12 were at high risk of bias and for the remaining 12 the risk of bias was unclear. In nine of the included studies there were no prosthetic failures within the first year, with no implant failures in seven studies and the mean rate of implant failure in all 26 trials was a low 2.5%. From 15 RCTs comparing immediate with conventional loading there was no evidence of a difference in either prosthesis failure (RR 1.90; 95% CI 0.67 to 5.34; 8 trials) or implant failure (RR 1.50; 95% CI 0.60 to 3.77; 10 trials) in the first year, but there is some evidence of a small reduction in bone loss favouring immediate loading (MD -0.10 mm; 95% CI -0.20 to -0.01; P = 0.03; 9 trials), with some heterogeneity (Tau² = 0.01; Chi² = 14.37, df = 8 (P = 0.07); I² = 44%). However, this very small difference may not be clinically important. From three RCTs which compared early loading with conventional loading, there is insufficient evidence to determine whether or not there is a clinically important difference in prosthesis failure, implant failure or bone loss. Six RCTs compared immediate and early loading and found insufficient evidence to determine whether or not there is a clinically important difference in prosthesis failure, implant failure or bone loss. From the two trials which compared occlusal loading with non-occlusal loading there is insufficient evidence to determine whether there is a clinically important difference in the outcomes of prosthesis failure, implant failure or bone loss. We did not identify any trials which evaluated progressive loading of implants. Overall there was no convincing evidence of a clinically important difference in prosthesis failure, implant failure, or bone loss associated with different loading times of implants. The quality of the evidence is assessed as very low due to high and unclear risk of bias of primary studies and there is some evidence of reporting bias so clinicians should treat these findings with caution. A high value of insertion torque (at least 35 Ncm) seems to be one of the prerequisites for a successful immediate/early loading procedure. More well-designed RCTs are needed and should be reported according to the CONSORT guidelines (www.consort-statement.org/), and registered with a trials registry.

Plain-language summary: This review looked at the effects of attaching artificial teeth either the same day that the implant was placed, or early (after only 6 weeks) compared to the usual delay of at least 3 months. Some studies also compared the artifical tooth being attached so that it did not touch the opposite tooth (non-occlusal loading). The search of studies was updated on 8th June 2012. The review found no evidence that attaching artificial teeth either immediately, after 6 weeks (early) or after at least 3 months (conventional) led to any important differences in the failure of the implant or the artifical tooth, or to the amount of bone which surrounded the implant (any bone loss would be an undesirable consequence). More research is needed in this area.