Data sourcesPubmed, Embase, Cochrane Central Register of Controlled Trials and the Web of Science databases. Hand searches of the journals European Journal of Orthodontics, Journal of Orthodontics, Journal of Clinical Orthodontics, Seminars in Orthodontics, American Journal of Orthodontics & Dentofacial Orthopaedics and Angle Orthodontist.Study selectionTwo reviewers independently selected studies. Randomised controlled trials (RCTs) and controlled clinical trials (CCTs) of orthodontic patients requiring extraction of the maxillary first premolars and closure of the spaces without anchorage loss were considered.Data extraction and synthesisData extraction and risk of bias assessment were carried out independently by two reviewers. Meta-analysis and sensitivity analysis were conducted.ResultsFourteen studies; seven RCTS and seven CCTs were included. In total 303 patients received TISADs with 313 control patients. Overall the quality of the studies was considered to be moderate. Overall the TISAD group had significantly less anchorage loss than the control group. On average, TISADs enabled 1.86mm more anchorage preservation than did conventional methods.ConclusionsThe results of the meta-analysis showed that TISADs are more effective than conventional methods of anchorage reinforcement. The average difference of 2mm seems not only statistically but also clinically significant. However, the results should be interpreted with caution because of the moderate quality of the included studies. More high-quality studies on this issue are necessary to enable drawing more reliable conclusions.