Inconclusive results were reported about the cleaning and disinfection accomplished by the two irrigation methods .
There is insufficient evidence to cl aim general superiority of any one of these methods .
The aim of this study was to systematic ally review and critically analyse the published data on the treatment outcome ( primary outcome ) and on the  cleaning and disinfection of root canals  ( secondary outcomes ) achieved by negative pressure irrigation as compared to syringe irrigation .
Statistics notes: Absence of evidence is not evidence of absence
R and omized controlled clinical trials are conducted to determine whether differences of clinical importance exist between selected treatment regimens . When statistical analysis of the study data finds a P value greater than 5 % , it is convention to deem the assessed difference nonsignificant . Just because convention dictates that such study findings be termed nonsignificant , or negative , however , it does not necessarily follow that the study found nothing of clinical importance . Subject sample s used in controlled trials tend to be too small . The studies therefore lack the necessary power to detect real , and clinical ly worthwhile , differences in treatment . Freiman et al. found that only 30 % of a sample of 71 trials published in the New Engl and Journal of Medicine in 1978 - 79 with a P value greater than 10 % were large enough to have a 90 % chance of detecting even a 50 % difference in the effectiveness of the treatments being compared , and they found no improvement in a similar sample of trials published in 1988 . It is therefore wrong and unwise to interpret so many negative trials as providing evidence of the ineffectiveness of new treatments . One must instead seriously question whether the absence of evidence is a valid justification for inaction . Efforts must be made to look for quantification of an association rather than just a P value , especially when the risks under investigation are small . The authors cite a recent trial comparing octreotide and sclerotherapy in patients with variceal bleeding  , as well as the overview of clinical trials evaluating fibrinolytic treatment for preventing reinfa rct ion after acute myocardial infa rct ion as examples
Inconclusive results were reported about the cleaning and disinfection accomplished by the two irrigation methods .
There is insufficient evidence to cl aim general superiority of any one of these methods .
The aim of this study was to systematic ally review and critically analyse the published data on the treatment outcome ( primary outcome ) and on the  cleaning and disinfection of root canals  ( secondary outcomes ) achieved by negative pressure irrigation as compared to syringe irrigation .