Table 2. Quality assessment of included studies.

	randomization	concealed allocation	blinding	incomplete outcome data	selective reporting	other biases	Qi
Cao 2012	mentioned	unclear	unclear	unclear	unclear	unclear	0.75
Chew 2010	mentioned	yes, sealed opaque envelopes	no	unclear	unclear	yes, conflict of interest	0.83
Eschertzhuber 2012	mentioned	unclear	yes	unclear	unclear	unclear	0.92
Li 2011	yes, random number	unclear	unclear	unclear	unclear	unclear	0.75
Ragazzi 2012	yes, random number	unclear	unclear	unclear	unclear	unclear	0.83
Russo 2012	yes, random number	yes, sealed opaque envelopes	unclear	unclear	unclear	no	0.83
Teoh 2010	yes, random number	yes, sealed opaque envelopes	blinded to patients	unclear	unclear	yes, conflict of interest	0.96
Theiler 2009	yes, random number	unclear	blinded to operators	unclear	unclear	yes, conflict of interest	0.88
Van Zundert 2012	yes, random number	yes, sealed opaque envelopes	blinded to observer	unclear	unclear	unclear	0.96
Yu 2011	yes, random number	unclear	unclear	unclear	unclear	unclear	0.83