Table 2.

Quality of bias assessment of the included studies according to the Cochrane guidelines

Study	Sequence generation	Allocation concealment	Blinding of participants, personnel and outcome assessors	Incomplete outcome data	Selective outcome reporting	Other sources of bias
Belfort et al 30	L	U	U	L	L	U
Chan et al 31	U	U	U	L	L	U
Davidson et al 32	U	U	U	L	L	U
Ishibashi et al 34	L	U	U	L	L	U
Kazumi et al 35	U	U	U	L	L	U
Kosoglou et al 36	U	U	H	L	L	U
Ooi et al 37	U	U	U	L	L	U
Sasaki et al 38	U	L	U	L	L	U
Vega et al 39	U	U	H	L	L	U
Wagner et al 40	U	U	H	L	L	U

H, high risk of bias; L, low risk of bias; U, unclear risk of bias.