Table 2.

Quality assessment of the included studies

Risk of bias for RCTs
Author	Year	Level of evidence	1	2	3		4	5	6	7
Kyung-wook	2016	II	U	U	N		N	Y	N	N
Raaij	2008	II	U	U	N		N	Y	N	N
Lee	2018	II	Y	U	N		N	Y	N	N
Bae	2016	II	Y	U	N		N	N	N	N
Kim	2017	IV	U	U	N		N	Y	Y	N
Newcastle-Ottawa assessment for cohort studies
Author	Year	Level of evidence	Selection				Comparability	Outcome
			1(**)	2(*)	3(**)	4(**)	1(**)	1(**)	2(*)	3(**)
Chiu	1999	III	*	*	*	*	**	*	*	*
Kuwano	2005	III	*	*	*	*	**	*	*	*
Hohmanm	2005	III	*	*	*	*	**	*	*	*
Giffin	2004	III	*	*	*	*	**	*	*	*
Noyes	2005	IV	*	*	*	*	**	*	*	*
Chen	2012	III	*	*	*	*	**	*	*	*
Ozkaya	2008	III	*	*	*	*	**	*	*	*
Altay	2016	III	*	*	*	*	**	*	*	*
Terauchi	2002	III	*	*	*	*	**	*	*	*
El-Assal	2010	II	*	*	*	*	**	*	*	*
Park	2017	IV	*	*	*	*	**	*	*	*
Newcastle-Ottawa assessment for case-control studies
Author	Year	Level of evidence	Selection				Comparability	Outcome
			1(**)	2(*)	3(**)	4(**)	1(**)	1(**)	2(*)	3(**)
Turkmen	2017	III	*	*			*	*	*	*
Nakamura	2017	III	*	*			*	*	*	*

A study was awarded a maximum of one star (*) for each item within the selection and outcome domains. A maximum of two stars (**) was givenfor comparability. More stars meant a low ROB