Table 2. Quality assessment of the studies included in the meta-analysis.

Studies	Assessment categories						Risk of bias
	A	B	C	D	E	F
Aichelmann-Reidy [18]	Yes	Unclear	No	Yes	No	No	Moderate
Novaes [19]	Unclear	Unclear	No	Unclear	No	No	Moderate
Tal [21]	Unclear	Yes	No	Yes	No	No	Moderate
Paolantonio [20]	Unclear	Unclear	No	Yes	No	No	Moderate
Barros [22]	Unclear	Unclear	No	No	No	No	High
Woodyard [23]	Yes	Unclear	No	Yes	No	No	Moderate
Cortes [24]	Yes	Unclear	No	No	No	No	High
Mahajan [25]	Yes	Unclear	No	Unclear	No	No	Moderate
Moslemi [26]	Yes	Yes	No	Yes	Y/w	No	Moderate
Ahmedbeyli [27]	Yes	Unclear	No	No	No	No	High

A, random sequence generation; B, allocation concealment; C, blinding of participants and personnel; D, blinding of outcome assessment; E, incomplete outcome data; F, selective reporting; Y/w, yes without impact on observed effect size.

Three levels of risk of bias were defined: low, all of the criteria were met; moderate, one criterion was not met; high, two or more criteria were not met.