Table 2.

Summary of the methodological quality analysis according to the Newcastle-Ottawa protocol to assess the risk of bias of the cross-sectional and case-control studies.

Case-control
Studies	Selection	Comparability	Exposure/outcomes
Ababneh et al. (60)	***	**	**
Castro et al. (10)	****	**	**
Levin et al. (63)	***	**	**
Li et al. (61)	****	*	**
Vettore et al. (56)	**	**	**
Vettore et al. (59)	***	**	**
Cross-sectional
Laforgia et al. (62)	***	-	**
Naghsh et al. (65)	***	**	**
Pal et al. (64)	***	**	**
Solis et al. (57)	***	**	**
Saletu et al. (58)	***	**	**

Case-control study: Selection- 1) Is the case definition adequate? *; 2) Representativeness of the Cases *; 3) Selection of controls *; 4) Definition of controls *; Comparability (maximum **); Exposure- 1) Determination of Exposure *; 2) Same verification method for cases and controls *; 3) Non-Response Rate *. Cross-sectional study: Selection- 1) Representativeness of the samples *; 2) Sample size *; 3) Non-respondents *; Comparability (maximum **); Result- 1) Evaluation of the result * or **; 2) Statistical test *.