Table 2.

Methodological quality score of the studies under review (Ottawa-Newcastle scale)

Study	Choice				Comparability		Result			Total
	1	2	3	4	5	6	7	8	9
Linn et al. 9 (1983)	*	*	-	*	*	-	**	*	-	7
Fried10 (1995)	*	*	*	*	-	-	-	*	*	6
Gray et al.11 (2010)	*	*	**	*	*	*	-	*	-	8
El Maroun et al.12 (2010)	*	*	*	*	*	*	-	*	*	8
Day et al.8 (2011)	*	*	*	-	*	*	*	*	*	8
Hayatbakhsh et al.5 (2011)	*	*	**	*	*	-	*	*	*	9
Salzwedel et al.13 (2015)	*	*	*	-	*	*	*	*	*	8
Leemaqz et al.14 (2015)	*	*	*	*	*	*	-	*	-	7
Fransquet et al.15 (2016)	*	*	*	*	*	*	-	*	-	7
Crume et al.16 (2018)	*	*	*	-	*	*	*	-	*	7
Eiden et al.8 (2018)	*	*	*	-	*	*	*	*	*	8
Corsi et al.17 (2019)	*	*	**	*	*	*	*	-	-	8
Sturrock et al.18 (2019)	*	*	*	*	*	*	-	-	*	7

1) Representative sample of exposure. 2) Selection of exposed. 3) Finding of exposure. 4) The outcome did not exist before the start of the study. 5) Adjustment for education level. 6) Adjustment for additional (secondary) confounding factor. 7) Outcome assessment. 8) Sufficient follow-up time. 9) Non-wear bias.