Table 2.

Methodological quality assessed using the modified NOS.

Study	Selection				Comparability		Exposurea/Outcomeb			Total stars
	1 c	2 c	3 c	4 c	5 d		6 c	7 c	8 c
Bolin, 1997 [13]	*	*	*	*		*	*	*	*	8
Williams, 2000 [14]	*	*	*	*	*	*	*	*	*	9
Aligne, 2003 [15]	*	*	*	*	*	*	*	*		8
Shenkin, 2004 [16]	*		*	*	*	*	*	*		7
Shulman, 2005 [17]	*	*	*	*		*	*	*		7
Tanaka, 2006 [18]	*	*	*	*	*		*	*		7
Iida, 2007 [19]	*	*	*	*		*	*	*		7
Ayo-Yusuf, 2007 [20]	*	*	*	*	*	*		*		7
Hanioka, 2008 [21]	*	*	*	*	*		*	*	*	8
Aida, 2008 [22]	*	*	*	*	*	*	*	*		8
Leroy, 2008 [23]	*	*	*	*	*	*	*	*	*	9
Tanaka, 2009 [24]	*		*	*	*	*	*	*		7
Julihn, 2009 [25]	*	*		*		*	*	*	*	7
Tanaka, 2010 [26]	*	*	*	*	*	*	*	*	*	9
Ditmyer, 2010 [27]	*	*	*	*		*	*	*		7

^acase-control format,

^bcohort format,

^cfor studies with case-control/cohort format: 1, definition of case/representativeness of exposed cohort; 2, representativeness of case/selection of non-exposed cohort; 3, selection of controls/ascertainment of exposure; 4, definition of controls/demonstration that outcome of interest was not present at the start of the study; 6, ascertainment of exposure/assessment of outcome; 7, same method for cases and controls/follow-up period of one year or more, 8, non-response rate of less than 25%/adequacy of follow up of cohorts;

^d5, study controls for oral health behavior and SES or dental visit.