Study Random selection
in the population 		Definition of inclusion
and exclusion criteria 		Report of losses
to follow-up 		Validated
measurements 		Statistical
analysis 		Risk of
bias
Alkan et al. [2] No Yes No Yes Yes High
Durham et al. [21] No Yes No Yes Yes High
Landes et al. [22] No Yes No Yes Yes High
Gunbay et al. [23] No Yes No Yes Yes High
de Gijt et al. [24] No Yes No Yes Yes High
Ploder et al. [26] No Yes No Yes Yes High
Del Santo et al. [25] No Yes No Yes Yes High
Seeberger et al. [27] No Yes No Yes Yes High
Malkoc et al. [28] No Yes No Yes Yes High