Table 3. Risks of bias of the studies evaluating mechanical properties.

Author/Year	Samples obtained through a standardized process	Single operator of the machine	Sample size calculation	Blinding of the testing machine operator	Specimens, test, and formulas according to standard specifications	Risk of bias
Abdulmohsen et al[10] (2016)	0	1	2	2	1	Moderate
Rayyan et al[24] (2015)	1	0	2	2	1	Moderate
Penate et al[25] (2015)	2	0	0	2	1	Moderate
Thompson and Luo[13] (2014)	0	1	2	2	0	Moderate
Yanikoğlu et al[23] (2014)	0	1	2	2	1	Moderate
Hamza et al [30] (2014)	0	1	1	2	0	Moderate
Poonacha et al[14] (2013)	0	1	2	2	0	Moderate
Jo et al[9] (2011)	0	1	2	2	1	Moderate
Alt et al[20] (2011)	0	1	2	2	1	Moderate
Zortuk et al[15] (2010)	1	1	2	2	1	Moderate
Nejatidanesh et al[7] (2009)	1	1	2	2	0	Moderate
Balkenhol et al[21](2009)	0	1	2	2	0	Moderate
Balkenhol et al[18] (2008)	0	1	2	2	0	Moderate
Kim and Watts[11] (2007)	0	1	2	2	1	Moderate
Akova et al[22] (2006)	0	2	2	2	1	Moderate
Kim and Watts[27] (2004)	0	1	2	2	0	Moderate
Hamza et al[28] (2004)	0	1	2	2	0	Moderate
Yap et al[12] (2004)	0	1	2	2	1	Moderate
Lang et al[16] (2003)	1	1	2	2	1	Moderate
Haselton et al[8] (2002)	0	1	2	2	1	Moderate
Ireland et al[19] (1998)	1	1	2	2	1	Moderate
Samadzade et al[29] (1997)	1	1	2	2	1	Moderate
Gegauff and Wilkerson[26] (1995)	0	1	2	2	0	Moderate
Diaz-Arnold et al[17] (1990)	0	1	2	2	1	Moderate