Table 2.

Confounding factors of selected studies.

	Guggenheimer et al., 2000 [20]		Saini et al., 2010 [21]		Bastos et al., 2011 [22]		Mohsin et al., 2014 [23]
Tobacco	Cases Now, 19.4% Ever, 37.5%	Controls U	Excluded		Cases 25 (17.2%)	Controls 30 (27%)	U
Other drugs taken	Cases Cardiovascular agents, 19.8%,  p < 0.01  Immunosuppressants, 2.7%,  p < 0.05  Anticonvulsants, 2.7%,  p < 0.05  Thyroid supplements, 8.4%,  p < 0.001  Antimicrobials, 10.4% Unknown, 5.2%	Controls Cardiovascular agents, 6% Immunosuppressants, 0.4% Anticonvulsants, 0.4% Thyroid supplements, 1.1% Antimicrobials, 8.6% Unknown, 7.1%	Cases Cardiovascular agents, 22.4% Antibiotics, 2.4% NSAID, 3.3% Antiasthmatic drugs, 1.4% Others, 2.4%	Controls Cardiovascular agents, 10% Antibiotics, 1% NSAID, 1.4% Antiasthmatic drugs, 1.7% Others, 1.7%	39.2% taking a daily medication, of which 73.3% were antihypertensives and 56% were antidepressants		U
Dentures users	Cases Complete or partial dentures, 12.3%,  p < 0.01	Controls Complete or partial dentures, 3%	U		U		U
DM diagnosis	U		U	Controls: excluded by fasting blood glucose level	U		U	Controls: excluded by fasting blood glucose level
Glycosylated hemoglobin (HbA1c)	11 ± 0.1		8,49 ± 2,25 Good (<7.5), 172 (41%) Moderate (7.6–8.9), 92 (21.9%) Poor (>9), 156 (37.1%)		Adequate (<7): 38 (26%) Inadequate (≥7): 108 (74%)		U
Diabetic complications	Nephropathy, 23.2% Neuropathy, 26.9% Retinopathy, 44.4% Peripheral vascular disease, 10.6%		14.5% U		65 (44.5%) Nephropathy, 20.3% Neuropathy, 16.5% Retinopathy, 63.2%		Excluded

U: unspecified.