Table 1.

Characteristics of the included studies

ID	Study characteristics						Outcome and exposure characteristics		Findings		Quality scores (9)
	First authors, year, country	Study subject	Age Mean ± SD	Study design	Sample size	Male%	Definition of hyperglycemia	Definition of periodontitis	Effect size (95% CI)	Confounders
1	Hendri Susanto, 2012, Indonesia [27]	Diabetic patient Healthy control	50.71 ± 10.3	Case–control	Case group: 101 Control group: 132	31.75%	HbA1c > 6.5%	PD (≥ 4 mm) and AL (≥ 3 mm)	OR: 3.58 (1.77–7.24)	_	7
								PD (≥ 5 mm) AL (≥ 2 mm)	OR: 4.20 (2.41–7.30)
2	Shu-Fen Chuang, 2005, Taiwa [17]	Diabetic patient Healthy control	57.5	Case–control	Case group: 85 Control group: 43	29.68%	HbA1c > 9%	CPI ≥ 4 mm; (PD ≥ 4 to 5 mm)	OR: 1.86 ( 0.98- 3.50)	_	6
3	Katz J, 2001, Israel [16]	Normal serum glucose levels Abnormal serum glucose levels	–	Cross-sectional	10,590	–	FBS > 120 mg/dl	CPI > 4.5	OR: 2.46 ( 1.86- 3.20)	_	6
4	Farzeen Tanwir, 2010, Karachi [29]	Controlled diabetic patients Uncontrolled diabetic patients	49.23 ± 9.49	Cross-sectional	Case group: 141 Control group: 143	38.10%	HbA1c > 7.5%	GI > 2 mm	OR: 2.49 (1.50–4.13)	Age, and gender	6
								PI > 2 mm	OR: 1.80 (1.11–2.93)
								PI > 2 mm	OR: 2.35 (1.37–4.02)
								CI > 0.75 mm	OR: 1.65 (0.98–2.78)
5	Shimazaki, 2007, Japan [25]	Women population	55.7 ± 18.8	Cross-sectional	584	0%	FBS > 110	PD ≥ 2 mm	OR: 2.20 (1.30–3.90)	Age, smoking status, lipid-lowering medication, and total cholesterol	9
								CAL ≥ 3 mm	OR: 1.70 (0.70–4.00)
6	Khader, 2008, Jordan [30]	Patients with metabolic syndrome Persons without metabolic syndrome	48.3 ± 13.0 46.1 ± 10.9	Cross-sectional	156	35.9%	FBS > 110 mg/dl	CAL > 3 mm	β = 8.0, SE = 3.5	Age, gender, education, income, smoking, frequency of tooth brushing	8
								PD > 3 mm	β = 7.9, SE = 3.6
								Average CAL	β = 2.3, SE = 0.14
								Average PD	β = 0.74, SE = 0.17
7	Kushiyama, 2009, Japan [12]	General population	40–70	Cross-sectional	1,070	26.7%	FBS > 110	CPI ≥ 3	OR: 1.27 (0.83 to 1.96)	Age, gender, and smoking habits	8
8	Benguigui, 2010, France [19]	General population	35–74	Cross-sectional	255	54.9%	FBS < 126 mg/dl	CAL ≥ 4 mm, with PD ≥ 5 mm,	OR: 0.88 (0.27–2.81)	Age, gender, educational level, smoking habits, alcohol consumption, CRP, and dental plaque	9
								CAL ≥ 6 mm, with PD ≥ 5 mm	OR: 1.55 (0.46–5.25)
9	Kwon, 2011, Korea [15]	General population	No periodontitis 37.79 Periodontitis 55.00	Cross-sectional	7,178	37.5%	FBS < 100 mg/dl	CPI ≥ 3(3.5 mm > pocket)	OR: 2.45 (2.20–2.74)	Age, smoking habits, alcohol intake, tooth brushing frequency and present number of teeth	9
10	Minagawa, 2015, Japan [22]	Elderly population	> 80	Cross-sectional	234	47.4%	HbA1c ≥ 6.0%	PD ≥ 5 mm or CAL ≥ 6 mm	OR: 1.42 (0.71–2.84)	Gender, income, education, smoking status, brushing frequency, exercise food intake, visit dentistry	9
11	Timonen, 2010, Finland [24]	General population	30 to 64	Cross-sectional	2,050	39.2%	FBS ≥ 6.1 mmol/L	PD ≥ 4 mm	RR: 0.91 (0.70–1.18)	Gender, age, education, plaque level, tooth brushing frequency, dental attendance pattern, and alcohol	8
							FBS ≥ 6.1 mmol/L	PD ≥ 6 mm	RR: 0.60 (0.32–1.13)
12	Thanakun, 2014, Taiwan [20]	Patients with metabolic syndrome Persons without metabolic syndrome	35–76	Cross-sectional	125	42.4%	FPG* levels ≥ 100 mg/dL	Severe Periodontitis CAL > 4 mm	OR: 1.81 (0.55 to 5.96)	Age, sex, alcohol consumption, education level, and frequency of tooth brushing	8
							FPG levels ≥ 100 mg/dL	Moderate/Severe Periodontitis (PD ≥ 4 mm and BOP > 10%)	OR: 0.88 (0.12 to 6.49)
13	Masanori Iwasaki, 2015, Japan [28]	Elderly population	75	Cohort	125	89.55%	HbA1c ≥ 6%	CAL ≥ 3 mm	RR: 0.86 (0.36–2.06)	Gender, income, education, smoking status, number of the teeth	7
								No. of teeth	RR: 1.88 (0.86- 4.10)
14	Wijnand J, 2017, Netherlands [23]	Periodontitis patient Without periodontitis patient	–	Case–control	313	48.27%	HbA1c > 6.5%	PD ≥ 5 mm CAL ≥ 6 mm	OR: 2.73) 1.60–4.68 (	Sex, age, ethnicity, education, smoking, history of periodontal treatment	7
								PD ≥ 4 mm CAL ≥ 3 mm	OR: 1.76 (1.03–3.00)
15	D´Aiuto, 2008, USA [18]	General population	Severe periodontitis 52.3 Moderate periodontitis 54.2 Mild or no periodontitis 38.7	Cross-sectional	13,677	62.0%	FBS > 110 g/dl	CAL > 6 mm (two sites not on the same tooth or greater) PD > 4 mm (one site or greater)	OR: 1.71 (1.16 –2.54)	Age, sex, years of education, poverty to income ratio, ethnicity, general conditions, and smoking	9
								CAL > 4 mm (two sites not on the same tooth) PD > 4 mm(one site)	OR: 1.13 (0.84–1.53)	Age, sex, years of education, poverty to income ratio, ethnicity, general conditions, and smoking
16	Morita, 2010, Japan [14]	Adult employees	37.3	Retrospective Cohort	1,023	71.0%	FBS ≥ 110 mg/dl	CPI > 3 (PD > 4 mm)	OR: 1.4 (1.0 to 2.1)	Age, gender, smoking habit, exercise, eating between meals, and healthy body weight	8
								Missing teeth: One or more	OR: 1.0 (0.6 to 1.5)
17	Morita, 2009, Japan [13]	Adult employees	43.3	Cross-sectional	2,478	81.8%	FBS ≥ 110 mg/dL	CPI > 3 (PD > 4 mm)	OR: 1.9 (1.4–2.7)	Age, gender, and smoking habit. CI, confidence interval
							HbA1c ≥ 5.5	CPI > 3 (PD > 4 mm)	OR: 2.0 (1.5–2.6)
18	LaMonte, 2014, USA [21]	Postmenopausal women	50 to 79 years	Cross-sectional	657	0%	FBS ≥ 100 mg/dL	tooth loss; ACH ≥ 3 mm or 2 sites CAL ≥ 5 mm or ≥ 1 tooth loss	OR: 0.96 (0.54 to 1.71)	Age, smoking, hormone therapy, history of diagnosed heart disease, tooth brushing, dental visits,	8
								≥ 2 interproximal sites with CAL ≥ 6 mm or ≥ 1 interproximal site with PD ≥ 5 mm	OR: 0.86 (0.44 to 1.70)
								PI ≥ 50% of sites	OR: 1.40 (0.83 to 2.32)
19	Lei Chen, 2010, China [26]	Periodontitis patient Without periodontitis patient	36–85	Case–control	140	63.04%	HbA1c > 8.0%	PD) 2.76 to 4.95 mm(	OR: 3.83 (1.78–8.26)	Age, gender, BMI, and smoking	7
							F-glucose	PD) 2.76 to 4.95 mm(	OR: 2.38(1.12–5.06)
							HbA1c > 8.0%	PD (2.26 to 2.75 mm)	OR: 2.96 (1.40–6.28)
							F-glucose	PD (2.26 to 2.75 mm)	OR: 2.05(0.97–4.30)

FBG Fasting plasma glucose test, MetS metabolic syndrome, PD Probing depth, CAL Clinical attachment loss, CPI Community Periodontal Indices, ACH alveolar crest height, PI plaque indices;