Table 1.

Main findings from the included studies in the review

Author & Year	Country	Study design	Sample Population	Setting	Knowledge and awareness outcomes	Main findings & recommendations
Mian et al. [35] (2020)	Saudi Arabia	Observational cross-sectional self- administered questionnaire.	Total: 202 participants. 10.9% T2DM male; 24.7% T2DM female. Age range: 30–60 years. Non-probability convenience sampling.	Hail City (North- West Saudi Arabia) College of Dentistry dental clinic.	63.4% aware of the oral issues associated with diabetes. 76.4% diabetics were aware of the effects of diabetes on oral health (59.1% diabetic males and 84% diabetic females). 31.82% diabetic males and 16% diabetic females talked to dentist about diabetes.	Majority aware of oral health issues related to diabetes. Communication gaps between healthcare providers and patients.
Hollatz et al. [33] (2019)	Germany	Cross-sectional observational questionnaire.	112 ACHD patients (10% syndrome- associated). 50% male. Age range: 18–77 years.	Out- and in-patient department of the German Heart Centre Munich.	38% unaware of the correlation between heart disease and oral health. 69.6% think that poor oral health is a risk factor for cardiac complications. ~  73% reported inadequate or non-existent knowledge of the correlation between cardiac complications and oral health.	CHD patients were not well informed about the importance of oral health. An interdisciplinary team of dentists, general practitioners, cardiologists must improve promotion of specific oral health education.
Parakh et al. [30] (2019)	India	Cross-sectional questionnaire.	447 T2DM patients. 53.70% male, 46.30% female. Age range: 25–60 years. Rural population.	Outpatient department; dental college.	Average knowledge about the oral manifestations of diabetes was 41%. Mean value knowledge score was 4.92/12, indicative of a significant lack of knowledge.	Poor knowledge of the oral manifestations of diabetes. All health professionals need to work together to improve promotion; outreach programs are recommended.
Sanchez et al. [39] (2019)	Australia	Quantitative cross-sectional questionnaire.	318 CVD Patients. 60.1% male. Age range: 18–94 years. Convenience sampling.	Out-patient cardiology services in Sydney: 4x cardiac rehab sites; 2x public cardiology clinics; 1x private clinic in affluent and disadvantaged locations.	51% had limited knowledge about the potential impact of poor oral health on cardiac condition. 75% incorrectly agreed that people with heart problems should avoid dental treatment. Only 10.7% received information on oral health-care in cardiac setting.	Poor knowledge of the link between periodontal disease and CVD. Weak correlation between participant education and oral health knowledge. Study had similar characteristics to CVD Australian population.
Rotman- Pikielny et al. [48] (2019)	Israel	Questionnaire.	258 patients. 83.9% osteoporosis; 11.8% osteopenia; 5.4% other medical condition. 93% female. Age range: 44–99 years.	Out-patient, single-centred Department of Endocrinology Tel Aviv University – affiliated secondary referral centre.	70% did not know, or did not respond to questions on association between osteoporosis, osteoporosis treatment and oral health. ~  46.5% claimed their dentist did not know their osteoporosis diagnosis.	Minimal knowledge regarding osteoporosis and oral health care; suspected communication gap between patients and medical staff. Dentists should review patient osteoporosis diagnoses.
Naorungroj et al. [32] (2018)	Thailand	Cross-sectional, self-administered questionnaire.	88 pregnant females. Mean age: 26.95 5.09. Non-random sampling.	Prenatal care centre, Yaring district, Pattani.	66% aware that poor oral health could affect general health. 52.4% aware that gingivitis during pregnancy could have adverse consequences to child. 50.6% disagreed that gingivitis during pregnancy is normal and there is no need for prevention.	Lack of oral health knowledg or limited oral health literacy. Oral health interventions and education programs are needed.
Wang et al. [26] (2018)	China	4th National Oral Health Survey. Face-to-face questionnaire.	Total: 9054. 1024 diabetic patients. 46.2% male 53.8% female Age range: 55–74 years. 40.0% rural diabetics. Random sampling.	Provinces, autonomous regions and municipalities of mainland China.	64.9% awareness rate of oral health knowledge in diabetic patients. Urban diabetics (68.9%) demonstrated a higher total score of oral health knowledge, compared to rural diabetics (59.4%). Rural diabetics are 5.5% more knowledgeable than rural non-diabetics.	Oral health knowledge of diabetics is not optimistic. Diabetics had a higher awareness rate of oral health knowledge, compared to non- diabetics. Improved oral health care access for rural diabetics is recommended.
Afolabi et al. [27] (2017)	Nigeria	Descriptive cross-sectional, interviewer- administered questionnaire.	120 diabetic patients. 6.7% T1DM; 85.8% T2DM; 7.5% unsure of type. 62.5% male, 37.5% female. Age range: 38–72 years. Simple random probability sampling.	Diabetic Clinic (Department of Medicine) of the Lago State University Teaching Hospital, Ikeja, Lagos, Nigeria.	90% knew that poor oral health can be injurious to general health. Only 27.5% received information about the influence of gum disease and diabetes. 43.0% agreed that a diabetic nurse was their primary source of oral health information.	Majority of patients had poor knowledge on association between diabetes and periodontal disease. Significant need for increased knowledge for diabetics, regarding oral complications.
Al Amassi et al. [29] (2017)	Saudi Arabia	Internet-based, cross-sectional questionnaire.	N = 278 diabetic patients. Male n = 115, female n = 163. Age: 18–64 years.	Online.	81% aware that diabetes may increase the risk of oral health problems; 75.9% aware that diabetes may increase the risk for periodontal problems, such as gum bleeding and teeth mobility; 36.3% are aware that diabetes may reduce salivary flow. Majority (74.4%) are aware of the importance of controlling diabetes to minimise oral health complications. Higher education levels corresponded with greater awareness. No significance for age or gender.	Acceptable level of awareness for diabetic patients regarding awareness of increased oral health problems. Further educational programs should be established for diabetic patients, especially those with low levels of education, to improve their oral health knowledge. Dentists to take more responsibility for this task.
Kejriwal et al. [43] (2017)	India	Questionnaire	300 diabetic patients. Male n = 200, female n = 100.	A.B Shetty Memorial Institute of Dental Sciences, Mangalore and K.S. Hegde Medical Academy and Hospital, Mangalore.	low knowledge about increased risk for oral diseases (50%), knowledge on systemic complications 81%.	Low knowledge about increased risk for oral disease, in comparison to their knowledge for systemic complications. Dental professionals to increase awareness of importance of maintaining good OH and organise programs to assist education.
Lasisi et al. [45] (2016)	Nigeria	Cross-sectional survey.	143 diabetic patients. Male n = 48. Age: 26–89 years.	University College Hospital, Ibadan, Oyo State, Nigeria.	20.3% were aware of the importance of good oral health to prevent oral disease in diabetics; 24.5% knew diabetes could worsen oral health condition, 17.5% mentioned having oral diseases could affect glycemic control. 2.1% could explain the reasons for the association between diabetes and oral health conditions. 46.9% agreed regular consultations with the dentist were necessary.	Poor oral health awareness, practices and status of patients with diabetes. Oral health education and care should be incorporated into treatment plan of patients diagnosed with DM. Physicians to be educated on oral health and hygiene importance.
Payal et al. [37] (2017)	India	Cross-sectional self-reported questionnaire- based survey.	320 pregnant females. 103 non-pregnant females. Age range: 19–36 years. Random sampling.	Various government maternity centres of central India.	19.38% pregnant females aware that oral hygiene can affect their growing baby.	Lack of awareness regarding the relationship between oral hygiene and pregnancy. Majority of pregnant females never visited the dentist. Affordable dental care, oral health education and motivation for pregnant patients is fundamental.
Shanmukappa et al. [41] (2017)	India	Descriptive cross-sectional survey.	600 diabetic patients. 63% participants did not know type of diabetes. 66.3% males.	Visiting diabetic centres and private dental clinics and from outpatient department of Bapuji Dental College and Hospital, Davangere.	Overall knowledge = 34.0% 46.8% sourced information from a dentist. 69.0% not aware that diabetics are more prone to gum infection than non-diabetics. 71.4% were not aware that gum disease treatment in diabetics can affect blood glucose control.	Educational level is proportional to oral health knowledge. Awareness of periodontal health was independent of age. Patients were more aware of systemic complications. More dental health campaigns and programs recommended.
Gaffar et al. [34] (2016)	Saudi Arabia	Cross-sectional, self- administered questionnaire.	197 pregnant females. Age range: 18+	Ministry of Health hospital in Dammam, Saudi Arabia. Prenatal clinic.	82.8% knew that oral health is affected by pregnancy. 44.7% pregnancy patients knew that pregnancy hormones can affect oral health. 22.6% knew that maternal oral health can affect pregnancy outcomes. 1/3 women relied on the dentist for oral health information.	Majority of participants (> 70%) revealed good oral health knowledge related to pregnancy. Pregnant women, with proper knowledge, were more likely to visit the dentist during pregnancy.
Rasouli- Ghahroudi et al [31] (2016)	Iran	Cross-sectional, self-administered questionnaire.	150 adult heart disease patients (ischaemic heart disease). 58.7% male; 3 6.7% female; 4.7% not specified. Mean age: 52.78.8.	Tehran Heart Centre, Tehran University of Medical Sciences: 78 in-patients & 72 outpatient cases.	~  75.0% had moderate and good knowledge about oral health. ~  24.3% agreed that CVDs cause oral diseases. 55% agreed oral disease cause CVDs.	High scores in knowledge of patients with CVD regarding relationship between general and oral health may be due to repeated health education programs.
Ummadisetty et al [46] (2016)	India	Self-constructed questionnaire.	203 patients. Approximately 29.6% diabetic. 123 male, 80 female. Age range: 40–55 years.	Department of Periodontitis, Narayana Dental College and Hospital, Nellore, AP.	61.7% diabetics agree there is a relationship between diabetes and chronic periodontitis. 60% diabetic population agreed their current oral status is related to diabetes.	High-risk age group has insufficient knowledge on the mutual relationship. Health professionals need to improve public education about the oral manifestations of diabetes.
Malkawi et al. [38] (2014)	Jordan	Self-designated questionnaire.	154 pregnant patients. Age range: 18–40 years. Voluntary sample.	Public health clinics and at private clinics in city of Irbid, Jordan.	Awareness: 68.2% pregnant women knew they need dental consultation during pregnancy. Knowledge: 53.2% of pregnant women reported having knowledge about the possible link between pregnancy and periodontal diseases.	Educational level was proportional to knowledge. Educational programs on oral-care during pregnancy are recommended.
Sahril et al. [44] (2014)	Malaysia	Cross-sectional, self-administered questionnaire.	4017 T2DM. 62.3%	Clinic with Family Medicine Specialist in Urban area.	> 60.0% patients did not know the association between diabetes and oral health. 18.1% had lack of awareness on the need for a dental check-up.	Lack of knowledge regarding the association of oral health and diabetes mellitus. Low demand for dental referral among patients. Poor oral health seeking behaviour. Recommendations: comprehensive oral health promotion program, healthcare workers to routinely refer patients for oral healthcare for holistic diabetic care.
Weinspach et al. [12] (2013)	Germany	Self- administered questionnaire.	448 subjects. 101 T1DM, 236 T2DM, 111 non-diabetic. 54.5% female, 45.5% male. Median age: 59.65 13.65 years.	Department of Conservative Dentistry, Periodontology and Preventive Dentistry of Hannover Medical School.	46.0% diabetics (64.4% T1DM, 38.1% T2DM) know that periodontitis and diabetes negatively affect each other. 42.4% diabetics (63.4% T1DM, 33.5% T2DM) knew that diabetics are most often affected by periodontitis than nondiabetics.	Deficient knowledge about mutual influence between periodontitis and diabetes. T1DM significantly more informed, than T2DM. Dentists and diabetologists to provide more oral care information.
Aggarwal et al. [40] (2012)	India	Self- administered questionnaire.	500 T2DM patients. 53.2% male, 46.8% female. Age range: 35–87 years. Convenience sampling.	Department of Oral Medicine and Radiology, Institute of Dental Sciences, Bareilly, Uttar Pradesh, India. Outpatient clinic.	Almost 61% believed diabetes had no influence on oral health. 79.4% never referred by physical for dental care.	Significant need for increase in knowledge of periodontal disease in diabetic patients. All health professionals need to support comprehensive oral care, as an integral part of general health.
Abiola et al. [36] (2011)	Nigeria	Cross-sectional, self- administered questionnaire.	453 pregnant patients. Age range: 20–44 years.	Antenatal care at Lagos State University Teaching Hospital (LASUTH); tertiary health facility.	14.8% agree that pregnancy is a cause of gum problems. 9.5% believe that pregnancy predisposes to tooth loss. 23.4% agree dental visits are unnecessary during pregnancy. Highly educated study participants.	Survey results displayed acceptable level of oral health knowledge. Oral health education during antenatal care is essential.
Bangash et al. [28] (2011)	Pakistan	Descriptive cross-sectional survey.	300 diabetic patients (T1DM n = 36, T2DM n = 264) Male n = 195, female n = 105.	Operative Department of Armed Forces Institute of Dentistry Rawalpindi, Pakistan.	64% patients had knowledge about the oral complications of diabetes.	Good knowledge of diabetic patients in Pakistan army - may be attributed to easily accessible medical facilities for early detection and prompt free treatment. Need for health education programs for motivating diabetic patients. Further studies recommended for large scale investigation, to assist with solutions.
Bowyer et al. [42] (2011)	England	Self-completed questionnaire.	229 diabetic patients. 62.5% male, 37.5% female. Age: 25. 7.2% T1DM; 87.0% T2DM; 5.8% Unknown.	14x general medical practices in Warwickshire.	22% aware of gums bleeding on brushing linked to diabetes. 13.1% aware of the link between swollen/tender gums and diabetes. 23.9% aware that delayed healing in the mouth is associated with diabetes. 69.1% did not have oral health advice.	Adult diabetic patients had poor awareness of the oral health complications linked to diabetes. Training and advice for health professionals and patients on oral health and diabetes is needed.
Eldarrat et al. [47] (2011)	United Arab Emirates	Self- administered questionnaire.	100 diabetic patients (58% T2DM, 26% T1DM, 16% unknown). 50% female, 50% male. Mean age: 47 years.	Out-patient diabetic clinic in Rashid Hospital in Dubai.	60% aware of their increased risk for periodontal disease. > 70% were unaware of harmful impact of xerostomia on oral health. 37% received knowledge of oral disease risk from dentists.	Patients more knowledgeable of systemic complications. Health professionals need to develop educational programs.

ACHD Adult Congenital Heart Disease, T1DM Type 1 Diabetes Mellitus, T2DM Type 2 Diabetes Mellitus