The present study is a cross-sectional study of PGCS (PERSIAN Guilan Cohort Study) performed from October 8, 2014, to January 20, 2017. 10,520 individuals aged 35 to 70 years old were included in the Prospective Epidemiological Research Studies in Iran (PERSIAN) in Guilan Province, Northern Iran. The criteria for exclusion from the study included the inability to attend the clinic for a physical examination, the presence of an intellectual disability, and a lack of willingness to participate in the research [16]. Eligible subjects were reached via phones by trained interviewers proficient in the region’s native language to communicate with participants. After obtaining informed consent, calibrated research colleagues recorded data encompassing clinical, laboratory, and demographic characteristics [17]. 2 midwives performed oral examinations to collect DMFT and oral health data. They were educated and supervised by a dentist. Also, the methodology suggested by WHO (Oral Health Surveys Basic Methods) was followed in all clinical procedures [18].

Blood pressure was measured twice in each arm at 10-minute intervals using Richter auscultatory mercury sphygmomanometers (MTM Munich, Germany). Participants were seated with their backs supported, legs uncrossed, and arms at heart level. Measurements were taken in a quiet room at 10-minute intervals between each, ensuring the cuff size was appropriately adjusted. The mean of the measurements was used for analysis. Hypertension was defined as systolic blood pressure ≥ 140 mmHg, diastolic blood pressure ≥ 90 mmHg, a prior diagnosis of hypertension by a health professional, or being on antihypertensive medication [11].

DMFT, a discrete variable, was used to evaluate oral health conditions. Interviewers obtained the DMFT score by examining individuals. The DMFT score was determined by counting the number of decayed (D), missing (M), and filled (F) teeth. The mean DMFT for all samples is calculated by dividing the total sum of all DMFT scores by the number of participants.

Variables, such as sex (male or female), age (35–44, 45–55, or > 55), years of education (illiterate, 1–5 years of schooling, 6–12 years of schooling, or university/college), SES (low, moderate, or high), physical activity (low, moderate, high), Smoking status (smoker, non-smoker), use of drugs, or alcohol (yes/no), BMI (< 18.5, 18.5–24.9, 25–29.9, > 30), use of mouthwash or floss (yes/no), tooth brushing frequency (once daily, twice or more daily, others, Irregular and No brushing), and co-morbid diseases (none, one, two, or more) were analyzed in individuals with or without hypertension to assess which factors were risk indicators [16].

Hookah, also referred to as a water pipe, shisha, or qualyan, is a device utilized for the consumption of tobacco. This device functions by passing the smoke through water before inhalation. It is estimated that approximately 100 million individuals globally engage in the use of hookahs [19].

Participants’ SES was assessed using a developed household wealth measure. Participants were asked about ownership of certain durable assets, such as a PC/laptop, CD/DVD player, cellphone, refrigerator, freezer, dishwasher, 3D TV, automobile, vacuum cleaner, sewing machine, air conditioner, oven, motorcycle, the number of rooms per capita, and the type of home residency. Additionally, they were asked about access to infrastructure services, such as piped drinking water and the Internet. We used principal component analysis (PCA) to construct the wealth index based on this information [20, 21].

Co-morbid diseases were defined as one of the following: ischemic heart disease, diabetes mellitus, history of MI (myocardial infarction), history of stroke, kidney failure, fatty liver, hepatitis B or C, chronic lung diseases, thyroid diseases, kidney stones or gall bladder, rheumatism diseases, chronic headaches, and epilepsy [16].

The Kolmogorov-Smirnov test evaluated the normality of variables. The ANOVA test was employed to investigate variations in the mean DMFT indices across the three groups. Additionally, the T-test assessed differences in the mean DMFT between the two groups. To compare two quantitative variables, the Pearson correlation coefficient was utilized. Multiple linear regression was utilized to determine risk factors influencing changes in DMFT. All analyses were conducted using IBM SPSS Statistics software, version 27. A significance level of less than 0.05 was used for all tests.