This cross-sectional study lasted 10 months, between January 2018 and October 2018, and it was carried out to determine if there is an association between ABO blood groups and Rh factor with periodontitis. Convenience Sampling was done and the study included 1009 subjects, 566 males and 443 females who aged between 20-65 years and visited the Faculty of Dental Medicine, Damascus University seeking either periodontal therapy or other treatments after acquiring ethical clearance from Damascus University and the patients’ written consents were taken to participate in the study.

The selection criteria were that the subjects had at least 20 teeth excluding the third molars, similar socio-economic backgrounds, no systemic disease, such as leukaemia, diabetes, metallic bone disease, whereas those who were smokers, alcoholics, pregnant females, individuals who underwent periodontal treatment or antibiotic therapy within the past six months and individuals who cannot perform routine oral hygiene were excluded. After obtaining complete dental and medical histories, participants were divided into three groups; group I (healthy), group II (gingivitis), group III (periodontitis). Healthy participants showed attachment loss ≤3 mm, periodontal pocket depth ≤3 mm and no clinical sign of gingivitis [1]. Those with gingivitis displayed a attachment loss ≤3 mm, periodontal pocket depth ≤3 mm and sign of gingivitis according to Löe H et al., index (redness, bleeding, change in gingival contour, absence of the stippling texture) [20]. Periodontitis group included participants who showed attachment loss ≥4 mm, periodontal pocket depth ≥4 mm and radiographic bone loss. The following clinical periodontal parameters were recorded using William’s periodontal probe: plaque index PI [21], gingival index GI [20], gingival bleeding index GBI [22] probing depth PD [23] (the distance between the gingival margin and the bottom of the pocket) and Clinical Attachment Loss CAL [23] (the distance between the cementoenamel junction and the bottom of the pocket).

Among group III patients, 60 of the participants who were classified as generalised chronic periodontitis patients were randomly selected to participate in the second stage of the study. However, patients included in this part of the study were only Rh-positive. In addition, the study was registered at clinical trials with registration number (NCT03644901).

The patients were allocated into the following four groups, 15 in each:

The inclusion criteria for participants were those who demonstrated the generalized form of chronic periodontitis (more than 30% of the teeth showed attachment loss ≥4 mm and periodontal pocket depth 4-6 mm).

The following clinical periodontal parameter were recorded at baseline and three months after treatment using William’s periodontal probe: Plaque Index (PI), Gingival Index (GI), Gingival Bleeding Index (GBI), Probing Depth (PD), Relative Attachment Level (RAL) [23] (distance between a prefabricated acrylic stent and the bottom of the pocket). All patients received supragingival plaque and calculus removal at the first visit, followed by scaling and root planing using manual scalers and curettes, CK6, U15 and Standard Gracey Curettes 5-6, 7-8, 11-12, 13-14 (Medesy, Italy), at the second visit. Also, chlorhexidine gluconate 0.12% mouthwash was prescribed twice a day for all patients and instructions of Modified Bass Brushing Technique were given. The above mentioned treatments were performed by the same practitioner at all time.

Blood samples were collected by finger prick technique using a disposable lancet, and blood samples were mixed with monoclonal antibodies, Anti A, Anti B, Anti D (G. Sanguineo, Spinreact, Spain) to determine the blood group based on the direct agglutination method. Forming a clump with Anti A denotes the presence of antigen A on the erythrocytes; thus blood group A and forming a clump with Anti B denotes the presence of antigen B on the erythrocytes; thus blood group B, while forming a clump with both antigens A and B denotes the presence of both antigens on the erythrocytes; thus blood group AB and the absence of a clump with both antibodies indicates that the erythrocytes present no antigen; thus, blood group O. Moreover, forming a clump with Anti D suggests that the erythrocytes are Rh positive.

Data was analysed using statistical software (IBM SPSS Statistics version 22). Chi-square test was used to assess the data to determine whether there is an association between ABO blood groups and Rh factor with the periodontal status, and Z-score with Bonferroni adjustment were used to eradicate type 1 error and determine which percentage is significant. Paired t-test was used to compare the differences in clinical parameters at baseline and three months after the treatment in each group. One-Way ANOVA with Tukey test were the chosen tests to assess the response to scaling and root planing among individuals with different blood phenotypes. The level of significance was set at 0.05.

This cross-sectional study lasted for 10 months, during which 1009 participants were examined to determine whether there exists a relationship between ABO blood groups and Rh factor with the periodontal status. Blood group A was the most prevalent (42.1%), among the participant population, followed by blood group O (33.9%), blood group B (15.7%) and blood group AB (8.3%). Rh positive participants constituted the majority of the study population (91.4%) and Rh negative accounted for the minority of the study population (8.6%) [Table/Fig-1].

The study population was made up of (27.3%) healthy subjects, (32.1%) with gingivitis and (40.6%) with periodontitis [Table/Fig-2]. It is evident from [Table/Fig-2] that there is an association between ABO blood groups and periodontal diseases, (p<0.05). Subjects with blood group A exhibited a higher percentage of gingivitis (45.9%) with a significant difference compared to those with periodontitis and healthy periodontium. Likewise, a higher percentage of periodontitis was found in blood group O subjects (57.9%) with a significant difference compared to subjects with gingivitis and healthy periodontium. Subjects with blood group B showed a higher percentage of healthy periodontium (46.2%) with a significant difference compared to periodontitis and gingivitis groups. Furthermore, subjects with blood group AB demonstrated a relatively high percentage of healthy patients (40.5%) with significant difference compared to gingivitis patients and no significant difference compared to periodontitis patients.

As for Rh factor, [Table/Fig-3] shows that there is an association between Rh factor and the periodontal status (p<0.05). Rh positive subjects showed a higher prevalence of periodontitis (40.3%) with a significant difference compared to healthy and gingivitis subjects, followed by gingivitis (34.3%) with a significant difference compared to healthy subjects.

For determining the level of response to scaling and root planing and the blood groups, 60 patients with generalised chronic periodontitis participated in this study to investigate if ABO blood groups play a role in the response to scaling and root planing. The study population was composed of (56.7%) males and (43.3%) females [Table/Fig-4]. The mean of the age was 51±7 years.

Scaling and root planing resulted in statistically significant improvements in all the clinical parameters three months after scaling and root planing in each blood group (p<0.05) [Table/Fig-5].

[Table/Fig-6] Illustrates that there was no statistically significant difference between the study groups in terms of responding to the nonsurgical periodontal treatment (p>0.05).

[Table/Fig-7] shows that there was no statistically significant difference between the study groups in terms of responding to the nonsurgical periodontal treatment (p>0.05).

Despite bacteria being the main cause of the periodontal diseases, various factors such as geographical location, race, age, smoking, diabetes and genetics play a role in the development of periodontal diseases, including gingivitis and periodontitis [3]. It is established that ABO blood phenotypes and rhesus factor frequencies vary among the human population according to location and race [6]. Similarly, the distribution of periodontal diseases varies according to these two factors as well. These facts may suggest an association between ABO blood groups with the incidence of periodontal diseases.

The present cross-sectional study showed that blood group A is the most prevalent followed by blood groups O, B and AB. These findings were in accordance with Demir T et al., and Koregol AC et al., while Agarwal V et al., who reported that blood group A was the most common followed by B, O and AB [12,14,24]. Those findings were in contrast with Francis TL et al., who reported that blood group O was the most predominant [16].

This study showed that the incidence of gingivitis was significantly higher in individuals with blood group A, and periodontitis was higher in individuals with blood group O. The results of our study match with the already conducted studies [12-14]. Likewise, Patel R et al., found that subjects with blood group B and O showed a significantly higher tendency towards periodontitis [15]. However, our findings were in conflict with Francis DL et al., who reported that there was no statistically significant difference between ABO blood groups with periodontal diseases [16]. This could be attributed to the fact that subjects in that study were divided into two groups only, with no periodontitis and with periodontitis, and our study had a larger sample size. Additionally, our observations contradict with those of Pai GP et al., [25]. They reported that a significantly higher percentage of participants with blood group O and AB were healthy compared to those with blood group B and A who had periodontal disease. This could be due to the patients’ classification system applied in each study. To illustrate, in present study, healthy participants and those with gingivitis were separated into two different groups, while in the Pai et al. study, participants with healthy periodontium and mild gingivitis were kept in the same sample group.

Regarding the association between Rh factor and periodontal status, data acquired from this research revealed a significant association between Rh positive and periodontitis followed by gingivitis. These observations were reflected in the findings of Demir T et al., and Anup P et al., both reported a significant relationship between Rh positive and gingivitis [12,13]. Furthermore, our results were compatible with Patel R et al., who demonstrated a significant relationship between Rh positive and periodontitis [15].

The findings of this research could be explained in the light of notion that antigens (A and B) of the ABO blood groups, which can be found in body fluids such as saliva, affect the periodontal status by acting as receptors for infectious agents that are concomitant with periodontal diseases. Another explanation is that these substances A, B and H, which is the precursor of antigen A and B, can also be found in tissues and correspond to the erythrocyte However, the expression of these antigens in tissues varies from individual to individual based on the secretor status. As a result, These substances may be modulators that contribute to the development of oral diseases in the stratified epithelium [26]. Moreover, the ABO antigens that are secreted to the saliva might prevent bacteria from being attached to the surface of the tooth. This could be attributed to the fact that bacteria use the lectins on their surfaces to attach to the surface of the tooth, and these lectins are often ABO antigens specific [27].

On a different note, the present study showed that there was no significant association between the level of response in patients with generalised chronic periodontitis to scaling and root planing based on their blood group. In our opinion, this could be because of the treatment that we provided to the patients included only scaling and root planing without applying any medication, such as topical antibiotics, which might have different results as the applied materials may interact with the ABO antigens that exist in saliva. To the best of our knowledge, this is the first research in literature that discusses whether individuals respond differently to the nonsurgical periodontal therapy based on their blood group.

In the cross-sectional study, the participants were recruited on the basis of Convenience Sampling (first arrived first included into a suitable group was followed), which resulted in the number of cases outnumbering the controls. Additionally, only Rh-positive patients were included in the second stage of the study, and Rh-negative patients might respond in a different way to scaling and root planing compared to Rh positive ones.

This study demonstrated that subjects with blood group A had a higher incidence of developing gingivitis and subjects with blood group O had a higher incidence of developing periodontitis. Moreover, according to present data, the Rh factor seems to play a significant role in the incidence of both periodontitis and gingivitis. A and O blood groups and Rh factor are possible risk factors for periodontal disease. The level of response to scaling and root planing does not differ among patients based on their blood groups. These findings expand our understanding of periodontal diseases as ABO blood groups and Rh factor might constitute a risk factor and explain why a periodontal disease might be more prevalent in some individuals than the others.

Future recommendation: In future, more studies are required to determine whether the level of response to scaling and root planing would differ based on blood phenotypes and when topical antibiotics are applied.