Salivary flow rate and oral health status in type 2 diabetics

results indicate significant reduction in diabetics as well as significant relation between metabolic control and salivary flow. Unstimulated and stimulated salivary flows were negatively and significantly correlated with periodontal parameters and DMFT. Conclusion The present findings indicate that decreased salivary flow rate could have a significant impact on oral health status in type 2 diabetics.


INTRODUCTION
Diabetes mellitus (DM) is metabolic syndrome characterized by chronic hyperglycemia caused by absolute or relative lack of insulin. Chronic hyperglycemia leads to many complications, which underlines the importance of adequate metabolic control. Glucose metabolism control significantly impacts the extent and severity of diseases associated with diabetes including those in oral cavity.
Saliva is biological fluid of fundamental importance for the preservation of oral health. Consequently, decreased salivary flow is frequently associated with numerous oral diseases. There is clear evidence that the prevalence, severity and progression of periodontal disease are higher in diabetics, although mechanisms for such association are not clearly understood [1,2]. The main etiological factor for the development of periodontal disease is dental plaque (biofilm). Increased amount of plaque in patients with diabetes is a result of increased salivary glucose and decreased salivary secretion. Bacteria from biofilm appear to act directly or indirectly, via cell and humoral components of specific and non-specific host responses [3]. It is well known that periodontal disease can have negative impact on metabolic control and the incidence of diabetes complications, but also the treatment of periodontal disease can favorably affect glycemic regulation [4,5]. The role of saliva in the maintenance of tooth integrity is also of great importance, as confirmed by Leone et al. [6]. The authors examined the influence of saliva on the occurrence as well as development of dental caries and concluded that the flow of saliva, undoubtedly, presents most important factor for the development of cavities. Due to reduced secretion of saliva, caries lesions develop rapidly affecting even the places that are not caries susceptible. A review of the literature reveals reduced salivary flow rate in patients with diabetes [7], which could explain increased dental caries incidence in this population. Some of the early, nonspecific signs of poorly-controlled diabetes include oral candidiasis and other opportunistic infections [8]. Oral candidiasis is frequently a sign of systemic immunosuppression. In fact, reduced salivary secretion combined with high concentration of glucose in saliva can accelerate the growth of fungi and their adherence to oral mucosal epithelial cells. Oral candidiasis is reported to be more prevalent especially in diabetic denture wearers [9], who do smoke and have poor glycemic control [10].
The aim of this study was to compare the salivary flow rate and oral health status in type 2 diabetics and healthy controls.

Study design and participants
The study involved 90 patients, 60 with type 2 diabetes and 30 without diabetes (control subjects), aged 45-65 years. With respect to level of HbA1c diabetic subjects were divided into the two groups: 30 better-controlled (HbA1c<9%) and 30 poorly-controlled (HbA1c≥9%), recruited from the Department of Endocrinology University Hospital Foca, Bosnia and Herzegovina. The 9% of HbA1c cut-off point has been suggested to represent an indicator for ineffective blood glucose management in type 2 diabetes [11].The control group consisted of 30 healthy subjects who visited Dental Clinic, Faculty of Medicine Foca, University East Sarajevo, for regular checkups. The study was approved by the institutional committee of ethics (No. 01-8/140) and was conducted in accordance with the Helsinki Declaration of 1975, as revised 1983. The presence of severe mental or systemic disorder, pregnancy, signs or symptoms of AIDS and antibiotic administration during the last 6 months were exclusion criteria in this study. After the study was explained to the patients, written informed consent was obtained from all patients recruited in the study.
Oral clinical examination was performed at the Dental clinic, Faculty of Medicine Foca, University of East Sarajevo, Bosnia and Herzegovina according to WHO criteria [12]. The examination was conducted using a dental mirror and both dental and periodontal probes. The following was determined: decayed, missing and filled teeth (DMFT); plaque index (PI), sulcus bleeding index (SBI), probing pocket depth (PPD) and clinical attachment level (CAL). Periodontal parameters were assessed at four sites around each tooth (mesiobuccal, distobuccal, mesiolingual and distolingual locations). Culture specimens to Candida spp. were obtained from dorsum of the tongue using a sterile cotton-tipped swab and inoculated into Sabouraud Dextrose Agar for 48 hours.
All patients were asked to abstain from eating for 2 hours before saliva collection [13]. Both unstimulated and stimulated saliva were collected using "a spit technique". Stimulated saliva was collected using 10% citric acid that was dropped onto the tongue [14]. Each patient was instructed to seat in dental chair with head tilted forward and instructed not to speak, do any head movements or swallow any saliva if present in the mouth during the procedure. After that, the patients were asked to spit in a sterile cup every minute for 5 minutes. Salivary flow was calculated in ml/min.

Statistical analyses
All statistical analyses were performed using SPSS version 19.0 for Windows. Results were expressed as mean values ± standard deviation (SD). The differences between the groups were assessed by ANOVA or chi-square test. Relationships between variables were evaluated by Pearson correlation coefficient. The value of p<0.05 was considered statistically significant.

RESULTS
Sociodemographic and clinical characteristics of all subjects are presented in Table 1. Study included 64 (57.8%) female and 26 (42.2%) male subjects. The mean age of the study population was 57.58±7.19. The healthy subjects had slightly more unstimulated salivary flow rate than well-controlled diabetics, although the difference was not statistically significant. Poorly-controlled diabetics had statistically significantly lower unstimulated and stimulated salivary flow rate than healthy control ( Table 2). Table 3 shows periodontal and dental health in all patients. Diabetic patients had poor periodontal health. A statistically significant difference was observed between the groups. In fact, both poorly and better-controlled diabetics had deeper periodontal pockets, more attachment loss, more bleeding on probing and higher mean value of plaque index than healthy subjects. Type 2 diabetics with poor metabolic control had significantly more decayed teeth and higher mean value of DMFT index than healthy control. Better-controlled diabetics had more decayed teeth and higher mean value of DMFT index than healthy control, but statistically significant differences between the groups were not observed. Also, the difference in prevalence of missing and filled teeth was statistically significant between the groups. Regarding the frequency of oral candidiasis, there was statistically significant difference between poorly controlled diabetics and healthy subjects. No statistically significant difference was found between well-controlled diabetics and healthy subjects in regards to candida isolation (Table 3).
Pearson correlation analyses revealed statistically significant negative correlation between unstimulated salivary flow rate (USFR) as well as stimulated salivary flow rate (SFR) and DMFT index, plaque index (PI), sulcus bleeding index (SBI), clinical attachment loss (CAL) and probing pocket depth (PPD). Negative but non-significant correlation was observed between USFR as well as SFR and oral candidiasis (Table 4).

DISCUSSION
Several studies reported reduced salivary secretion of both unstimulated and stimulated saliva in diabetics [15,16]. The pathogenic mechanisms linking diabetes and hyposalivation are not fully understood. Dehydration as a result of prolonged hyperglycemia and resultant polyuria is considered to be the main cause of salivary glands hypofunction. However, dehydration by itself cannot explain functional changes in salivary glands. It is believed that the two most common degenerative complications of diabetes, neuropathy and microangiopathy are crucial for pathologic changes in the structure of salivary glands [17]. Increased concentration of calcium in parotid and submandibular saliva can explain higher prevalence of sialolithiasis in diabetics and consequently oligosialia. Also, influence of glycemic control on salivary flow is still controversy [11,18]. The present findings show that the mean USFR was highest in healthy subjects, but there was no significant difference between groups. Similar results were presented in the study of Panchbhai et al. [19]. Results of our study indicate statistically significant SFR reduction in diabetics and significant corelation between metabolic control and salivary flow. Our results are in agreement with the study of Chavez et al. that also confirmed this relationship [20].
Recent studies clearly indicated that diabetes is an important risk factor for periodontitis [21,22]. Diabetes is considered to promote periodontitis through an exaggerated inflammatory response to the periodontal pathogens [23]. Some studies indicate that although diabetes presents a risk factor for periodontitis, periodontitis may, on the other hand, have a negative effect on the metabolic control of diabetes. [4,5,24]. Results of our study demonstrated  deeper periodontal pockets, more attachment loss, more bleeding on probing and higher mean value of plaque index in poorly-controlled diabetics. These results are in accordance with the findings of Mohamed et al. [25]. Moreover, our findings indicated that both, unstimulated and stimulated salivary flow rate, were negatively and significantly correlated with periodontal parameters. It has been shown that diabetic patients with xerostomia are more susceptible to periodontal infection [26]. Some studies confirmed that periodontal disease was strongly related to salivary flow rate [27]. Previous studies reported contradictory results about relationship between dental caries and diabetes mellitus. Our results showed significantly increased number of decayed teeth in poorly controlled diabetics. Similar results were obtained in study by Bakhshandeh et al. where subjects with better glycemic control had significantly lower number of decayed teeth compared to those with poor glycemic control [28]. In contrast, Syräjlä et al. revealed no association between the HbA1c level and dental caries [29]. Apart from metabolic control of diabetes, development of dental caries is affected by many other factors, among which dental plaque presence is the most important. It is well established that development of caries is a result of metabolic events in dental plaque over time and that it can be increased in terms of impaired function of saliva. High glucose level in saliva and gingival crevicular fluid can cause increase of saliva cariogenic organisms in both supragingival and subgingival plaque in diabetics [30]. Salivary flow reduction leads to impaired antimicrobial actions of saliva as well. In our study, salivary flow rate was negatively and significantly correlated with DMFT, in contrast to the results of study by Karjalainen et al. [31]. Moore et al. reported an association between a low salivary flow rate and slightly increased incidence of dental caries [32]. As a contradictory result, Collin et al. reported higher prevalence of dental caries among those with higher salivary flow rate [33].
According to the literature, prevalence of oral candidiasis was reported to be higher in patients with diabetes type 2 compared to healthy persons [34,35]. In addition to changes in the composition and quantity of saliva, the presence of infection with Candida spp. in type 2 diabetics is also associated with impaired cellular immunity. The high prevalence of Candida spp. is especially pronounced in diabetic denture wearers. Candida spp. can co-aggregate with bacteria in biofilm of denture surface that than become a reservoir of aforementioned microorganisms with further potential to colonize oral mucosa. It has been estimated that 33. 3% of diabetics in our study were diagnosed with oral candidiasis and that is in accordance with the study by Shenoy et al. [36]. Similar results were reported by Guggenheimer et al. [37]. All those findings support the role of diabetes mellitus as a predisposing factor for increased Candida spp colonization of oral mucosa. In accordance with the study of Navazesh et al. [38], results of our study also showed negative correlation between salivary flow rate and oral candidiasis although without statistical significance.