Discussion
The pregnant group showed increased flow rate and decreased buffer and pH when compared to the non pregnant women. Saliva is regarded as one of the important factors in regulating oral health.8 About 600ml of serous and mucous saliva containing minerals, electrolytes, buffers, enzymes, growth factors enzyme inhibitors and immunoglobulin’s, cytokines, mucin and other glycoproteins is produced by the human salivary gland produce every day. At the same time it possesses antimicrobial components and buffering agents that act to maintain oral tissue.9 Many studies have shown that saliva has a close relationship between the serum parameters, hence it can be used in detecting physiological and pathological changes in the body.5-9
Pregnancy is a process which brings about alterations in the composition and functions of all systems of the body. It is also accompanied with profound metabolic biochemical and hormonal, changes.10 Studies undertaken previously to estimate the stimulated and unstimulated salivary flow rate between pregnant and non-pregnant women have shown mixed results. The studies done by Lane and others shows no significant change in the salivary flow rate between the pregnant and non pregnant women.11,12 other studies shows significant reduction in the salivary flow rate in the pregnant groups.10, 13
Unstimulated whole saliva reflects basal salivary flow rate and it provides protection to oral tissues3. Unstimulated salivary provides a precise parameter to analyze the salivary gland status while the stimulated saliva provides information about the functional reserves.14
The increase of salivary flow in this study may be due to the hormonal changes that take place during pregnancy. Saliva composition and secretion is modulated by many hormones but the exact mechanism how these hormones bring about these changes is poorly understood.10
The increased production of hormones during pregnancy is mainly due to the placenta, which takes over the production of progesterone and estrogen in the pregnancy. Estrogen levels rise more than 100- folds from the beginning of pregnancy.15 Estrogen has a vasodilatory effect on the major arteries and increases blood flow in the target tissue. The possible effects of estrogen on blood flow in the salivary glands is not known but increased blood flow is associated with increased secretion of saliva.16
A number of studies have reported an increase in salivary flow rate when estrogen is used for hormonal replacement therapy (HRT), this suggests that estrogen may play an important role in oral mucosal and salivary gland physiology.13,17
For direct action steroid hormones require specific receptors in the target tissue.16 Estrogen receptors (ERs) are responsible for the effects of estrogen. There are basically two types of receptors, ERα and ERβ. ERβ is identified recently in salivary gland acinar and ductal cells.17
Importantly, the expression of ERβ in oral epithelial cells and salivary gland acinar and ductal cells suggests that estrogens may regulate the physiology of these tissues through the ERβ subtype. Thus suggestive of the sensitivity of oral tissue to estrogen and its application in HRT17 and also in the present study which showed increase in the un-stimulated and stimulated salivary flow among the pregnant women.
Pregnant patients are uncomfortable and distressed due to the profuse salivation which is termed as sialorrhea or ptyalism.18, 19 The increase in the salivary flow during pregnancy in the present study can be attributed to these factors.
It is believed that nausea and vomiting are necessary components of sialorrhea in pregnancy and certain hormones contribute to this relationship (morning stickiness). In this respect, more than 70% of all pregnant women encounter nausea and vomiting which is accompanied by excessive salivation.18, 19Human chorionic gonadotropin (HCG) has been implicated in nausea, increased salivation and vomiting because of the high levels produced during pregnancy.
Pregnancy induces decreased gastroesophageal sphincter tone and prolonged gastric emptying times. These changes along with decreased esophageal tone lead to ptyalism. Further decreased large bowel motility which leads to increased water and constipation absorption.19 Hence these factors can be hypothesized to the increase in the saliva flow.
Salivary pH is closely related to the buffer capacity (Figure 1).20
Figure 1: Salivary Buffer Systems (i) Bi-Carbonate Buffer System: Activates at Normal Salivary Flow were in the Bicarbonate Ion Modulates the Salivary pH (ii) Phosphate Buffer System: Activates at Low Salivary Flow were in the Hydrogen Phosphate Ion Modulates the Salivary pH (iii) Protein Buffer System: Role of Various Salivary Proteins in Maintaining Salivary pH
The inorganic and protein composition of saliva changes during the course of pregnancy.13 Salivary gland HCO3- originates partly from plasma and partly from the salivary gland carbon dioxide. The reduction in pH value during pregnancy, is related to the effect of progesterone hormone, which is known to decrease plasma bicarbonate level during pregnancy resulting in a decrease in the pH and buffering capacity.13
The activity of salivary peroxidase a marker enzyme of estrogen action increases significantly during pregnancy along with specific progesterone receptors in human salivary glands. Progesterone receptors are induced by estrogen receptors but it is still not known which type of cells are the potential targets in the salivary gland.16
The most important protein of saliva is α-amylase which is secreted by parotid gland. Increasing trend of this enzyme activity may lead to increased microorganism substitution and reduced pH of saliva. It was found that α-amylase activity increase during 10 and 21 weeks of gestation.10
Hormonal changes may also affect the composition of saliva. During pregnancy, when the serum concentration of estrogens is elevated, IgA increases, whereas sialic acid and the pH and buffer capacity decrease in saliva.13These factors have led to the decrease in the pH and the buffering capacity of saliva in the pregnant group.
Conclusion
A significant increase in the flow rate of both unstimulated and paraffin stimulated saliva was seen in pregnant women in the third trimester with a reduction in pH and buffering capacity when compared to the non pregnant women in the same age group. The increase in the salivary flow may be attributed to the increase in estrogen and progesterone secretion and the decrease in the pH and buffering capacity may be due to the decreased plasma HCO3- ion concentration and increase in the α amylase concentration. However to obtain a more conclusive conformation of this hypothesis more studies have to be carried out. In conclusion the present study provides further evidences for the modification of saliva during pregnancy.
Conflict of Interest:
None.
Acknowledgements:
We express our deep sense of gratitude and profound thanks to my respected teacher Dr. Asha ML, Professor and Head of the Department of Oral Medicine and Radiology, Sri Hasanamba Dental College and Hospital, Hassan for her constant encouragement, guidance and support in every aspect of this study.
We are grateful to Dr. S Ravindra, Principal, Sri Hasanamba Dental College and Hospital, Hassan for providing us with all the college facilities to carry out this study successfully.
Disclosure of Interests: None
Contribution to Authorship:-
Dr. Naveen S was the principal investigator for the study. Collection of all the data and samples were done by him.We are grateful to our respected teacher Dr. Asha ML, professor and Head, Department of Oral Medicine and Radiology for her relentless help and suggestions for the study at all times. Dr. Shubha G, Dr. Anju Anu Jose and Dr. Atul Anand Bajoria for their help in interpreting the study results and analyzing the discussion of the study.
Details of Ethics Approval:-
An ethical approval (no. SHDCH/2010-11/ETH/14) was taken from the institutional ethical committee before the start of the study.
Funding: None
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