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The Role Saliva Plays in Your Mouth

What is saliva?

Saliva is a fluid produced by your salivary glands. It’s made up of water, electrolytes (like sodium, potassium, calcium, magnesium, bicarbonate, and phosphates), immunoglobulins, proteins, mucins, nitrogenous products, and enzymes, and is essential to everyday functions like eating, swallowing and speaking [1, 2].

Saliva is 99% water, so drinking enough is essential for keeping your mouth moist [2]. Saliva has an average pH of between 6 and 7, although this can vary between 5.3 and 7 [2]. 

How is saliva produced?

Saliva gland diagram

Saliva is created and fed into your mouth by three major salivary glands and hundreds of minor ones. The major glands are located opposite your molars and on the floor of your mouth, while the minor glands are located everywhere, including your lower lip, tongue, palate, cheeks and pharynx [2].

Saliva is secreted by acini cell clusters, flowing out into ducts where its chemical composition is altered [1]. The ducts from various cell clusters then merge before emptying into your mouth [1].    

Saliva Flow

Wondering how much saliva all your glands and clusters produce each day? Most people have an unstimulated salivary flow rate of between 0.3 and 0.4 millilitres per minute, adding up to between 1 litre and 1.5 litres per day [2, 3]! Our salivary flow rates vary according to the time of day and year – peak flow occurs during the afternoon and winter, while low flow occurs during sleep and summer [3, 4].      

Why is saliva important?

Saliva has a number of important functions, including eating, speaking and swallowing. Let’s have a look at each of them in turn. 

Lubrication & Bolus Creation

Rub your fingers together. Do they feel rough? Is there friction between them? That’s what the inside of your mouth would feel like without saliva. 

Saliva is a natural lubricant that protects our mouths and throats from abrasion, especially when we’re chewing [4]. It helps soften food, and also acts as a binding agent for the creation of a bolus, which is the ball your mouth forms from chewed food particles to help you safely swallow [5].        

This is why people with conditions like dry mouth often have trouble eating – their low saliva flow rates mean swallowing can be difficult and sometimes even painful. 

Enabling Speech

The lubricating effects of the mucins (a type of complex protein molecule) in saliva also help us speak [2]. Most of the sounds we make with our mouths require lubrication between our tongue, cheeks and lips, which is why having a dry mouth can make talking difficult.

Maintaining Oral pH Levels

Tooth PH

Maintaining neutral pH levels in the mouth is another important function of saliva [6]. This process, known as ‘buffering’, helps neutralise the damaging acids produced by dental plaque bacteria, which feed off fermentable carbohydrates found in food [7].

Saliva can do this because it contains bicarbonate and phosphate – both minerals help your teeth stay healthy by preventing demineralisation, and also prevent the growth of acid-tolerating bacteria, which can drive out good bacteria and cause even more problems for your oral health [7].

Washing Away Food Particles

Saliva is a bit like your mouth’s natural cleaning agent – once you’ve swallowed most of your food or drink, it helps sweep up the remnants and clear them out of your mouth. On average, each swallow involves about 0.3 millilitres of saliva [4].

Why is this important? Because if fermentable carbohydrates like sucrose and glucose are left in your mouth, dental plaque bacteria metabolise them, creating acids that damage your teeth [4]. The same goes for acidic foods or drinks – the longer they sit against the surface of your teeth, the more damage they’re doing [4]. 

That’s why washing your mouth out after eating can often be a good idea, especially if you have reduced salivary flow.

Remineralisation of Teeth

Tooth demineralization diagram

Demineralisation – when the enamel on your teeth gets stripped away – occurs when acids diffuse through the acquired enamel pellicle (AEP) and dissolve the enamel itself [2, 4]. If having acid burning into your teeth sounds bad, that’s because it is! Demineralisation is just the scientific term for tooth decay, which can lead to holes in your teeth and a whole variety of health problems.

Saliva helps not only by neutralising the acids, but also by re-forming the AEP, which is a protective barrier that stops your teeth getting damaged when rubbing against things [4]. Once the AEP is reformed, your tooth’s enamel can start to remineralise (grow back) [2, 4].    

Preventing Bacteria

Bacteria image

In addition to regulating the pH of your mouth, which helps fight bad acid-tolerating bacteria, saliva also contains anti-bacterial, anti-viral and anti-fungal proteins and peptides. This helps prevent many unpleasant bacteria from colonising your mouth [4].

Although some bacteria can still survive in the oral cavity, like the bacteria that cause gingivitis and periodontitis, saliva inhibits their growth so your mouth stays healthy [4].    

Enabling Taste

Your tongue is covered with taste receptor cells, which are clustered into groups known as taste buds. When you put something in your mouth, you’ll experience one of five basic tastes: sweet, salty, umami, bitter or sour [8]. Lipid sensors also allow us to taste fat [8]. 

Saliva plays a role in this process because it acts as an interface between taste receptors and the food or drink in our mouths, and certain proteins and hormones present in it can actually shape how we perceive taste [9]. This is why people with dry mouths often have altered or reduced senses of taste [9].         

Digestion of Starches

Saliva contains a digestive enzyme called amylase, which helps break down starch, a type of carbohydrate present in foods like potatoes, bread, cereal, rice, grain and pasta. Amylase splits large starch molecules into dextrin, then into maltose, and finally into glucose, which can be used by your body as an energy source [10]. 

Although most of your body’s amylase is produced by your pancreas, salivary amylase begins breaking down starch in your mouth and throat, before the process is stopped by the acid in your stomach [10]. 

Healing of Oral Wounds

Because saliva contains over 1,000 active peptides, it acts as a kind of natural healing balm that stimulates wound closure and your body’s inflammatory response [11]. It helps wounds heal faster without leaving scar tissue, and increases the release of inflammatory cytokines that help prevent infection [11].

The best part? Although saliva is mostly applied to wounds inside your mouth, recent studies have indicated that it has clear potential as a healing agent for external skin wounds as well [11]! In the near future, we might start seeing this incredible fluid being contributed by donors to help hospital patients recover from serious wounds [11].      

Conclusion

Saliva is a fascinating fluid that is essential to everyday activities like eating, swallowing and speaking. It’s responsible for:

  • Lubrication and bolus creation
  • Enabling speech
  • Maintaining oral pH levels
  • Washing away food particles
  • Remineralising teeth
  • Preventing bacteria
  • Enabling taste
  • Breaking down starches
  • Healing of oral wounds

This importance is exactly why saliva-reducing conditions like dry mouth, also known as xerostomia, can be so damaging. To learn more the causes and effects of dry mouth, head over to the next article in this series.

What Causes Dry Mouth?

References

[1] Tiwari, M. (2011) Science behind human saliva. Journal of Natural Science, Biology and Medicine.  2(1), 53–58. DOI: 10.4103/0976-9668.82322

[2] Humphrey, S. P. & Williamson, R. T. (2001) A review of saliva: Normal composition, flow, and function. The Journal of Prosthetic Dentistry. 85(2), 162–169. DOI: 10.1067/mpr.2001.113778 

[3] Dawes, C. & Wong, D. T. W. (2019) Role of Saliva and Salivary Diagnostics in the Advancement of Oral Health. Journal of Dental Research. 98(2), 133–141. DOI: 10.1177/0022034518816961 

[4] Dawes, C., Pedersen, A. M. L., Villa, A., Ekström, J., Proctor, G. B., Vissink, A., Aframian, D., McGowan, R., Aliko, A., Narayana, N., Sia, Y. W., Joshi, R. K., Jensen, S. B., Kerr, A. R. & Wolff, A. (2015) The functions of human saliva: A review sponsored by the World Workshop on Oral Medicine VI. Archives of Oral Biology. 60(6), 863–874. DOI: 10.1016/j.archoralbio.2015.03.004 

[5] Jalabert-Malbos, M.-L., Mishellany-Dutour, A., Woda, A. & Peyron, M.-A. (2007) Particle size distribution in the food bolus after mastication of natural foods. Food Quality and Preference. 18(5), 803–812. DOI: 10.1016/j.foodqual.2007.01.010 

[6] Pedersen, A. M. L., Sørensen, C. E., Proctor, G. B., Carpenter, G. H. & Ekström, J. (2018) Salivary secretion in health and disease. Journal of Oral Rehabilitation. 45(9), 730–746. DOI: 10.1111/joor.12664 

[7] Marsh, P. D., Do, T., Beighton, D. & Devine, D. A. (2015) Influence of saliva on the oral microbiota. Periodontology 2000. 70(1), 80–92. DOI: 10.1111/prd.12098 

[8] Lee, A. & Owyang, C. (2017) Sugars, Sweet Taste Receptors, and Brain Responses. Nutrients. 9(7), 653. DOI: 10.3390/nu9070653 

[9] Neyraud, E. (2014) Role of Saliva in Oral Food Perception. Saliva: Secretion and Functions. 61–70. DOI: 10.1159/000358789 

[10] Peyrot des Gachons, C., & Breslin, P. A. S. (2016) Salivary Amylase: Digestion and Metabolic Syndrome. Current Diabetes Reports. 16(10). DOI: 10.1007/s11892-016-0794-7 

[11] Neves, C. R., Buskermolen, J., Roffel, S., Waaijman, T., Thon, M., Veerman, E. & Gibbs, S. (2019) Human saliva stimulates skin and oral wound healing in vitro. Journal of Tissue Engineering and Regenerative Medicine.  13(6), 1079–1092. DOI: 10.1002/term.2865

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