Scope - Communication Resource Centre

Saliva Management

The Profile of Saliva

What is Saliva and where is it made?

Saliva is made by salivary glands that are found in the underlying tissues of our mouths. The basic unit of salivary glands are clusters of cells called acini. These cells secrete a fluid that contains water, electrolytes, mucus and enzymes all of which flow out into a series of collecting ducts. The main salivary glands are the:

A line diagram of the head showing the three main glands

Parotid glands
Submandibular glands
Sublingual glands

Each gland is found in symmetrical pairs in the head. Each gland has a tube shaped duct that carries the saliva produced into the mouth. There are also smaller saliva-producing glands that are dotted throughout the mouth and contribute to the overall amount of saliva produced.

How the glands make Saliva

The type of nerve system that controls saliva production is the autonomic nervous system, which controls both the volume and type of saliva secreted15. The secretion of saliva by each gland is controlled by two different types of nerves; sympathetic and parasympathetic nerves.

The parasympathetic nerve supply is most active during the day, whilst eating and creates more watery, or serous saliva; predominantly produced by the parotid gland, and partly by the submandibular gland.

The parasympathetic system turns up the flow of saliva by releasing a chemical, acetylcholine, which stimulates the glands to make more saliva. If these glands get diseased, damaged, or affected by drugs, they may not make enough saliva, leading to dry mouth .

The sympathetic nerve supply produces predominantly thicker mucous saliva mainly by the sublingual and partly the submandibular glands. This may occur when in certain situations, fear, stress or anger are aroused. This is also the case during hard physical exercise.

The Parotid gland
The Parotid glands are the largest of the glands and lie between the back of the jaw and each ear1 and secretes about 25% of the total saliva amount at rest2. Each gland is surrounded by a hard capsule called the parotid capsule. The parotid mainly produces watery, or serous saliva. It's duct opens in the mouth just opposite the crown of the 2nd upper molar tooth. The gland's productions are predominantly controlled by a nerve called the Glossopharyngeal Nerve (CN IX) which originates in the superior salivatory nucleus of the medulla in the brainstem. For a more detailed description of neuroanatomy and function related to saliva

The Submandibular Gland
The submandibular glands are of intermediate size and lie just inside the lower-back parts of the mandible (jaw) in the floor of the mouth. A part of the gland curls inwards around the mylohyoid muscle. The submandibular produces most of the saliva at rest (about 60%)4 and its ducts are 5cm long, emptying underneath the tongue at the floor of the mouth. The type of saliva produced is both serous and mucous saliva: the amount of each is altered depending on which nerves (parasympathetic or sympathetic) are in control.

The submandibular gland is innervated predominantly by the facial nerve (CNVII). The nerve fibres begin in the superior salivatory nucleus in the pons of the brainstem. More information

The Sublingual Glands
The sublinguals are the smallest glands and are located just under the floor of the mouth, above the mylohyoid muscle. You can feel it as a ridge under your tongue. These secrete around 5% of total saliva at rest and produces mainly mucous saliva secreting glands, although some serous saliva is also produced. It's major and minor ducts also empty at the at the floor of the mouth in a row along with the submandibular duct2. The nerve controlling sublingual production follows the same pathway as the nerve controlling the submandibular gland (CNVII). More information

Chart showing Distribution of Saliva production at rest

Approximate distribution of saliva is based on figures from Johnson & Scott, 1993; Sreebny, 2000; Diaz & Marek, 2002.

Where does Saliva go?

Saliva is primarily involved at the beginning of the swallowing process.

When food is placed before the nose or eyes, the sight and smell of food stimulates the autonomic nervous system which in turn sends messages to the glands instructing them to produce saliva. The saliva created is secreted into the mouth. It is mixed up with the food and swallowed.

Why have Saliva?

Saliva has many uses within the human body. It primarily:

Begins digestion
The enzyme Amylase in saliva begins the process of the breaking down of carbohydrates of food in the mouth.
Lubricates the tongue and lips for smooth and clear articulation of speech
Protects the lining of the mouth from damage caused by abrasive foods and objects
Assists with acidity levels in the digestive tract. Bicarbonate ions regulates the pH levels in the mouth and eosphagus
Acts as a solvent so that substances in the mouth can be tasted.
Maintains a clean and hygienic mouth Carries anti-bacterial agents (immunoglobulins). They destroy micro-organisms and remove toxic substances

Influences on saliva production

The general pattern of saliva production is that it is greater during the day than at night and when upright rather than lying down. However, from person to person, the production of saliva can vary . Many external and internal elements can influence saliva production:

Mood (eg. Anxiety, depression)
Gender. Evidence has shown that males produce greater amounts and rates of flow of saliva than females.
Age. Although there is conflicting evidence in regards to this, several studies have found that the prevalence of oral dryness increases with aging and that the resting flow rate of saliva decreases with age.
The amount of water you drink. Reducing bodywater content may lead to less saliva flow at rest.
Chewing. It is generally agreed that chewing creates more whole saliva flow, particularly of the parotid secretions and thus serous saliva. Nerve endings or receptors (periodontal mechanoreceptors) ascertain the force and frequency of chewing and feedback the information so that the amount of saliva secreted from the parotid is adapted accordingly
Taste. Research has found that saliva contains specific proteins that are growth factors that make taste buds develop and mature. Without these growth factors, taste buds degenerate. Decreased salivary flow results in a clinically significant oral imbalance that may manifest as altered taste sensation.
Smoking. Saliva production may be increased.
Sight of Food. It is commonly thought that saliva is produced upon the sight of food.

Facts and Figures

Most mature salivary glands produce about 600mls per day. Resting or unstimulated whole saliva is produced at a rate of 0.3-0.5ml/minute while stimulated saliva is 1.0-3 ml/minute.

Natural Development of Saliva Control

Drooling is the unintentional loss of saliva from the mouth and it can give the appearance of excessive saliva production, although this is not always the case. Drooling is considered a normal phenomenon in children before they develop adequate oral neuromuscular (nerve and muscle) control related to positioning, activity, oral muscle functioning, and the integration of these muscle movements. This is achieved about the age of 18-24 months.

Drooling occurs normally when a child is acquiring a new motor skill, and until the skill becomes automatic, the drooling may continue. When a child cuts a new tooth, drooling occurs before, during and just after the event.

Since the production of saliva is related to the digestion of food, infants produce only a small amount of saliva before the age of 3 months as their only diet is cow's or breast milk. The minimum amount is made for the purpose of keeping the mouth moist and clean. However, as the child grows, glands enlarge and more saliva is produced. As the textured food changes from liquids to semi solids, chewing skill develop. The infant is then required to learn to control the saliva amounts that fill the mouth whilst they are not eating.

Saliva Control Stages of Development

There is a naturally occurring process of development characterised by landmarks of saliva control achievement (Morris and Klein, 2000).

After 3 months

Infants begin to produce greater amounts of saliva. If lying flat, face up or reclining; gravity will enable the saliva to follow its due course with the swallow. They may drool when:

a baby initiates head lifting or turning, or when gravity works against the normal path, drooling may occur.

6 months

Infants control their saliva lying face down, on their backs and in supported sitting positions. They may drool when:

Teething or using their hands for reaching or using objects
Beginning to attempt tasks requiring concentration or finer use of their fingers or hands (due to a reduction in mouth control)
Before, after or during a meal; they produce more saliva

9 months

Even during larger movements such as rolling, sitting or belly-crawling; drooling is absent. The child will not generally drool around mealtimes.They may drool when:

Cutting a tooth
Eating certain foods

15 months

Drooling is no longer present when continuously attempting newly acquired advanced movements such as walking. They may drool when:

Teething
Concentrating on advanced fine finger movements like self-feeding, random-play or undressing.

24 months

Children have developed the structure and control of their nerves and muscles to engage in the fine finger movements mentioned above, manipulating small objects and forming two-word speech combinations all without drooling.

References

Berkovitz, B. J. & Moxham, B. J. 1988. A textbook of head and neck anatomy. Wolfe Medical; London, GB. Brand, R. W. & Isselhard D. E. 1990. Anatomy of orofacial structures, 4th ed. Mosby; St. Louis. Christensen, C.M., and M. Navazesh. 1984. "Anticipatory salivary flow to the sight of different foods" : Appetite: (5), 307-15. Diaz, A.A and Marek, C.A. 2002. "The impact of saliva on patient care: a literature review" : Journal of Prosthetic Dentistry: Sep 88(3): 337-43. Heine, R.G. 1994. "The protective role of saliva in gastro-oesophageal reflux" : 'A Seminar on Research in saliva control'. Department of Child Development and Rehabilitation Pediatrics, Royal Children's Hospital: Parkville, Victoria. Henkin, 2000. Retrieved September 21, 2003, from www.tasteandsmell.com/may03.htm Jensen Kjeilen, J., Brodin,P., Aarss,H. and Berg,T. 1987. "Parotid salivary flow in response to mechanical and gustatory stimulation in man" : Journal of Physiology Scandinavia: (131) 169-75. Johnson H. & Scott, A. 1993. A practical approach to Saliva control. MacGregor, I. 1988. "Smoking, saliva and salivation" : Journal of Dentistry: (16), 14-17 Morris, S. & Klein, M. 2000. Pre-Feeding Skills: A comprehensive resource for feeding development. Therapy Skills Builder, Communication Skill Builders; Tucson, Arizona. Nedefors T., Isaksson R., Mornstad H., et al. 1997. "Prevalence of symptoms of dry mouth in an dault Swedih population- relation to age, sex and pharmacotherapy": Commun Dent Oral Epidemiol: (25), 211-16. Palmer, J.M. 1993. Anatomy for Speech and Hearing (4th Ed); Baltimore, Maryland; Williams & Wilkins Co. Pangborn, R. M., and I. M. Sharon. 1971. "Visual deprivation and parotid response to cigarette smoking" : Physiological Behaviour: (6), 559-61. Scott, A. 2002. Issues in saliva management: Everything you need to know about the salivary gland and secretions (Victorian Continuing Professional Development seminar). Snell, R.S. 1995. Clinical anatomy for medical students, 5th Ed. Little, Brown & Co; Boston, USA Sreebny, L. & Broich, G. 1987. "Xerostomia (dry mouth)": The salivary system. Ed. Sreebny, L. Boca Raton, FL: CRC Press, Inc. Sreebny, L. M., 2000. "Saliva in health and disease: An appraisal and update" : International Dental Journal: (50), 140-61. White, K.D. 1975. The significance of individual differences in the control of saliva. Unpublished Ph. D. Dissertation, University of Queensland.