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	Articles of Interest Direct Measurement of Oral Dryness (xerostomia) with the Periotron® System
	NATURE AND SOURCES OF SALIVA Saliva is the main fluid produced in human mouths and comes from 3 pairs of major and about 200 to 400 minor salivary glands. The saliva from the major glands include the parotids which produce a watery (serous) secretion, the sublingual and minor glands which produce a slimy (mucinous) fluid, and the submandibulars which produce a mixture of these two kinds of secretions. The saliva secreted from the submandibular glands has a low visco-elasticity (ability to stretch), one that is closer to that from the parotids than that from the sublinguals or minor salivary glands. This is largely because of the serous to mucinous proportions produced. Whole saliva is a mix of these various secretions. Should the serous proportion decrease as appears to occur in individuals with drier mouths, the saliva mixture, namely whole saliva, becomes more viscous and even ropey.
	HYPOSALIVATION AND ORAL DRYNESS A deficiency in the production of saliva is referred to as hyposalivation. It can be easily measured by collecting saliva by expectoration for a fixed period of time. A suitable method is that described by Sreebny (Recognition and treatment of salivary induced conditions. International Dental Journal 39: 197, 1989) where three 2-minute collections are made and the values are averaged. Values below 0.1 to 0.2 ml per minute for resting whole saliva is considered to be indicative of hyposalivation and usually gives the feeling of a dry mouth. The effects of insufficient saliva in the mouth are severalfold. Most significant is the feeling of oral dryness, which is generally most evident in the regions of the hard palate and the lips (Wolff and Kleinberg, Oral mucosal wetness in hypo- and normo- salivators. Archives of Oral Biology 43: 455, 1998). This comes about through reduction in the thickness of the film of residual saliva that covers the mucosal surfaces. Residual saliva is the film remaining on the teeth and oral soft tissue surfaces immediately after swallowing. Before the next swallowing episode, non-residual saliva builds up as the salivary glands continue to produce this fluid. The new saliva mixes with the residual saliva and when enough is secreted, the swallowing reflex is triggered. In this way, the residual saliva is changed. When asleep, saliva flow is drastically reduced and the need to swallow as well. Residual saliva plays a key role in preventing the dry feeling which is detected by nerve endings in the mucosa, probably mechanoreceptor A-delta and c fibers. Also, residual saliva acts as a lubricating film that enables the teeth to slide over one another, and prevents the roughness that would otherwise occur when the tongue is run over tooth and mucosal surfaces.
	HYPOSALIVATION, DENTAL CARIES AND DENTINAL HYPERSENSITIVITY Saliva is an excellent protector against the demineralization of the hard tissues which occurs in the mouth when there is excess acid present on the teeth either from sugars converted to acid by their fermentation by dental plaque bacteria or from acidic foods, beverages and oral products such as a number of the present day mouthwashes. In individuals who suffer from hyposalivation, there is not enough saliva to adequately protect the teeth from acid dissolution by either of these means. In dental caries, the acids come from sugars that are fermented by the bacteria in dental plaque. In dentinal hypersensitivity, the acid comes mainly from acidic foods such as soft drinks, juices, alcoholic beverages, and citric fruits. Brushing with an abrasive toothpaste enhances tooth substance loss. When the cementum of roots are exposed because of gingival recession, the open tubules of the uncovered dentine enable oral stimuli to reach the nerve fibers in the pulp via hydrodynamic movement of the fluid in the open dentinal tubules. This causes the brief periods of sharp pain characteristic of dentinal hypersensitivity. Saliva prevents the pH of the plaque on tooth surfaces from becoming too acidic and causing tooth demineralization and formation of dental caries lesions. It also contains calcium and phosphate ions which prevent tooth demineralization and formation of cavities from taking place by the simple process of mass action. The calcium and phosphate in saliva also favors re-mineralization which is particularly helpful in plugging dentinal tubules and reducing dentinal pain.
	CAUSES OF ORAL DRYNESS The main cause of oral dryness is the approximately 400 medications that produce hyposalivation as a side effect (Sreebny and Schwartz, A reference guide to drugs and dry mouth. Gerodontology 5: 75, 1986). Certain medical conditions such as Sjögren's syndrome, other auto-immune conditions and radiation treatment for oral and neck cancer also lead to hyposalivation and a dry mouth condition. In normal individuals, a film of saliva always covers the surfaces of the teeth and oral mucosa. The latter have fine nerve endings which are able to sense when there is not enough saliva on the mucosal surfaces. As pointed out above, the film of saliva left immediately after swallowing is the residual saliva. Residual saliva levels throughout the mouths of dry mouth and normal individuals have been extensively measured. On the one hand, while these have shown a characteristic pattern of wetness of mucosal surfaces throughout dry or normal mouths; on the other, they differed in that residual saliva levels were always lower in dry mouth individuals. Needing emphasis is that the wetness pattern is remarkably similar and consistent in all individuals. Where difference is seen are in the levels. Least residual saliva is found on the hard palate and most saliva is observed on the posterior of the tongue and the mucosal surfaces near the oral openings of the ducts from the major salivary glands. The residual saliva levels on the hard palate are very easy to measure and can be used as an indictor of the presence and severity of the oral dryness condition.
	MEASUREMENT OF ORAL MUCOSA WETNESS LEVELS Oral mucosal wetness is the opposite of oral mucosal dryness. Levels of mucosal wetness can be assessed by measurement of residual saliva levels with Sialopaper™ strips and the Periotron micro-moisture meter. These strips are shaped like a frying pan and are pressed flat against the hard palate with a finger of a gloved hand. Collection is done for 5 seconds and the strip is transferred to the sensors of the Periotron® meter where the volume is measured electronically. Sialopaper strips each have a diameter of 7.5 mm and cover a mucosal area of 44.15 square mm. Saliva film thickness in micro-meters (um) is determined simply by dividing the volume in microliters by this area and multiplying by 1000. Research has identified the threshold of oral dryness to be a residual hard palate saliva level below about 10 to 15 microns. Such a low mucosal wetness level is usually accompanied by a low rate of saliva flow, a more acidic saliva pH, and a more visco-elastic saliva. When the proportions of the parotid to other saliva gland secretions are altered, as often occurs when the saliva flow is less, the visco-elasticity of the saliva changes. In this situation, the saliva becomes more viscous and stretchable as the parotid proportion decreases. Oral dryness is a factor that needs to be considered in dealing with oral malodor. A high percentage of individuals have an uncomfortable mouth feel and often believe that they also have bad breath when actually they may not. Since the number of patients in this category may be significant, oral dryness as part of management of bad breath patients should be measured as described above.