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CLINICAL ASPECTS OF SALIVARY BIOLOGY FOR
THE DENTAL CLINICIAN
LAURENCE J. WALSH stimulated salivary flow rate to the prevention of dental caries Saliva performs a multiplicity of roles within the oral cavity, and dental erosion can be also explained by improved clearance and like many things in life, its importance is usually not of substrate due to more rapid movement of the salivary film, appreciated until it is absent. Impairment of salivary parameters and, in the case of dental caries, greater activity of salivary is commonly not recognized by clinicians (Walsh, 2000).
Patients may present with a range of signs and symptoms Reductions in the quantity of salivary secretions or changes in which may be due to an underlying deficit in saliva production the properties of saliva are responsible for a host of related oral at rest. Reductions in saliva production during eating are much and dental problems which impact directly upon quality of life.
more apparent in terms of symptoms, and this generally brings it more to the patient's attention. In contrast, deficits in the difficulties in eating and speaking production of saliva at rest can easily pass unnoticed. In elderly alterations in taste (dysgeusia) patients and medically compromised patients, where the use of increased plaque formation multiple medications is common, salivary dysfunction is increased risk of dental caries, dental erosion, and frequently seen. periodontal diseases The functions of saliva include: mucosal abrasions and mucosal irritation Lubricating the oral tissues (for swallowing and speech), Assisting the special sense of taste, by acting as a solvent for ions, and through proteins such as gustin, impaired retention of full dentures. maintaining the health of the oral mucosa, through growth These oral problems may in turn influence medical status, in factors which promote wound healing, and cystatins, which that patients lose interest in eating and may suffer from inhibit destructive enzymes such as cysteine proteases, malnutrition as a consequence.
assisting in digestion, through amylase and lipase, dilution and clearing of material from the oral cavity, Control of salivary secretion
buffering acids from dental plaque and from consumed Time of day has a substantial influence on the resting flow foods and drinks, and preventing erosion caused by rate of saliva. The resting flow rate decreases during sleep and episodes of prolonged exposure to weak acids (e.g. wines increases during the waking hours. The maximal resting salivary and black cola softdrinks) or short-term exposure to strong flow rate occurs during the mid-afternoon. Understanding this acids (e.g. reflux and vomiting).
pattern is essential when assessing the resting flow rate in the serving as a reservoir for ions (calcium, phosphorus, and clinical setting.
fluoride) for remineralization With a typical resting flow rate of 0.03 mL/minute, the total controlling the oral microflora, through immunological amount of saliva secreted during 8 hours of sleep will be only (IgA), enzymatic, peptide and chemical mediators (Edgar et 15 mL, whilst during the two hours of stimulated flow during al. 1994; Walsh 2000, Brostek et al. 2006). eating and 14 additional waking hours of resting flow Salivary stimulation elicited reflexively by taste and contribute a further 700 to 1000 mL. mastication leads to an increase in the pH and buffering Autonomic parasympathetic and sympathetic nerves regulate capacity (due primarily to elevated levels of bicarbonate), as salivary gland secretory activity. Taste, tactile stimuli from the well as supersaturation of saliva with calcium and phosphate.
tongue and oral mucosa, and proprioceptive stimuli from These factors influence the balance between enamel masticatory muscles and the periodontal ligament excite the demineralization and remineralization. The importance of inferior and superior salivary nuclei within the brain. These nuclei are also influenced by the cerebral cortex. These Laurence J. Walsh, BDSc, PhD, DDSc, GCEd, FFOP(RCPA) neurological influences underpin the effect of psychological School of Dentistry, The University of Queensland status on resting salivary flow rates.
Stimulation of parasympathetic nerves causes the release of Correspondence:Professor LJ Walsh water and ions, but not proteins, whereas sympathetic School of Dentistry, The University of Queensland stimulation causes the release of proteins packaged within 200 Turbot Street, Brisbane QLD 4000, Australia acinar cells. These mechanisms work in partnership in Fax. +61-7-33658118, Email. [email protected] controlling salivary flow.
Because increased salivary flow causes the fluid environment Direct mechanical stimulation in and around the mouth is a of the oral cavity to become alkaline, there is a direct powerful stimulus of salivation. For this reason, it is essential association between a more alkaline environment caused by that the resting flow rate of saliva is assessed at the start of a increased salivary flow and mineralization of foci within consultation, before any dental procedures have been supragingival plaque, leading to the formation of dental calculus. The increased calculus formation reflects not only the A range of hormones can influence salivary flow (and thereby higher pH, but also the occurrence of highly ionised phosphate its composition) by acting directly on acinar or ductal elements 4 ] in the saliva and plaque resulting from breakdown within the salivary glands. Antidiuretic hormone, which of organic phosphates by salivary phosphatase enzymes. An increases water reabsorption in the distal tubule in the kidney, example of this is seen in individuals with cystic fibrosis, who has the same action on salivary gland ducts. These water-saving because of altered exocrine gland function have increased mechanisms underpin the dramatic effects of body hydration levels of Ca2+ and PO 3- in their submandibular saliva. Such on resting salivary flow. Negative fluid balance and systemic persons often show a marked tendency to form supragingival dehydration decrease resting salivary flow. As a consequence, a reduced volume and increased viscosity of saliva in the anterior floor of mouth contribute to a sensation of thirst. However, Salivary enzymes and mucins
thirst itself is an imperfect indicator of body fluid balance.
Saliva is such a complex biological fluid that it is practically Female sex hormones can also increase resting salivary flow.
impossible to replicate it from individual components. Not This explains why resting salivary flow is often increased during surprisingly, the majority of its components are hydrophilic pregnancy and decreased during menopause. Similarly, the (water-loving), however some hydrophobic components are male sex hormone testosterone is also known to increase present. The most notable of these is the enzyme lipase, which resting salivary flow. is secreted the von Ebner's glands of the posterior tongue.
Being hydrophobic, lipase can enter globules of fat, in which it Components of saliva
breaks down fatty acids.
Saliva as a fluid is a composite of the secretions of major and Saliva has a limited role to play in assisting digestion. The pre- minor salivary glands. Saliva also contains material derived from digestive function of saliva is mediated by a number of the gingival sulcus, a point which has diagnostic relevance in enzymes, including amylase, lipase, and a range of proteases terms of salivary markers of periodontal destruction. The and nucleases. Amylase can breaks down starch and glycogen composition of saliva varies from site to site within the mouth into smaller components such as limit dextrins and maltose. By of the one individual, and changes according to the time of day breaking down complex carbohydrates which may adhere to and proximity to meals. Its properties are affected by the level the teeth, amylase may serve a limited protective role.
of hydration and general health of the individual.
The mucins of saliva are glycoproteins with many short Saliva can be considered a filtrate of the serum in as much as oligosaccharide residues on each molecule. They bind water by it is derived from the blood. It follows that the process of saliva hydrophilic interactions, and this bound water is essential for production is linked to overall body fluid balance and that maintaining hydration of the oral mucosa. Salivary mucins exist blood flow through salivary gland tissues (from branches of the in both high and low molecular weight forms. Low molecular maxillary and other arteries) has a major effect on the weight sulpho-mucins assist in clearing bacteria from the oral production of saliva. Water makes up approximately 99% of cavity by binding to and aggregating microorganisms. The the volume of saliva, and serves as the solvent for the other levels of low molecular weight mucins (such as MG2) in resting components that make up saliva.
saliva decrease with age. The total flow rate for saliva (both stimulated and The interplay between water and mucins has a dramatic unstimulated) ranges between 500 to 1500 mL per day in an effect on the viscosity of saliva, particularly for the secretions of adult, and the average volume of resting saliva present in the the submandibular salivary gland. Reduced water results in a oral cavity is 1 mL. relative increase in the concentration of mucins, making the The resting saliva is derived from the submandibular gland saliva more viscous in consistency and sticky in nature. (60%), sublingual glands (5%), parotid glands (20%), and Mucins are essential for the lubricating functions of saliva.
other minor glands (15%). Parotid saliva (also termed serous When salivary flow rates are low, wearing of mandibular saliva) is high in bicarbonate ions and amylase, while dentures becomes a major problem because of trauma to the submandibular gland secretion (mucinous saliva) is high in denture-bearing mucosa. With a full upper denture, commonly mucins and calcium. In fact, the concentration of calcium in lack of retention (due to loss of cohesion) and chronic fungal submandibular saliva (3.7 mmol/L) is considerably higher than infections are commonplace. that in plasma (2.5 mmol/L) or in pooled whole saliva (1.35 Salivary mucins serve other functions in addition to lubricating the oral cavity, and preventing dehydration of the oral mucosa. Salivary mucins protect the mucosal surface and increase salivary pH and buffer capacity, and facilitate limit the extent of abrasion of the oral mucosal epithelial cells remineralization, but will also exert ecological effects on the caused by normal masticatory function. An even coating of oral flora. Specifically, higher salivary pH will suppress tendency mucins also gives a smoother surface for the flow of air during for aciduric (acid tolerate) microorganisms to grow, particularly cariogenic mutans streptococci and Candida albicans.
Mastication of foods and chewing gum is a powerful Salivary antibacterial systems
stimulus of the secretion of sodium bicarbonate into the Saliva contains a broad range of antibacterial agents.
parotid saliva. Strong acids are powerful gustatory stimuli of Immunoglobulin A (IgA) is a major component of saliva salivary secretion, as can be seen clinically when residues of proteins, and is able to aggregate bacteria and prevent phosphoric acid or acidulated fluoride products contact the adhesion. IgG and other immunoglobulins derived from the tongue. Salt, sweet and bitter are less effective stimulants of gingival crevice is also present in saliva, however little salivary secretion than acids. While a reflex of increased salivary complement fixation is possible in saliva as levels of key flow in response to acids has an obvious protective function in complement components are too low. The contribution of normal individuals, the stimulatory effect of acids has little if gingival crevicular fluid to resting salivary flow is very small, in any therapeutic value in patient care. In fact, frequent use of the order of 10-100 µL/hr.
citric acid-based drops or sweets to stimulate salivary flow is The enzyme amylase can inhibit the growth of some species contra-indicated in patients with salivary gland dysfunction of bacteria. Lysozyme breaks down the peptidoglycan in the because of the limited buffer capacity of their saliva. cell wall of some Gram positive bacteria, including Phosphate also contributes to the buffering capabilities of Streptococcus mutans. Lactoperoxidase catalyzes the oxidation saliva, particularly in the resting saliva situation. A range of of salivary thiocyanate by hydrogen peroxide to the toxic proteins in the saliva play a minor role in buffering. In addition molecule hypothiocyanite, which inactivates bacterial enzymes.
to these proteins, peptides such as sialin assist by promoting Histatins are histidine-rich proteins which inhibit the growth the production of amines (which exert an alkalinizing effect) of Candida albicans and Streptococcus mutans. Lactoferrin from enzymatic breakdown of salivary proteins and by oral binds ferric ions and thereby inhibits bacteria from gaining the bacteria. Similarly, urea in the saliva can be broken down to essential nutrient of iron. It can be degraded by some bacterial proteases. The related molecule apolactoferrin also exerts antimicrobial effects on a range of microorganisms, including Salivary components involved in the process of
Saliva contains a range of inorganic ions including calcium, Salivary buffer systems
phosphates, fluoride, magnesium, sodium, potassium, and In the healthy state, the pH of resting saliva is maintained in a narrow range between 6.7 and 7.4. The bicarbonate (HCO3- Several components of saliva help maintain supersaturation ) buffer system is the major buffer system present in saliva. As of saliva with calcium and phosphate ions. Statherin inhibits in the peripheral blood, the combination of sodium precipitation and crystal growth of calcium phosphate. It is a bicarbonate, carbonic acid, and gaseous carbon dioxide is an phospho-protein with a strong affinity for calcium and for effective means of removing protons (hydrogen ions) from the enamel and other apatite surfaces. Many of the key system. When considering the dynamics of this buffer system, biochemical properties of human salivary statherin are it should be remembered that saliva has a higher level of possessed by phosphopeptides derived from casein (CPP).
dissolved carbon dioxide than normal room air (5% vs. less Statherin and CPP share partial sequence homology with than 1 %), and is present in saliva both as bicarbonate (H2O + phospho-proteins from mineralised tissues such as dentine and CO2 ? H2CO3 ? HCO3- + H+ ) as well as dissolved CO2 gas. bone. Proline-rich proteins work in a similar fashion to The concentration of bicarbonate ion in resting saliva is statherin, and bind to the surface of calcium phosphate crystals approximately 1 mmol/L, and this increases to over 50 mmol/L to prevent their growth. Together with citrate, these proteins on stimulation. As the concentration of bicarbonate ion bind a considerable portion of the total calcium in the saliva, increases, so does the pH and buffer capacity of the saliva. This and help to maintain the correct calcium-phosphate ionic ratio.
is a key point in interpreting salivary diagnostic tests. Because Citrate as an ingredient in many carbonated drinks and of diurnal variations in resting flow rate, there are sports/energy drinks poses a major risk for dental erosion by corresponding variations in levels of bicarbonate and thus in binding calcium and depressing the concentration of free the pH and buffer capacity. The resting pH will be lowest during calcium ions in saliva.
sleep and immediately upon waking, and then increases during Proline-rich proteins are a key component of pellicle, and the waking hours. bind strongly by their amino terminus to enamel. The trailing As bicarbonate levels in the saliva increase, this will not only carboxyl terminus is the site of adhesion for some bacteria in the early stages of plaque formation, and is also the binding achieve the greatest remineralization. Topical applications of site for tannins from the diet. very high concentration fluoride products encourage the formation of an extremely dense surface layer on such lesions, effectively "locking in" the surface components. Once formed, Saliva controls the equilibrium of mineral gain and loss in an the low permeability of this layer hinders further natural repair. erosive or cariogenic oral environment. The importance of With the notable exception of phosphopeptides, all currently saliva in this role is demonstrated graphically in patients with used topical fluoride agents deposit soluble fluoride as calcium salivary dysfunction, and in desalivated animals. fluoride (CaF2) on the surface of tooth structure or within Protective properties of saliva that increase on stimulation on lesions. This calcium fluoride serves as a source of fluoride for salivary flow include salivary clearance, buffering power, and the subsequent formation of fluorapatite when the pH falls.
degree of saturation with respect to tooth mineral. These Other fluoride sources include non-specifically-adsorbed benefits are maximized when saliva is stimulated after the fluoride, fluorapatite, and fluorohydroxyapatite. It is important consumption of fermentable carbohydrates, by reducing the to remember that fluorapatite is formed from CaF2 when the fall in plaque pH leading to demineralization and by increasing pH drops, but is not formed during topical application. The the potential for remineralization. As shown by the studies of reservoir effect gained from calcium fluoride formation is Edgar and colleagues at Liverpool, when gum is chewed to similar to that which occurs in phosphopeptide products, stimulate saliva after a carbohydrate intake, plaque acid because their delivery system is also pH dependent. Using production is neutralized, and incipient lesions in enamel are fluoride-containing phosphopeptides topically bolsters the capacity of the intra-oral fluoride reservoir. The capacity of this The site distribution of lesions of dental caries and dental reservoir to supply ions for a prolonged period is crucial to the erosion demonstrates the level of protection offered by the success of topical treatments in preventing and arresting dental salivary film. Sites of predilection for dental caries and dental caries and dental erosion.
erosion are those where exposure to saliva is limited, such as fissures and proximal sites followed by cervical surfaces for Clearance of substrates and acids
The term "Oral clearance" refers to the elapsed time Saliva affords both static protective effects, which act between the introduction of a substance to the oral cavity and continuously, and dynamic effects, which act during the time- the moment when its presence there can no longer be course of a challenge. Salivary buffering and sugar clearance detected. There are a number of ways to express oral clearance are important dynamic effects of saliva which prevent including half life (50% of the original concentration) and demineralization. Comparing these two effects, buffering of detection threshold (the time taken to reach a concentration at acids is the most important as it is linked directly with enhanced which the substance is no longer detected).
remineralization. The oral clearance function of saliva can be demonstrated Fluoride in saliva (from dentifrices and dental materials, and using clearance of a substrate such as sucrose or glucose. A derived from ingested foods and drinks) may promote simple and informative clinical procedure for assessing oral remineralization and inhibit demineralization (Edgar & Higham, clearance by saliva is to assess glucose clearance using the 1995). Fluoride from the saliva accumulates in dental plaque.
detection threshold/minimal concentration method. The Low to moderate levels of fluoride (up to 40 ppm) inhibit technique involves the use of an enzymatic reagent, glycolytic fermentation of sugars by dental plaque bacteria.
impregnated in a paper strip (glucose urine analysis tape), This has been demonstrated by in vivo studies of enamel blocks which reacts with any glucose present. The glucose challenge when fluoride was added to sucrose at levels up to 5 ppm.
can be provided by a glucose solution or a solid glucose sweet Moreover, fluoride levels in resting saliva correlate well with the (such as a jelly bean). The test tape contains glucose oxidase, occurrence of caries arrest and reversal or regression (the peroxidase and a chromogenic substance. In the presence of conversion of disappearance of white spot lesions into sound glucose, the tape changes colour as a result of oxidation of enamel) (Woltgens et al. 1995). glucose and production of hydrogen peroxide.
Fluoride-releasing dental materials such as glass ionomer Oral clearance of fermentable substrates and acids is affected cements can contribute to fluoride levels in dental plaque and greatly by the stimulated salivary flow rate. This influence is (potentially) in the saliva per se, however it appears that such site-dependent, such that the most rapid clearance occurs in materials reduce or prevent secondary caries primarily through sites immediately adjacent to major salivary gland ducts.
the effects of fluoride on the surrounding tooth structure.
Assessing glucose clearance at several test sites such as the Remineralization can occur in the body of natural enamel anterior floor of mouth (lingual to 31) and maxillary vestibule caries lesions, especially when the surface layer is thin or lost.
(labial of tooth 11) over a range of measurement times will A key point is that fluoride should be delivered to enamel reveal that clearance lingual to 31 occurs within 30 seconds in carious white spot lesions in moderate concentrations to most individuals. In contrast, the labial maxillary site near the midline typically requires 20 minutes to clear glucose cariogenic through sustained release of sucrose. The inclusion of polyols such as xylitol into chewing gums Because the protective effects of saliva (including clearance) improves the oral health benefits which can be gained by are increased greatly by stimulation, strategies for salivary regular gum chewing. These polyols are unable to be stimulation should be considered as part of an overall fermented, and may directly inhibit plaque formation by preventive regimen for an at-risk patient. These may include biochemical effects on dental plaque microorganisms.
eating patterns which lead to saliva stimulation, as well as the use of sugar-free chewing gum. In terms of eating patterns, the Phosphopeptides and saliva
work of Geddes at Glasgow has shown that if a "meal" Human saliva contains lows levels of phospho-proteins, and includes an item which contains carbohydrate such as sucrose, the major role of stabilising of ACP is performed by statherin.
glucose, or fructose that can be fermented rapidly by the Bovine (cow) milk is the source material used for preparation of acidogenic microorganisms in dental plaque, there will be rapid phosphopeptide products for dental use in humans, such as acid production and the plaque pH will fall. Moreover, if one Recaldent ™ and GC Tooth Mousse.
sugary item is followed by another, the demineralizing Phosphopeptide products may be of three types: potential may be enhanced. casein phosphopeptides alone (CPP), Other items eaten immediately before, during, or after the phosphopeptides with amorphous calcium phosphate consumption of the sugary item can influence the plaque pH.
(CPP-ACP), which contains 18% calcium ion and 30% If the non-sugary item stimulates salivary flow, it will have a pH- phosphate ion on a weight basis, raising effect. The remineralizing potential may be enhanced if, phosphopeptides with amorphous calcium fluoride for instance, calcium or fluoride is released from the food. This phosphate (CPP-ACFP). has relevance not only to foods but to food-derived dental The latter is designed to provide all the essential building products such as phosphopeptides. For example, when milk or blocks of remineralization (calcium, phosphate, fluoride, water) cheese products are consumed at the end of a meal, the localised at the tooth surface and within dental plaque.
proteins they contain can buffer pH changes induced by acidic Importantly, as plaque enzymes such as phosphatases and or acidogenic (fermentable) foodstuffs, and can also exert a peptidases slowly degrade CPP products, the net effect is a pH topical effect through phosphopeptides. Ending an evening rise because of ammonia release. Use of CPPs with fluoride, or meal with a low fat cheese platter, or using low fat cheese the inclusion of fluoride can impair phosphatase enzyme sticks as a between meal snack, are examples of how a dietary activity, maintaining the duration of action of the molecular pattern can be altered to increase the natural caries preventive actions of these foods. CPP products (particularly CPP-ACFP) build upon the scientific foundation of components of milk in caries Gum chewing and salivary function
prevention. There is a considerable literature regarding fluoride Chewing gum stimulates salivary flow, and thereby compounds administered with calcium-rich food for dental augments its protective properties (e.g. clearance, buffering, caries prevention. It is, nonetheless, important to distinguish pH, and supersaturation with minerals). Chewing sugar-free between fluoridated milk (where the bio-availability of the gum elevates plaque pH and thus favours mineralisation. This fluoride is low), and CPP-ACPF, where the bio-availability of the natural repair can be enhanced by including phosphopeptides fluoride is high.
in the gum, as has been shown by Reynolds and colleagues The anti-cariogenic actions of CPP products are mediated by who assessed demineralised slices of enamel mounted in intra- topical effects, including: oral appliances (Reynolds 1987; Reynolds 1998).
Modulation of levels of bio-available calcium and During gum chewing, the flow rate peaks during the first phosphate, by localising ACP in dental plaque to maintain minute. Beyond this point, a high flow rare can be maintained supersaturation of free calcium and phosphate ion activities by continual chewing. Surprisingly, the flow rate is not Buffering plaque pH changes increased dramatically by chewing faster, with a similar flow enhanced remineralisation and reduced rate of dissolution rate over a range of chewing frequencies between 35 and 130 of hydroxyapatite chewing actions per minute, as shown by Dong and co- impairment of the adherence and growth of Streptococcus workers. Because a regular gum chewing habit causes a mutans and Streptococcus sobrinus.
prolonged increase in the unstimulated salivary flow rate, CPP can bind up to 25 calcium ions, 15 phosphate ions and chewing sugar-free gum is an important preventive oral health 5 fluoride ions per molecule, and can stabilise calcium behaviour. It is important to stress that sugar (sucrose)- phosphate in solution. Otherwise, in conditions of neutral or containing gums must be avoided are less stimulatory to alkaline pH, clusters and nuclei of amorphous calcium salivary flow than sugar-free gums. Sugar-containing gums do phosphate (ACP) form which readily precipitate out of solution.
not promote mineralisation but rather can be directly Through their multiple phosphoseryl residues, CPP can sequester their own weight in calcium phosphate to form forensic identification of the blood type of their source. With colloidal complexes. By binding to forming clusters of ACP via the recent development of single cell DNA fingerprinting, phosphoseryl residues, CPP prevent these clusters growing to desquamated mucosal epithelial cells, neutrophils and other the critical size required for nucleation and precipitation leukocytes within the saliva provide the DNA which is an (Reynolds, 1998). Complexes between casein phosphoproteins invaluable key to identification. and amorphous calcium phosphate complexes (CPP-ACP) have been shown to exert anti-cariogenic effects in laboratory, Clinical testing of saliva parameters
animal, and human in situ caries models. These complexes While the composition of saliva is complex, its properties in localize ACP in dental plaque and substantially increase the relation to defending the oral hard tissues can be assessed at level of calcium phosphate, which in turn serves as a reservoir the chairside in a relatively simple manner using the GC Saliva for free calcium and phosphate ions. The net effect is that the Check Buffer kit (Walsh, 2001). At the same appointment, an plaque fluid (and saliva) is maintained in a state of assessment of dental plaque maturity and plaque fermentation supersaturation with respect to tooth enamel for both calcium can be made using the GC Saliva Check + pH test kit, providing and phosphate ions, which suppresses demineralization and a comprehensive approach to patient assessment (Walsh, enhances remineralization. This can be exploited clinically for prevention of dental caries and dental erosion.
A widely used systematic method for assessing salivary parameters follows a sequence to check the physical and Saliva as a diagnostic fluid
chemical properties of saliva which relate strongly to the risk of Because it can be collected easily and non-invasively, saliva is dental erosion and dental caries. The test sequence is divided an ideal fluid for the diagnosis of a range of conditions. The into two parts, the first of which assesses the resting range of analytes includes: parameters, and the second which assesses the stimulated Microorganisms, such as Streptococcus mutans Markers of periodontal destruction Viruses, such as hepatitis C Antibodies to viruses, such as HIV The first phase of the test is to assess the production of saliva Blood group substances at rest. While a number of sensitive technologies have been Therapeutic drugs developed which can measure the output of individual minor Alcohol and illicit drugs salivary glands, a visual screening method is rapid and effective, Steroid hormones, such as cortisol, oestrogen, and produces a result which is of immediate value to the progesterone, testosterone and aldosterone clinician. After gently blotting the inside surface of the lower Heavy metals such as mercury, bismuth, and lead.
lip, the surface of the everted lip can be examined for the The relatively low protein concentration of saliva ensures that presence of droplets of saliva. Approximately, each square drugs and hormones which normally are bound to carrier centimeter of the lower lip will contain the duct of one minor proteins in the plasma are present in the unbound (free) form.
salivary gland, and each of these produces one visible droplet Many lipid-soluble hormones can be found in saliva in amounts every minute when functioning at the normal resting salivary that are proportional to their concentrations in plasma. Saliva flow rate. Patients can be screened for the presence or analysis allows for regular monitoring of the systemic levels of absence of these droplets. Younger patients may have droplets these hormones.
evident on the lip after as little as twenty or thirty seconds.
In patients with uncontrolled diabetes mellitus, the level of Regardless of the patient's age, if droplets cannot be seen after glucose (which is normally very low) is elevated substantially as sixty seconds, the resting salivary flow is below the normal spill-over of glucose from the plasma occurs. These patients range, and this should be investigated, for example is the tend to suffer from salivary dysfunction with a reduction in patient's fluid balance negative because of low water intake, or both resting and stimulated salivary flow rates, and in some the excessive intake of agents which cause fluid loss, for patients bilateral parotid gland enlargement. The underlying example caffeine from tea and coffee or alcohol. mechanisms include negative fluid balance and auto-immune The second phase of the test is to examine the viscosity of lymphocytic sialodenitis. the saliva at rest. This also uses a simple visual method rather From the standpoint of forensic science, several components than complex testing apparatus. Where the resting saliva is of the saliva are important analytes. The ABO blood group dysfunctional, its appearance changes dramatically, and it substances (which are carbohydrate-protein complexes) are begins to appear bubbly, frothy and sticky. Normal resting saliva found in the saliva of 80% of the population, who are known has a clear watery appearance. These changes reflect as "secretors". Levels of blood group substances in the saliva organizations of the mucins and glycoproteins within the saliva increase with the rate of secretion. The presence of blood as the amount of water varies. By examining resting saliva in group substances has allowed saliva residues to used for the floor of the mouth, and in the vestibule, a simple subjective Fig.1. An overview of the saliva testing process. A, Assessing the resting flow rate using the droplet time. B, Collecting resting saliva. C, Testing the
pH of resting saliva. D, Components used for testing pH and buffer capacity, comprising pH test paper, a collection vessel for saliva, and buffer test
strips (packed in foil). E, Measuring the pH of the resting saliva. F, Collecting stimulated saliva into a graduated container. G and H, Applying
stimulated saliva to pH test paper using a pipette. I and J, Testing buffer capacity using test pads impregnated with acid.
assessment can be made as to whether this saliva is (a) clear excess saliva is drained away by placing the strip on its side and watery, (b) bubbly or (c) white and frothy. It will be noticed onto some absorbent paper or disposable tissue. The colour of that in the latter case, the saliva will also have a glutinous sticky the test pad after five minutes can then be compared with the reference chart, and scored as either green, blue, red or partial The third phase of the test is to assess the pH of the saliva at results between these colours. A score is then calculated with rest. This is done by asking the patient to expectorate the green providing the highest score, and red the lowest. Patients remaining saliva in their mouth into the cup provided in the test whose buffering abilities are normal show a very high score.
kit. A single piece of pH test paper is dipped into this, and once Where patients show depressed buffering capacity, a careful wet, is removed immediately and the colour compared to the review of the other results is necessary, since patients with reference chart. This assessment must be done while the paper inflamed or damaged salivary glands tend to show depressed is still moist so that the most accurate result can be achieved.
flow rate when stimulated, depressed pH when stimulated, and Saliva which has a neutral pH at rest will give a green reading also depressed buffering capacity when stimulated. One on the test. Values below neutral pH will show orange and situation where buffering capacity can be reduced, but other yellow, and the values which are near the critical pH of dental parameters are normal, is in the early stages of pregnancy.
hard tissues will be orange to red. Clinical applications of saliva testing
Stimulated saliva One can use the Saliva Check Buffer test kit in a range of Having now assessed the patient's saliva at rest, the clinician clinical situations. In patients who present with cervical dentinal can move on to examine the properties of the stimulated saliva.
hypersensitivity, one may see several areas where there is It is necessary to obtain a sufficiently large sample of stimulated cervical tooth loss from dental erosion. Such a patient may saliva by having the patient chew a small piece of paraffin wax.
have a resting salivary pH of 5.6 which is near the critical The saliva which is collected in the cup is then used for the threshold for demineralization, while the stimulated pH at 7.6 is normal, as is their buffer capacity. One would be prompted The first of these is the quantity of saliva produced in a time to look very carefully at the hydration levels of such a patient. period which allows calculation of the stimulated salivary flow In a patient who has accelerated tooth wear, the resting pH rate. Patients with normal flow rates will produce a sufficiently may be rather low, for instance near 5.4. If the stimulated pH large sample in two minutes to allow measurement. Where the was also low, for example 5.8, and the buffer capacity below patient's stimulated flow rate is suppressed, a five minute normal, this indicates a more complex problem which affects collection period should be used. It is important to leave the the gland tissues, such as organic salivary gland disease.
patient in privacy when collecting this sample. The volume can Where there is dramatic loss of tooth structure, this could then be assessed and the flow rate per minute determined.
occur by wear of softened tooth structure. The resting salivary Flow rates less than 0.7mL/minute indicate dysfunction in pH may be low, and near the critical threshold. If the stimulated stimulated saliva production. This can be due to severe pH was normal and the buffer capacity also normal, one would dehydration, or more frequently to damage to the glands, e.g.
concentrate on occupation, recreation and medication in the by infiltration of cells from the immune system. This can occur first instance. Closer examination of the maxillary incisors in a number of conditions, including chronic hepatitis C would provide a clue as to the presence of reflux disease.
infection, HIV infection and a range of autoimmune conditions In a patient with incipient root surface caries, the resting flow such as Sjogren's syndrome. rate may be low, and the resting pH may also be low (e.g. at The fifth test is to measure the pH of the stimulated saliva.
5.6), while the stimulated pH could be more near the normal This is done by dipping a small piece of pH test paper into the range (at 6.8). In such a patient, low buffer capacity would sample, and scoring the colour against the reference chart suggest major salivary gland disease, such as Sjogren's while the paper is still wet. In general, the pH of the stimulated syndrome, which is not uncommon in elderly female patients. saliva should be at least one full pH unit above that of the saliva Similarly patients with cervical lesions which encircle the at rest. This is so because of the increased concentration of teeth, a low flow rate, high viscosity, and low resting pH (such bicarbonate ion present in parotid saliva which is the dominant as 5.8) would not be unexpected. If there was also a low buffer component of the stimulated pools of saliva which has been test result, this would imply damage to the functional capacity of the salivary glands. A cause of this is lymphocytic sialodenitis The sixth and final component of the testing program is to associated with diabetes mellitus. assess the buffering capacity of the stimulated saliva. This is Even in younger patients, saliva testing can give important done using a series of buffer test pads. The buffer test strip is information to assist their clinical management. In patients in removed from its foil pack and a small disposable pipette used their 20's who show an increase in their caries rate, such as this to draw up saliva from the collection cup. One drop of saliva 25 year old woman, encircling lesions on the canines and is then dispensed on to each of the three test pads, and any premolar teeth signify an acidic salivary environment at rest.
Salivary profiling may show a low resting salivary pH just above efficient means for screening patients for salivary dysfunction.
the critical threshold, and lower than normal buffer capacity.
Subjective visual evidence of xerostomia, such as pooling and These problems may reflect the use of legal or illicit medicines, frothing of saliva in the sublingual regions ("beer froth" including anti-depressants or methadone. appearance), and the appearance of white mucinous strands of Saliva testing helps to point the clinician in particular saliva residues on the oral mucosa is informative in making the directions and away from others, and it provides a means to diagnosis. Because saliva becomes more viscous and mucinous assess changes over time as various factors in the patient's in nature as the resting flow reduces, a simple test of saliva lifestyle are altered.
viscosity is useful. Viscosity can be graded using the so-called "web" test. In this procedure, a tongue blade or dental mirror Recognition of salivary dysfunction
is used to lift pooled saliva from the floor of the mouth or Salivary dysfunction is a common problem, and is common buccal mucosa. As the instrument is withdrawn as web is undiagnosed orodental disorder. It is important to note that formed, which when stretched will eventually break. Normal symptoms of the patient are not a completely reliable indicator saliva can maintain a vertical salivary web for a small distance of salivary gland function. In other words, the absence of (2-5 cm), whereas the web distance for the viscous saliva of the symptoms does not necessarily indicate normal salivary gland xerostomic patient can be as much as 15 cm.
function, as some patients may not be aware of diminished output until the flow rate is less than half the normal rate.
A clinical protocol for systematic patient
Many major medical disorders are associated with xerostomia (dry mouth), and these are usually recognised by health 1. Listen to symptoms
professionals. However, other more common factors in the Oral dryness during the waking hours aetiology of xerostomia are often overlooked, particularly Oral dryness on waking medication usage. While several hundred medications are Lack of lubrication during eating, talking or swallowing recognised to induce xerostomia, this is not always listed as an Salivary web formation during swallowing adverse effect in prescribing guides. Self-administered and Altered taste perception over-the-counter medications such as expectorants and Impaired retention of full upper dentures decongestants) are particularly important in this context. Impaired lubrication of lower dentures Since multiple medication usage (poly-pharmacy) is common Mucosal irritation from foods and dental home care amongst medically compromised and elderly patients, it is prudent to examine routinely all such patients for salivary Other potentially related complaints such as halitosis dysfunction. Moreover, in the elderly, salivary dysfunction as a side effect of medications is more common because of delayed 2. Listen to the history
metabolism and clearance of drugs by the liver and kidney Duration and severity of symptoms Known exacerbating and relieving factors The ability to identify a particular aetiologic factor (e.g. a Medical conditions associated with salivary dysfunction medication, or inadequate fluid intake) may in turn suggest an Other medical conditions approach for treating the problem at its source.
Prescribed medications Care should be taken not to exclude a diagnosis of "Over the counter" medications xerostomia simply because the flow rate was within the normal Past medical treatments range at one time-point. Measurement of salivary resting flow Past dental treatment rate may be performed simply visual parameters, as outline Use of home care products below. Alternatively, the flow may be estimated by timed collection of unstimulated saliva into a calibrated receptacle. A 3. Listen to the patient's lifestyle
resting flow rate below 0.3 mL/min may be regarded as Patterns of fluid intake indicative of xerostomia. Care should be taken to identify Dietary patterns for fermentable carbohydrates factors which may influence a particular recording (e.g.
Preferred snacking patterns smoking, exercise, a recent meal or other oral activity). This is Intake of caffeine of prime importance with medications, since there will be Intake of alcohol periodic fluctuations in salivary resting flow in accordance with Intake of acidic foods and drinks the pharmacokinetics of the medication. Thus, xerostomia may Intake of nicotine be most marked in the period following absorption and Intake of illicit substances distribution of the drug, and resting flow rates may return to Patient's occupation normal levels prior to the next dose being taken. Patient's recreational habits Visual assessment of resting saliva is a simple and time- Major stressful events in the patient's life 4. Look for Signs
Menopausal hormone imbalance Soft tissue changes Thalassaemia major Dryness of the vermilion border of the lip Chronic protein-energy malnutrition Dryness of the oral mucosa Loss of filiform papillae of the tongue Side effect of recreational drugs Cratering and fissuring of the tongue Increased plaque formation on the tongue Alcohol (dehydration, liver cirrhosis) Related mucosal pathology such as oral candidal infections Absence of saliva in response to gland palpation Opiates (heroin, methadone, narcotics, etc) Hard tissue changes Increased caries rate (particularly cervical caries) Medications Increased rate of non-carious loss of tooth structure by Multiple teeth with cervical dentinal hypersensitivity from Anti-Parkinsonian agents Failure to form supragingival calculus from plaque in the l ower incisor region Anti-depressants (TCA, SSRI) Increased plaque accumulation on the teeth and appliances Identify Causal factors
Inadequate fluid intake Anti-neoplastic agents Strenuous physical activity Cardiac antiarrhythmics Outdoors occupation Dehydrating work environment Driving/travelling long distances Caffeine (black cola softdrinks, energy drinks, coffee, Narcotic analgesics Monoamine oxidase inhibitors Polyuria in uncontrolled diabetes mellitus Systemic bronchodilators Skeletal muscle relaxants Salivary gland pathology Head and neck or total body irradiation Lymphocytic sialodenitis in HIV, hepatitis C, and With regard to medications, several hundred medications are diabetes mellitus recognised to induce salivary dysfunction, and this important Primary Sjogren's syndrome side effect is not always listed as an adverse effect in Secondary Sjogren's syndrome associated with prescribing guides. Over-the-counter medications (e.g.
connective tissue diseases including expectorants and decongestants) are particularly important. rheumatoid arthritis, Since multiple medication usage (polypharmacy) is common amongst elderly and medically compromised patients, it is systemic lupus erythematosus, prudent to examine routinely all such patients for salivary dysfunction, even in the absence of overt caries or other dermatomyositis, and pathology. It is prudent to note the time when medications suspected of contributing to xerostomia are taken, as salivary Graft-vs-host disease in bone marrow transplant effects will typically be most marked in the period following absorption and distribution of the drug, while resting flow rates may return to near normal levels prior to the next dose being taken. Care should be taken not to exclude a diagnosis Psychological stress of xerostomia simply because the flow rate was within the Depressive illnesses normal range at one time point. This false negative diagnosis is Chronic renal failure most likely to occur when patients are seen at times of the day when the flow is highest (mid-afternoon) because of the Use minimal intervention approaches for caries circadian rhythm.
removal (e.g. ART) Use GIC (Fuji IX, Fuji VII) to restore lesions as part of 6. Measure Parameters
the overall caries control strategy Salivary resting flow Visually assess lower lip labial gland secretion Suppress cariogenic microorganisms Assess resting salivary volume in the oral cavity (pooling) Dietary modification Inspect salivary viscosity (frothy, bubbly, sticky) Reduce the frequency of cariogenic between-meal Measure resting salivary pH using pH paper or pH meter (N.B. It is important to bear in mind the influence of factors Reduce levels of acidic foods and drinks between which can affect the resting flow rate, such as position (sitting or supine), proximity to meals/eating, time of day (diurnal Use a xylitol-containing chewing gum variation, medication intake), anxiety level, smoking, and Apply chlorhexidine gel intermittently (e.g. weekly) recent physical activity) Improve oral hygiene Stimulated salivary flow Regular toothbrushing (twice daily) Estimate flow rate by volume collected over a defined Regular interdental cleaning (at least daily) Use a detergent (sodium lauryl sulphate)-free Measure stimulated salivary pH using pH paper or pH meter dentifrice if mucosal burning occurs Determine buffer capacity using challenge strips with weak Assess levels of pathogens by solid phase immuno-assay Review salivary parameters at recall appointments Monitor salivary levels of mutans streptococci 7. Manage Problems
Monitor caries increment Ensure adequate hydration Look for caries arrest and reversal Limit intake of caffeine, alcohol, and other diuretics Look for changes in the mineralizing potential of Ensure adequate water intake Use an oral hydrating gel Apply lip balm regularly Preventive home care programs for patients with
Sleep on the side to avoid mouth breathing at night Construct a denture with an internal reservoir Frequent use of bland rinses (saline or sodium bicarbonate) and rehydrating or mucosal protective products (such as Increase the pH and buffer capacity of saliva Laclede Oral Balance gel) can provide relief from symptoms of Gain extrinsic bicarbonate via mouthrinse or oral dryness. Many patients with profound xerostomia suffer from mucosal irritation, and are unable to tolerate the use of Increase intrinsic bicarbonate via chewing a sugar-free some commercial rinses, which may contain alcohol or flavouring agents. GC Dry Mouth gel stabilizes oral pH in the Rinse thoroughly after ingesting acidic foods and neutral range and relieves symptoms of oral dryness. Many other products used for oral dryness have an acidic pH, which presents an erosion risk in xerostomic patients.
Salivary stimulants, such as pilocarpine, may also be Use a phosphopeptide chewing gum (Recaldent) or employed, but these can exert problematic gastro-intestinal topical gel (Tooth Mousse Plus or Tooth Mousse) at side effects (Edgar & Higham, 1995). It is essential that sugar-containing or acidic (citrus) sweets as Use a fluoride dentifrice (1000 or 5000 ppm) for salivary stimulants be discouraged as these will accelerate dental caries in the hyposalivated state. Patients should be Tooth surface protection (exposed root surfaces) with encouraged to apply a lip lubricant at regular intervals.
Use of sugarless chewing gums (e.g. Recaldent) is of major Use a dentifrice as a self-applied topical agent for importance for promoting salivary function. The antibacterial, early cervical and proximal lesions buffering, and lubricant qualities of saliva improve with Use home fluoride gel (1.23% neutral NaF) in high increasing flow rates, such that stimulating the flow with gums improves the protection afforded to the oral cavity by the Apply fluoride varnish at recall appointments salivary secretions (Imfeld, 1999). Other ingredients in chewing gums, such as xylitol and The denture surfaces can be cleaned and then the denture phosphopeptides, provide additional preventive benefits and immersed for a short period in dilute sodium hypochlorite to assist in maintaining oral health.
reduce the fungal load. In addition, antifungal creams (such as Home use of a neutral sodium fluoride gel or high fluoride miconazole) or suspensions can be directly applied to the fitting dentifrice on a daily basis will maintain salivary fluoride surface of a denture, and the denture then put in the mouth to concentrations and inhibit mineral loss from dental hard give a sustained effect. Severe denture-related fungal infections tissues. Neutral fluoride gel may be applied at home on a require expert attention. toothbrush. In general, acidulated fluoride products are Regular dental review (at least three monthly) is important contraindicated for patients with salivary dysfunction, as they for ensuring that oral hygiene is maintained at an adequate may cause dental erosion, dentine hypersensitivity, or mucosal standard, and dental caries and other conditions are controlled.
Maintenance dental sessions should include oral hygiene Xylitol and casein phosphopeptides exert modest suppressive reinforcement, removal of plaque, and surface treatments with effects on mutans streptococci, however additional fluoride varnish or phosphopeptides. Adequate monitoring will antimicrobial targeting is worthwhile in patients with very high ensure that the oral health status is maintained, and the need caries activity. for extensive restorative work is minimised.
Chlorhexidine gluconate gel (0.2 %) is the agent of choice for chemical plaque control in patients with salivary dysfunction, since this agent possesses proven anti-plaque, Brostek AM, Bochenek AJ, Walsh LJ. Minimally invasive anti-gingivitis, and anti-caries activity. It causes profound dentistry: A review and update. Shanghai J Stomatol 2006; inhibition of cariogenic mutans streptococci. The gel formulation is preferred as this is alcohol-free. The alcohol Edgar WM, Higham SM. Role of saliva in caries models. Adv content of some chlorhexidine rinses is problematic because Dent Res 1995; 9(3): 235-8. mucosal burning. Chlorhexidine gel (0.2 %) does not cause Edgar WM, Higham SM, Manning RH. Saliva stimulation and mucosal burning, and can be applied easily with a toothbrush.
caries prevention. Adv Dent Res 1994; 8(2): 239-45.
Topical CPP-ACP preparations (GC Tooth Mousse and Tooth Imfeld, T. Chewing gum- facts and fiction: a review of gum- Mousse Plus) are available as topical thick pastes for clinical use chewing and oral health. Crit Rev Oral Biol Med 1999; in tray carriers or brushed directly onto the teeth. In addition to their use in preventing dental caries or dental erosion, these Reynolds EC. The prevention of sub-surface demineralisation preparations are well suited to the management of cervical of bovine enamel and change in plaque composition by casein in dentinal hypersensitivity, a condition which is often associated an intra-oral model. J Dent Res 1987; 66: 1120-7.
with reduced salivary flow or pH. Reynolds EC. Anticariogenic complexes of amorphous calcium The thick creamy consistency of CPP-ACP products is well phosphate stabilized by casein phosphopeptides: a review. Spec suited for self-application by patients. Importantly, CPP-ACP is Care Dentist 1998; 18(1): 8-16. completely safe if ingested, which is an important Walsh LJ. Preventive dentistry for the general dental consideration for products which will be used by patients in practitioner. Australian Dental Journal. 45(2): 76-82. 2000.
Walsh LJ. Saliva testing: good practice, good sense. Singapore, Antifungal therapy should be considered in xerostomic GC Asia dental Pte Ltd, 2001.
patients who have a history of recurring oral candidosis.
Walsh LJ. Dental plaque fermentation and its role in caries risk Chlorhexidine gel exerts mild anti-fungal effects and can be assessment. International Dentistry (Australasian Edition).
used together with alkalinizing mouthrinses (such as sodium bicarbonate) to suppress levels of candida species in the oral Woltgens JH, Etty EJ, Gruythuysen RJ, Geraets WG. Influence of fluoride in saliva during the early cariogenic changes in the If dedicated topical antifungal agents are used, care must be enamel of boys and girls. ASDC J Dent Child 1995; 62(3): 192-6 taken that the preparation is free of sucrose or other fermentable substrates. Suspensions or lozenges of nystatin or amphotericin are used commonly for treatment of candidoses. Prof LJ Walsh played a major role in the development of the Tissue surfaces beneath dentures and the denture surface GC Saliva-Check Buffer test kit. However he has no commercial itself typically are heavily contaminated with fungal organisms.
interest in this product.

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