Conclusions
Introduction
The most important internal modifying factors related to dental caries are salivary hypofunction, some chronic diseases, impaired host factors, and unfavorable macroanatomy and microanatomy and eruption stage of the teeth that favor plaque retention. Of utmost importance is impaired salivary function, particularly stimulated salivary secretion rate.
Salivary factors
Salivary secretion rate, the buffering effect, and possibly the in vivo concentrations of some salivary constituents, such as fluoride, hypothiocyanite, and agglutinins (possibly including IgA), seem to be the most important determinants of caries susceptibility and/or activity.
About 0.5 to 1.0 L of saliva is produced per day. Most (about 80%) is secreted by stimulation during meals and only a minimal amount is produced during sleep; changes in the SSR reflect physiologic demand. The normal ranges for unstimulated and stimulated whole saliva are 0.25 to 0.35 and 1.00 to 3.00 mL/min, respectively. A rate of less than 0.1 mL/min for unstimulated saliva and < 0.7mL/min for stimulated saliva is regarded as hyposalivation and is associated with significantly increased caries risk. Epidemiologic studies have shown about 20% to 25% of the population
older than 50 years of age to have stimulated SSR values of less than 0.7 mL/min and a higher caries prevalence than people with normal SSR.
Oral symptoms associated with salivary gland hypofunction include dry mouth (xerostomia), which is the most common symptom among elderly people with reduced unstimulated SSR. Other typical oral symptoms are difficulty in swallowing and eating dry foods and burning or tingling sensations, especially on the tongue.
Extreme hyposalivation and xerostomia (in systemic disease such as Sjogren’s syndrome) may be associated with extraoral symptoms, such as dryness of the eyes, the nose, and the vagina.
Among principal causes of salivary gland hypofunction and xerostomia, the most common is the long-term use of medicine or drugs, in particular psychotherapeutic agents, antihistamines, antihypertensive and diuretic agents, and some analgesics. The most severe hyposalivation and xerostomia is associated with therapeutic irradiation to the head and neck area and some systemic diseases, particularly Sjogren’s syndrome.
The principle properties of saliva that protect the teeth against caries are the clearance and dilution of oral microorganisms, dietary sugars, and so on; the neutralizing and buffering of the acids in plaque; the supply of ions for remineralization; and endogenic as well as exogenic antiplaque and antimicrobial factors. The most important of these functions is the clearance of oral microorganisms and food components (particularly sugar) from the mouth to the gut; effective clearance is dependent on an abundant flow of stimulated saliva. The clearance and dilution effects of saliva on sugar reduce acid formation in plaque.
Provided that the plaque is not impenetrable, saliva also significantly reduces the risk
of demineralization of the tooth surface by its neutralizing and buffering effect on
plaque acid. In individuals who clean all tooth surfaces once or twice a day, no such
thick plaque should accumulate. The buffering effect is strongly correlated to the
stimulated SSR, because the most important buffer is the bicarbonate system, mostly
originating from stimulated saliva of the parotid gland.
The physicochemical integrity of dental enamel in the oral environment is entirely
dependent on the composition and chemical behavior of the surrounding fluids (saliva
and plaque fluids). The main factors governing the stability of enamel apatite are pH
and the free active concentrations of calcium, phosphate, and fluoride in solution, all
of which can be derived from saliva. Under normal conditions, in the absence of
thick, undisturbed plaque and/or very high frequency of acidic dietary products, teeth
do not dissolve in saliva, because saliva is supersaturated with calcium, phosphate,
and hydroxyl ions, which constitute the mineral salts of the tooth. In individuals with
a regular supply of fluoride, eg, daily use of fluoride toothpaste, both the saliva and
the plaque fluid will also contain abundant fluoride ions. In the dynamic equilibrium
of the carious process, the supersaturation of saliva provides a barrier for
demineralization and a driving force for remineralization.
The saliva contains many different organic macromolecules and some other small
organic proteins that together protect the oral cavity from infection as well as wear,
dryness, and erosion. Among them are the antimicrobial lactoferrin, peroxidases, and
agglutinins as well as secretory IgA. In isolation, the effect of any of the above
components is weak, and future research should be directed toward combinations or
clusters of salivary components or variables typical of caries-active and cariesinactive
individuals and populations. Instead of individual salivary variables, it is
likely that some functional measures of saliva, such as bacterial aggregation rate,
promotion of bacterial adherence to saliva-coated hydroxyapatite, bacterial growth
and enzyme inhibition, and cell killing are more closely related to carious activity.
Each of these properties may be mediated by multiple proteins and each varies among
human subjects.
Saliva is seldom in direct contact with the tooth surface but is separated from it by the
acquired pellicle, an acellular layer of adsorbed salivary proteins and other
macromolecules on the enamel surface. This thin layer forms the base for subsequent
adhesion of microorganisms, which under certain conditions may develop into dental
plaque. Although thin, the pellicle is important in protecting the enamel against
abrasion and attrition and serves as a diffusion barrier.
The protective properties of saliva that increase on stimulation include salivary
clearance, buffering power, and degree of saturation with respect to tooth mineral:
The maximum effect occurs when saliva is stimulated after the consumption of
fermentable carbohydrates, reducing the fall in plaque pH that normally leads to
demineralization and increasing the potential for remineralization. Production of
plaque acid is neutralized and experimental lesions in enamel are remineralized when
saliva is stimulated after a carbohydrate intake. The pH-raising effects are more easily
explained by the buffering action of the stimulated saliva than by clearance of
carbohydrates. Remineralization is dependent on the presence of fluoride in the saliva.
Because the protective effect of saliva can be mobilized by appropriate salivary
stimulation, a combination of frequent topical application of fluoride and salivary
stimulation is of great importance in patients with hyposalivation and xerostomia.
Therapeutic stimulation of secretion, whether systemic or local, has the great
advantage of providing the benefits of natural saliva. Although pilocarpine
hydrochloride appears to be the most effective systemic sialagogue presently
available, its usefulness in the management of salivary hypofunction is limited.
Frequent and adequate intake of water is also important in therapeutic stimulation.
Physiologically, saliva is stimulated by fiber-rich, well-flavored, aromatic food. The
most promising local saliva-stimulating agents for caries prevention are the recently
introduced fluoride chewing gums, to be chewed for 20 minutes after every meal. A
chewing gum containing chlorhexidine is also now available. Combining fluoride and
chlorhexidine chewing gums would not only improve salivary stimulation but also
prolong fluoride clearance time and provide chemical plaque control, directly after the
acid attack.
Patients without sufficient residual salivary function to benefit from attempts to
stimulate natural secretion, are offered symptomatic treatment designed to relieve oral
dryness. For such patients, artificial saliva that contains fluoride should be
recommended as a supplement to frequent water intake.
