Caries Management - Science and Clinical Practice. Группа авторов
is lying next to the enamel (EN), which in this case has been removed artificially.
The pellicle plays an important role in protecting the dental hard tissue against mechanical and chemical damage: mechanically, so it is not worn away, and chemically because the pellicle serves as a permselective diffusion barrier,27 limiting what can pass through it, including plaque acids.
Fig. 1.13 Example of a patient who suffers from hyposalivation (unstimulated flow rate of 0.05mL/min) and xerostomia due to the use of antidepressants. The oral mucosa is dry and caries (arrows) is seen located primarily along the gingival margin.
Hyposalivation
Hyposalivation is a diagnosis made when the unstimulated salivary flow rate is less than 0.1mL/min and/or when the stimulated flow rate is less than 0.7mL/min.28
The following conditions can influence the flow rate and lead to hyposalivation:
• Medications—for example, antidepressants, diuretics, antihistamines, antihypertensives, antiemetics, narcotics
• Radiation
• Autoimmune diseases, AIDS, diabetes mellitus
• Menopause
• Eating disorders
• Salivary gland stones
Xerostomia is the subjective feeling (symptom) of a sensation of oral dryness, which often impairs oral function and even the overall quality of life. A salivary flow rate below 0.16mL/min increases the risk of developing caries29 (Fig. 1.13), which is related to the reasons mentioned above (low clearance rate, less supersaturation with respect to important electrolytes).
NOTE
Saliva is the liquid of the oral cavity and reduces dissolution of the dental hard tissue by its clearance ability, by means of its content of electrolytes, and its content of antimicrobials. Hyposalivation therefore increases the risk of caries development.
Changes in Teeth and Saliva with Aging
Most tissues in the human body have a physiological turnover of their components. The rate of turnover varies from tissue to tissue; in the pulp tissue the turnover is considered to be high, while it is limited for the dentin and cementum. Tooth enamel is a tissue with no biological turnover after it is formed. Alteration of enamel during a lifetime is thus physico-chemically related. Wear will cause loss of incisal protuberances, perikymata, and imbrication lines resulting in a flattening of the teeth with age (cf. Fig. 1.14a,b). At the crystal level, old enamel has a higher content of fluoride,30 the reason for which will be covered in Chapters 2 and 12.
Fig. 1.14a,b Dentition of a young (a) and old (b) person. Wear is a natural aging process that only turns pathologic if it is excessive for the respective age and results in clinical symptoms.
At least two age-dependent changes take place in the dentin; namely physiological dentin formation and gradual obturation of the dental tubules. The former is referred to as secondary dentin formation, to differentiate it from primary dentin formation which occurs until the tooth is fully formed, while the latter is referred to as dentin, or tubular sclerosis. The changes in the dentin during a lifetime have some clinical and cosmetic implications31; thus the diminishing size of the pulp chamber due to the secondary dentin formation may prevent pulp reaction and pulp exposure, but may also complicate pulp treatment. Tubular sclerosis results in a reduction in the sensitivity and permeability of dentin, although the latter may prevent ingress of toxic agents deeper into the dentin. The sum effect of changes in the dentin (condensation) influences the color of the teeth, thus owing to the translucence of the enamel, the color of older teeth is more yellow than younger teeth (Fig. 1.14b).
The most striking age-related change in the cementum is that its width nearly triples with age. To the best knowledge of the authors this has no clinical implication.
The pulp changes with age—in general from a cell-rich and fiber-poor tissue to a cell-poor and fiber-rich tissue.31 These changes are important from a clinical point of view, as the reactivity of an old pulp is different from the young one. This must be taken into consideration when choosing between different treatment options.
As described above, more than 99% of saliva is water, thus less than 1% is electrolytes and organic components. What happens to these components with age? Most data32,33 indicate that there are changes in the structure of the salivary glands due to age, but it seems that these changes are not sufficient to significantly influence the three components (water, electrolytes, and organics) in such a way that the tendency for developing caries increases. Instead of relating the increasing prevalence and incidence of caries seen in elderly people to age-related disorders of the salivary glands, we should rather consider age as a possible contributory factor to increasing patient vulnerability.33
Dental professionals should be able to differentiate between signs of natural aging/wear and signs of pathological processes. However, it should be kept in mind that the transition between “natural aging” and “disease” is mostly fluid, and the definition of what is “disease” is often controversial.
Dental Plaque or Dental Biofilm?
Definition. Dental plaque is a general term for the complex microbial community found on the tooth surface embedded in a matrix of polymers of bacterial and salivary origin.34 The term “dental plaque” has been used by the dental profession since G.V. Black (see Preface) defined it at the end of the 19th century. Professionals use it clinically for describing visible accumulations of microorganisms on teeth. More recently the term “dental biofilm” has been used to describe dental plaque. Biofilms are defined as “3-D accumulations of interacting microorganisms attached to a surface, embedded in a matrix of extracellular polymers.”35 Biofilms are also found on other, water-covered surfaces, for example, the waterlines in dental units and in aquariums. Throughout this book the authors will use both terms for visible accumulations of microorganisms on the teeth.
NOTE
In the context of caries, dental plaque or dental biofilm is the same—meaning visible accumulation of microorganisms mixed with intercellular substance on the teeth.
Classifying Oral Microorganisms
The Dutchman Antonie van Leeuwenhoek was the first to discover small organisms in dental plaque by means of simple microscopy. Actually what he saw was microorganisms of differing morphology—some small and round, some quite long, some lying still, and some moving. Since then, microorganisms in the oral cavity have been examined using simple and more complex light microscopes; sometimes the microorganisms are colored, other times not so (e.g. gram+ or gram−)(Table 1.2). The microorganisms