Lecture one- OIntroduction to operative dentistry

Definitions:
Dental caries is an infectious microbiological disease of the teeth that results in localized dissolution and destruction of the calcified tissues.
 Dental plaque:
 A gelatinous mass of bacteria adhering to the tooth surface, Plaque formation is a natural. The plaque bacteria metabolize refined carbohydrates for energy and produce organic acids as a by-product. These acids may cause a carious lesion by dissolution of the tooth s crystalline structure. Carious lesions progress as a series of exacerbations and remissions as the pH at the tooth surface varies with the changes in plaque metabolism. The availability of simple carbohydrates, such as sucrose, greatly stimulates plaque metabolism. Exacerbations of caries activity are characterized by periods of high bacterial metabolic activity and low pH in the plaque near the tooth surface. During intervening episodes when few carbohydrates are available, there is little bacterial metabolic activity, and the pH rises near the surface of the tooth. Remineralization of the damaged tooth structure occurs as the local pH rises above 5.5. Saliva contains high concentrations of calcium and phosphate ions in solution that serve as a supply of raw material for the remineralization process. The evidence for the role of bacteria in the genesis of caries in animal and human models has been studied, leading to the following conclusions:
1. Teeth free from bacterial infection, either in germ-free animals or unerupted teeth in humans, do not develop caries.
2. Antibiotics are effective in reducing caries in animals and humans.
3. Oral bacteria can demineralize enamel in vitro and produce lesions similar to naturally occurring caries.
4. Specific bacteria can be isolated and identified from plaque over various carious lesions. About 200 to 300 species of bacteria, yeast, and even protozoa appear to be indigenous to the human oral cavity but it has become clear that a relatively small group of bacteria is primarily responsible for the two major oral diseases, caries and periodontal disease. S. mutans serotypes have been demonstrated to have significant potential to cause caries, but because of their significant genetic and biochemical differences, they should not be simply referred to as the single species S. mutans (MS). MS and lactobacilli can produce great amounts of acids (acidogenic), are tolerant of acidic environments (aciduric), are vigorously stimulated by sucrose, and appear to be the primary organisms associated with caries in man. Organisms that cause caries are termed cariogenic. The degree to which a tooth is likely to become carious is described as its cariogenicity potential. MS are present as a pandemic infection in humans; that is, MS are found in everyone regardless of race, ethnic background, or geographic origin. Normally MS exist in the mouth as an insignificantly small component of the oral flora. In patients with multiple active carious lesions, MS have become a dominant member of the plaque flora. MS are most strongly associated with the onset of caries while lactobacilli are associated with active progression of cavitated lesions. Pathogenic properties of cariogenic bacteria There are a number of organisms, normally present in plaque, which can cause caries. These cariogenic bacteria can:
• transport sugars and convert them to acid (acidogenic).
• produce extracellular and intracellular polysaccharides which contribute to the plaque matrix; intracellular polysaccharides can be used for energy production and converted to acid when sugars are not available
• live at low pH (aciduric).

Theories of caries process:
There are a number of possibilities, each of which has consequences:
1• The specific plaque hypothesis proposed that only a few organisms out of the diverse collection in the plaque flora were actively involved in the disease. Preventive measures targeting specific bacteria (e.g. immunization) would be a logical consequence of this hypothesis.
2• The non-specific plaque hypothesis considered the carious process to be caused by the overall activity of the total plaque microflora. A consequence of this approach is that all plaque should be disturbed by mechanical plaque control (tooth brushing).
3• The ecological plaque hypothesis proposes that the organisms associated with disease may be present at sound sites. Demineralization will result from a shift in the balance of these resident microfloras driven by a change in the local environment. Frequent sugar intake (or decreased sugar clearance if salivary secretion is low) encourages the growth of acidogenic and aciduric species, thus predisposing a site to caries. The consequence of this hypothesis is that both mechanical cleaning and some restriction of sugar intake are important in controlling caries progression.

Classification of dental caries:
Carious lesions can be classified in different ways; this section introduces and defines this terminology.
1. Lesions can be classified according to their anatomical site. Thus lesions may be found in pits and fissures or on smooth surfaces.
2. Lesions may start on enamel (enamel caries) or on exposed root cementum and dentine (root caries).
3. Primary caries denotes lesions on unrestored surfaces. Lesions developing adjacent to fillings are referred to as either recurrent or secondary caries, Residual caries is demineralized tissue left in place before a filling is placed.
4. Carious lesions may also be classified according to their activity. A progressive lesion is described as an active carious lesion whereas a lesion that may have formed earlier and then stopped is referred to as an arrested or inactive carious lesion. This concept of activity is very important as it impinges directly on management because active lesions require active management. However, the distinction between active and arrested may not be straightforward.
5. Rampant caries is the name given to multiple active carious lesions occurring in the same patient, frequently involving surfaces of teeth that are usually caries-free. It may be seen in the permanent dentition of teenagers and is usually due to poor oral hygiene and taking frequent cariogenic snacks and sweet drinks between meals.
6. Early childhood caries is a term used to describe dental caries presenting in the primary dentition of young children.
7. Bottle caries or nursing caries are names used to describe a particular form of rampant caries in the primary dentition of infants and young children. The problem is found in an infant or toddler who falls asleep sucking a bottle (called a nursing bottle) which has been filled with sweetened fluids (including milk). Alternatively, nursing caries may be found in infants using a pacifier dipped in sweetener or in children who have a prolonged demand breast-feeding habit.

Pits and fissures:
Pit-and-fissure caries has the highest prevalence of all dental caries, the pits and fissures provide excellent mechanical shelter for organisms and harbor a community dominated by S. sanguis and other streptococci. The relative proportion of mutant streptococci (MS) most probably determines the cariogenic potential of the pit and fissure community. The appearance of MS in pits and fissures is usually followed by caries, 6 to 24 months later. Sealing the pits and fissures just after tooth eruption may be the single most important event in providing their resistance to caries. The initial lesions develop on the lateral walls of the fissure. Demineralization follows the direction of the enamel rods, spreading laterally as it approaches the DEJ. Soon after the initial enamel lesion occurs, a reaction can be seen in the dentin and pulp. Forceful probing of the lesion at this stage can result in damage to the weakened porous enamel and accelerate the progression of the lesion. Clinical detection at this stage should be based on observation of discoloration and opacification of the enamel adjacent to the fissure. These changes can be observed by careful cleaning and drying of the fissure. Remineralization could happen in the enamel because of trace amounts of fluoride in the saliva may make progression of pit-and-fissure lesions more difficult to detect. Finally extensive cavitation of the dentin and undermining of the covering enamel will darken the occlusal surface. Progression of caries in pits and fissures.

Smooth enamel surfaces:
The proximal enamel surfaces immediately gingival of the contact area are the second most susceptible areas to caries; these areas are protected physically and are relatively free from the effects of mastication, tongue movement, and salivary flow. The types and numbers of organisms making up the proximal surface plaque community are variable. Important ecologic determinants for the plaque community on the proximal surfaces are the topography of the tooth surface, the size and shape of the gingival papillae, and the oral hygiene of the patient. A rough surface (caused by caries, a poor quality restoration [new or old], or a structural defect) restricts adequate plaque removal. This results in retention of a more advanced plaque stage, favoring the occurrence of caries or periodontal disease at the site. In very young patients, the gingival papilla completely fills the interproximal space under a proximal contact and is termed a col. Apical migration of the papillae creates more habitats in exposed environments for tooth surface-colonizing bacteria. Increasing the exposed surface area has a stimulating effect on the growth of MS. Initial demineralization (indicated by the shadow in the enamel) on the proximal surfaces is not detectable clinically or radiographically. All proximal surfaces are demineralized to some degree, but most are remineralized and become immune to further attack. The presence of small amounts of fluoride in the saliva virtually ensures that remineralization and immunity to further attack will occur.When proximal caries first becomes detectable radiographically; the enamel surface is likely to still be intact. An intact surface is essential for successful remineralization and arrest of the lesion. Demineralization of the dentin (indicated by the shading in the dentin) occurs before cavitation of the surface of the enamel. Treatment designed to promote remineralization can be effective up to this stage. Cavitation of the enamel surface is a critical event in the caries process in proximal surfaces. Cavitation is an irreversible process and requires restorative treatment/correction of the damaged tooth surface. Cavitation can only be diagnosed by clinical observation. The use of a sharp explorer to detect cavitation is problematic because excessive force in application of the explorer tip during inspection of the proximal surfaces can damage weakened enamel and accelerate the caries process by creating cavitation. Fiber-optic illumination and dye absorption are promising new evaluation procedures, but neither is specific for cavitation. Advanced cavitated lesions require urgent restorative intervention to prevent pulpal disease, limit tooth structure loss, and remove the focus of infection.