body of the lesion and surface zone can be seen clearly. If the process of dental caries
continues, support for the surface layer will become so weak that it will crumble like
an eggshell, creating a cavity. Once a cavity is formed, the process of dental caries
continues in a more sheltered environment and the protein matrix of enamel and then
dentine is removed by proteolytic enzymes produced by plaque organisms.
The progression of caries is traditionally described as enamel caries progressing
through to the amelodentine junction at which the enamel breaks down and a cavity
forms. Although it is now understood that the process is not this simple and cavitation
can occur at an earlier stage⎯the enamel cavity and frequently at a much later stage
when the caries has progressed significantly into dentine. 218HFigure 6.6 shows the labial
surface of a maxillary canine with a variety of stages of carious lesion ranging from
white spot enamel caries to dentine cavity.
The ability of early carious lesions ('precavitation carious lesions') to remineralize is
now well understood; periods of demineralization are interspersed with periods of
remineralization, and the outcome⎯health or disease⎯is the result of a push in one
direction or the other on this dynamic equilibrium. The shorter the time during which
plaque-covered teeth are exposed to acid attack and the longer the time
remineralization can occur, the greater is the opportunity for a carious lesion to heal.
Satisfactory healing of the carious lesion can only occur if the surface layer is
unbroken, and this is why the 'precavitation'stage in the process of dental caries is so
relevant to preventive dentistry. Once the surface has been broken and a cavity has
formed, it is usually necessary to restore the tooth surface with a filling. The carious
process is driven by the plaque on the surface and therefore it is possible to arrest the
caries by effective removal of plaque even after cavitation has occurred. However, the
lost tissue cannot be replaced.
The first stage of dental caries to be visible is the 'white spot' precavitation lesion
stage. This can occur within a few weeks if conditions are favourable to its
development. In the general population, though, it commonly takes 2-4 years for
caries to progress through enamel into dentine at approximal sites.
The most important of the natural defences against dental caries is saliva. If salivary
flow is impaired, dental caries can progress very rapidly. Saliva has many functions,
which are listed in 219HTable 6.1. The presence of food in the mouth is a powerful
stimulus to salivation, with strong-tasting acid foods being the best stimulants. Saliva
not only physically removes dietary substrates and acids produced by plaque from the
mouth, but it has a most important role in buffering the pH in saliva and within
plaque. Fast-flowing saliva is alkaline⎯reaching pH values of 7.5-8.0⎯and is vitally
important in raising the pH of dental plaque previously lowered by exposure to sugar
and carbohydrates. Because teeth consist largely of calcium and phosphate, the
concentration of calcium and phosphate in saliva and plaque is thought to be
important in determining the progression or regression of caries. Also, it is well
known that fluoride aids the remineralization process. Although it may seem sensible
to try to maximize the availability of calcium, phosphate, and fluoride in the environs
of the tooth, in practice, fluoride is much the most important.
Key Points
Dental caries: