Dental caries is a bacteria-associated progressive process of the hard tissues of the coronal and root surfaces of teeth. The net demineralization may begin soon after tooth eruption in caries susceptible children without being recognized by dental professionals. This process may progress further resulting in a caries lesion that is the sign and/or the symptom of the carious process. Caries is in other words a continuum which may by assessed falsely when only a certain time point is considered. Figure 1 shows different stages of the carious process.
Caries diagnosis implies more than just detecting lesions. Consequently, caries diagnosis -as an intellectual process - is the determination of the presence and extent of a caries lesion. Furthermore the judgement of its activity is an integral part of diagnosis.
Since diagnosis is a mental resting place on the way to treatment decision, it is intimately linked with the treatment plan to be followed. Thus diagnosis must include an assessment of activity because active lesions require active management (non-operative and operative treatment) whereas arrested lesions do not. The problem, however, is the assessment of the activity. The detection process may miss lesions (false negatives) or may overlook lesions that are present (false positives). The assessment of activity may be similarly wrong. For treatment decisions made in the clinic, the diagnosis should also express the individual patient's caries activity, which may be defined as the sum of new caries lesions and the enlargement of existing lesions during a given time (Wyne, 1993). It is a compound diagnosis comprising the immediate past caries experience, lesion progression and the clinical appearance of the lesions. The most important parameters for estimation of caries activity are the clinical appearance of a lesion and patient factors such as salivary flow, sugar intake and oral hygiene (Lagerlöf & Oliveby, 1996). Thus, caries activity can be evaluated by the assessment of factors associated with the pathogenesis of the disease and on the basis of data obtained from clinical examination. There are some clinical signs to get some idea of lesion's activity. An active initial lesion is dull and has a rough surface, it shows bleeding on probing in a patient with otherwise healthy periodontal conditions, it may be covered with plaque and on vestibular surfaces it is more adjacent to the gingival margin. An inactive lesion is shiny and has a smooth surface, and it is less adjacent to the gingival margin (Figure 2).
Fig. 2. Inactive carious lesion on the buccal surface. Note the shiny appearance and the position at some distance from the gingival margin.
Clinical-visual diagnosis may be amenable to longitudinal monitoring even though the assessment is qualitative. It would be easier to have a device that would not only detect demineralization but quantify it as well. Then monitoring progression or arrestment would be simple; use the device again and see in what direction the numbers change. The concept is hugely appealing so no wonder researchers have made such efforts to develop, test and perfect such devices. All these methods for caries detection are based on the interpretation of one or more physical signals. These are causally related to one or more features of a caries lesion. First, the signals must be received using a receptor device and classified. The classification of a signal is part of the diagnostic decision-making process. However, none of the methods is capable of processing all these signals to a status that could be called diagnosis. "The art of identifying a disease from its signs and symptoms" is a process that cannot be replaced by a machine or a device.
Caries measurement should be seen in the context of the objectives of modern clinical caries management and the continuum of disease states, ranging from sub-surface carious changes through to more advanced lesions (Figure 3). Measurement concepts can be applied to at least three levels: the tooth surface, the individual, or the group/population. According to Pitts (2004) modern clinical caries management can be seen as comprised by seven discrete but linked steps: (1) Caries detection represents a yes/no decision as to whether caries is present; (2) lesion measurement assesses defined stages of the caries process, taking into account the histopathological morphology and appearance of different sizes and types of lesion and the diagnostic threshold(s) being used; (3) lesion monitoring by repeated measures at a series of examinations is used when lesions are less advanced than the stage judged to require operative intervention of preventive care aiming either to arrest or to reverse the lesion to be assessed; (4) caries activity measures would be very valuable, but are relatively poorly developed and tested at present; (5) diagnosis, prognosis, and clinical decision-making are the important human processes in which all the information obtained from steps 1 to 4 is synthesized; (6) interventions/treatments, both preventive and operative, are now routinely used for caries management; and (7) outcome of caries control/management assesses caries management by examining evidence on the long-term outcomes.
Early diagnosis of the caries lesion is important because the carious process can be modified by preventive treatment so that the lesion does not progress. If the caries disease can be diagnosed at an initial stage (e.g. white spot lesion) the balance can be tipped in favour of arrestment of the process by modifying diet, improving plaque control, and appropriate use of fluoride. Using non-invasive quantitative diagnostic methods it should be possible to detect lesions at an initial stage and subsequently monitor lesion changes over time during which preventive measures could be introduced.
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