How is Caries Diagnosed?

In medicine, a diagnosis is defined as “the art or act of identifying a disease from its signs and symptoms.”3 In this classic form of diagnosis, the challenge is to ascribe a pattern of certain signs (objective) and symptoms (subjective) that the patient manifests to an underlying disease and exclude other potential diseases in a differential diagnosis.4 For caries, this form of diagnosis is still found in many countries without a highly developed health care system, and is often used for dental emergency care. The patient appears with complaints (signs and symptoms), and the suspected cause (such as caries, pulpitis) is identified and delimited from all other causes (such as acute periodontitis) in a differential diagnosis. If caries is identified as the cause of the symptoms, it is frequently in an advanced stage and requires emergency treatment.

In many countries with a highly developed health care system, the diagnosis of caries uses a different approach that does not precisely fit the above definition.5,6 Caries is diagnosed primarily in regular dental health care visits, and the goal is the early detection of the disease. The patient generally does not voice any complaints. In this context, diagnosis takes on the character of a screening. That is, the dentist looks initially for the specific patterns or signs of a known disease (caries in this case), and the number of differential diagnoses for these patterns of signs is very limited.6 The challenge in this form of diagnosis is detection, including early stages (using appropriate methods), the correct assessment of the lesion, and the subsequent choice of an appropriate therapy. Although this form of diagnosis is very different from classic medical diagnosis,6 it is not restricted to dentistry and is becoming increasingly relevant in other disciplines of general medicine in which secondary, preventive strategies are pursued in the early diagnosis and therapy of diseases (such as colon cancer or coronary heart disease). Screening examinations enable early detection and consequently non-, micro-, or minimally invasive therapies.

One risk associated with screening examinations is false positive findings that can lead to overtreatment (see below).7 The intervals between dental check-ups primarily depend on the patient′s individual caries risk (see Chapter 7 and 24). Beyond the screening for caries, other oral diseases such as periodontitis and diseases of the mucosa are screened in these check-ups, and the individual′s risk of these diseases is also considered.

The Truth About Caries

From the aforementioned, we could conclude that it is recommendable to detect the signs of caries as early as possible, so that the disease can be identified and treated promptly. Such an approach is based on an essentialistic perspective. That is, it is assumed that a (hidden) process or disease called “caries” exists, which converts the causes of caries into the typical signs and symptoms of the disease ( Fig. 9.1 ).8 Consequently, the aim of diagnostics is to reveal the underlying hidden disease by highly precise methods to find out the “truth”, whether caries is there or not. But where does caries actually start? The most characteristic sign of caries is a mineral loss of dental hard tissues. However, the physiological fluctuations of pH in the oral cavity constantly cause mineral losses and subsequent mineral gains. On the one hand, beginning mineral losses (incipient lesions), which might only be detectable with special diagnostic tools, often have no pathological value and may remineralize without intervention. On the other hand, these lesions might also represent early stages of later cavities. According to the essentialistic concept, which assumes the existence of a disease independent of its signs and symptoms, one would say that caries is the underlying cause of these lesions.8 Thus, many people will be classified as “caries diseased.” This might be unjustified, since not every individual will develop cavities from early lesions, possibly causing symptoms and functional problems. From the above said it becomes clear that it is not possible to define a commonly accepted start/beginning of caries.

The nominalistic approach, therefore, assumes that there is no disease called “caries” which is independent of the signs and symptoms; rather, we have assigned the name “caries” to the pathological process as well as to its signs and symptoms ( Fig. 9.1 ). The logical result is that only the signs and symptoms and not the hidden disease are problematic and hence relevant to the patient. This also means that there is no “truth” about caries: whether a tooth or somebody has caries or not depends on our definition.

The nominalistic approach has consequences for caries diagnostics. Because here, in contrast to the essentialistic concept, no disease is searched for behind the symptoms—it does not make sense to search for early abstract signs of the disease with more and more precise diagnostic tests. In the nominalistic approach, the only the diagnostic information that is relevant is that which yields therapies which will result in a health benefit for the patient.1,8 Strictly speaking, all other diagnoses are then superfluous. This yields a problem, since the quality of diagnostic methods used in scientific examinations is generally measured against their ability in determining signs and symptoms compared with a “gold standard.” Often microscopic or laboratory methods are employed in such investigations as gold standards which can detect abstract signs of the disease with high accuracy. The relevance of these signs detected by the gold standards in the prognosis of a disease or the success of the related therapy is generally not investigated, since then such investigations are very time-consuming and expensive. For example, essentialistic thinking resulted in the common practice that in scientific studies diagnostic tools were tested for their ability to detect “dentin caries,” that is, the histological effect on dentin, which could be easily proven with microscopic techniques in vitro. Consequently, in the clinic the discovery of discolored dentin during cavity preparation was interpreted as a confirmation of the diagnosis “dentin caries,” meaning “this tooth requires a restoration.” Today, it is assumed that the histological effect on dentin per se is only of subordinate importance for the prognosis, and consequently in the diagnosis of caries. Rather, cavitation in the surface of the lesion appears to be relevant to the prognosis, and hence diagnosis, in the majority of cases.

Cross table for a diagnostic testing of healthy patients (healthy) versus unhealthy patients (unhealthy)a

		Disease
		Yes	No
Test	Positive	True positive	False positive	Positive predictive value:
	Negative	False negative	True negative	Negative predictive value:
		Sensitivity:	Specificity:
aIn an ideal case, all unhealthy are tested positive (true positive), and all healthy are tested negative (true negative). In reality, the test also gives negative results for healthy (false negative) and positive results for healthy (false positive). The sensitivity expresses the proportion of unhealthy who were correctly tested as unhealthy. The specificity indicates the proportion of the healthy who were correctly identified as being healthy. The positive predictive value expresses the proportion of those who were tested positive who are actually unhealthy. The negative predictive value expresses the proportion of those who were tested negative who are actually healthy. These values can be expressed as a percentage by multiplying the fraction with 100%.

Diagnostic Errors and Their Consequences

As described in the above paragraphs, each diagnostic test is subject to errors. That is, a positive test does not always mean that caries is present, and a negative test does not always guarantee the absence of caries. Frequently, both false positive and false negative test results are produced ( Table 9.1 ). As a result, the patient is either overtreated (in the case of false positive findings) or undertreated (in the case of false negative findings).

To better illustrate the problems of diagnostic errors, let us consider an example from the field of jurisprudence: Legal judgments, like medical tests, are also subject to error. A judgment (or “test” in our case) always seeks to condemn only the guilty (true positive) and exonerate the innocent (true negative). However, every judge or jury will make mistakes from time to time and incorrectly exonerate the guilty (false negative) and incorrectly condemn the innocent (false positive).

The sensitivity and specificity of different diagnostic methods has been described in the previous chapters. The better the test, the lower its error rate will be (high level of sensitivity and high level of specificity). Frequently, however, increasing the sensitivity will reduce the specificity. A strict judge (high level of sensitivity) will exonerate fewer of the guilty, but he or she will probably unjustly condemn more of the innocent (low specificity). In contrast, a judge who primarily tries not to condemn the innocent (high level of specificity) will probably tend to exonerate more of the guilty (low level of sensitivity). Similarly, the search for early stages of caries (such as discolored fissures) with the aim of correctly identifying more caries (increased sensitivity) will automatically increase the number of false positive findings and hence reduce the level of specificity.

Various diagnostic procedures and categorization methods were presented in the previous chapters. Even though dental diagnoses are still based on clinical examinations, additional diagnostic methods can be used to help detect and assess caries, particularly in tooth surfaces that are impossible or difficult to inspect visually. By using additional diagnostic methods, a greater number of caries lesions can frequently be identified to reduce the number of false negative findings (increase of sensitivity). However, in addition to increasing the number of true positive findings (and hence the sensitivity), the number of false positive findings is also increased by merely adding up the positive findings from different methods.6

To illustrate this problem, let us again use an analogous example from the legal profession: The fallibility of court judgments is a familiar problem. If every suspect who was exonerated by a court were to therefore undergo a second trial with a different judge and witnesses (additional diagnostic measure), the number of correctly condemned criminals (true positive findings) might be increased, and fewer perpetrators would mistakenly be let free. However, the number of the unjustly condemned would necessarily increase (false positive findings), since more of these errors would also occur. For this reason, not every positive finding should be considered a definite sign of caries, and the positive findings from several methods should not be simply added up. Instead, the fallibility of each diagnostic method should be considered, and contradictory results should be carefully evaluated, eventually using additional methods.8

For similar reasons, it is not recommendable to use every method for screening. As explained above, dental examinations frequently take on the character of a screening. The sensitivity and specificity of a test always depend on the prevalence of the disease. In a screening, the prevalence of the disease is, however, frequently low (many healthy teeth were examined to find a few diseased teeth). When the prevalence is low, the number of false positive findings increases, and the predictive value of the test decreases.

Once more, we will take an example from the legal profession to provide an illustration: If every citizen were to undergo a trial for any crime without any justifiable suspicion, it is highly probable that more criminals would be justifiably imprisoned. However, the number of innocent prisoners condemned due to a miscarriage of justice would be substantially higher. For similar reasons, it does not make sense to investigate all the occlusal surfaces of a patient using a moderately specificity diagnostic method (such as laser fluorescence). This method would yield an unnecessary number of false positive readings. Instead, such methods should be restricted to tooth surfaces where based on previous clinical or radiological examinations potential caries is assumed.6

The Diagnostic Process

The diagnostic process in dental check-ups involves several steps. First, the signs and symptoms characteristic of caries need to be identified (detection). This is followed by a precise description of the (severity) stage and activity status of the lesion (assessment).9,10 Several methods can be used to detect and describe caries, which will produce both confirmatory as well as contradictory information. The findings are then combined to form a diagnosis which is used to select a therapy ( Fig. 9.2 ).2,11 The therapeutic decision involves two elements: 1) whether or not the disease needs to be treated; 2) which therapy is appropriate.5

During the dental examination, the individual steps of the diagnostic process are frequently performed unconsciously. Unfortunately, diagnostic steps are often combined with therapeutic planning where the dentist only determines which tooth surface needs to be filled with which material.4,12,13 The reason for this is probably a historical one and linked to the reimbursement system, which in many countries only gives money for operative treatment, not for prevention. Since in earlier times caries was treated almost exclusively with restorations—owing to the few therapeutic alternatives and high prevalence and activity of caries—it was not necessary to identify early stages of caries. Diagnosis primarily consisted of the detection of cavitated lesions (a cavity did or did not exist), and the presence of caries automatically led to restorative therapy.14

Today, caries is progressing relatively slowly in many countries and population groups, and there are numerous therapeutic options (see below). To select the right therapy for the specific stage of caries, a more precise description of the disease is required. In addition to describing the stage of caries, identifying the activity of caries is now considered just as important. Since the goal of many therapies is to arrest the progress of caries, active stages that require treatment need to be distinguished from inactive stages that do not require (any more) therapy. In therapeutic approaches that seek to arrest caries, observing lesions over a longer period is frequently the only way to monitor the success of therapy. If the dental findings are restricted to simply documenting the presence or absence of caries, a great deal of information is lost, and the appropriate therapy for the specific stage or cause cannot be selected.

Stay updated, free dental videos. Join our Telegram channel

Join