Diagnostics and Epidemiology: 8 Epidemiology of Caries and Noncarious Defects
The early chapters of this book (Chapters 1–3) dealt with the fundamental ecology of the oral cavity with particular reference to teeth. Factors were presented that could trigger an imbalanced equilibrium between teeth and biofilm, resulting in caries. The origin of noncarious defects of enamel and dentin was also considered. In the subsequent chapters, a caries model (Chapter 4) as well as clinical aspects of caries and noncarious defects were introduced (Chapters 5–7). From all of this it becomes clear that the caries process is also influenced by a series of more indirect factors that do not directly affect the surface of the tooth. For example, a parent′s lack of education can affect a child′s knowledge as well as his or her attitude and behavior towards toothbrushing, which in turn directly affects the rate of caries. If only for this reason, the knowledge and assessment of indirect (population-based) factors affecting the development of caries and other defects of the tooth′s hard substances are crucial for the dental professional. The evaluation of these indirect factors is part of epidemiology.
Beyond the observations and findings regarding the patient and his or her teeth as well as an awareness of indirect factors, a specific treatment decision also depends on the frequency and severity of caries that the dentist observes and will then expect again in the patient population. To prevent the injection of subjectivity when assessing the prevalence, incidence, and distribution of a disease, knowledge of the empirical data is essential to more accurately evaluate the disease load. The treatment decision for the individual (tooth surface) should be based on an awareness of the relevant data in the respective population. These data are provided by epidemiology.
The term “epidemiology” refers to a scientific method that describes the spread, distribution, and severity of a disease in the overall population or individual groups of the population, along with the factors that influence the disease. The descriptive field of epidemiology answers the questions of “how many” and “which” persons are affected, and “the degree of severity” of the disease. These purely descriptive epidemiological investigations are primarily observational.1 In addition, information can be gained about the etiology of the disease by using epidemiological methods to investigate the factors that may play a role for disease pathogenesis (analytical epidemiology). Analytical epidemiology also promotes an awareness of the cofactors and options for controlling diseases. Furthermore, the methods of epidemiology are used in scientific studies to determine the effects of specific measures for controlling or preventing diseases. One example of the latter is to investigate the influence of fluoridation on the caries incidence (experimental or interventional epidemiology).
In detail, this chapter covers the following topics:
The importance, fundamentals, and methods of epidemiology
The validity and limits of conventional indices for describing caries and noncarious defects
Current developments in the prevalence and occurence of caries
The prevalence of noncarious defects of the dental hard tissues.
Descriptive epidemiology: Provides statistics about disease conditions (spread, severity, and alterations).
Analytical epidemiology: Statistical analysis of factors related to disease, recovery, and prevention that provide information on the etiology of diseases and options for controlling them.
Experimental epidemiology: Analyzes the influence of factors being related to prevention or recovery from a disease under controlled conditions.
General Relevance of Epidemiology
From the statistics on the prevalence of diseases, specific conclusions can be drawn about medical treatments and/or the need for medical care. Oral epidemiology allows to evaluate preventive and therapeutic interventions and can be used as a basis for cost-benefit analyses. Epidemiology is an established, essential resource for planning and evaluating strategies in dental care, and for answering questions in medical research. Beyond its descriptive power, epidemiology provides the necessary information for political and health policy decisions that go far beyond a numerical understanding of disease conditions and can have significant medical and social consequences.2
Since epidemiology is playing an increasingly greater role in the fundamental research of health and health care, the planning, implementation, evaluation, and interpretation of epidemiological studies have to fullfil a series of requirements.1,2 In addition to the relevant quality assurance measures required in research (calibration of the investigator, e.g., by repeated examinations to identify reliability within and between rates), the principles of medical ethics and data protection3 must also be considered. Furthermore, the authors of a study are expected to interpret the results of their epidemiological research and to communicate their findings through scientific and public media.4
Epidemiology uses different types of study. In cross-sectional studies, the prevalence of a disease and its potential causative or at least associated factors can be determined.5 In cross-sectional studies, caution is required when offering interpretations that go beyond mere descriptions, since distorting influences (termed confounders) are frequently large because the factors are determined retrospectively.
Longitudinal studies require at least two examinations of the same study population, using the same investigative methodology. The collected data provide information on the incidence of diseases, and the conclusions regarding the etiological disease parameters are generally more accurate than those derived from cross-sectional studies. Furthermore, longitudinal studies are divided into retrospective and prospective cohort studies. In retrospective studies, current findings are collected and evaluated using historical information. In prospective studies, a study hypothesis is postulated and tested by comparing existing data with data collected in the future ( Fig. 8.1 ).
Important parameters used to characterize the investigated cohort population are gender, age, geographic location, and social status of the investigated individuals. Social strata are assigned using the variables “education,” “occupation,” or “income.” Sociological parameters also generally cover the opinions and behavior of the specific study population. In considering the sociological parameters, medical and dental information is weighed and sociological relationships are identified which can be used to help in describing or clarifying the phenomena of oral morbidity.2
Types of epidemiological study:
Cross-sectional study: Collection of disease data, possibly including the determination of potential associated factors at a single point in time. Offers fast results and is economical, but subject to the danger of misinterpretation. Example: Caries and plaque status on 5-, 12- and 15-year-olds in a certain period.
Retrospective cohort study: Longitudinal studies extending into the past. A survey of present data is evaluated with reference to influences from the past. Fast results and economical, but no proof of a causal relationship. Provides plausible hypotheses. Example: Caries status of children from various regions related to the level of fluoride in the drinking water back in time.
Prospective cohort study: Longitudinal study extending into the future. Data are collected in the future to test a hypothesis. Takes a long time, is expensive, and confirms causal relationships. Example: Caries status as well as urinary fluoride concentration of children is followed from ages 2 to 6 and their relation evaluated.
Descriptive Epidemiology of Caries and Noncarious Defects
Epidemiological Identification of Caries
Caries can be identified either clinically or radiologically (Chapters 5 and 6). Caries is identified much more sensitively by radiologic means.6 However, in addition to organizational reasons that may preclude the taking of x-ray images, in many countries x-rays for purely epidemiological purposes are not permitted. Consequently, most epidemiological data regarding caries are derived from clinical investigations under field conditions (under non-optimal conditions). Frequently, caries lesions are only identified under difficult conditions in accessible tooth surfaces (little light, no dry surfaces, no tooth cleaning before the examination). This limits the detection of caries lesions in epidemiological studies and must be taken into consideration when interpreting the results.
Frequently, the epidemiological description of caries is in terms of prevalence. Prevalence means the occurrence of a disease within a group at a specific point in time. The percentage of individuals suffering from the disease is given in relation to the entire investigated population. Occasionally, however, “prevalence” is misinterpreted as the investigation of individuals and subsequent averaging of the extent of caries and its consequences for the group. This type of calculation yields the DMF number that is correctly identified as the caries experience (see below).
Instead of the prevalence of caries expressed as a percentage of the individuals affected by caries, sometimes the percentage of individuals who do not have the disease is used (caries-free persons). Various aspects need to be taken into consideration when using this term. In the epidemiology of caries, “diseased” persons are to be understood both as those with untreated carious defects and those with treated caries. In addition, the underlying categorization of caries as a disease also needs to be considered. Frequently, only lesions involving dentin are defined as carious defects in epidemiological terms.7
This perspective negates the view of caries as a dynamic process at the tooth surface that proceeds from initial demineralization over long periods and results in macroscopically identifiable caries. Generally, only the advanced stages of the disease are considered. Restricting the epidemiological identification of caries to this late stage—which is also characterized as the identifiable tip of the “caries iceberg” 8—does not consider the long developmental process leading to this stage. Thus, the choice of threshold for when to record the tooth or surface as carious is an important issue in epidemiological studies. Frequently caries is recorded only when it is cavitated or at least clearly extended into dentin. This way, only the top of the caries iceberg is considered. However, if caries is recorded also in noncavitated stages (e.g., a white spot lesion), then the caries prevalence or experience will be higher ( Fig. 8.2 ).
Earlier, the frequency of individuals without caries in a population was also defined as the percentage of people with “naturally healthy dentition.” Today, this term is not used, since it suggests the complete absence of any oral disease. The term caries-free which was preferred for a long time is now also deprecated, since it can be misinterpreted as referring to an absence of untreated carious lesions, and this overlooks fillings which are in fact treated caries lesions.5
For both caries experience and caries prevalence, a definition of the threshold is required at which a tooth surface can be considered diseased, to allow the reported data to be properly interpreted. Individuals without caries experience do not reveal any untreated caries lesions at the specified caries level, and they also do not show any consequences of caries (fillings or extractions). A group of people in which all the members exhibit this finding at a specific time has a caries prevalence of 0%.
Indices for Coronal Caries
Data on the caries prevalence of a population, especially in age groups with a generally high caries experience, do not sufficiently describe the disease since the average extent of the disease in individuals is not identified. More precise survey instruments are required such as the DMF index.9
The DMF index, suggested in the late 1930s (Klein et al. 1938), includes carious changes and their therapies such as fillings or extractions:9
“D” stands for decayed teeth or tooth surfaces that have been “destroyed” by caries,
“M” stands for missing teeth that were removed due to carious decay, and
“F” stands for filled teeth or tooth surfaces due to caries.
The DMFT index (“T” = teeth) can be calculated from these data from the combined findings for a tooth. If either a D, M, or F component applies to a tooth, the tooth is included in the index. The DMFT value equals the sum of corresponding teeth for an individual; in cohort studies, the DMFT values of the individual members of the cohort are averaged. If wisdom teeth are not included, the DMFT can range from 0 to 28 ( Table 8.1 ).
If at least one tooth surface is carious or filled, the entire tooth is identified as a DMF tooth. The DMFT index provides a more precise description of dental health than just the prevalence. Nevertheless, equating (for example) a tooth which has one surface with a filling to an extracted tooth does not precisely reflect the level of the disease. Consequently, surveys at the tooth surface level taking into account decayed, filled, or missing components separately are customary for detailed investigations, especially in analytical or experimental oral epidemiology.
The sum of tooth surfaces affected by caries is the DMFS value (S = surfaces). Although the DMFS is the more reasonable survey instrument, the World Health Organization (WHO) prefers the DMFT index, since it is easier to standardize under a range of investigative conditions and is therefore easier to compare.7,10 Worldwide more investigations are performed with the DMFT, and this index is therefore generally used in comparisons.
By definition, the DMF index refers to caries and its consequences. It therefore should only include teeth or tooth surfaces that are filled or missing due to caries. This means that teeth missing due to tooth agenesis or other causes, or teeth that are provided with restorations for other reasons than caries, are not included in the index. If permanent teeth are missing, it is generally assumed that they were extracted due to caries unless stated otherwise by the investigated individual, or unless typical configurations (such as the absence of all first premolars) render this scenario implausible. Due to the uncertainty associated with this assumption regarding the actual reason for tooth loss, the DMF index can only approximate the caries incidence in adults and seniors.
Permanent teeth are counted in the DMF index. If the index is to reflect the caries of deciduous teeth, the index is in lower case as the dmf index. If not otherwise indicated, only permanent teeth are included in mixed dentition; deciduous teeth are not included even if they are carious. However, it may be appropriate to indicate the overall incidence of caries (dmft + DMFT or dmfs + DMFS) in certain investigations/age groups. For epidemiological surveys of caries during the transitional dentition phase, different indices are used such as the def index (e = extracted), or the index is restricted to d and f (df index) to differentiate between teeth that are missing from caries or physiological reasons, or to circumvent this differentiation.
For epidemiological purposes, caries in the crown is generally only identified visually and not by using a sharp probe. This procedure corresponds to the WHO recommendations for epidemiological field studies7 in which a standardized blunt periodontal probe is preferred over a dental probe. This takes into consideration the fact that the aggressive use of a sharp probe would not improve the detection and evaluation of occlusal caries, for example. As noted in Chapter 5, the improper use of a sharp-tipped probe to detect and evaluate caries can damage the surface enamel and thereby promote the progression of formerly noncavitated caries lesions.11,12 A thin probe of course has certain advantages over a thicker, blunt probe when applied without pressure to detect and evaluate changes to approximal caries. Since, however, the time to examine a large number of persons is frequently restricted in epidemiological studies, sharp probes are not used, in order to spare the investigated surface of the crowns from the aggressive use of the sharp instrument.
Restricting the epidemiological investigation of caries to lesions that involve the dentin (D3 lesions) has increasingly been considered inappropriate.4 Such defects represent an advanced stage of caries. Limiting the noted caries to such defects overlooks developing caries since initial lesions or those limited to the enamel are not included. When only D3MFT changes are considered, it remains unclear whether a reduction of caries includes a reduction of early stages of caries, or whether the disease has merely reverted to earlier stages of caries without cavitation. In addition, a problem with this procedure is that a greater percentage of the actual caries experience remains unrecorded as the prevalence of severe forms of caries decreases. For this reason, the occurrence of noncavitated caries lesions is also noted in current surveys (D1 level4) ( Fig. 8.3 ). In addition, the lesions can be divided into active and nonactive lesions.
In Health Services Research, it is meaningful to consider the individual components of the DMF index (D, M, or F components). This can yield important information on the Unmet Restorative Treatment (UNT) index. The UNT is the percentage of untreated carious teeth in relation to the overall caries4; in children, this is preferably in relation to the sum of untreated and filled teeth (DT * 100/[DT+FT]).
In children and adolescents, caries is not normally distributed4,5,14 ( Fig. 8.4 ). Consequently, the calculations of the DMF average and standard deviation are helpful for comparative purposes, but do not provide a sufficiently precise picture of the disease. In the case of skewed distributions, the distribution frequency of individual levels of findings is useful. Another proposed instrument for describing the epidemiological prevalence of caries in risk groups is the significant caries index (SiC), the DMFT value for the one-third of children with the highest caries incidence.15 It is not a separate survey instrument and is based on the DMF distribution.5
One result of the attempt to identify lesions as early as possible by epidemiological means is to use the ICDAS criteria (International Caries Detection and Assessment System, see Chapter 5) for epidemiology.16 Initial efforts have revealed that this is possible in principle.17 It remains to be seen whether this detection and assessment system for caries that was validated for identifying caries in occlusal surfaces18 will gain acceptance, despite the fact that it is more time-consuming,18 under epidemiological field conditions.