Introduction to the epidemiology of periodontal diseases

Gingivitis and periodontitis are the inflammatory diseases of periodontal tissues. Gingivitis is the inflammation of the gingival tissue and periodontitis is characterized by clinical attachment loss. For centuries, man has tried to understand the cause of these diseases, their prevention, and treatment. Epidemiology is the study of a health-related state in terms of its determinants and distribution. There is a famous remark from Lord Kelvin (1824-1907) (British mathematician and physicist), “Until you can count it, weigh it, or express it in a quantitative fashion, you have scarcely begun to think about the problem in a scientific fashion”. Our knowledge regarding the epidemiology of periodontal diseases has changed tremendously in the last 50-60 years. The methods of recording periodontal status have also improved in the last many years. In the following discussion, we shall discuss in detail the present status of periodontal diseases in different populations and various periodontal indices that are used to record gingival and periodontal status in epidemiological studies.

Definition of epidemiology

Epidemiology has been defined as the study of the distribution and determinants of health-related states or events in a population and the application of this study for the prevention and control of health problems 1. The word epidemiology (Epi- among, demos- people, logos- study) is derived from the term ‘epidemic’. Epidemiological studies are done to evaluate the health status of the population rather than the health status of an individual. Epidemiological data provides us the basis for planning the health care programs according to the needs of populations in different parts of the world. After the collection of epidemiological data, the amount of disease is quantified based on the data analysis.

Measures of disease frequency

Prevalence:

Prevalence is defined as the number of cases in a population at a given point in time. Prevalence depends on both, the number of people who have had the disease in the past and the duration of the disease. Prevalence may be point prevalence or period prevalence. Point prevalence is the number of persons in a defined population who have a specified outcome (e.g. disease) at a point in time (such as at the present point of time). On the other hand, period prevalence is the number of persons who had the disease at any time during the specified time interval (such as over the last 12 months).

Incidence:

Incidence describe the frequency of occurrence of new cases during a time period. Incidence is calculated as the number of new cases of a disease in a defined population within a specified time period divided by the number of cases who are at risk of having that disease at that designated time period.



Risk factors and risk indicators for periodontal diseases

Risk is defined as the probability that an event will occur in the future, or the probability that an individual develops a given disease or experiences a change in health status during a specified interval of time 2. There are various risk factors which have been found to be associated with the progression of periodontal diseases. These include oral hygiene status, smoking, stress, genetic markers, ethnicity, host response, systemic conditions, and socioeconomic status. The measures used to express health risk include absolute, relative and attributed risk.

Absolute risk:

An absolute risk is the probability that an individual will develop the disease over a specified period of time.

Relative risk:

Relative risk is basically the comparison of a health risk between two populations. The higher relative risk in a particular population suggests a higher probability of disease occurrence in that population as compared to the other populations. The relative risk is measured in terms of odds ratio. The odds ratio is the probability of occurrence of a disease to the probability of its non-occurrence. This ratio can be calculated in studies using backwards research design such as, case-control studies.

Attributed risk:

Like relative risk, attributed risk also measures comparison of a health risk between two populations. However, as compared to relative risk, it is assessed as the difference in the incidence rates of occurrence of the disease between the exposed and non-exposed individuals.

Epidemiological study designs

There are two basic approaches to assess the relationship between exposure and outcome: experimental and observational. More commonly used design is experimental, where laboratory-based research is done. In epidemiological studies, experimental design is rarely used and their role is usually limited to observing the occurrence of disease in people who are already segregated into groups. The primary difference between experimental and observation studies is that in experimental studies investigator plays an active role in exposing the population to the causative agent or removing it, whereas, in observational studies the investigator has only observational role, noting what happens in exposed and nonexposed groups during a particular duration of time. In observational studies, the investigator observes without any intervention other than to record, count and analyze the result. The observational studies are of various types including cohort study, case-control study, cross-sectional study, ecological study and hybrid design. The three commonly used study designs are as follows,

Cohort studies:

These are prospective studies. The starting point of a cohort study is the selection of the study population or cohort. The study population is then investigated to find out individuals who are exposed to the risk factor. The entire population is then…………. Content available in the book………………. Content available in the book…………….. Content available in the book………

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Advantages and disadvantages of cohort studies:

Using a cohort study design is sometimes necessary because randomized controlled trials may be unethical. For example, you cannot deliberately expose people to cigarette smoke. Most of the research which relies on risk factors is based on cohort studies. Another advantage of cohort studies is that a single study can examine various outcome variables. For example, a study on smokers can simultaneously record deaths from lung, cardiovascular, and cerebrovascular disease. These studies can also predict the probability of the outcome of interest depending on variable factors. However, where a certain outcome is rare then a prospective cohort study is inefficient. Further, the subjects under observation may be lost during the course of the study due to migration or death. Finally, the results of the studies may get affected by various biases.

Cross-sectional studies:

These studies are primarily used to determine the prevalence of a health-related state. Here, all the related data is collected from an individual at one point in time. These studies are used to identify that whether subjects were exposed to the relevant agent and whether they have the outcome of interest at a particular point in time. Out of all the subjects, some will not have exposure to the relevant agent and nor will have the outcome of interest. These studies are primarily carried out by designing a questionnaire or interview. The questionnaire type of study is cheap but has less response rate. On the other hand, interview type of study is expensive but has a high response rate. Also, in questionnaire type of study large sample size is required, but in interview type of study small sample is required.

Advantages and disadvantages of cross-sectional studies:

The main advantage of cross-sectional studies is that the subjects are not deliberately exposed, treated or not treated. Thus, there are rare, if any ethical issues. All the data can be collected at a point of time and multiple outcomes can be studied. These studies are comparatively cheaper than other studies and provide quick results. There is no follow-up and fewer resources are required to run the study. The cross-sectional studies using data originally collected for other purposes are often unable to include data on confounding factors and other variables that affect the relationship between the putative cause and effect, which is a drawback of these studies.



Case-control studies:

As compared to cohort and cross-sectional studies, case-control studies are usually retrospective. Going back in time, the investigator determines that whether the outcome is related to the risk factor to which the affected individual was exposed in the past. In situations where the outcome is rare, case-control studies may be the only feasible approach. As these are retrospective studies, these cannot, therefore, be used to calculate the relative risk. However, with these studies, odds ratios can be calculated which in turn, usually approximate to the relative risk.

Advantages and disadvantages of case-control studies:

When the outcome is rare, a lot of information can be generated by case-control studies from a relatively few subjects. A case-control study is the only option when there is a long latent period between exposure to risk factor and disease. These studies require a few subjects so are less expensive. Furthermore, a large number of variables can be considered because of small sample size. The major problems associated with case-control studies are the familiar ones of confounding variables and bias.

Epidemiology of periodontal diseases

Lӧe et al. (1965) 3 initially established a correlation between plaque and gingivitis in non-population studies. Since then a lot of population-based studies have been done to find out the prevalence of periodontal diseases. Albandar (1998) 4 reported that 82% US adolescent population had overt gingivitis and signs of gingival bleeding. Reports from other parts of the world also reported similar or higher prevalence 5-7. Many studies have confirmed a parallel relationship between poor oral hygiene levels in a population and the occurrence of gingivitis. However, the presence of gingivitis is a poor indicator of subsequent periodontitis development 8-10.

Global prevalence of periodontitis:

Data from various studies strongly suggests a less pronounced relationship between dental plaque and severe periodontitis. It has been observed that the presence of aggressive periodontal destruction has been observed in subsets of populations distributed globally. However, gingivitis proportionate to the presence of plaque may be found with variable distribution in each population. The severe form of periodontitis has been observed in a small subset of the population in the United States 11, Europe 12, Africa 13 and Asia & Oceania 14. Studies in many other populations have reported a low occurrence of severe forms of periodontitis, which may be related to the lack of standardized study design or disease measurement criteria.

     The most important factor in the standardization of studies related to periodontitis is the method of periodontal probing. However, the probing depth is not an accurate indicator for periodontitis. For example, in the case of gingival enlargement pseudo-pockets may be present and in cases of recession, pocket depth does not reflect the attachment loss. Further, probing depth does not accurately measures the periodontal tissue destruction over a long duration of time. The occurrence of severe periodontitis in these subsets of populations can be explained on the basis of………..Content available in the book………………. Content available in the book…………….. Content available in the book………

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     Africans have the highest prevalence of periodontitis followed by Hispanics and Asians. Prevalence of periodontitis also varies in rich and poor populations. The rich population has better access to the dental treatment and thus have better periodontal status as compared to the poor. Other factors associated with more prevalence of periodontitis in poor groups in a population are stress, ignorance and lack of education. There is a general consensus based on various studies that the prevalence of severe periodontitis is less as compared to chronic periodontitis. In a survey done on Canadian population, 2110 adults aged 35-44 years were examined for the prevalence of periodontitis. 73.6% of subjects examined had a pocket depth of ≥ 4mm whereas 21.4% had a pocket depth of ≥6mm 17. Another national study carried out in France assessed the periodontal status of the population aged 35-44 years 18. CPITN index was used to study a representative sample of 1000 subjects. The results of the study demonstrated that 26.6% of dentate subjects had shallow pockets (4-5 mm) whereas 1.6% of subjects had deep pockets (> 6 mm). In a cross-sectional study 19 a random sample of 1,115 Danish adults aged 35-44 years and 65-74 years were studied for the prevalence of periodontitis. The results of the study demonstrated that in younger age group, 42% of subjects had moderate periodontitis while 6.2% had severe periodontitis.

     On the other hand, in older age group, 82% of subjects had moderate periodontitis and 20% has severe periodontitis. A national survey in Australia investigated the prevalence of periodontitis based on the Center for Disease Control (CDC) classification 20. It was observed that 20.5% of Australian adults had moderate and 2.4% had severe periodontitis. 42.5% of the Australian population had clinical attachment loss of ≥4 mm.

Global prevalence of periodontal diseases in children and adolescent:

Various gingival and periodontal diseases may be seen during childhood and adolescence. Gingival diseases are primarily non-destructive and infectious in nature. The most common gingival disease is plaque-induced gingivitis, which is a nonspecific bacterial infection. Infections which are nonplaque induced are less common and include lesions caused by certain bacteria, viruses and traumatic lesions 21. The periodontal diseases seen in children and during circumpubertal age include, aggressive forms of periodontitis, previously referred to as pre-pubertal or circum-pubertal or juvenile forms of periodontitis.

     Various surveys have been done to find out the prevalence of gingival and periodontal diseases in children. One of the largest surveys conducted was that by the national institute of dental and craniofacial research (NIDCR) on school children in the United States. Based on data obtained from these surveys, Albandar et al. (1997) 22 reported that the prevalence of early-onset (Grade C) (aggressive) periodontitis was 0.4% in 13-15 years old children and 0.8% in 16-19 years old group. Furthermore, prevalence differed with ethnicity also (whites 0.06%, blacks 2.6% and Hispanics 0.5%). The prevalence rates were higher for Grade B (chronic) periodontitis in both the age groups, with 2.3% in 13-15 years age group and 3.2% in 16-19 years age group.

     Melvin et al. (1991) 23 studied the bitewing and panoramic radiographs of 5,013 male and female recruits in the United States with the age group of 17-26 years. The overall prevalence of Grade C periodontitis was found to be 0.76% which was similar for both males and females. However, the prevalence was different for different races with highest for blacks (2.9%) and lowest for Caucasians (0.09%). A survey was conducted by Tinoco et al. (1997) 24 on Brazilian population, which was aimed to identify young subjects (12-19 years) with Grade C periodontitis in very low socioeconomic areas in three Brazilian cities. The overall prevalence of aggressive periodontitis was found to be 0.3% of the whole sample with a range from 0.1-1.1% in three cities 25. Similarly, a survey done by Saxen (1980) 26 in Finland, examined over 8096 young subjects (16 years of age). The bitewing radiographs obtained from the national dental care program were examined for bone loss. 0.35% of subjects demonstrated bone loss and 0.1% of subjects had Grade C periodontitis. In a study done on Nigerian student population (10-19 years) in schools, periodontitis, which was defined as probing depth ≥ 3 mm was found in 40.8% in 10-14 years old students and 50.3% in 15-19 years old students 27.



Prevention of periodontal diseases

The information which is gathered from epidemiological studies in a given population serves as the basis for planning the strategies to prevent the periodontal diseases. Three strategies have been suggested to prevent periodontal diseases 28, 29,

  1. Population strategies
  2. Secondary preventive strategies
  3. Identification of high-risk groups for periodontitis

Population strategies:

These deal with educating the population regarding the disease and how it can be prevented. These are aimed at inculcating behavioral changes at a community level, which prevent the occurrence of disease. The unfavorable behaviors, if present in that population, are attempted to be changed. 

Secondary preventive strategies:

These strategies involve identification of individuals with periodontal problems and customizing treatment plan according to the individual needs. Although, health education is an important component of this strategy, but it is more specific according to the periodontal needs of the population under study.

Identification of high-risk groups for periodontitis:

The identification of the individuals or the groups in the population who are at higher risk of developing periodontitis is another strategy. The early identification of these individuals or groups helps in preventing the development of periodontitis in the future.

     The implementation of any of the above strategy for the prevention of periodontal disease in a population depends on the nature of the periodontal disease in that population, risk factors for the disease in that population and convenience of implementation of the selected strategy. The most important factor facilitating long-term prevention of periodontal disease is behavioral modifications. Better oral hygiene habits, cessation of smoking and other behavioral promotional programs are helpful in the prevention of periodontal diseases in a population.

Conclusion

The study of the epidemiology of periodontal diseases is essential to formulate strategies to minimize the incidences of periodontal diseases as well as to formulate the treatment strategies for different populations under different sets of environmental conditions. The pattern and frequency of occurrence of these diseases are different in different populations depending upon various factors like socioeconomic status of the individuals in that particular population, access to the dental health care system, genetic and environmental factors, and many others. Hence, all these factors must be considered while making dental health policies for a particular population to effectively prevent and treat periodontal diseases.

References

References are available in the hard copy of the website.

Periobasics: A Textbook of Periodontics and Implantology

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