advances in the epidemiological study of oral-facial …

ADVANCES IN THE EPIDEMIOLOGICALSTUDY OF ORAL-FACIAL DISEASES

B. A. BURT1, J. E. ALBINO2, J. P. CARLOS3, L. K. COHEN3 , R. DUBNER3,J. A. GERSHEN4, AND J. C. GREENE5

2The University of Michigan, Ann Arbor, Michigan 48109-2029; 2State University of New York atBuffalo, Buffalo, New York 14260; ^National Institute of Dental Research, Bethesda, Maryland 20892;4University of California, Los Angeles, California 90024; and 5University of California, San Francisco,

California 94143

B:

Adv Dent Res 3(l):30-41, May, 1989

ABSTRACT

loth demographic patterns and disease distribution are changing rapidly in the United States. These> developments have led to the recognition that the epidemiology of many conditions is poorly under-

stood, and that other research has thus been hindered. Four areas of epidemiological study were chosen fordetailed analysis of how new technology will affect the conduct of future research. These areas, selected becauseinformation about them will be increasingly needed in an aging society, were periodontitis, temporomandibulardisorders (TMD) and other orofacial pain, salivary gland disturbances, and health services research. The po-tential effect of new technology was examined in the short, intermediate, and long term.

While the nature of epidemiological study is unlikely to change with the advent of new technology, the scopeof potential studies will become broader. Advances in diagnostic techniques from elsewhere will permit farmore precise diagnosis than is possible at present. Computer technology will permit an efficient system ofepidemiological surveillance to provide current data on trends in tooth loss, caries, and periodontitis — datawhich will complement the results of national surveys. Analytical studies to produce hypotheses on the etiologyof oral conditions, especially in such poorly-understood areas as chronic pain and TMD, will help direct clinicalresearch in those areas.

INTRODUCTION

Epidemiology is the study of the distribution anddeterminants of health-related states and events inpopulations, and the application of this study to con-trol of health problems (Last, 1983). In the last 50 orso years, the definition has been broadened fromconcern only with communicable disease epidemics,in the study of which epidemiology emerged as arecognizable science, to take in all phenomena relatedto health status. There are four categories of deter-minants of disease, which are:

(a) Genetic Core: genetic and biological endowment,from broad divisions such as race and genderto the multitude of genetic factors that definehuman individuality;

(b) Physical Environment: either broad, as in air

A report of the AADR ad hoc Committee on New Frontiers in OralHealth Research30

quality or living standards, or narrow, such asfluoride in dental plaque;

(c) Social Environment: broad divisions, which in-clude political and economic systems, familyorganization, cultural mores, health care pro-visions, work and educational settings; and

(d) Psychosocial Environment: behavior, attitudes, andlifestyles, as they affect beliefs about health anddisease and actions on such matters as diet,exercise, and use of tobacco, drugs, and alco-hol.

Epidemiology has many uses, such as definition ofwhat is normal and abnormal, discernment of histor-ical trends, description of the natural history of dis-eases, and the assessment of risk of contracting diseaseas related to the determinants just outlined. Its mostimportant use, however, is probably in detection ofcauses in disease etiology (Morris, 1975). Epidemio-logical analysis seeks associations between diseaseoutcomes and risk factors or suspected etiologicalagents; cause-and-effect relationships are usually de-

Vol. 3 No. 1 ADVANCES IN EPIDEMIOLOGY 31

termined by strength and consistency of associationsin a number of studies, as illustrated by the extensiveresearch linking cigarette smoking with lung cancer(Doll and Bradford Hill, 1956, 1964; US Public HealthService, 1975; Breslow, 1980).

Technological developments will influence the fu-ture conduct of epidemiological studies, principallyby improving methods for diagnosing and quantify-ing disease and its determinants. The purpose of thispaper is to review the current and potential applica-tions of epidemiology in dental research, and to un-dertake a critical examination of how new technologywill affect it in the immediate and longer-term future.

THE NATURE OF RESEARCH

IN ORAL EPIDEMIOLOGY

Epidemiology evolved as a science in the great ep-idemics of the 19th century, when recurring publichealth crises demanded urgent action at a time ofonly rudimentary understanding of disease. Devel-opment of epidemiology was therefore driven by apublic-health imperative. Oral epidemiology, as abranch of the parent discipline, emerged only somegenerations later with the identification of fluoride incaries prevention (Striffler et al., 1983). While oral ep-idemiology is nothing more or less than the appli-cation of epidemiological principles and methods tothe study of oral conditions, its relative youth has sofar restricted it largely to descriptive measurementrather than searches for causes (the fluoride story beinga notable exception).

A distinctive feature of oral epidemiology, as prac-ticed to date, is its customary sources of data. Themajority of reports in medical epidemiology are basedupon analysis of existing data from sources such asvital statistics, disease registries, hospital admissionsand discharges, insurance claims, and physicians'records. This is especially true when diseases studiedare of low prevalence, where original data collectionwould be too expensive. By contrast, oral epidemiol-ogy has usually relied upon original data collectionfrom clinical examinations carried out by the re-searchers themselves. This is because the most com-mon oral diseases are highly prevalent, and alsobecause descriptive statistics were necessary to definetheir distribution prior to more complex applications.Databases, in the sense in which they are utilized inmedical epidemiology, have only just begun to bedeveloped for research into the epidemiology of oralconditions. While the roots of oral epidemiology inclinical dentistry should not be lost, the study of less-common oral conditions will require greater use ofdatabases where a rich assortment of co-variablespermits more precise detection of disease determi-nants to be achieved. It will also require greater useof analytical techniques from the parent discipline.

Descriptive Studies

Descriptive epidemiological studies are most usefulin monitoring disease trends in a population, whereresults can be used to plan or evaluate programs andpolicies for disease control, dentist and auxiliary de-velopment, and financing of dental care. The declinein caries among children, for example, was identifiedby critical comparison of results from a series of de-scriptive epidemiological studies (Burt, 1978; US Pub-lic Health Service, 1981). The current question —whether periodontal diseases are declining — will intime be answered the same way. Since the patternsof oral diseases strongly influence the practice of den-tistry, descriptive epidemiology will clearly continueto fill a fundamental role.

Several well-conducted surveys, beginning in 1960,have provided national data on oral health. Thesesurveys have been administered by either the Na-tional Center for Health Statistics (NCHS) or by theNational Institute of Dental Research (NIDR). Thescope of these surveys has been confined largely tocaries, periodontal disease, and tooth loss. Funda-mental questions on the extent of conditions such astemporomandibular disorders (TMD) and othersources of orofacial pain have not yet been assessedin a national survey, mainly because methods to doso have not been developed.

Economic constraints have dictated that dental databe excluded from some national surveys. They werecollected in the first National Health and NutritionalExamination Survey (NHANES I) of 1971-74 (US PublicHealth Service, 1979), but they were omitted from theNHANES II survey of 1976-80. In addition, shortageof resources at NCHS has resulted in some data tak-ing a long time to be analyzed. These considerationsled NIDR to conduct its first national survey, of chil-dren aged 5-17, in 1979-80 (US Public Health Service,1981). NIDR then surveyed adults in 1985-86 (USPublic Health Service, 1987), and repeated the surveyof children in 1986-87.

Data from national surveys of oral health could beusefully supplemented by results of state-wide andsmaller surveys of purposive samples or specialgroups. The philosophy here is that national surveysof representative samples of population are neces-sarily complicated and expensive, and therefore can-not be expected to be mounted more frequently thanevery 5-10 years. In addition, national surveys can-not provide local data, such as for a city or region ofa state. If local surveys were carried out to standard-ized protocols, and optimum use made of electronicdata collection, transfer, storage, and analysis, a sur-veillance system could be set up in which dental datafrom local surveys could be fed into a national "clear-inghouse" and disseminated regularly. The Centersfor Disease Control (CDC), which have been con-ducting disease surveillance of this kind for years,and which already have a dental program (the DentalDisease Prevention Activity), seem the most appro-

32 BURT et al. Adv Dent Res May 1989

Enamel crystal structureEnamel minerals

Ca. P. FSaliva quantitySaliva qualityImmune responseHost behaviorHost attitudes

S. mutansLactobacilliOther bacteria

Plaque quantityPlaque quality

EnzymesMinerals

Bacterial substrateProtective factors

SocioeconomicsCulture

Plaque-forming abilitycalculus-forming abilityphagocyte responseoral hygiene behaviorattitudes to oral health

spirochetesCram-negative anerobesother bacteria

OTHER:immune response,genetic andsocial factors

ENVIRONMENTAL

plaque,calculus,roughened tooth surfaces,defective restorations,defective appliances,tooth anatomy, position,traumatic occlusion,smoking

Fig. 1 — Multifactorial depiction of dental caries and periodontaldisease.

priate agency to coordinate these activities. Inherentmethodological concerns are recognized, but the ben-efits to be obtained from such a system are potentiallyhigh.

Several state-wide surveys have been held in recentyears-for example, in North Carolina in 1976-77(Hughes et al., 1982), Iowa in 1980 (Beck et al., 1982),and South Carolina in 1982-83 (South Carolina De-partment of Health and Environmental Control, un-dated). Other state-wide and smaller local surveysare in process or being planned. A dental surveillancesystem therefore includes little that is not being doneat present. It basically suggests standardization of these

current activities, and collection and transmission oftheir findings on a systematic basis.

Analytical StudiesLast (1983) defines an analytical study as an hy-

pothesis-testing method of investigating the associ-ation between a given disease or health state or otherdependent variable and possible causative factors.Three types of analytical studies are recognized: cross-sectional (or prevalence), cohort (prospective or lon-gitudinal), and case-control (retrospective). Althoughcross-sectional data are usually collected for descrip-tive reports, oral health data from sources like NCHSnational surveys can be related to a variety of otherhealth parameters as well as to factors in the physical,social, or psychosocial environments (Ismail et al., 1984;Chen and Lowenstein, 1984).

Cohort or case-control studies are usually carriedout with data from purposive or convenience groupsof participants, such as persons in a particular typeof employment or in a specific geographic area. Pa-tients in hospitals or dental schools can be studied totest certain hypotheses, though the potential for se-lection bias with such populations has to be recog-nized. Analytical studies test hypotheses by measuringthe strength of association between a group's diseaseexperience with host factors, environmental mea-sures, or behavioral variables. Where associations arestrong and consistent, cause-and-effect can be im-puted, but the multifactorial etiology of disease (il-lustrated for dental caries and periodontal disease inFig. 1) means that analytical epidemiological studiesdefine necessary causes rather than "prove" etiology(Morris, 1975).

The best-known example of analytical epidemiol-ogy in dentistry concerns fluoride. A lengthy and still-continuing series of studies began with the early cross-sectional observations regarding fluorosis, fluoridecontent of water, and caries prevalence (Black andMcKay, 1916; Dean et al., 1941, 1942), then pro-gressed to the first supplemental water fluoridationstudies in the United States and elsewhere. Thesepioneering studies are frequently assumed to be lon-gitudinal, although, with the exception of the Neth-erlands study (Backer Dirks et al., 1961), they weresequential cross-sectional rather than cohort designsin both study and control communities (Arnold et al.,1962; Ast et al, 1962; Blayney and Hill, 1967; Huttonet al., 1956). The next series of studies were the nu-merous clinical trials for testing other fluoride regi-mens for caries prevention (Knutson and Armstrong,1943; Rugg-Gunn et al., 1973; DePaola et al., 1977;Glass and Shiere, 1978).

Analytical study of periodontal disease was ham-pered for years by the lack of indices for quantifyingdisease status, which in turn reflected poor under-standing of its natural history. Following the devel-opment of the first widely-accepted index (Russell,1956), associations between gingival inflammation andplaque/calculus deposits were identified from cross-


sectional analytical studies (Russell and Ayers, 1960;Greene, 1963, 1967). Other cross-sectional studies atthat time were able to rule out the theory that peri-odontal diseases were primarily nutritional disorders(Russell, 1963).

Case-control studies —a retrospective design inwhich a group of persons with the disease in question("cases") is compared to a group without it ("con-trols") to measure similarities and contrasts in diseasedeterminants (Schlesselman, 1982) —are rare in oralepidemiology. Classification of persons into those withand without oral diseases has not historically beenused much in high-prevalence populations; summaryindices of the common oral diseases characteristicallymeasure intensity rather than prevalence. It is un-certain whether characterization of persons with "less"or "more" disease, rather than the usual classificationof those "with disease" or "without disease", is avalid design for case-control studies. The relative lackof databases in dental research, mentioned previ-ously/ has also hampered the use of case-controlstudies.

Case-control studies have the advantage of beingrelatively quick and inexpensive. They are limited inthe sense that their results cannot be taken to showa cause-effect relationship, but they can strongly sug-gest it; hypothesized relationships can then be testedin prospective studies. Case-control studies are a use-ful design to begin exploring etiologies of conditionsabout which little is known, such as various soft tis-sue lesions, TMD, and other orofacial pain syn-dromes.

Clinical Trials for Preventionand Treatment of Oral Diseases

The randomized clinical trial is an experimental ap-plication of the epidemiological method, designed totest the hypothesis that a particular agent or regimenis efficacious in favorably altering the natural historyof a disease. Probably the earliest example of a trueclinical trial in dentistry, though it was not referredto as such at the time, was a study to test the efficacyof silver nitrate applications to prevent caries (Kleinand Knutson, 1942). Numerous trials since then havetested various forms of fluoride for the prevention ofcaries, effects of educational approaches on oral hy-giene behavior, the effectiveness of different treat-ments to control loss of attachment and bony supportin periodontitis, and the efficacy of various mouth-rinses to control plaque formation.

Most clinical trials in oral research have been forcaries prevention in children, methods for which havenow been developed to a high state of precision. Re-sults of trials using randomized stratified allocationof children to test and control groups, double-blinddesigns, assessment of measurement error, and care-ful data analysis have no doubt contributed signifi-cantly to the caries decline. But with the caries declinein children, such trials will be seen less frequently inthe future. Those that will be mounted will be in-

creasingly confined to special groups of caries-sus-ceptible children, which allows numbers of participantsto be kept in bounds but diminishes the generaliza-bility of results.

An increase can be expected in clinical trials forplaque-control mouthrinses for home use. Furtherdevelopment of drugs to control periodontitis is alsolikely, and clinical trials for such products will be re-quired. These studies will need to be carefully de-signed because of the long-term nature of periodontitis.At present, such trials are difficult because of diag-nostic imprecision in periodontitis. With more precisediagnosis added to the constantly improving studydesigns, clinical trials for periodontitis treatments willbecome more frequent and more efficient. Trials fortesting therapies for ulcers, herpes, and other soft-tissue lesions will likely become more frequent as well.

To date, dentistry has seen little development ofclinical trials to assess the efficacy of different sur-gical, technical, and restorative treatments for oraldiseases. Examples of evaluation trials that have beendone are the studies to compare the efficacy of var-ious methods of treating deep periodontal pocketsand loss of attachment —studies which have substan-tially altered the approach to such treatment (Ramfjordet al, 1973; Knowles et aL, 1979). Trials have also beenconducted to test behavioral interventions to reducefear and anxiety among dental patients (Ayer andCorah, 1984).

Broader application of these study philosophies anddesigns, however, would help rationalize many areasof dental treatment. There is ample need for trials toassess the efficacy of treatments for malocclusions andTMD, both conditions upon which large amounts ofmoney are being spent for untested therapies. Suchstudies will not be easy. In addition to considerablelogistic difficulties, for example, randomization is moredifficult than in caries prevention trials, and the prob-lem of separating a true treatment effect from varia-tion among providers will have to be dealt with.

Personnel Needs

Epidemiology is a complex science that requiresspecialized training, just as do other areas of oral re-search. Training should include advanced course-work in statistics, epidemiology, research design, andcomputer applications; courses as necessary in pa-thology, microbiology, immunology, genetics, envi-ronmental health, sociology, psychology, andeconomics; a thorough understanding of past devel-opments in epidemiology, and sufficient understand-ing of research in other fields to facilitate multidisci-plinary studies. Graduates of specialized trainingprograms should be employed in Federal agencieslike NIDR, NCHS, CDC, and the National Center forHealth Services Research. Others are needed in den-tal schools, and in state and local health departments.Research advances will be slow without a "criticalmass" of trained oral epidemiologists.

34 BURT et al

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Fig. 2-Age and gender structure of the United States, 1982-2080.Source: U.S. Department of Commerce, 1984.

TECHNICAL AND SOCIAL CHANGE

There are two areas where changes will affect thepractice of epidemiological research across the board.One is advances in computer technology, the otheris the demographic shift in the age-structure of Amer-ican society.

ComputersThe availability of computers means that projects

can now be conceived and carried out which wouldpreviously have been impossible; the range of vari-ables collected in a study can be increased greatly,while the capacity to analyze them has already ex-panded. As the speed, power, and storage capacityof computers continue to grow, so more ambitiousprojects with complicated data analysis can bemounted. Computers permit the recording andanalysis of the total range of genetic, physical, social,and psychosocial risk factors associated with the con-ditions under study. The capacity to collate and ana-lyze many of these factors has probably exceeded ourability to measure them validly and reliably.

Adv Dent Res May 1989

The need for oral epidemiological research to makebetter use of databases has already been discussed;even now, there are questions which could probablybe answered more efficiently by analyzing existingdata rather than by mounting new studies. To in-crease the number of databases, records from vir-tually all studies involving original data collection,when initial analysis is completed, should be rou-tinely stored in computer banks for general analyticuse. Ways to make databases from dental insurancegroups more available to researchers would also re-lease a data source of potentially high value in healthservices research. A central agency-such as CDC,NIDR, or the National Technical Information Ser-vice — could store and publicize these databases, andcomputer networks would make them readily acces-sible to researchers.

For those studies in which original data collectionis required, direct data entry into computers ratherthan on a paper record has already been employedin field examinations (Eklund et al., 1987), and thenewer portable computers are making this approacheven more convenient. Field computers allow for agreat savings in time between data collection andanalysis, and errors are reduced at data entry. Wherestandard protocols can be used, software for analysiscan also be employed by the researcher in the field,thus greatly facilitating the process of data analysis.The development of a system of oral disease surveil-lance, discussed earlier, would largely depend on theuse of computerized data-entry systems and simpleanalysis packages to be successful.

Demographic ChangeThe "graying of America", the dimensions of which

for the next 100 years are illustrated in Fig. 2, hasraised a host of social and public policy issues thatwill not be resolved easily. The principal impact isthat older persons will continue to make up an in-creasing proportion of the population. Their absolutenumbers will also expand rapidly as the U.S. popu-lation grows to over 300 million (US Department ofCommerce, 1984). They will also be living longer, andretaining more teeth (Weintraub and Burt, 1985). Thesefacts have raised many research questions about thenature of the aging process, its sociology and psy-chology as they relate to oral diseases, and the oraldisease conditions usually associated with age.

Disease trends can be interpreted more easily whensociety is separated into its various age-cohorts, forthe various life experiences of the generations haveinfluenced many factors differently, oral status in-cluded. For example, it cannot be taken from the cur-rent caries decline in children that coronal caries hasnecessarily been prevented permanently; it is possi-ble that the carious attack may just be postponed un-til later in life. If this is occurring, the impact on thepractice of dentistry will be profound. Even with thepresent older age-cohorts, there is some evidence thatcaries experience is increasing, and service demands


are highly likely to increase (Douglass and Gammon,1984). There has been some epidemiological studyamong older age-groups, both descriptive (Beck etaL,1984, 1985; Hand and Whitehall, 1986) and analytical(Douglass et al, 1983; Burt et al, 1985), but the oralhealth of older persons still requires further study.Root caries is associated with gingival recession (Ny-vad and Fejerskov, 1982; Burt et al, 1986), and gin-gival recession is more prevalent among dentate olderpersons, so aging of society and greater tooth reten-tion can be expected to increase the size of the rootcaries problem. While periodontitis may not be a nat-ural consequence of aging for most persons up to age74 (Page, 1984; Abdellatif and Burt, 1987), it is pos-sible that diminished resistance becomes a factor inlater years. These and related issues will require fur-ther research if the oral health of older persons is tobe optimized.

FRONTIERS FOR RESEARCH

Epidemiology is an applied science; its theoreticalbasis and its methods are of little interest to anyoneoutside the field. It is only in its applications that ittakes on form: the epidemiology of periodontal dis-eases, of oral cancer, and so on. Epidemiology is notas equipment-dependent as the laboratory sciences,so developments in areas like cell biology, which willtransform laboratory and clinical research over thenext 30 years, will affect epidemiology principally inthe hypotheses tested and the diagnostic methodsused. Today's diagnostic methods, based largely onclinical observation, will give way to more objectivetests for the presence of diseases or their determi-nants.

To illustrate the impact of new technology on oralepidemiology, we have selected four research areaswhich will become more important with the aging ofAmerican society, and in which diagnostic impreci-sion has impeded research:a. Periodontitis: Probably the major oral disease interms of research interest for the immediate future.While caries has waned as a public health problemin American children, the nature of the disease processin periodontitis has been the subject of vigorous de-bate in recent years. The concept of site selectivity(Haffajee et al, 1982), the "burst" hypothesis for pro-gression of lesions (Socransky et al., 1984), the in-creasing acceptance that periodontitis and gingivitisare distinct diseases (Poison and Goodson, 1985), andrecent evidence suggesting a relatively low preva-lence of generalized periodontitis (U.S. Public HealthService, 1987) —all have provoked spirited discus-sion. While many earlier beliefs are now stronglyquestioned, the fact remains that periodontitis has amajor impact upon the oral health of millions of peo-ple, and will continue to do so for some time.b. TMD and other orofacial pain: The extent and dis-tribution of chronic pain in the facial area, with the

exception of TMD to some extent, are almost com-pletely unknown. Differentiation of some syndromesfrom TMD is often difficult. It is obvious to cliniciansthat chronic orofacial pain is a nightmare for the un-fortunate persons who suffer from it, and methodsof treatment are acknowledged to be inadequate. Sys-tematic study has been extremely difficult in the pastbecause of the problems with measuring pain, com-pounded by the problem of assessing the impact ofbehavioral and personality factors.Even the epidemiology of TMD is poorly understood,as is the efficacy of the various methods devised totreat them. Patients appear to be predominantly whitefemales aged 20-40, but it is not clear whether this isthe group principally affected or whether they justconstitute the main group of patients. In the mean-time, large sums of money are being expended bythe public on TMD treatment. TMD is not uncom-mon, and many think that its occurrence is increas-ing. The absence of a scientific basis for the study ofTMD stems largely from the absence of a case-defi-nition, the frequently diffuse nature of symptoms,uncertainty about the importance of clinical signs (suchas clicks, occlusal sliding, and limitations of mandi-bular movement), and how these signs relate to per-sonality and behavioral profiles.

c. Salivary gland dysfunction: It has already been statedthat these conditions could be a factor in what ap-pears to be a greater degree of coronal caries amongolder persons than previously imagined (Beck et al.,1985). Research on the effects of destruction of thesalivary glands, usually from radiation therapy forcancer of the head and neck, has shown how thenow-xerostomic patient is highly susceptible to car-ies. But subtler forms of salivary dysfunction proba-bly occur, perhaps as a natural consequence of aging,possibly from drugs commonly used in old age (Foxet al., 1985), and possibly from other pathologicalcauses. The impact of salivary gland dysfunction oncaries has been principally assessed from the quan-titative aspect of saliva flow (Abelson and Mandel,1981) rather than from qualitative aspects. So far, thereis little knowledge of how salivary gland dysfunc-tions influence periodontal diseases. Even the detec-tion of these conditions has been hindered bydiagnostic difficulties; crude measurements of sali-vary flow rates are frequently all that has been ac-complished in clinical studies.d. Health services research: The provision of healthservices was described earlier as a subsection of thesocial environment. Health services research, definedas "the inquiry to produce knowledge about thestructure, processes, or effects of personal healthservices" (Institute of Medicine, 1979), has been in-cluded as a "frontier" condition because of the im-portance of linking epidemiological findings to thefactors influencing receipt of dental care. Health ser-vices research also illustrates the breadth of applica-tion of the epidemiological method. The emergenceof clinical epidemiological study in dentistry, espe-


daily its application in clinical decision analysis(Douglass and McNeil, 1983), is probably the mostdirect merging of epidemiological science with clini-cal dentistry.

Health services research in dentistry has been ap-plied to a breadth of issues pertinent to understand-ing the organization, financing, and delivery of dentalcare. Areas of research focus have included studieson the utilization of dental services, quality of dentalcare, measurements of the need for treatment, accessto dental care, special population groups, and theassessment of oral health status. The epidemiologicalmethod can be applied to studies on care delivery,whereby groups of people who receive different ex-posures to various arrangements for receipt of dentalcare can be compared. Outcomes in such studies canbe expressed in terms of both oral health status andsocial/behavioral aspects, such as frequency of use ofservices and satisfaction with care received.

There are two outstanding examples of large-scalestudies of this type. One is the first International Col-laborative Study, coordinated by the World HealthOrganization, which related the impact of the oralhealth care delivery system to the oral health statusof recipients in ten nations (Arnljot et al., 1985). Theother is the Rand Health Insurance Experiment, whichallocated families in different geographic locations inthe United States to several health care financing plansand followed their use of service and health outcomesover five years (Manning et al., 1985).

Each of these areas will be looked at in turn toassess what impact various new technological devel-opments might have in the immediate future, the in-termediate future, and in the long term.

a. PeriodontitisShort-term developments: Diagnosis of periodon-

titis is now based on clinical and radiographic as-sessment of gingival inflammation, probing pocketdepth, and clinical loss of attachment. Diagnosis willcontinue to be clinically based for the immediate fu-ture—indeed, there will probably always be aspectsof clinical assessment. But some new technologieswill reduce the art of measurement in the gingivalcrevice and increase the science.

Periodontal probes in which the probing pressurecan be electronically monitored assist in standardiz-ing probing forces (Poison et al., 1980). Used in clin-ical studies, this computerized probe has not yet beenproven for field studies. Another computerized peri-odontal probe which aids in detecting the cemento-enamel junction (Jeffcoat et al., 1986) is still devel-opmental, but if it reaches the point where it can beemployed in the field, it could substantially reducethe problems associated with measurement validityand reliability. Cost and portability are probably themain determinants of its future practicality. Other di-agnostic measures for which the technology alreadyexists may join precision-probing in certain periodon-tal studies. For example, measures of gingival crevi-

cular flow are already useful, and instruments whichcould measure certain constituents of crevicular flowas well as its quantity may prove to be even morediagnostically useful.

Intermediate-term developments: Diagnosis ofperiodontal conditions will move more to biologicmeasurements of disease indicators to complementclinical assessment. Technology exists at present foridentification of periodontopathic bacteria by in-officeantibody screening, and enzyme activity, but it is likelyto be some years before these methods become stan-dard in field studies. Indeed, it is not yet certain thatall will fulfill their initial promise.

DNA probing, which is in limited use now, in-volves identification of bacteria by reading the geneticcode, thus potentially allowing for a higher degree ofreliability in bacterial identification than currently ex-ists. At present, DNA probing identifies only thepresence or absence of a limited number of species,but the number of species capable of being identifiedshould grow quickly. One particular benefit of DNAprobing and immunologic tests for future epidemio-logical studies is that they can be carried out withdead bacteria, whereas cultivation methods requirelive bacteria.

Advances in nuclear medicine have been appliedonly experimentally in periodontal research to date(Jeffcoat et al., 1985), but by this time may have be-come more commonplace diagnostic aids for deter-mining bone loss. The method tested in beagle dogsuses an intravenous injection of a trace of diphos-phonate compound labeled with the radionuclide 99m-technetium. The short half-life (6 hr) and gamma en-ergy level are ideal for imaging bone; the materialdetects the metabolic change that precedes architec-tural change in bone.

The development of a technique for producinghuman monoclonal antibodies in the test tube (Cas-ali et al., 1986) can be expected to lead to improvedmethods of diagnosis for a variety of conditions.The complexity and expense of monoclonal anti-body techniques, however, make their future inepidemiological studies uncertain. Bacterial identi-fication by enzyme activity appears to be a reason-able-cost technique; initial tests suggest that theability of subgingival plaque to hydrolyze N-ben-zoyl-DL-arginine-2-naphthylamide (BANA) is a re-liable marker for the presence of high proportionsof spirochetes in the plaque sample (Loesche et al.,1987). Further tests of this approach in epidemio-logical studies are planned.

Long-term developments: In the future, it can beexpected that diagnosis of periodontal susceptibilityand active disease will be carried out almost entirelyby extra-oral tests using bacterial, immunological,nuclear, or genetic markers, and that these tests willbe relatively simple and inexpensive. This will makeepidemiological studies much simpler and more di-rectly useful, and could also permit early identifica-tion of periodontitis-susceptible individuals. By this

Vol. 3 No. 1 ADVANCES IN EPIDEMIOLOGY

time, it is likely that periodontitis will be sufficientlywell understood that it will no longer be considereda public health problem.

b. TMD and Other Orofacial PainShort-term developments: The major advances in

the measurement of pain over the last decade havemade it feasible to begin descriptive epidemiologicalresearch. These new methods can be subdivided intomeasures of the patient's verbal report, measures ofbehavior, and physiological measures. Until recently,verbal report measures were considered unreliableand fraught with subject and experimenter bias. Theyusually involved simple measures of pain threshold,pain tolerance, and the use of category scales to as-sess the magnitude of pain or pain relief. Recent re-search, however, has resulted in major improvementsin pain scales that utilize cross-modality matchingprocedures, measures of pain discrimination, and theuse of quantifiable pain descriptors. Adjectives thatdescribe a component of the patient's pain experi-ence, such as its intensity {i.e., mild, moderate, in-tense), have become reliable and objective measureswhen they are quantified by cross-modality matchingto known sensory measures, such as line length ortime duration (Gracely et al, 1978). In addition, theuse of experimental pain stimuli produces su-prathreshold ratings of the pain experience along dif-ferent dimensions, such as intensity andunpleasantness. These responses can then be com-pared to the patients' reports of their clinical pain(Heft et al, 1980).

Behavioral measures of pain include simple reflexmeasures, such as the jaw opening reflex or leg flex-ion in response to noxious or painful stimuli. Morecomplex behavior includes facial expressions or vo-calizations. These kinds of behavior can be betterquantified by means of TV taping and waveform ana-lyzers of different sounds. TV monitoring has provedto be useful in assessing other types of motor beha-vior that might be altered when a patient is in pain.

Physiological measures that correlate with pain in-clude levels of muscle activity from painful sites,autonomic nervous system activity, and electrophys-iological records of nerve activity. The latter includesmeasures of the activity of populations of neurons{i.e., compound action potentials or EEG activity) andrecordings of single-nerve action potentials from pe-ripheral nerve fibers.

For research in the epidemiology of TMD, the mostimmediate need is a case-definition: specification ofnormal and abnormal joint movement to add to clin-ical and psychological measures. An NIDR-spon-sored workshop in October, 1984 (proceedings notpublished), proposed that a case-definition be basedon (a) subjective pain, (b) clinically-determined painfrom tenderness on palpation of the joint or associ-ated muscles, and (c) dysfunction assessed by limi-tation of movement or joint sounds.

In addition to the advances in measuring pain just

described, technological developments in tomogra-phy, arthrography, pressure algometry, and mag-netic resonance imaging may assist in future TMDstudies, though their application to epidemiology willnot be automatic because of high cost and ethical con-siderations. Computerized tomography involvesmultiple radiographic exposures from different an-gles. These multiple images are then combined withcomputer assistance to provide three-dimensionalimages. This potentially powerful diagnostic tech-nique is clearly expensive, and the degree of expo-sure to radiation it entails presents ethical difficultiesin epidemiological studies. Arthrography requires in-jection of a radio-opaque dye into the joint prior toradiography, sometimes with tissue reaction to thedye. It is also considered a technically demandingprocedure. The pressure algometer has been shownto be reliable in measuring myofascial trigger-pointsensitivity (Reeves et al, 1986). While the necessityof adhering to strict methodological guidelines hasbeen demonstrated (Fricton and Schiffman, 1987), al-gometry appears to be a promising approach in TMDstudy. Magnetic resonance (MR) imaging —in whichthe patient is physically placed in an MR scanner toact as an external magnetic field, and the images aretransmitted by radio frequency waves —has severaladvantages over computerized tomography and ar-thrography. It provides soft-tissue contrast that theothers do not, it is non-invasive, and it does not sub-ject the patient to ionizing radiation. The techniquehas already been tried in a small study of sympto-matic and asymptomatic patients, with encouragingresults (Manzione et al, 1986). The drawback is thatthe procedure is extremely expensive and requires asophisticated institutional base.

Intermediate-term developments: Over time, theabove pain assessment methods will be combined withmeasures of various metabolites that are associatedwith the onset of clinical pain. For example, the stressof oral surgical procedures leads to a release of opioidpeptides from the pituitary and monoamines fromthe adrenal medulla. The levels of opioid peptides inplasma and cerebrospinal fluid are closely related topatient pain reports following oral surgery. Drug ma-nipulations that alter pain levels also alter levels ofthese opioid peptides (Hargreaves et al, 1986). Theperipheral inflammatory process is also associated withthe release of various neuropeptides into the tissuefluid, and the levels of some of these compounds alsoappear to be related to patient reports of pain. Thefact that they correlate well with verbal report assaysof pain will lead to improved and highly objectivemethods for measuring pain before and after varioustreatments. Epidemiological studies in the interme-diate future will be able to make increasing use ofthese new biochemical assays as measures of clinicalpain.

For TMD studies, magnetic resonance imaging maybecome more available and less expensive. In itspresent form, it is not a portable item of field equip-


ment, but developments on the MR principle mayreach the point where it will become much simpler.What seems unlikely to change, however, are theethical constraints on use of radiographic and arthro-graphic techniques for non-symptomatic persons.

It can also be expected by this time that behavioraland personality measurement, an important aspectof TMD diagnosis in many cases, will be advancedbeyond current procedures. Analytical studies to seeketiology of TMD are likely to be mounted when allthe physical, biological, and psychological factors likelyto be involved can be measured with precision.

Long-term developments: With a growing varietyof descriptive and analytical studies, together withother basic and clinical research on orofacial pain, itcan be expected that in the long term these conditionswill be controlled. Although recent research has re-vealed that the brain has its own pain-suppressingsystems, these systems cannot be activated undernormal physiological conditions. These pathways areassociated with a host of neurochemicals such as dif-ferent opioid peptides, monoamines such as sero-tonin and norepinephrine, and many recentlydiscovered neuropeptides. The future developmentof new approaches to activating these systems willresult in methods by which people can control theirown pain. In addition, the release of neurochemicalmarkers associated with activation of these pain-sup-pressing systems will provide additional objective as-says of pain and its magnitude.

Non-invasive, multi-dimensional imaging tech-niques will most likely have reached the point wherecapturing TMD images for diagnosis is no more ar-duous than exposing a dental x-ray film is today. Epi-demiological diagnosis will be simple enough thatcohort studies and clinical trials to test treatmentmethods could be conducted without special con-cerns. These and related studies will produce meth-ods for determining the susceptibility of individualsto TMD and permit preventive measures to be insti-tuted. Treatment and preventive methods will beevaluated through clinical trials.

c. Salivary Gland DysfunctionShort-term developments: Recent research has

greatly expanded knowledge of how saliva formationtakes place, and has raised diagnostic consciousnessto the possibility of subtle salivary disorders whichat present defy definitive diagnosis. Several ion chan-nels and carrier-mediated transporters for transepi-thelial cell water movement are now recognized, andmost neurotransmitter receptor control mechanismsinvolved have been identified. Current research fordiagnosis of gland dysfunction is based on experi-mental imaging methods and use of isotopic probes.At present, none of these mechanisms has advancedto the stage of clinical applications.

Intermediate-term developments: The techniquesdescribed are likely to have reached the point of di-rect clinical applications, but may still be expensive

and impractical for field use. Epidemiological re-search at this time may be focused on determinationof the roles played by particular constituents of sa-liva, and so would require precise identification ofthese constituents from groups of subjects with andwithout particular clinical syndromes. When molec-ular and immunological probes reach the point ofpractical and relatively inexpensive use, then classicepidemiological studies can be mounted.

One practical result of an ability to diagnose var-ious degrees of salivary dysfunction would be to re-late these conditions to various medical and socialfactors. As one example, some xerostomic drugs arealready known. As more such drugs, and drug com-binations, become identified through the results ofsuch studies, health practitioners could have readyaccess to this information through computer banksto assist their treatment of patients.

Long-term developments: The development ofhighly specific diagnostic probes may reach the pointwhere initial diagnosis can be carried out at homewith a kit from the local drug store. Screening ex-aminations, such as for elderly persons in the high-risk group for xerostomia (bearing in mind that "theelderly" in 40 years' time will be older than today'selderly), might be carried out with simple tests innursing homes or in the patient's home. A degree ofdiagnostic precision will allow subtle dysfunctions ofsalivary glands to be readily identified.

d. Health Services ResearchShort-term developments: Health services research

as an applied field has relied upon systematic analy-sis of complex data sets, use of empirical methods,and collaborative efforts of dental researchers withother disciplines. It relies on descriptive and analyt-ical studies to explore research questions that ulti-mately affect the formulation and implementation ofdental health policy. For the immediate future, healthservices researchers will continue to address issuesthat emanate from the upward spiral of dental carecosts, questions about the financing of dental care,the maldistribution of services, and the need forprofessional consensus as to the quality and appro-priateness of dental care.

More research will be carried out in the area ofquality assessment, especially of high-cost serviceslike implants and TMD surgery. Current methods toevaluate structure, process, and outcome of dentalcare will be refined, and additional quality assess-ment tools will be developed. For example, validationstudies will be performed to compare indirect reviewof dental records with direct assessment via clinicalexamination of patients. Reliable and valid qualityassessment methods will be used to evaluate alter-native delivery systems and the various mechanismsavailable to finance dental care; studies to evaluatethe effect of payment source on costs, quality of care,health status, and behavior will become more com-monplace. Other studies will assess the impact of


business practices, advertising, and use of para-professional providers on the quality of care, and theability of state agencies to influence quality.

With limited resources, more short-term emphasiswill be placed on studies that focus on the relation-ship between the allocation of dental care resourcesand oral health status. Purchasers of dental care, in-cluding large corporations and the Federal Govern-ment, will be looking for ways to maximize benefitsfor dollars spent. In response to this need, there willbe an increase in the development of research pro-tocols in cost-effectiveness and cost-benefit analysis.Also, more studies evaluating the dental health prob-lems of target populations to determine costs andquality of care will emerge.

There will also be further emergence of clinical ep-idemiology (Sackett et aL, 1985) in dental research,especially the use of decision analysis. With moreempirical data on treatment outcomes, decisionanalysis will be employed more as a systematic ap-proach to determining appropriate treatment (Doug-lass and McNeil, 1983).

Intermediate-term developments: More studies willfocus on the relationship between process and out-come of dental care. Researchers will determine themost cost-effective therapies by systematically study-ing factors such as length of treatment, retention ofvarious restorations, and the negative effects of thesetherapies. By development of norms of care and ex-pected dental outcomes, it will be possible for un-dertreatment, over/treatment, unnecessary treatment,and mistreatment to be identified. It will also be pos-sible to develop indices of therapeutic need that willbe used to translate existing conditions into appro-priate treatment interventions.

The impact of the aging population on the dentaldelivery system will be studied extensively as we ap-proach and enter the 21st century. Health servicesresearchers will examine the consumption of dentalservices by the elderly in terms of expenditures anddemands on the dental care system. For example,there will be increased research on what the aged canexpect from the dental care system as the elderly in-cur greater out-of-pocket costs and as benefits andeligibility for care are reduced.

Clinical epidemiology by this time is likely to havemade decision analysis a regular part of the dentalschool curriculum. Other research will focus on thefinancing of dental care and the effects of reimburse-ment changes on cost, access, and quality of care. Aschanges occur in Federal, state, and private sectorreimbursement policies, alternative ways of reim-bursing dental providers will be studied, and reim-bursement incentives to promote alternative ways ofdelivering dental care will be evaluated.

Long-term developments: State, regional, and na-tional data banks will pool useful information pro-vided by governmental agencies, purchasers of carein the private sector, fiscal intermediaries, and indi-vidual dental practices. Health services researchers

will thus have immediate access to on-line data, in-cluding utilization rates, service mix, and costs, forevery conceivable combination of providers, popu-lation groups, and payment sources. Analysis of thisinformation will be used to influence decisions ofproviders and payers and to improve understandingof the functioning of the dental delivery system. Forexample, by examination of differences and similar-ities in dental practice patterns, it will be possible forconsensus on standards of care for general and spe-cialty practice to be developed.

There will be movement toward adopting more ex-perimental designs in lieu of survey methods in con-ducting health services research. Cause-and-effectrelationships between variables will thus be devel-oped by the assigning of subjects to alternative treat-ment interventions and control groups. For example,it will be possible to determine the efficacy of variousquality assurance systems by randomly assigningdental practices within a capitation or fee-for-servicenetwork to alternative interventions. The ability ofdifferent systems to detect and correct quality of caredeficiencies will then be assessed.

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