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RESEARCH REPORT |
1 Centers for Disease Control and Prevention/Division of Oral Health/Surveillance, Investigations, and Research Branch, 4770 Buford Highway, MSF10, Chamblee, GA 30341, USA; and
2 School of Industrial and Systems Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0205, USA;
* corresponding author, sig1{at}cdc.gov
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: root caries • incidence • increment
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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Very few public dollars are allocated to adult dental disease. Dental care is one of the few health areas not covered by Medicare (US Government program that covers medical costs for adults over age 65 years), and only a limited safety net exists to provide dental care to low-income adults. Medicaid frequently covers only emergency dental care for adults; approximately 15% of state Medicaid programs (US program funded by Federal and state governments that covers medical costs for the poor) provide no adult dental benefits, and approximately 45% cover only tooth extraction and emergency services (Oral Health America, 2003). With the exception of water fluoridation, virtually all community prevention programs target children and youth (Association of State and Territorial Dental Directors and Centers for Disease Control and Prevention, 2002). As a result, decay among adults is more likely to remain untreated; the mean number of untreated decayed surfaces among American adults (1.8) (Winn et al., 1996) is about 4 times that among US schoolchildren (0.4) (Kaste et al., 1996).
Documenting the burden of root caries is important, because this condition can be prevented and/or arrested in its early stages with fluorides, and such early preventive treatments have been shown to lower overall treatment costs (US Department of Health and Human Services, 2000; Leake, 2001). In this study, we systematically reviewed published studies of root caries incidence (the proportion of population developing caries in at least 1 root surface), root caries increment (the mean number of root surfaces becoming decayed or filled per person), and root caries attack rate (proportion of root surfaces at risk for caries [i.e., sound, exposed], which developed caries). We also estimated the total caries increment (root plus coronal) by analyzing data from studies that presented both root and coronal caries increments.
One previous study has summarized the findings of 5 North American studies on new root caries (Leake, 2001). Our study adds the findings of 6 studies conducted among populations living in advanced market economies and uses different assumptions on how to adjust for negative reversal and to derive annual estimates of incidence. Our study also differed from the earlier one in its use of standard meta-analysis methods to derive summary statistics, its use of a random-effects model, and its use of a test for heterogeneity to determine if study outcomes should be pooled.
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METHODS |
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Data Abstraction
Each of the authors pilot-tested an abstraction form developed for this project (Appendix Table 1). We abstracted the same article and met to discuss and compare our findings. Because all reviewers agreed on the reported means and variances of the measures of new caries, we divided the authors into two review teams.
We sorted articles by location and assigned all articles with the same location to the same team to make sure that we were not double-counting some populations that may have appeared in more than one article. After each team member independently abstracted the assigned article, the team completed a consensus abstraction form.
Inclusion Criteria
We included studies conducted after 1980 with populations aged 45 yrs and above and that reported or contained sufficient information for a variance to be calculated. We also tried to exclude populations with characteristics that would not be similar to those of the general US population (i.e., we excluded findings from among special populations with diseases/conditions such as cancer or decreased salivary flow, those who were institutionalized, or those who were exposed to caries-prevention regimens other than fluoride toothpaste and fluoridation). We also excluded studies lacking evidence that informed consent had been obtained from subjects and/or that approval had been obtained from an Internal Review Board. Eleven studies met our inclusion criteria (Appendix Table 2). We also examined the validity of each study based on whether the study population was randomly selected and examiners were calibrated (Appendix Table 3).
Data Adjustment
We reported outcome measures for the shortest study to minimize potential bias resulting from the attrition of study subjects. In some of the studies, individuals who dropped out had significantly higher levels of disease at baseline. For studies reporting caries increment or attack rate for periods greater than 1 yr, we assumed that the outcomes measured were independently and identically distributed for each yr; thus, we calculated the annual value by dividing the reported measure by the number of yrs in the reported interval and estimated the standard error for these values by dividing the reported standard error for the interval by the square root of the interval in yrs.
To estimate annual incidence, we calculated the probability that no disease was incurred over the study interval and then took the nth root of this value (where n represents number of yrs in the study) to calculate the probability that no disease was incurred in a given yr. We subtracted this value from 1 to obtain the annual incidence.
Some studies reported separate results for specific groups. For these studies, we estimated the outcome measure for the entire study population by taking the weighted average for specific groups and calculating the associated standard error according to the following formula:
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We excluded studies that reported increment or attack rate but did not report the variance, standard deviation, or standard error for that rate. For studies reporting incidence rates without the standard errors for these rates, we calculated the standard error according to the following formula:
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To make the findings of studies that adjusted for negative reversals more comparable with the results of studies that did not, we also, when possible, reported estimates of new disease that did not subtract out negative reversals.
Analysis
For each study, we calculated the 95% confidence interval for the outcome measure of interest (root caries incidence, root caries increment, root and coronal caries increment, and root caries attack rate). We used a random-effects model (Der Simonian and Laird [hereafter referred to as DSL]; Normand, 1999) to estimate summary measures and their 95% confidence intervals across all studies. Thus, in the absence of heterogeneity, our summary measures should be generalizable to other populations meeting our inclusion criteria.
We tested for heterogeneity among outcome measures with a chi-square test (QW) (Normand, 1999). To identify potential sources of heterogeneity, we examined the Pearson correlation coefficients between each root caries measure and the population’s baseline risk (as measured by mean number of decayed and filled root surfaces at baseline, mean number of exposed root surfaces, and mean number of teeth; Appendix Table 4, the population’s baseline age, and study design characteristics (as measured by study length, and whether the study subtracted out negative examiner reversals; Appendix Tables 4 and 5).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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). For the 6 studies meeting the validity criteria, the DSL summary annual estimate was 20.7% (95% CI, 13.4–28.0%), and for the 6 US studies, it was 25.8% (95% CI, 17.9–33.7%). Among US studies, the lowest incidence rate was 14.1% in North Carolina. Because heterogeneity was present, the summary measures should be interpreted with caution. Incidence increased with age; thus, age may have been one source of heterogeneity (Appendix Table 4).
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). For the 7 studies meeting the validity criteria, the DSL summary estimate was 0.47 surfaces (95% CI, 0.32–0.62), and for the 6 US studies it was 0.49 surfaces (95% CI, 0.38–0.60). Again, we could not reject the null hypothesis of homogenous means when we included non-US studies in the summary measure calculations. Among US studies, however, we could reject the null at the 5% level of significance but not at the 10% level.
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Seven studies reported total annual caries increment (root plus coronal caries increment) (Fig. 3). Findings ranged from 0.84 surfaces (Canada) to 1.63 surfaces (Florida), and the DSL summary measure was 1.31 surfaces (95% CI, 1.01–1.61 surfaces). Of the 6 studies meeting the validity criteria, the DSL summary measure was 1.32 surfaces (95% CI, 0.97–1.66 surfaces). Of the 4 US studies, the lowest total annual caries increment equaled 1.12 surfaces (North Carolina), and the DSL summary measure was 1.39 (95% CI, 1.16–1.63 surfaces). We could reject the null hypothesis of homogenous means at the 5% level of significance for all combinations of studies; for the US studies, however, we could not reject the null at the 2.5% level of significance.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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The results of this systematic review were, in some instances, markedly different from those reported at the Consensus Development Conference (Leake, 2001) because of differences in underlying assumptions. For example, using our methodology to estimate summary incidence for the NIH study population, we estimated that incidence to be almost twice as high (15.3% vs. 8.2%). The main reasons for the discrepancy were that we included only adults aged 45 and above, used the shortest study interval rather than the longest, and, when possible, reported unadjusted or crude findings.
We believe that using the shortest study duration reduces sample bias, because study subjects at highest risk are more likely to drop out (an occurrence especially likely among the elderly). For example, in the North Carolina study, subjects who dropped out of the study between the third- and fifth-year examinations had significantly higher rates of caries incidence over the first 3 yrs than those who did not (Lawrence et al., 1996). In the Iowa study, most of the subjects who dropped out between 18 mos and 3 yrs did so because of severe illness or death, and those who dropped out had significantly higher caries increments during the first 18 mos of the study (Hand et al., 1988a). We also suspect that annualizing incidence may be problematic, because distortions attributable to annualization may become more pronounced as the study duration increases if the probability of developing caries is positively correlated with the probability of having developed caries in previous periods (i.e., recurrent caries within the person). For example, consider a two-year study consisting of two subjects, A and B, in which A developed new caries in both years and B developed caries in neither year. If the incidence of caries was measured separately for each year, the incidence for each year would equal 50%, whereas if the incidence was measured from baseline to the end of the second year and was annualized by being divided by the number of study years, it would equal only 25%. Although studies with longer intervals are less likely to capture recurrent caries at both the person and tooth levels, the problem is more pronounced for incidence measures, because recurrent caries on the same tooth will underestimate both incidence and increment, whereas new caries on a different tooth within the same individual will underestimate only incidence.
We also believe that crude estimates may provide better estimates of new caries than do estimates that net out negative reversals. Beck et al.(1995) argue that as baseline caries prevalence increases, the probability of examiner reversals increases and the probability of examiner increments decreases. Thus, they propose a prevalence-based adjustment for examiner reversals—multiply the crude increment by the complement of the number of reversals divided by baseline frequency. With Beck’s adjustment as the gold standard, the percentage deviation from the true value is higher when netting out negative reversals as compared with the crude method. Beck et al.(1995) found that, relative to the adjusted increment, the crude method overestimated the root caries increment by 10%, while netting out negative reversals underestimated it by 38%. Slade and Caplan (2000) found that, for root caries increment and attack rate, estimates from the crude method overestimated those obtained with the adjusted method by approximately 21%, while net estimates underestimated adjusted values by approximately 45%.
In conclusion, we found that the annual root caries increment and root + coronal increment were 0.47 and 1.31 surfaces, respectively. A review of studies conducted in the late 1970s and 1980s among children aged 5 to 15 yrs found that, among children living in fluoride-deficient communities, the mean annual coronal caries increment was 1.4 surfaces, and among children living in fluoridated communities, it was 0.8 surfaces (Garcia, 1988). Thus, older adults may experience similar or higher levels of new caries than do schoolchildren, the primary recipients of caries-prevention programs.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Received November 24, 2003; Last revision April 30, 2004; Accepted May 28, 2004
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REFERENCES |
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