摘要：Objectives. We assessed the relative influences of age, period, and cohort effects on trends in caries experience of permanent teeth in 4 different populations. Methods. We used data from England and Wales, United States, Japan, and Sweden in which numerous cross-sectional, nationally representative surveys have been conducted periodically since the early 1960s. For each country, trends in caries experience (measured by DMFT index—the number of decayed, missing, and filled permanent teeth) were analyzed in an age, period, and cohort (APC) analysis using partial least square regression. Results. A strong effect of age manifested in caries experience, period and cohort effects aside. Caries levels increased through to adolescence; thereafter, there was a larger increase in DMFT in adulthood. Compared with the aging effect, period and cohort effects on caries experience were small. Population DMFT scores decreased over time in all countries except Japan. Cohort effects on caries experience displayed a nonlinear pattern in all 4 countries, with slightly lower caries levels among the oldest and most recent generations. Conclusions. Despite marked recent declines in caries among children, caries levels increase with age and remain problematic in adults. Dental caries is the single most prevalent chronic condition in the world, affecting slightly more than a third of the world’s population. 1,2 Dental caries rates in children have declined dramatically in the past 30 years in most industrialized countries. 3 Therefore, it was assumed by planners that the decline in children would affect all age groups and caries could become a minor dental health problem when the post-1970s cohorts get older. That assumption was not based on a rigorous analysis of the relative influences of age, period, or cohort effects on caries trends. It is a well-established finding that caries increases as people age. Observational population-based studies indicate that most caries occurs in adulthood and not in children. In the best longitudinal study of dental caries to date, with several oral examinations through the first half of life and high participation rates, caries progressed inexorably in most participants of the Dunedin study (New Zealand) from age 5 years to 38 years, despite wide scale free access to dental care and preventive measures in childhood and adolescence. 4–6 Despite the widely known facts that caries increases as people age, there has never been a detailed analysis of whether the changes in caries levels were more closely related to chronological age, period (year at examination), or cohort (year of birth). The outcome of such an analysis has implications for setting targets and choosing preventive strategies. Age, period, and cohort effects all refer to some type of time-related variation in the outcome of interest, but they carry distinct substantive meanings. 7 Age effects refer to variation associated with different age groups; whether caries risk is greater at younger ages. Thus, age effects reflect the biological and social processes of aging internal to individuals and represent developmental changes across the life course. Period effects refer to variation over time periods or calendar years that affect all age groups simultaneously. For example, dental caries is less likely to occur after a particular event (such as the wide scale use of fluoride toothpaste since the early 1970s) that affects everybody irrespective of age. Lastly, cohort effects refer to variation among groups born in different years. For example, individuals born in Japan during the Second World War were less likely to develop caries during childhood because of food rationing, which included low exposure to sugars. 7,8 A clear distinction between age, period, and cohort influences has important implications for both theory and policy. Consistent age variations in a health outcome across time and place reflect the developmental nature of true age changes within individuals. On the other hand, period and cohort effects reflect the influences of social forces. Period variations often result from shifts in social, historical, and cultural environments. Cohort variations may reflect the effects of early life exposure to environmental, socioeconomic, and behavioral factors that act persistently over time to produce differences in life course health outcomes for specific cohorts. 9,10 Therefore, analyses that distinguish between the 3 influences should provide a better understanding and help identify the underlying social and environmental factors that are amenable to modification. 7 Although only a longitudinal panel study design provides data from true birth cohorts that follow exactly the same individuals over time, the synthetic cohort approach, if based on census data or repeated national representative sample surveys, allows for the classic age-period-and-cohort (APC) analysis that traces essentially the same groups of individuals from the same birth cohorts over a segment of the life span. 7 Therefore, we hypothesized that age effects on caries experience in permanent teeth would be stronger than period and cohort effects. In other words, despite improvements in caries levels seen in recent years (period effects) and in new generations (cohort effects), levels of dental caries increase from childhood to adulthood (age effects). To test that hypothesis, we assessed the relative influences of age, period, and cohort effects on trends in caries experience of permanent teeth in 4 different populations.
