Introduction and objectives
Dental caries is a chronic, cumulative disease which affects nearly every individual in New Zealand; however, no studies have investigated longitudinal patterns of caries experience to show how this disease progresses over time at the population level. Furthermore, disparities in the experience of dental caries experience across the social classes are significant, pervasive, and relevant to public health policy. Thus, the objective of this research was to identify and describe developmental trajectories of caries experience in the permanent dentition to age 32, if present, and to explore the ways in which these trajectories may help in investigating and explaining social class disparities in caries experience.
Method
Longitudinal caries data from participants (males and females) in a longstanding birth cohort study, the Dunedin Multidisciplinary Health and Development Study, were used in primary analysis in this Study. The Dunedin Multidisciplinary Health and Development Study is a longstanding study of health and development in a complete cohort of Dunedin-born males and females. New dental data were collected when the Study members were aged 32 years of age; however, Study members had also previously received dental examinations at ages 5, 9, 15, 18, and 26 years. Data on Study members’ social status, education, income, and related measures were also collected at several points through their lives.
Cumulative DMF scores and DMF increment scores were calculated, and social class differences in the experience of dental caries and tooth loss were investigated. The primary analysis was based upon the DMFS data collected in the Study, and was conducted using a longitudinal latent class analysis technique called Group-Based Trajectory Analysis, based in the SAS macro program PROC TRAJ, a specialised mixture model that estimates means for multiple groups within a population. Using this approach, Study members were assigned to 3 distinct groups on a maximum likelihood basis, (based on their dental caries experience patterns over time), giving distinct trajectories of dental caries experience. The nature of these trajectories and their determinants and consequences were then investigated, with particular emphasis upon their social determinants and consequences for oral-health-related quality of life.
Results
Data from a total of 955 Study members was included for the trajectory analysis in this study. By the time they had reached age 32 years, the prevalence of dental caries experience was 96.8%, and 22.8% of Study members had lost a tooth due to dental caries. The overall mean DMFS (Decayed, Missing, and Filled Surfaces) score had reached 16.5 at age 32 years, having accumulated since the age 5 years assessments, when the mean DMFS score was 0.0.
Three distinctive trajectories of caries experience were identified; these were categorised as “high” (~15%), “medium” (~43%), and “low” (~42%) trajectories of DMFS scores. All three trajectories showed a relatively linear increase in DMFS with age; however, the two higher trajectories were more ‘S-shaped’ and were linearised following adjustment for the number of unaffected surfaces remaining at each age.
The trajectories which individuals followed was highly associated with socio-economic status (SES), both for childhood SES and SES in adulthood. Individuals of low SES were more likely to have trajectories with high rates of decay, while, for those of high SES, trajectories with low rates of dental caries were more common.
Conclusions
The outcomes of this study suggest that:
(1) among individuals following a similar caries trajectory, caries rate is relatively constant across time;
(2) social disparities in dental caries experience exist and are important;
(3) dental caries trajectories are important in the development of those social disparities; and
(4) social disparities in dental caries trajectories appear to affect oral health-related quality of life.
