title: The amount of care delivered: challenges of indices in oral health studies.
abstract: Untreated dental caries is the most prevalent medical condition worldwide, with considerable variations in prevalence between regions and countries. The care index (CI) and the restorative index (RI) are generally used to make comparisons between and within countries of levels of care delivered. However, several methodological challenges can be identified that limit the interpretation and comparison of these indices. The objective of this manuscript was to evaluate these challenges and to provide solutions.
  
  
  
  Five challenges were identified: (i) the comparability of CI and RI, (ii) the use of multiple definitions of CI and RI, (iii) CI and RI measured for surfaces or teeth, (iv) the skewness of F/D(M)F (restored teeth or surfaces as a fraction of the total number of decayed, (missing), and filled teeth or surfaces), and (v) the relationship between CI, RI and D(M)F. Time-series data were obtained - for people aged 25-44 years with low socioeconomic status - from four cross-sectional studies performed in 1995, 2002, 2007 and 2013 in the Netherlands, and those data were subjected to descriptive analyses.
  
  
  
  The analyses showed that the choice of index and definition had a major impact on the results, which varied in terms of absolute size and trends. Moreover, CI and RI are expressed as mean scores, but the distributions of F/DMF and F/DF were highly skewed. CI and RI may therefore mask groups of individuals who still need care. The proportion of individuals receiving most restorative care was much higher in the group with low levels of caries than in the groups with more caries. This implies that, when the need for care decreases over time, the restorative care indices can be expected to increase, even though there may be no improvement in the amount of care delivered.
  
  
  
  We argue that epidemiological studies of oral health in the future should clarify the definitions used to describe the care delivered and investigate subgroups of F/DMF or F/DF in categories based on the extent of caries. These figures could be used to monitor changes in treatment provision and to highlight inequalities in the provision of care.
authors.affiliation: Department of Child Health, TNO, Leiden, The Netherlands.
authors.forename: Paula
authors.initials: P
authors.lastname: van Dommelen
authors.affiliation: Department of Child Health, TNO, Leiden, The Netherlands.|Center for Dentistry and Oral Hygiene in Groningen, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Annemarie A
authors.initials: AA
authors.lastname: Schuller
mesh_terms: D000328:Adult; D003430:Cross-Sectional Studies; D004245:DMF Index; D003695:Delivery of Health Care / Q000706:statistics & numerical data*; D003731:Dental Caries / Q000453:epidemiology / Q000628:therapy; D003793:Dental Restoration, Permanent / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D008297:Male; D015233:Models, Statistical; D009426:Netherlands / Q000453:epidemiology; D009909:Oral Health / Q000706:statistics & numerical data*; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires
keywords: DMF Index; caries; epidemiology; methodology; policymakers; public health; statistics