EVALUATING THE VALIDITY OF PROBING ATTACHMENT LOSS AS A SURROGATE FORTOOTH MORTALITY IN A CLINICAL-TRIAL ON THE ELDERLY

Most periodontal trials are based on the assumption that the superior treatment, as judged by short-term intangible changes in probing attac hment levels (the surrogate), is also the treatment most likely to aff ect tooth mortality. This assumption is valid if: (1) the surrogate is informative about tooth mortality, and (2) the surrogate captures a s ubstantial proportion of the treatment effect on tooth mortality (e.g. , > 50% or 75%). The goal of this study was to evaluate whether both c onditions were satisfied in a randomized controlled trial (RCT) of eld ers at high risk for dental diseases. The results suggested that the f irst condition for a valid surrogate was satisfied: Both one- and two- year changes in probing attachment level were informative about tooth mortality risk. A 1-mm loss measured over a one-year period was associ ated with a 56% increased tooth mortality risk (relative risk= 1.56; 9 5% confidence interval, 1.08 to 2.26; p = 0.017); a 1-mm loss measured over a two-year period was associated with a 102% increased risk for tooth mortality (relative risk = 2.02; 95% confidence interval, 1.26 t o 3.25; p = 0.004). The second condition necessary for a valid surroga te could not be confirmed in the present trial. With 95% confidence, i t was concluded that one-year changes in probing attachment level meas urements did not capture a significant proportion of the treatment eff ect (point estimate, 6%; 95% confidence interval; -38% to 53%). No use ful statements could be made regarding the proportion of treatment eff ect captured by two-year changes, due to the width of the confidence i nterval (point estimate, 18%; 95% confidence interval; -151% to 140%). It is concluded that (1) the evidence surrounding the one-year change in probing attachment level indicates that it can be ruled out as bei ng anything more than a weak surrogate marker for tooth mortality, and (2) further research is required to study the validity of two-year ch ange in probing attachment level as a surrogate marker. Due to charact eristics of the population and the treatments investigated, the genera lizability of these findings to other RCTs is questionable.