Drawing causal inferences in epidemiologic studies of early life influences.

Observational studies can describe associations between early life exposures and subsequent outcomes in human populations. It is challenging to draw causal inferences from these associations because exposures often occur many years before the outcome and are related to other early life exposures. An approach is required that combines traditional epidemiologic and statistical principles with the use of novel and sophisticated analytic methods. To minimize the bias in longitudinal studies of early origins, researchers need to do all they can to reduce losses to follow-up and to describe individuals who are lost to follow-up. To reduce the role of chance, researchers should concentrate on effect sizes and the strength of the evidence to support these effect sizes, and they should be cautious in their interpretation of subgroup analyses. More complex analytic approaches can and should be used to handle missing data and repeated measurements. Addressing the issue of confounding is not straightforward. Statistical adjustment for the confounders measured in a study may help, but a lack of attenuation does not guarantee that the association is not confounded. Ecologic studies, observational studies in populations with different confounding structures, and the follow-up of randomized trials (where these exist) can be informative. Genetic and nongenetic instrumental variable approaches (eg, Mendelian randomization) may also provide causal insights. These approaches to confounding often require the comparison of data from different populations or a combination of studies to ensure adequate power to provide robust estimates of the causal effect.

Energy absorption and hardness of chair-side denture soft lining materials.

The purpose of this study was to evaluate the hardness and energy absorption properties of four commercially available chairside silicone denture soft lining materials and to compare their properties with those of a heat-polymerized silicone denture liner. The denture lining materials investigated were four auto-polymerising silicone soft liners (GC Reline Soft, Ufigel SC, Elite Soft Relining and Tokuyama Sofreliner S) and a heat-polymerised silicone liner (Molloplast B). The soft liners were processed according to manufacturers' instructions. The specimens for hardness testing were 38 x 38 x 3 mm. The specimens for energy absorption test were 10 x 10 x 3 mm. In each test ten samples of each material were tested. There was strong evidence that Tokuyama Sofreliner S and, to a lesser extent, Ufigel SC, were less stiff and more resilient than Molloplast B. There was also strong evidence that both GC Reline Soft and Elite Soft Relining were harder than Molloplast B, while Ufigel SC and Tokuyama Sofreliner S were softer In conclusion differences existed between hardness and energy absorption properties of the soft lining materials.