Dentine Fluoride as a Biomarker for Childhood F intake: Reliability

The main hypothesis of this study is that the dentine fluoride of exfoliated primary second molars is a good indicator of cumulative fluoride intake.  Appropriate collection of exfoliated teeth, dissection of the dentine and reliable measurement of fluoride content were essential first steps. 

Objectives:   To confirm the reliability of the storage and analytical techniques used to obtain dentine fluoride values.  

Methods: Exfoliated teeth from the Iowa Fluoride Study sample were collected,  catalogued and stored during the development of the fluoride evaluation technique.  Dentine was separated from the enamel using mechanical means, sectioned into 200-300 micron thick coronal dentine pieces, and subjected to micro-diffusion and fluoride electrode analysis. Teeth having more than one section available for analysis (2-4 per tooth) were used in evaluating reliability of the methodology, based upon the intra-class correlation coefficient (ICC); natural logarithm transformations were used to achieve conformance to normality assumptions. The Wilcoxon Signed Rank test was used to evaluate the possibility of systematic differences in dentin F between the first and second samples of a given tooth.  A 0.05 level of significance was used. 

 Results:   A wide range of dentin fluoride values were obtained, corresponding to the large differences in fluoride intake.  Reliability assessment based on measurement of the first two sections taken, representing the best physical samples, showed an excellent (ICC=0.977) and highly significant (p<0.0001) level of agreement.  There was no evidence of any systematic difference in dentin F measurement between the first and second samples (p=0.40, Wilcoxon Signed Rank test).  Evaluation of reliability based on all 52 sections from 22 teeth yielded a similar result:  ICC= 0.967 (p<0.0001), again indicating excellent levels of reliability. 

Conclusion:   Collection, storage, sectioning, micro-diffusion and ion-specific electrode analysis of replicate samples yielded excellent reliability.