Fluoride: From Nutrient to Suspected Neurotoxin.

The recollections of a former public health officer and research scientist who maintained good relations with both pro- and anti-fluoridationists over the course of a 60-year career in which fluoride has gone from being a "nutrient" to a suspected neurotoxin.

Short term serum pharmacokinetics of diammine silver fluoride after oral application.

BACKGROUND: There is growing interest in the use of diammine silver fluoride (DSF) as a topical agent to treat dentin hypersensitivity and dental caries as gauged by increasing published research from many parts of the world. While DSF has been available in various formulations for many years, most of its pharmacokinetic aspects within the therapeutic concentration range have never been fully characterized. METHODS: This preliminary study determined the applied doses (3 teeth treated), maximum serum concentrations, and time to maximum serum concentration for fluoride and silver in 6 adults over 4 h. Fluoride was determined using the indirect diffusion method with a fluoride selective electrode, and silver was determined using inductively coupled plasma-mass spectrometry. The mean amount of DSF solution applied to the 3 teeth was 7.57 mg (6.04 µL). RESULTS: Over the 4 hour observation period, the mean maximum serum concentrations were 1.86 µmol/L for fluoride and 206 nmol/L for silver. These maximums were reached 3.0 h and 2.5 h for fluoride and silver, respectively. CONCLUSIONS: Fluoride exposure was below the U.S. Environmental Protection Agency (EPA) oral reference dose. Silver exposure exceeded the EPA oral reference dose for cumulative daily exposure over a lifetime, but for occasional use was well below concentrations associated with toxicity. This preliminary study suggests that serum concentrations of fluoride and silver after topical application of DSF should pose little toxicity risk when used in adults. CLINICAL TRIALS REGISTRATION: NCT01664871.

The use of minimization in clinical trials.

Since its introduction in 1974 the use of the term Minimization has been broadened to include other algorithms. All algorithms use patient characteristics to determine the assignment that produces the best overall balance between treatment groups. They differ in whether or not they use all of the data from each previously assigned subject to assign subsequent subjects so the methods are classified as complete or partial minimization. PubMed, Citation Index and Cochrane searches determined the frequency of articles using these types of minimization and a subset was selected for detailed review regarding the adequacy of the usage and reporting of minimization. In the past 10 years usage has increased three fold over the previous decade but is still less than 2% of clinical trials. None of the studies makes maximum use of minimization and they are not following good reporting practices. Concerns about the use of minimization have involved selection bias and statistical analysis. Several modifications to minimization are suggested to reduce the possibility of selection bias so that adding randomization will rarely be required. Separating primary and secondary analyses can avoid the statistical problems that minimization poses. The two types of analyses are distinguished by opposite limiting signs, providing reliable, simplified statistical results. This will improve data utilization and make clinical trials more reproducible. Minimization should be the method of choice in assigning subjects in all clinical trials.

Rank-Minimization for balanced assignment of subjects in clinical trials.

Minimization (M) is the most popular algorithm for balancing large numbers of subject variables in treatment groups of small clinical trials. However, its use has been limited because of its complexity, vulnerability to selection bias and lack of a generally accepted method for statistical analysis of the data. Rank-Minimization (RM) is a promising new algorithm. It is less complex since it does not require unique programming for each clinical trial to convert continuous to categorical variables. In this study RM is compared to M for balance of variables and vulnerability to selection bias in 1000 simulated trials using 200 subjects with 15 continuous variables. With RM there were no instances of significant imbalance to cause rejection of the null hypothesis, i.e. a Student's t> or =2, although it occurred in 0.4% of the 15000 tests for M. For moderate imbalance, i.e. 1< or = t < 2, the figures were 3% (RM) and 12% (M). The probability of guessing the next assignment was 0.636 (RM) and 0.683 (M). The smaller figure is superior to that of restricted randomization in blocks of five per treatment group. Improvement in balance, a decrease in vulnerability to selection bias and ease of application along with improvements in the statistical analysis should result in the general acceptance of RM for assigning subjects to treatment groups in clinical trials.

Optimum inorganic ion concentrations for hematopoiesis cultures.

Current limitations in the ability to culture hematopoietic cells may be due to the use of ion concentrations that reflect those in the general circulation rather than those expected at hematopoietic sites. Expected changes in calcium, phosphate and hydroxyl ion are calculated indirectly using published data. Results indicate doubling of normal concentrations for the first week, followed by 2 weeks of smaller elevations as the osteon undergoes resorption and replacement. The period of 3 weeks fits the expected time of the three stages of differentiation and proliferation of erythrocytes to the maturation phase. Mimicking the high concentrations of these ions in vitro may require the development of dynamic flow cultures because of problems with precipitation of calcium phosphate crystals. After 3 weeks 10% less than normal concentrations is expected as the bone mineral is replaced over a period of months, allowing a static system for maturation.