FL: Fluoride Exposure in the US (2010)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To quantify the diffused benefits of water fluoridation from fluoridated communities to non-fluoridated communities. 

Inclusion Criteria:
  • Children from the National Survey of Oral Health in US School Children: 1986-1987
  • Child's exposure to alternative fluoride sources could be determined
  • All past residences were on a public water system
  • Child's residence history could be determined
  • The date at which fluoridation began in the public water system could be determined
  • The child's age was consistent with the total number of years at listed residences
  • The child had at least one permanent tooth
  • The child was at least six years old and no older than 17 years
  • The sample of the school's water supply was ≤4ppm.
Exclusion Criteria:
  • Did not meet inclusion criteria
  • Parents did not answer questionnaire
  • Parents could not list all previous residences
  • Parents could not definitively indicate whether the child received fluoride drops or tablets, participated in a school fluoride program or received a fluoride treatment at dental office. 
Description of Study Protocol:

Recruitment

Data from the National Survey of Oral Health in US School Children: 1986-1987 containing oral health data on 40,693 US school students in grades K-12.

Design

Cross-sectional analysis of relationship between various direct and indirect fluoride sources and decayed, missing and filled permanent tooth surfaces.

Blinding used

As this was an analysis of an existing data set, authors were blinded as to measures and outcomes.

Intervention

None

Statistical Analysis

Multiple linear regression

Data Collection Summary:

Timing of Measurements

1986-1987

Dependent Variables

Number of decayed, missing and filled permanent tooth surfaces

Independent Variables

  • Years of fluoride exposure (years child lived in residence with fluoride content ≥0.7ppm)
  • Lifetime fluoride exposure: High (≥50% of their life in residence with fluoride exposure≥0.7ppm) vs. low (<50% of their life in residence with fluoride exposure≥0.7ppm) 
  • Average annual diffusion exposure: Based on estimate of exposure based on "state coverage" (percent of communities with optimal fluoride exposure based on Fluoridation Census in the 1970s and 1980s) and adjusted for residences in that state and time at residences: Categorized into high, medium and low diffusion exposure
  • Age
  • Sex
  • Race
  • Whether child received fluoride drops (yes/no)
  • Whether child received fluoride tablets (yes/no)
  • Whether child received fluoride treatment at dentist office (yes/no)
  • Whether child received fluoride treatment in a school program (yes/no).

Control Variables

All variables entered into model along with significant (P<0.01) interactions.

Description of Actual Data Sample:
  • Initial N: 40,693 children
  • Attrition (final N): 18,507 children
  • Age: Six to 17 years
  • Ethnicity:
    • White: 64.85%
    • Black: 17.64%
    • Hispanic: 13.35%
    • Other: 4.19%
  • Other relevant demographics: None
  • Anthropometrics: None reported
  • Location: US.
Summary of Results:

Diffusion exposure was significantly associated with two other the predictor variables:

  • Years of fluoride exposure (P<0.05): where years of fluoride exposure was lowest in the low diffusion group (M=1.51, SE=0.51), followed by the medium fluoride exposure group (M=5.63, SE=0.94), with the highest years of fluoride exposure in the high diffusion exposure group (M=8.32, SE=0.71)
  • Race (P<0.01).

Multivariate analysis

The following predictors were significantly associated with the number of decayed, missing and filled permanent tooth surfaces:

  • Years of fluoride exposure (P=0.025, = -0.12)
  • Age (P<0.001, =0.78)
  • Diffusion exposure (medium compared to low: P=0.02, =0.90; high compared to low: P=0.035, =0.83)
  • Race (other compared to white: P=0.033, = -1.4)
  • Sex (male, P=0.001, =0.82)
  • Whether the child had fluoride sealant (P=0.006, =1.17)
  • Whether the child received fluoride tablets (P=0.002, =1.08)
  • Whether the child received fluoride treatment from a dentist (P<0.001, = -1.13)
  • Whether the child received fluoride from a school program (P=0.034, = -0.88).

The model also included the following significant interactions:

  • Age x diffusion level
  • Age x race (other)
  • Age x sex (male)
  • Age x use of sealant
  • Years of fluoride exposure x use of fluoride drops
  • Age and years of fluoride exposure x use of fluoride tablets
  • Age x fluoride from a dentist.

Lifetime Fluoride Exposure by Diffusion Exposure

In order to get a clearer estimate of the effect of diffusion of fluoride the authors examined the difference in lifetime exposure to fluoride by diffusion exposure categories in children who were not exposed to fluoride in other ways (e.g., sealants, tablets, drops, treatments by dentist and at school, adjusting for age). The report the following mean number of decayed, missing and filled permanent tooth surfaces:

Diffusion Exposure Category Lifetime Fluoride Exposure
  Low High
Low 4.06 2.62
Medium 3.36 2.62
High 2.89 2.93

The results indicate that the mean number of decayed, missing and filled permanent tooth surface areas decreased for children in with higher diffusion exposure, but only for those children who lived less than half their life in well fluoridated areas. In short, holding other forms of fluoride exposure constant, children who have an overall lower lifetime exposure to optimally fluoridated water benefit from diffused exposure to fluoride.

 

Author Conclusion:

In summary, US children residing in non-fluoridated areas with low diffusion exposure in 1986-1987 experienced higher levels of dental caries than did children living in fluoridated communities or children living in non-fluoridated areas with high diffusion exposure. 

Funding Source:
Government: Centers for Disease Control and Prevention
Reviewer Comments:

Strengths

  • National sample
  • Large sample size
  • Controlled for a number of different fluoride sources.

Weaknesses

State coverage, the variable instrumental to the estimation of the diffusion effect of fluoride is both a very crude measure (ignoring that diffusion can be quite different within different areas of a state) and is based on the Fluoride Census (a data source known to be inaccurate). Thus, while the authors demonstrate that there likely exists a benefit of diffused fluoride, their estimates are unlikely to be accurate for any particular child or community.

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) N/A
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) N/A
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) Yes
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? No
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? No
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? N/A
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? No
  7.5. Was the measurement of effect at an appropriate level of precision? No
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes