Periodontal Disease Prevention Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Periodontal Disease Prevention Study (NCT01584479), a registered phase not stated study. The primary outcome is Percentage of Participants With Tooth Loss Over 16 Year Period.

2. Clinical Question

The study asks whether the frequency of dental cleanings is associated with periodontal outcomes among adults classified by risk of periodontal disease progression. The primary objective focuses on patients classified as low risk; secondary objectives include patients classified as high risk.

The brief summary also describes evaluating the relationship between preventive-service frequency and periodontal outcomes, and whether risk assessment can help distinguish groups with different outcomes. Because this is a retrospective cohort study and the registry does not report a like-for-like control comparison, differences between the groups would not by themselves establish that cleaning frequency caused an outcome difference.

3. Trial Design

The Periodontal Disease Prevention Study (NCT01584479) is listed as a completed retrospective cohort study sponsored by the University of Michigan. The registry gives a study start of 2010-12, a primary completion date of 2012-03, and enrollment of 5117. It describes analysis of a large dental claims database to examine preventive-service frequency, periodontal outcomes, and risk stratification.

The registry lists four groups: low-risk and high-risk groups receiving one visit, and low-risk and high-risk groups receiving two visits. The group descriptions identify low-risk participants by absence of the listed history and risk factors, and high-risk participants by one or more of them. The labels experimental and control appear in the group names, but the record identifies this as a retrospective cohort and does not state allocation. The registry specifically notes that this is not a randomized comparison and that the arms are not a like-for-like control comparison.

The primary objective concerns the low-risk groups. The high-risk comparison is a secondary objective. The primary outcome is tooth loss over 16 years. Other listed outcomes concern dental claims, periodontal claims, periodontal surgery claims, tooth loss in relation to risk category and systemic-disease history, and evaluations for dental caries and oral cancer within risk categories. The registry lists six outcome measures and reports zero analyses. Details of the cohort-entry rules, follow-up construction, adjustment strategy, and statistical analysis plan are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

Population: See Giannobile et al 2013 manuscript included

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Participants With Tooth Loss Over 16 Year Period, measured over 16 years.

The primary endpoint is the percentage of participants with tooth loss over 16 years. The registry defines the measure as the cumulative percentage of participants with tooth loss during that period. It is therefore an event-occurrence measure: it records whether participants experienced tooth loss over the stated follow-up, rather than describing the number of teeth lost or the timing of each event.

In general, cumulative event percentages can make outcomes easier to interpret by expressing how common an event was in a defined population over a specified period. Tooth loss is a direct dental outcome, while the listed claims-based secondary measures describe service use and recorded care. These endpoints address different aspects of dental health and should not be treated as interchangeable.

The registry record does not report the primary endpoint value for any group, a between-group estimate, or an uncertainty interval. It also does not describe how tooth loss was ascertained in the claims database, how participants without complete follow-up were handled, or whether the stated 16-year period applied uniformly to the groups. Without those details and the endpoint results, the measure’s observed magnitude and precision cannot be assessed.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The record identifies a retrospective cohort approach using a dental claims database. In general, a cohort analysis compares outcomes among groups defined by exposure or characteristics, rather than assigning participants to treatments at random. Here, the groups are described by risk category and preventive-care frequency. The record does not state how the cohort was assembled, how exposure was assigned from claims, or how the timing of care and outcomes was aligned.

What does the primary measure represent?

The endpoint is a cumulative percentage: the proportion of participants recorded as having tooth loss over the stated 16-year period. A percentage is a binary-outcome summary when each participant is classified as having or not having the event during the period. This summary does not, by itself, describe when tooth loss occurred, how many teeth were lost, or whether participants had different lengths of observation. The record does not report those details or the group-specific endpoint percentages.

How should uncertainty be understood?

In general, a confidence interval expresses the range of estimates reasonably compatible with the data under the statistical model and its assumptions. A narrow interval indicates greater precision than a wide interval; neither the interval nor a point estimate establishes that an association is causal. The registry does not report a confidence interval or another uncertainty measure for the primary endpoint. There is therefore no basis in the posted results to assess precision or to distinguish a potentially small association from a larger one.

For a binary percentage, the statistical uncertainty depends on the event and non-event information and on the analysis model. In a cohort study, uncertainty estimates may also depend on how participants were selected, followed, and grouped. The registry record does not report enough analysis detail to determine which methods were used. No recalculated comparison is reported in the registry record, so there is no recalculated estimate to compare with a sponsor analysis.

What does the observational design imply?

Random assignment can help balance measured and unmeasured characteristics between groups, on average. The registry does not describe random assignment and explicitly identifies the study as non-randomized. As a general matter, observational comparisons may be affected by confounding: a characteristic can be associated with both the care received and the outcome. The named risk factors are central to the study’s risk classification, but the record does not state how classification was measured, whether additional characteristics were considered, or whether statistical adjustment was performed. Thus, the group labels alone do not establish comparability.

The record describes the low-risk comparison as the primary objective and the high-risk comparison as a secondary objective. It also lists several other outcomes, including claims-based outcomes and evaluations for dental caries and oral cancer. When multiple outcomes or comparisons are examined, the chance of at least one apparently notable result can increase. In general, a prespecified analysis plan and transparent reporting of all planned comparisons help readers interpret such results. The registry does not report a multiplicity strategy, and it reports zero analyses.

What do the planning assumptions mean?

The record describes sample-size illustrations using a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and a target effect expressed as a stated fraction of the observed effect. These are planning assumptions for illustrations, not evidence of the study’s own design choices. The record explicitly distinguishes the illustrations from the trial’s design. They should not be read as observed power: power is a design concept, whereas an observed result is interpreted through its estimate and uncertainty. The registry does not report a sample-size justification for the cohort study.

The illustrations are not a substitute for the missing endpoint analysis. Their interpretation depends on the effect used as a reference and the assumptions stated for the calculation. The registry record does not report the numerical planning results or enough details to judge whether the illustrative assumptions match the cohort’s actual data structure. In particular, the listed assumptions do not explain how risk categories, incomplete claims histories, or unequal follow-up were handled in the study.

Overall, the methods information supports identifying the study as a claims-based retrospective cohort with risk-stratified groups and a cumulative tooth-loss endpoint. It does not support reconstructing an adjusted analysis, evaluating model fit, or estimating an effect. The statistical methods actually used are not reported in the registry record.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Low Risk Experimental Group", "Low Risk Control Group", "High Risk Experimental Group", "High Risk Control Group")
n      <- c(732, 1686, 852, 1847)
events <- c(120, 233, 188, 312)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Low Risk Experimental Group  732  120  16.4  13.8  19.3  13.9  19.2  13.9  19.3
ARM  Low Risk Control Group  1686  233  13.8  12.2  15.6  12.3  15.5  12.3  15.6
ARM  High Risk Experimental Group  852  188  22.1  19.3  25.0  19.4  25.0  19.4  25.0
ARM  High Risk Control Group  1847  312  16.9  15.2  18.7  15.3  18.7  15.3  18.7

11. Multiplicity, Missing Data and Analysis Populations

The registry lists six outcome measures. The primary measure is the percentage of participants with tooth loss over 16 years; listed secondary outcomes address dental claims, periodontal claims, periodontal surgery claims, tooth loss in relation to risk category and systemic-disease history, and dental caries and oral cancer evaluations within risk categories. The primary and secondary objectives also distinguish low-risk and high-risk comparisons.

When an analysis examines multiple outcomes or comparisons, multiplicity can make isolated results harder to interpret. In general, methods such as prespecifying a primary comparison or adjusting for multiple testing can help address this issue. The registry does not report whether any such approach was used, nor does it describe a hierarchy among the secondary outcomes beyond identifying the primary objective and the secondary objectives.

The registry reports zero analyses, so it does not provide estimates with which to assess the outcome pattern or any multiplicity adjustment. Missing-data methods are not reported in the registry record. The record does not say how incomplete claims, missing risk-factor information, loss to follow-up, or participants with unavailable endpoint status were handled.

Analysis populations and inclusion or exclusion rules are also not reported in the registry record. Although enrollment is listed as 5117, the record does not describe how that enrollment relates to the analysis population for each outcome or group. No assumptions about complete follow-up, imputation, or the handling of missing observations can therefore be made from the recorded information.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The adverse-event record lists serious events and other events separately for the four risk-by-cleaning-frequency groups. For the Low Risk Experimental Group, the serious-event at-risk count is 732 and the serious events affected count is 0; the other-event at-risk count is 732 and the other events affected count is 0. For the Low Risk Control Group, those counts are 1686 and 0 for serious events, and 1686 and 0 for other events. For the High Risk Experimental Group, the counts are 852 and 0 for serious events, and 852 and 0 for other events. For the High Risk Control Group, the counts are 1847 and 0 for serious events, and 1847 and 0 for other events.

These are the recorded event counts, not a comparative safety analysis. The registry lists no serious adverse-event terms. Death counts are not reported in the registry record. Zero recorded events should not be interpreted as proof that no events occurred; the record does not explain event ascertainment, reporting completeness, or follow-up for these entries. The listed safety figures also do not address the unreported primary tooth-loss results.

13. What the Result Does, and Does Not, Mean

The record establishes that investigators intended to examine whether preventive-care frequency was associated with periodontal outcomes in low-risk and high-risk dental patients. It identifies the primary endpoint as the cumulative percentage with tooth loss over 16 years and lists additional claims-based and dental outcomes. It does not report the primary endpoint results or any statistical analyses.

Accordingly, the recorded information cannot answer whether the one-cleaning and two-cleaning groups differed in tooth loss, how large any difference was, or how precisely it was estimated. It cannot establish that the groups had the same outcomes, either. The study objectives describe questions; they are not findings.

Even if a group difference were reported elsewhere, the registry’s description of a retrospective cohort and its statement that the arms are not a like-for-like control comparison would matter to interpretation. In general, differences in participant characteristics, risk status, care-seeking, and observation can influence both exposure and outcome. The registry does not report the analytic details needed to assess whether such differences were addressed. An observed association from this design would not, on its own, demonstrate a causal effect of cleaning frequency.

The adverse-event entries report zero serious and zero other events in each group, but the record does not provide detail sufficient to treat those entries as evidence that no events occurred. The posted record is therefore informative about the intended questions, group descriptions, and outcome definitions, but not about the study’s primary outcome result or the strength of evidence for a relationship between cleaning frequency and tooth loss.

14. Why This Trial Matters Statistically

This study is statistically notable for combining a claims-based cohort design with risk stratification. The stated risk factors include history of periodontitis, smoking, diabetes, and IL-1 genetic variations. The investigators’ question is not only whether preventive-service frequency is associated with outcomes, but whether the relationship differs across the defined risk categories. That makes clear group definitions and transparent reporting of comparisons particularly important.

The primary endpoint also illustrates the distinction between an outcome and a care-utilization measure. Tooth loss is defined as a cumulative percentage over 16 years, while several secondary measures are based on dental claims or evaluations. These outcomes can answer different questions, and conclusions about one should not automatically be extended to another.

The design highlights a common challenge in clinical and health-services research: observational data can cover routine care, but groups receiving different care may not be directly comparable. Statistical adjustment can address some measured differences, but the registry does not report whether it was used or how. Without an endpoint estimate, an uncertainty measure, and methods for handling confounding and missing information, readers cannot assess the magnitude or credibility of an association.

The record also demonstrates why registrations and results serve different purposes. It describes objectives and planned outcome concepts, but reports zero analyses. The objectives help identify what investigators intended to study; they do not establish what the data showed. This distinction is essential when interpreting registry records that contain a detailed rationale but no posted outcome estimates.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

Important design and reporting details are not reported in the registry record. These include the cohort-entry criteria, the definition and ascertainment of one versus two annual cleanings from claims, the method for measuring tooth loss, the timing of outcome follow-up, and how incomplete observation was handled. Although the endpoint is described over 16 years, the record does not explain how that period was constructed for participants or how it relates to the study dates listed.

The record does not report analysis populations, adjustment methods, estimates, confidence intervals, p-values, or a statistical analysis plan. It also does not explain how the listed risk factors were obtained or classified, or whether other potential confounders were considered. The study is explicitly described as non-randomized, with allocation not stated and arms not considered a like-for-like control comparison. These features limit the interpretation of any unreported or hypothetical difference between groups.

The enrollment figure of 5117 does not show how many participants contributed to each outcome analysis, and no analysis is reported. The registry lists outcome and adverse-event information, but does not report missing-data handling or event-ascertainment procedures. As a general limitation of claims-based research, records may reflect billed or recorded care rather than every clinical event or service; the registry does not explain how this issue was addressed in this study.

Finally, the registry’s adverse-event entries do not include serious-event terms and do not report death counts. The absence of those details limits interpretation of the safety record as well as the outcome record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Periodontal Disease Prevention Study — NCT01584479.
• Registry record last updated 2015-07-09; status last verified 2015-06.
• Results first posted 2015-07-09.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

NCT01584479, the Periodontal Disease Prevention Study, is listed as a completed retrospective cohort study sponsored by the University of Michigan. The study dates are recorded as starting 2010-12, with primary completion on 2012-03, and enrollment is listed as 5117.

The study examines dental cleaning frequency in low-risk and high-risk groups using a dental claims database. Its primary endpoint is the percentage of participants with tooth loss over 16 years. The record lists six outcome measures but reports zero analyses, and it does not report the primary endpoint result.

The group descriptions compare one and two visits, but the record states that allocation was not stated and that the arms are not a like-for-like control comparison. The posted information defines the research question and outcomes, but does not establish an effect of cleaning frequency.