Preventing and Arresting Dental Root Surface Caries in Community-dwelling Older Adults: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Preventing and Arresting Dental Root Surface Caries in Community-dwelling Older Adults (NCT02360124), a randomized phase 2, phase 3 study. The primary outcome is Number of New Tooth Root Caries Lesions.

2. Clinical Question

3. Trial Design

The registry record describes a randomized, double-masked, parallel-group clinical trial, with phases listed as phase 2 and phase 3. The sponsor was The University of Hong Kong. The study started in 2012-01, reached primary completion in 2015-04, and is listed as completed. The registry enrollment is 323. The brief summary says that 300 subjects would be recruited, so the record contains both a planned recruitment figure and a separate enrollment figure.

Participants were assigned to three groups: control, silver diammine fluoride, or silver diammine fluoride with potassium iodide. The control care included individualized oral hygiene instructions and toothpaste containing 1,000 ppm fluoride. In the intervention groups, the study solution was painted onto exposed tooth root surfaces. The summary describes follow-up examinations at 6-month intervals over a 30-month trial period. It says those examinations assessed new root caries and whether active lesions found at baseline had become arrested. The registry record does not provide further details about the randomization procedure or how masking was maintained.

The outcome results list 80 participants for control, 95 for silver diammine fluoride, and 82 for silver diammine fluoride with potassium iodide. These are the group counts attached to the posted outcome means. The registry record does not explain how these counts relate to the enrollment figure, nor does it state whether the outcome counts reflect exclusions, missing follow-up, or another analytic selection. That uncertainty matters when interpreting how broadly the reported group means represent the enrolled trial population.

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.

6. Primary Endpoint

The registry lists the primary outcome as Number of New Tooth Root Caries Lesions, measured over 30 months.

The primary endpoint is the number of new tooth root caries lesions, expressed as the mean number of new carious root surfaces per participant at 30 months. The description defines a new lesion as a root surface that was sound at baseline and decayed at the evaluation examination. This endpoint therefore concerns the appearance of lesions during follow-up, rather than the status of lesions already present at baseline.

Counting new lesions gives a clinical measure of incident disease over the specified follow-up period. The registry summary also describes assessing whether active root caries found at baseline became arrested, and a secondary outcome is listed as the proportion of inactive root caries lesions. Those are distinct questions from the primary endpoint: arrest of existing lesions does not itself count as prevention of new lesions.

The outcome is reported as a mean with a standard error for each group. A mean conveys the average lesion count, while the standard error describes uncertainty around that estimated group mean. The registry record does not report the distribution of individual lesion counts, the proportion of participants with no new lesions, or an adjusted estimate for the primary endpoint. Interpretation should therefore stay focused on the posted group means and the reported unadjusted comparisons.

7. Results Posted in the Registry

• Silver Diammine Fluoride: mean 0.43 versus 1.10 on control; difference -0.67 (95% CI -1.03 to -0.31), standardized effect d = -0.58; z-test p = <0.001.
• Silver Diammine Fluoride and KI: mean 0.56 versus 1.10 on control; difference -0.54 (95% CI -0.92 to -0.16), standardized effect d = -0.44; z-test p = 0.005.

8. Statistical Interpretation

9. Statistical Methods Explained

The outcome is a count of new carious root surfaces, but the registry reports it as a continuous measure summarized by a mean and standard error. The comparisons are reported as mean differences against control. These are unadjusted comparisons in the posted results. The record lists no analyses in its analysis count, and it does not describe a statistical analysis plan or a model used to produce the posted estimates.

What does a mean difference describe?

A mean difference expresses how far apart two group averages are, with the sign depending on which group is subtracted from which. In these comparisons, negative estimates accompany lower reported means in the intervention groups than in control. The mean difference is about averages, not a guarantee that each participant's outcome moved in the same direction. A group average can also conceal variation among individuals, which is why the distribution of individual counts would be useful context. That distribution is not reported in the registry record.

What does the standard error describe?

The standard error describes the precision of an estimated mean, not the spread of individual participants' outcomes. A smaller standard error generally indicates a more precisely estimated mean under the assumptions of the analysis. It should not be interpreted as a measure of how similar participants were to one another. The posted group means are accompanied by standard errors, but the registry record does not report standard deviations for the individual outcome data. It also does not describe any modeling of the count distribution.

As a general statistical point, count outcomes can be unevenly distributed, and some participants may have more events than others. When variation in counts exceeds what a simple model assumes, over-dispersion can make model-based uncertainty too small unless the method accounts for it. The record does not say whether over-dispersion was assessed or how the outcome distribution was handled. This is a methodological uncertainty, not evidence that the posted estimates are necessarily invalid.

How should the p-values be read?

The unadjusted p-values are p < 0.001 for the silver diammine fluoride comparison with control and 0.005 for the comparison of silver diammine fluoride with potassium iodide against control. In general, a p-value measures how incompatible the observed data are with a specified null model, assuming the model and analysis conditions hold. It is not the chance that the null hypothesis is true, and it does not measure the size or practical importance of an effect. The registry record does not report a multiplicity adjustment, so the listed p-values should be understood as unadjusted rather than as results corrected across the comparisons.

What do the intervals add?

A confidence interval gives a range of estimates compatible with the data under the method used to construct it. It conveys uncertainty around an estimated difference and complements a p-value by showing the direction and range of plausible values under that method. Both reported comparison intervals lie below zero, consistent with the negative mean differences. Their endpoints are not repeated; the important point for interpretation is that neither reported interval crosses zero. The registry record does not specify the confidence level or the detailed method used to construct these intervals, so those details should not be inferred.

Randomization supports comparing groups as assigned, but the registry record does not describe the randomization sequence, allocation concealment, adherence, or an intention-to-treat analysis. It labels the trial double-masked, without saying which roles were masked or how masking was preserved. These omissions limit assessment of the procedures behind the estimates. The record reports no analyses in its analysis count and gives no analysis populations, missing-data method, covariate adjustment, or prespecified statistical model. These features should be treated as unreported rather than assumed to have followed a particular standard method.

The two active-treatment comparisons each use control as the reference. A separate comparison between the active groups would answer a different question and is not included in the registry results. Similarly, statistical significance against control does not establish equivalence or a difference between the active regimens. General interpretation of estimates should distinguish the question the comparison answers from questions it does not answer.

10. Confidence Intervals and Precision

The control mean is 1.1 new lesions, with a standard error of 0.16. The reported mean for silver diammine fluoride is 0.43, with a standard error of 0.09; its mean difference from control is -0.67. The comparison interval lies wholly below zero, and the unadjusted p-value is p < 0.001. The silver diammine fluoride and potassium iodide mean is 0.56, with a standard error of 0.11; its mean difference from control is -0.54. Its interval also lies wholly below zero, with an unadjusted p-value of 0.005.

Intervals matter because a point estimate alone does not show how much uncertainty surrounds the estimated difference. Here, both interval ranges support a negative mean difference under the reported analysis, but the registry record does not specify the confidence level or interval-construction method. The interval therefore should not be assigned an unstated confidence level or treated as capturing every source of uncertainty, including possible missing data or analysis choices.

The standard errors describe precision of the arm means; they are not standard deviations and do not tell the reader how much participants' outcomes varied. The record does not give participant-level distributions, standard deviations, or adjusted estimates. It also does not explain the difference between enrollment of 323 and the outcome group counts of 80, 95, and 82. These omissions make it difficult to evaluate precision beyond the reported estimates and intervals. The findings are more informative than point estimates alone, but their interpretation remains conditional on the analysis and the data represented in the posted results.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. They are illustrations based on the observed effect, rather than the trial's original design calculation. The listed assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, a normal approximation, and an effect to detect set at the stated fraction of the observed effect. The registry record does not report the trial's own original sample-size assumptions or justification.

For the comparison of silver diammine fluoride with control, planning for 100% of the observed effect gives 48 participants per arm for 80% power and 64 participants per arm for 90% power. Planning for 75% of the observed effect gives 85 participants per arm for 80% power and 113 participants per arm for 90% power. Planning for 50% of the observed effect gives 190 participants per arm for 80% power and 254 participants per arm for 90% power.

For silver diammine fluoride with potassium iodide compared with control, planning for 100% of the observed effect gives 82 participants per arm for 80% power and 110 participants per arm for 90% power. Planning for 75% gives 145 participants per arm for 80% power and 194 participants per arm for 90% power. Planning for 50% gives 326 participants per arm for 80% power and 437 participants per arm for 90% power.

The 80% and 90% columns describe the probability of detecting the specified effect under the planning assumptions if that effect is present and the assumed model applies. A smaller target effect requires more participants, as the planning figures illustrate. These are not observed power calculations; they are planning illustrations based on effects seen in the trial.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -0.670; pooled standard deviation σ = 1.163.
2. n = 2 × (1.96 + 0.842)² × 1.163² / -0.670² = 47.3, rounded up to 48 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -0.67                      # observed difference in means
sigma <- 1.16332441710039                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(2360124)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 48 (80% power), 64 (90% power)
 75% of observed effect: n per arm = 85 (80% power), 113 (90% power)
 50% of observed effect: n per arm = 190 (80% power), 254 (90% power)
power.t.test: 48.3 
Simulated power at n = 48 per arm: 0.798 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry record lists two outcome measures and one secondary outcome, described as the proportion of inactive root caries lesions. It posts comparisons of each active-treatment group against control for the primary outcome. The record does not report a direct comparison between the active groups, nor does it describe a prespecified hierarchy among outcomes or comparisons.

The two p-values are identified as unadjusted. The registry record does not state whether multiplicity was considered in the trial's analysis plan or whether any adjustment was performed outside the posted results. When several outcomes or comparisons are examined, the chance of at least one apparently unusual result can increase; as a general statistical matter, prespecifying the primary question and any adjustment strategy helps readers interpret that possibility. No such strategy is reported, so the posted p-values should not be described as multiplicity-adjusted.

The registry analysis count is zero, and no analysis population is specified. Although group counts accompany the outcome means, the record does not explain how participants were selected for those analyses, how missing observations were handled, whether all randomized participants were included, or whether analyses followed randomized assignment. The enrollment figure is 323, while the outcome group counts are 80, 95, and 82. The record does not reconcile these counts. It would be inappropriate to infer that the difference represents a particular amount of loss to follow-up or a specific exclusion process.

The record also does not state whether the primary comparison was adjusted for baseline values or other covariates, whether any interim analysis took place, or whether the analysis was prespecified. These are not details that can be recovered from the posted summary results. Their absence limits evaluation of the risk of selective analysis and the suitability of the reported uncertainty calculations. It does not, by itself, establish that the analyses were inappropriate; it means the registry record does not allow those questions to be resolved.

14. 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 serious adverse event figures list 108 participants at risk in control, 107 in the silver diammine fluoride group, and 108 in the silver diammine fluoride and potassium iodide group. The reported serious-event count is zero in each group. The other adverse event count is also zero in each group, using the same at-risk counts. No serious adverse event terms are listed.

These figures describe the safety entries in the registry record and should not be read as proof that no event could have occurred. They are limited to the groups, event categories, and counts posted. The at-risk counts differ from the group counts reported for the primary outcome; the record does not explain the difference. Death counts are not reported in the registry record. The safety entries do not provide event definitions, follow-up-specific detail, severity grading beyond the serious-event category, or a narrative account of ascertainment. They therefore offer a limited account of reported events, not a complete description of all possible harms.

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

The posted primary-outcome means are lower in both intervention groups than in control at the 30-month assessment. The mean difference is -0.67 for silver diammine fluoride versus control, with an unadjusted p < 0.001, and -0.54 for silver diammine fluoride with potassium iodide versus control, with an unadjusted p-value of 0.005. Both reported intervals lie below zero. These findings describe the reported group averages and their statistical uncertainty, not individual outcomes.

The results do not establish a direct difference between the two active interventions, because the registry record reports each active group against control rather than against one another. Nor do the estimates alone show the probability that a participant will develop a lesion, how the outcome is distributed across participants, or whether baseline lesions became inactive. The latter question is addressed by a secondary outcome, but the registry record does not provide its result in the registry entries.

Statistical evidence in these comparisons should not be translated into a claim that an intervention works or does not work. The interpretation depends on the population enrolled, the analyzed participants, endpoint ascertainment, and analysis methods. The registry describes randomization and double masking, but does not report many procedural and analytic details needed to assess those features fully. Enrollment is 323, while the primary-outcome group counts are 80, 95, and 82, and the reason for that difference is not reported in the registry record.

The safety figures report no serious or other adverse events in the listed groups, but the registry record's safety details are limited and deaths are not reported. Together, the efficacy and safety entries are a narrow registry summary. They support understanding what outcomes were posted and how precisely the primary comparison was estimated, while leaving important questions about analysis populations, missing data, and other outcomes unanswered.

16. Why This Trial Matters Statistically

This trial is statistically informative because its primary endpoint is a count of new root caries lesions observed over a defined follow-up period, and the registry posts group means, standard errors, mean differences, intervals, and unadjusted p-values. Seeing both estimates and uncertainty is more useful than relying on a significance label alone. The two control comparisons show how the reported mean counts differ under the registry's stated comparison order.

The three-group randomized design distinguishes control care from two related intervention regimens, including one with potassium iodide. That structure creates more than one clinically relevant comparison, which makes clarity about the reference group and multiplicity important. The registry reports each active group against control but does not report a direct comparison between active regimens. Recognizing that distinction prevents the control comparisons from being mistaken for evidence about which active regimen has the lower mean.

The record also illustrates why enrollment, analysis counts, and safety populations need to be distinguished. Enrollment is 323, while the primary-outcome group counts and the safety at-risk counts are different sets of figures. Since the registry does not explain their relationship, readers cannot determine from this record alone how missing observations, exclusions, or analysis populations affected the results.

Finally, the posted planning illustrations show how sample-size requirements depend on the effect targeted and the chosen power. These are not the trial's original design assumptions. Their value is educational: they demonstrate that planning around a smaller effect calls for larger groups under the stated assumptions. Keeping that planning exercise separate from the observed results helps avoid confusing a retrospective illustration with a prospective design justification.

17. 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.

The registry record leaves several trial-specific details unresolved. It lists enrollment as 323, while the brief summary says 300 subjects would be recruited, and the primary-outcome group counts are 80, 95, and 82. The record does not explain how these figures relate, whether all randomized participants contributed outcome data, or why the outcome counts differ among groups. The safety at-risk counts are separate figures and are not reconciled with the outcome counts.

The primary endpoint is clearly described as new root surfaces changing from sound at baseline to decayed at evaluation, but the record does not give a participant-level distribution or report how multiple lesions within a participant were handled analytically. It reports group means and standard errors, without stating the statistical model or whether features of count data, such as over-dispersion, were considered. The interval construction method and confidence level are also not reported in the registry record.

The trial is labeled randomized and double-masked, but the registry does not explain sequence generation, allocation concealment, who was masked, or how masking was maintained. It does not report adherence, the analysis population, missing-data handling, baseline adjustment, an interim-analysis plan, or a statistical analysis plan. The posted p-values are unadjusted, and no multiplicity strategy is described. The secondary outcome is named, but its numerical result is not included in the registry entries.

The safety results list zero serious and zero other events for the reported at-risk groups, but deaths are not reported, and the safety record lacks event descriptions and further ascertainment details. These limitations constrain how fully the findings can be assessed from the registry alone. They do not identify the direction of any bias or prove that an unreported procedure was absent; they mark what cannot be established from this record.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Preventing and Arresting Dental Root Surface Caries in Community-dwelling Older Adults — NCT02360124.
• Registry record last updated 2016-07-25; status last verified 2016-06.
• Results first posted 2016-05-19.
• 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.

21. Record Summary

NCT02360124 is a completed, randomized, double-masked, parallel-group trial sponsored by The University of Hong Kong, with phases listed as phase 2 and phase 3. The study began in 2012-01 and reached primary completion in 2015-04. Its registry enrollment is 323, and the primary outcome is the number of new tooth root caries lesions at 30 months.

The posted means are 1.1 for control, 0.43 for silver diammine fluoride, and 0.56 for silver diammine fluoride with potassium iodide. Each active group is compared with control, with negative mean differences and intervals below zero. The unadjusted p-values are p < 0.001 and 0.005, respectively. The record does not report the trial's original sample-size justification, analysis populations, or missing-data methods. Safety entries list zero serious and other events in each group, while deaths are not reported in the registry record.