Effect of Non-surgical Periodontal Therapy on Gingival Crevicular Fluid Interleukin-21 Levels: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Effect of Non-surgical Periodontal Therapy on Gingival Crevicular Fluid Interleukin-21 Levels (NCT02861937), a randomized na study. The primary outcome is Pocket Depth.

2. Clinical Question

The distinction between the study’s stated biological focus and its posted numerical primary outcome matters when interpreting the results. The brief summary states that interleukin-21 was present across periodontal health and disease and describes changes following non-surgical therapy. However, the numerical estimates available for the primary outcome concern pocket depth. They do not quantify interleukin-21 concentrations or changes in those concentrations.

The registry labels the study randomized, double-masked, and parallel. It does not explain how participants were randomized, what was masked, or whether assignment was randomized among the clinical-status groups. Those design details are not reported in the registry record. The estimates should therefore be read as comparisons among the recorded groups, rather than as a complete account of a randomized treatment contrast.

3. Trial Design

The study is registered as randomized, double-masked, and parallel, with total enrollment of 34. The listed groups are Group I (Control Group), with 10 participants; Group II (Test Group I), with 12; and Group III (Test Group II), with 12. The group descriptions correspond to healthy gingiva, chronic gingivitis, and chronic periodontitis. The registry lists non-surgical periodontal therapy as the intervention.

The record gives a study start of 2014-04 and primary completion of 2014-09, and reports the status as completed. It identifies Krishnadevaraya College of Dental Sciences & Hospital as the sponsor. The listed phase is NA. The registry does not report the study’s original sample-size justification, randomization procedure, allocation concealment, or detailed masking procedures. The treatment schedule and group-specific procedures are also not fully described in the posted record.

The primary outcome is Pocket Depth, defined as the deepest probing pocket depth in a participant’s mouth. It was measured with a University of North Carolina {UNC}-15 periodontal probe and a customized occlusal stent. The measurement is described as the distance from the crest of the gingival margin to the base of the pocket. The stated outcome time point is 6 weeks.

The result record reports a mean and standard deviation for each group, followed by unadjusted mean-difference comparisons of each test group with the control group. The comparisons report confidence intervals and p-values. The registry does not report the analysis model, covariate adjustment, or handling of repeated measurements. Although the registration is labelled randomized, the group descriptions indicate different clinical-status categories; the relationship between randomization and those categories is not explained. The numerical comparisons therefore need to be interpreted in light of the information actually recorded, not as evidence of an undocumented allocation process.

The brief summary discusses interleukin-21 concentrations in gingival crevicular fluid and describes their relation to periodontal destruction and non-surgical therapy. The posted numerical primary endpoint, however, is pocket depth. Numerical interleukin-21 results are not reported in the registry record, and the relationship between that summary and the posted primary-outcome analysis is not explained.

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.

Before assignment: 12 chronic gingivitis, 12 chronic periodontitis patients and 10 healthy individuals were included as control. Patients systemically healthy having more than or equal to 14 functional teeth, patients had not received any form of surgical/non surgical periodontal therapy or received antibiotics within the past 6 months.

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: A total of 34 patients with 19 males and 15 females in the age group of 20-60 years were included. Patients were divided into 3 groups to collect Gingival Crevicular Fluid (GCF) samples for the study.

6. Primary Endpoint

The registry lists the primary outcome as Pocket Depth, measured over 6 weeks.

Pocket depth is a clinical measurement of the distance from the gingival margin to the base of a periodontal pocket. In this study, the recorded value for each participant was the deepest probing pocket depth in the mouth, measured with a University of North Carolina {UNC}-15 periodontal probe and a customized occlusal stent. The unit is millimetres, and the stated assessment time is 6 weeks.

This measure is used to describe the depth of the pocket around the teeth. The registry’s group descriptions also use probing depth as one part of the clinical definitions for gingivitis and periodontitis. A maximum value represents the deepest recorded site in the participant’s mouth, rather than an average over all sites. It therefore describes the most pronounced pocket measurement recorded for each participant and does not convey how measurements varied across that person’s mouth.

The primary outcome is reported as a group mean with a standard deviation. A mean describes the group’s average recorded depth, while the standard deviation describes how spread out individual measurements are around that average. The reported means at 6 weeks are 1.6 for the control group, 2.5 for Group II, and 6.75 for Group III. The registry record does not state whether these values are follow-up measurements only or changes from an earlier measurement.

Although the study title and brief summary emphasize interleukin-21 in gingival crevicular fluid, that biomarker is not the numerical primary outcome shown in the posted results. The registry record does not report numerical interleukin-21 values or an endpoint definition for a quantitative interleukin-21 analysis.

7. Results Posted in the Registry

• Group II (Test Group I): mean 2.50 versus 1.60 on control; difference 0.90 (95% CI 0.46 to 1.34), standardized effect d = 1.73; z-test p = <0.001.
• Group III (Test Group II): mean 6.75 versus 1.60 on control; difference 5.15 (95% CI 4.43 to 5.87), standardized effect d = 5.65; z-test p = <0.001.

8. Statistical Interpretation

9. Statistical Methods Explained

What does a group mean describe?

A mean is the arithmetic average of the measurements in a group. For this outcome, it summarizes the deepest probing pocket depth recorded for each participant. The control group mean is 1.6, the Group II mean is 2.5, and the Group III mean is 6.75. A mean is useful for comparing typical levels across groups, but it does not show every individual value, the shape of the distribution, or where pocket depths occurred within each mouth.

The standard deviation describes spread around the group mean. The reported values are 0.516 for the control group, 0.522 for Group II, and 1.138 for Group III. A larger standard deviation indicates greater dispersion among participant-level measurements, on the scale of the outcome. It is not the same as the uncertainty in the group mean; uncertainty also depends on the number of participants and the analysis method.

What is a mean difference?

A mean difference expresses the distance between two group means in the outcome’s original units. The registry reports Group II compared with the control group as 0.9, and Group III compared with the control group as 5.15. These are unadjusted comparisons. Because pocket depth is measured in millimetres, the differences are also expressed on that scale. They summarize the observed group contrast, but they are not automatically causal effects.

Interpretation depends on how groups were formed. The registry labels the trial randomized, yet its descriptions define groups by periodontal health or disease. It does not explain whether participants were randomized to treatment, randomized among clinical-status categories, or assigned in another way. It also does not report baseline outcome values or a model adjusting for them. Without those details, a group mean difference should not be treated as proof that the procedure produced the contrast.

What does a confidence interval contribute?

A confidence interval describes statistical uncertainty around an estimate under the assumptions of the analysis. It gives a range of values that are compatible with the observed data and method, rather than a guarantee that the true value falls within that specific interval. The intervals reported for both unadjusted comparisons exclude zero. That is consistent with the reported p-values of p < 0.001. Confidence intervals do not account for unreported bias, errors in measurement, missing outcomes, or inappropriate analysis assumptions.

How should p-values be read?

A p-value evaluates how compatible the data are with a specified null hypothesis under the analysis assumptions. Here, the reported unadjusted p-values are p < 0.001 for each comparison with the control group. They do not give the probability that the null hypothesis is true, and they do not measure the probability that the findings occurred “by chance.” They also do not quantify clinical importance. The estimate and its interval give more direct information about the size and precision of the group contrast.

Why can unequal spread matter?

Some statistical procedures assume that variability is similar between groups. When that assumption does not hold, a pooled-variance method can misstate uncertainty. Other approaches can allow group variability to differ. The posted comparisons include group-specific standard deviations and an estimated pooled standard deviation, but the registry does not name the analysis procedure or explain its assumptions. The reported standard deviations are close for the control and Group II, while Group III has a larger reported standard deviation. This makes it relevant to know how the analysis handled variation; that detail is not reported in the registry record.

More generally, over-dispersion means that observed variation is greater than a model expects. If not accommodated, standard errors and confidence intervals may be too optimistic. This is a general statistical concern, not evidence that over-dispersion occurred in this study. The outcome is a continuous measurement, and the registry does not report a diagnostic assessment of its distribution or variance structure.

What do the reported comparisons leave unresolved?

The comparisons are described as unadjusted. The record does not state whether the analysis used all randomized participants, only participants with observed outcomes, or another analysis population. It does not report missing outcome counts, imputation, protocol deviations, or an intention-to-treat approach. Those omissions matter because exclusion of participants or unbalanced missingness can affect group estimates.

The registry lists five outcome measures, but secondary posted results are not reported. The numerical estimates addressed concern the primary pocket-depth outcome. The study title and brief summary discuss interleukin-21, yet the registry does not give its numerical results, measurement variability, or inferential analysis. Therefore, the statistical interpretation is limited to the available pocket-depth summaries and comparisons.

The trial’s original statistical analysis plan, sample-size justification, and interim-analysis plan are not reported in the registry record. These details should not be inferred from the posted p-values or from planning illustrations based on observed effects. General statistical interpretation can explain what the estimates represent, but it cannot replace missing information about the study’s planned methods.

10. Confidence Intervals and Precision

Precision concerns how much uncertainty surrounds an estimate. The mean differences are reported with confidence intervals: the interval for Group II compared with control excludes zero, and the interval for Group III extends from 4.431 to 5.869. The interval endpoints for the first comparison are not repeated because the posted lower endpoint is reported to more than three decimal places. Both comparisons have p < 0.001.

The interval for Group III indicates that, under the comparison method and its assumptions, the data are compatible with a range of positive mean differences. The estimate of 5.15 is the center of the reported contrast, while the interval conveys uncertainty around it. The interval for Group II also excludes zero, indicating a positive contrast under the reported unadjusted analysis. An interval is more informative about magnitude and precision than a p-value alone, but it does not address whether the groups were comparable before treatment.

Precision is affected by sample size, measurement variability, and the analysis method. The groups contain 10, 12, and 12 participants, and the reported standard deviations are 0.516, 0.522, and 1.138. These summaries indicate that the amount of observed variation differs across groups, particularly for Group III. The registry does not report whether the interval calculation accounted for unequal variances or whether any adjustment was used.

Confidence intervals quantify sampling uncertainty under a statistical model. They do not include uncertainty from outcome measurement, selective reporting, missing data, or ambiguities in the design. The record also does not report a baseline-adjusted estimate. Thus, narrow or statistically distinct intervals would not resolve whether the group contrasts can be attributed to therapy rather than to differences in clinical status or other unrecorded factors.

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 for 80% power and participants per arm for 90% power. They are not total sample sizes for both arms. The listed assumptions are two-sided significance level 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set as a stated fraction of the observed effect. These are planning illustrations based on the observed contrasts, not the trial’s original design assumptions.

For the Group II comparison, planning for 100% of the observed effect gives 6 participants per arm for 80% power and 7 participants per arm for 90% power. Planning for 75% of the observed effect gives 10 participants per arm for 80% power and 13 participants per arm for 90% power. Planning for 50% of the observed effect gives 21 participants per arm for 80% power and 28 participants per arm for 90% power.

For the Group III comparison, the corresponding figures are 1 and 1 participants per arm for 100% of the observed effect, 1 and 2 for 75%, and 2 and 3 for 50%, with the 80% power figure stated first in each pair. Very small planning estimates can arise when the observed contrast is large relative to the observed variability; they should not be read as a recommendation for a future study without design review.

In general, 80% power means that a study designed under the stated assumptions would have an 80% chance of detecting the specified effect if that effect were the true one; 90% power expresses a higher chance under the same conditions. Smaller effects require more participants to detect with the same power. A sample-size curve represents how the planning requirement changes as the effect to detect changes. These figures are not observed power. The registry does not report the original sample-size justification, so these illustrations do not explain why the study enrolled 34 participants.

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 = 0.900; pooled standard deviation σ = 0.519.
2. n = 2 × (1.96 + 0.842)² × 0.519² / 0.900² = 5.2, rounded up to 6 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 <- 0.9                      # observed difference in means
sigma <- 0.519308578785292                     # 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(2861937)
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 = 6 (80% power), 7 (90% power)
 75% of observed effect: n per arm = 10 (80% power), 13 (90% power)
 50% of observed effect: n per arm = 21 (80% power), 28 (90% power)
power.t.test: 6.3 
Simulated power at n = 6 per arm: 0.770 (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 lists five outcome measures, but secondary outcome results are not reported. The numerical results available for interpretation concern pocket depth. The study title and brief summary also emphasize interleukin-21, but quantitative results for that biomarker are not reported in the registry record. Without the full set of outcome estimates, it is not possible to assess whether all planned outcomes were reported or whether the posted primary endpoint was selected from a larger set.

Multiplicity arises when several outcomes, time points, groups, or statistical comparisons are tested. Each additional test can increase the chance of at least one small p-value under a global null hypothesis. The record reports two comparisons with the control group, both with p < 0.001, but does not state whether a multiplicity adjustment was planned or applied. It also does not report a prespecified hierarchy of outcomes or comparisons. The p-values should therefore be understood as the posted unadjusted results, not as evidence that a correction was or was not required.

Missing-data handling is not reported in the registry record. The posted arm sizes are 10, 12, and 12, but the record does not state whether every participant had a 6-week pocket-depth measurement, whether any measurements were excluded, or how missing values were handled. It also does not report whether the analysis included all randomized participants or only participants with recorded outcomes.

The analysis population is likewise not described. The registry does not identify an intention-to-treat population, a per-protocol population, or another prespecified analysis set. It does not report the protocol deviations or the handling of participants who did not complete therapy. These omissions limit assessment of potential bias and make it difficult to connect the randomized label to the actual analyzed groups.

The statistical analysis plan, including any interim analyses and multiplicity procedures, is not reported in the registry record. No particular plan should be inferred from the available p-values or outcome summaries.

14. Safety Results

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

Deaths

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 zero serious adverse events in each group: 0 among 10 participants in the control group, 0 among 12 in Group II, and 0 among 12 in Group III. It also lists zero other adverse events and zero deaths in each group. No serious adverse-event terms are listed.

These figures mean that no events of those categories were recorded in the posted safety results for the listed participants. They do not establish that no events occurred outside the recorded follow-up or that the procedure has no risk. A record with no reported events can still be limited by the number of participants observed, the duration and completeness of safety follow-up, and how events were collected and classified. Those details are not reported in the registry record.

The safety figures are descriptive. With no recorded events, the registry does not provide a comparative estimate of event risk or an uncertainty interval. The zero counts should not be interpreted as proof of equivalent safety across groups.

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

The posted results show differences in mean deepest pocket depth across the recorded groups at 6 weeks. The mean is 1.6 for the healthy control group, 2.5 for Group II, and 6.75 for Group III. The unadjusted mean differences compared with control are 0.9 for Group II and 5.15 for Group III, each with p < 0.001. These findings describe the measurements and comparisons reported in the registry.

They do not establish that non-surgical periodontal therapy caused the differences. The groups are described by different clinical states, while the registry’s randomized label is not accompanied by details explaining how participants were allocated. Baseline pocket-depth results, adjusted analyses, and the analysis population are not reported. As a result, the contrasts cannot be separated from possible differences that existed between the groups or from other unreported features of the study.

The results also do not quantify interleukin-21. Although the title and brief summary focus on gingival crevicular fluid interleukin-21, numerical biomarker values, uncertainty estimates, and a corresponding analysis are not reported in the registry record. The pocket-depth findings cannot substitute for those missing biomarker results.

The confidence intervals and p-values describe statistical uncertainty under the reported unadjusted comparisons. They do not establish clinical importance, remove potential bias, or show how measurements changed from baseline. The record does not provide enough information to assess the full analysis plan, missing outcomes, multiplicity, or whether the results represent all randomized participants.

Accordingly, the defensible conclusion is limited to the recorded group summaries and unadjusted comparisons. The registry reports larger mean pocket depth in the test groups than in the healthy control group at the stated follow-up, with statistically distinct unadjusted comparisons. It does not, on its own, show that treatment produced those differences or provide numerical evidence for the interleukin-21 statements in the brief summary.

16. Why This Trial Matters Statistically

This trial is statistically notable because its stated biological focus and its posted numerical primary outcome are not the same. The title and brief summary discuss interleukin-21 in gingival crevicular fluid, while the numerical primary outcome is the deepest pocket depth at 6 weeks. That difference affects what the posted estimates can support: the available comparisons concern a clinical measurement, not a biomarker concentration.

The clinical groups also raise an interpretation issue. The record labels the study randomized, double-masked, and parallel, but describes groups by periodontal health or disease and does not explain the allocation process. Randomization can support causal comparisons when the treatment assignment and analysis are clearly documented. Without those details, the reported differences are best read as group contrasts rather than assumed treatment effects.

The record illustrates why effect estimates, uncertainty, and design context need to be considered together. Both unadjusted comparisons have p < 0.001, but a small p-value cannot resolve ambiguity about group formation, baseline differences, or missing-data handling. The confidence intervals describe uncertainty under the comparison method, not uncertainty from every possible source of bias.

The sample-size planning illustrations also require context. They are calculated from the observed effects and stated assumptions, rather than from the study’s original design rationale. They can show how the sample-size requirement changes when planning for a smaller effect, but they cannot establish that the completed study was adequately planned or that its observed effects will recur.

These statistical considerations make the registry record useful for distinguishing the observed measurements from broader claims. Clear reporting of allocation, endpoint results, analysis populations, and uncertainty is essential when interpreting comparisons in a small study with clinically distinct groups.

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 limitations unresolved. The title and brief summary emphasize interleukin-21, but the posted numerical primary outcome is pocket depth. Numerical interleukin-21 results are not reported in the registry record, so the stated biomarker changes cannot be evaluated from the posted estimates.

The groups are described as healthy, chronic gingivitis, and chronic periodontitis, but the relationship between these clinical categories and the randomized label is not explained. The record does not describe the randomization sequence, allocation concealment, what was masked, or whether allocation was randomized across clinical-status groups. The comparison with the healthy control group may therefore reflect underlying clinical differences as well as any treatment-related differences.

The primary outcome is the deepest pocket depth in each participant’s mouth. This maximum measurement does not describe the distribution of pocket depths across sites, and the record does not report baseline values or change from baseline. The timing and completeness of outcome measurement are also not described beyond the stated 6-week timeframe.

The registry does not report missing-data methods, the analysis population, a detailed statistical analysis plan, or adjustment for the two comparisons. Secondary posted outcome results are absent. It is also unclear whether every enrolled participant contributed to each posted analysis. These omissions limit assessment of bias, multiplicity, and the robustness of the estimates.

The enrollment is 34, with group sizes of 10, 12, and 12. The record does not report the original sample-size justification. Planning illustrations based on the observed effects cannot substitute for that information. Safety results list no adverse events or deaths, but safety follow-up details are not reported.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Effect of Non-surgical Periodontal Therapy on Gingival Crevicular Fluid Interleukin-21 Levels — NCT02861937.
• Registry record last updated 2020-09-02; status last verified 2020-08.
• Results first posted 2020-08-26.
• 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

NCT02861937 is a completed, randomized, double-masked, parallel study sponsored by Krishnadevaraya College of Dental Sciences & Hospital. The record lists enrollment of 34, a study start of 2014-04, and primary completion of 2014-09.

The groups are described as clinically healthy gingiva, chronic gingivitis, and chronic periodontitis, with 10, 12, and 12 participants. Non-surgical periodontal therapy is the listed procedure. The primary numerical outcome is deepest pocket depth in millimetres at 6 weeks. Reported means are 1.6, 2.5, and 6.75, respectively; unadjusted comparisons of the test groups with control have p < 0.001.

The title and brief summary discuss interleukin-21, but numerical biomarker findings are not reported in the registry record. Details of randomization, the analysis population, missing-data handling, multiplicity, and the original sample-size justification are also not reported.