Comparative Evaluation of Post-endodontic Pain Using Two Rotary Instrumentation Systems: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparative Evaluation of Post-endodontic Pain Using Two Rotary Instrumentation Systems (NCT02621034), a randomized na study. The primary outcome is Post-operative Pain on the Visual Anlogue Scale (VAS) at the 6-hour Post-operative Interval.

2. Clinical Question

3. Trial Design

The registry describes a randomized, single-masked, parallel-group clinical trial. It lists three procedure arms: control with K-file hand instrumentation, Reciproc with a rotary reciprocating protocol, and One Shape with a continuous rotation protocol. The recorded enrollment is 150, and the posted outcome gives 50 participants in each arm. The trial status is completed.

The primary outcome is continuous: post-operative pain measured on the Visual Analogue Scale at 6 hours. For this outcome, the registry reports a mean and standard deviation for each group. It also reports two unadjusted comparisons, each against the control group. The reported mean-difference estimates are -1.8 for Reciproc and -1.5 for One Shape. The record does not describe a direct statistical comparison between the two rotary systems.

The record lists a start of 2015-12 and a primary completion of 2016-02. It does not report the trial's original sample-size assumptions or justification, the method used to generate the random allocation sequence, how allocation was concealed, or what single masking meant in practice. The identities of the people who were masked are not reported in the registry record. The record also does not provide additional details about the treatment setting, eligibility criteria, or participant characteristics. Those omissions limit how fully the trial conduct and the reach of its results can be assessed from the registry information alone.

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

Reasons for not completing this period:

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 Post-operative Pain on the Visual Anlogue Scale (VAS) at the 6-hour Post-operative Interval, measured over 6 hours.

The primary endpoint is post-operative pain on the Visual Analogue Scale at the 6-hour post-operative interval. The registry describes the VAS as a continuous measure, commonly presented as a horizontal or vertical line. Its stated anchors are “no pain” at 0 and “pain as bad as it could be” or “worst imaginable pain” at 10. The reported unit is units on a scale.

A continuous pain score retains more gradation than a simple classification such as pain present or absent. Reporting a group mean describes the average recorded score, while the standard deviation describes how spread out individual scores were around that average. These summaries address different features of the outcome: the mean indicates the group’s central level, and the standard deviation indicates variation among the observations.

A measurement at a specified post-operative interval gives the result a clear time reference. The registry’s primary endpoint is at 6 hours; it should not be interpreted as an assessment of pain at other times. Although the endpoint description names the VAS anchors, the record does not report additional details about how the scale was administered, how scores were collected, or how missing scores were handled. The endpoint therefore describes the registered pain measure and time point, but not the full measurement process.

7. Results Posted in the Registry

• Reciproc: mean 3.20 versus 5.00 on control; difference -1.80 (95% CI -2.96 to -0.64), standardized effect d = -0.61; z-test p = 0.002.
• One Shape: mean 3.50 versus 5.00 on control; difference -1.50 (95% CI -2.62 to -0.38), standardized effect d = -0.53; z-test p = 0.009.

8. Statistical Interpretation

9. Statistical Methods Explained

The posted outcome is continuous and summarized by group means and standard deviations. A mean gives the arithmetic average of recorded scores; a standard deviation describes how dispersed the scores are around that average. A small standard deviation relative to the mean indicates more clustering around the group average than a larger standard deviation would, but neither statistic alone reveals the full shape of the score distribution. Individual observations, distribution plots, and details of data collection are not reported in the registry record.

What does a mean difference represent?

A mean difference expresses the contrast between group averages in the units of the endpoint. Here the outcome is measured in units on the pain scale. The posted estimates are -1.8 for Reciproc versus control and -1.5 for One Shape versus control. The negative signs indicate that the estimated contrasts are in the direction of lower scores in the rotary groups, consistent with the group means. The registry record does not report a separate direct contrast between the two rotary arms.

A mean difference retains the original outcome scale, which can make its magnitude easier to relate to the measurement than a standardized measure. The record also includes pooled standard deviations and standardized effect-size values, but the main interpretation can be grounded in the score-scale estimates and their confidence intervals. A standardized effect expresses a contrast relative to variability; it does not replace the original scale or establish whether a difference matters clinically. No threshold for a clinically important difference is reported in the registry record.

How should the p-values be read?

The unadjusted p-values are 0.002 for Reciproc versus control and 0.009 for One Shape versus control. A p-value is a summary of how unusual data at least this incompatible with the null model would be if that model and the test assumptions were correct. It is not the probability that the null model is true, nor does it measure the chance that the result arose “by chance” in a general sense. A p-value also does not measure the effect’s size, its practical importance, or the likelihood that a future study will reproduce the estimate.

The record labels these comparisons unadjusted. That matters when several contrasts or outcomes are considered, because testing more than one hypothesis can affect the interpretation of nominal p-values. The registry record does not report a multiplicity procedure, so no adjusted p-values or family-wise interpretation can be inferred. The available outcome record lists three outcome measures, but secondary posted results are not reported. The record lists no analysis records. Details of the sponsor’s statistical analysis plan are not reported in the registry record.

What do the confidence intervals add?

A confidence interval reflects the sampling uncertainty around an estimate under a specified statistical method. The interval for Reciproc versus control is -2.958 to -0.642; the interval for One Shape versus control is -2.617 to -0.383. Each interval provides a range of contrasts compatible with the data and the method. The widths show that the exact size of each contrast is uncertain, even though both intervals lie on the negative side of zero. A confidence interval is not a range that contains a fixed proportion of individual participants’ scores, and it is not a guarantee that the true contrast is inside the particular interval.

Interpretation depends on the assumptions behind the estimator and interval, including how the observations were collected and whether the analysis appropriately reflects the trial design. The registry record identifies randomization and parallel groups but does not describe the detailed analysis method, missing-data approach, or analysis population. The calculated comparisons are unadjusted; no covariate adjustment is reported. The registry record also does not report whether any prespecified analysis differed from the posted calculation.

Why are group variability and sample size relevant?

Uncertainty in a mean comparison depends in part on the amount of information in each group and on the variability of the outcome. More variation makes group averages less precise when other design features are held constant. The reported standard deviations are 2.8 for control, 3.1 for Reciproc, and 2.9 for One Shape, with 50 participants reported in each arm. The comparison summaries also list standard errors of 0.396 and 0.438 for the control and Reciproc means, and 0.396 and 0.410 for control and One Shape. These standard errors describe the estimated sampling variability of the respective means, not the spread of individual scores.

General statistical context: when outcomes vary more than a simple model assumes, conventional standard errors may be too small and uncertainty may be understated. This is one reason analysts examine the scale, distributions, and model assumptions. The registry does not provide raw observations or enough detail to assess distributional assumptions, so it is not possible to verify those features from the record.

The summary comparisons are not evidence of a causal effect solely by virtue of having p-values or confidence intervals. Randomization is a design feature intended to support comparable groups, but interpretation also depends on how allocation, follow-up, measurement, and analysis were carried out. Several of those operational details are not reported in the registry record. The results should therefore be read as registry-posted group summaries and unadjusted comparisons, with uncertainty, rather than as a complete account of all trial methods.

10. Confidence Intervals and Precision

The Reciproc comparison has a mean-difference estimate of -1.8, with a 95% confidence interval from -2.958 to -0.642. The One Shape comparison has an estimate of -1.5, with a 95% confidence interval from -2.617 to -0.383. The intervals quantify uncertainty in the estimated contrasts under the analysis used. Both are entirely below zero, while their breadth indicates that the exact size of the contrast is not known precisely.

In general, a confidence interval is generated by a procedure that, across repeated studies under its assumptions, would cover the target parameter at the stated rate. It does not mean there is a 95% probability that the fixed true value lies within this particular calculated interval. Nor does it describe the range of individual pain scores. The interval concerns the group contrast, not individual outcomes.

The two intervals overlap. That overlap is not a formal test comparing Reciproc directly with One Shape. The registry reports each rotary protocol against control and does not provide a direct estimate, confidence interval, or p-value for the difference between the rotary groups. Comparing their point estimates visually or informally cannot substitute for that contrast.

Precision also depends on the quality and completeness of the underlying measurements and on the analysis assumptions. The registry record does not report missing outcome handling, the analysis population, or enough detail to independently assess the model and interval calculations. The intervals therefore describe the uncertainty reflected in the posted comparisons, not every possible source of uncertainty in the trial.

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 illustrations give participants per arm, not total events. They use a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. For each comparison, the effect to detect is a stated fraction of the observed effect. These are planning assumptions for illustrations, not the trial’s original design assumptions; the trial’s original sample-size rationale is not reported in the registry record.

For Reciproc versus control, planning for 100% of the observed effect gives 43 participants per arm for 80% power and 57 participants per arm for 90% power. Planning for 75% of the observed effect gives 76 participants per arm for 80% power and 101 participants per arm for 90% power. Planning for 50% of the observed effect gives 170 participants per arm for 80% power and 227 participants per arm for 90% power.

For One Shape versus control, planning for 100% of the observed effect gives 57 participants per arm for 80% power and 76 participants per arm for 90% power. Planning for 75% of the observed effect gives 101 participants per arm for 80% power and 135 participants per arm for 90% power. Planning for 50% of the observed effect gives 227 participants per arm for 80% power and 304 participants per arm for 90% power.

The 80% and 90% power columns describe the planned probability of detecting the assumed effect under the stated model and assumptions if that effect were the true one. Higher target power requires more participants under otherwise identical assumptions. The illustrations also show that smaller effects need more participants. This is not observed power: it is not a retrospective measure of whether the completed trial had a good chance of detecting its result, and it does not establish the probability that the reported findings are true.

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 = -1.800; pooled standard deviation σ = 2.954.
2. n = 2 × (1.96 + 0.842)² × 2.954² / -1.800² = 42.3, rounded up to 43 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 <- -1.8                      # observed difference in means
sigma <- 2.95381109754839                     # 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(2621034)
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 = 43 (80% power), 57 (90% power)
 75% of observed effect: n per arm = 76 (80% power), 101 (90% power)
 50% of observed effect: n per arm = 170 (80% power), 227 (90% power)
power.t.test: 43.3 
Simulated power at n = 43 per arm: 0.800 (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 reports two primary-outcome comparisons against control, with unadjusted p-values. It does not report a procedure for controlling multiplicity, such as an adjustment to the significance threshold or p-values. The values should therefore be understood as unadjusted comparisons, not as results adjusted for considering multiple contrasts. The record lists three outcome measures, but it does not post secondary outcome results. Whether other outcomes or analyses were planned or conducted is not reported in the registry record.

The record also lists zero analysis records. This does not erase the posted group summaries and comparisons, but it means the registry does not provide analysis-level descriptions that would clarify the prespecified model, covariates, test choices, or outcome handling. A statistical analysis plan and the timing of any analyses are not reported in the registry record. Interim analyses are not reported in the registry record.

Missing-data handling is not reported in the registry record. It does not say whether all randomized participants contributed an outcome measurement, whether any measurements were excluded, or how missing values were treated. The analysis population—such as whether the comparisons followed an intention-to-treat approach—is also not reported. Without that information, the posted arm summaries cannot establish precisely which participant set each estimate represents.

Randomization is recorded, but details about allocation concealment, masking procedures, and how masking was maintained are not reported. The record identifies the study as single-masked without identifying who was masked. These omissions do not show that methods were inadequate; they mean that the registry record alone does not permit a complete assessment of those safeguards. Similarly, the record does not report protocol deviations or reasons for any exclusions. Interpretation should remain tied to what is documented: the registered design and the posted outcome values.

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

The posted results describe lower mean pain scores at the 6-hour interval in the Reciproc and One Shape groups than in the control group. The unadjusted mean-difference estimates are negative, and their confidence intervals lie below zero. This is a statistical description of the registry-reported endpoint and comparisons. It does not establish that either procedure produces a particular outcome for an individual, or that the observed difference is clinically important.

The registry record does not state a threshold for a meaningful difference on the pain scale. Statistical evidence against a null model and clinical importance are distinct questions. The confidence intervals indicate uncertainty about the size of the group contrasts; they do not determine whether a difference matters to patients or clinicians. No additional basis for a clinical-importance judgment is reported in the registry record.

The results do not directly rank Reciproc and One Shape. Each is compared with control, and no direct rotary-versus-rotary estimate is posted. Nor should the result at 6 hours be generalized to pain at other time points, since the reported primary endpoint is explicitly tied to that interval. The record does not provide participant characteristics or further setting details needed to judge how well these findings might transfer to other populations or clinical contexts.

The record also does not support a conclusion about safety. Adverse-event fields report zero participants at risk and zero affected in each group, while deaths are recorded as null. With no participants reported at risk in those fields, they do not establish that adverse events did not occur. The adverse-event information is insufficient for a meaningful comparative safety assessment.

Overall, the posted values provide a narrow account of group pain scores and unadjusted comparisons. They should be interpreted with the stated uncertainty and registry omissions in view. They are not medical advice and do not alone establish a general effect, a clinically important benefit, or the absence of harms.

15. Why This Trial Matters Statistically

This trial is statistically instructive because it reports a continuous patient-reported outcome across three randomized parallel groups and gives both descriptive summaries and unadjusted contrasts. The group means convey the central scores, while standard deviations show that scores varied within groups. The mean differences retain the pain-scale units, and the confidence intervals make uncertainty visible rather than presenting the point estimates as exact values.

It also illustrates why a comparison needs a clearly identified reference group. Both posted contrasts use K-file hand instrumentation as control. Those estimates answer a different question from a direct comparison of Reciproc with One Shape. Similar-looking group means or overlapping intervals are not a substitute for a direct contrast and its uncertainty.

The registry record illustrates the difference between statistical and clinical interpretation. The p-values address compatibility with a null model under test assumptions, whereas clinical importance requires context and a meaningful-difference criterion. That criterion is not reported. The endpoint’s specific time point also matters: a result at 6 hours does not describe pain across other intervals.

Finally, registry completeness shapes what can be learned. Randomization and masking are identified, but key details about analysis populations, missing data, multiplicity, and conduct are not reported. The outcome values still permit a bounded statistical reading, but not a full audit of methods or a complete assessment of generalizability. Clear reporting of these elements is important for interpreting precision and potential sources of bias.

16. 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 important limits on interpretation. It does not report participant characteristics, eligibility criteria, clinical setting, or how participants were recruited. The findings therefore cannot be placed in a more specific population context from this record alone. The record names the procedures but does not describe detailed treatment delivery beyond the brief arm descriptions.

The endpoint record does not explain how or by whom the VAS was administered, whether the scale was horizontal or vertical in practice, or how the outcome was recorded. Although the registry gives a primary time point and scale description, it does not report missing outcome handling or whether the posted means include all randomized participants. The analysis population is not reported in the registry record.

The comparisons are unadjusted, and no multiplicity procedure is reported. The registry also does not give a direct comparison between the two rotary protocols, an adjusted estimate, or results for secondary outcomes. It is not possible to determine from the record whether the posted analysis exactly follows a prespecified plan, because the analysis plan and its assumptions are not reported.

Safety interpretation is particularly constrained: the adverse-event fields show zero at risk and zero affected in each arm, and deaths are null. Those entries do not establish that no adverse events occurred. The registry record does not provide additional adverse-event details with which to assess harms.

These gaps do not establish that the trial was conducted poorly. They limit what can be verified from the registry record and counsel against extending the reported outcome beyond the specific comparison and time point documented.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: Comparative Evaluation of Post-endodontic Pain Using Two Rotary Instrumentation Systems — NCT02621034.
• Registry record last updated 2016-06-06; status last verified 2016-03.
• Results first posted 2016-06-06.
• 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.

20. Record Summary

The registry describes a completed randomized, single-masked, parallel-group trial comparing K-file hand instrumentation with Reciproc and One Shape protocols. Enrollment is recorded as 150, and the primary outcome is mean post-operative VAS pain at 6 hours.

The posted group means are 5.0 for control, 3.2 for Reciproc, and 3.5 for One Shape. The unadjusted mean differences versus control are -1.8 for Reciproc and -1.5 for One Shape, with confidence intervals below zero. The registry does not report a direct comparison between the rotary groups, the original sample-size justification, missing-data handling, or a multiplicity procedure. These results describe the posted endpoint and comparisons, with the limitations of the registry record.