Evaluation of Aerosol in a Dental Clinic: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Evaluation of Aerosol in a Dental Clinic (NCT04659928), a randomized phase 4 study. The primary outcome is Number of Bacterial Colony Forming Units (CFUs).

2. Clinical Question

3. Trial Design

The registry record identifies this as a randomized, double-blind, parallel-group Phase 4 trial. It is marked completed and reports enrollment of 41. The listed start date is 2021-07-21, and the primary completion date is 2024-05-02. The sponsor is The University of Texas Health Science Center, Houston.

Four groups are represented in the posted outcome results. Two received HVE suction only, with either hydrogen peroxide or placebo. The other two received HVE suction together with an extraoral vacuum aspirator, again with either hydrogen peroxide or placebo. The reported group sizes are 10, 10, 11, and 10, respectively. The record identifies the design as randomized and double-blind, but the details of sequence generation, allocation concealment, and which people were masked are not reported in the registry record.

The study’s stated purpose was to evaluate external evacuation units and mouth rinses during aerosol-generating procedures in a dental clinic and to determine the risk level to dental practitioners during those procedures. The outcome description focuses on CFUs collected around the dental chair. It states that sampling was planned at baseline, one hour before treatment. Thus the results discussed for the primary endpoint describe baseline CFU levels by assigned group. A treatment-period or post-treatment primary endpoint is not reported in the registry record.

The registry lists four outcome measures and two secondary-outcome entries, both concerning CFUs at each location. It reports no analyses in the registry record. The posted group summaries and pairwise estimates can still be described, but the record does not establish the planned statistical analysis or explain how the four groups were intended to be compared as a whole.

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 Bacterial Colony Forming Units (CFUs), measured over Baseline.

The primary endpoint is the average number of bacterial colony-forming units (CFUs), a continuous measure of colonies counted from environmental samples. The registry record says sampling occurred at baseline, one hour before treatment. Four agar petri dishes were to be placed at distances of 2 ft, 3 ft, 4 ft, and 6 ft from the dental chair headrest, and an impinger was to be positioned 2 ft from the headrest. Counts were made after a 72-hour incubation period, and the average number of CFUs is the reported measure.

As a general statistical concept, an average gives a single summary of the measured quantity across observations or sampled locations. It can help compare the central level of a continuous outcome between groups, while individual measurements may vary around that average. CFUs provide a way to quantify bacterial colonies captured in the sampled environment. That makes the outcome relevant to the study’s stated interest in aerosol during dental procedures, but the record does not report a direct infection outcome or a measure of clinical risk.

Interpretation also depends on timing. Because the primary outcome timeframe is baseline and the description specifies measurement before treatment, these group means characterize the reported pre-treatment measurements. They should not be read as measurements of change caused by the assigned suction or rinse combination.

7. Results Posted in the Registry

• High Volume Evacuation (HVE) Suction Only and Hydrogen Peroxide: mean 47.20 versus 70.70 on control; difference -23.50 (95% CI -82.33 to 35.33), standardized effect d = -0.33; z-test p = 0.434.
• HVE Suction and Extraoral Vacuum Aspirator (EVA) and Hydrogen Peroxide: mean 125.30 versus 70.70 on control; difference 54.60 (95% CI -57.82 to 167.02), standardized effect d = 0.43; z-test p = 0.341.
• HVE Suction and Extraoral Vacuum Aspirator (EVA) and Placebo: mean 116.70 versus 70.70 on control; difference 46.00 (95% CI -60.09 to 152.09), standardized effect d = 0.38; z-test p = 0.395.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is described as a continuous measure summarized by a mean and standard deviation. A mean represents the arithmetic average of measurements, while the standard deviation describes their spread around that average. A small standard deviation indicates measurements tend to be closer to the mean; a large one indicates greater variability. Here, the posted standard deviations differ notably across groups, so the group means alone do not convey the full pattern of observed variation.

What does a mean difference represent?

Each posted comparison expresses the difference between one group mean and the HVE suction-only-and-placebo mean. The sign identifies the direction of the difference: a negative value corresponds to a lower reported mean in the compared group, and a positive value corresponds to a higher reported mean. The size of the difference is expressed in CFUs, the same units as the outcome. These comparisons are pairwise; they do not provide a single overall test of whether any of the four group means differ.

The comparison estimates are accompanied by 95% confidence intervals. As a general statistical concept, a confidence interval describes the uncertainty around an estimate under the method used to calculate it. Its endpoints identify values that are reasonably compatible with the observed data and the assumptions of that method. An interval including zero is compatible with no mean difference, but it can also include nonzero differences. The interval is not a guarantee that the true value lies within its endpoints, nor does it identify the probability that a specific effect is true.

How should the p-values be read?

The posted p-values are unadjusted. In general, a p-value measures how unusual data at least as incompatible with a specified null hypothesis would be if that hypothesis and the analysis assumptions held. A larger p-value does not establish that the null hypothesis is true, and a smaller p-value does not quantify the size or practical importance of a difference. The values of 0.434, 0.341, and 0.395 should therefore be interpreted alongside the estimated differences and their confidence intervals, rather than as stand-alone answers.

The registry record does not report the statistical method used for the sponsor’s analysis, a prespecified threshold for interpreting p-values, or an adjustment for making multiple comparisons. The displayed pairwise comparisons should not be treated as evidence that multiplicity was handled. When several hypotheses are tested, the chance of at least one apparently notable result can rise; adjustments or a prespecified testing strategy can address that issue. Which approach, if any, was planned is not reported in the registry record.

Why does variability matter?

As a general concept, high variability makes it harder to estimate a group mean precisely from a limited number of observations. This can lead to wide confidence intervals even when the estimated means differ. The posted standard deviations include 16.38 in the HVE-only-and-hydrogen-peroxide group, 98.06 in the reference group, 155.4 in the HVE-and-EVA-and-hydrogen-peroxide group, and 143.4 in the HVE-and-EVA-and-placebo group. These are descriptive measures of spread, not uncertainty intervals for the means.

Over-dispersion is a general term for variability greater than a statistical model expects. It matters because a model that understates the spread can produce standard errors that are too small and confidence intervals that are too narrow. The registry record does not report whether over-dispersion was assessed or whether a particular distributional model was used. Because CFU counts can be variable, the displayed means and standard deviations are useful summaries, but the record does not provide enough analysis detail to evaluate model fit or alternative summaries.

What is and is not established about the analysis?

The registry identifies randomization, double masking, and a parallel design. These labels describe broad design features, not the full statistical plan. Details of randomization, masking implementation, the primary comparison, handling of missing data, analysis population, covariate adjustment, and interim analyses are not reported in the registry record. Nor does the record provide a protocol-based sample-size justification. The planning illustrations use the observed comparisons and stated planning assumptions; they are not evidence of the original design plan.

As a general principle, randomized assignment can support comparisons between assigned groups when the design and analysis are implemented appropriately. But the posted endpoint is measured at baseline, and the registry record does not describe an analysis of a later outcome or change from baseline. The group summaries and contrasts should therefore be read as descriptions of the posted baseline data. They do not establish a causal effect of the intervention combinations on post-procedure CFU levels.

10. Confidence Intervals and Precision

Precision concerns how narrowly the data locate an estimated difference. The 95% confidence intervals for the three comparisons are broad: -82.33 to 35.33 for HVE suction only with hydrogen peroxide; -57.82 to 167.0 for HVE suction with EVA and hydrogen peroxide; and -60.09 to 152.1 for HVE suction with EVA and placebo. Each interval includes zero, the value corresponding to no mean difference.

As a general statistical explanation, a confidence interval conveys uncertainty in an estimate under the method used. A wide interval means that the data are compatible with a broader range of possible differences. Here, the intervals allow both lower and higher means relative to the reference group. They do not demonstrate equivalence or show that any difference is too small to matter. A formal equivalence or noninferiority conclusion would require a prespecified margin and a suitable analysis; these are not reported in the registry record.

Group sizes are 10, 10, 11, and 10, and the standard deviations vary substantially. Limited group sizes and marked variability can contribute to imprecision. The registry record does not include raw observations, so the effects of unusual measurements or the distribution of CFU counts cannot be assessed from the posted summaries alone. The estimates should consequently be read as uncertain baseline contrasts rather than precise estimates of intervention effects.

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 describe participants per arm, not total events. They are illustrations based on the observed effect, not the trial’s own original design assumptions. The calculation assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation; each planning scenario targets the stated fraction of the observed effect. The original trial’s sample-size assumptions and justification are not reported in the registry record.

For each comparison, the displayed planning scenarios use 100%, 75%, and 50% of the observed effect. These are hypothetical effect sizes for planning, not additional observed results. For example, the row for planning for 75% of the observed effect asks how many participants per arm would be needed to target an effect smaller than the full observed estimate. Smaller effects are harder to distinguish from random variation, so they require more participants under the stated assumptions.

The 80% power column gives the illustrative number of participants per arm for an analysis to have an 80% chance of detecting the target effect at the stated significance level, if the assumptions hold. The 90% power column gives the corresponding per-arm number for a 90% chance. For the HVE-only-and-hydrogen-peroxide comparison, the figures are 148 and 198 participants per arm for the full observed effect, 263 and 351 for 75% of that effect, and 590 and 790 for 50% of that effect. For HVE with EVA and hydrogen peroxide, the figures are 87 and 117, 155 and 207, and 348 and 466. For HVE with EVA and placebo, they are 110 and 147, 196 and 262, and 440 and 588.

These are planning illustrations, not observed power. They should not be read as evidence that the completed trial had a particular probability of detecting an effect, nor as recommendations independent of the assumptions. The displayed curve represents the same general relationship between target effect and required sample size; it is a planning aid rather than a result from additional 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 = -23.500; pooled standard deviation σ = 72.028.
2. n = 2 × (1.96 + 0.842)² × 72.028² / -23.500² = 147.5, rounded up to 148 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 <- -23.5                      # observed difference in means
sigma <- 72.0279096491148                     # 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(4659928)
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 = 148 (80% power), 198 (90% power)
 75% of observed effect: n per arm = 263 (80% power), 351 (90% power)
 50% of observed effect: n per arm = 590 (80% power), 790 (90% power)
power.t.test: 148.4 
Simulated power at n = 148 per arm: 0.791 (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 reports three pairwise comparisons against the HVE suction-only-and-placebo group. The associated p-values are unadjusted. It does not report whether the trial used a prespecified multiplicity procedure, a gatekeeping strategy, or a single primary comparison. When several comparisons are considered, multiplicity can increase the chance of a false-positive finding across the family of tests. Whether that concern was addressed in the sponsor’s analysis is not reported in the registry record.

The record does not report the planned analysis population, such as whether results were intended to follow randomized assignment or another population definition. It also does not describe exclusions, protocol deviations, or how participants were handled if outcome data were incomplete. Missing-data methods and the amount or pattern of missing outcome data are not reported in the registry record. Without those details, the degree to which the posted summaries represent all randomized participants cannot be fully assessed.

The registry identifies the study as randomized and double-blind, but it does not specify the method used to generate or conceal allocation, the people masked, or how masking was maintained. The analysis method, any covariate adjustment, assumptions about outcome distributions, and the handling of repeated or location-specific measurements are also not reported in the registry record.

Interim analyses, stopping rules, and a formal statistical analysis plan are not reported in the registry record. The record lists four outcome measures and two secondary-outcome entries concerning CFUs at each location, but it does not state how those outcomes relate to a prespecified testing hierarchy. These absences limit assessment of selective reporting and of how the displayed comparisons fit into the trial’s full analysis plan. They do not, by themselves, establish that any particular procedure was or was not used.

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 results report zero serious adverse events, zero other adverse events, and zero deaths in each of the four groups. The reported numbers at risk were 10 in each of the two hydrogen peroxide groups, 11 in the HVE-only-and-placebo group, and 10 in the HVE-and-EVA-and-placebo group. These counts describe the adverse-event reporting in the registry record.

As a general interpretation, zero reported events means that no events of the specified type were recorded among the listed participants at risk; it does not prove that the underlying risk is zero. With small group sizes, absence of a recorded event offers limited information about uncommon events. The record does not provide event narratives, severity grades beyond the serious/other categories, attribution assessments, or a description of the observation period for adverse events. It also does not report whether there were events that were assessed but not classified as adverse events.

The safety figures should therefore be read as counts recorded in the registry, not as a comprehensive estimate of safety or a comparison demonstrating that one combination is safer than another.

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

The posted data show baseline average CFU counts in four randomized groups with different combinations of HVE suction, EVA, hydrogen peroxide, and placebo. The reference group’s reported mean was 70.7 CFUs. The other group means were 47.2, 125.3, and 116.7. The corresponding comparisons had estimates of -23.5, 54.6, and 46.0, with confidence intervals that all included zero.

Those results do not establish that the groups have the same baseline levels, because the intervals are broad and the group sizes are limited. They also do not establish a difference attributable to an intervention. The primary endpoint timeframe is baseline, one hour before treatment, so the posted comparisons do not measure a treatment-related change in CFUs during or after a procedure. A non-significant p-value is not proof of no effect, and a difference in observed group means is not, by itself, evidence of a treatment effect.

The study’s stated purpose includes evaluating external evacuation units and mouth rinses during aerosol-generating dental procedures and determining practitioner risk. The posted primary endpoint is an environmental bacterial count. No practitioner infection outcome or direct measure of COVID-19 risk is reported in the registry record. Accordingly, the CFU results should not be interpreted as a direct estimate of infection probability or clinical risk.

The findings are best understood as imprecise summaries of the baseline CFU measurements recorded across the four groups. Understanding effects during treatment would require relevant outcome measurements and an analysis that addresses the timing and design of those measurements. Such results and analysis details are not reported in the registry record.

16. Why This Trial Matters Statistically

This trial illustrates a common challenge in clinical and environmental research: a measured surrogate or process outcome may be relevant to a study’s purpose without directly answering a clinical-risk question. Bacterial CFU counts quantify colonies captured in the dental environment, while the stated broader aim includes practitioner risk during aerosol-generating procedures. The distinction matters when interpreting what the endpoint can support.

It also highlights how timing affects the estimand—the quantity a study is intended to estimate. The primary endpoint is described as a baseline measure taken before treatment. Comparisons of baseline means can describe the groups’ measured starting levels, but they do not quantify changes after using suction equipment or rinses. In general, a treatment-effect question requires a clearly specified outcome time and an analysis aligned with that timing.

The combination of small group sizes and large standard deviations in several groups produces broad confidence intervals. This is a useful reminder that a point estimate alone can overstate how much information the data contain. Intervals communicate that the observed differences are compatible with materially different values, including values on either side of zero.

Finally, the registry record does not report the analysis plan, handling of missing data, multiplicity approach, or original sample-size justification. These details are important for judging how confirmatory the posted comparisons are and how they were selected. The record supports a careful description of the outcome summaries and their uncertainty, while leaving important questions about the intended and conducted analysis unresolved.

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.

Several trial-specific limitations constrain interpretation. The primary outcome is explicitly measured at baseline, one hour before treatment. The posted comparisons therefore do not show post-treatment CFU levels or change from baseline, despite the study’s broader aim of evaluating equipment and mouth rinses during aerosol-generating procedures. No such later primary outcome is reported in the registry record.

The group sizes are small: 10, 10, 11, and 10 participants. The standard deviations range from 16.38 to 155.4 across groups, indicating substantially different levels of observed spread. The confidence intervals are correspondingly broad, and all include zero. Raw participant-level and location-level data are not reported in the registry record, limiting assessment of skewness, outliers, or how individual sampling locations contributed to the average.

The endpoint description mentions petri dishes at four distances and an impinger, while the primary outcome is stated as an average CFU count. The exact construction of that average, including how measurements across locations and collection methods were combined, is not reported in the registry record. The record also does not report outcome data separately by location in the posted results.

The statistical analysis plan, analysis population, handling of missing data, multiplicity strategy, interim analyses, and original sample-size rationale are not reported in the registry record. Although the trial is identified as randomized and double-blind, implementation details are also absent. These reporting gaps make it difficult to determine how the posted pairwise comparisons relate to the prespecified study questions or whether they account for the trial’s design and multiple outcomes.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Evaluation of Aerosol in a Dental Clinic — NCT04659928.
• Registry record last updated 2025-07-08; status last verified 2025-06.
• Results first posted 2025-07-08.
• 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

NCT04659928 is a completed, randomized, double-blind, parallel-group Phase 4 study sponsored by The University of Texas Health Science Center, Houston. It enrolled 41 participants and evaluated combinations of HVE suction, an extraoral vacuum aspirator, hydrogen peroxide, and placebo in a dental clinic.

The primary outcome is the average number of bacterial CFUs at baseline. Four groups have posted means and standard deviations, and three comparisons use HVE suction only with placebo as the reference. The estimated differences are imprecise, and all reported confidence intervals include zero. The primary endpoint is measured before treatment, so these results describe baseline group measurements rather than treatment-related changes. The registry record does not report the detailed statistical plan, analysis population, missing-data methods, or a practitioner-risk outcome.