Effect of the DentalVibe Injection System on Pain During Local Anesthesia Injections in Children: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Effect of the DentalVibe Injection System on Pain During Local Anesthesia Injections in Children (NCT03374982), a randomized na study. The primary outcome is Self Reported Pain Rating Using Wong-Baker FACES Scale.

2. Clinical Question

The registry describes a randomized, single-masked crossover study. The two sequences were DentalVibe on then off, and DentalVibe off then on. The central statistical feature is that the same child was scheduled to experience both conditions. This differs from a parallel-group comparison in which each participant receives only one condition. In a crossover design, ratings may be related within a child, but the registry record does not report how that relationship was incorporated into the analysis.

The primary outcome is a subjective rating recorded immediately after injection. The clinical question is therefore about the distribution of children’s reported pain scores under the two injection conditions, not an objective measurement of tissue response or a later assessment. The registry gives group means and standard deviations, but does not report participant-level paired differences or the analysis method used to compare the conditions.

3. Trial Design

The registry lists a randomized, single-masked, crossover trial and an enrollment of 23. It is marked completed. The listed study dates are 2018-02-19 for the start and 2018-04-03 for primary completion. The sponsor is the University of Nebraska. The phase is listed as not applicable.

Each child was scheduled for two separate restorative appointments. DentalVibe was used during local anesthetic injections at both appointments, with the device turned on at one appointment and off at the other. Random assignment determined the order: one sequence received the on condition first and the off condition second; the other received the off condition first and the on condition second. This order assignment is important because experiences or ratings might vary across appointments, although the registry record does not report whether period or sequence effects were assessed.

The outcome was collected after each injection. The child was shown the Wong-Baker FACES Pain Rating Scale and asked to choose a face corresponding to the level of hurt during the injection. The primary outcome timeframe is immediately after local anesthetic delivery. Follow-up is described as continuing for any necessary recommended dental treatment, but the registry does not specify a duration for that follow-up.

The registry lists one primary outcome measure and no posted secondary outcome measures. It lists no statistical analyses. The original statistical plan, including the planned treatment of the crossover structure, is not reported in the registry record. Likewise, the basis for the original enrollment target, any interim analyses, and any prespecified method for handling missing outcome measurements are not reported. The registry’s enrollment and posted outcome counts should therefore be distinguished from details about the intended analysis, which are not available in the record.

4. Participant Flow and Accounting

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

Overall Study

5. Baseline Characteristics

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

6. Primary Endpoint

The registry lists the primary outcome as Self Reported Pain Rating Using Wong-Baker FACES Scale, measured over Immediately after local anesthetic delivery.

The primary endpoint is the mean self-reported pain rating on the Wong-Baker FACES scale immediately after local anesthetic delivery. The registry describes pictures of facial expressions linked to a numerical scale from 0, meaning no hurt, to 10, meaning the worst hurt. A child selects the face associated with the level of hurt experienced during the injection.

A self-report measure is relevant because pain is a subjective experience. Asking the child directly captures the child’s own rating rather than relying only on an observer’s interpretation. The scale’s visual faces may help children communicate a response, while the associated numerical values allow ratings to be summarized and compared statistically. These measurements remain ratings, not direct readings of pain intensity on an objective physical scale.

The registry summarizes the endpoint using a mean and standard deviation for the DentalVibe-on and DentalVibe-off conditions. The mean describes the average recorded rating in a condition; the standard deviation describes how spread out the ratings were around that average. A mean alone does not convey the full range of children’s responses, and the standard deviation is not a confidence interval for the mean.

The timing matters: the stated endpoint is assessed immediately after delivery of local anesthetic. It does not represent pain at a later time, overall dental experience, or a measure of treatment success. The registry does not report additional psychometric details, such as how the scale was analyzed for this study or whether any ratings were missing.

7. Results Posted in the Registry

• DentalVibe Off: mean 5.13 versus 3.57 on control; difference 1.56 (95% CI -0.33 to 3.45), standardized effect d = 0.48; z-test p = 0.105.

8. Statistical Interpretation

9. Statistical Methods Explained

The registry reports a continuous outcome summarized by a mean and standard deviation. These statistics answer different questions. The mean is the arithmetic average of the recorded ratings in a condition. The standard deviation describes the spread of individual ratings around that average. A larger standard deviation indicates greater variation in the observed scores; it does not quantify uncertainty in the mean in the same way as a confidence interval.

What does the mean difference represent?

The posted comparison is a mean difference of 1.56, defined in the record as the DentalVibe-off mean minus the DentalVibe-on mean. Because the off-condition mean is higher, the point estimate indicates that the average recorded rating was higher in that condition in this sample. This is a descriptive contrast and does not by itself establish a causal effect or show that every participant gave a higher rating under that condition.

A mean difference is measured in the original scale’s units, so it can be interpreted in relation to the 0-to-10 rating scale. Its uncertainty is represented by a confidence interval. The registry’s interval crosses zero, meaning that values consistent with the reported uncertainty include a difference in either direction as well as no difference. A confidence interval is not a range containing a fixed proportion of individual children’s scores; it describes uncertainty about the estimated group contrast under the assumptions of the analysis.

What does the p-value say?

The unadjusted p-value is 0.105. In general, a p-value measures how incompatible the observed data, or data more extreme, would be with a specified null model of no difference, assuming that model and the analysis assumptions are appropriate. It is not the probability that the null hypothesis is true, and it does not give the probability that the observed result occurred by chance. The registry does not report the full statistical model or its assumptions, so the p-value should be read as the posted unadjusted result rather than as a complete account of the analysis.

A p-value does not measure the size or importance of a difference. The estimate and interval are needed to understand the direction and range of plausible values. In this case, the interval’s inclusion of zero and the p-value of 0.105 indicate uncertainty in the contrast. They do not prove equality between the conditions.

Why does the crossover design matter?

In a crossover study, each participant receives both conditions, commonly in different periods and in an assigned order. A participant’s two ratings may be more alike than ratings from different participants because some children may generally use higher or lower values on the scale. An analysis that uses the within-child pairing can account for this correlation and may provide a different estimate of uncertainty from an analysis that treats the condition observations as independent.

Order and period can also matter in crossover designs. Ratings could vary between appointments, and the sequence itself may be relevant to interpretation. These are general considerations for crossover analyses, not claims that such effects occurred in this trial. The registry lists the two treatment sequences but does not report whether the posted comparison accounts for within-child pairing, period, sequence, or other design features. The statistical analysis plan is not reported in the registry record.

Why can over-dispersion matter?

As a general statistical concept, over-dispersion means that observed variation is greater than a model assumes. If a model understates the variability, its standard errors may be too small and its confidence intervals too narrow. Conversely, an analysis that represents variation appropriately can better reflect uncertainty. The registry reports standard deviations for the two conditions, but it does not report a distributional assessment or model diagnostics. Since the endpoint is a bounded rating scale, the mean and standard deviation are useful summaries but cannot show whether the distribution is symmetric, concentrated at particular values, or affected by values near the scale limits.

The posted comparison also gives a pooled standard deviation of 3.268 and a standardized effect estimate of 0.477. Standardized effects express a contrast relative to a measure of variability and are sometimes used for planning illustrations. They are not in the original rating units, and they do not replace the mean difference. The registry does not describe these quantities as the primary inferential analysis.

In general, analysis should match the allocation and measurement structure. Here, randomization concerns treatment order, while each child was expected to contribute ratings under both conditions. The record’s listed arm summaries show 23 observations for each condition, but no analysis entries are posted. It is therefore not possible to reconstruct a paired analysis, assess assumptions, or determine how incomplete pairs were handled from the registry summary alone.

10. Confidence Intervals and Precision

The posted mean difference is 1.56 points, with a confidence interval extending from -0.329 to 3.449. That interval includes zero and spans both negative and positive differences. Thus, the estimate is uncertain about whether the average rating was higher in the on condition or the off condition in the population represented by the analysis. The interval also shows that the data are compatible with a range of magnitudes, rather than pinning down a single value.

A confidence interval conveys precision, not the distribution of individual ratings and not certainty that the true value lies inside the particular interval. In general, a narrower interval indicates a more precise estimate and a wider interval indicates greater uncertainty, conditional on the statistical model and assumptions. Here, the interval’s width relative to the scale and its crossing of zero are important features for interpretation.

The reported standard deviations, 3.13 for DentalVibe on and 3.4 for DentalVibe off, indicate substantial spread in ratings around the means. Those figures describe variability in individual observations; they are not themselves measures of precision for the mean difference. The standard errors listed for the condition means are 0.653 and 0.709, but the registry does not state how the standard error for the crossover comparison was derived or whether paired observations were used.

Because the registry does not report the analysis model or the paired data, the interval should be interpreted as the interval attached to the posted unadjusted comparison. It should not be treated as a verified interval from a model that fully accounts for all crossover features. The record also does not report a threshold for a difference considered practically important. Statistical precision alone therefore cannot determine whether any particular value within the interval would be meaningful to patients or clinicians.

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 assumptions. The calculation assumes a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation; the effect to detect is the stated fraction of the observed effect. The original sample-size justification and design assumptions are not reported in the registry record.

For planning based on 100% of the observed effect, the illustration gives 69 participants per arm for 80% power and 93 participants per arm for 90% power. For planning based on 75% of the observed effect, it gives 123 participants per arm for 80% power and 164 participants per arm for 90% power. For planning based on 50% of the observed effect, it gives 276 participants per arm for 80% power and 369 participants per arm for 90% power.

In general, 80% power means that, if the assumed effect and calculation assumptions were correct, a study of the stated size would have an 80% chance of producing a result that meets the specified statistical significance criterion. The 90% column describes a higher chance under those same assumptions. Greater power generally requires more participants for a given effect, and smaller effects need more participants to detect than larger effects. The illustrations are not observed power and are not a report of the trial’s original target or actual analysis.

Because these figures use a simple planning framework, they should not automatically be treated as design recommendations for a crossover study. The registry does not report whether the original enrollment target used paired-data assumptions, nor does it provide the correlation between a child’s ratings under the two conditions. Those details can influence planning for a crossover design.

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 = 1.560; pooled standard deviation σ = 3.268.
2. n = 2 × (1.96 + 0.842)² × 3.268² / 1.560² = 68.9, rounded up to 69 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 <- 1.56                      # observed difference in means
sigma <- 3.26778977291992                     # 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(3374982)
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 = 69 (80% power), 93 (90% power)
 75% of observed effect: n per arm = 123 (80% power), 164 (90% power)
 50% of observed effect: n per arm = 276 (80% power), 369 (90% power)
power.t.test: 69.9 
Simulated power at n = 69 per arm: 0.796 (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 one primary outcome measure and no posted secondary outcome measures. It lists zero posted analyses. The record does not report a statistical analysis plan, a hierarchy of outcomes or tests, or a multiplicity adjustment. It is therefore not possible to determine whether the posted comparison was the only analysis performed, whether other analyses were planned, or how any multiple comparisons were handled.

Multiplicity is a general concern when many outcomes, time points, subgroups, or statistical tests are examined. Each additional test can increase the chance of at least one apparently unusual result under a null model. This does not establish that multiple testing occurred in this trial; it explains why a prespecified analysis plan is useful. The registry record does not describe any interim analyses or stopping rules.

The record lists an enrollment of 23 and condition-level outcome summaries with 23 observations for DentalVibe on and 23 for DentalVibe off. It does not explicitly report the number of complete paired records used in the comparison or whether any participants lacked an outcome at either appointment. A crossover analysis may require both condition measurements for a participant, depending on the method. The handling of incomplete pairs, missing ratings, or withdrawals is not reported in the registry record.

The analysis population is also not described in sufficient detail. The registry does not state whether all randomized participants were included in the primary comparison, whether the analysis followed assigned sequence, or whether any per-protocol or other population was used. These are distinct analysis choices, and the posted arm summaries do not settle them. The record does not report imputation methods or sensitivity analyses for missing data. As a result, the potential influence of missingness and analysis-population decisions cannot be assessed from the posted summary.

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 registry’s adverse-event figures report zero serious adverse events for DentalVibe on and zero for DentalVibe off. The listed number at risk is 23 for each condition. The registry also reports zero other adverse events in each condition and zero deaths. No serious adverse-event terms are listed.

These figures describe what was recorded in the registry for the stated groups and outcome reporting. They do not establish that no events of any kind occurred outside the registry’s definitions or collection process. The record does not provide further detail about event definitions, severity grading, ascertainment, or the period over which events were monitored. It also does not report a separate safety analysis or explain how crossover exposure was handled for adverse events.

Counts of zero should be read as zero reported events in the listed data, not as proof that an event is impossible or that risk is absent. With a small study, event counts alone cannot precisely characterize uncommon events. These safety figures are descriptive and do not support broad conclusions about safety in other populations or settings.

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

The registry reports lower average pain ratings in the DentalVibe-on condition than in the DentalVibe-off condition in this study: the means were 3.57 and 5.13, respectively. The posted mean difference, defined as off minus on, was 1.56. Ratings varied within each condition, and the unadjusted comparison had a p-value of 0.105. Its confidence interval crosses zero, so the result remains uncertain about the direction and magnitude of the average difference.

This does not establish that the two conditions produce the same ratings. A result that does not meet a conventional significance threshold is not proof of equivalence. Nor does the point estimate alone establish a reliable difference. The registry does not report a prespecified equivalence margin or a threshold for a clinically meaningful change, so neither equivalence nor practical importance can be assessed from the reported comparison.

The result concerns children’s immediate self-reported ratings after local anesthetic delivery, using the Wong-Baker FACES scale. It is not a measure of later pain, overall dental experience, or a broader health outcome. The study population was children age 5–11 years requiring bilateral dental treatment at a specific pediatric dental clinic and able to understand and speak English. Applying the result to other ages, settings, or treatment circumstances requires caution.

The crossover design means that children were scheduled to experience both conditions in a randomized order. The registry does not explain whether the analysis accounted for the pairing of observations, sequence, or period. This missing information limits how confidently the posted uncertainty can be interpreted. The results are best read as the registry’s descriptive summaries and unadjusted comparison, not as a complete statistical evaluation of every feature of the design.

The safety figures report no serious or other adverse events and no deaths in the listed conditions. They are counts from this record and do not demonstrate absence of risk. Overall, the posted data describe a small trial with variable ratings and an imprecise comparison; they do not settle the broader question for all children or clinical settings.

16. Why This Trial Matters Statistically

This trial is statistically instructive because its crossover design gives each child experience with both injection conditions. Such designs can make within-person comparisons informative, since stable differences between participants may be less influential when the same person contributes measurements under each condition. That potential advantage depends on the analysis recognizing the paired structure. The registry does not report whether it did so, making the design-analysis match a central interpretive issue.

The outcome also illustrates the distinction between an average and the spread of individual responses. The means differ, but the standard deviations are sizeable relative to that contrast. A group average can conceal children with very different ratings, and the registry’s summaries do not show individual changes or the distribution of scores. The confidence interval and p-value communicate uncertainty about the average contrast, while neither describes each child’s experience.

The record is also a useful reminder that statistical significance is not the same as practical importance. The posted p-value is 0.105 and the interval crosses zero, but those details do not establish that the conditions are equivalent. A meaningful-difference threshold is not reported. Without such a threshold, readers cannot judge the estimate against a stated standard of practical relevance.

Finally, transparent reporting matters for reproducibility and interpretation. The registry identifies the randomized sequences and endpoint, yet does not report the statistical analysis plan, handling of missing data, or details of how the crossover structure entered the comparison. These omissions prevent a full assessment of assumptions and analysis choices. The posted data still allow a descriptive reading, but more complete reporting would be needed to evaluate the inferential analysis in depth.

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 that constrain interpretation. Most importantly, it lists a crossover design but does not report whether the comparison used the within-child pairing. The posted group means and standard deviations do not reveal the correlation between each child’s two ratings, and the analysis details are not reported. This makes it difficult to assess the precision of the estimate in relation to the design.

The registry does not report whether period or sequence effects were evaluated. Children received the conditions at separate appointments in randomized order, so the timing and order are elements of the design that may be relevant to analysis. This is a methodological consideration, not evidence that an order effect occurred.

The study enrolled 23 children, and the outcome is a subjective rating on a bounded scale. The record does not provide the distribution of scores, individual paired differences, or information about score patterns near the scale limits. The means and standard deviations alone cannot show whether the data were symmetric or whether a few ratings strongly influenced the averages.

The analysis population, missing-data handling, and any sensitivity analyses are not reported. Although each condition summary lists 23 observations, the registry does not state explicitly how many complete pairs contributed to the comparison or how incomplete measurements would have been handled. The original sample-size justification is also not reported.

Generalizability is limited by the stated eligibility and setting: children age 5–11 years requiring bilateral dental treatment at one university pediatric dental clinic and able to understand and speak English. The record does not report further participant characteristics that would help assess representation. Follow-up is described in relation to necessary recommended dental treatment, but its duration is not specified.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Effect of the DentalVibe Injection System on Pain During Local Anesthesia Injections in Children — NCT03374982.
• Registry record last updated 2024-01-03; status last verified 2023-12.
• Results first posted 2024-01-03.
• 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

The registry record describes a completed randomized, single-masked crossover study sponsored by the University of Nebraska, with enrollment of 23. Children were scheduled for local anesthetic injections with DentalVibe on and off in randomized order. The primary endpoint was the child’s Wong-Baker FACES pain rating immediately after injection.

The posted mean ratings were 3.57 with the device on and 5.13 with it off, with standard deviations of 3.13 and 3.4. The unadjusted mean difference was 1.56, with a reported p-value of 0.105 and a confidence interval that crosses zero. The registry reports zero serious adverse events, zero other adverse events, and zero deaths in the listed conditions.

The registry does not report the statistical analysis plan, whether the comparison accounted for paired crossover measurements, missing-data handling, or the original sample-size rationale. These omissions limit assessment of the inferential analysis beyond the posted summaries.