Curved Soft-Picks on Plaque Accumulation on Patients With Gingivitis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Curved Soft-Picks on Plaque Accumulation on Patients With Gingivitis (NCT02883244), a randomized na study. The primary outcome is Change in Interproximal Plaque by Modification of the Quigley-Hein Plaque Index at 14 Days.

2. Clinical Question

3. Trial Design

The registry describes a randomized, single-masked, parallel-group trial. Participants were assigned to Soft-Picks Advanced or floss, with the latter described as waxed tape floss. The record does not state who was masked, how randomization was generated or concealed, or whether participants used their assigned device according to a standardized schedule. Those details are not reported in the registry record.

The listed enrollment was 50, and the study status is completed. The record gives a start date of 2016-12 and a primary completion date of 2017-05. It identifies the condition as gingivitis and lists Sunstar Americas as the sponsor. The phase is recorded as not applicable.

The primary outcome was change in interproximal plaque by a modified Quigley-Hein Plaque Index at 14 days, measured from baseline. The outcome description refers to visually assessed tooth surfaces in qualifying interproximal test units. Scores were on a scale from 0 to 5, with 0 described as no debris or stain on the clinical crown and 5 as plaque coverage over more than two third of the tooth surface. The record's wording about the assessed surfaces and units is retained as written; further operational details are not reported.

Secondary outcomes listed in the record include ease of use, gingivitis by the UNC Modified Gingival Index, bleeding on probing, and probing pocket depth. The first three have posted numerical summaries. Numerical results for probing pocket depth are not reported in the registry record. The reported follow-up times are 28 days for the secondary outcomes and 14 days for the primary outcome. The record does not describe the trial's original sample-size rationale, analysis populations, or handling of missing observations.

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: All subjects received professional prophylaxis and assigned manual toothbrush and dentifrice. Group was assigned 3 weeks or more after professional prophylaxis.

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 Change in Interproximal Plaque by Modification of the Quigley-Hein Plaque Index at 14 Days, measured over Baseline and 14 days.

The primary endpoint is change in interproximal plaque score between baseline and 14 days. It uses the modified Quigley-Hein Plaque Index, a visual scoring measure in which the registry describes a 0-to-5 scale. The outcome definition states that change equals the 14-day score minus the baseline score. On the scale description, higher scores represent more plaque coverage, so a negative change indicates a lower score at follow-up than at baseline, while a positive change indicates a higher score.

Measuring change allows the comparison to focus on how scores moved over the follow-up interval, rather than only comparing follow-up scores without reference to baseline. Interproximal sites are relevant to the stated study question because the devices are intended for cleaning spaces between teeth. The registry describes assessment of qualifying interproximal test units and visually scored tooth surfaces, but does not report additional details about assessor training, reproducibility, or the exact aggregation of surface scores into each participant's endpoint.

The primary result is a comparison of mean changes between the randomized arms. It is not a direct measure of long-term cleaning habits, sustained use, or clinical outcomes beyond the specified plaque score and follow-up. The posted primary summary reports group means and standard deviations, plus an unadjusted mean difference and confidence interval. The registry record does not report an adjusted primary analysis or additional analytic details.

7. Results Posted in the Registry

• Floss: mean -0.07 versus 0.03 on control; difference -0.10 (95% CI -0.70 to 0.50), standardized effect d = -0.09; z-test p = 0.742.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Performance (Easy to Use) of an Assigned Product

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Floss: mean 3.37 versus 3.80 on control; difference -0.43 (95% CI -0.54 to -0.32), standardized effect d = -2.25; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Floss than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Change in Gingivitis by UNC Modified Gingival Index at 28 Days

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Floss: mean 0.03 versus -0.02 on control; difference 0.05 (95% CI -0.15 to 0.25), standardized effect d = 0.14; z-test p = 0.627.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Floss and the control. The interval gives the range of effects that remain compatible with the data.

Change in Gingivitis by Bleeding on Probing at 28 Days

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Floss: mean 13.00 versus 7.00 on control; difference 6.00 (95% CI -4.92 to 16.92), standardized effect d = 0.31; z-test p = 0.281.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Floss and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes broaden the focus beyond the 14-day plaque measure to include perceived ease of use and gingivitis measures at 28 days. Their overall pattern is mixed rather than a single consistent signal across every type of outcome. The ease-of-use comparison differs more clearly between arms in its posted numerical summary, whereas the gingivitis summaries are less decisive and their uncertainty intervals include zero. These endpoints measure different constructs, so their results should not be treated as interchangeable confirmations of the primary endpoint.

The secondary findings do not overturn or explain the primary plaque result. They concern later follow-up and different measures, and the registry does not report an analysis linking changes in plaque to changes in gingivitis or ease of use. A between-arm pattern in a subjective product-performance score does not establish sustained behavior, while a gingivitis measure cannot be assumed to be a direct substitute for the plaque index.

Probing pocket depth is listed among the secondary outcomes, but numerical results are not reported in the registry record. This means that the full set of listed secondary questions cannot be assessed from the posted outcome summaries.

Unadjusted secondary results carry less weight when multiple outcomes are examined because the chance of encountering an apparently notable result can increase across repeated comparisons. The registry does not report a multiplicity adjustment or identify a hierarchy for interpreting secondary outcomes. These findings are therefore best treated as descriptive and exploratory rather than as independent confirmatory evidence. Their interpretation also depends on outcome definitions, missing-data handling, and analysis choices that are not fully described in the record.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Performance (Easy to Use) of an Assigned Product
• Change in Gingivitis by UNC Modified Gingival Index at 28 Days
• Change in Gingivitis by Bleeding on Probing at 28 Days
• Change in Gingivitis by Probing Pocket Depth at 28 Days

9. Statistical Interpretation

10. Statistical Methods Explained

The registry posts continuous outcomes as means with standard deviations. A mean describes the center of the observed scores, while a standard deviation describes their spread around that mean. For the primary outcome, the reported change is defined as the score at 14 days minus the baseline score. The group means therefore describe average change, not average plaque level at either visit alone.

What does the mean difference represent?

The posted primary mean difference is -0.1, calculated as the floss mean change relative to the Soft-Picks Advanced mean change. A negative contrast indicates that the floss group's mean change was lower on the score scale than the Soft-Picks Advanced group's mean change. Because the scale assigns larger values to greater plaque coverage, the sign describes direction on that scale; it does not establish a meaningful clinical advantage. The registry does not report a threshold for a clinically important difference.

The contrast is an unadjusted comparison based on the posted group summaries. It is not presented as an adjusted model estimate. The registry record reports no analysis entries and does not describe covariate adjustment, a repeated-measures model, or other modeling choices. The calculated comparison should therefore be read as a straightforward summary-statistic comparison, not as evidence that any particular model was used by the trial investigators.

Why is a confidence interval useful?

A confidence interval expresses uncertainty around an estimated difference. In general, it gives a range of values compatible with the observed data under the method used to calculate it. The primary interval, from -0.695 to 0.495, includes zero and allows values on either side of zero. That means the data do not pinpoint a single direction or magnitude with high precision. A confidence interval is not a guarantee that the true value lies within its bounds, and it does not replace consideration of the outcome's clinical meaning.

What does the p-value say?

The unadjusted p-value for the primary comparison is 0.742. 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. It is not the probability that the null hypothesis is true, nor is it a measure of the size or importance of an effect. The registry record does not report a prespecified analysis plan or a multiplicity adjustment for the outcomes.

What role does randomization play?

Random allocation is intended to reduce systematic differences between comparison groups, on average, by assigning participants independently of their expected outcomes. It does not guarantee identical groups, particularly in a small study. The registry identifies the design as randomized but does not report the sequence-generation or allocation-concealment procedures. The record also does not describe which individuals were masked. These omissions limit assessment of how the design was implemented, without changing the fact that the registry classifies the trial as randomized and single-masked.

Why might variation matter?

For a continuous measure, variability affects how precisely a group mean and between-group contrast can be estimated. Large within-group spread relative to the contrast can leave a broad interval, as in the primary summary. General statistical methods sometimes account for over-dispersion when outcome variability is greater than a model expects; the registry does not report an over-dispersion model or a reason to assume one was used. The posted standard deviations are descriptive and should not be mistaken for standard errors or confidence limits.

The primary endpoint is a change score, and the registry does not report whether the comparison adjusted for baseline score. It also does not describe how missing observations were handled, whether all randomized participants were analyzed, or whether any participants discontinued. Those choices can affect interpretation of estimates, especially when observed outcome counts differ across endpoints. The appropriate conclusion is limited to the posted summaries and the analysis details that are actually recorded.

11. Confidence Intervals and Precision

The primary estimate is a mean difference of -0.1, with a 95% confidence interval from -0.695 to 0.495. The interval extends both below and above zero, so the observed comparison does not determine the direction of the underlying difference. Its width indicates that the estimate is not highly precise: values across a meaningful span on the score scale remain compatible with the posted data and calculation.

Precision is affected by the amount of variation in scores and the number of observations contributing to the estimate. The primary group standard deviations were 1.02 and 1.12, while the reported group outcome counts were 26.0 and 24.0. These summaries describe the information available for the primary comparison; they do not establish why the interval has its observed width. The registry does not report a prespecified precision target or a clinically important difference against which to judge the interval.

The p-value of 0.742 and the interval are related ways of describing the comparison under the reported unadjusted calculation. Neither establishes equivalence. To support an equivalence conclusion, a study would need a defined margin and an analysis framed around that margin; those elements are not reported in the registry record. Likewise, the interval alone does not say whether every value it contains would matter in practice.

Confidence intervals describe uncertainty in an estimate, not the full range of individual participant responses. The standard deviations describe spread of participant-level scores around group means, while the confidence interval pertains to uncertainty in the estimated between-group mean difference. These quantities answer different questions and should not be used interchangeably.

12. 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 primary planning figures are participants per arm, not total events. They are illustrations based on the observed effect, rather than a record of the trial's original design calculation. The planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation; the effect to detect is the stated fraction of the observed effect. The original sample-size assumptions for the trial are not reported in the registry record.

For planning for 100% of the observed effect, the illustration gives 1,795 participants per arm for 80% power and 2,402 participants per arm for 90% power. For planning for 75% of the observed effect, it gives 3,190 participants per arm for 80% power and 4,270 participants per arm for 90% power. For planning for 50% of the observed effect, it gives 7,177 participants per arm for 80% power and 9,608 participants per arm for 90% power.

In plain terms, 80% power describes the chance of detecting the specified effect under the stated planning assumptions if that effect is the true one; the 90% column uses a higher target chance under the same framework. The figures increase when the target effect is smaller, because smaller differences are generally harder to distinguish from sampling variability. The accompanying curve visualizes this relationship between the effect being targeted and the planning requirement.

These are planning illustrations, not observed power. They should not be read as a retrospective measure of the probability that this completed trial found a result, and they do not show that the trial was designed using these assumptions.

13. 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 = -0.100; pooled standard deviation σ = 1.069.
2. n = 2 × (1.96 + 0.842)² × 1.069² / -0.100² = 1,794.2, rounded up to 1,795 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 <- -0.1                      # observed difference in means
sigma <- 1.06908449931082                     # 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(2883244)
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 = 1,795 (80% power), 2,402 (90% power)
 75% of observed effect: n per arm = 3,190 (80% power), 4,270 (90% power)
 50% of observed effect: n per arm = 7,177 (80% power), 9,608 (90% power)
power.t.test: 1795.1 
Simulated power at n = 1,795 per arm: 0.797 (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.

14. Multiplicity, Missing Data and Analysis Populations

The record lists a primary plaque outcome and several secondary outcomes, but does not report a statistical analysis plan, a testing hierarchy, or a procedure for controlling multiplicity. When investigators examine multiple outcomes or time points, unadjusted tests do not account for the fact that several comparisons have been considered. As a general matter, this can make isolated low p-values less persuasive as confirmatory evidence. The posted secondary results should therefore be interpreted with caution, especially in the absence of a reported prespecified strategy.

The registry reports no analysis entries. It does not state whether the primary comparison was prespecified in a protocol, whether any interim analyses were conducted, or how potential deviations from an analysis plan were handled. These matters are not reported in the registry record, and no assumptions about them can be made from the summary results.

Outcome counts vary across the posted summaries. The primary plaque outcome reports 26.0 participants for Soft-Picks Advanced and 24.0 for floss. The posted 28-day summaries have different counts for the Soft-Picks Advanced arm in some outcomes. The record does not explain the differences, identify reasons for unavailable measurements, or state whether all randomized participants were included in each analysis. Missing-data methods, imputation, and sensitivity analyses are not reported.

The analysis population is also not described. The registry does not say whether results follow an intention-to-treat approach, a per-protocol approach, or another population definition. Nor does it report exclusions after randomization or how adherence was assessed. These omissions make it difficult to evaluate the potential influence of missing observations or post-randomization decisions on the estimates.

For these reasons, the posted comparisons are informative as summaries of the recorded outcomes but do not resolve questions about multiplicity, missingness, or the trial's full analysis strategy. Those details are not reported in the registry record.

15. 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 1% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports no serious adverse events in either arm and no deaths in either arm. For other adverse events, it records 1 affected participant among 26 at risk in the Soft-Picks Advanced group and 5 affected participants among 24 at risk in the floss group. These are the posted counts, not estimates of comparative risk adjusted for follow-up or other factors.

The serious-event figures should be read as event reporting within the registry record, not as proof that serious events cannot occur. The record does not provide event descriptions for the other adverse events, their severity, timing, relationship to the devices, or information about how completely events were monitored. It also does not report a statistical comparison of adverse-event counts. The available information supports only a descriptive account of the recorded counts over the study period.

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

The central result is an unadjusted comparison of mean change in plaque score over 14 days. The estimate is close to zero, and its confidence interval includes values on both sides of zero. The posted data therefore do not provide a precise estimate of the direction or magnitude of the difference between the assigned devices on this endpoint.

This finding does not establish that the devices are equivalent, nor does it show that either product is ineffective. A non-significant p-value is not proof of no difference. Equivalence or non-inferiority would require an appropriate design, a prespecified margin, and analysis directed at that question; those features are not reported in the registry record. The results also do not determine whether a difference within the interval would be important to patients or clinicians, because a clinically important threshold is not reported.

The inference is limited to the measured outcome, follow-up, and participants represented in the posted summaries. A 14-day visual plaque score is not itself evidence about long-term habits, sustained product use, or outcomes beyond the index. The record's stated interest in ease of use does not establish that any observed score difference led to a lasting hygienic routine. Likewise, 28-day gingivitis measures do not directly answer the primary plaque question.

The findings should not be generalized automatically to other populations, devices, floss products, schedules, or clinical settings. Details about participant characteristics, product-use instructions, adherence, and the analysis population are not reported. Randomization is a strength of the design classification, but the record does not describe how allocation was implemented or who was masked.

In short, the registry supports a cautious description of the observed comparison and its uncertainty. It does not support a broad conclusion about comparative effectiveness, equivalence, long-term behavior, or safety beyond the recorded adverse-event counts.

17. Why This Trial Matters Statistically

This trial illustrates why a point estimate and its uncertainty should be read together. The primary mean difference is small, but the interval is wide enough to include values in either direction. Focusing only on the point estimate could make the comparison seem more conclusive than the data warrant; focusing only on the p-value would omit the range of plausible estimates and their potential relevance.

It also shows the distinction between a nonsignificant result and evidence of equivalence. A study can fail to show a statistically clear difference while still leaving substantial uncertainty about the size of that difference. The registry does not report an equivalence margin or a design intended to test equivalence, so the primary result should be described as uncertain rather than as proof that the products perform the same.

The secondary outcomes demonstrate another practical issue: outcomes with different meanings and time points cannot simply be combined into one conclusion. Ease of use, plaque accumulation, gingivitis, bleeding on probing, and probing pocket depth address related but distinct questions. Without a reported multiplicity strategy, outcome hierarchy, or analysis plan, secondary patterns are more appropriately viewed as descriptive.

Finally, planning illustrations based on an observed effect are not the same as a trial's original sample-size rationale. Their assumptions and purpose need to be distinguished from what the completed study was designed to detect. Here, the original design assumptions are not reported, and the planning calculations are illustrations rather than observed power.

18. 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 follow from the information recorded. The primary follow-up is 14 days, while the listed secondary measures are at 28 days. The record therefore does not establish whether the observed short-term plaque-score patterns persisted beyond those assessments. Longer-term outcomes are not reported in the registry record.

The primary measure is a visual plaque score, but the registry does not report assessor training, inter-rater reliability, or whether outcome assessors were masked. The trial is described as single-masked, but the masked party is not identified. This limits assessment of how measurement and expectations may have affected the recorded outcomes.

The entry does not describe participant characteristics beyond the gingivitis condition, detailed eligibility criteria, adherence, device-use instructions, or the handling of missing observations. It also does not define the analysis population or report a statistical analysis plan. These omissions constrain assessment of how representative the observed groups are and how robust the estimates may be to analytic choices.

The study compares the specified curved Soft-Picks Advanced device with waxed tape floss. The results should not be assumed to apply to other designs or products. Numerical probing pocket depth results are not reported in the registry record, limiting interpretation of that listed secondary outcome. The record also gives no clinical threshold for an important difference in plaque or gingivitis scores, making it difficult to translate score contrasts into practical importance.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Curved Soft-Picks on Plaque Accumulation on Patients With Gingivitis — NCT02883244.
• Registry record last updated 2018-12-11; status last verified 2017-05.
• Results first posted 2018-11-16.
• 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.

22. Record Summary

NCT02883244 is a completed, randomized, single-masked, parallel-group device trial sponsored by Sunstar Americas. The record lists enrollment of 50 and compares curved Soft-Picks Advanced with waxed tape floss in patients with gingivitis. The primary outcome is change in interproximal plaque by a modified Quigley-Hein Plaque Index from baseline to 14 days.

The posted primary comparison is a mean difference of -0.1, with a 95% confidence interval from -0.695 to 0.495 and an unadjusted p-value of 0.742. Selected 28-day secondary summaries and adverse-event counts are also recorded. The registry does not report the original sample-size assumptions, a statistical analysis plan, analysis populations, or missing-data methods. The primary estimate is uncertain and does not establish equivalence.