Comparison of Masticatory Efficiency Between Complete Denture With Zero-degree Teeth and Anatomic Teeth in Patients With Severely Resorbed Ridge: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparison of Masticatory Efficiency Between Complete Denture With Zero-degree Teeth and Anatomic Teeth in Patients With Severely Resorbed Ridge (NCT02359955), a randomized na study. The primary outcome is EMG (Masseters EMG Are Recorded After Patient Wears Complete Denture for Three Months).

2. Clinical Question

3. Trial Design

The registry record describes a randomized, single-masked, crossover study with an enrollment of 20. Participants were assigned to one of two sequences: zero-degree teeth followed by anatomic teeth, or anatomic teeth followed by zero-degree teeth. Thus, each participant was intended to receive both denture types, with sequence order varying across participants. The record does not explain who was masked, how masking was maintained, or how randomization was generated.

The registry lists the study phase as not applicable. Its start date is 2014-06 and its primary completion date is 2015-05. The status is recorded as unknown. The sponsor is Haixin Qian. The record does not report a protocol rationale for the enrollment, planned treatment-period duration beyond the three-month outcome timeframe, or details of any interval between denture periods.

The primary outcome is masseter EMG amplitude after three months of wearing a complete denture. The description says that EMG measurements from 20 chewing strokes were recorded for amplitude and duration, with amplitude reported as the average across those strokes. The registry also lists the Masticatory Efficiency Index as a secondary outcome, measured at three months. It records three outcome measures but lists one secondary outcome title.

The posted primary summaries give separate results for right and left masseters under each denture type. The secondary summaries distinguish the two treatment sequences. These summaries do not include participant-level paired observations or a reported crossover analysis. The registry record lists no sponsor-reported statistical analyses, so details such as period adjustment, sequence effects, and handling of within-participant correlation are not reported.

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 EMG (Masseters EMG Are Recorded After Patient Wears Complete Denture for Three Months), measured over three months.

The primary endpoint is the mean amplitude of masseter muscle EMG activity, measured in microvolts after a participant had worn a complete denture for three months. The registry description says that EMG amplitude and duration were recorded across 20 chewing strokes; the reported amplitude is the average value from those strokes. Separate means and standard deviations are posted for the right and left masseters with zero-degree teeth and with anatomic teeth.

EMG amplitude is a continuous measure of electrical activity in the masseter muscles during chewing. In general, continuous measurements can describe the magnitude of a physiological response and allow comparison of group averages, while their spread indicates how much observations vary. The endpoint is therefore a physiological measure related to chewing activity, not a direct report of patient preference or a complete measure of everyday function.

The registry record does not report a threshold for a clinically important difference in EMG amplitude or explain how a difference in microvolts should be interpreted for patients. The posted endpoint is also distinct from the Masticatory Efficiency Index, which is listed as a secondary outcome. The results should consequently be read as measurements of the stated outcomes, not as direct evidence about broader clinical benefits.

7. Results Posted in the Registry

• Amp Value of Left Masseter of Zero Degree Teeth: mean 0.87 versus 0.72 on control; difference 0.15 (95% CI -0.17 to 0.47), standardized effect d = 0.29; z-test p = 0.353.
• Amp Value of Right Master of Anatomic Teeth: mean 1.07 versus 0.72 on control; difference 0.35 (95% CI -0.02 to 0.72), standardized effect d = 0.58; z-test p = 0.064.
• Amp Value of Left Masseter of Anatomic Teeth: mean 1.21 versus 0.72 on control; difference 0.49 (95% CI -0.01 to 0.99), standardized effect d = 0.61; z-test p = 0.053.

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.

Masticatory Efficiency Index

• 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:
  • Group 2 Anatomic Teeth: mean 0.33 versus 0.33 on control; difference 0.01 (95% CI -0.06 to 0.07), standardized effect d = 0.10; z-test p = 0.827.
  • Group 1 Anatomic Teeth: mean 0.34 versus 0.33 on control; difference 0.01 (95% CI -0.07 to 0.09), standardized effect d = 0.11; z-test p = 0.808.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Group 2 Anatomic Teeth and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Group 1 Anatomic Teeth and the control. The interval gives the range of effects that remain compatible with the data.

The registry lists the Masticatory Efficiency Index as a secondary outcome and posts summaries for the two treatment sequences. Across those summaries, the reported means are close in scale, and the simple recalculated contrasts have confidence intervals that include zero. This broad pattern does not establish that the denture types produce equivalent masticatory efficiency; it indicates that the posted summaries do not resolve a difference clearly.

The secondary outcome addresses a different aspect of chewing from masseter EMG amplitude. It can therefore complement the primary physiological measure, but it should not be treated as a substitute for it. A broadly similar lack of clear separation across the outcomes may be consistent with uncertainty in this study, not proof that the outcomes are identical or that one validates the other. No relationship between the index and EMG is reported.

The registry record lists no sponsor-reported analyses for the secondary outcome. The posted comparisons are unadjusted recalculations, and the record does not describe a prespecified testing hierarchy or a multiplicity adjustment. When several outcomes or contrasts are examined, the chance of at least one apparently notable result can increase. Unadjusted secondary results therefore carry less weight as confirmatory evidence than results from a prespecified, appropriately analyzed primary comparison.

Because the trial is a crossover, sequence-specific summaries also need cautious interpretation. The record does not report a paired crossover analysis or explain whether treatment period and sequence were considered. The overall secondary pattern can be described, but it cannot establish the absence of a treatment difference or resolve potential design-related effects.

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

• Masticatory Efficiency Index

9. Statistical Interpretation

10. Statistical Methods Explained

What does a mean describe?

A mean is the arithmetic average of the recorded values for an outcome group. For this study, the primary outcome is EMG amplitude, a continuous measurement expressed in microvolts. The registry reports mean amplitudes separately by masseter side and denture type. A mean provides a compact description of the group's measurements, but it does not show every participant's value or explain why values vary.

The standard deviation describes the spread of observations around a mean. A larger standard deviation indicates more variability in the recorded values. It is not the same as the standard error, which describes the uncertainty in an estimated mean. The posted summaries include standard deviations, while the recalculated contrasts also include standard errors for the component means.

How should a mean difference be read?

A mean difference expresses the estimated contrast between two group means in the outcome's original units. Here, the comparisons are expressed in microvolts. A positive estimate means the second mean in the contrast is higher than the reference mean under the posted ordering; it does not by itself establish that the difference is real, clinically important, or attributable to the denture type.

The posted comparisons are simple, unadjusted recalculations from summary statistics. They are not identified as sponsor-reported analyses. Because the study is described as a crossover, each participant's measurements under the two denture types would ordinarily be related. A paired analysis can account for that relationship. The available group summaries do not include the within-participant differences needed to reconstruct such an analysis, and the registry record does not report a crossover model or adjusted estimate.

What does a confidence interval communicate?

A confidence interval gives a range of values compatible with the data under the method used to calculate it. In general, a narrower interval represents greater precision, while a wider interval represents greater uncertainty. The posted 95% confidence intervals describe uncertainty around the recalculated mean differences; they do not guarantee that the true difference lies within the interval, and they do not measure the probability that a particular treatment is better.

When an interval includes zero, the data are compatible with no mean difference as well as with differences in either direction covered by the interval. This is why an interval should be considered alongside the point estimate, the outcome scale, study design, and any clinically meaningful threshold. No such threshold is reported in the registry record.

What does an unadjusted p-value say?

A p-value describes how surprising data at least as incompatible with a null hypothesis would be if that hypothesis and the statistical model were correct. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of an effect. The posted p-values are labelled unadjusted. They therefore do not account for the possibility that multiple outcome contrasts were examined.

The registry record lists no sponsor-reported analyses. In particular, it does not report whether the study's analysis accounted for the crossover structure, denture sequence, treatment period, or potential carryover. A statistical adjustment for these design features can affect both the estimate and its uncertainty. They cannot be recovered from the marginal means and standard deviations alone.

Why does the study design matter?

In a crossover study, participants serve as their own comparison by receiving each treatment in sequence. This can reduce the influence of stable differences between participants when the analysis uses within-participant contrasts. However, the interpretation depends on how measurements are related across periods and on whether period or sequence effects matter. The registry record describes the two sequences but does not report a washout interval or a method for assessing these effects.

Accordingly, the posted recalculations are useful as descriptive, unadjusted comparisons of the available summaries. They should not be mistaken for a fully specified analysis of the randomized crossover trial. The record does not report missing-data methods, an analysis population, a prespecified multiplicity strategy, or a statistical analysis plan. Those omissions limit how confidently the posted results can be linked to a particular inferential procedure.

11. Confidence Intervals and Precision

The 95% confidence intervals around the primary mean differences are broad relative to the point estimates, and each spans zero. For the left masseter with zero-degree teeth, the interval extends from -0.166 to 0.466 microvolts. For the right masseter with anatomic teeth, it extends from -0.021 to 0.721 microvolts. For the left masseter with anatomic teeth, it extends from -0.006 to 0.986 microvolts. These ranges indicate that the recalculated estimates are not precise enough to rule out no mean difference or a range of differences in either direction.

Confidence intervals are useful because they show uncertainty and effect size together. A p-value alone cannot indicate how large an effect might be, whereas an interval places plausible values on the outcome scale. Here, the estimates are unadjusted recalculations from posted summary statistics. They do not represent a sponsor-reported crossover analysis, and their precision may differ from that of an analysis using paired participant-level measurements.

Precision is not the same as clinical importance. The registry record does not state what difference in microvolts would matter to patients or clinicians, so the intervals cannot be classified as excluding or including a clinically meaningful effect. The record also does not provide an analysis accounting for sequence or period. These uncertainties make the intervals informative as descriptions of the recalculated contrasts, but not a complete account of uncertainty for the trial's intended crossover comparison.

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 planning figures are participants per arm for 80% power and participants per arm for 90% power. They are not total events; event-based planning applies to time-to-event outcomes, and this trial's listed outcomes are continuous. The figures are illustrations based on the observed effects, not the original study's design assumptions. The registry record does not report the trial's own sample-size justification or assumptions.

The planning calculation uses a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. Each planning scenario uses a stated fraction of the observed effect: the full observed effect, 75% of it, or 50% of it. The 80% column means the planned sample size is intended to give an 80% chance of detecting the chosen effect under those assumptions if the effect is present. The 90% column expresses the corresponding target with a higher chance of detection.

Smaller effects are harder to distinguish from random variation, so the planning illustrations require more participants per arm when the target is reduced to a smaller fraction of the observed effect. The curve represents this same planning relationship across effect sizes. These estimates are not observed power: they are forward-looking planning illustrations based on effects estimated from this small trial and assumptions that may not match a future study. The original crossover design also differs from a simple equal-allocation two-arm planning calculation, so these figures should not be read as a retrospective assessment of whether the trial was adequately designed.

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 = 0.150; pooled standard deviation σ = 0.510.
2. n = 2 × (1.96 + 0.842)² × 0.510² / 0.150² = 181.7, rounded up to 182 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 <- 0.15                      # observed difference in means
sigma <- 0.510392006206994                     # 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(2359955)
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 = 182 (80% power), 244 (90% power)
 75% of observed effect: n per arm = 324 (80% power), 433 (90% power)
 50% of observed effect: n per arm = 727 (80% power), 974 (90% power)
power.t.test: 182.7 
Simulated power at n = 182 per arm: 0.802 (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 registry record lists one primary outcome, with measurements reported separately for right and left masseters and comparisons involving the zero-degree and anatomic denture summaries. It also lists the Masticatory Efficiency Index as a secondary outcome. The posted results include multiple contrasts, but the record does not report a multiplicity plan, such as a prespecified order of testing or an adjustment for examining several comparisons.

Multiplicity matters because repeated statistical tests can make apparently notable results more likely even when there is no underlying effect. The posted p-values are unadjusted. They can be read as descriptive inferential summaries for their individual contrasts, but should not be treated as confirmatory evidence across all outcomes and comparisons. The record does not say whether any additional analyses were planned or conducted.

Missing-data handling is not reported in the registry record. It does not state whether all randomized participants contributed outcome measurements, how incomplete treatment periods were handled, or whether any values were imputed. The primary summaries list 20 observations for each denture and side, while the secondary summaries list 10 observations for each sequence-specific group. Those posted counts do not explain participant flow or establish the analysis population for every outcome.

The registry record also does not report whether analyses followed an intention-to-treat principle, were restricted to participants completing both periods, or used another population definition. For a crossover study, these distinctions matter because missing measurements in one treatment period can affect which paired comparisons are available. No sensitivity analysis or missingness assessment is listed. The absence of these details limits assessment of potential bias and reproducibility.

Finally, no sponsor-reported statistical analyses are listed. The record does not describe an analysis plan for period, sequence, carryover, within-participant correlation, or multiplicity. These are unreported methodological details, not evidence that a particular approach was or was not used outside the registry record.

15. Safety Results

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

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The registry posts safety counts by treatment sequence. In the zero-degree-teeth-then-anatomic-teeth sequence, 10 participants were listed as at risk for serious adverse events and 10 for other adverse events; zero were affected in either category. In the anatomic-teeth-then-zero-degree-teeth sequence, the corresponding at-risk counts are also 10, with zero affected by serious or other adverse events.

These figures describe the adverse-event entries in the registry record. They do not establish that no adverse events occurred outside the recorded categories or reporting period, and the record does not give a timeframe for these counts. Death counts are not reported in the registry record. The sequence-level presentation also does not separate events by denture treatment period. With a small study and no further event details, the counts should be read as limited descriptive safety reporting rather than proof of absence of risk.

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

The posted results describe EMG amplitudes and a masticatory efficiency index for patients receiving both complete-denture types in a randomized crossover design. The primary descriptive means are higher in the anatomic-teeth summaries than in the zero-degree summaries. However, the recalculated primary comparisons have confidence intervals that include zero, and the registry record lists no sponsor-reported analyses. These findings do not establish a clear difference between denture types from the posted summaries.

That interpretation is not equivalent to concluding that the dentures have the same effects. A result that does not clearly distinguish two conditions can reflect uncertainty as well as a small or absent difference. The confidence intervals show a range of values compatible with the recalculated comparisons, and no clinically important difference threshold is reported to judge whether any part of that range would matter to patients.

The study's crossover structure is important. A suitable paired analysis could use the fact that each participant received both denture types, but participant-level paired results and the sponsor's analysis are not reported. The available recalculations should therefore not be presented as a definitive adjusted treatment comparison. The record also does not report how period, sequence, possible carryover, or missing measurements were handled.

The secondary outcome provides another measure related to chewing, but its unadjusted comparisons do not resolve the uncertainty. Multiple outcomes and contrasts without a reported multiplicity plan warrant caution, and the study's posted sample-size illustrations are not evidence of observed power or of the original design rationale.

In short, the registry record offers descriptive outcome summaries and unadjusted recalculations for a small crossover study. It does not establish equivalence, a clinically meaningful advantage, or a definitive absence of difference. Nor do the posted safety counts prove that adverse effects cannot occur. Interpretation should remain limited to what the record reports.

17. Why This Trial Matters Statistically

This trial is statistically interesting because its randomized crossover design has each participant receive both denture types. In general, a crossover can make within-participant comparisons informative by controlling for stable differences between people. That advantage depends on analyzing the paired measurements and considering treatment period and sequence. The registry record describes the sequences but does not report how those features were handled in analysis.

The posted outcomes also illustrate why a point estimate and its uncertainty should be considered together. The primary summaries differ descriptively, but the unadjusted confidence intervals for the recalculated contrasts include zero. The estimates alone can suggest a direction, while the intervals show that the evidence remains uncertain. Without a clinically important difference threshold, statistical uncertainty cannot be translated into a judgment about practical importance.

Another lesson is the distinction between registry summaries and a complete analysis report. The record provides outcome means and standard deviations and lists no sponsor-reported analyses. It does not explain missing-data handling, the analysis population, crossover adjustments, or multiplicity. Those omissions restrict the conclusions that can be drawn even when numerical summaries are available.

Finally, the sample-size illustrations show how planning depends on the effect targeted: smaller target effects require more participants per arm under the stated planning assumptions. These are planning calculations based on observed effects, not evidence about the study's original rationale or its observed power. Keeping descriptive results, inferential uncertainty, and future-study planning distinct is essential when interpreting this record.

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 limitations are specific to the information reported for this trial. Although the design is described as a randomized crossover, the posted primary comparisons are recalculations from summary statistics and do not show a paired participant-level analysis. The registry record does not report adjustment for period or sequence, or whether carryover was considered. It also does not state whether a washout interval was used.

The record lists no sponsor-reported analyses and does not describe a statistical analysis plan. It is therefore unclear which comparisons were prespecified, how the separate masseter measurements were treated, or whether the secondary outcome was intended as confirmatory. No multiplicity strategy is reported, and the available p-values are unadjusted.

Missing-data methods and analysis populations are not reported. The posted group counts alone do not describe participant flow, completeness across treatment periods, or the handling of participants without measurements for both dentures. No sensitivity analyses are listed. The registry also does not give a clinically important difference threshold for EMG amplitude or the masticatory efficiency index, limiting interpretation of practical relevance.

The record describes the population as edentulous patients with severely resorbed ridges, but does not report detailed eligibility criteria or demographic information. It does not provide further information on masking, outcome-assessor procedures, or the timing of safety observation. The safety counts are presented by sequence and do not distinguish events by denture period. These gaps restrict assessment of generalizability, bias, and safety reporting.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Comparison of Masticatory Efficiency Between Complete Denture With Zero-degree Teeth and Anatomic Teeth in Patients With Severely Resorbed Ridge — NCT02359955.
• Registry record last updated 2015-05-20; status last verified 2015-05.
• Results first posted 2015-04-09.
• 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

NCT02359955 is a randomized, single-masked crossover study of complete dentures with zero-degree teeth and anatomic teeth in edentulous patients with severely resorbed ridges. The registry lists an enrollment of 20, a start date of 2014-06, a primary completion date of 2015-05, and an unknown status.

The primary outcome is masseter EMG amplitude in microvolts after three months of denture wear. The secondary outcome is the Masticatory Efficiency Index. The record posts outcome summaries and simple unadjusted recalculations, but lists no sponsor-reported analyses. It does not report a crossover analysis plan, missing-data methods, or a multiplicity strategy. The posted results are therefore best interpreted as descriptive and uncertain, rather than as a definitive adjusted comparison.