To Compare Free Gingival Grafts and Connective Tissue Grafts Around Implants With Lack of Keratinized Mucosa: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for To Compare Free Gingival Grafts and Connective Tissue Grafts Around Implants With Lack of Keratinized Mucosa (NCT03338686), a randomized na study. The primary outcome is The Increase in Keratinized Mucosa (in mm) Between the Two Grafts.

2. Clinical Question

3. Trial Design

The registry identifies this as a completed, randomized, parallel-group clinical trial with no masking. The listed enrollment is 14. The record gives a start date of 2016-01-07 and a primary completion date of 2018-10-09. The sponsor is the University of Alabama at Birmingham. The phase is listed as not applicable.

The interventions are free gingival graft (FGG) and connective tissue graft (CTG) followed by laser gingivoplasty. The registry’s primary-outcome description says that some participants received only one graft type, while some received FGG and CTG at different implant sites. This makes the unit of assignment and the relationship between the groups important when interpreting the comparison. The record labels the design randomized and parallel, but does not clearly explain how randomization relates to participants who received both procedures at different sites.

The primary outcome is the increase in keratinized mucosa, measured in millimeters from baseline to 12 months. The registry also lists changes in tissue thickness at 2 mm and 5 mm from GM as secondary outcomes. The listed outcome summaries include a mean and standard deviation for each primary-outcome arm. However, the posted arm counts are 9 for FGG and 12 for CTG followed by laser gingivoplasty, while the registry lists enrollment of 14 and describes overlap in participants between graft groups. The record does not clarify how these counts relate to participants, implant sites, or the analysis population.

The registry reports no analyses. It does not report the randomization procedure, allocation concealment, masking of outcome assessment, or a statistical analysis plan. Those details are not reported in the registry record and cannot be inferred from the design labels alone.

4. Participant Flow and Accounting

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

Overall Study

Analysis population for the primary outcome, as defined in the registry: FGG group has 2 participants who only received FGG (n=2) and 7 participants who received FGG (n=12) and CTG at different implant sites (total of 14=2+12). CTG group has 5 participants who only received CTG (n=5) and 7 participants who received FGG and CTG (n=7) at different implant sites (total of 12=5+7).

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 The Increase in Keratinized Mucosa (in mm) Between the Two Grafts, measured over From baseline to 12 months.

The primary endpoint is the increase in keratinized mucosa (KM), measured in millimeters from baseline to 12 months. The registry describes quantifying KM width at 12 months following soft tissue grafting and comparing the increase between FGG and CTG. The posted summaries are means with standard deviations, consistent with a continuous outcome.

KM width is a clinical measure that directly reflects the tissue dimension the grafting procedures are intended to augment in this study. A change from baseline focuses the endpoint on the amount of increase rather than only the final measurement. The 12-month timeframe identifies the point at which the registry says the outcome was assessed; the record does not provide further detail about measurements at other time points.

A group mean describes the average recorded change in that group, while the standard deviation describes the spread of individual observations around the mean. These summaries help characterize the observed outcome, but do not by themselves show how precisely the difference between groups has been estimated. The registry reports no confidence interval or statistical test for the primary comparison, and it does not clearly identify whether the counts refer to people, implant sites, or another analysis unit. That ambiguity matters because the primary description indicates that some participants contributed sites treated with both graft types.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry classifies the primary endpoint as continuous and reports each arm’s mean and standard deviation. These are useful descriptive statistics: the mean gives the average recorded increase in keratinized mucosa, and the standard deviation describes how dispersed the observations are around that average. They do not alone provide a direct estimate of the between-group contrast or its uncertainty.

What does a confidence interval add?

In general, a confidence interval expresses the uncertainty around an estimated quantity, such as a mean difference between groups. A narrower interval indicates greater precision, while a wider interval indicates less precision. It also shows which values remain compatible with the analysis and its assumptions. The registry record does not report a confidence interval for the primary comparison, so the precision of a comparative effect cannot be evaluated from the posted summary statistics alone.

Why does the analysis unit matter?

The record describes participants who received FGG and CTG at different implant sites. When an individual contributes observations under both treatments, observations from that person may be related rather than independent. In general, an analysis that treats related observations as independent can misstate uncertainty. Appropriate methods may account for clustering or pairing, depending on the assignment and measurement structure. The registry does not state the assignment unit, whether the outcome counts are people or sites, or how within-person dependence was handled. It is therefore not possible to identify the intended comparative method.

What do the standard deviations tell readers?

In general, a standard deviation describes variation among observed measurements, not uncertainty in the estimated mean and not the precision of a treatment contrast. The primary summaries report standard deviations of 1.88 for FGG and 1.05 for CTG followed by laser gingivoplasty. These values characterize spread in the posted groups, but do not resolve the uncertainty caused by the unclear analysis unit or possible dependence between observations.

What can be inferred from the reported analysis status?

The registry lists zero analyses. It provides descriptive primary-outcome values but no inferential analysis, model specification, p-value, confidence interval, or adjusted estimate. There is no reported statistical plan explaining whether the comparison was intended to be based on change scores, final measurements, participant-level summaries, site-level observations, or a model accounting for repeated or clustered measurements. These details are not reported in the registry record.

General statistical practice distinguishes descriptive results from inferential results. Descriptive results summarize the observed data. Inferential methods estimate uncertainty and assess how compatible the observations are with possible underlying effects, conditional on the model and its assumptions. A difference in posted group means should not be presented as a statistically established effect in the absence of a reported analysis. No recalculated comparison is included, and no sponsor analysis is available to take precedence.

How should sample-size illustrations be understood?

The registry’s sample-size assumptions describe planning illustrations based on an observed effect, a two-sided significance level of 0.05, equal allocation, and a normal approximation. The illustrations are not the trial’s original design justification, and they are not observed power. In general, planning calculations show the number of participants per arm that a hypothetical future study might require under specified assumptions. They do not change the evidential strength of a completed study and do not compensate for missing comparative estimates or unclear analysis units.

For continuous outcomes, planning calculations depend on the target effect and variability assumptions. In general, a smaller effect to detect requires more information than a larger effect, all else being equal; more variability also makes a given contrast harder to estimate precisely. The registry does not report a protocol-based sample-size justification or explain the trial’s original design assumptions. The planning illustrations should therefore be read as hypothetical design aids, not as evidence that the trial was adequately powered.

Why can over-dispersion or clustering matter?

In general, over-dispersion means that observed variability is greater than a statistical model expects. A model that understates variability can make uncertainty appear too small. The endpoint is continuous, and the registry provides standard deviations rather than a model-based variance estimate. More specifically, if multiple implant sites from the same participant were analyzed, clustering within participants could affect uncertainty even if the individual measurements themselves do not show over-dispersion. The registry does not report a model or diagnostic assessment, so neither issue can be evaluated from the record.

The central methodological limitation is not a technical choice that can be reconstructed from the means and standard deviations. The record omits the inferential analysis and leaves the relationship between participants, sites, and arm counts unclear. Statistical interpretation should remain descriptive unless those details are available from an analysis report.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Free Gingival Graft", "Connective Tissue Graft Followed by Laser Gingivop")
n   <- c(9, 12)
m   <- c(3.29, 1.29)
sp  <- c(1.88, 1.05)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Free Gingival Graft  9  3.290  1.880  1.845  4.735
CARM  Connective Tissue Graft Followed by Laser Gingivop  12  1.290  1.050  0.623  1.957

11. Multiplicity, Missing Data and Analysis Populations

The registry lists three outcome measures: the primary increase in keratinized mucosa and secondary changes in tissue thickness at 2 mm and 5 mm from GM. The two secondary outcomes are identified in the record, but their results are not reported. The registry does not describe a multiplicity adjustment or a hierarchy for interpreting the outcomes. Whether adjustments were planned or used is not reported in the registry record.

Multiplicity matters in general when several outcomes or comparisons are examined, because the chance of a chance-positive finding can increase as more tests are considered. The record does not provide enough detail to determine how the outcomes were analyzed or whether this concern was addressed. No inference about the secondary endpoints can be made from their titles alone.

Missing-data methods are also not reported in the registry record. The record does not explain whether outcome measurements were unavailable, how missing observations were handled, or whether any imputation or sensitivity analysis was performed. The posted counts—9 for FGG and 12 for CTG followed by laser gingivoplasty—do not match the listed enrollment of 14 in a straightforward way, and the outcome description indicates that some participants contributed to both graft groups at different implant sites. The record does not clarify the denominators or explain whether these are participant or site counts.

Analysis populations are not described. The record does not say whether the reported summaries include all randomized participants, only participants with available measurements, or another population. It also does not report an intention-to-treat analysis or a per-protocol analysis. These omissions limit assessment of missingness, exclusions, and the relation between randomization and the posted results.

12. 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 record lists no serious adverse events, no other adverse events, and no deaths in the groups shown. The at-risk counts are 2 for FGG, 5 for CTG followed by laser gingivoplasty, and 7 for the combined FGG + CTG group. These are registry counts for the listed safety groups; because the outcome description indicates that some participants received both graft types at different implant sites, the groups should not be treated as necessarily independent or added to infer a total.

Zero recorded events means that no events were reported in these safety summaries. It does not establish that the procedures have no risks. In general, when the number of people or observations under follow-up is limited, an absence of recorded events cannot rule out uncommon events or events that were not captured. The record does not provide further detail about safety-monitoring methods, the duration of adverse-event follow-up, or event definitions beyond the serious and other adverse-event categories.

No serious adverse-event terms are listed. The safety figures are descriptive and do not provide a comparative statistical analysis. They should be read as registry reporting, not as proof of equivalence in safety between procedures.

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

The registry reports mean increases in keratinized mucosa of 3.29 mm for FGG and 1.29 mm for CTG followed by laser gingivoplasty, with standard deviations of 1.88 and 1.05, respectively. These values describe the posted outcome summaries at the stated 12-month timeframe. They do not, by themselves, establish a statistically reliable difference between approaches.

The record does not include a confidence interval, p-value, or other inferential comparison for the primary endpoint. It also does not clearly explain whether the posted arm counts represent participants or implant sites, even though its description indicates that some participants received both graft types at different sites. The comparison’s precision and the handling of within-participant dependence are therefore uncertain from the registry record.

The results should not be taken as a definitive answer about which procedure is preferable. The registry provides no reported statistical analysis and no secondary-outcome results for tissue thickness at 2 mm or 5 mm from GM. It also does not report the analysis population, missing-data approach, or a multiplicity plan. Those limitations prevent a complete assessment of the evidence.

In general, a trial result is most informative when the effect estimate, uncertainty, analysis population, and methods are reported clearly. The posted means are useful descriptive information, but a mean is not a treatment-effect conclusion. The results also do not establish that the procedures are equivalent, that one has no effect, or that safety is identical. The adverse-event record reports zero events in the listed categories, but does not rule out events that were uncommon or not captured.

14. Why This Trial Matters Statistically

This trial is statistically notable because its registry description suggests that some participants received both graft types at different implant sites. That structure can affect how observations should be compared. If measurements from the same participant are related, the analysis needs to account for that dependence when estimating uncertainty. The record does not explain whether assignment and analysis occurred at the participant or site level.

The posted primary summaries also have counts that are not readily reconciled with the listed enrollment. Enrollment is 14, while the arm summaries report 9 and 12, and the outcome description refers to overlapping participants. Without a clear account of the analysis unit and denominators, readers cannot determine how many independent observations underpin the means or how precisely a comparison could be estimated.

The registry’s outcome focuses on change in keratinized mucosa from baseline to 12 months, an interpretable continuous measure aligned with the study question. Yet the record reports only group means and standard deviations, without a comparative estimate or uncertainty interval. This illustrates why descriptive summaries and inferential results serve different purposes: the former show the observed group data, while the latter are needed to judge precision and compatibility with different effects.

The record also identifies tissue thickness as a secondary outcome but does not report those results. Transparent reporting of outcome estimates, analysis units, missing data, and statistical methods would allow readers to evaluate the clinical measurements and the design more fully. The current registry record supports a description of the posted summaries, not a conclusive comparative statistical interpretation.

15. 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 main limitation is incomplete reporting of the analysis structure. The registry labels the trial randomized and parallel, while its primary-outcome description says some participants received FGG and CTG at different implant sites. It does not clearly state the unit of randomization or analysis, or how observations from the same participant were handled. This is important for interpreting uncertainty in a comparison.

The reported counts are also difficult to reconcile. The registry lists enrollment of 14, but the primary-outcome arms report 9 and 12. The description includes overlapping participants, and the record does not make clear whether arm counts refer to people, sites, or another unit. The incomplete wording of the group-count description further limits interpretation of the analysis population.

No inferential primary-outcome analysis is posted. There is no reported confidence interval, test statistic, p-value, or adjusted estimate. The registry also does not report the statistical analysis plan, missing-data methods, analysis populations, or a protocol-based sample-size justification. It lists two secondary tissue-thickness outcomes but does not provide their results or a multiplicity strategy.

The trial is unmasked, according to the registry, and the record does not state whether outcome assessors were masked. Further procedural and follow-up details are not reported in the registry record. The adverse-event summaries show zero events in the listed categories, but their limited detail does not allow a comprehensive appraisal of safety ascertainment. Together, these reporting gaps mean the posted means should be treated as descriptive and interpreted cautiously.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: To Compare Free Gingival Grafts and Connective Tissue Grafts Around Implants With Lack of Keratinized Mucosa — NCT03338686.
• Registry record last updated 2021-09-22; status last verified 2021-08.
• Results first posted 2021-04-08.
• 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.

19. Record Summary

The registry record describes a completed, randomized, parallel-group trial with no masking, sponsored by the University of Alabama at Birmingham. Listed enrollment is 14. The interventions are FGG and CTG followed by laser gingivoplasty.

The primary outcome is increase in keratinized mucosa in millimeters from baseline to 12 months. The posted means are 3.29 mm for FGG and 1.29 mm for CTG followed by laser gingivoplasty, with standard deviations of 1.88 and 1.05. The corresponding arm counts are 9 and 12. The record lists secondary outcomes for tissue-thickness change at 2 mm and 5 mm from GM, but does not report their results.

The registry reports no analyses and no inferential comparison for the primary outcome. Its description indicates that some participants received both graft types at different implant sites, while the relationship between enrollment, arm counts, participants, and sites is not clearly explained. No serious adverse events, other adverse events, or deaths are recorded in the listed safety groups.