This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for A Comparison Between Primary and Secondary Flap Coverage in Extraction Sites: A Pilot Study (NCT03136913), a randomized na study. The primary outcome is Mean Difference in Alveolar Bone Height Change.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT03136913 |
| Phase | NA |
| Condition | Loss of Teeth Due to Extraction |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | None (open label) |
| Enrollment | 13 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Tufts University |
| Results posted | Yes |
2. Clinical Question
Population
People undergoing tooth extraction and ridge preservation. The registry record says 13 participants were enrolled. Its primary-outcome description says 20 sites from 10 participants were analyzed, with one open-flap and one closed-flap site for each participant.
Intervention
Open Flap Technique (OFT), described as healing by secondary intention. The flaps remain in position for secondary-intention healing, with a non-resorbable membrane and freeze-dried bone allograft used for ridge preservation.
Comparator
Closed Flap Technique (CFT), described as healing by primary intention. The flaps provide primary coverage, with the same types of membrane and bone allograft described for the open-flap group.
Primary question
How does the mean difference in alveolar bone height change compare between open and closed flap coverage after extraction and ridge preservation? The endpoint is measured in millimeters, with ridge height assessed before extraction and again 3-5 months after ridge preservation. The record does not report the direction used to define the between-technique difference or a numerical result.
3. Trial Design
The registry record describes a randomized, parallel-group pilot study with no masking. It lists 13 participants enrolled and a completed status. The recorded study dates are 2015-02-17 for the start and 2016-04-01 for primary completion. The record does not report the randomization procedure, allocation concealment, or any details about how the assignment sequence was generated.
The two procedures share the described ridge-preservation materials: a non-resorbable membrane, Cytoplast® TXT-200, and freeze-dried bone allograft, MinerOss® Cortical and Cancellous Chips (FDBA). The comparison is the position and coverage of the flaps during healing. CFT uses primary coverage, while OFT leaves the flaps in position for healing by secondary intention. The record says that the open technique uses sutures to secure the membrane.
There is an important design detail to keep in view when interpreting the endpoint. Although the study model is recorded as parallel, the primary-outcome description says each of 10 participants contributed one OFT site and one CFT site. That means the described outcome observations include two sites from each participant. The registry record does not explain how the site-level observations were assigned, whether the within-participant pairing was part of the randomization, or how dependence between sites from the same participant was handled in an analysis.
The registry record lists three outcome measures and names post-operative pain/discomfort and percentage new bone formation as secondary outcomes. It lists no analyses. A protocol, statistical analysis plan, masking procedures, and details about follow-up beyond the endpoint timeframe are not reported in the registry 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.
Before assignment: Two randomization schemes were created using the statistical package R Version 2.11.1. One randomization scheme was used if the subject has more than 1 set of qualifying sites (the inclusion criteria specify bilateral sites) and randomized which set would be included in the study. The other randomization scheme was used to randomize which side is in Group 1 and which side is in Group 2. The two sites (one set) chosen to be in the study each had a 50% chance of being in either group.
Overall Study
| Stage | All Study Participants (OFT vs CFT) |
|---|---|
| STARTED | 13 |
| Subjects Received Both Intervention | 10 |
| COMPLETED | 8 |
| NOT COMPLETED | 5 |
Analysis population for the primary outcome, as defined in the registry: 20 sites were analyzed of 10 participants, 10 OFT sites and 10 CFT sites, 1 OFT and 1 CFT for each subject, were analyzed
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.
| Characteristic | Unit | All Study Participants (OFT vs CFT) |
|---|---|---|
| Participants analysed | 10 | |
| Age, Continuous | years | 56.4 (SD 9.1) |
| Sex: Female, Male: gender – Female | Participants | 2 |
| Sex: Female, Male: gender – Male | Participants | 8 |
6. Primary Endpoint
The registry lists the primary outcome as Mean Difference in Alveolar Bone Height Change, measured over < 6 months post extraction and ridge preservation.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | mm |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is titled “Mean Difference in Alveolar Bone Height Change” and is a continuous measure in millimeters. The record describes measuring alveolar ridge height before tooth extraction and again 3-5 months after ridge preservation, using impressions, stone models or casts, and a stent to measure ridge height and width. The stated timeframe is < 6 months post extraction and ridge preservation.
Bone height is relevant to the study’s stated objective because the investigators sought to compare the two coverage techniques in relation to healing and bone loss after extraction. A change measure uses the pre-extraction height as a reference for the later measurement. Comparing the mean change between techniques is intended to describe how the groups differ on average, rather than to report only a later measurement without its starting point.
The registry record does not specify the exact calculation used for change, the sign convention for the between-technique difference, or a clinically important threshold. It also does not report the observed group means, standard deviations, mean difference, or uncertainty interval. Therefore, the endpoint’s definition can be described, but the magnitude and precision of the observed contrast cannot be interpreted from the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record establishes that the study was a randomized pilot comparison of OFT and CFT, but it does not report a numerical result for the primary endpoint. The record identifies mean difference in alveolar bone height change as the primary outcome and describes how ridge height was to be assessed. It does not give group-level changes, a between-group estimate, standard deviations, a confidence interval, or a test result. Consequently, the registry record does not establish the size, direction, or statistical precision of any difference in bone-height change.
The primary-outcome population description states that 20 sites from 10 participants were analyzed, with 10 OFT sites and 10 CFT sites, and one site of each type for each participant. The record separately gives total enrollment as 13. These counts describe different aspects of the study: enrollment and the sites named in the primary-outcome description. The record does not explain why the number of participants contributing to the endpoint differs from the enrollment count, or whether the remaining participants had missing measurements, were excluded, or did not contribute sites. Those reasons are not reported in the registry record.
The paired-site description also matters for interpretation. Measurements from two sites in the same participant may be related, rather than behaving like measurements from unrelated participants. General statistical explanation: when observations are dependent, an analysis that treats them as independent can misstate uncertainty. A paired or clustered analysis can account for the relationship, depending on the design and estimand. The record does not report which method, if any, was used to account for the two sites per participant.
The randomized designation describes the study’s allocation type, but randomization alone does not supply the missing outcome estimate or its uncertainty. With no reported analysis, readers cannot assess whether the groups differed at baseline, how complete the measurements were, or whether the intended comparison was analyzed according to assignment. These details are not reported in the registry record.
As a pilot study with 13 participants enrolled and 20 sites described for the primary outcome, the record documents a small study rather than a result that can be judged from the endpoint description alone. No conclusion about the comparative outcomes can be drawn from the missing primary result. The posted record supports describing the study question, procedures, and recorded endpoint population, but not claiming that either technique had a larger, smaller, or more precise change.
Any sample-size figures associated with planning are illustrations based on the observed effect and stated assumptions, not observed power or evidence that the study was designed with those assumptions. In this record, the planning assumptions are a two-sided significance level of 0.05, equal allocation, and a normal approximation. The calculated planning values are not reported in the registry record. A planning exercise cannot replace a reported estimate and confidence interval from the study’s actual outcome data.
9. Statistical Methods Explained
What does a mean difference describe?
General statistical explanation: a mean summarizes the average value of a measured outcome within a group. For a continuous endpoint such as height change in millimeters, a between-group mean difference describes the contrast between the groups’ average changes. Its sign and size depend on which group is subtracted from which; the registry record does not state that convention. The mean difference is an estimate of the contrast in the analyzed data, not a guarantee that every participant or site had a change of that size.
The record identifies the endpoint as a mean difference but does not report the component group means or the estimated contrast. Nor does it describe the precise formula for calculating each site’s change from baseline. Without those details and the outcome values, the numerical result cannot be reconstructed. A label for an endpoint is not itself an outcome finding.
Why does a confidence interval matter?
General statistical explanation: a confidence interval expresses uncertainty around an estimated effect. Its width reflects the precision of the estimate under the method used. A narrow interval is more precise than a wide interval, while an interval that includes values in different directions may leave uncertainty about the direction or magnitude of the contrast. The interval must be interpreted in relation to the outcome scale and the study question.
No confidence interval for the primary comparison is reported in the registry record. Therefore, precision cannot be assessed, and it is not possible to determine from this record which values are compatible with the observed data under a stated analysis. A p-value alone, even if one were reported, would not describe the range of plausible effect sizes; in this record, no primary p-value is reported either.
How does the site structure affect analysis?
The primary-outcome description says that each of 10 participants contributed one OFT site and one CFT site. General statistical explanation: outcomes from sites within the same participant may share participant-level influences and therefore be correlated. If the analysis ignores that dependence, its uncertainty estimate may not match the data structure. A paired comparison can use the within-participant relationship; other methods can account for clustering. The appropriate approach depends on how the study was designed and what contrast is intended.
The registry record gives a parallel model but also describes one site of each type per subject. It does not explain how those descriptions relate to the allocation process, or state whether an analysis accounted for within-participant pairing. No analysis methods are listed. It is therefore not possible to determine whether the site-level structure was incorporated in a reported estimate, or to evaluate the consequences of any method used.
What do randomization and masking contribute?
General statistical explanation: random allocation is intended to reduce systematic differences between groups at the start of a study, on average, when implemented appropriately. It does not ensure that groups are identical in a small study, and it does not correct problems arising after allocation, such as missing measurements or analysis choices. The registry record calls the study randomized but does not report sequence generation, concealment, or a baseline comparison.
The record lists masking as none. In a procedure comparison, participants and clinical staff may know which technique was used, although the registry record does not specify who measured the endpoint or whether outcome assessment was masked. Knowledge of treatment assignment can be relevant to how outcomes are collected or assessed; the record does not provide enough detail to evaluate that possibility.
What does the planning illustration mean?
General statistical explanation: a sample-size planning illustration asks how many participants per arm might be needed to detect an assumed effect under specified statistical assumptions. The registry record states that its planning illustration uses a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the target effect expressed as a fraction of the observed effect. It also distinguishes participants per arm for ordinary outcomes from total events for time-to-event calculations; the primary endpoint is continuous.
Those calculations are planning illustrations, not observed power and not a description of the trial’s original design. The record explicitly says they are computed from the observed effect rather than the trial’s own design. The registry record does not report an original sample-size justification or the numerical planning estimates. A post-study calculation based on an observed estimate cannot establish that an effect is real or precise; the estimate and its uncertainty should be considered directly.
General statistical explanation: over-dispersion is relevant when observed variability exceeds what a chosen model assumes, often affecting standard errors and intervals. This endpoint is recorded as a continuous mean with standard deviation, and the registry record does not identify an over-dispersion issue or a model. It would not be appropriate to assume a specific model or correction from the endpoint label alone.
10. Multiplicity, Missing Data and Analysis Populations
The registry record lists three outcome measures and names post-operative pain/discomfort and percentage new bone formation as secondary outcomes alongside the primary endpoint. It does not report the full specifications for all outcome measures, a hierarchy among the secondary outcomes, or a plan for adjusting statistical inference for multiple comparisons. Whether any multiplicity adjustment was prespecified is not reported in the registry record. When several outcomes are examined, the chance of at least one apparently unusual result can increase; general statistical explanation, the extent of that issue depends on the analyses and the inferential plan.
The record lists no analyses. It does not report whether the primary outcome was tested once or with additional time points, subgroups, or alternative definitions. Such analyses, if conducted, are not reported in the registry record. The absence of reported analyses means there is no basis for assessing the handling of multiple comparisons or selective outcome reporting.
Missing-data information is also not reported in the registry record. The record states that 13 participants were enrolled, while the primary-outcome population description refers to 10 participants and 20 sites. It does not say why the endpoint description includes fewer participants than the enrollment total, whether any measurements were unavailable, or how missing values were handled. No imputation method, complete-case rule, or sensitivity analysis is described.
The analysis population is not reported in the registry record beyond the statement about the sites and participants analyzed. It is not stated whether participants were analyzed according to randomized assignment, whether any exclusions occurred after allocation, or whether the analysis was based on all enrolled participants with available outcomes. These omissions limit assessment of how the reported population relates to the randomized groups, especially given the paired-site description.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Open Flap Technique (OFT) | 0 | 10 | 0.0% |
| Closed Flap Technique (CFT) | 0 | 10 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Open Flap Technique (OFT) | 0 of 10 |
| Closed Flap Technique (CFT) | 0 of 10 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Open Flap Technique (OFT) | 0 of 10 |
| Closed Flap Technique (CFT) | 0 of 10 |
The registry record reports no serious adverse events and no other adverse events in either technique group. For OFT, 10 were recorded as at risk for serious events and 10 for other events; the corresponding affected counts are 0 and 0. For CFT, the at-risk counts are also 10 for serious events and 10 for other events, with 0 affected in each category. The record lists no top serious-event terms.
These figures describe the adverse-event counts recorded for this study. They do not establish that no events could occur, and they do not by themselves demonstrate equivalent safety between techniques. The study enrolled 13 participants, while the safety groups each list 10 at risk; the record does not explain how those group counts relate to enrollment or the sites described for the primary outcome. The registry record also does not report the safety observation period, event-collection procedures, or whether all participants completed safety follow-up.
General statistical explanation: when no events are observed in a small group, the data still allow uncertainty about the underlying event frequency. The observed count is not a precise estimate of risk, and comparisons based on zero recorded events cannot establish that the groups have identical event profiles. The figures should therefore be read as the events recorded in this study, with the limitations of the stated group counts and unreported follow-up details.
12. What the Result Does, and Does Not, Mean
The record defines a clinically focused comparison: open versus closed flap coverage during extraction and ridge preservation, with alveolar bone height change as the primary endpoint. It also identifies pain/discomfort and percentage new bone formation as secondary outcomes. The available registry information is useful for understanding the study question, procedures, endpoint timing, and the population description attached to the primary outcome.
It does not, however, report the outcome estimates needed to determine what the study observed. No numerical mean difference, group means, standard deviations, confidence interval, or primary analysis result is reported in the registry record. Accordingly, the record does not support a claim that one technique had more or less bone-height change, nor does it establish how precise such a comparison would be. The secondary outcome titles do not provide their results either.
General statistical explanation: a study result is best understood as an effect estimate together with its uncertainty and the design and analysis choices that produced it. A statistically significant result, if reported, would not by itself describe clinical importance; a non-significant result would not prove equality. Here, the primary result is not reported, so even those distinctions cannot be applied to the study’s findings.
The pilot designation, enrollment count, and analyzed-site description indicate the scale and structure of the work but do not substitute for the missing estimates. The site-level observations may be paired within participants, while the registry model is listed as parallel. How that structure was handled in analysis is not reported in the registry record. This is relevant to uncertainty and should be resolved before interpreting any effect estimate, if one is available in another record.
The appropriate reading is therefore narrow: the registry record documents a randomized pilot comparison and its intended measurement approach, but it does not report enough results to judge the comparative outcome. It neither demonstrates benefit nor demonstrates lack of effect. That restraint reflects the reported information, not a conclusion about what the procedures would do in other settings.
13. Why This Trial Matters Statistically
This study raises several important statistical questions because the design description and endpoint population involve different units of observation. The registry records a parallel model, yet says that each of 10 participants contributed an OFT site and a CFT site. A site is the unit measured, while the participant is the unit within which two sites are linked. Distinguishing these units is essential when estimating an average contrast and its uncertainty.
General statistical explanation: when each participant contributes observations under both conditions, the within-participant comparison can remove some variation shared by that participant. But the two observations cannot automatically be treated as independent. Analysis should reflect the actual allocation and measurement structure. The registry record does not state how randomization was applied or how the paired sites were handled, making the structure a central issue for readers of any eventual analysis.
The enrollment and endpoint counts also invite a transparent account of the analysis population. The record lists 13 enrolled participants and 10 participants contributing the described sites. Knowing why the counts differ would help readers assess exclusions, incomplete follow-up, or other explanations; those details are not reported in the registry record.
Finally, the registry record specifies an outcome and measurement window but reports no numerical result or analysis. A clear report of the estimate, uncertainty, handling of within-participant correlation, and missing outcomes would make the evidence interpretable. The statistical importance of this pilot lies not in an unreported result, but in the need to connect the clinical question to the correct unit of analysis and a transparent account of who contributed data.
14. 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 does not report the primary outcome estimate, group summaries, confidence interval, or inferential test. This is the main limitation for interpreting the comparative findings: the intended endpoint is described, but its observed value and precision cannot be assessed.
There is a difference between the total enrollment of 13 participants and the primary-outcome description of 10 participants contributing 20 sites. Reasons for the discrepancy, participant flow, and any exclusions are not reported in the registry record. The record also does not report whether outcome data were missing or how missingness was handled.
The study is described as randomized and parallel, while the primary-outcome population has one site of each technique per participant. The relation between those descriptions and the allocation method is not explained. Nor is the statistical handling of sites nested within participants reported. This leaves uncertainty about whether the analysis, if performed, reflected the apparent pairing.
The record lists no analyses and does not report a statistical analysis plan, endpoint calculation details, a sample-size justification for the trial, or multiplicity procedures. Masking is listed as none, but the record does not specify who assessed the endpoint or whether assessment was masked. The timing of the endpoint is described as < 6 months, with measurements 3-5 months after ridge preservation; further detail about variation in assessment timing is not reported in the registry record.
These are limitations of the information available in the registry record. They do not establish that the study team did not conduct analyses or collect additional information; such information is simply not reported in the registry record.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: A Comparison Between Primary and Secondary Flap Coverage in Extraction Sites: A Pilot Study — NCT03136913.
- Registry record last updated 2021-08-12; status last verified 2021-07.
- Results first posted 2021-08-12.
- 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.
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18. Record Summary
NCT03136913 is a completed randomized pilot study comparing open and closed flap coverage in extraction-site ridge preservation. The registry record lists 13 participants enrolled, no masking, and a parallel model. It describes use of a non-resorbable membrane and freeze-dried bone allograft in both techniques.
The primary endpoint is mean difference in alveolar bone height change, measured in millimeters, with ridge height assessed before extraction and 3-5 months after ridge preservation. The primary-outcome description identifies 20 sites from 10 participants, with one site per technique for each participant. Secondary outcomes are post-operative pain/discomfort and percentage new bone formation.
No analyses or numerical primary outcome results are reported in the registry record. Reasons for the difference between enrollment and the described endpoint population, the handling of paired sites, and missing-data procedures are also not reported.