Ridge Preservation After Tooth Extraction Using Cortical Versus Cancellous Freeze Dried Bone Allograft: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Ridge Preservation After Tooth Extraction Using Cortical Versus Cancellous Freeze Dried Bone Allograft (NCT01588444), a randomized na study. The primary outcome is Histologic Percentage of Vital Bone Formation.

2. Clinical Question

The clinical question concerns the composition of healing tissue after tooth extraction, rather than a patient-reported outcome or a longer-term clinical outcome. The primary endpoint records the percentage of vital bone in a bone-core sample. It is therefore a tissue-level measure of healing at the stated follow-up interval. The registry record describes the objective as histologically evaluating and comparing healing in extraction sockets grafted with the two materials.

The comparison is between two forms of freeze-dried bone allograft, not between grafting and no grafting. The posted results do not establish what would have happened without grafting, nor do they report outcomes for molar extractions. They address the recorded histologic endpoint in the trial groups. The registry does not report a formal hypothesis, a prespecified direction of difference, or a statistical test for the comparison.

3. Trial Design

The registry describes a randomized, parallel-group trial with no masking. Participants were assigned to cortical or cancellous freeze-dried bone allograft, and each group received its allocated material rather than crossing between treatments. The registry lists enrollment of 40. For the primary outcome, each arm has 20 participants listed. The trial status is completed.

The intervention descriptions identify both materials as LifeNet products. The cancellous arm is described as mineralized freeze-dried bone allograft from LifeNet Health; the cortical arm is described as cortical freeze-dried bone allograft from LifeNet Health. The study population in the brief description is people receiving extraction of non-molar teeth, with ridge preservation as the purpose of grafting.

The primary outcome was assessed histologically in bone cores at 18-20 weeks after grafting. The endpoint is reported as a median percentage of vital bone with an interquartile range. The registry lists a primary outcome and no posted secondary outcomes. It lists no posted analyses.

The registry record gives a study start of 2010-10 and primary completion of 2012-07. The listed phase is NA. Details of how the random sequence was generated, whether allocation was concealed, who was responsible for assigning materials, and whether outcome assessors were masked are not reported in the registry record. The record also does not report the actual analysis population or whether all enrolled participants contributed evaluable bone-core results.

Random assignment is intended to make treatment groups comparable on average, but it does not by itself show that the groups were balanced in this particular trial. With no posted analysis of the group comparison, the descriptive results can be read as observed group summaries, not as a quantified causal contrast. The lack of masking is stated; further information about safeguards against bias is 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.

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.

Population: patietns requring tooth extraction adn ridge preservation

6. Primary Endpoint

The registry lists the primary outcome as Histologic Percentage of Vital Bone Formation, measured over 18-20 weeks after grafting.

The primary endpoint is the histologic percentage of vital bone formation in bone cores, measured 18-20 weeks after grafting. In plain terms, it describes the proportion of the sampled tissue classified as vital bone at the specified assessment. The registry reports this endpoint using a median and an interquartile range for each treatment group.

As a general statistical rationale, a histologic measure can characterize tissue composition directly at the sampled site. It is useful for a question focused on healing within the extraction socket, because the measurement concerns the tissue seen in a bone core rather than an indirect clinical proxy. That rationale does not make the endpoint a complete measure of healing, and it does not establish how the histologic result relates to later clinical outcomes. Such relationships are not reported in the registry record.

A median describes the middle of the ordered observations and is less affected by unusually high or low observations than an arithmetic mean. An interquartile range describes the middle half of the observed values, from its lower to upper boundary. These summaries indicate the distribution's center and spread, but do not show every individual result or quantify uncertainty around a treatment-group difference.

The cancellous group had a median of 12.98% vital bone, with an interquartile range of 10.06% to 31.04%. The cortical group had a median of 16.08%, with an interquartile range of 12.12% to 30.25%. No confidence interval for the between-group contrast, test statistic, or p-value is reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical information in the registry is limited to descriptive primary-outcome summaries. The endpoint is expressed as a percentage of vital bone, with the median and interquartile range reported for each group. No inferential analysis is posted. The following concepts are general explanations of how to read these measures; they are not claims about unreported methods used by the investigators.

What does a median describe?

When observations are placed in order, the median is the central value. It describes the center of a distribution without relying on the distance of every observation from the center in the same way as a mean. This can be helpful when observations are skewed or when extreme values might pull a mean. The choice to report a median does not itself establish that the data were skewed, nor does it reveal the investigators' reason for choosing it. That reason is not reported in the registry record.

For this outcome, the reported medians are 12.98% for cancellous FDBA and 16.08% for cortical FDBA. These are sample summaries. They do not reveal the full set of individual observations or how the groups compare after accounting for uncertainty. A reader should not treat the median in either arm as the expected result for every participant.

What does the interquartile range describe?

The interquartile range extends from the lower quartile to the upper quartile and covers the middle half of the ordered observations. It gives a sense of the spread of observed values while being less affected by extreme observations than the full range. Here, the reported intervals are 10.06% to 31.04% for cancellous FDBA and 12.12% to 30.25% for cortical FDBA.

An interquartile range describes variation in the sample; it is not an estimate of uncertainty around the median or around the difference between groups. It also does not show the shape of the whole distribution, such as whether values cluster near one boundary or whether there are outliers. No individual-level distribution or additional summary of shape is reported in the registry record.

Why does the distinction between spread and precision matter?

Observed outcomes can vary among participants even when they receive the same intervention. A spread measure describes that participant-to-participant variation. Precision concerns how uncertain an estimated quantity is, such as a group median or a contrast between groups. Confidence intervals are one common way to communicate precision. As a general explanation, narrower intervals indicate greater precision under the analysis assumptions; wider intervals indicate less precision. No confidence interval is reported for this trial's group contrast.

Likewise, a p-value from a specified test would address how compatible the observations are with a particular null hypothesis under that test's assumptions. It would not directly measure the size or clinical importance of a difference. The registry record does not post a p-value, test statistic, or formal comparison, so none can be interpreted for this endpoint.

What can randomization contribute?

Random allocation is designed to reduce systematic differences between groups at the point of assignment, including differences that might not be measured. In general, randomization supports a fair comparison when allocation is implemented as intended and outcomes are analyzed appropriately. It does not guarantee that the realized groups are identical, particularly in a trial with limited enrollment. The registry identifies randomization but does not report sequence generation, allocation concealment, baseline characteristics, or an adjusted analysis. Those omissions prevent a fuller assessment of how the comparison was implemented and analyzed.

The parallel design means the two groups are compared as separate assigned groups. The registry does not describe a crossover or repeated-treatment comparison. It also states that masking was absent. Whether the person assessing the histologic samples knew the assigned material is not reported in the registry record. That detail can matter for measurements involving classification or interpretation, although the record does not establish that assessment was affected.

How should planning calculations be read?

The record describes planning illustrations based on a fraction of the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. Such calculations are planning exercises under stated assumptions; they are not observed power and do not add evidence to the trial's results. The record does not report the trial's own sample-size justification. No planning calculation can substitute for a confidence interval or a direct analysis of the posted outcome.

In general, a sample-size calculation depends on assumptions about the effect to detect, variability, allocation, and the testing approach. If those assumptions differ from the data-generating conditions, the planning result may not describe the precision ultimately achieved. The registry does not report the assumptions used by investigators when designing this trial, so the stated planning illustration should not be interpreted as the original design rationale.

Why can over-dispersion matter?

As a general concept, over-dispersion means observed variability is greater than a statistical model assumes. When a model underestimates variability, standard errors and intervals can be too small, and tests may appear more decisive than warranted. This issue is most directly relevant to models for counts or other outcomes with a specified variance structure. The posted primary endpoint is a percentage summarized by medians and interquartile ranges, and no model-based analysis is reported. The registry therefore gives no basis to assess over-dispersion in a fitted model for this endpoint.

The central methodological limit is that descriptive summaries are available without the corresponding inferential analysis. They characterize the observed outcome distributions, but do not quantify uncertainty in the contrast or provide evidence from a formal test. General statistical concepts can clarify that distinction, but cannot fill in analyses that are not reported.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists the histologic percentage of vital bone formation as the primary outcome and reports no posted secondary outcomes. It also lists no posted analyses. The presence of a single listed primary endpoint does not tell readers whether other outcomes were measured but not reported, whether multiple analyses of the primary endpoint were considered, or what strategy was used to address multiplicity. Those details are not reported in the registry record.

Multiplicity is a general concern when several outcomes, time points, subgroups, or statistical comparisons are tested. Repeated testing can increase the chance of a result appearing notable by chance unless the analysis plan addresses that issue. The record does not report a multiplicity adjustment or a plan for choosing among analyses. It would be inappropriate to infer that no multiplicity concerns existed solely because no secondary results are posted.

Missing-data handling and analysis populations are also not reported in the registry record. Although 20 participants are listed in each outcome group, the record does not clarify whether these were all enrolled and randomized participants, all participants with an available bone-core result, or another analysis population. It does not report missing outcome counts, reasons for missingness, exclusions, or imputation methods. The population field for the primary outcome is blank.

The registry record does not say whether the primary comparison used an intention-to-treat, per-protocol, or other analysis population. It also does not report a prespecified analysis plan, adjustment for baseline variables, or sensitivity analyses. These omissions matter because the treatment contrast can depend on which participants and measurements are included and on how missing outcomes are handled. The group medians remain descriptive of the posted results, but the record does not provide enough information to assess the robustness of a comparative estimate.

11. 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 reports zero serious adverse events and zero other adverse events in each group. For both categories, 20 participants are listed as at risk in the cancellous FDBA group and 20 in the cortical FDBA group. The event counts are therefore registry-reported counts for the listed groups and categories, not a complete description of every possible safety outcome.

These zero counts should be read as no events recorded in the posted fields, not as proof that no adverse experiences occurred under any definition or during every relevant period. The record does not describe the event collection process, observation window, attribution rules, or completeness of reporting. Deaths are not reported in the registry record, and no top serious-event terms are listed.

As a general statistical point, small group counts provide limited information about the frequency of uncommon events. Zero observed events does not establish that the underlying event risk is zero. The posted figures also do not support a comparative safety analysis, because the registry reports no inferential comparison. They describe the adverse-event counts entered for the trial groups and should not be extended beyond those reported categories and participants.

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

The posted results show the distributions of the primary histologic endpoint in the two graft groups at 18-20 weeks after grafting. The median was 12.98% vital bone for cancellous FDBA, with an interquartile range of 10.06% to 31.04%. For cortical FDBA, the median was 16.08%, with an interquartile range of 12.12% to 30.25%. These figures describe the observed sample; they do not establish the size or precision of a treatment effect.

The results do not show whether a between-group difference is statistically distinguishable from chance variation. No inferential comparison, confidence interval for the contrast, or p-value is reported in the registry record. The overlap between the interquartile ranges cannot answer that question, and the medians alone are not a substitute for a formal comparison.

The study concerns ridge preservation after extraction of non-molar teeth using either cortical or cancellous freeze-dried bone allograft. It does not compare grafting with no grafting. Its primary outcome is histologic tissue composition at the stated assessment interval, not a reported long-term clinical endpoint. The registry does not report how this measure relates to later outcomes or to other patient groups.

The safety fields record zero serious and zero other adverse events in each arm, with 20 participants at risk per group. Those records do not prove that no events occurred outside the entered categories or reporting process. Deaths are not reported in the registry record.

Overall, the record supports a limited descriptive reading: the two groups have the reported medians and interquartile ranges, with no posted inferential analysis to quantify their contrast. It does not justify a conclusion about clinical benefit, equivalence, or absence of a difference. Such conclusions would require evidence and analyses not reported in the registry record.

13. Why This Trial Matters Statistically

This trial illustrates why a registry result needs to be read according to the kind of statistic it reports. Medians and interquartile ranges can make a distribution easier to understand, especially when the outcome is not summarized with a mean and standard deviation. But descriptive summaries answer a different question from an inferential comparison. They show what was recorded in each group, not how precisely the groups differ.

The distinction is particularly important in a randomized trial. Randomization creates a design intended to support a fair comparison, but the credibility of a treatment contrast also depends on implementation, outcome availability, and analysis. The registry identifies a randomized parallel-group design and reports 20 participants in each outcome group. It does not report allocation details, analysis populations, handling of missing observations, or a test and estimate for the primary comparison. Thus, the design information cannot replace the missing comparative analysis.

The endpoint also highlights the difference between a biologic or histologic measure and a broader clinical outcome. A percentage of vital bone in a core sample provides information about tissue composition at 18-20 weeks after grafting. It is not by itself a report of later clinical outcomes, and the record does not describe a relationship between the histologic measure and those outcomes.

Safety counts offer another useful lesson in interpretation. A recorded zero is a count in a registry field, not proof of zero underlying risk. The reporting window and ascertainment approach are not described, and deaths are not reported. Clear distinction between observed counts and conclusions about risk is essential when event information is sparse.

For biostatistical readers, the main point is disciplined scope: identify the randomized comparison, endpoint, summary measures, and reporting gaps before drawing conclusions. The registry contains useful descriptive information, but uncertainty around the treatment contrast remains unquantified.

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 main trial-specific limitation in the registry record is the absence of an inferential analysis for the primary endpoint. The medians and interquartile ranges are posted, but no estimate of the between-group contrast, confidence interval, test statistic, or p-value is reported. This limits assessment of the magnitude and precision of the comparison.

The outcome summaries list 20 participants per arm, while enrollment is reported as 40. The record does not state the analysis population or confirm how many participants contributed usable histologic measurements. Missing outcomes, exclusions, and reasons for missingness are not reported. The population field for the primary outcome is blank.

The trial is described as randomized and unmasked, but details of random-sequence generation and allocation concealment are not reported. The record does not say whether histologic assessors were masked, whether baseline characteristics were assessed, or whether any adjusted analysis was planned. These omissions limit evaluation of the trial's implementation and possible sources of bias.

The endpoint is histologic percentage of vital bone measured in bone cores at 18-20 weeks after grafting. The registry does not report longer-term follow-up or other clinical endpoints, so the results have a restricted outcome and time scope. The stated study population concerns non-molar extractions; other populations and extraction types are not addressed by the posted primary results.

The registry reports no secondary outcomes and no analyses. It does not report a sample-size justification, multiplicity strategy, statistical analysis plan, or missing-data method. The adverse-event fields contain zero reported serious and other events in each group, but event ascertainment and reporting windows are not described; deaths are not reported. These limitations arise from the information recorded and should not be mistaken for proof that the corresponding procedures or data were absent from the conduct of the trial.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Ridge Preservation After Tooth Extraction Using Cortical Versus Cancellous Freeze Dried Bone Allograft — NCT01588444.
• Registry record last updated 2015-10-22; status last verified 2015-10.
• Results first posted 2014-10-06.
• 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.

18. Record Summary

NCT01588444 is a completed randomized, unmasked, parallel-group study sponsored by The University of Texas Health Science Center at San Antonio. The registry lists enrollment of 40, a study start of 2010-10, and primary completion of 2012-07. The trial compared cortical with cancellous freeze-dried bone allograft for ridge preservation after non-molar tooth extraction.

The primary outcome was histologic percentage of vital bone formation in bone cores at 18-20 weeks after grafting. The cancellous group had a median of 12.98% and an interquartile range of 10.06% to 31.04%; the cortical group had a median of 16.08% and an interquartile range of 12.12% to 30.25%. The registry reports no posted analyses or secondary outcomes, and no inferential comparison for the primary endpoint.

Zero serious and zero other adverse events are recorded in each group, with 20 participants at risk per group. Deaths are not reported in the registry record. Analysis-population details, missing-data handling, the sample-size justification, and further statistical methods are not reported in the registry record.