A Study of Certain Prevail Implants Used for the Preservation of Crestal Bone in Short Fixed Bridge Cases.: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study of Certain Prevail Implants Used for the Preservation of Crestal Bone in Short Fixed Bridge Cases. (NCT00728754), a randomized na study. The primary outcome is Crestal Bone Regression (Amount of Bone Measured) Around Each Implant Unit.

2. Clinical Question

The registry describes a prospective, randomized-controlled, multicenter comparison in short-span fixed bridge cases. Its stated null hypothesis is that crestal bone changes after placement and loading would be the same for the lateralized implant and a similar non-lateralized implant. The primary outcome is a continuous measurement in millimeters, based on radiographs of each study implant. The measurement is averaged to obtain a mean amount of crestal bone loss or gain for each implant unit.

The posted outcome is at the 1 year timeframe. The registry reports mean values and standard errors for the two arms, and a mean difference with a confidence interval and an unadjusted p-value. It does not report a separate hypothesis-test analysis record. The question is therefore about the numerical contrast and its uncertainty, rather than a definitive conclusion about whether the designs are equivalent. A non-significant result would not by itself establish that the designs have the same effect; demonstrating equivalence requires a specified margin and a suitable analysis, neither of which is reported in the registry record.

3. Trial Design

This was a prospective, randomized-controlled, multicenter study with a parallel-group model. Allocation was randomized, and masking was listed as none. The registry lists the phase as not applicable. The study was completed, with a recorded start of 2005-03 and primary completion of 2007-07. Enrollment was 61.

The two device arms were the Osseotite Certain Prevail implant, described as lateralized, and the Osseotite Certain implant, described as non-lateralized. The registry’s brief summary says the study would evaluate the performance of the Prevail design compared with the non-lateralized version. The stated null hypothesis concerned whether crestal bone changes after placement and loading would be the same between the designs. The record does not specify the randomization method, allocation concealment, or the number of centers.

The primary outcome was crestal bone regression, measured in millimeters from a radiograph of each study implant and averaged for each implant unit. Its timeframe was 1 year. The record identifies the primary measure as a mean with standard error. Although the outcome description refers to patients receiving implants, it clarifies that the reported counts at the analysis time point represent implants followed at the 12 month follow-up. The arm summaries list 24.0 implants for the Prevail group and 28.0 for the non-lateralized group.

Osseous integration is listed as a secondary outcome. The registry lists two outcome measures, but no analysis records. Details such as the original sample-size justification, the intended statistical model, handling of missing follow-up measurements, and any planned interim analyses are not reported in the registry record. The posted results should therefore be interpreted as the recorded arm summaries and comparison, without assuming an unreported protocol or analysis plan.

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: Pre-treatment included a screening visit (enroll those meeting all inclusion criteria), signing informed consent, and pre-surgical data collection.Patients returned for implant placement surgery, followed by temporary prosthesis placement at 2 months.

Implant Placement Surgery

Permanent Prosthesis Placement

Reasons for not completing this period:

One year post placement follow-up

Reasons for not completing this period:

Two year post placement follow-up

Analysis population for the primary outcome, as defined in the registry: population analyzed was all patients receiving implants enrolled in the study, those reported here actually represent the number of implants being followed at the 12 month follow-up time point (time of analysis).

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 Crestal Bone Regression (Amount of Bone Measured) Around Each Implant Unit, measured over 1 year.

The primary endpoint measures crestal bone regression around each implant unit. The registry describes the measurement as millimeters of crestal bone observed on a radiograph, averaged to represent mean bone loss or gain for each implant. The specified assessment timeframe is 1 year. Radiographic measurement provides a continuous outcome, so the result is expressed as a mean rather than as a count of participants with an event.

This endpoint is relevant to the study’s stated question because the proposed design difference is lateralization, and the study aims to compare crestal bone changes around the two implant types. The mean summarizes the central level of the recorded measurement in each arm. The standard error indicates the estimated uncertainty of that arm mean; it is not the spread of individual implant measurements. The registry does not provide a standard deviation for the endpoint or individual observations.

The displayed arm means are -0.744 millimeters for the Prevail implant and -0.845 millimeters for the non-lateralized implant. The registry describes the endpoint as bone loss or gain but does not give additional interpretive detail about the sign convention. These values should therefore be read as recorded on the reported scale, without assigning an unreported clinical interpretation to the negative sign. The primary-outcome description also distinguishes the number of implants followed from the broader wording about patients receiving implants. This distinction matters when interpreting the denominator and the unit represented by the mean.

7. Results Posted in the Registry

• Osseotite Certain Implant: mean -0.84 versus -0.74 on control; difference -0.10 (95% CI -0.56 to 0.36), standardized effect d = -0.12; z-test p = 0.671.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: each implant has a radiographic crestal bone measurement, and the arm results are expressed as means. A mean difference compares the average measurement in one arm with the average in the other. Here the posted contrast is -0.101 millimeters for the non-lateralized implant relative to Prevail. The sign indicates the direction of the contrast as calculated for that ordering; it does not, without a defined sign interpretation and clinical context, say whether the difference is important.

The standard error describes the precision of an estimated mean. It is not the same as the variability among individual implant measurements. A standard error generally becomes smaller when an estimate is based on more observations or when the underlying measurements are less variable. The registry gives standard errors of 0.188 and 0.144 millimeters for the two arms. It does not report the standard deviations of the individual measurements. The comparison summary includes a pooled standard deviation of 0.839 millimeters, but the registry does not identify a fuller analysis method or covariate adjustment for the reported endpoint.

A confidence interval gives a range of values compatible with the observed data under the assumptions of the analysis. For the mean difference, the posted interval is -0.565 to 0.364 millimeters. Because the interval includes zero, the data are compatible with no difference in means under the comparison’s assumptions. They are also compatible with nonzero differences in either direction. A confidence interval is not a range containing a fixed proportion of individual implant measurements, and it is not a guarantee that the true value lies within the limits.

The p-value assesses how unusual the observed result, or a result more extreme, would be if the null hypothesis and analysis assumptions held. The posted unadjusted p-value is 0.671. It does not measure the size or clinical importance of the difference, nor the probability that the null hypothesis is true. The confidence interval is useful alongside the p-value because it conveys the range of effect estimates consistent with the observed data, rather than only indicating whether a statistical threshold was crossed.

As a general statistical point, a nonsignificant result is not proof of no effect. An equivalence or non-inferiority question requires a margin that defines which differences would be small enough to be treated as acceptable, along with an analysis designed for that question. No such margin or analysis is reported in the registry record. The stated null hypothesis of equal bone changes does not by itself make the study an equivalence trial.

As a general point, the unit of analysis should align with the unit to which the outcome pertains. The primary description says measurements are obtained for each implant unit, and the posted endpoint counts refer to implants followed at 12 months. It also describes the analyzed population in terms of patients receiving implants. The registry does not clarify whether any patient contributed measurements from more than one implant, or how within-patient dependence was addressed if that occurred. Measurements from implants in the same patient can be correlated; treating correlated observations as independent can affect standard errors and confidence intervals. The record does not report enough detail to determine whether this issue arose or how it was handled.

As a general statistical point, the standard error for an arm mean reflects sampling uncertainty under the model used, while the spread of individual outcomes reflects heterogeneity among observed units. These quantities answer different questions. A narrow confidence interval would indicate a more precise estimate of the mean contrast, but would not imply that individual measurements are similar. Conversely, substantial individual variation does not necessarily prevent a mean from being estimated precisely when the data provide adequate information. The registry does not report individual measurements, so that distribution cannot be assessed from the listed summaries.

The registry lists no analysis records. It therefore does not report a detailed statistical analysis plan, including whether assumptions were checked, how missing endpoint data were handled, or whether any covariates were considered. The posted comparison is unadjusted, and no adjusted result is listed. The comparison is not marked as recalculated, and the discrepancy flag is false. There is no registry-reported sponsor analysis to set against the posted comparison in the record summarized for this study.

Randomization can support a fair comparison by reducing systematic differences between groups, on average, when allocation is implemented appropriately. It does not guarantee that groups are identical, and it does not resolve concerns about incomplete follow-up, outcome measurement, or analysis choices. Masking was listed as none. That fact is relevant when considering how outcome ascertainment might be influenced, but the registry does not describe radiograph reading procedures or whether measurement assessors were otherwise kept unaware of assignment. These details are not reported in the registry record.

10. Confidence Intervals and Precision

The reported mean difference is -0.101 millimeters, with a 95% confidence interval from -0.565 to 0.364 millimeters. The interval includes zero and spans estimates in both directions. It therefore does not pin down the direction of the difference with confidence. The unadjusted p-value is 0.671, consistent with the interval’s inclusion of zero under the reported comparison.

Precision concerns the range of plausible values around an estimate, not whether the estimate is clinically important. The interval is wide enough to include differences meaningfully farther from zero than the point estimate, but the registry record does not define a clinically important difference for this endpoint. Without such a threshold, it is not possible to label the interval as excluding or including clinically important effects.

The standard errors for the arm means are 0.188 millimeters for the Prevail arm and 0.144 millimeters for the non-lateralized arm. The endpoint counts are 24.0 and 28.0 implants followed at the 12 month time point. These are implant counts, as clarified by the outcome description, rather than a clear report of the number of patients contributing measurements. The record does not explain whether multiple implants from a patient were included or how that possibility was accounted for in the precision estimates.

A confidence interval is conditional on the analysis assumptions and the data used. Missing follow-up information, dependence among measurements, or other analytic choices can affect precision, but their handling is not reported in the registry record. The interval should be interpreted as precision for the posted unadjusted mean comparison, not as a guarantee about every possible analysis or the longer-term outcome.

11. 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, not total event counts. They are illustrations based on fractions of the observed effect: the full observed effect, 75% of the observed effect, and 50% of the observed effect. The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The sample-size figures are planning illustrations computed from the observed effect, not the trial’s original design assumptions; those original assumptions are not reported in the registry record.

The 80% power column gives the number of participants per arm that the planning calculation estimates would be needed to detect the specified effect under its assumptions with 80% power. The 90% power column gives the corresponding number per arm for 90% power. Power is the chance of detecting an effect of the specified size under the assumed model if that effect is present. The figures are not counts observed in this trial and should not be confused with the endpoint follow-up counts.

Smaller effects are harder to distinguish from random variation, so the planning illustration calls for more participants per arm when a smaller fraction of the observed effect is used. For example, planning for 75% of the observed effect gives 1,945 participants per arm for 80% power and 2,603 participants per arm for 90% power; planning for 50% gives 4,375 and 5,857 participants per arm, respectively. These are planning estimates, not observed power. They do not establish what the original investigators intended or whether the completed trial met its original design target.

12. 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 = -0.101; pooled standard deviation σ = 0.839.
2. n = 2 × (1.96 + 0.842)² × 0.839² / -0.101² = 1,093.7, rounded up to 1,094 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 <- -0.1005                      # observed difference in means
sigma <- 0.838871855291379                     # 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(728754)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 1,094 (80% power), 1,465 (90% power)
 75% of observed effect: n per arm = 1,945 (80% power), 2,603 (90% power)
 50% of observed effect: n per arm = 4,375 (80% power), 5,857 (90% power)
power.t.test: 1094.7 
Simulated power at n = 1,094 per arm: 0.796 (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.

13. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures, with crestal bone regression identified as the primary outcome and osseous integration listed as a secondary outcome. The primary measure is reported at the 1 year timeframe. The record does not provide a full analysis plan that explains how the primary and secondary outcomes were prioritized or how conclusions across multiple outcomes were to be controlled. No multiplicity adjustment is reported.

As a general statistical point, evaluating multiple outcomes or multiple time points can increase the chance of obtaining at least one apparently unusual result by chance. A prespecified hierarchy or adjustment can address some of that concern. The registry record does not report whether such methods were planned or used, and only the primary outcome summaries and comparison are included in the results. The secondary outcome is named but no result is reported in the registry record.

The record does not describe how missing 1 year radiographic measurements were handled, whether all randomized participants were included in the analysis, or whether the analysis followed an intention-to-treat approach. The endpoint description says the analyzed population was patients receiving implants enrolled in the study, while noting that the reported follow-up counts represent implants being followed at 12 months. It does not state how many randomized participants did not contribute an endpoint measurement or why.

These omissions limit assessment of potential bias from incomplete follow-up and of how closely the posted analysis followed the original plan. The registry lists no analysis records. The reason for the absence of those records, and the details of the statistical plan, are not reported in the registry record. This does not establish that a particular method was or was not used outside the posted record; it means those details cannot be evaluated from the registry information.

14. 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 5% reporting threshold.

Most frequent non-serious adverse event terms

The serious adverse-event summaries report zero affected participants in each arm: 0 of 29 at risk in the Osseotite Certain Prevail group and 0 of 32 at risk in the Osseotite Certain group. No serious adverse-event terms are listed. These figures describe the safety entries recorded for the stated at-risk groups; they are separate from the implant counts used for the primary endpoint.

The summaries also report 5 other adverse events in each group, with 29 and 32 participants at risk, respectively. The registry does not provide event descriptions in the listed summary. Deaths are not reported in the registry record. The absence of reported serious events should be read as a feature of the posted record, not as proof that no event could occur or that the devices have no risks. The record does not provide additional details about event definitions, collection procedures, severity or causal assessment for the other events, or the time period covered by the safety counts.

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

The posted results describe a comparison of mean crestal bone measurements at 1 year. The Prevail arm mean was -0.744 millimeters, while the non-lateralized arm mean was -0.845 millimeters. The reported mean difference for non-lateralized relative to Prevail was -0.101 millimeters. The 95% confidence interval, -0.565 to 0.364 millimeters, includes zero, and the unadjusted p-value was 0.671. These data do not show a statistically clear difference in the posted unadjusted comparison.

That conclusion is narrower than saying the implant designs produce the same result. The interval allows for differences in either direction, and the record gives no equivalence margin by which to decide whether the compatible differences are small enough to count as practically equivalent. The finding also does not establish that either device is better or worse. The registry does not define a clinically important threshold for this endpoint, so clinical importance cannot be inferred from statistical significance or from the point estimate alone.

The result is specific to the radiographic crestal bone outcome at the stated follow-up. It does not answer questions about outcomes not reported, longer-term measurements, or all aspects of implant performance. Osseous integration is listed as a secondary outcome, but its result is not reported in the registry record. The safety summaries show zero serious adverse events reported in each at-risk group and 5 other events in each group, but they do not give further event descriptions.

Interpretation is also limited by missing analysis details. The registry lists no analysis records and does not explain missing-data handling, the method used for the comparison, or how possible multiple implants per patient were treated. The posted arm counts refer to implants followed at 12 months, while the population description also refers to patients. These details matter for judging the uncertainty and generalizability of the estimate. The result should therefore be understood as the recorded comparison, with the reported precision and the limits of the registry information in view.

16. Why This Trial Matters Statistically

This study illustrates an important distinction between a failure to detect a difference and evidence that two treatments are equivalent. The stated null hypothesis concerned equal crestal bone changes, and the posted unadjusted p-value is 0.671. That result does not establish equality. The confidence interval includes zero but also spans nonzero values in both directions. A claim of equivalence would need a prespecified margin defining an acceptable difference and an analysis designed to test it; neither is reported in the registry record.

The trial also shows why effect estimates and uncertainty should be considered together. The mean difference is -0.101 millimeters, but its confidence interval extends from -0.565 to 0.364 millimeters. The point estimate alone would give an incomplete picture of the range of values compatible with the observed data. The arm standard errors and implant follow-up counts provide additional context, but they do not replace details about the analysis population and assumptions.

Finally, this record highlights the importance of transparent reporting. It identifies a randomized, parallel-group design and gives arm summaries, yet it does not report the original design assumptions, a detailed analysis plan, missing-data procedures, or analysis records. The endpoint description clarifies that counts refer to implants followed at 12 months, an important distinction for interpreting the unit of analysis. Clearer information about these aspects would make it easier to judge how robustly the posted estimate addresses the study’s question.

17. 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 recorded for this trial. Masking was listed as none, and the record does not describe how radiographs were read or whether the people measuring bone changes were unaware of treatment assignment. Because the primary endpoint depends on radiographic measurement, the absence of information about measurement procedures makes it difficult to assess the potential for assessment-related influence.

The population wording and reported counts are not fully aligned. The primary-outcome description refers to patients receiving implants, then clarifies that the reported counts at the 12 month analysis time point are implants being followed. The arm summaries list 24.0 and 28.0 implants. The registry does not say whether patients contributed more than one implant or explain how any within-patient correlation was handled. This matters because the number of implants is not necessarily the same as the number of independent participants.

The record does not report the original sample-size assumptions or justification, a detailed analysis plan, missing-data handling, interim analyses, or the method used to account for any additional outcomes. There are no analysis records listed. The result is posted as an unadjusted comparison, but further model details are not reported. The registry also does not provide a result for the listed secondary outcome, osseous integration, and does not define a clinically important difference for crestal bone regression.

Safety reporting is limited in the posted summary: other adverse events are counted but not described, and deaths are not reported in the registry record. Follow-up beyond the stated 1 year primary-outcome timeframe is not described in the results summarized for this study. These gaps constrain evaluation of the result and should not be filled by assumptions about procedures or data that are not recorded.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: A Study of Certain Prevail Implants Used for the Preservation of Crestal Bone in Short Fixed Bridge Cases. — NCT00728754.
• Registry record last updated 2026-07-28; status last verified 2022-03.
• Results first posted 2011-11-17.
• 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.

21. Record Summary

The completed registry record describes a prospective, randomized-controlled, multicenter, parallel-group study comparing a lateralized Osseotite Certain Prevail implant with a non-lateralized Osseotite Certain implant. Enrollment was 61, and masking was listed as none. The primary outcome was mean crestal bone regression in millimeters at 1 year, measured from radiographs for each implant unit.

The posted means were -0.744 millimeters for Prevail and -0.845 millimeters for the non-lateralized implant. The mean difference was -0.101 millimeters, with a 95% confidence interval from -0.565 to 0.364 millimeters and an unadjusted p-value of 0.671. The registry lists osseous integration as a secondary outcome but does not report its result in the record summarized for this study.

No analysis records are listed. Original design assumptions, missing-data methods, and several details needed to evaluate the endpoint analysis are not reported in the registry record.