A Study of the Performance of Certain Prevail Implants Used in Short Fixed Cases: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study of the Performance of Certain Prevail Implants Used in Short Fixed Cases (NCT00723944), a randomized na study. The primary outcome is Crestal Bone Regression (Amount of Bone Measured) Around Each Implant Unit.

2. Clinical Question

The study asks whether crestal bone measurements after placement and loading differ between two implant designs in short-span fixed bridge cases. One design, Osseotite Certain Prevail, is lateralized; the Osseotite Certain comparison design is not. The registry describes the null hypothesis as the same crestal bone changes for the two designs.

The endpoint is a continuous measurement in millimeters, averaged for each implant unit from radiographic observations. The comparison concerns the observed means in the analyzed implants; it is not a direct measure of every aspect of implant performance. Osseous integration is listed as a secondary outcome. The record does not report further detail about how that secondary outcome was assessed.

3. Trial Design

This was a prospective, randomized, multicenter study with a parallel-group design. Participants were assigned to receive one of two dental implant designs: Osseotite Certain Prevail, described as lateralized, or Osseotite Certain, described as non-lateralized. Masking is recorded as none. The study is marked completed, and the enrollment is 102.

The registry lists a start date of 2005-02 and primary completion in 2007-04. It identifies partial edentulism and tooth disease as conditions. The phase is listed as NA. The intervention category is device for both implants. These details describe the registered study, but the record does not provide the randomization sequence method, allocation concealment method, or additional procedural detail about implant placement and loading.

The primary endpoint is mean crestal bone regression around each implant unit at 1 year. The record describes radiographs as the measurement source and states that observed crestal bone measurements are averaged to obtain the mean loss or gain for each implant unit. The primary results are reported only for implants achieving integration, defined as lack of mobility, through the 12 months follow-up stage. There are 48 implants in the Prevail results and 37 in the Certain results.

The registered enrollment and the endpoint analysis counts refer to different reported quantities: enrollment is the study-level count, while the endpoint description restricts the analyzed results to integrated implants. The registry does not explain the full path from enrollment to those endpoint counts, or identify reasons why implants were not included in the primary results. The record lists Osseous Integration as a secondary outcome and indicates one posted secondary outcome. It does not report a statistical analysis for that secondary outcome.

The registry record does not report the original sample-size justification, detailed statistical analysis plan, planned interim analyses, or methods for handling missing data. Those omissions limit what can be concluded about design choices beyond the randomized, multicenter, parallel structure and the stated endpoint.

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 represents all patients receiving test and control implants enrolled in the study, but only those implants achieving integration (lack of mobility) were analyzed and reported here up to the 12 months follow-up stage.

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 is the mean amount of crestal bone regression measured around each implant unit, expressed in millimeters, at 1 year. The record says that radiographs are used to observe and measure crestal bone, with measurements averaged to obtain a mean value for each implant unit. The outcome is continuous: it can take a range of values rather than counting only whether an event did or did not occur.

This endpoint is used to describe bone changes around the implant over follow-up and to compare the average measurement between the lateralized and non-lateralized designs. The registry’s stated null hypothesis is that crestal bone changes after placement and loading are the same for both designs. The reported group means are -0.770 for Osseotite Certain Prevail and -0.665 for Osseotite Certain. Both values are reported as mean measurements, with standard errors of 0.157 and 0.116, respectively.

The analysis population is important to interpreting the endpoint. The record says that results include only implants achieving integration, defined as lack of mobility, through the 12 months follow-up stage. Thus, the reported means describe that subset rather than every implant enrolled or assigned. The registry does not report additional detail about the radiographic measurement procedure, assessor masking, or the handling of repeated measurements. Osseous Integration is listed as a secondary outcome, but the primary endpoint remains the one-year continuous bone measurement.

7. Results Posted in the Registry

• Osseotite Certain Implant: mean -0.66 versus -0.77 on control; difference 0.11 (95% CI -0.28 to 0.49), standardized effect d = 0.11; z-test p = 0.587.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a continuous variable: mean crestal bone regression measured in millimeters. For a continuous outcome, a group mean describes the average of the observed measurements, while a standard error describes uncertainty in the estimated mean. A standard error is not the same as the spread of individual measurements; it concerns the precision of the estimated average. The record reports means and standard errors for each group and an unadjusted mean difference with a confidence interval and p-value.

What does the mean difference represent?

The comparison is expressed as the mean for Osseotite Certain minus the mean for Osseotite Certain Prevail. The group values are -0.665 and -0.770, and the reported mean difference is 0.106. A positive value on this scale means the Certain group’s mean measurement is numerically higher than the Prevail group’s mean. This is a comparison of the recorded endpoint values; it does not by itself establish that one design is clinically preferable. The registry’s endpoint description allows for mean bone loss or gain, but the record does not give a clinical threshold for interpreting the size of the difference.

How should the p-value be read?

The unadjusted p-value is 0.587. In general, a p-value describes how unusual data at least as discrepant as those observed would be under a specified null model, assuming that model and its assumptions hold. It is not the probability that the null hypothesis is true, and it does not measure the probability that the result will replicate. A p-value also does not describe the size or clinical importance of a difference. Here, the value should be read alongside the estimated difference and its confidence interval, rather than in isolation.

Why is the confidence interval important?

The 95% confidence interval for the mean difference is -0.276 to 0.488. In general, a confidence interval gives a range of values compatible with the data and the method used, expressing uncertainty about the estimated difference. Its inclusion of zero means that no mean difference is among the values compatible with the interval. The interval also contains positive and negative values, so the direction is uncertain. The interval does not establish equivalence, and its range should not be interpreted without a clinical threshold, which the registry does not report.

What does the analysis population mean?

The registry states that only implants achieving integration, described as lack of mobility, were analyzed and reported for the primary endpoint through the 12 months follow-up stage. The resulting group counts are 48 for Prevail and 37 for Certain. In general, restricting an analysis to a post-assignment subset can make the result different from one that includes all randomized participants or implants. The record does not explain why all enrolled or assigned cases are not represented in these counts, so the effect of the restriction cannot be determined from the registry record.

What is not described?

The registry does not report a detailed statistical analysis plan, a model specification, adjustment for covariates, missing-data methods, or a method for accounting for any clustering or repeated measurements. The record describes a multicenter study and an implant-unit measurement, but does not say how center-level or within-participant dependence was handled. These details matter in general because observations may not be statistically independent when they arise from the same participant or clinical site. Without a reported method, it is not possible to determine whether or how such structure was considered.

The record lists one secondary outcome, Osseous Integration, but does not provide a posted statistical analysis for it. It also does not report whether any interim analyses were planned or conducted, or whether multiplicity adjustments were specified. These should be treated as unreported design and analysis details, rather than inferred from the endpoint results.

10. Confidence Intervals and Precision

The reported mean difference is 0.106 millimeters, with a 95% confidence interval from -0.276 to 0.488. This interval conveys substantial uncertainty about the exact size and direction of the difference: it spans zero and includes values on either side. The posted p-value for the unadjusted comparison is 0.587. Together, these statistics indicate that the estimated difference is not precise enough to rule out no difference or differences in either direction within the interval.

In general, a confidence interval is a range generated by a statistical method that, under its assumptions, reflects uncertainty in an estimate. It is not a range containing a known proportion of individual participants’ measurements, nor does it give the probability that the true difference falls inside this particular interval. Precision depends on factors such as the amount of information in the data and the variability of measurements. The registry reports standard errors of 0.157 for Prevail and 0.116 for Certain, but does not report the individual-level measurement distributions.

The interval should be considered alongside the analysis population: only implants achieving integration through the 12 months follow-up stage were included. The precision statement therefore applies to the reported comparison in that subset, not automatically to all enrolled participants. The registry does not report a threshold for a clinically important difference. Without such a threshold, the interval cannot be used to classify the range of differences as clinically trivial or important.

The interval is consistent with uncertainty, not proof that the designs are identical. Equivalence or non-inferiority would require a prespecified margin and a suitable analysis, which are not reported in the registry record.

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 events. The comparison is a continuous outcome, not a time-to-event outcome. The planning illustration assumes a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. It uses the stated fraction of the observed effect as the effect to detect. The registry does not report the trial’s own original sample-size assumptions or justification.

For planning around 100% of the observed effect, the illustration gives 1,241 participants per arm for 80% power and 1,661 participants per arm for 90% power. For planning around 75% of the observed effect, it gives 2,205 participants per arm for 80% power and 2,952 participants per arm for 90% power. For planning around 50% of the observed effect, it gives 4,961 participants per arm for 80% power and 6,641 participants per arm for 90% power.

In general, power is the chance that a planned study will detect an effect of a specified size under its assumptions if that effect is present. The 80% and 90% columns describe different planning targets: the latter uses a higher probability of detecting the chosen effect, with a correspondingly larger required sample in these illustrations. Smaller effects need more participants to distinguish them from random variation under the same assumptions. These are planning illustrations based on the observed effect, not observed power and not a reconstruction of the trial’s original design.

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 = 0.106; pooled standard deviation σ = 0.939.
2. n = 2 × (1.96 + 0.842)² × 0.939² / 0.106² = 1,240.1, rounded up to 1,241 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 <- 0.1057                      # observed difference in means
sigma <- 0.939478657785122                     # 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(723944)
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 = 1,241 (80% power), 1,661 (90% power)
 75% of observed effect: n per arm = 2,205 (80% power), 2,952 (90% power)
 50% of observed effect: n per arm = 4,961 (80% power), 6,641 (90% power)
power.t.test: 1241.1 
Simulated power at n = 1,241 per arm: 0.797 (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 the primary crestal bone regression endpoint and one secondary outcome, Osseous Integration. It reports two outcome measures in total, but no statistical analyses for the secondary outcome are posted. The record does not say whether the investigators planned to test multiple endpoints, multiple time points, or multiple contrasts, or whether any adjustment for multiple testing was intended.

In general, multiplicity arises when several statistical tests are conducted and can increase the chance of at least one apparently positive result by chance. Adjustments or a prespecified hierarchy can be used to manage that issue, but neither a method nor an analysis hierarchy is reported in the registry record. It is therefore not possible to determine how multiplicity was addressed, or whether it affected interpretation of the primary comparison. The reported p-value is explicitly unadjusted.

The primary endpoint population is restricted to implants that achieved integration through the 12 months follow-up stage. Although the record gives endpoint counts of 48 and 37, it does not explain the exclusions from the enrolled population, report reasons for missing measurements, or describe any imputation or other missing-data procedure. It also does not state whether analysis was planned on an intention-to-treat basis or another basis. The registry’s description of the analyzed subset is the available basis for interpreting the posted means.

In general, missing-data handling can matter when the availability of an outcome is related to the outcome itself or to participant characteristics. The record does not include enough information to assess that possibility. It also does not state whether the restriction to integrated implants was prespecified, how integration was assessed over time, or what happened to implants not meeting that condition.

The registry records randomization but does not report sequence generation or allocation concealment. It lists no masking. The statistical plan, interim analysis procedures, and methods for accounting for multicenter structure are also not reported in the registry record. These omissions do not show that methods were not used; they mean that their use cannot be established from the posted record.

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 figures are reported for 52 participants at risk in the Osseotite Certain Prevail group and 50 at risk in the Osseotite Certain group. The number reported as affected by a serious adverse event is 0 in each group. The registry does not list serious adverse event terms, and deaths are not reported in the registry record.

These counts describe what is posted for the stated at-risk groups. A reported count of zero is not proof that an event is impossible or that the two groups have identical safety profiles. It should be interpreted in light of the number at risk, the follow-up and collection procedures, and the completeness of reporting; further details about these procedures are not reported in the registry record.

The record also lists other adverse events, with 4 affected in the Prevail group and 19 in the Certain group, among the stated at-risk groups. Those are separate from the serious adverse event counts and should not be conflated with them. The registry does not provide additional detail about the nature, severity, timing, or attribution of those other events.

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

The posted primary endpoint results describe one-year mean crestal bone measurements among implants reported as achieving integration. The Prevail group mean is -0.770 millimeters and the Certain group mean is -0.665 millimeters. The reported mean difference is 0.106 millimeters for Certain relative to Prevail, with a 95% confidence interval from -0.276 to 0.488 and an unadjusted p-value of 0.587.

These data do not establish that the two implant designs have the same mean outcome. The confidence interval includes zero and values in both directions; the comparison therefore does not precisely determine the direction or size of a population mean difference. The result also does not establish that either design is better or worse in clinical terms. The registry does not report a clinically important difference threshold, and a numerical difference alone cannot establish a clinically meaningful effect.

The result concerns a specific endpoint, follow-up time, and analysis subset. It does not by itself summarize all aspects of implant performance, long-term outcomes, or the experience of all enrolled participants. The primary analysis includes only implants achieving integration through the 12 months follow-up stage. The registry does not explain the reasons for this restriction or describe the missing-data approach, so the degree to which the posted results represent all randomized cases cannot be determined.

The randomized design is relevant to comparing the assigned interventions, but the record does not provide details about allocation concealment, the analysis plan, or adjustment for center or other factors. It also records no masking. These reporting limits make it inappropriate to infer more than the posted comparison supports. The finding is best read as an imprecise, unadjusted comparison of the reported means, rather than evidence of equivalence or a definitive statement about implant performance.

16. Why This Trial Matters Statistically

This study illustrates several statistical distinctions that matter in clinical research. First, a continuous endpoint such as mean crestal bone measurement is summarized by group averages, but the averages do not describe every implant. The reported comparison estimates a difference between those averages and uses a confidence interval to show uncertainty around that estimate.

Second, statistical compatibility with no difference is not the same as proof that two interventions are equivalent. The confidence interval includes zero, but it also spans differences in both directions. Equivalence requires a clinically justified margin and a design and analysis intended to test whether the difference falls within that margin. Such a margin is not reported in the registry record.

Third, analysis populations shape what a result means. The endpoint results include only implants achieving integration through 12 months, rather than all enrolled participants or assigned implants. Recognizing that restriction prevents the reported estimate from being generalized automatically to the full enrolled population. The registry does not explain why cases are absent from the endpoint analysis.

Finally, sample-size planning depends on the effect chosen for detection and the desired power. The planning illustrations show that smaller target effects require more participants under their stated assumptions. They are not evidence about the trial’s original sample-size planning and are not a measure of power observed after the study was completed. Together, these points demonstrate why estimates, uncertainty, analysis populations, and design assumptions need to be read as a connected set rather than reducing a trial to a single p-value.

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.

The endpoint results are limited to implants reported as achieving integration, defined as lack of mobility, through the 12 months follow-up stage. The registry does not report why the endpoint counts are smaller than the overall enrollment, whether missingness differed between groups, or how absent measurements were handled. This leaves uncertainty about how representative the analyzed subset is of all enrolled participants and assigned implants.

The record gives a mean and standard error for each group but does not describe the individual measurement distribution, the radiographic reading procedure in detail, or whether outcome assessors were masked. Masking is recorded as none. The registry also does not say how measurements from implants in the same participant, or observations across study centers, were handled statistically. Such details can matter when measurements are related rather than independent.

The reported comparison is unadjusted, and a full statistical analysis plan is not reported. No clinically important difference threshold is given, so the size of the mean difference cannot be classified as clinically unimportant or important from the registry information. The confidence interval is broad enough to include zero and values on both sides, leaving direction and magnitude uncertain.

The study is described as multicenter and randomized, but the registry record does not report the sequence-generation or allocation-concealment methods. It also does not report the original sample-size justification, interim analyses, or methods for multiplicity. The posted safety information includes serious adverse event counts, but the registry does not report deaths or serious-event terms. These reporting gaps limit a comprehensive assessment of design, analysis, missingness, and safety; they do not establish that unreported procedures were absent.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: A Study of the Performance of Certain Prevail Implants Used in Short Fixed Cases — NCT00723944.
• Registry record last updated 2026-07-28; status last verified 2022-03.
• Results first posted 2011-11-22.
• 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 registry record describes a completed, prospective, randomized, multicenter, parallel-group study with enrollment of 102. It compared the lateralized Osseotite Certain Prevail implant with the non-lateralized Osseotite Certain implant. Masking is recorded as none.

The primary endpoint was mean crestal bone regression around each implant unit at 1 year, measured in millimeters from radiographs. The reported means were -0.770 for Prevail and -0.665 for Certain. The unadjusted mean difference was 0.106, with a 95% confidence interval from -0.276 to 0.488 and p = 0.587. The primary endpoint results include only implants achieving integration through the 12 months follow-up stage.

Osseous Integration is listed as a secondary outcome. The record does not report the original sample-size justification, detailed statistical plan, missing-data methods, or reasons for the primary endpoint analysis counts. Serious adverse events are reported for 0 of 52 at risk in the Prevail group and 0 of 50 at risk in the Certain group; deaths are not reported in the registry record.