Fabrication of a Definitive Cad/Cam Titanium Abutment Prior to Guided Surgery: a Pilot Study.: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Fabrication of a Definitive Cad/Cam Titanium Abutment Prior to Guided Surgery: a Pilot Study. (NCT02218541), a randomized na study. The primary outcome is Number of Participants With Abutment Margin Exposure > 0.

2. Clinical Question

3. Trial Design

The registry record describes a randomized, single-masked, parallel-group study and labels it a pilot study. It lists an enrollment of 22 and the condition as a single edentulous space. The record does not specify who was masked, how randomization was carried out, or whether allocation was concealed. It also does not report further details about the planned sample-size justification or the procedures used to implement the guided surgery.

Participants were assigned to one of two device interventions. In one arm, the abutment margin was placed 0.5 mm below the gumline; in the other, it was placed 1.5 mm below the gumline. The study summary describes digitally planned implant placement using CT data and says the investigation concerned fabricating an abutment before implant placement. The registry does not report additional details about the digital workflow or clinical procedures.

The study started in 2014-10, had a primary completion date of 2017-05, and is listed as completed. Its phase is recorded as NA. The sponsor is University of North Carolina, Chapel Hill. The primary endpoint timeframe is up to 6 months post surgery; its description refers to margin exposure between groups at 6 months. The primary outcome results list 5 participants in the 0.5 mm arm and 9 in the 1.5 mm arm. The registry does not explain how these endpoint denominators relate to the planned enrollment of 22.

Two secondary outcomes are listed: the number of participants with a soft tissue response of bleeding and the number with provisional crown fit at delivery. The registry record names these outcomes but does not include their results in the registry record reported for this analysis.

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

Reasons for not completing this period:

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 Number of Participants With Abutment Margin Exposure > 0, measured over up to 6 months post surgery.

The primary endpoint counts participants with any abutment margin exposure, defined in the outcome title as exposure greater than zero. It is reported as a participant count, rather than as a continuous measurement of the amount of exposure. The timeframe is up to 6 months post surgery, and the endpoint description identifies the comparison at 6 months post surgery.

This outcome addresses a practical question raised by the study: whether a margin fabricated before surgery is visible after implant placement and restoration. A binary count provides a direct way to compare how many participants in each arm had any exposure. It does not describe how much of the margin was exposed, how long exposure persisted, or the degree of visibility for an individual participant. Those details are not reported in the registry record.

The posted results give 0 participants with exposure among 5 in the 0.5 mm arm and 0 among 9 in the 1.5 mm arm. Thus, the observed counts are identical at zero, while the numbers of participants represented in the two arms differ. A count of zero in both groups does not establish that the underlying risk is zero; it describes only the posted observations. No confidence interval is reported for the primary outcome in the registry record, so the precision of an effect estimate cannot be read from an interval in the posted results.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is binary at the participant level: each participant either had any abutment margin exposure greater than zero or did not. The registry reports counts of participants with the event, rather than the degree of exposure. For this type of outcome, an analysis may compare the event counts across arms, but the method and the amount of information in the data matter. In this study, no events are recorded in either arm, and the endpoint denominators are small.

What does Fisher exact testing do?

The registry reports a Fisher exact test for the two-arm primary comparison, with p = 1.00. In general, Fisher's exact test evaluates the compatibility of a two-by-two arrangement of group membership and event status with a null hypothesis of no association. It calculates probabilities from the observed counts, rather than relying on a large-sample approximation. This can make it suitable for sparse categorical data, including situations with small counts or empty cells.

A test p-value is not an effect estimate. It does not give the difference in event rates, the relative effect, or a measure of precision. It also does not say how likely the null hypothesis is to be true. In this case, the reported p-value accompanies zero events in both groups. The result should be read alongside those counts, not as evidence that the arms are identical. The registry record does not report an effect estimate or confidence interval for the primary comparison.

Why does the absence of events matter?

When an endpoint has no observed events in either arm, the data contain little direct information about how often exposure might occur in the populations represented by the arms. A zero count is an observed result, not a guarantee of zero underlying risk. A comparison can also be difficult to express as a relative effect when both observed event counts are zero. The registry record does not report a numerical effect estimate for this endpoint. The posted event counts and test result therefore provide the available inferential summary without establishing the size or precision of a difference.

What can a confidence interval add?

As a general statistical concept, a confidence interval gives a range of values compatible with the data and analysis method, and communicates uncertainty in an estimate. A narrow interval typically indicates greater precision than a wide interval, though interpretation depends on the chosen measure and assumptions. No confidence interval is reported for this primary comparison. Without one, readers cannot use the registry record to assess a numerical range for the between-arm effect. The p-value alone does not replace that information.

How should the study's stated expectations be treated?

The study summary describes expected visibility of about half of the time with the 0.5 mm margin and about 10% of the time with the 1.5 mm margin. These statements are the investigators' hypothesis in the registry summary. They are not the result of the posted primary analysis. The endpoint results instead give participant counts with any exposure, and both counts are zero. No additional numerical comparison between the stated expectations and observed outcomes is reported.

What do the planning illustrations mean?

General sample-size planning uses assumptions about an effect size, significance level, allocation, and analysis method to illustrate how many participants might be needed to detect a specified effect. The record's planning description says its illustration uses the observed effect, a two-sided significance level of 0.05, equal allocation, and a normal approximation; it describes the effect to detect as a stated fraction of the observed effect. Such calculations are planning illustrations, not observed power and not the trial's own design justification. The registry record does not report the study's sample-size justification. With no observed primary events in either arm, the record does not provide an informative observed effect on which to base a meaningful numerical interpretation of those planning assumptions.

The planning description distinguishes participants per arm for non-time-to-event outcomes from total events for time-to-event outcomes. The primary endpoint is a participant count, not a time-to-event outcome. No numerical planning sample sizes are included in the registry record reported for this analysis, and none can be inferred from the planning description alone.

Overall, the reported inferential method is Fisher exact testing, and the available primary result comprises the two arm counts and p-value. The registry does not report a confidence interval, a numerical effect estimate, or further information about the statistical analysis plan. Those omissions limit how precisely the comparison can be described.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Abutment Margin 0.5 mm Subgingival", "Abutment Margin 1.5 mm Subgingival")
n      <- c(5, 9)
events <- c(0, 0)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Abutment Margin 0.5 mm Subgingival  5  0  0.0  0.0  52.2  0.0  43.4  0.4  45.9
ARM  Abutment Margin 1.5 mm Subgingival  9  0  0.0  0.0  33.6  -0.0  29.9  0.3  30.8

11. Analyses Reported by the Sponsor

The registry reports a Fisher exact test for the primary comparison, with p = 1.00. It does not report an effect estimate or confidence interval alongside that test. The primary counts are 0 participants with exposure among 5 in the 0.5 mm arm and 0 among 9 in the 1.5 mm arm.

No separate recalculated effect estimate is available for comparison with the reported test. The registry record does not identify a discrepancy between the posted analysis and a recalculation. The reported Fisher exact result is therefore the available inferential result; it should be interpreted together with the zero counts and the limited endpoint denominators. It does not quantify a difference or establish equivalence. The registry record does not provide further details about the analysis procedure beyond identifying the test as Fisher exact.

12. Multiplicity, Missing Data and Analysis Populations

The registry lists 3 outcome measures and 3 analyses. It names the primary outcome as the number of participants with abutment margin exposure greater than zero, and lists two secondary outcomes: participants with a soft tissue response of bleeding and participants with provisional crown fit at delivery. The registry entries reported for this analysis do not include results for those secondary outcomes.

When a study examines multiple outcomes or performs multiple tests, the chance of at least one apparently unusual result can increase. General approaches to multiplicity include prespecifying a primary outcome, adjusting significance thresholds, or interpreting secondary analyses as exploratory. The registry record does not report a multiplicity adjustment, a testing hierarchy, or how the listed analyses were prioritized. It is therefore not possible to determine from the record whether or how multiplicity was addressed.

The primary outcome has arm denominators of 5 and 9. The record lists planned enrollment of 22 but does not explain why the primary endpoint denominators differ from enrollment. It does not report participant flow, reasons for non-inclusion, the number with missing primary endpoint data, or a method for handling missing outcomes. Missingness should not be assumed from the difference in counts alone; the reasons and analysis population are not reported in the registry record.

The record also does not describe whether the primary analysis followed an intention-to-treat principle, used a per-protocol population, or applied another population definition. Although the trial is described as randomized, the analysis population and the handling of participants after allocation are not specified. Those details matter because the interpretation of a randomized comparison depends on knowing which participants contributed to the outcome analysis and how departures from the assigned intervention were handled.

The safety record uses 11 participants at risk in each arm, whereas the primary outcome results list 5 and 9. These are distinct denominators for separately reported outcomes. The registry does not explain their relationship, so they should not be combined or used to infer participant flow. Overall, the information needed to evaluate multiplicity and missing-data handling is not reported in the registry record.

13. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The adverse-event record reports 11 participants at risk in each arm. In both the 0.5 mm and 1.5 mm arms, 0 serious adverse events are reported, 0 participants are listed with other adverse events, and 0 deaths are reported. These are the posted safety counts for the groups and outcomes described in the registry.

A zero count means that no events were recorded in the reported group data; it does not establish that the underlying event risk is zero. The registry record does not provide further detail about event definitions, collection procedures, exposure time, or confidence intervals for these safety counts. The absence of serious events in the record should therefore be understood descriptively, not as a precise comparative safety estimate.

The safety denominators differ from those listed for the primary endpoint. The registry does not explain that difference, and the separate figures should not be treated as if they describe the same analysis population. No serious adverse event terms are listed in the registry entries reported for this analysis.

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

The primary result means that no participants with abutment margin exposure greater than zero were recorded in either posted arm: 0 of 5 with the margin placed 0.5 mm below the gumline and 0 of 9 with the margin placed 1.5 mm below the gumline. The registry reports a Fisher exact test p-value of 1.00. These observations describe the participants represented in the outcome results through the stated follow-up timeframe.

The result does not show that the two margin depths are equivalent. Equivalence requires a design and analysis that define an acceptable range of differences and estimate the comparison with sufficient precision. The registry record does not report an equivalence framework or a confidence interval. Nor does the result establish that exposure cannot occur: zero observed events in a limited set of participants does not rule out events in a broader population.

The finding also does not answer every question raised by the study. The primary outcome counts whether any exposure occurred; it does not quantify the extent or duration of exposure. The registry lists secondary outcomes for soft tissue response of bleeding and provisional crown fit at delivery, but their results are not reported in the registry record for this analysis. It does not report a detailed account of follow-up or participant-level outcome data.

The study summary's expectations about visibility—about half of the time for the 0.5 mm margin and about 10% of the time for the 1.5 mm margin—are hypotheses stated in the registry summary. They are not estimates derived from the posted primary counts. The primary results alone cannot establish whether those expectations were met across a larger population.

Accordingly, the result is best read as a small set of posted observations with no recorded primary events in either arm and no evidence of a difference from the reported test. It does not provide a precise estimate of how the margin depths compare, nor does it establish that their outcomes are the same.

15. Why This Trial Matters Statistically

This study is statistically notable because its primary endpoint is a binary event count and neither arm has a recorded event. With sparse data of this kind, a test result can be reported, but the information available for estimating a difference is limited. The Fisher exact p-value of 1.00 is a test summary; it does not replace an effect estimate or an interval describing uncertainty.

The registry also illustrates why denominators matter. The primary outcome lists 5 participants in one arm and 9 in the other, while the planned enrollment is 22. The safety record uses 11 participants at risk in each arm. These figures relate to different reported outcomes, and the registry does not explain their relationship. Keeping each outcome's denominator attached to its result avoids treating separate counts as if they described a single analysis population.

The study's stated hypothesis and its primary outcome are not identical in form. The summary describes anticipated visibility at different frequencies, while the primary outcome records the number of participants with any margin exposure. That distinction matters when interpreting whether the observed endpoint directly addresses the investigators' stated expectations. The record does not report a numerical effect estimate or confidence interval that would support a more precise comparison.

More broadly, a randomized design does not remove the need to report analysis populations, missing-data handling, and the planned approach to multiple outcomes. Those details are not reported in the registry entries and limit appraisal of how the results were derived. The study is labeled a pilot, but the record does not report a sample-size justification or other basis for the enrollment target. Its principal statistical contribution in the registry is therefore descriptive: it records zero primary events in both groups and reports the Fisher exact test, while leaving substantial uncertainty about the comparison's precision.

16. 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 primary endpoint denominators are 5 in the 0.5 mm arm and 9 in the 1.5 mm arm, despite a listed enrollment of 22. The registry record does not explain this difference or report participant flow, reasons for non-inclusion, or the number with missing endpoint data. The result therefore cannot be related to the full enrolled group with confidence from the registry entries alone.

Both observed primary event counts are zero. This leaves no recorded event contrast between arms and limits the information available about the comparative outcome. The registry reports no confidence interval or numerical effect estimate for the primary comparison. The Fisher exact p-value of 1.00 does not itself show that the arms are equivalent or that the underlying event risk is absent.

The record describes the trial as single-masked but does not specify who was masked. It does not provide details of sequence generation, allocation concealment, the analysis population, or the handling of missing data. It also does not report an approach to multiplicity across the listed outcomes and analyses. These omissions restrict assessment of potential sources of bias and the interpretation of the reported test.

The primary endpoint is framed as any exposure, not the amount or duration of exposure. The study summary discusses visibility, but the registry does not report further measurement details that would connect the binary count to severity or persistence. The primary timeframe is up to 6 months post surgery, while the endpoint description refers to 6 months; detailed follow-up information is not reported.

The safety denominators are 11 participants at risk in each arm, distinct from the primary endpoint denominators. The registry does not explain the difference. It also does not report event definitions or additional detail about safety assessment. Finally, although the record calls this a pilot study and gives a planned enrollment, the sample-size justification and any interim analysis plan are not reported in the registry record.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: Fabrication of a Definitive Cad/Cam Titanium Abutment Prior to Guided Surgery: a Pilot Study. — NCT02218541.
• Registry record last updated 2018-07-27; status last verified 2018-05.
• Results first posted 2018-07-27.
• 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.

20. Record Summary

NCT02218541 is a completed randomized, single-masked, parallel-group pilot study sponsored by University of North Carolina, Chapel Hill. It concerns abutment margins placed 0.5 mm or 1.5 mm below the gumline in the context of digitally planned, guided dental implant surgery for a single edentulous space. The listed enrollment is 22.

The primary outcome is the number of participants with abutment margin exposure greater than zero, with a timeframe up to 6 months post surgery. The posted results report 0 of 5 participants in the 0.5 mm arm and 0 of 9 in the 1.5 mm arm with exposure, and a Fisher exact test p-value of 1.00. No confidence interval or numerical effect estimate is reported. The record lists two secondary outcomes, but their results are not included in the registry record reported for this analysis. Safety results list zero serious adverse events, zero other adverse events, and zero deaths in both arms, with 11 participants at risk per arm.