Zirconia Based Fixed Dental Prostheses: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Zirconia Based Fixed Dental Prostheses (NCT02220764), a non-randomized na study. The primary outcome is Number of Fixed Dental Prostheses (FDPs) With Failure.

2. Clinical Question

The clinical question is comparative, but the study design limits what can be concluded from a difference between groups. Participants were not randomly allocated, and the registry does not report how the groups were formed or whether their clinical characteristics were similar. Differences in the observed outcomes, if reported, could therefore reflect factors other than support type. Such factors might include patient or treatment characteristics, but the record does not identify which factors were measured or considered in the analysis.

The objective refers to complication rates, while the primary endpoint focuses specifically on prosthesis removal. These are related but not interchangeable concepts: the primary endpoint does not, by itself, count every complication that might occur without removal. A secondary outcome concerns prostheses with chips, but results for that measure are not reported in the registry record. The primary outcome results are also not reported, so the stated research question cannot be answered from the recorded outcome information.

3. Trial Design

This was a prospective clinical study of zirconia-based fixed dental prostheses. The record lists a parallel model, non-randomized allocation, and no masking. It records the study as completed, with enrollment of 32. The sponsor was Technische Universität Dresden. The recorded study start was 2008-05 and the primary completion date was 2013-11.

The parallel design indicates that the tooth-supported and implant-supported groups were considered as separate groups in the study. However, the record explicitly identifies the comparison as non-randomized and cautions that the arms are not a like-for-like control comparison. It does not report the process used to allocate participants or prostheses to the groups. Nor does it report whether investigators, participants, or outcome assessors were masked; the masking entry is none.

The study describes long-span prostheses, with the objective applying to prostheses with at least 4 units. The arm descriptions distinguish tooth-supported from implant-supported zirconia prostheses. Other treatment details, such as how the prostheses were made, fitted, or monitored, are not reported in the registry record. Further eligibility criteria and participant characteristics are not reported either.

The primary outcome timeframe is 3 years. Its definition is based on whether a prosthesis needed removal over the observation period. The record also lists a secondary outcome concerning fixed dental prostheses with chips. It lists three outcome measures and one analysis, but the specific analysis methods and the link between that analysis and each measure are not reported in the registry record.

The record gives an enrollment figure, but does not report a sample-size justification or explain how the planned enrollment was chosen. It also does not report the statistical analysis plan, any interim analyses, or details about the handling of participants who did not complete follow-up. These omissions prevent a fuller assessment of how the study was designed to estimate or compare outcomes.

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 Fixed Dental Prostheses (FDPs) With Failure, measured over 3 years.

The primary endpoint is the number of fixed dental prostheses with failure over 3 years. The registry defines failure as a need to remove the prosthesis during the observation period. This is a count-based outcome: it records how many prostheses meet the failure definition, rather than describing the time until each failure or the severity of a complication.

Removal can be a clinically consequential outcome and gives the endpoint a clear operational definition. A stated definition is important because it indicates which events qualify and helps readers distinguish the primary outcome from broader notions of complications. The endpoint is narrower than all possible problems with a prosthesis. For example, a complication that does not lead to removal would not meet the stated failure definition, although a chip is listed separately as a secondary outcome.

To compare groups meaningfully, a count needs to be interpreted in relation to the number of prostheses observed and the duration and completeness of follow-up. The record gives a 3-year timeframe but does not report primary outcome counts, group-specific denominators for this endpoint, or a comparison estimate. It is therefore not possible to assess the observed frequency of failure or the precision of any difference from the registry outcome information.

In general, a count endpoint may be analyzed using methods that account for the amount of exposure and the variability in the counts. Which method is appropriate depends on the data structure and analysis plan. The registry record does not report the primary endpoint analysis method or enough outcome information to assess its assumptions.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Count outcomes record how many events or units meet a definition. For this study, the primary measure is the number of prostheses classified as failures because they needed removal during the 3-year observation period. The fact that the outcome is a count does not identify the statistical method used. The registry record does not report that method, the model specification, or the assumptions used in the primary analysis.

What does a count analysis need to account for?

In general, count data can vary more than a simple model assumes. This is called over-dispersion: the observed variation is greater than the variation expected under a model such as a basic Poisson model. If over-dispersion is present and ignored, uncertainty estimates can be too small, which can make confidence intervals too narrow and tests too optimistic. This is a general statistical consideration, not a claim about these study data. The record does not report whether over-dispersion was assessed or how it was handled.

Exposure and follow-up also matter. A count accumulated over a longer observation period, or among more prostheses, has a different interpretation from the same count accumulated over less exposure. The registry states a 3-year timeframe, but does not report detailed follow-up time, endpoint-specific denominators, or whether every prosthesis was observed for the full period. It does not report whether the analysis used a rate, a count model, or another approach.

Why does non-randomized allocation affect the comparison?

In general, random allocation helps balance both measured and unmeasured characteristics between groups, on average. Without randomization, group membership can be associated with other characteristics that also relate to the outcome. A crude comparison may then combine the association with support type and the effects of group differences. The registry explicitly identifies the allocation as non-randomized and says the arms are not a like-for-like control comparison.

Statistical adjustment can sometimes address measured differences, but it cannot automatically remove bias from unmeasured factors or from factors measured inaccurately. The registry does not report baseline characteristics, a prespecified adjustment set, or an adjusted effect estimate. It is therefore not possible to determine whether an adjusted analysis was conducted or whether it adequately addressed differences between groups.

What does the analysis entry tell readers?

The registry lists one analysis, but does not report its method or provide a primary outcome estimate. An analysis count alone does not reveal whether the analysis was descriptive or inferential, whether it accounted for follow-up, or whether it adjusted for other variables. It also does not show whether the analysis included every enrolled participant or only those with complete outcome information.

In general, a confidence interval helps communicate the uncertainty around an estimated effect, while a hypothesis test evaluates data against a specified null model. Both depend on the chosen analysis and its assumptions. The primary outcome confidence interval and test result are not reported in the registry record. Thus, there is no reported inferential result to interpret for the central comparison.

How should planning calculations be read?

General sample-size planning estimates depend on assumptions about the target effect, variability, allocation, significance level, and desired power. The record describes planning illustrations based on a stated fraction of the observed effect, a two-sided significance level of 0.05, equal allocation, and a normal approximation. These are planning assumptions, not evidence that the study was designed with those assumptions or that it had a particular observed power.

Planning based on an observed effect is especially dependent on that effect estimate. If the estimate is imprecise, planning values derived from it can also be unstable. A planning illustration does not change the uncertainty in the original study and does not establish that a result is reliable. The record does not report the study's own sample-size justification, and the outcome information does not include a primary effect estimate from which to judge the substantive findings.

In general, a two-sided test considers departures in either direction from a null value. Equal allocation is an assumption for the planning illustration, not a description of the recorded group sizes. The record reports 24 and 8 at risk for adverse-event reporting, and does not state that the primary analysis used equal group sizes. The normal approximation is another planning assumption; the record does not report whether it was used in an actual outcome analysis.

Because the primary results and analysis details are absent, readers cannot check model fit, distributional assumptions, missing-data handling, or sensitivity to analytic choices. These are not merely technical details: for a non-randomized comparison, the method and the population analyzed are important to judging what a contrast can mean. The registry record does not provide enough information to assess those matters.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists three outcome measures and one analysis. It does not report a statistical analysis plan describing which outcomes were primary for testing, whether additional comparisons were planned, or how multiplicity was handled. The primary outcome is identified as the number of prostheses with failure, and a secondary outcome concerns prostheses with chips. Results for the chip outcome are not reported in the registry record.

In general, testing several outcomes or making several comparisons can increase the chance of finding an apparently notable result by chance. Prespecified priorities and multiplicity procedures can help clarify how results should be interpreted. Since the registry does not report such procedures, it is not possible to assess whether multiplicity was considered or to distinguish planned from exploratory analyses.

The record does not report missing-data counts, loss to follow-up, exclusions, or the number included in the primary endpoint analysis. It does not state how missing outcomes were handled, whether any imputation was used, or whether a sensitivity analysis was performed. These details matter because an analysis based only on participants with observed outcomes can be biased if missingness is related to the outcome or differs by group.

Analysis populations are also not described. The record does not say whether the primary analysis included all enrolled participants, all treated prostheses, or a subset with available follow-up. The adverse-event at-risk counts do not establish the primary endpoint denominators. Without endpoint-specific denominators and missing-data information, readers cannot evaluate completeness of follow-up or the population underlying any primary comparison.

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 5% reporting threshold.

The registry lists 0 serious adverse events among 24 at risk in the tooth-supported group and 0 among 8 at risk in the implant-supported group. For other adverse events, it likewise lists 0 affected in each group, with 24 and 8 at risk respectively. No serious adverse-event terms are listed.

These are event counts as recorded, not estimates of the probability that an event could occur. In general, observing no events in a group does not prove that the underlying risk is zero; estimates based on sparse event data are uncertain. The record does not provide confidence intervals or other uncertainty estimates for these safety entries.

The at-risk figures belong to the adverse-event information and should not be substituted for primary endpoint denominators. Serious adverse events, other adverse events, prosthesis failure, and prostheses with chips are distinct measures. The registry does not report whether adverse-event ascertainment was complete throughout follow-up or how these events were defined.

Death figures are not reported in the registry record. The recorded zero counts should therefore be read narrowly as the listed adverse-event counts, not as evidence about every possible safety outcome or about the primary failure endpoint.

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

The record establishes that investigators planned a prospective comparison of tooth-supported and implant-supported zirconia prostheses, with failure defined as removal during a 3-year period. It also establishes that the allocation was non-randomized and that the registry lists safety counts for the two groups. Those details describe the study question and some aspects of its recorded conduct.

The record does not report the primary endpoint results. There is no reported number of failures by group, no primary effect estimate, and no uncertainty interval or test result. Consequently, it does not show whether the groups differed in failures, how large any difference was, or how precise an estimate might be. The stated null hypothesis remains a hypothesis rather than a reported finding.

The safety counts are not a substitute for the primary outcome results. Zero serious and other adverse events in the recorded at-risk groups does not imply that there were zero prosthesis failures. Nor can those counts establish the absence of all complications, particularly because the endpoint definition counts only failures requiring removal and the secondary chip outcome has no reported result.

Even if outcome comparisons were available, the non-randomized design would limit causal interpretation. An observed difference could reflect differences between the groups as well as the type of prosthesis support. The registry does not report enough information about group formation, baseline characteristics, adjustment, or missing outcomes to determine how well such alternative explanations were addressed.

The most defensible reading is therefore descriptive: the registry records a completed prospective study with a comparative objective, a defined primary endpoint, and adverse-event counts. It does not provide the primary findings needed to answer the comparative question. No conclusion about whether either support type has more or fewer failures can be drawn from the registered outcome information.

13. Why This Trial Matters Statistically

This study is statistically instructive because a clear clinical comparison does not automatically produce a clear causal comparison. The objective contrasts tooth-supported with implant-supported prostheses, but the allocation was non-randomized. That distinction matters: group differences can be associated with factors other than the support type, and the registry itself warns against treating the arms as a like-for-like control comparison.

The endpoint also illustrates why operational definitions matter. Failure is defined as removal of the prosthesis, giving the primary outcome a specific threshold. That definition supports consistent interpretation, but it does not capture every possible complication. The separately listed chip outcome highlights that different clinical events may require distinct measures and analyses.

Another statistical lesson is the importance of complete result reporting. The record provides the study objective and timeframe but no group-specific primary counts or comparative estimate. Without those results, readers cannot assess the effect's direction, magnitude, or precision. A study can be completed and have a defined endpoint while its registry entry still lacks the information required to evaluate the stated primary question.

Finally, safety counts and primary efficacy outcomes answer different questions. The adverse-event entries show no recorded affected participants in the listed categories, while the primary failure outcome is not reported. Keeping these measures distinct prevents an apparently reassuring safety count from being misread as evidence about prosthesis survival or failure. The record is a useful example of why design, endpoint definition, outcome reporting, and interpretation must be considered together.

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 largest limitation for interpretation is the absence of primary outcome results. The registry does not report the number of failures in either group, a comparative estimate, or uncertainty around that estimate. It therefore cannot support a direct statistical assessment of the central research question.

The non-randomized design is an additional limitation. The registry cautions that the arms are not a like-for-like control comparison, and does not describe the allocation process or baseline characteristics. The record also does not report whether adjustment was undertaken, which variables were considered, or how potential confounding was addressed.

Details needed to assess outcome completeness are not reported. The registry does not give the primary endpoint denominators, follow-up completeness, missing-data counts, exclusions, or analysis populations. The adverse-event at-risk counts should not be taken as primary endpoint denominators. Without these details, readers cannot assess whether the outcome information represents all enrolled participants or a subset.

The analysis method, model assumptions, multiplicity approach, and sample-size justification are not reported in the registry record. Although the record lists an analysis and describes assumptions for planning illustrations, it does not provide enough information to assess the actual primary analysis or the rationale for enrollment.

The registry defines failure narrowly as removal and lists a separate chip outcome, but does not report results for either endpoint. Other clinical outcomes, further prosthesis details, and participant characteristics are not reported in the registry record. These limitations constrain both statistical interpretation and understanding of how the recorded findings would apply beyond the specific study groups.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Zirconia Based Fixed Dental Prostheses — NCT02220764.
• Registry record last updated 2015-03-24; status last verified 2015-03.
• Results first posted 2015-03-24.
• 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

The registry record describes a completed prospective clinical study titled Zirconia Based Fixed Dental Prostheses. Its objective was to compare complications between long-span tooth-supported and implant-supported zirconia fixed dental prostheses. Enrollment was 32; the study used a parallel model, non-randomized allocation, and no masking. The sponsor was Technische Universität Dresden.

The primary outcome was the number of prostheses with failure over 3 years, with failure defined as requiring removal. A secondary outcome concerned prostheses with chips. The registry does not report primary outcome results, a comparative estimate, or the analysis method. It lists adverse-event counts of 0 serious events and 0 other events in each group, with 24 at risk in the tooth-supported group and 8 at risk in the implant-supported group.

Because allocation was non-randomized, the groups are not a like-for-like control comparison. The registry record does not report the primary endpoint denominators, missing-data handling, analysis populations, or sample-size justification. The available information describes the design and outcomes planned, but does not answer the primary comparative question.