Orthodontic Patient Experience of Intraoral Scans Versus Alginate Impressions: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Orthodontic Patient Experience of Intraoral Scans Versus Alginate Impressions (NCT05194956), a randomized na study. The primary outcome is Orthodontic Patient Comfort.

2. Clinical Question

The trial also set out to investigate operator experience and preference. Listed secondary outcomes include pain, relative speed, nausea and/or coughing, likely recommendation, operator ease and confidence, and operator experience of sickness or coughing. These outcomes broaden the subject beyond the primary comfort comparison, but the primary endpoint is the patient’s own report immediately after a procedure.

The crossover format means participants experienced both procedures, rather than being assigned to experience only one. One sequence began with alginate impressions and then used an intraoral scan; the other began with the scan and then used alginate impressions. The registry describes a minimum 4-6 weeks washout period between procedures. The clinical question is therefore about comparative experience under the trial’s sequence and timing, not a general judgment about every aspect of either method.

3. Trial Design

The registry identifies this as a randomized, single-masked, two-period crossover trial conducted in a UK secondary care setting. The sponsor is University Hospitals of Derby and Burton NHS Foundation Trust. The registry lists the study as completed, with enrollment of 86. Its summary describes a design involving 84 participants ready to begin orthodontic treatment. These are distinct registry figures: the record does not explain the difference between the planned count in the summary and the enrollment figure.

Participants were assigned to one of two orders. In one, alginate impressions came first and the intraoral scan followed after a washout period; in the other, the scan came first and alginate impressions followed. The registry specifies a minimum 4-6 weeks washout period. After each procedure, participants completed a modified visual analogue scale questionnaire about their experience. This setup makes it possible to compare the two procedures within participants while also requiring consideration of treatment order and period.

The primary endpoint was patient comfort immediately following the intervention. The posted arm summaries list 42 participants in each sequence, with mean scores of 9.2 for the alginate-first sequence and 7.7 for the scan-first sequence. These are sequence-arm summaries. They should not automatically be read as treatment-only means, because each sequence includes both procedures at different times.

The registry lists 11 outcome measures and 31 analyses, with 10 secondary outcomes posted. It identifies a two-period two-treatment crossover ANOVA and a mixed models analysis among the reported analyses. Detailed information about randomization procedures, the masking arrangements, the handling of period and sequence effects, and the exact analysis populations is not reported in the registry record. The study dates are listed as 2022-05-31 for the start and 2023-01-03 for primary completion.

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.

Period 1

Washout Period

Reasons for not completing this period:

Period 2

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

Population: The primary analysis was intended to be completed on all patients, after imputing any missing data. However, the primary analysis was carried out on complete records only, although there were 2 patients who withdrew after their first procedure. The missing data for these two patients was not imputed because the imputation of two values using multiple imputation would not add any value to the statistical analysis or results. In addition, the required sample of 84 patients had been achieved.

6. Primary Endpoint

The registry lists the primary outcome as Orthodontic Patient Comfort, measured over Immediately following intervention.

The primary endpoint is orthodontic patient comfort measured immediately following each intervention. The instrument is a 100mm modified visual analogue scale. It records a continuous score from 0 to 100, and the registry states that higher scores indicate a more negative experience. The endpoint therefore captures the participant’s subjective experience rather than an objective measure of procedure duration, image quality, or clinical outcome.

Patient-reported comfort is relevant to the stated trial objective, which concerns experience and preference. A scale can represent a range of reported experience rather than forcing a response into a small number of categories. In general, continuous scales can retain more gradation in participants’ responses, although interpretation depends on how the scale is presented, completed, and analysed. The record calls this a modified visual analogue scale but does not report details about its validation, how scores were elicited, or whether any particular difference was considered important to participants.

The immediate timing links the reported rating closely to the procedure just completed. It does not establish how participants might feel later, or whether the score predicts later preference or satisfaction. Because participants experienced both procedures in a crossover, the comparison also depends on the order in which the procedures were received and on the analysis accounting for the repeated observations. Those analytic details are not fully described in the registry record.

The primary outcome is a mean score with a 95% confidence interval. In general, a confidence interval describes uncertainty around an estimated quantity under the assumptions of the analysis. It does not indicate the range of individual participants’ scores, and it does not by itself establish whether a score difference is meaningful to patients.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary measure is continuous: it is a score on a scale, and the registry reports means with 95% confidence intervals. The design is a randomized crossover with two procedures delivered in two periods, in different orders. The analytic question is not simply whether the mean in one sequence is different from the mean in the other. Each sequence includes both procedures, so a treatment comparison needs to use the repeated observations and account for the design.

What does a crossover analysis do?

In a crossover trial, participants receive more than one intervention. Their responses can therefore be compared within the same person, which may reduce the influence of stable characteristics that differ across people. But the results may also depend on which intervention came first, what period an outcome was measured in, and whether the first experience affects the next one. In general, analysis should reflect the repeated measurements and the trial’s treatment order. The registry names a two-period two-treatment crossover ANOVA, but does not list its terms or explain how period, sequence, or possible carryover were handled.

The sequence-specific means are useful descriptive statistics, but they do not independently isolate a treatment effect. The alginate-first sequence and scan-first sequence each contain an experience with both methods. The reported net mean difference from a crossover ANOVA is therefore the registry’s more direct treatment comparison. Its estimate is 8.5, with a 95% confidence interval of 3.75 to 13.15. The record does not give enough coding information to say which treatment minus which treatment produces the positive sign.

How should the confidence intervals be read?

A 95% confidence interval expresses the uncertainty in an estimate under the assumptions of the statistical model. In repeated sampling under those assumptions, intervals constructed in this way would cover the target quantity at the stated frequency. For a reader, the interval communicates a range of estimates compatible with the data and model; it is not a range containing 95% of individual scores. The reported crossover ANOVA interval, 3.75 to 13.15, lies on the positive side of zero. The mixed models interval, -21.29 to -5.33, lies on the negative side. Their opposite signs make it important to know how each model defined its contrast before describing the treatment direction.

The individual sequence summaries also have confidence intervals: 2.46 to 15.97 for the alginate-first sequence and 0.87 to 14.51 for the scan-first sequence. These intervals describe uncertainty around sequence means, not the treatment contrast itself. Comparing overlap or non-overlap of separate intervals is not a substitute for the trial’s intended crossover analysis.

What do the p values add?

A p value evaluates how unusual data at least as discrepant as those observed would be under a particular null hypothesis and model. It is not the probability that the null hypothesis is true, nor does it quantify clinical importance. The crossover ANOVA reports p < 0.001, and the mixed models analysis reports p = 0.001. Each is associated in the registry with an estimated net mean difference and confidence interval. The registry also lists ANOVA p values of 0.198 and 0.749, without identifying the corresponding terms. Those values cannot be interpreted as tests of a particular treatment, period, or sequence effect from the available information.

Why might methods produce different estimates?

The registry reports both a crossover ANOVA and a mixed models analysis. In general, these methods can represent repeated observations and design structure in different ways, and results can depend on model specification, coding, assumptions, and included observations. The record gives no detailed model formula, no explanation of contrast coding, and no account of which observations entered each analysis. The crossover ANOVA estimate is 8.5; the mixed models estimate is -13.31. Their signs and magnitudes differ, and the registry record does not explain the difference. It would not be appropriate to select an explanation or reinterpret either estimate without those details.

In general, over-dispersion is an issue when observed variability exceeds what a model assumes; an unsuitable variance structure can affect standard errors and uncertainty. The record does not report an over-dispersion assessment, and the scale’s continuous outcome and named analyses do not establish that such an issue arose. This is a general consideration, not a reported finding of this trial.

How do planning calculations differ from trial results?

Sample-size calculations are planning exercises based on assumptions about the effect to detect, significance level, allocation, and statistical method. The registry’s stated planning assumptions refer to a two-sided significance level of 0.05, equal allocation, a normal approximation, and effects expressed as fractions of the observed effect. Such illustrations are not observed power and are not evidence that the trial was adequately powered for a particular clinical difference. The record does not report the trial’s own sample-size justification. No planning calculation can replace interpretation of the estimates, their confidence intervals, and the analysis limitations.

For this crossover comparison, clarity about the estimand—the exact contrast the analysis intends to estimate—is especially important. The endpoint gives a direction for interpreting raw scores: higher is more negative. But the registry does not say which procedure is subtracted from which in each model. Together with the opposed signed estimates, this prevents a definitive reading of which procedure had the higher or lower adjusted comfort score from these reported contrasts alone.

10. Analyses Reported by the Sponsor

The registry reports a two-period two-treatment crossover ANOVA estimate of 8.5, with a 95% confidence interval from 3.75 to 13.15 and p < 0.001. It also reports a mixed models estimate of -13.31, with a 95% confidence interval from -21.29 to -5.33 and p = 0.001. The two analyses do not give the same signed estimate, and the record does not provide contrast coding or sufficient model details to reconcile them.

No separate recalculated estimate is reported in the registry record, so there is no posted recalculation to compare numerically with the registry’s analyses. The two estimates should not be treated as interchangeable or combined. A difference in sign might reflect how contrasts were coded, a difference in model specification, or another issue, but the record does not establish the reason. It is not possible to choose among those explanations from the posted information.

The sequence means and their confidence intervals are descriptive, while the crossover ANOVA and mixed models estimates are model-based comparisons. Neither sequence mean alone identifies the treatment contrast. To interpret either model result in the scale’s stated direction, the contrast definition and fuller analysis specification would be needed. The registry does not report those details.

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 11 outcome measures, 31 analyses, and 10 posted secondary outcomes. This means the primary comfort result is part of a broader set of outcomes and analyses. When many hypotheses are examined, the chance of at least one apparently notable result can increase. In general, multiplicity procedures or a clear distinction between confirmatory and exploratory analyses can help readers understand how multiple testing was addressed. The registry record does not report a multiplicity adjustment, a hierarchy among outcomes, or which analyses were designated confirmatory beyond identifying the primary endpoint.

The record does not report how missing outcome data were handled, whether any participants withdrew, or the number of complete observations available for each analysis. The posted primary endpoint summaries list 42 participants in each sequence. That count does not explain whether all randomized participants contributed data to every analysis, whether incomplete responses were excluded, or how any missing scores were treated. Methods such as imputation, complete-case analysis, or a likelihood-based approach should not be presumed.

The analysis population is also not described in enough detail to determine whether results follow an intention-to-treat principle, a per-protocol definition, or another approach. The registry lists enrollment of 86, while its summary describes 84 participants and the sequence summaries list 42 in each sequence. The record does not reconcile these figures or give a participant flow account. Consequently, the relationship between enrollment, treatment exposure, and the analysis set is unclear.

The registry does not report a prespecified statistical analysis plan, interim analyses, rules for excluding observations, or how multiplicity across the reported models was managed. These omissions do not establish that the analyses were inappropriate; they limit the reader’s ability to assess whether the displayed analyses were planned, how robust they are to missingness, and how much weight to place on individual p values among the wider set of outcomes.

12. 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 registry reports zero serious adverse events among 84 people at risk in the alginate impression group and zero among 86 people at risk in the intraoral scan group. It reports zero deaths in both groups. These are event counts over the recorded safety groups, not estimates of the primary comfort outcome.

The record also lists zero other adverse events among 84 at risk for alginate impressions and zero among 86 at risk for intraoral scanning. No top serious adverse-event terms are listed. The values should be read as the registry’s reported counts for these groups. They do not establish that no discomfort or transient symptom occurred: nausea, coughing, and pain are listed as experience outcomes, distinct from the adverse-event totals.

Because the study is a crossover, participants may have experienced both procedures. The group-specific numbers at risk are not explained in detail, and the registry does not describe how safety exposure time or repeated exposure was handled. The record also does not report additional detail about event definitions, ascertainment, or confidence intervals for event rates. Therefore, zero recorded serious events is a descriptive finding in this study, not proof that serious events are impossible or that risks are identical between procedures.

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

The results concern reported comfort during orthodontic record-taking with intraoral scanning and alginate impressions in the trial’s setting and participants. The primary endpoint is a patient-reported score immediately after the intervention, with higher values defined as a more negative experience. The registry reports a crossover ANOVA net mean difference of 8.5 and a mixed models net mean difference of -13.31, both with confidence intervals that exclude zero. The opposing signs and differing magnitudes mean that the registry information does not support a consistent directional conclusion about which method received the more favorable adjusted comfort score.

The results do not establish that one method is better for all patients, operators, or clinical circumstances. They do not address whether either approach improves orthodontic outcomes, image or model quality, treatment decisions, cost, or environmental impact. Those topics appear in the contextual description, but they are not the primary endpoint result. The primary endpoint reflects immediate subjective comfort, not a comprehensive assessment of the procedures.

The estimates also do not show how large a difference participants would consider important. The registry does not report a minimally important difference for the modified visual analogue scale. Statistical evidence against a zero difference is not equivalent to evidence that a difference matters to patients. Conversely, a non-significant p value on another analysis would not prove equivalence. The two unnamed ANOVA p values, 0.198 and 0.749, cannot be interpreted as tests of a specific clinical question without knowing what they test.

Because this is a two-period crossover, the comparison is tied to the assigned order, the washout period, and the statistical handling of repeated measurements. The record does not detail these model specifications or reconcile the treatment contrast coding. The findings should therefore be understood as the results of analyses recorded by the registry, with uncertainty about their direction and model interpretation.

Finally, the record reports no serious adverse events in either safety group. That finding describes the observed event counts and does not establish absence of all adverse experiences or equal risk. Taken together, the posted results offer evidence about immediate patient-reported experience, but not a complete basis for choosing a procedure or judging its broader clinical value.

14. Why This Trial Matters Statistically

This trial raises a statistical issue common to crossover studies: the order-specific summaries are not the same as a direct treatment comparison. Each sequence received both methods, so interpretation depends on analysis that distinguishes treatment from period and sequence. The registry names crossover ANOVA and mixed models approaches, but does not provide enough detail to reconstruct their contrasts or determine how the sequence structure was represented.

The two reported model estimates make that distinction consequential. The crossover ANOVA gives a net mean difference of 8.5, while the mixed models analysis gives -13.31. Both are reported with confidence intervals and small p values, but the signs point in opposite directions. Statistical significance alone cannot resolve which method had the more favorable score, especially when the endpoint’s direction is specified but the contrast coding is not. Transparent reporting of the estimand, model specification, and contrast definition is essential to make the effect interpretable.

The study also illustrates why precision and importance are separate questions. Confidence intervals quantify statistical uncertainty under model assumptions, while a threshold for a meaningful patient-reported difference would help place the estimate in context. No such threshold is reported for this modified visual analogue scale. A p value cannot substitute for either an interpretable effect direction or a judgment about practical importance.

Finally, the registry lists many outcomes and analyses, while not reporting the multiplicity approach, handling of missing data, or analysis populations. These details matter when readers assess how robustly the primary result is distinguished from a broader set of comparisons. The trial’s crossover design can be efficient for comparing experiences, but its advantages depend on clear reporting of the repeated-measures analysis and the assumptions needed to interpret it.

15. 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 registry record does not explain why the study summary describes 84 participants while the enrollment figure is 86. The primary outcome summaries list 42 participants per sequence, but a participant flow account and analysis-population definitions are not reported. This leaves uncertainty about how enrollment, completion, and inclusion in the primary analysis relate to one another.

The primary endpoint uses a modified visual analogue scale, but the record does not report validation details, administration instructions, or a threshold for a meaningful difference. The scale direction is stated, yet the reported model contrasts are not defined. That is a specific interpretive limitation because the crossover ANOVA and mixed models estimates have opposite signs. The record does not explain whether the distinction is due to coding, model specification, or another reason.

The study is described as single-masked, but the registry does not identify who was masked or how masking was maintained. It does not report the randomization method, participant flow by period, or whether all participants completed both procedures. It also does not explain how period effects, sequence effects, or potential carryover were assessed. A minimum 4-6 weeks washout period is described, but the registry does not report evidence about whether that interval was sufficient to avoid carryover.

Several analysis details are not reported: the full statistical model, the analysis population, missing-data procedures, and whether multiplicity was addressed. The registry lists several outcomes and analyses, including two ANOVA p values without named terms. These gaps prevent a complete assessment of how the primary result was selected and how robust it is to analytic choices.

The population described in the summary is limited to people ready to start orthodontic treatment, with stated exclusions for cleft lip and/or palate and recent research involvement. The record does not provide enough detail to assess how closely the enrolled participants represent other orthodontic settings or populations. The findings should be interpreted within the trial’s reported context rather than assumed to apply broadly.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Orthodontic Patient Experience of Intraoral Scans Versus Alginate Impressions — NCT05194956.
• Registry record last updated 2025-03-18; status last verified 2024-12.
• Results first posted 2025-03-18.
• 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.

19. Record Summary

NCT05194956 is a completed randomized, single-masked, two-period crossover trial sponsored by University Hospitals of Derby and Burton NHS Foundation Trust. It compares intraoral scanning with alginate impressions for orthodontic records. The registry lists enrollment of 86 and describes two sequences, with a minimum 4-6 weeks washout period between procedures.

The primary outcome is patient comfort immediately following each procedure, measured on a 100mm modified visual analogue scale; higher scores indicate a more negative experience. Sequence-arm means are 9.2 and 7.7. The registry reports a crossover ANOVA net mean difference of 8.5, with a 95% confidence interval of 3.75 to 13.15 and p < 0.001, and a mixed models estimate of -13.31, with a 95% confidence interval of -21.29 to -5.33 and p = 0.001. The record does not explain the differing signed estimates.

There are no reported serious adverse events in either safety group. The registry lists 11 outcome measures, 31 analyses, and 10 posted secondary outcomes. Details about missing data, analysis populations, multiplicity, and the model contrasts are not reported in the registry record.