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Dental Medicine and Oral Health Sciences

A lack of evidence for the superiority of digital over conventional impressions in crown marginal fit

Clinical Question: In adults needing single-unit crown, how do digital impressions made with intraoral scanners compare to conventional impressions with respect to the crown marginal fit?

Clinical Bottom Line: Limited and low quality evidence from the included systematic review suggests that digital impressions may produce better marginal fit than conventional impressions, the results are clinically meaningful, not statistically significant, not clinically precise. The evidence from the RCT suggests that there is no clinically meaningful and statistically significant difference in marginal fit between two impression techniques, the results although not precise. The applicability of the results is compromised by mixed results, low quality evidence (lack of rigorous methodology, low statistical power and high risk of bias) and imprecision, more studies with rigorous methodology are needed.

The use of either conventional or digital impression for single unit crown are indicated in a clinical setting. Indeed, both methods produce crowns with clinically acceptable marginal fit.

Evidence search:

("Crowns"[MeSH Terms] or crowns[tw]) AND (analog[tw] OR conventional[tw] OR alginate[tw] OR pvs[tw] OR polyvinyl siloxane[tw]) AND ("photography, dental"[MeSH Terms] OR "computer-aided design"[MeSH Terms] OR intraoral scanner[tw] OR digital scanner[tw]) AND ("2009/10/20"[PDat] : "2019/10/17"[PDat] AND English[lang])

Search date: October 15th 2019 - additional search: TRIP, C.A.T. (U.Texas), Cochrane

Author, year Source of evidence Population Characteristics Methods

1. Sakornwimon et al., 2017
PMID: 28222872

Randomized Controlled Trial

Population: adults in need of single molar crown

  • mean age: 39 years old
  • gender: 13 women and 3 men

Sample size: n=16

Setting: Bangkok, university setting

Randomization and allocation concealment: unclear

Intervention/control: digital impression vs. standard PVS impression

  • 2 groups of participants of 8, impression techniques in different sequence
  • single clinician prepared all the teeth
  • marginal fit measured by blinded examiner using silicone replicas under stereomicroscope

Primary outcome: mean marginal fit

Secondary outcome: patient satisfaction

Analysis: paired t-test (mean difference in clinical marginal fit of zirconia crowns)

Key Results

Both methods produced clinically acceptable crowns with marginal discrepancies less than 120 m. The Mean Difference (MD) in crown marginal fit between conventional and digital techniques for buccal, mesial, lingual and distal surfaces were respectively: 4.85 (95% CI -20.37, 30.07); 3.67 (95% CI -20.24; 27.58); -11.68 (95% CI -39.95, 16.58) and 24.07 (95% CI -0.12, 48.26). MD (patient
satisfaction ‘overall preference’) = 1.5 (95% CI 0.30, 2.71).

Evidence Comments

The results have not shown clinically meaningful (threshold 0.25 mm) and statistically significant difference in crown marginal fit for all four dimensions between two impressions techniques. The results are not clinically precise. The patients’ satisfaction results are not clinically meaningful and precise (threshold 5).

Strengths: calibrated and blinded examiner, patient important outcome measure

Limitations: unclear methods of randomisation and allocation concealment, participants are not blinded, no baseline data table, small sample size, no regression analysis.


Author, year Source of evidence Population Characteristics Methods

2. Tsirogiannis et al., 2016.
PMID: 27061627

Systematic Review

In vitro: 8

Design: experimental

In vivo: 4

non-randomized clinical trials

In vivo studies

Population: adolescents and adults in need of a single crown

  • Age range: 16-65 years
  • Sample size: n=72
  • Crowns fabricated, n=149

Setting: Spain, Italy, Germany (university setting), Germany (private practice)

Search: PubMed, studies published in English
Intervention/control: fabrication of single tooth ceramic crowns with digital vs conventional impressions methods

Outcome: mean marginal fit

Analysis: metaregression ( mean difference, MD in crown marginal fit between conventional and digital

Key Results

Total 530 literature sources, four in-vivo non-randomized clinical trials. Publication years: 2010 – 2014. Both methods produced clinically acceptable crowns with marginal fit less then 120 μm. MD = 27.2 (95% CI -5.3; 59.7).

Evidence Comments

The marginal fit values of ceramic restorations fabricated after conventional impressions were 27 μm higher than the values when the digital impressions method was used.

The results are clinically meaningful, not statistically significant and not clinically and statistically precise.

Strengths: MeSH terms and key words, two independent reviewers, PRISMA diagram, risk of bias assessment, the same intraoral scanner was used, all restorations were made of zirconium oxide, metaregression.

Limitations: only one database, no grey literature search, language restriction, non-randomized clinical trials, two studies had no comparison group, no summary table, non-validated tool to assess the risk of bias, moderate-high heterogeneity, no publication bias assessment, small sample sizes (14 to 25 subjects/study).


The included studies’ population and our population of interest are the same – the adult patients needing single crowns. The study settings include university settings in different countries such as Thailand, Italy, Spain and Germany which may affect the generalisability of the results due to different treatment philosophies and techniques employed in different parts of the world (example: bevelled vs butt-joint margins). On the other hand, the fact that the studies’ treatment was provided in a university setting by experienced dental clinicians and a dental lab technician providing the crowns, improves generalisability to the Canadian population in the sense that competent, trained professionals provided the treatments. The interventions studied and the assessed outcome are relevant to our question since the study compared digital impression to conventional PVS impression in the production of a single unit-crown and its resultant marginal fit. In making any decision, clinicians should consider the cost difference between digital versus conventional impressions methods, with the former being significantly more costly. Further consideration should be given to secondary outcomes such as time saved and patient satisfaction, both of which are greater with digital impression methods. The applicability of the results is compromised by low quality evidence (lack of rigorous methodology, low statistical power and high risk of bias) and imprecision, more studies with rigorous methodology are needed.

Authors: Maria Gueorguieva, Nicolas Ouellet, Omar Elsabbagh and Henry Assad (DMD3 students)

Faculty mentors: Raphael Freitas de Souza, Sreenath Madathil, Svetlana Tikhonova

Acknowledgments: Martin Morris (librarian)

Date: March 14th, 2020

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