Digital vs Conventional Impressions: Fit Evidence

Introduction

Dental laboratories increasingly receive intraoral scan files in place of, or alongside, conventional elastomeric impressions and stone casts. Marginal adaptation is critical for oral health and the longevity of fixed prostheses, and although digital scanning is associated with greater speed and ease, whether these advantages translate into better marginal adaptation has been debated [PMID 40610310].

For laboratories in India that are deciding how to accept, verify and process digital cases, the practical questions are whether restorations made from scans fit as well as those made from conventional impressions, for which materials and spans this holds, and where the limits of the evidence lie. This article summarises the systematic review evidence on accuracy and marginal fit, and sets out what it means for laboratory workflow.

1. Marginal fit of single crowns and short-span prostheses

Overview of systematic reviews. Porto and colleagues analysed 18 systematic reviews, 11 of which included meta-analyses. Four of 10 articles in vivo and 4 of 7 articles in vitro reported better marginal adaptation with digital scanning. For single-unit crowns, 4 of 6 in vivo studies and 3 of 5 in vitro studies favoured digital scanning; for partial fixed prostheses, 2 of 3 studies in both settings supported digital superiority. No study reported that the conventional technique was better. However, most articles were rated "critically low" or "low" in quality by AMSTAR 2 [PMID 40610310].

Meta-analyses of clinical studies.

A 2018 review of ten clinical studies found mean differences of -9.0 µm (95% CI -18.9 to 0.9) for marginal gap and -15.6 µm (95% CI -42.6 to 11.4) for internal gap. The authors concluded that low-quality evidence suggested similar performance for both techniques [PMID 29389337].
A 2023 meta-analysis of ten in vivo studies of single-unit ceramic crowns reported a mean difference for marginal fit of 6.54 µm, with substantial heterogeneity (I² = 93%); the results suggested no significant difference between the impression systems, marginally favouring digital impression, and the authors concluded that the digital workflow provided a clinically acceptable marginal fit [PMID 37102534].
A 2026 meta-analysis of ten clinical studies of zirconia CAD-CAM restorations, including four randomised trials at low risk of bias, found significantly better marginal fit (mean difference -15.42 µm; 95% CI -29.75 to -1.08) and internal fit (mean difference -21.22 µm; 95% CI -36.61 to -5.83) with digital scanning, while noting that both approaches produced clinically acceptable results [PMID 42386430].

Combined in vitro and in vivo evidence. An earlier meta-analysis, based mainly on in vitro studies, found similar marginal misfit between techniques overall, but reported that marginal and internal discrepancies were greater for stone die casts, whereas digital dies produced restorations with the smallest discrepancies [PMID 26946916].

In our reading, the evidence consistently shows that restorations made from intraoral scans fit at least as well as those made from conventional impressions for single crowns and short-span prostheses, but the size of any advantage is small and the certainty of the evidence is limited.

2. Does the restoration material change the picture?

The material appears to modify the comparison. The 2025 overview found that, for zirconia, digital techniques outperformed conventional methods in 4 of 5 in vivo studies and in all in vitro studies, whereas no significant differences emerged for lithium disilicate and cobalt chromium restorations [PMID 40610310].

Zirconia single crowns. A meta-analysis of 17 studies found a pooled standardised mean marginal difference of -0.89 (95% CI -1.24 to -0.54; P<.001) in favour of digital scanning, and concluded that digital scanning of prepared teeth for single-unit zirconia restorations resulted in better marginal accuracy than conventional techniques using elastomeric impression materials [PMID 32284188].
Zirconia fixed partial dentures. A meta-analysis of nine studies (one clinical and eight in vitro; 118 restorations) found significantly better marginal fit (SMD -0.68) and intaglio fit (SMD -0.51) with digital scans. Digital scanning showed significantly better marginal accuracy for 3-unit than for 4-unit prostheses, and a cement spacer of 50 µm or less improved both marginal and intaglio fit in the digital group [PMID 34696907].

3. The whole workflow, not only the impression

For a laboratory, the impression is only the first step; the fabrication pathway also contributes to fit. Hasanzade and colleagues grouped studies into four workflows: conventional impression and fabrication, conventional impression with digital fabrication, digital scanning with conventional fabrication, and fully digital scanning and fabrication. In eight clinical trials and 21 in vitro studies, the fully digital group had significantly less internal discrepancy than the conventional-impression/digital-fabrication group in the clinical studies (P=.009), and significantly better marginal adaptation than that group in vitro (P=.001). The authors concluded that a completely digital workflow yielded restorations with comparable or better marginal adaptation than the other methods [PMID 32928518].

A randomised crossover trial in 10 participants compared three fully digital workflows for zirconia 3-unit frameworks with a conventional workflow comprising a polyether impression, manual waxing, lost-wax technique and a cast metal framework. In the shoulder region, the digitally fabricated zirconia frameworks presented similar or better fit, whereas in the occlusal regions the conventionally fabricated metal frameworks achieved a more favourable fit [PMID 30396708]. A meta-analysis of randomised trials likewise found no significant difference in marginal fit of tooth-supported prostheses in any region measured, except the occlusal region, where conventional impression showed more favourable fit [PMID 37369705]. In our reading, because the framework material differed between arms in that trial, the occlusal finding may reflect fabrication and material as much as the impression method.

4. Where conventional impressions still hold an advantage

The evidence does not favour digital scans in every situation.

Long-span and full-arch work. A rapid umbrella review of 11 systematic reviews found that most supported intraoral scanning as being as precise and accurate as the conventional approach, and that clinical data supported similar accuracy for fixed dental prostheses of less than 4 units. For more extensive definitive fixed solutions or removable prostheses, the conventional approach was recommended [PMID 36162879]. A review of 32 studies of influencing factors reported that, for whole-arch scanning, intraoral scanning is susceptible to more deviation, and that accuracy is enhanced by reducing the span of scanning and ensuring that scanned surfaces exhibit minimal irregularities [PMID 29989757].
High-precision impression materials in vivo. A systematic review of six clinical studies concluded that conventional impressions performed with high-precision impression materials showed greater accuracy than digital impressions, although the authors differed on whether this caused misfit of the final restoration [PMID 32069344].
Diagnostic full-arch records. For full-arch records of the natural dentition, a meta-analysis of in vivo studies found no significant difference between digital and conventional impressions in linear measurements; the 3D deviation between digital and alginate impressions was 0.09 mm, and the 3D precision of both techniques was less than 0.1 mm [PMID 35786783].

5. Implant cases, chairside time and patient acceptance

Laboratories handling implant restorations should note that the accuracy of intraoral scan impressions of implant-supported restorations varied greatly depending on the scanning strategy, and that trueness and precision in partial and complete arches remain unclear. In full arches, the scan procedure needed significantly less time than the conventional one (mean difference 8.59 min), with a prosthetic survival rate of 100% in the follow-up studies [PMID 38055096]. Digital scanning was also more time-efficient and preferred by patients for comfort, anxiety, nausea and time perception [PMID 33678434]. A meta-analysis of randomised trials reported survival rates of implant-supported prostheses made from digital impressions ranging from 97.3 to 100% [PMID 37369705].

Importantly, no clinical trial has compared the survival of full-coverage restorations made from digital and conventional impressions [PMID 29389337].

Practical implications for dental laboratories

The following checklist is our interpretation of the evidence above. It is not a protocol tested in the studies cited, and does not replace the judgement of the prescribing dentist or the laboratory technician.

Accept intraoral scans as an evidence-supported input for single crowns and short-span fixed prostheses [PMID 40610310][PMID 36162879].
Expect the clearest fit advantage for zirconia restorations, and similar results for lithium disilicate and cobalt chromium [PMID 40610310][PMID 32284188].
Where possible, keep the workflow digital from scan to fabrication rather than converting scans to physical models only to re-digitise them [PMID 32928518][PMID 26946916].
Review cement spacer settings for zirconia prostheses; a spacer of 50 µm or less improved fit in the digital group of one meta-analysis [PMID 34696907].
Check occlusal adaptation of CAD-CAM frameworks, where conventional workflows performed better in clinical studies [PMID 30396708][PMID 37369705].
For full-arch, long-span or removable work, confirm with the dentist whether a conventional impression or additional verification is preferable [PMID 36162879][PMID 29989757].
For implant cases, ask for details of the scanning strategy, which strongly influenced accuracy [PMID 38055096].
In our reading, request scans with clearly visible, unobstructed finish lines and return incomplete scans before production, since accuracy depends on the scanned surfaces exhibiting minimal irregularities [PMID 29989757].

How D4dent helps dental laboratories

D4dent's lab order workflow keeps the requested work, tooth number, shade, scan files and written instructions together on each case, so that a laboratory receiving a digital case has the files and the prescription in one place. Case communication is tied to the case itself, which, in our reading, makes it easier to query an unclear margin or request a rescan before production begins. Laboratories can follow each case from intake through production, quality check and dispatch, as described on the D4dent for labs page, and dentists can see how orders are sent and tracked on the lab orders page for dentists. Within the wider ecosystem, dentists also use clinical resources, the dentist community, AI diagnostics and teleconsultation, so that laboratory work sits within a connected clinical workflow. D4dent connects patients, doctors, clinics, laboratories, dealers and X-ray centres in one ecosystem.

Frequently asked questions

Are crowns made from intraoral scans as accurate as crowns made from conventional impressions?

Systematic reviews indicate that they are at least comparable. A 2025 overview of 18 systematic reviews concluded that digital scanning delivered equivalent or better marginal adaptation than conventional impression making, and no included study reported that the conventional technique was better. Most of the reviews, however, were rated critically low or low in methodological quality.

Is the advantage of digital scans clinically meaningful?

The measured differences are small. A meta-analysis of clinical trials reported a mean difference in marginal gap of -9.0 micrometres (95% CI -18.9 to 0.9) between digital and conventional impressions, and graded the evidence as low quality, suggesting similar performance. A 2026 meta-analysis of 10 clinical studies of zirconia restorations found a mean difference of -15.42 µm in favour of digital scanning, while noting that both approaches produced clinically acceptable results.

Does the restoration material matter?

It appears to. The 2025 overview found that digital techniques outperformed conventional methods for zirconia in 4 of 5 in vivo studies and in all in vitro studies, whereas no significant differences emerged for lithium disilicate and cobalt chromium restorations.

Are intraoral scans suitable for full-arch or long-span work?

Caution is warranted. A rapid umbrella review found that clinical data supported similar accuracy for fixed dental prostheses of less than 4 units, and recommended the conventional approach for more extensive definitive fixed solutions or removable prostheses. A review of influencing factors reported that intraoral scanning is susceptible to more deviation in whole-arch scanning.

Do digital impressions improve restoration survival?

This has not been established. A systematic review of clinical trials identified no studies comparing digital and conventional impressions with respect to the survival of full-coverage restorations, and concluded that research is lacking to draw robust conclusions on this outcome.

Limitations to keep in mind

Most systematic reviews in this field were rated critically low or low in methodological quality [PMID 40610310], and much of the evidence derives from in vitro studies [PMID 26946916]. Heterogeneity was substantial in several meta-analyses [PMID 37102534][PMID 29389337], and pooled differences of a few micrometres may not be clinically important. Scanner technology changes rapidly, so older reviews may not reflect current devices, and the reviews reported differences between individual systems [PMID 29989757]. No trial has compared restoration survival by impression method [PMID 29389337], and none of the reviews was specific to India. Figures are taken from published abstracts; readers should consult the full texts before citing specific values.

Conclusion

The best available evidence indicates that crowns and short-span fixed prostheses fabricated from intraoral scans achieve marginal fit equivalent to or better than those made from conventional impressions, with the clearest advantage for zirconia [PMID 40610310][PMID 42386430][PMID 32284188]. Differences are small and supported by low-certainty evidence [PMID 29389337], conventional workflows may still achieve better occlusal fit [PMID 30396708][PMID 37369705], and conventional impressions remain the recommended approach for extensive fixed and removable work [PMID 36162879]. In our reading, laboratories can accept digital cases with confidence for routine single-unit and short-span work, provided that scan quality is checked at intake and the case information travels with the files.

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References

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Digital vs Conventional Impressions: Accuracy and Marginal Fit Evidence for Dental Labs