Conventional versus Digital Dental Impression Techniques: What Is the Future? An Umbrella Review

Abstract

A prosthetic rehabilitation, whether supported by implants, teeth, or mucous membranes, must be functionally and aesthetically adequate, so it is essential that the oral structures are reproduced as accurately as possible. The purpose of this overview is to evaluate the accuracy, time of digital impressions, and patient preference compared to those of conventional high-precision in vivo impressions. This umbrella review was developed following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) statement and was registered in the PROSPERO systematic review registry. The search method and study selection were based on the PEO (Population–Exposure–Outcome) model, a modified version of the PICO model. Systematic reviews regarding the dental impression technique made using an intraoral scanner versus the analog impression technique made with high-precision impression materials were searched electronically up to 1 February 2023 among articles published in English, through numerous registries and databases, such as PROSPERO e, Scopus, MEDLINE/ PubMed, BioMed Central, and Cochrane Library. The records screened totaled 2942, but only 23 systematic reviews were included in this umbrella review. The Assessing the Methodological Quality of Systematic Reviews (AMSTAR) 2 tool was used to evaluate the quality assessment of the systematic reviews included in this umbrella review. Accuracy, time, and patient preference for digital impressions were compared with those of high-precision conventional impressions. A total of 23 systematic reviews were included in this umbrella review. From the analysis of this umbrella review, the data on the accuracy between the two methods of taking the impression are conflicting, especially as regards full-arch rehabilitations. However, the digital impression seems to be preferred over the analog one as regards time and patient preference. However, there is limited high-quality evidence available for studying conventional and digital implant impressions. The results obtained are limited to the type of review performed, and the type of studies included was limited by the settings and study designs. Furthermore, another important limitation highlighted was that the digital scanners analyzed in the various studies are not the same, and the number of missing teeth or implants inserted is not the same. More in vivo clinical studies and RCTs are needed to increase the level of evidence for impression procedures.

1. Introduction

In industrialized countries, there has been an improvement in the quality of life, and this has led to a lengthening of the average life, leading to an increase in partial or complete edentulism, which requires complex prosthetic rehabilitation.

A prosthetic rehabilitation, whether supported by implants, teeth, or mucous membranes, must be functionally and aesthetically adequate, so it is essential that the oral structures are reproduced as accurately as possible.

Therefore, one of the most important phases for successful restoration is the impression-taking process [1].

In fact, it is of fundamental importance that the anatomy of the teeth or the position of the dental implants and the morphology of the tissues and mucous are detected in the most accurate and precise way possible to have 3D models or reconstructions as close to reality [2,3].

To date, impression-taking can be performed in both conventional and digital methods.

The conventional impression-taking technique has several disadvantages, including patients’ poor tolerance for the texture, taste, and smell of the material. Some authors have described that conventional impressions are one of the most unpleasant experiences during the appointments necessary for the creation of fixed [4,5], removable [4], and implant prostheses [6].

Added to this are the physical properties of the material, which can create a disadvantage in workflow management [7].

In recent years, to try to overcome these limits and due to the advancement of technology, research has identified alternative methods to circumvent the disadvantages of the impression-taking phase and improve the feedback of patients undergoing implant–prosthetic rehabilitation.

A valid alternative to conventional impressions is intraoral scans that use a beam of light (structured light or laser) projected onto the surface of the teeth. The intraoral scanner can capture dental arches, implants, and tissues using high-resolution cameras and allows a pre-visualization of the tooth, tissue, or implants in three dimensions [8], reduced working times, less complex workflow, and better patient-reported results [9,10,11,12,13,14,15,16].

The impressions taken have a reduced risk of distortion, a problem often encountered in conventional impressions caused by the physical properties of the materials used, and the results, therefore, are very accurate [17].

Furthermore, intraoral scanners can optimize workflows thanks to the ability to easily rescan a missing area; however, any errors with traditional impressions force the operator to repeat the whole procedure [15].

Today, it is possible, thanks to computer-aided design (CAD) and computer-aided manufacturing (CAM), to have a completely digitized workflow, even in the creation of prosthetic products.

The major use of the digital workflow is associated with treatment with fixed prostheses [18] and with implant–prosthetic treatments [19].

Furthermore, it has been seen that the intraoral scan of a small area, such as that of a single quadrant, may be sufficient to provide adequate information for the fabrication of various prosthetic products, including single crowns or fixed prostheses of few elements [20,21].

Studies have described that not only are quadrant scans effective over time, but they are also less prone to accuracy deviation than full arch scans [22].

In fact, it has been shown that the larger the scanned area, the lower the accuracy [23].

However, oral scans also have limitations, such as problems with excessive salivation by the patient, reflective restorations, floating mucosa, and different scanning protocols [22,23,24,25].

Patient comfort is an important factor that can influence the choice of impression technique. Patient-reported outcome measures (PROMs) are of paramount importance in dental practice as the assessment of patient perceptions of a specific treatment must be considered.

PROMs have been the focus of several studies evaluating subjective patient satisfaction with comfort and speed for conventional and digital impression techniques [9,10,11,12,13,14,15,26].

Individual patient comfort and satisfaction are generally described in terms of the absence of pain or discomfort, such as procedure time, retching, and the result of the final prosthesis in terms of fit and esthetics [27,28].

The evaluation of the labor time required for the procedure for taking digital impressions compared to conventional ones has been studied, but due to limitations in the number of clinical studies available, it has not been possible to reach definitive conclusions.

In a recent review, the working time for the procedure for taking digital impressions was analyzed by comparing the times between impressions by quadrants and that of the entire arch and evaluating the comfort of the patients in the two procedures [28].

The data in the literature are numerous and controversial, also due to the numerous limitations in the reviews considered. Different study settings and study designs, different scanners used to take the impression, and the number of teeth or implants considered are all variables that can affect results.

The purpose of this overview is to evaluate whether there are differences in the accuracy, that indicates how close a measurement is to the accepted value of taking a digital versus conventional impression; differences regarding the time parameter between the digital impression and the conventional one, and patient satisfaction in taking the digital impression compared to the conventional one based on the in vivo studies present in the literature.

2. Materials and Methods

2.1. Study Protocol

This umbrella review was performed following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) statement [22] and was registered in the PROSPERO (International Prospective Register of Systematic Reviews) systematic review register (ID: CRD42023397778) as recommended by Booth et al. [25].

The search method and study selection were based on the PEO (Population–Exposure–Outcome) [29] model, a modified version of the PICO model [30].

The research question was focused on

• P—Population: subjects with dental implants or natural stumps on which precision impressions must be taken digitally or traditionally.
• E—Exposure: dental impressions made using an intra-oral scanner were compared to analog impressions made with high-precision impression materials in prosthetic dentistry.
• O—Outcomes: accuracy, time of digital impressions, and patient preference in comparison to those of high-precision conventional impressions in vivo.

2.2. Search Strategy

All kinds of systematic reviews, with and without meta-analysis, concerning dental impressions technique, using an intra-oral scanner in comparison to analog impressions technique with high-precision impression materials in prosthetic dentistry were electronically searched till 1 February 2023 among articles published in English through numerous registries and databases, such as PROSPERO e, Scopus, MEDLINE/ PubMed, BioMed Central, and Cochrane Library by two independent reviewers (G.S.) and (F.D.A), combining the reported keywords with Boolean operators:

(‘digital impression’ OR ‘intraoral digital impression’ OR ‘intraoral scanner’ OR ‘intraoral digital scanner’ OR ‘conventional impression’ OR ‘accuracy’)

AND

(‘prosthetic dentistry’ OR ‘prosthetic’ OR ‘dentistry’ OR ‘dental prosthesis’ OR ‘implant prosthesis’)

To search the main scientific databases, we applied the filters “Review” on the Scopus library and “Systematic Review” and “Meta-analysis” on the MEDLINE/PubMed database.

No filters were applied on the BioMed Central database, on the Cochrane library, and on the PROSPERO register.

Data collection was conducted in the main scientific search engines, including articles from the last 10 years, to obtain results that do not concern obsolete impression techniques.

2.3. Study Selection and Eligibility Criteria

Results were screened according to the inclusion and exclusion criteria that were established before the study research.

Inclusion Criteria

• Reviews with or without metanalysis that compare digital and conventional impressions in prosthetic dentistry that include in vivo studies.
• Systematic review with or without metanalysis
• Reviews published in the last 10 years ago
• Reviews published in the English language.

Exclusion Criteria

• Reviews with or without metanalysis that compare digital impressions and conventional impressions in prosthetic dentistry that include only in vitro studies.
• Clinical studies
• Reviews published more than 10 years ago.
• Reviews not published in the English language.

Zotero reference manager tool was used to eliminate duplicates and the titles that were obtained were analyzed by two Authors (M.D.P.) and (F.D.A.), and then, the same two reviewers independently read the relevant abstracts of reviews.

From the abstracts, which were judged most relevant, the complete texts were obtained, which were independently screened by the authors themselves. A third reviewer (G.S.) was called in case of doubts or disagreements.

Two authors also performed a manual search and screened the bibliographies of the included reviews for any titles relevant to this umbrella review.

No restrictions were applied for the number and the kind of studies included in the systematic review.

2.4. Data Extraction and Collection

Data were extracted by two authors (G.S.) and (F.D.A.), autonomously and independently, and a third author (F.G.) was involved in case of disagreement. Each systematic review (with or without meta-analysis) included in the present umbrella review recorded the following criteria:

○

First, author of the journal, year of publication, kind of journal, funding, and quality of the study.

○

Number and design of studies included in each systematic review, population, and sample size.

○

Accuracy, preference patience, and accuracy among conventional and digital impressions.

○

Main outcomes

○

conclusions

2.5. Data Synthesis

A narrative synthesis of the data about population, exposure, and outcomes was conducted and was synthesized through a descriptive statistical analysis using the Microsoft Excel software 2019 (Microsoft Corporation, Redmond, WA, USA):

2.6. Quality Assessment

The Assessing the Methodological Quality of Systematic Reviews (AMSTAR) 2 tool, accessed online (https://amstar.ca, accessed on 19 August 2022) on 19 August 2022, was used to evaluate the quality assessment of the systematic reviews included in this umbrella review [31].

The quality assessment was divided into high, with zero or one non-critical weakness; moderate, with more than one non-critical weakness; low, with one critical flaw with or without non-critical weaknesses; and critically low, with more than one critical flaw with or without non-critical weaknesses.

3. Results

3.1. Study Selection

A total of 4271 records were found from the electronic search, specifically 73 from BioMed Central, 693 from MEDLINE/PubMed, 242 from the Cochrane Library, 651 from Prospero, and 2612 from Scopus databases.

In total, 1325 duplicates were eliminated, and 2942 title abstracts were screened.

Of these 2942 title abstracts, 2904 tile abstracts were excluded, and only 37 abstracts were relevant for this systematic review, so the full texts were screened, and 14 articles were excluded, particularly because (n = 4) they were a systematic review in vitro studies; (n = 2) analyzed the production process; (n = 4) did not analyze impression techniques; (n = 2) analyzed the accuracy of the material, (n = 1) compared different types of scanners, and (n = 1) was a narrative review.

The study-selection flowchart is illustrated in Figure 1.

The excluded studies are included in

Table 1. Studies excluded and reasons.

Authors, Year	Reason for Exclusion	Title 1	Title 2
Ahmed, 2021 [32]	Analyzes the manufacturing process of removable partial dentures	entry 1	data
L. C. Aragón, 2016 [33]	In Vitro Studies’ review	entry 2	data
Albanchez-González, 2022 [34]	In Vitro Studies’ review
Chochlidakis, 2016 [35]	In Vitro Studies’ review
Kustrzycka, 2020 [36]	Compare different types of scanners
Mühlemann, 2018 [37]	Analyzes the manufacturing process of implant-supported reconstructions
Mangano, 2017 [38]	Is a Narrative Review
Tabesh, 2022 [39]	Analyzes the accuracy of the material
Morsy, 2021 [40]	Analyzes the accuracy of the material
ValentI, 2022 [41]	Does not analyze impression techniques
Parize, 2021 [42]	In Vitro Studies’ review
Yang, 2022 [43]	Does not analyze impression techniques
Yen Mai, 2022 [44]	Does not analyze impression techniques
Cicciu, 2020 [45]	Analyzes the accuracy of the material

The table shows the Authors, year, and motivation for the exclusion.

.

Due to the heterogeneity of the data contained in the included systematic reviews, it was not possible to make a meta-analysis.

3.2. Study Characteristics and Qualitative Synthesis

At the end of the research, a total of 23 systematic reviews were included in the present umbrella review. The characteristics and outcomes from included studies are synthesized in

Table 2. The main features of included reviews: author, year of publication, reference, journal of publication, and kind of review with meta-analysis (if present). Number and design of included studies, population, sample size; kind of workflow; main outcomes and conclusions.

Authors, Year Reference Journal Meta-Analysis Funding	Studies (Number and Design) Population Sample Size	Kind of Workflow	Type of Intraoral Scanner	Outcomes	Conclusions
Sivaramakrishnan, 2020 [46] Aust Dent J Network Meta-analysis	RCT or PS 14 studies included 471 patients (236 digital impressions compared to 235 conventional impressions) to evaluate patient preference; 589 patients (278 digital impressions and 311 conventional impressions) to evaluate the time	digital vs. conventional impression	TRIOS, iTERO, CEREC Omincam	Patients preferences Time
Flugge, 2018 [47] Clin Oral Implants Res. A systematic review and Meta-analysis	RCT and no RCT, RS, case series, and experimental study 79 studies were included 77 experimental studies, 1 RS, and 1 RCT. 11 studies about digital impressions and 59 studies about conventional impressions. 9 studies compared the two kinds of impressions	digital vs. conventional impression	CEREC, CBCT, iTERO, LAVA, iMetric 3D, Everest	Fit of implant-supported prosthesis	Few data are available about the accuracy of digital and conventional implant impressions to give clinical advice
de Oliveira, 2020 [48] Clin Oral Implants Res. A systematic review and Meta-analysis	RCT, observational studies 10 studies were included Seven RCT and 3 observational studies patients: 214 Single implant crowns: 278	digital vs. conventional impression for single implant crowns	iTero—Align Tech in, CEREC-Omnicam, Carestream dental-CS3600, 3 Shape TRIOS	impression time patient preference, time efficiency	The digital workflow has demonstrated better results than conventional workflow for patient preference, time efficiency, and impression time
Alikhasi, 2017 [49] Implant Dent. A systematic review	In vitro studies Pilot clinical studies 10 studies were included 8 in vitro studies and 2 clinical studies Sample size in vivo: 49 Sample size in vitro: 91	Digital vs. conventional impression	TRIOS, iTERO, CEREC Omincam	Accuracy	No statistical differences among the techniques
Giachetti, 2020 [50] Int J Prosthodont. A systematic review	Clinical studies 6 studies were included Sample size: 74	Digital vs. conventional impression with Fixed crowns	TRIOS, LAVA, iTERO, CEREC	Trueness precision	Conventional impressions with high-precision impression materials seem more accurate than digital impressions
Hasanzade, 2019 [51] J Evid Based Dent Pract. A systematic review and Meta-analysis	33 studies were included 8 prospective studies; 26 in vitro studies (1 study contained both in vivo and in vitro data) Sample size in vivo: 372 Sample size in vitro: 832	Internal and Marginal Fit for Full-fixed Prosthesis	TRIOS, LAVA; CEREC, iTERO	marginal gap internal gap	Marginal adaptation does not show differences between the digital and conventional groups for in vivo studies, but differences were found for in vitro studies, where the digital impression showed better marginal adaptation
Nagarkar, 2018 [52] The Journal of the American Dental Association. A systematic review and meta-analysis	Crossover RTs, no RTs Parallel-group RT 10 studies were included: 7 crossover RT There were 2 no RCTs and only 1 parallel-group randomized trial Sample size: 291	Digital versus conventional impressions for full-coverage restorations	LAVA, BlueCam, TRIOS, TRUE def., iTERO	Survival of full coverage restorations Marginal gap, internal gap, and occlusal and interproximal contacts.	No differences were found between the two kinds to take impressions
Tsirogiannis, 2016 [7] J Prosthet Dent. A systematic review and Meta-analysis	12 studies were included: 4 prospective clinical trials 8 in vitro studies	The marginal fit of single ceramic restorations made with impressions taken by the digital method and conventional method was evaluated.	N.S.	marginal fit of the ceramic single-tooth restorations	From the results obtained, no statistically significant difference was observed between the marginal gap of restorations made by digital and conventional impressions
Gallardo, 2018 [53] J Prosthet Dent. A systematic review and Meta-analysis	RCT and observational studies 5 studies were included: 3 RCT and 2 prospective clinical trials	Digital vs. conventional impression	iTERO, TRIOS	Patient preferences in working time	Current evidence suggests that patients prefer the digital workflow Emerging data suggest that patients prefer digital workflow to conventional analog workflow
Tabesh, 2021 [54] J Prosthet Dent. A systematic review and Meta-analysis	In vitro and in vivo studies 17 studies were included (8 clinical) Sample size: 1068	The marginal fit of single-unit zirconia restorations made with impressions taken by the digital and conventional methods was evaluated.	LAVA, CEREC, iTERO, TRIOS	Survival of restorations, operator perception, marginal accuracy, and the internal fit. internal fit rather than on marginal accuracy	The results show that single-unit zirconia restorations made by using digital scanning of teeth have better marginal accuracy than those made by conventional techniques
Hasanzade, 2021 [55] J Prosthet Dent. A systematic review and Meta-analysis	There are 36 studies included in this systematic review of which 8 are prospective clinical studies and 29 in vitro studies (1 of these contained both in vivo and in vitro data) Sample size in vivo: 372	Compare the marginal and internal gap of complete single crowns	LAVA, CEREC, iTERO, TRIOS	marginal gap internal gap	The data obtained showed that restorations produced with the digital workflow have a comparable if not better marginal fit than those obtained with other methods
Bandiaky, 2022 [56] J Prosthet Dent. A systematic review and Meta-analysis	RCT and PS Of the 16 studies included in the review, 14 are RCTs or parallel-group studies and 2 are comparative prospective studies Sample size in vivo: 599	The purpose of the study was to compare tooth-supported fixed prosthetic restorations made by digital methods and those made by conventional impressions	LAVA, CEREC Ominicam, iTERO, TRIOS	Clinical time; Patient comfort; Marginal fit	The results showed that digital techniques are comparable to conventional ones in terms of clinical time and marginal fit. There is also evidence of greater patient comfort during the impression-taking stages with digital methods compared with conventional impression techniques
García-Gil, 2020 [57] J Clin Exp Dent. A systematic review	Seventy-six studies were included in this review. Of these, 19 were in vitro studies and 8 were in vivo studies. Sample size clinical studies: 85	The purpose of the work was to evaluate the accuracy and practical utility of intraoral scanners in implant treatments.	LAVA, CEREC, iTERO, TRIOS	Accuracy of impression and efficiency	The data obtained showed that digital impressions in implantology are a viable alternative in cases of one or two contiguous implants. As for full arch rehabilitations, there is a need for new studies
Papaspyridakos, 2014 [58] Int J Oral Maxillofac Implants. A systematic review	In vitro and clinical studies 76 studies were included	Accuracy of Implant Impressions for Partially and Completely Edentulous Patients	N.S.	Accuracy splinted vs. nonsplinted, Open-tray vs. closed-tray impression techniques	From the data obtained, it was found that the splinted impression technique is more accurate in both partially and fully edentulous cases. it was also found that the closed spoon technique is more accurate in fully edentulous patients, with no particular differences with the open spoon technique in partially edentulous patients. Overlapping accuracy was observed among the different impression materials. The angle of implant emergence affects the accuracy of impressions while there are insufficient data to analyze the effect of implant connection type
Ahlholm, 2018 [59] J Prosthodont. A systematic review	In vitro and in vivo studies 11 studies were included 8 in vitro 3 in vivo size sample: 140	Digital vs. conventional impression	LAVA, CEREC, iTERO	marginal gap internal gap trueness precision time	The data obtained showed that digital impression methods are a viable alternative to conventional impression techniques in the fabrication of short crowns. A higher speed with a shorter lead time was observed for digital impressions. Even in implant–prosthetic rehabilitations, making crowns and FDPs with digital impressions allow for a clinically acceptable fit. However, based on the data obtained, the conventional impression technique is recommended in cases of whole arch rehabilitations
Papaspyridakos, 2020 [60] J Prosthodont. A systematic review and meta-analysis	Eighteen studies were included in this review including 9 in vitro studies and 1 clinical study for impression analysis in fully edentulous patients and 6 in vitro studies and 2 clinical studies in partially edentulous patients.	Digital vs. Conventional Implant Impressions	3M True Def., CEREC, iTERO, TRIOS	The accuracy and influence of implant angle on 3D accuracy were evaluated.	Data obtained mainly from in vitro studies have shown that the accuracy of 3D digital impressions is comparable to that of conventional implant impressions. However, further in vivo studies are needed to evaluate the accuracy in clinical practice
Siqueira, 2021 [61] Clin Oral Investig. A systematic review	RCTs and PS 17 studies were included RCTs: 9 PS: 8 Sample size: 437	Intraoral scanning and conventional procedure in fixed prosthodontics and implant dentistry	LAVA, CEREC, iTERO, TRIOS, 3M True def., Carestream-CS3600	working time patient comfort	IOS is faster than CI. By assessing the degree of preference and overall patient comfort, it can be said that IOS can improve the patient experience
Joda, 2017 [62] BMC Oral Health A systematic review	RCTs 3 studies were included sample size: 48 patients	The purpose of the study was to compare digitized methods with analog or analog-digital methods for the production of tooth- or implant-supported fixed prosthetic restorations.	iTero, Carestream	Economics esthetics patient-centered outcomes survival and success rate to assess any complications with follow-up at least 1 year under function.	It has emerged that research appears to be slower than technology in the area of digital applications, so there is a need for well-designed RCT studies
de Paris Matos, 2021 [63] J Prosthet Dent. A systematic review and Meta-analysis	Of the 11 included studies, 10 had a crossover design of which 2 had a split-mouth design. In total, 1 study had a parallel design.	Comparison between conventional impression and intraoral digital scan for prosthetic rehabilitation	N.S.	The patient’s degree of discomfort, presence/absence of nausea, and unpleasant taste were assessed.	From the data obtained, it was found that intraoral digital scanning is a suitable alternative to conventional impression-taking procedures in that it decreases the discomfort of patients both in terms of the absence/presence of nausea and taste and breathing difficulties
Schmidt, 2022 [64] Clin Oral Impl Res A systematic review	RCTs 8 studies were included Simple size: 225	The accuracy of impressions taken by digital technique in implant cases in clinical studies was evaluated.	iTero, TRIOS, True Def. 3M	Measurement of accuracy	From the literature review, the number of clinical studies to evaluate the accuracy of impressions taken by the digital method is insufficient. However, the accuracy of IOS for digital impressions in patients rehabilitated with implants appears to be clinically acceptable
Manicone, 2021 [65] J Prosthet Dent. A systematic review and meta-analysis	RCTs and OS 12 studies were included 2 were randomized crossover trials 7 studies were observational studies sample size: 447 patients	The purpose of this work was to evaluate and compare the impression-taking step performed by digital scanning and conventional technique for the fabrication of implant-supported prosthetic restorations	CS3600, CEREC, iTERO, TRIOS	Patient preferences; procedure working time	The results showed that digital scanning is more efficient than conventional technical impression-taking in terms of time
Kong, 2022 [66] Clin Oral Investig. A systematic review and Meta-analysis	In vivo studies 13 studies were included	The purpose of the work was to compare the linear and three-dimensional accuracy of digital versus conventional impressions	LAVA, CEREC, iTERO, TRIOS, True Def. 3M	Linear dimensions of tooth width, complete and anterior Bolton ratio, intercanine distance (ICD), and intermolar distance (IMD) were evaluated.	The results showed that the accuracy and precision of impressions taken by the digital technique are superimposable to those taken by the traditional alginate technique for the full arch
BishtI 2021, [67] Clin Oral Implants Res. A systematic review and Meta-analysis	Clinical studies 7 studies were included	The purpose of this work was to compare implant-supported prosthetic restorations made by digital methods and those made by conventional techniques.	CS3600, CEREC, iTERO, TRIOS	The patient’s degree of anxiety, pain, shortness of breath, discomfort, and taste were assessed.	The data obtained showed that patients showed a preference for digital impressions while there were no differences between coated and monolithic restorations

Abbreviations: randomized clinical trial, “RCT”; prospective studies “PS”; retrospective studies “RS”; randomized trial “RT”; observational studies “OS”; intercanine distance “ICD”; intermolar distance “IMD”, not specificized “N.S.”.

, and the total number of involved study participants is included in the reviews, and the total clinical studies included in the reviews are shown in

Table 3. The total number of involved study participants included in the reviews and total clinical studies included in the reviews.

Author	The Total Number of Involved Study Participants	Clinical Studies Included
Sivaramakrishnan [46]	1060	14 RCT
Flugge [47]	NS	1 RCT
de Oliveira [48]	214	7 RCT
Alikhasi, [49]	49	2 CS
Giachetti [50]	74	6 CS
Hasanzade [51]	372	8 PS
Nagarkar [52]	291	8 CS
Tsirogiannis [7]	145	4 CS
Gallardo [53]	155	3 RCT 2 PS
Tabesh [54]	1068	8 CS
Hasanzade [55]	372	8 CS
Bandiaky [56]	599	14 RCT
García-Gil [57]	85	8 CS
Papaspyridakos [58]	32	4 CS
Ahlholm [59]	140	3 CS
Papaspyridakos [60]	19	3 CS
Siqueira [61]	437	17 RCT
Joda [62]	48	3 CS
de Paris Matos [63]	NS	11 CS
Schmidt [64]	225	8 CS
Manicone [65]	447	12 CS
Kong [66]	496	13 CS
BishtI [67]	367	7 CS
	TOT = 6.695	TOT = 174

Abbreviations: randomized clinical trial, “RCT”; clinical studies, “CS”, prospective studies “PS”.

.

3.3. Digital vs. Conventional Outcome: Time

Time is an important outcome for the operator but also for patients. The evaluation of the labor time required for the procedure for taking digital impressions compared to conventional ones has been studied, but it has not been possible to reach definitive conclusions, as showed in

Table 4. Characteristics and time outcomes from included studies. Source: first author, year; main results, statistical analysis and p value

Authors	Main Results	Statistical Analysis	p Value
Sivaramakrishnan, 2020 [46]	The time is greater for digital impressions	Time: 2.72 [0.08, 5.32]	Time: p < 0.005
Cunha de Oliveira, 2020 [48]	The results showed better efficiency in terms of time for digital impression-taking.	MD: 8.22 [95%CI: 5.48, 10.96]	p < 0.01
Gallardo, 2018 [53]	The results showed a faster procedure for the conventional technique in 2 studies while a faster procedure for the digital technique in 3 studies.	NS	NS
Bandiaky, 2022 [56]	The data obtained showed that digital scanning techniques are superimposable to conventional ones in terms of operative time.	digital scans: 784 ± 252 s; conventional impressions: 1125 ± 159 s	p > 0.5
Siqueira, 2021 [61]	In the following review, it appears that the technique with IOS is faster than the conventional technique in both single quadrant and full arch scan cases.	NS	NS
Manicone, 2021 [65]	Digital scanning was found to be more time-efficient	SMD: −1.96 [−3.09, −0.83]	p < 0.001
Ahlholm, 2018 [59]	The time taken to taking the impression is less if it is made by digital technique.	Digital impression: 248.48 ± 23.48 s. Conventional impression: 605.38 ± 23.66 s.	NS
Bishti, 2021 [67]	Patients showed a high preference for optical impressions	MD: −10.91 [−21.90, 0.08]	p = 0.05

Abbreviations: MD, standard deviation of the mean; SMD, standard mean difference; NS, not specificized; VAS, visual analog scale.

.

3.4. Digital vs. Conventional Outcome: Patience Preference

Patient satisfaction or comfort is an important factor for the clinician in choosing an impression technique. Patient satisfaction is described through the absence of pain or discomfort, the time taken for the clinical procedure, and the result of the final prosthetic product in terms of fit and aesthetics. The main results and the statistical analysis are shown in

Table 5. Characteristics and patience preference outcomes from included studies. Source: first author, year; main results; statistical analysis and p value.

Author	Main results	Statistical Analysis	p Value
Sivaramakrishnan, 2020 [46]	The data showed a general preference for impressions taken by digital technique.	Overall: 31.23 [5.95, 163.87]	p < 0.001
De Oliveira, 2020 [48]	The data obtained showed better clinical efficiency in terms of operative time and patient preference for the digital workflow than the conventional one.	NS	NS
Gallardo, 2018 [53]	A preference for digital workflow over conventional workflow has emerged on the part of patients.	NS	NS
Bandiaky, 2022 [56]	Patients report greater comfort in impression-taking procedures using digital techniques than those taken using conventional analog techniques.	The mean VAS score: - conventional impressions: 39.6 ± 9.3 - digital scans: 67.8 ± 21.7	p < 0.05
Siqueira, 2021 [61]	Based on the results obtained in terms of general patient preference and comfort, and in terms of the reliability of prosthetic outcomes, the intraoral scanner can be a means to improve procedures.	NS	NS
Joda, 2017 [62]	It was found that the too low number of quality RCT studies does not allow us to establish a patient preference for one or the other technique.	NS	NS
De Paris Matos, 2021 [63]	The data obtained showed that the discomfort reported by patients during the impression-taking phase is lower in cases using intraoral scanning.	SMD: 15.02 [8.33–21.73]	p < 0.001
Manicone, 2021 [65]	Patients consider the impression-taking stage made by intraoral scanning more comfortable.	SMD: 1.86 [0.26, 3.45]	p = 0.02
Bishti, 2021 [67]	Patients showed a high preference for optical impressions.	MD: 22.83 [12.29, 33.36]	p = 0.002

Abbreviations: MD, standard deviation of the mean; SMD, standard mean difference; NS, not specificized.

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3.5. Digital vs. Conventional Outcome: Accuracy

Another important parameter considered in this overview is accuracy, which represents the ability of a measurement to approach the actual value to be reproduced. The main results and the statistical analysis are shown in

Table 6. Characteristics and patience accuracy outcomes from included studies. Source: first author, year; main results; statistical analysis and p value.

Author	Discussion	Statistical Analisys	p Value
Flugge, 2018 [47]	Due to the limited amount of available data on the accuracy of digital impressions and conventional impressions in vivo, it is not possible to derive adequate clinical recommendations.	NS	NS
Marzieh Alikhasi, 2017 [49]	Due to the heterogeneity of the included studies, it is not possible to conclude whether the use of an intraoral scanner is better clinically than conventional techniques. More in vivo and in vitro studies need to be conducted to evaluate the accuracy of scanners.	NS	NS
Giachetti, 2020 [50]	The data obtained from the following review showed that impressions taken by conventional technique with high-precision materials were more accurate than those taken by digital technique.	The selected studies reported different values of accuracy: - precision: from 21.7 ± 7.4 µm to 176.7 ± 120.4 µm - trueness: 80.01 ± 7.78 µm to 118.9 µm	NS
Hasanzade, 2019 [51]	The data obtained in vitro showed that fingerprints result in better marginal adaptation while in vivo no significant differences were found.	In vitro - SMD: −0.76 [−1.23, −0.29] In vivo: - SMD: −0.59 [−0.93, −0.24]	p = 0.002
Nagarkar, 2018 [52]	The data obtained are insufficient to determine the difference in accuracy between fingerprinting and conventional techniques.	Marginal gap - SMD: −9.0 µm [−18.9, 0.9] Internal gap - SMD: −15.6 µm [−42.6, 11.4]	p = 0.003
Tsirogiannis, 2016 [7]	The data obtained showed no significant difference in the marginal gap of single-unit ceramic restorations made after digital or conventional impressions.	NS	NS
Tabesh, 2021 [54]	The data obtained showed that in teeth prepared for zirconia single-unit crown dentures, digital intraoral scanning exhibited greater marginal accuracy than those prepared with impressions taken using conventional techniques.	−0.89 mm (95% CI: −1.24, −0.54)	p < 0.001
Hasanzade, 2021 [55]	Digital methods are more efficient at producing restorations with comparable if not better marginal fit than other methods.	0.25 (−0.09, 0.59)	p = 0.006
Bandiaky, 2022 [56]	The data obtained showed that the marginal fit of restorations made with impressions taken with digital techniques is superimposable to those made with conventional impressions.	Marginal fit - digital scanning techniques: 80.9 ± 31.9 mm - conventional impressions: 92.1 ± 35.4 mm	p > 0.005
García-Gil, 2020 [57]	Further studies are needed to evaluate the accuracy of digital techniques.	NS	NS
Papaspyridakos, 2014 [58]	From the data obtained, it was found that the splinted impression technique is more accurate in both partially and fully edentulous cases. it was also found that the closed spoon technique is more accurate in fully edentulous patients, with no particular differences with the open spoon technique in partially edentulous patients. Overlapping accuracy was observed among the different impression materials. The angle of implant emergence affects the accuracy of impressions while there are insufficient data to analyze the effect of implant connection type.	NS	NS
Ahlholm, 2018 [59]	It has been shown that for the fabrication of implant-supported crowns and FDPs, digital impression systems provide a clinically acceptable fit.	Accuracy marginal fit - Conventional impression: 173.0 and 133.5 µm - digital impression: 111.4 and 80.2 µm	NS
Papaspyridakos, 2020 [60]	Data obtained mainly from in vitro studies have shown that the accuracy of 3D digital impressions is comparable to that of conventional implant impressions.	In vitro: 8.20 μm (95% CI: −53.56, 37.15) In vivo: 52.31 μm (95% CI: 6.30, 98.33)	In vitro: p = 0.72 In vivo: p= 0.03
Schmidt, 2022 [64]	From the literature review, the number of clinical studies to evaluate the accuracy of impressions taken by the digital method is insufficient. However, the accuracy of IOS for digital impressions in patients rehabilitated with implants appears to be clinically acceptable.	Linear distance: - CARES Mono: 162 ± 77 μm - AnyOne: 98.9 ± 96.33 μm - N-series, Neo-series: upper jaw conventional 45 ± 35 μm, digital 40 ± 29 μm; lower jaw conventional 46 ± 27 μm, digital 79 ± 50 μm	NS
Kong, 2022 [66]	The results showed that the accuracy and precision of impressions taken by the digital technique are superimposable to those taken by the traditional alginate technique for the full arch.	ICD: −0.11 [−0.47,0.26] IMD: 0.04 [−0.49, 0.58]	p = 0.88

Abbreviations: MD, standard deviation of the mean; SMD, standard mean difference; NS, not specificized; ICD, intercanine distance; IMD, intermolar distance.

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3.6. Quality Assessment

Most of the studies were judged of low quality or moderate quality through the Assessing the Methodological Quality of Systematic Reviews (AMSTAR) 2 tool, as illustrated in

Table 7. Level of evidence of systematic reviews with meta-analysis included according to the AMSTAR 2 tool.

Level	Description	Sivaramakrishnan [46]	Flugge [47]	de Oliveira [48]	Alikhasi, [49]	Giachetti [50]	Hasanzade [51]	Nagarkar [52]	Tsirogiannis [7]	Gallardo [53]	Tabesh [54]	Hasanzade [55]	Bandiaky [56]	García-Gil [57]	Papaspyridakos [58]	Ahlholm [59]	Papaspyridakos [60]	Siqueira [61]	Joda [62]	de Paris Matos [63]	Schmidt [64]	Kong [66]	BishtI [67]
High	No or one non-critical weakness: the systematic review provides an accurate and comprehensive summary of the results of the available studies that address the question of interest			✓					✓			✓
Moderate	More than one non-critical weakness: the systematic review has more than one weakness but no critical flaws. It may provide an accurate summary of the results of the available studies that were included in the review					✓	✓			✓	✓						✓	✓	✓	✓		✓	✓
Low	One critical flaw with or without non-critical weaknesses: the review has a critical flaw and may not provide an accurate and comprehensive summary of the available studies that address the question of interest	✓	✓		✓			✓					✓	✓	✓	✓					✓
Critically low	More than one critical flaw with or without non-critical weaknesses: the review has more than one critical flaw and should not be relied on to provide an accurate and comprehensive summary of the available studies

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4. Discussion

The aim of this overview is to analyze and summarize the data in the literature that compares digital impression techniques and conventional ones. We took into consideration three parameters: working time, patient preference, and accuracy in impressions taken with conventional and digital techniques.

The high number of publications on this topic confirms the growing interest in using digital technology in dentistry [11]. The increase in published papers, however, has not been matched by a significant increase in important data, as much of the information comes from in vitro studies. More scientific evidence supports in vivo studies, which may shed light on the limitations affecting the performance of digital scanners in clinical settings. Thus, clinical trials can help manufacturing industries overcome these flaws, thereby promoting the advancement of digital dental technologies. In vivo trials could also help practicing dentists by describing the proper technique for improving the quality of digital workflow performance in a clinical setting.

4.1. Accuracy

The lack of unanimity on clinically tolerable values for dental impression accuracy is an important barrier to the current review. In contrast, the scientific literature has repeatedly stated that the marginal gap and internal gap of a fixed prosthesis should be up to 120 m and 50 to 100 m, respectively, after cementation [68]. As a result, it cannot be said that impressions with a level of imprecision greater than these values are unsuitable for clinical purposes. Furthermore, both conventional and digital production procedures are susceptible to errors, which can result in restoration misalignment. As a result, the imprecision values for conventional and digital impressions should be regarded as more severe than those for indirect restorations.

An important difference to keep in mind is that between precision and accuracy; in fact, to evaluate in vivo precision, the common protocol foresees taking the impressions of the same subject several times with each impression method and superimposing these impressions on each other to verify the respective differences. Instead, to evaluate in vivo accuracy, the protocol provides for the superimposition of the dental models obtained from the same subject but with a different impression method.

In this umbrella review, 15 studies evaluated the accuracy of digital and conventional impressions. Everyone agrees that there is a need for a greater number of in vivo clinical studies, in particular RCT studies, to have a greater number of useful data for operative purposes. Giachetti [50] states that conventional impressions, made using high-precision impression materials, have shown a greater accuracy than digital impressions. However, Tabesh [54] and Hasanzade [55] reported higher marginal fit accuracy values of restorations produced with digital workflow than those produced with conventional impressions. Hasanzade [51], Tsirogiannis [7], Bandiaky [56], Papaspyridakos [58,60], and Kong [66] concluded that there is no difference in accuracy between conventional and digital impressions. Regarding the factors influencing fingerprint accuracy, Papaspyridakos [58] and Flügge [47] agreed that the most inaccuracy was found in the posterior (molar) and anterior regions due to the particular angles and undercut surfaces of the molars and the steep areas of the incisors [69,70,71]. This information can be used to make suggestions for the design of the tooth preparation, allowing the intraoral scanner to read the teeth more accurately. These findings indicate that a smooth, undercut-free preparation is preferable [72,73,74,75]. This possibility requires more evidence. As previously stated, these publications compare digital models to traditional models. While impression materials can be considered highly accurate, some degree of imprecision is always present [76,77].

Additionally, all stages of the conventional workflow can introduce errors, from creating, handling, storing, and applying impression materials such as traditional plaster casts. The sum of the inaccuracies, which occur in each phase of the workflow, can lead to an incorrect match between the restoration and the tooth or implant [76,77,78].

This phenomenon can lead to biological complications such as secondary caries, endodontic and periodontal disease, or peri-implantitis, as well as mechanical complications such as decementation or restoration failure [79,80,81,82,83].

A marginal discrepancy causes periodontal and peri-implant pathologies, which, in any case, lead to the failure of prosthetic treatments [84,85,86,87,88,89].

Another limitation of the present study is that the majority of specimens used to evaluate the accuracy of intraoral scanners consisted of intact teeth. Therefore consequently, the scan of the prepared teeth remains unknown. This issue should be carefully evaluated with further investigations because the performance of digital scanners is strictly related to the shape of the scanned objects [19,28,90,91].

4.2. Impression Time

In terms of time efficiency, some variation between studies was described; however, it appears that IOS impressions take less time than conventional impressions. IOS has also been linked to shorter average repetition time but higher average repetition count. This is because it seemed that doctors could more easily rescan a missing area, unlike analog impressions, where any error or lack would require repeating the entire procedure.

The type of IOS system used [92,93], the operator experience and comfort level, and the start and end points chosen to measure the procedure work time are all parameters that can influence the efficiency results in weather.

In fact, some Authors have described how [11,92] work times could be lengthened if older IOS systems were used. In addition, the specific type of traditional impression technique used versus digital impressions should also be evaluated.

A major advantage of digital impressions is the ability to rescan missing areas and preview areas, allowing for real-time feedback, unlike an error in a conventional impression, which is often only detectable after the impression material has hardened or a plaster cast has been poured. While rescanning to “fix” a poor aspect of the scan can be beneficial, it is important to note that avoiding the need for this extra step with an optimal scan strategy can reduce the overall work time of the procedure.

In the present work, there are seven works that have compared the times during the impression phase with the conventional and digital techniques. De Oliveira et al. [48], Siqueira et al. [30], Manicone et al. [64], and Ahlholm et al. [59] agree that the time taken during the impression-taking phase is less when performed with the digital technique than with the conventional one. Gallardo et al. [53] and Bandiaky et al., 2022 [56] report overlapping data, in terms of operating times, between conventional and digital impression-taking. Only Sivaramakrishnan et al. [46] stated that time is greater for digital impressions than conventional impressions.

4.3. Patient Preferences

In terms of patient preference, almost all the reviews analyzed agree that patients prefer to take the impression of using digital technology over the traditional technique [94]. De Oliveira et al. [48] observed how digital workflow improved clinical efficiency in terms of impression time, patient preference, and time efficiency. Gallardo et al. [53] agreed that current evidence suggests that patients prefer digital workflow over traditional techniques. Bandiaky et al. [56], Siqueira et al. [61], de Paris Matos et al. [63], Manicone et al. [65], and Bishti et al. [67] demonstrate how intraoral scanning causes less discomfort for patients than traditional impression techniques and how intraoral scanner can improve the patient experience as measured by general preference and comfort.

Joda et al. [62] instead state that due to the small number of RCTs, it is not possible to establish a patient preference between digital and conventional impressions.

4.4. Clinical Considerations

Considering the data emerging from this umbrella review, important clinical considerations need to be made, as well as considering other reviews.

Three parameters were taken into consideration: working time, patient preference, and accuracy in the impressions taken with conventional and digital techniques.

But a further distinction must be made on the type of prosthetic restoration that was to be performed after taking the impression. In fact, some considerations must be made on revisions that consider one or more pillars of natural teeth, one or more dental implants.

4.4.1. Clinical Considerations for Dental Impressions

Regarding the taking of impressions on natural teeth with the traditional method and with the digital one, most of the authors agree that patients prefer the digital method to the conventional one as they are considered more comfortable [53].

As far as accuracy is concerned, there do not seem to be major differences, even if there are numerous differences between the studies, from the type of scanner used to the type of fixed rehabilitation used [34,45,59].

However, some authors, such as Tabesh, have described how digital impressions on teeth prepared for single-unit zirconium restorations have resulted in better marginal accuracy than conventional techniques using elastomeric impression materials [39].

4.4.2. Clinical Considerations for Implant Impressions

Zhang et al., in a recent systematic review, described that full-arch implant digital impressions taken using intraoral scanners are not accurate enough for clinical application. In particular, the main parameters influencing the accuracy are the inter-implant distance, the type of scan body, the type of intraoral scanner, and the operator’s experience, while other parameters such as angulation, connection, and depth of the implant do not affect the accuracy of full-arch implant fingerprints [94].

Papaspyridakos [58] and Schmidt have instead described that there is little information for implants’ digital impressions; however, regarding the taking of conventional impressions on complex rehabilitations on implants, Papaspyridakos [58] has described that the open tray impression technique is more accurate than the tray impression technique closed; conventional impression-taking on splinted implants results in greater accuracy than non-splinted implants; the accuracy of the conventional impression is not influenced by the type of material used (polyether or polyvinylsiloxanes) and the angulation of the implants if greater than 20 degrees, negatively influences the accuracy of the impression.

Flugge described in a recent review how, regardless of the various impression techniques, conventional angled implant impressions are significantly less accurate than those of parallel implants. In contrast, there are no statistically significant differences in impression accuracy between the angled implant digital impressions versus the parallel implants [47].

Manicon et al. found that implant digital impression was more time efficient than conventional impression-taking for implant-supported restorations [65].

4.5. Limitations of the Study and Distorted Quality of the Research

The reviews included in this overview have very different goals, and not all reviews and ratings are created equal. The results concerning the digital method in prostheses on implants, but also fixed prostheses on natural teeth and removable prostheses are treated.

However, problems arise with fingerprint studies versus conventional ones, even between reviews analyzing the same items.

For example, reviews that look at different implant impression methods include studies where the number of missing teeth or implants is not the same (from single case to full case).

The result is that the information is not clear, and the conclusions are ambiguous.

This variability in the objectives of the various reviews included can serve as the basis for this overview.

Most of the studies were rated as low or moderate quality, and one as critically low quality, by the methodological quality assessment tool of systematic reviews (AMSTAR) 2 [30].

The biased quality of the included reviews and the lack of adequacy of the RCTs included in the analyzed reviews pose two other limitations of this systematic review.

It should also be noted that the reviews included have different settings and have a moderate to high risk of bias.

5. Conclusions

Although there is no high-quality evidence available for the study of conventional and digital implant impressions, there are numerous reviews on the subject.

From the analysis of this umbrella, some important conclusions can be drawn from the parameters analyzed.

Both digital impression methods appear to be comparable. However, conflicting results have been obtained regarding the accuracy of data between the two methods of impression-taking, particularly for full arch implant rehabilitations.

Furthermore, the lack of unanimity on the clinically tolerable values for the accuracy of dental impressions is another major obstacle that emerged from the present review. Therefore, it was not possible to give clear conclusions on this parameter, although some clinical considerations can be extrapolated.

In terms of patient preference, nearly all reviews included in this overview agree that patients prefer to appear to be using digital technology over traditional techniques.

In terms of time efficiency, some variation between studies has been described; however, iOS impressions appear to take less time than conventional impressions.

However, the results obtained are influenced by numerous factors, such as the type of revision performed, the type of study design, the type of intraoral scanner used, and the impression material used in the traditional method of taking the impression.