3D Digital Impression Systems Compared with Traditional Techniques in Dentistry: A Recent Data Systematic Review.

The advent of new technologies in the field of medicine and dentistry is giving improvements that lead the clinicians to have materials and procedures able to improve patients’ quality of life. In dentistry, the last digital techniques offer a fully digital computerized workflow that does not include the standard multiple traditional phases. The purpose of this study is to evaluate all clinical trials and clinical randomized trials related to the digital or dental impression technique in prosthetic dentistry trying to give the readers global information about advantages and disadvantages of each procedure. Data collection was conducted in the main scientific search engines, including articles from the last 10 years, in order to obtain results that do not concern obsolete impression techniques. Elsevier, Pubmed and Embase have been screened as sources for performing the research. The results data demonstrated how the working time appears to be improved with digital workflow, but without a significant result (P = 0.72596). The papers have been selected following the Population Intervention Comparison Outcome (PICO) question, which is related to the progress on dental impression materials and technique. The comparison between dentists or practitioners with respect to classic impression procedures, and students open to new device and digital techniques seem to be the key factor on the final impression technique choice. Surely, digital techniques will end up supplanting the analogical ones altogether, improving the quality of oral rehabilitations, the economics of dental practice and also the perception by our patients.


Background
Nowadays, with the advent of new technologies, the field of biomedicine, medicine and biotechnologies has also been influenced, often with improvements that affect both clinicians and

Protocol and Registration
The following systematic review of the literature was registered with PROSPERO (Prospectively Registered Systematic Reviews), with protocol number 150499, dated 11/09/2019. This systematic review and meta-analysis have been conducted according to PRISMA (Transparent Reporting of Systematic Review and Meta-Analyses) protocol [9][10][11] and PICO (Population Intervention Comparison Outcome) study design [12][13][14][15][16]. Conducting a systematic review largely depends on the objective and quality of the included studies. For this reason, it may be necessary to modify the original protocol of the review during its conduct. The PRISMA Statement recognizes the dynamic nature of this process and guarantees a correct assessment of the quality of the systematic review, following a path suitable for analyzing the included studies.

Eligibility Criteria
Results were screened accordingly to defined eligibility criteria, inclusion and exclusion criteria were defined during the study design.
Inclusion Criteria

Information Sources
The results for this systematic review have been extrapolated by the most important academic and scientific information sources as Pubmed, Embase, Elsevier, in order to obtain the highest number of results possible.

Study Selection
The focus question of this systematic review of PICO (Population Intervention Comparison Outcome) study design [12] is: Are digital impression techniques more accurate and efficient in time for dental impression compared to conventional analogical techniques?

Data Collection Process
The authors have independently collected the data. Two independent reviewers (Luca Fiorillo and Salvatore Crimi) by two different universities collected and screened all the results. The reviewers collected data and created tables. A third expert author (Marco Cicciù) revised all the obtained data. Reviewers compared decisions and resolved differences by comparing the manuscripts. A complete independent dual revision was performed to review full-text articles.

Data Items
This systematic review of the literature, as already specified, was conducted in accordance with the PRISMA statement. The PICO simplification method was used to carry out the main question of this scientific article. The authors manually analyzed the data independently, and the one-way ANOVA statistical analysis was conducted on the available results. The analysis of variance (ANOVA) is a set of statistical techniques belonging to the inferential statistics where comparisons are made in the internal variability between two groups, and the variability between the groups. ANOVA is a technique developed by Fischer, used for the statistical interpretation of biological data and to test the differences between sample means. It is necessary to take into account the relative variances, in order to proceed with the analysis. The test is aimed at establishing whether two or more sample averages can be derived from populations that have the same parametric average. The analysis of variance is, therefore, used when the considered averages are greater than two.

Risk of Bias in Individual Studies
Authors have evaluated individual risk of bias as follow. Please see Table 1.

Summary Measures
According to selected studies, some measure could be compared. Main outcome of the selected results is showed in this table (Tables 2 and 3).

Synthesis of Results
The results of the individual Clinical Trials and Randomized Controlled Trials have been obtained by individual authors and manually analyzed. The purpose of obtaining as many raw data as possible is to perform a meta-analysis of the results. Not all articles among the results have comparable outcomes and parameters.

Risk of Bias Across Studies
This type of work brings together all the studies in the literature in the last ten years demonstrating the digital instrumental investigation technique. Full text and abstract accessible articles in English have been considered. The risk of bias across studies has been evaluated according to Higgins et al. [13][14][15][16].

Additional Analyses
One-way ANOVA test has been conducted for Time outcome. Time was one of the outcomes evaluated and could be compared by different studies. One-Way ANOVA test considerate mean time about digital or conventional techniques for each study, where available. A mean value has been considered in studies that showed different digital techniques with different results (Table 4).

Study Selection
The results were selected based on the Materials and Method section. The first step gave a high number of results, without filters. A total of 614 papers were found and then following the first filter application (last 10 years, in order to obtain data about not obsolete instrumentation or impression techniques) the results were 528. The authors evaluated only full text article for information availability (345) on human studies (429), in English language (334). Only Randomized Clinical Trial and Clinical Trial were considered (25), and after a screening and a full text reading, only 12 articles presented sufficient information for conducting this review (Figures 1 and 2).

Study Characteristics
Single study features have been evaluated and showed in Table 3.

Results of Individual Studies
Two papers recently published by Cave and Chandran have been evaluated as pertinent, but not included in the review cause not RCT [17,18].
Zitzmann et al. [19] evaluated the differences between digital and conventional techniques in VAS questionnaire results completed by dental students. The authors evaluated the TRIOS Pod system (3Shape, Copenhagen, Denmark) quotient too, and it indicated that dental student used time in digital techniques more efficiently. The majority of students perceived Intra Oral Scanner IOS as easier than the conventional technique. Most (72%) preferred the digital approach using IOS to take the implant impression to the conventional method (12%) or had no preference (12%). Zeltner et al. [20] investigated the differences in monolithic lithium disilicate crown fabrication on the same abutment with different workflows, digital or conventional. Some authors evaluated laboratory centralized milling techniques versus chairside milling techniques too. The differences between the treatment modalities (Lava, iTero, Cerec inLab, and Cerec) were not statistically significant (p > 0.05). Sailer et al. [21] 3M). Scan time has been evaluated with significant differences on 2 digital techniques on 3 vs. Conventional techniques. Participants preferred conventional techniques and they preferred digital method without powdering. The total time for the complete-arch impressions, including the preparation (powdering) and the occlusal registration, was shorter for the conventional impression than for the digital scans. Cappare et al. [22] evaluated differences on full arch scans with both conventional and digital techniques, differences that were not statistically significant (p > 0.05) in marginal bone loss were found between control and test groups. Significantly less time was spent to perform digital impression procedure (p < 0.05). Digital workflows needed less time once again. Sakornwimon et al. [23] evaluated marginal gap and patient's preferences between conventional impressions (Polyvinyl siloxane) and digital scans. Crowns were evaluated intraorally through a blinded examination and a stereomicroscope; this evaluation reported no significant discrepancies as opposed to VAS results where patients. Visual analog scale scores for digital impressions were statistically significantly higher than those for PVS impressions in every topic (p < 0.05). Joda et al. [24] in a randomized controlled trial evaluated time, difficulty, and operator's preference in using digital versus conventional impression techniques. Working time showed significant differences between the two groups. Difficulty and applicability of IOS was perceived more favorable compared to conventional impressions, and effectiveness of IOS was rated better by the majority of students (88%) and dentists (64%). While 76% of the students preferred IOS, 48% of the dentists were favoring conventional impressions, and 26% each IOS and either technique. Another crossover study of Joda et al. [25] evaluated outcome differences on digital intraoral scanning and polyether impressions. They assessed patients' perception and satisfaction with a VAS questionnaire. Clinical time was recorded by an operator too. All patients would prefer the digital workflow if they could choose between the two techniques in the future. Gjelvold et al. evaluated differences on time, clinical condition and dentist and patient's satisfaction (VAS) between digital and conventional impression techniques. The results of this study demonstrated that the digital technique was more efficient and convenient than the conventional impression technique (14:33 ± 5:27, and 20:42 ± 5:42, respectively (p < 0.0001)) [31]. Gherlone et al. [26] randomly selected patients who underwent full-arch immediate-load rehabilitation. They evaluated time and accuracy of digital and conventional rehabilitation. The digital impression procedure required significantly less time than the conventional procedure (p < 0.001). Benic et al. [27] evaluated time, patients' discomfort and operator difficulty between 4 different techniques, 3 digital and 1 conventional with polyvinyl siloxane. Their results showed that there were no statistical differences between both, digital or conventional techniques. The total working time for the conventional impression was significantly lower than that for Lava and Cerec. With regard to the working time without powdering, the differences between the methods were not statistically significant. Boeddinghaus et al. [28] evaluated three differences on 3 intraoral scanners (Sirona CEREC AC Omnicam (OCam), Heraeus Cara TRIOS and 3M Lava True Definition (TDef)) and a conventional impression model (EXA'lence, GC, Tokyo, Japan). The authors evaluated fitting and marginal gap. Yuzbasioglu et al. [32] evaluated differences in time spending and in patient's satisfaction with two different impression methods techniques. Conventional impressions were taken with a polyether impression material (Impregum, 3 M ESPE), and bite registrations were made with polysiloxane bite registration material (Futar D, Kettenbach). Digital impressions and bite scans were performed using an intra-oral scanner (CEREC Omnicam, Sirona). Time was shorter for digital impressions technique and patients stated that digital impressions were more comfortable than conventional techniques. [29,30].

Synthesis of Results
A synthesis of results has been provided in detailed form in Table 5.

Additional Analysis
According to results is possible to perform an analysis of variance about 2 different group, the considered outcome is time (Table 6 and Figure 3).
According to ANOVA test P = 0.72596.

Summary of Evidence
It was possible to conduct an analysis of the treated topic, once the individual reviewer results and the conclusions of the investigated articles were extrapolated. In this section, evaluating the synthesis of the individual articles conclusions, benefits or disservices of each methodic can be summarized as follows.
Recently, Cave and Keys [17] performed a systemic review about the working time of the two impressions technique. They concluded that the digital impression technique in reducing anxiety and nausea could be considered more comfortable for the patients than a conventional impression technique. However, the topic is still highly debated in the recent literature and Chandran et al. [18] explained how the digital impressions are superior to a conventional one, without any statistically significant differences, based on assessment of accuracy, patient preference and operator preference.
Iin a RCT, Zitzmann et al. [19] Analyzed both digital and conventional using difficulty on different impression techniques. No experienced dental student found a digital tool easier than conventional impression techniques. According to Zeltner et al. [20], no significant differences were found between conventional or digital workflow in prosthodontic. Authors showed how a conventional workflow can facilitate the better manufacture of occlusal regions. Moreover, centralized milling production provided better results than chairside milling. Sailer et al. [21] in their RCT showed how digital techniques could improve chair time and how participants prefer no powder-need digital techniques for digital scans. Cappare et al. [22] evaluated how digital workflows provide accuracy and predictability. It is a reliable alternative for full arch rehabilitations with a marginal fit precision. Sakornwimon et al. [23] found that conventional and digital techniques present no differences on crowns marginal gap but patients' satisfaction is higher with the "digital way". Joda et al. [24] demonstrated, on a dentist and dental students' group, how digital scanning is more efficient than conventional techniques for single implant or single quadrant impression. Also, they demonstrated a high level of acceptance by operators. Joda et Bragger [25] showed how, based on their findings, that patients preferred digital technique, particularly because of their efficiency in terms of time. Gjelvold et al. [31] concluded that the digital technique was more efficient and convenient than an analogical, conventional one. According to Gherlone et al. [26], it is possible to realize full-arch rehabilitation, with a satisfactory accuracy way, using digital instruments. Benic et al. [27] demonstrated how a conventional impression technique was more time-effective than digital, and no statistical differences were found with respect to patient discomfort. Boeddinghaus et al. [28] concluded that the digital intraoral impression could be considered a valid alternative to conventional one. Yilmax [29] in his research documented the "time" perception of the patients. The digital advent in the field of dental impression technique reduces the number of appointments and allows the formation of a soft tissue emergence profile, similar to that of the definitive crown.
A different point of view is underlined by Runkel et al. [30]. In a paper published in 2019 authors underlined that despite the rapid advancement of the computer-aided technology for dental therapy purposes, the implementation of this technique is not as fast as its technical development.
Yuzbasioglu et al. [32] demonstrated how digital methods for impressions in dentistry could be more time-efficient and preferred by patients. Some studies, therefore, consider the digital impression as optimal with regard to the economy of the time and therefore financial of the medical office. However, some studies, are inconsistent in this topic and, as can be seen, it is not a significant parameter.
Some studies in the literature report the problem of impression infection management, and the management of the latter over time, in the dental laboratory [32][33][34][35], the impression material stability during time [34], or material working phase and mixing issues [36][37][38]. This is an issue that does not exist in the case of optical impressions. As far as quality is concerned, the latter did not show statistically significant parameters. Digital equipment is starting to be used in the medical field, and above all in the dental field, it is now possible to have a completely digital workflow [4,8,[39][40][41].
Ortensi et al. recently demonstrated how the application of new materials and digital techniques must guarantee a predictability of the final goal from the beginning to the end of treatment. The possibility of showing the patients the planning treatment as well as the avoiding analogue impression technique is highly appreciated by the patients (Figures 4 and 5) [42][43][44][45].
A, digital diagnosis, and therapeutic programming, with a digital plane preview, should be the future for clinicians and prosthodontics practitioners [46,47]. The traditional impression technique is based on a copy of the oral situation, with acquisition materials and subsequent casting in plaster. This working method has spread in clinical practice; however, the impression materials tend to contract in size due to the chemical reaction of the material. Instead, the plaster, used later, will show a dimensional expansion. It should be noted that the impression procedure is at the origin of the manufacture of the product, and therefore, potential errors introduced in this phase will affect the rest of the work. In the case of implant prostheses, a failure to adapt the scaffolding will generate stress on the implants, which will affect the bone interface, causing failure in some cases. Prosthetic complications, such as loosening of the screw or its fracture, could also be related to inadequate insertion of the prosthesis. However, no technique has proved to be effective. Impressions on implants have shown good accuracy. With an impression system, the data through the intraoral scanner could be transmitted through files to the laboratory for the manufacture of a definitive prosthesis. It is also known that implants, in response to bone compression, show only a range of motion of 3-5 µm in the axial direction and 10-50 µm in the horizontal direction. An intraoral scanner could overcome some errors associated with taking the traditional impression and in production, such as the fact that it communicates with the laboratory directly through a virtual world avoiding errors in preserving the impression. In the literature, there are reports regarding the digital impression technique on dental implants, but most deal with fabrications of customized anatomical abutments and zirconia prostheses. All definitive prostheses, with the different cemented, screwed methods, require accuracy in the bar-implant connection. The scanner copies the implant fixture exactly in the mouth like traditional impressions. Once the image is captured and registered by an intraoral scanner, the CAD software through algorithms could precisely position the implant in the virtual model. In addition, the new technological developments of the optical impression provide the digital creation of a model through analogues, as the traditional laboratory technique requires. Registration errors, however minimal, occur during the acquisition procedures, arising from the length of the arch. When comparing intraoral scanners in whole arch acquisition procedures, the acquisition width should be considered to consider the errors that can be encountered. Once the scan has taken place and the data has been acquired, the software processes every single data to create a virtual 3D model, then the CAD builds the resin model from the collected data. The lack of homogeneity in the results between the cited studies indicates that it is not possible to determine a conclusion about whether the working time appears to improve with digital workflow. Indeed, a significant change is the introduction of digital technology into dental practice. "Digital Dentistry" is becoming more prevalent each year. Recently, digital impression techniques with three-dimensional (3D) intra-oral scanners have been attracting attention gaining in popularity around the world. These intra-oral scanners capture digital images of the dental arches and record occlusal relationships, which could directly be used for computer aided design (CAD) and manufacture (CAM) of a dental prosthesis. Intra-oral scanners have the potential to replace conventional impression materials for several reasons. However, accuracy and precision of the impression may be influenced by various clinical factors, such as the difference in the operator's skill or the patients' condition, which could only be evaluated by in vivo studies. To date, only a small number of in vivo studies, investigating the accuracy of this impression technique has been reported. Accuracy could only be evaluated in comparison, preferably with a gold standard; which is not easy to establish in the oral cavity. Regarding precision, there is only a limited number of in vivo studies in the literature [48][49][50][51].

Limitations
The main limitation of the study is the low number of works evaluated, despite the fact that almost all of them have agreed results. The studies included in this review, unfortunately, presented data not comparable to each other. Therefore, it was not possible to conduct a meta-analysis of the literature. The only comparable numerical data was that of time. Certainly, further studies will be necessary, and useful to obtain more precise information about these techniques, which over time, will replace the analog ones.

Conclusions
According to the obtained results in this systematic review, it is certainly possible to say that digital techniques represent a valid alternative in the field of dentistry. The optical impression system compared to the analogue one with the impression materials has a comparable result. Moreover, it is necessary to remember how dentists appeared more distrustful in difficulty, compared with dentistry students. Furthermore, patients have a better perception of the use of digital rather than conventional impressions. The total work time for the impression taking would appear to be lower with digital techniques, but despite this, the data is still not significant. The authors recommend the use of intraoral scanners, which from the formation of a virtual image creates an accurate physical model that gives efficiency to the dental structure and makes the work lighter. This improved way of working should benefit the dentist, the laboratory and the patient.