Influence of Material Selection on the Marginal Accuracy of CAD/CAM-Fabricated Metal- and All-Ceramic Single Crown Copings

Clinical performance of polymer frameworks in dental prostheses: A systematic review

STATEMENT OF PROBLEM

High-performance polymers including polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) have been used as substitutes for metal frameworks in dental prostheses. However, the clinical performance of polymer-based frameworks is still uncertain.

PURPOSE

The purpose of this systematic review was to compare the clinical performance of PEEK and PEKK with that of metal frameworks for different dental prostheses.

MATERIAL AND METHODS

This review follows the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Six databases and non-peer-reviewed literature (without language or follow-up restrictions) were searched for studies conducted before February 2022. Only clinical studies, either randomized clinical trials (RCTs) or nonrandomized clinical trials (N-RCTs), comparing the clinical performance of polymer and metal frameworks were included. The risk of bias and certainty of the evidence were assessed with the RoB 2.0, ROBINS-I, and GRADE. Biologic (plaque and gingival indices, probing depth, bleeding scores, implant stability quotient, marginal bone loss) and mechanical outcomes (ridge base relation, prosthetic marginal gap, and fracture) were assessed.

RESULTS

Only 9 studies (7 RCTs and 2 N-RCTs) were included, all with moderate to serious risk of bias and low to very low certainty of evidence. No meta-analysis was possible, but qualitative analysis revealed lower plaque and gingival indices, probing depth, and marginal bone loss, with higher survival rates for implant-supported fixed prostheses and overdentures fabricated with PEEK than for metal frameworks. No significant differences were found between groups for removable partial dentures. The marginal fit of PEEK frameworks was also better for single crowns. Three fractures were reported in the 3 PEKK fixed dental prostheses with cantilevers.

CONCLUSIONS

PEEK and PEKK seem to be promising materials for dental prostheses, with acceptable response from the periodontal tissue. However, further well-designed studies are necessary to better understand their clinical and long-term limitations.

Digital Impressions Versus Conventional Impressions in Prosthodontics: A Systematic Review

The accuracy of definitive impressions has a significant impact on the quality of the final prosthesis. Elastic impression materials are commonly used in the traditional approach to replicate anatomical structures while indirectly fabricating prostheses. Digital impression has gained increasing popularity due to its various advantages, including three-dimensional previsualization, cost-effectiveness, and reduced time consumption. The objective of this study is to evaluate existing studies to provide an overview of the comparative advantages of digital impression techniques over conventional techniques. The review will focus on evaluating the accuracy, patient acceptability, operator preference, and time effectiveness of digital impression techniques in comparison to conventional techniques. The Population, Intervention, Comparison, and Outcome framework served as the basis for this study's search strategy. We conducted a comprehensive literature review by electronically searching articles published between 2000 and 2023 in PubMed, Medline, Cochrane, and the Web of Science. Furthermore, additional manual searches were conducted. The study examined the differences between optical impressions and traditional impressions in terms of accuracy, patient outcomes, and operator outcomes. It included both clinical and preclinical studies as well as randomized controlled trials. In conclusion, this review provides a short summary indicating that digital impressions exhibit comparable accuracy to conventional impressions without any statistically significant difference. This conclusion is based on an evaluation of accuracy, patient preference, and operator preference.

Digital Evaluation of Trueness and Fitting Accuracy of Co-Cr Crown Copings Fabricated by Different Manufacturing Technologies

INTRODUCTION

The dentistry industry has seen a number of exciting new advancements in recent years, many of which have been made possible by the introduction of automated technologies such as computer-aided design and computer-aided manufacturing (CAD/CAM). Despite the fact that these new approaches simplify the fabrication process in favor of decreased material consumption and improved time efficiency, it is possible that they may have an effect on the prosthesis's fitness, which in turn may affect how long they will last.

PURPOSE

The purpose of this in vitro study was to evaluate the trueness and fitness of cobalt-chromium (Co-Cr) crown copings fabricated by selective laser melting (SLM), milling, and conventional casting methods.

MATERIALS AND METHODS

A zirconium die was fabricated and scanned with a laboratory scanner to manufacture the Co-Cr metal copings for three groups (n = 12). In group A, the copings were fabricated by a 3D printing technique called SLM; in group B, the copings were fabricated by the milling technique; and in group C, the copings were fabricated by the conventional lost-wax method. After fabrication, the trueness and the internal fitness of the copings were evaluated using a metrology software program (Geomagic Control X, 3D Systems Inc., Rock Hill, SC). The one-way ANOVA and Tukey's honestly significant difference test were used to statistically analyze the data.

RESULTS

The highest root mean square (RMS) value of trueness was for CAD/CAM milling, and the highest mean of horizontal gaps was for the casted (lost-wax technique) group. There were highly significant differences in the mean RMS value of trueness and the mean horizontal gaps between the three groups.

CONCLUSION

The fabrication method of Co-Cr crown copings has an effect on the trueness and fitness of the copings.

To Evaluate the Marginal Adaptation of Porcelain Fused to Metal Crown with Different Base Metal Alloys

INTRODUCTION

The success of any restoration depends on the marginal seal. The adaptation of castings, luting cement, and the surface structures of the margins are all important factors in achieving marginal seal.

AIM

The aim of this study was to evaluate the vertical marginal discrepancy of cast copings obtained by employing conventional casting technique with two different base metal alloys with two different finish lines before and after porcelain firing.

MATERIAL AND METHODS

A total of forty wax copings were fabricated with stainless steel die assembly and divided into four groups with ten specimens for each metal and each finish line. Measurements were recorded from coping margin to the stainless steel die margin for vertical marginal gap recordings. Each metal coping was finished, and porcelain application was completed. Copings with porcelain were placed on their respective dies, again subjected to the same measuring microscope for checking the vertical marginal discrepancy by the same operator and results.

RESULTS

The results of the present study showed that the mean vertical marginal gaps of all the cast copings obtained in each group (G1-G8) were within clinically acceptable limits. The mean vertical marginal gap of G1 was 135.36 ± 2.30 μm, G2 was 67.22 ± 4.25 μm, G3: 39.47 ± 2.98 μm, G4: 71.00 ± 3.97 μm, G5: 109.57 ± 2.98 μm, G6: 109.57 ± 2.98 μm, and G8: 114.58 ± 2.40 μm.

CONCLUSION

The difference in the vertical marginal gap of cast copings obtained in different groups was statistically highly significant at 0.005 level, while the difference in the vertical marginal gap of cast copings obtained at different points was statistically nonsignificant.

Effect of different finish line preparations on the marginal and internal adaptation of cobalt-chromium metal alloy copings fabricated by using CAD-CAM technology: A systematic review and meta-analysis

STATEMENT OF PROBLEM

The marginal and internal adaptation of a fixed dental prosthesis depends on a variety of factors, finish line designs being one of them. A clear consensus as to which finish line design can provide a better marginal and internal adaptation with respect to cobalt-chromium metal alloy copings fabricated by using computer-aided design and computer-aided manufacturing (CAD-CAM) technology is lacking.

PURPOSE

The purpose of this systematic review and meta-analysis was to evaluate the effect of different finish line preparations on the marginal and internal adaptation of cobalt-chromium metal alloy copings fabricated by using CAD-CAM technology.

MATERIAL AND METHODS

Electronic (PubMed, Cochrane, EBSCOhost, and Google Scholar) and manual searches were conducted for articles published from January 2010 to December 2020 to identify relevant studies evaluating the effect of different finish line preparations (chamfer, deep chamfer, shoulder, rounded shoulder) on the marginal and internal adaptation of cobalt-chromium metal alloy copings fabricated by using CAD-CAM technology.

RESULTS

A total of 573 articles were obtained via electronic search, and 10 articles were obtained through manual search, of which 24 in vitro studies were selected after title, abstract, and full-text screening and were included for both qualitative and quantitative analyses. The marginal adaptation was evaluated under the parameters of marginal gap, absolute marginal discrepancy, and vertical marginal discrepancy, whereas internal adaptation was evaluated under the parameters of internal gap, cervical discrepancy, axial discrepancy, and occlusal discrepancy. The methods of CAD-CAM fabrication (direct metal laser sintering, hard milling, and soft milling) were considered under the subgroup analysis.

CONCLUSIONS

An overall better marginal and internal adaptation was observed with shoulder and rounded shoulder finish line designs when CAD-CAM methods were used for coping fabrication. Marginal and internal adaptation in chamfer and deep chamfer finish line designs showed better results with soft milling and direct metal laser sintering methods, whereas shoulder finish line showed better results with hard milling.

Effect of cement space on marginal discrepancy and retention of CAD/CAM crown

This research aimed to evaluate the effect of cement space on the marginal discrepancy and retention of computer-aided design/computer-aided manufacturing (CAD/CAM) crowns. A total of 30 premolar Frasaco teeth were machined to receive crowns with cement spaces of 70, 90, and 110 μm. The marginal discrepancy measurements were done before and after cementation. Pull-off test was conducted using universal testing machine (UTM). Data was analyzed using two-way mixed ANOVA with post-hoc Bonferroni test and Kruskal-Wallis test. The crowns with cement space of 70 μm showed a significantly higher absolute marginal discrepancy than those with 90 and 110 μm. No significant effect on the crown retention was found. Within the limitations of this study, modifying cement space to 90 μm and 110 μm may improve the marginal adaptation of CAD/CAM crown, whereas adjusting cement space from 70 to 110 μm did not significantly affect the crown retention.

Application of multi-directional forged titanium for prosthetic crown fabrication by CAD/CAM

Titanium are often used as dental materials, pure titanium present low strength and titanium alloy is reported poor biocompatibility, respectively. To overcome the problem, we fabricated high-strength multi-directional forged (MDF) titanium with improved mechanical properties without changing the chemical composition and evaluated its applicability in prosthetic crowns. Cutting tests: the average absolute value of the difference before and after cutting was calculated as the uncut amount. Surface evaluations: MDF titanium, pure titanium, and the Ti-6Al-4V alloy were the surface properties (the surface roughness, the contact angles, glossiness) of the samples were evaluated. The fitness test used digital data. These demonstrated that the good workability of high-strength MDF titanium. The surface-roughness and contact-angle properties of MDF titanium and pure titanium were similar. The fitness test showed no significant differences between MDF titanium and pure titanium crowns. These results suggest that MDF titanium is promising for fabricating prosthetic crowns in dental applications.

Marginal Accuracy of Milled Versus Cast Cobalt Chromium Alloys in Long Span Implant-Supported Frameworks: A Systematic Review and Meta-analysis

Aim:

To assess if milled cobalt chromium (Co-Cr) alloy offers significantly better marginal accuracy than cast Co-Cr alloy for screw-retained long-span dental implant framework.

Materials and Methods:

A search PICO was formulated using suitable keywords and an electronic search was initiated. The databases of PubMed, Cochrane Library, Google Scholar and Embase were searched for related articles. Bibliographies of randomised control trials and reviews, identified in the electronic search, were analysed for studies published outside the electronically searched journals. Electronic search identified 26 studies. A total of 16 studies were eliminated after reading the abstracts. Out of the remaining 10 studies, 3 were eliminated based on the inclusion and exclusion criteria, and finally 7 studies were finalised for systematic review.

Results

Data were extracted from the included studies and analysed. The obtained data were suitable for meta-analysis, which showed an overall effect size z = 4.97 ( P < .001) at 95% CI showing a significant statistical difference between milled and cast Co-Cr frameworks.

Conclusion:

Milled cobalt chromium frameworks are significantly more accurate than cast frameworks for long-span implant-supported frameworks used in dental prosthetic rehabilitation. More randomized controlled trials need to be conducted with a larger sample size to get a more authentic conclusion in a clinical scenario.

Effect of the amount of light energy transmitted through CAD/CAM resin block on bonding performance of four types of resin cement adhesive systems

Resin-ceramic hybrid materials for computer-aided design/computer-aided manufacturing (CAD/CAM resins) have been developed. In this study, the effects of the amount of light energy transmitted through the four types of 1.5-mm-thick CAD/CAM resin blocks on the bond performance of corresponding resin cement adhesive systems consisting of an adhesive and a dual-curable resin cement were examined. The bond strengths of the four types of resin cement adhesive systems decreased with decreasing the amount of light energy transmitted through CAD/CAM resin block, due to a decrease in the light-curable ability of dual-curable resin cements. However, the degradation behavior of the bond strengths was strongly affected by the types of adhesives and initiator systems utilized. The adhesive consisting of a dimethacrylate monomer and redox-initiators enhanced the bonding performance of the dual-curable resin cement more effectively than the adhesive, which consists of a dimethacrylate monomer and photo-initiators or a γ-me thacryloxypropyltrimethoxysilane and a 10-methacryloyloxydecyl dihydrogen phosphate.

Marginal discrepancy of 3-unit Co-Cr metal copings fabricated with additive and subtractive manners: A comparative study

Background

Poor marginal adaptation may give rise to a series of biological complications. Despite its importance, comparative studies on marginal adaptation of metal-ceramic fixed restorations fabricated with newer methods are limited.

Aim

Therefore, it was aimed to assess the marginal accuracy of copings fabricated with subtractive and additive manners used in contemporary dentistry.

Materials and Methods

For a typodont model, 60 three-unit cobalt-chrome metal copings were fabricated by selective laser sintering (SLS), hard alloy milling (HAM), and soft alloy milling (SAM) in comparison to casting (C). Marginal discrepancy assessment was performed by using replication technique. Mesiodistal and buccopalatal cross-sections of silicone replicas were investigated under a stereomicroscope at × 80 magnification. A total of 960 measurements were subsequently made by means of corresponding image-review software on captured images after calibration of the software to μm scale. Obtained data were subjected to nonparametric Kruskal Wallis and Tamhane post-hoc tests (α =0.05).

Results

Marginal adaptation of C group was significantly inferior to test groups in both canine- and premolar-teeth measurements (P < 0.05). Marginal fit was found to be tooth dependent (P < 0.001). HAM, SAM, and SLS groups exhibited analogous marginal discrepancy values on canine-tooth measurements. Differences among these groups were not statistically significant (P > 0.05). SAM and SLS groups demonstrated better marginal adaptation than others on premolar-tooth measurements. Also, no statistically significant difference was detected between SAM and SLS groups (P > 0.05).

Conclusions

SAM group demonstrated superior marginal accuracy. All groups had clinically acceptable marginal discrepancy values (<120 μm), except cast group.

Corrosion Resistance and Ion Release of Dental Prosthesis of CoCr Obtained by CAD-CAM Milling, Casting and Laser Sintering

Corrosion resistance and ion release behavior have been evaluated for thirty dental restoration samples obtained by three different manufacturing systems: computer-aided design and manufacturing (CAD-CAM), traditional casting and laser sintering. The alloy used was the CoCr alloy (same batch) generally used in clinical dentistry. Corrosion resistance has been evaluated by electrochemical testing in an artificial saliva medium at 37 °C. Corrosion parameters such as critical current density (icr), corrosion potential (Ecorr), and passive current density (ip), have been determined. Cobalt and Chromium ions released from the different samples have also been analyzed in an artificial saliva medium at 37 °C by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) at different immersion times. The casted samples showed higher corrosion rates and ion-release levels. The CAD-CAM milled samples presented lower ion-release levels and better corrosion resistance due to the total solubility of the chemical elements in only one phase with the same chemical composition. This homogeneity avoids the formation of electrochemical corrosion. Moreover, the absence of defects and residual stresses increases the corrosion resistance. Casted and laser sintered prostheses have shown the presence of Cr, W, and Nb rich-precipitates which are detrimental to the corrosion resistance. These precipitates produce a decrease in the Cr content on the surface. It is well known that the corrosion resistance increases with the Cr content by the formation of Chromium oxide on the surface that increases passivation. Consequently, the decrease in Cr induces an increase in corrosion and ion release.

Influence of the CAD-CAM Systems on the Marginal Accuracy and Mechanical Properties of Dental Restorations

The aim of this study was to compare the quality of different computer-assisted-design and computer assisted manufacturing systems (CAD-CAM) generated by only one scanner, focusing on vertical fit discrepancies and the mechanical properties. A master model was obtained from a real clinical situation: the replacement of an absent (pontic) tooth, with the construction of a fixed partial denture on natural abutments with three elements. Nine scans were performed by each tested and 36 copies were designed using a dental CAD-CAM software (Exocad). The frameworks were manufactured using three-axis and five-axis, with the same batch of the chrome-cobalt (CrCo) alloy. The frameworks were not cemented. A focus ion beam-high resolution scanning electron microscope (FIB-HRSEM) allowed us to obtain the vertical gap measurements in five points for each specimen. Roughness parameters were measured using white light interferometry (WLI). The samples were mechanically characterized by means of flexural tests. A servo-hydraulic testing machine was used with a cross-head rate of 1 mm/min. One-way ANOVA statistical analysis was performed to determine whether the vertical discrepancies and mechanical properties were significantly different between each group (significance level p < 0.05). The overall mean marginal gap values ranged: from 92.38 ± 19.24 µm to 19.46 ± 10.20 µm, for the samples produced by three-axis and five-axis machines, respectively. Roughness was lower in the five-axis machine than the three-axis one, and as a consequence, the surface quality was better when the five-axis machine was used. These results revealed a statistically significant difference (p < 0.005) in the mean marginal gap between the CAD-CAM systems studied. The flexural strength for these restorations range from 6500 to 7000 N, and does not present any statistical differences’ significance between two CAD-CAM systems studied. This contribution suggests that the number of axes improves vertical fit and surface quality due to the lower roughness. These claims show some discrepancies with other studies.

Mechanical Properties of CoCr Dental-Prosthesis Restorations Made by Three Manufacturing Processes. Influence of the Microstructure and Topography

The aim of this study is to compare the mechanical properties of three different dental restorations’ manufacturing processes (CADCAM milling, casting and laser sintering) generated by only one laboratory scanner focusing on marginal fit analysis and their mechanical properties. A chrome-cobalt (Cr-Co) alloy from the same batch was used for three different methods to make an implant abutment. This simulates a maxillary right first molar that was fixed in a hemi-maxillary stone model. Five scans were performed by each tested framework. Nine frameworks were manufactured for each manufacture procedure. Field-Emission Scanning Electron Microscope (FE-SEM) direct vision was used to marginal gap measurement in five critical points for each specimen. In order to fix the samples in the microscope chamber, the restorations were submitted at a compression load of 50 N. The samples always have the same orientation and conditions. The resolution of the microscope is 4 nm and it is equipped by J image software. The microstructure of the samples was also determined with the FE-SEM equipped with EDS-microanalysis. Roughness parameters were measured using White Light Interferometry (WLI). The arithmetical mean for the Ra and Rq of each sample was calculated. The samples were mechanically characterized by means of microhardness and flexural testing. Servo-hydraulic testing machine was used with cross-head rate of 1 mm/min. Two-way ANOVA statistical analysis was performed to determine whether the marginal discrepancies and mechanical properties were significantly different between each group (significance level p < 0.05). The overall mean marginal gap values were: from 50.53 ± 10.30 µm for the samples produced by CADCAM to 85.76 ± 22.56 µm for the samples produced by the casting method. Laser sintering presents a marginal gap of 60.95 ± 20.66 µm. The results revealed a statistically significant difference (p-value < 0.005) in the mean marginal gap between the CADCAM systems studied. The higher flexure load to fracture for these restorations were for CADCAM restoration and the lower was for the casting samples. For these restorations, CADCAM Restoration yielded a higher flexure load to fracture and Casting ones yielded the lower. Porosity and microstructure play a very important role in the mechanical properties.

New Intraoral Scanner-Based Chairside Measurement Method to Investigate the Internal Fit of Crowns: A Clinical Trial

To measure the internal fit of the computer-aided designed/computer-aided manufactured (CAD/CAM) crowns, a new scanner-based chairside approach was investigated in patients, and the results were compared to the established silicone replica technique and a digital laboratory replica method. Thirty full-coverage crown preparations were included. Based on a digital impression with an intraoral scanner (IOS, Trios 3), three CAD/CAM measurement copings (‘COM’, resin composite; ‘ZIR’, zirconium dioxide; ‘NPA’, non-precious alloy) were fabricated for each tooth preparation. The internal fit of the measurement copings was analyzed with three different evaluation methods: IOS-based digital approach (D-IOS), digital replica method with laboratory software (D-GOM), and conventional silicone replica technique (CV-SR). The congruence between the determined target parameter of the 80-µm cement space and the actual measured internal gap was investigated. Statistical analysis was performed by ANOVA (p-value < 0.05). No significant difference was determined between the three evaluation methods. However, significant differences were observed for the three coping materials (p-value < 0.05), the single measurement position (marginal, axial, and occlusal fit) (p-value < 0.05), and the interaction between the coping material and the measurement position (p-value < 0.05). COM revealed the smallest internal gap, followed by ZIR and NPA. Regardless of the coping material, the occlusal gap was higher than the axial and marginal gaps. Furthermore, only the internal gaps of the marginal area almost matched the target parameter of 80-µm for the cement space. D-IOS is effective for measuring internal fit of single crowns in different clinical settings.

A systematic review on the accuracy of zirconia crowns and fixed dental prostheses

Purpose

The aim of this study was to review the fit and assess the accuracy of tooth-supported single and multi-unit zirconia fixed dental prostheses.

Background

The fit of zirconia restorations has been reported in several studies, but the accuracy of the manufacturing process is seldom discussed or used when drawing conclusions on the fit.

Materials and methods

A literature search of articles published in PubMed between 2 March 2013 and 1 February 2018 was performed using clearly defined inclusion and exclusion criteria. 841 articles were found and 767 were excluded after screening the title and abstract. After full-text analysis another 60 articles were excluded which left 14 articles to be included for data extraction. Fit was the mean of distances reported in the studies and accuracy was the fit minus the pre-set spacer

Results

For marginal gap of single crowns and multi-unit FDPs combined, the fit was 83 μm and the accuracy was 59 μm. The internal gap fit was 111 μm and the accuracy 61 μm. For the total gap, the fit was 101 μm, and the accuracy of the zirconia restorations was 53 μm.

Conclusions

Within the limitations of the present systematic review the fit of zirconia single crowns and multi-unit FDPs may be regarded as clinically acceptable, and the accuracy of the manufacturing of zirconia is ∼60 μm for marginal, internal, and total gap. Also, digital impressions seem to be associated with a smaller gap value.

Influence of Intra-Oral Scanner (I.O.S.) on The Marginal Accuracy of CAD/CAM Single Crowns

The aim of this in vitro study was to compare the quality of digital workflows generated by different scanners (Intra-oral digital scanners (I.O.S.s)) focusing on marginal fit analysis. A customized chrome-cobalt (Cr-Co) implant abutment simulating a maxillary right first molar was fixed in hemi-maxillary stone model and scanned by eight different I.O.S.s: Omnicam^® (Denstply Sirona, Verona, Italy) CS3500^®, CS3600^®, (Carestream Dental, Atlanta, GA, USA), True Definition Scanner^® (3M, St. Paul, MN, USA), DWIO^® (Dental Wings, Montreal, Quebec, Canada), PlanScan^® (Planmeca Oy, Helsinki, Finland), 3D PROGRESS Plus^® (MHT, Verona, Italy), TRIOS 3^® (3Shape, Copenhagen, Denmark). Nine scans were performed by each tested I.O.S. and 72 copings were designed using a dental computer-assisted-design/computer-assisted-manufacturing (CAD/CAM) software (exocad GmbH, Darmstadt, Germany). According to CAD data, zirconium dioxide (ZrO₂) copings were digitally milled (Roland DWX-50, Irvine, CA, USA). Scanning electron microscope (SEM) direct vision allowed for marginal gap measurements in eight points for each specimen. Descriptive analysis was performed using mean, standard deviation, and median, while the Kruskal⁻Wallis test was performed to determine whether the marginal discrepancies were significantly different between each group (significance level p < 0.05). The overall mean marginal gap value and standard deviation were 53.45 ± 30.52 μm. The minimum mean value (40.04 ± 18.90 μm) was recorded by PlanScan^®, then 3D PROGRESS Plus^® (40.20 ± 21.91 μm), True Definition Scanner^® (40.82 ± 26.19 μm), CS3500^® (54.82 ± 28.86 μm) CS3600^® (59,67 ± 28.72 μm), Omnicam^® (61.57 ± 38.59 μm), DWIO^® (62.49 ± 31.54 μm), while the maximum mean value (67.95 ± 30.41 μm) was recorded by TRIOS 3^®. The Kruskal⁻Wallis tests revealed a statistically significant difference (p-value < 0.5) in the mean marginal gaps between copings produced by 3D PROGRESS Plus^®, PlanScan, True Definition Scanner, and the other evaluated I.O.S.s. The use of an I.O.S. for digital impressions may be a viable alternative to analog techniques. Although in this in vitro study PlanScan^®, 3D PROGRESS Plus^® and True Definition Scanner^® may have showed the best performances, all I.O.S.s tested could provide clinically encouraging results especially in terms of marginal accuracy, since mean marginal gap values were all within the clinically acceptable threshold of 120 μm.