Fit of 4-unit FDPs made of zirconia and CoCr-alloy after chairside and labside digitalization--a laboratory study

Influence of artificial landmarks on the accuracy of complete arch scans in the partially edentulous maxilla: An in vitro study

STATEMENT OF PROBLEM

Scan path length and the presence of edentulous alveolar ridge sections have a negative influence on scanning accuracy. How different artificial landmarks combined with an adapted scanning method affect accuracy is unclear.

PURPOSE

The purpose of this in vitro study was to determine the influence of 2 different artificial landmarks combined with an adapted scanning method on the scanning accuracy of a partially edentulous maxillary model.

MATERIAL AND METHODS

The model simulated a maxilla with 6 prepared teeth to accommodate a complete arch fixed partial denture. Five ceramic precision balls (ball center P1-P5), distributed buccally to the dental arch, were used to detect the dimensional and angular changes between the reference model and the intraoral scans. One intraoral scanner (Primescan) was used to make 30 scans each with either the scanning strategy recommended by the manufacturer (M) or with an adapted scanning strategy and the use of a bar (B) or 4 plates (P) as artificial landmarks in the dorsal palate. Data were statistically analyzed using a generalized least squares regression model (α=.05).

RESULTS

Scanning with artificial landmarks reduced the maximum absolute distance deviations (M: 249 μm, B: 190 μm, P: 238 μm) and the maximum angle deviations (M: 0.31 degrees, B: 0.28 degrees, P: 0.26 degrees). Vertical distance deviations were improved by 10 to 50% with the use of artificial landmarks. Absolute mean distance deviations were significantly lower for group M (P<.001). In contrast, with artificial landmarks, mean angle (P<.001) and mean vertical distance deviations (P<.014) improved significantly.

CONCLUSIONS

Scanning with artificial landmarks in the dorsal palate combined with an adapted scanning method improved the scanning accuracy and reliability of vertical distance deviations.

Effect of cement spacer on fit accuracy and fracture strength of 3-unit and 4-unit zirconia frameworks

BACKGROUND

Cement spacer is essential for compensating deformation of zirconia restoration after sintering shrinkage, allowing proper seating and better fracture resistance of the restoration. Studies assessing the effect of cement spacer on fit accuracy and fracture strength of zirconia frameworks are missing in the literature. Therefore, the aim of this study was to evaluate the effect of different cement spacer settings on fit accuracy and fracture strength of 3-unit and 4-unit zirconia frameworks.

METHODS

Sixty standardized stainless-steel master dies were manufactured with 2 prepared abutments for fabricating 3-unit and 4-unit zirconia frameworks. The frameworks were assigned into 6 groups (n = 10) according to cement spacer setting (30 μm, 50 μm, and 80 μm) as follows: 3-unit frameworks; 3u-30, 3u-50, 3u-80, and 4-unit frameworks; 4u-30, 4u-50, and 4u-80. The frameworks were assessed for fit accuracy with the replica method. The specimens were cemented to their corresponding dies, and the fracture strength was measured in a universal testing machine. The Weibull parameters were calculated for the study groups and fractured specimens were inspected for failure mode. Two-Way ANOVA followed by Tukey test for pairwise comparison between study groups (α = 0.05).

RESULTS

The cement spacer had a significant effect on both fit accuracy and fracture strength for 3-unit and 4-unit frameworks. The 50 μm spacer had significantly better fit accuracy followed by 80 μm, and 30 μm spacers. Both 50 μm and 80 μm spacers had similar fracture strength, and both had significantly better strength than 30 μm spacer.

CONCLUSIONS

For both 3-unit and 4-unit zirconia frameworks, 50 μm cement spacer can be recommended over 30 μm and 80 μm spacers for significantly better fit accuracy and adequate fracture strength.

The internal and marginal adaptation of lithium disilicate endocrowns fabricated using intra and extraoral scanners: An in-vitro study

OBJECTIVES

The impression technique highly influences the adaptation of ceramic restorations. Not enough information is available to compare the marginal (MF) and internal fit (IF) of endocrowns fabricated with various digitization techniques. Therefore, this in-vitro study aimed to compare the MF and IF of lithium disilicate (LDS) endocrowns fabricated through direct and indirect digital scanning methods.

MATERIALS AND METHODS

One extracted maxillary molar was used to fabricate endocrowns. The digitization of the model was performed with (G1) direct scanning (n = 10) utilizing an intraoral scanner (IOS), (G2) indirectly scanning the conventional impression taken from the model using the same IOS (n = 10), (G3) indirectly digitalizing the obtained impression using an extraoral scanner (EOS) (n = 10), and (G4) scanning the poured cast using the same EOS (n = 10). The MF and IF of the endocrowns were measured using the replica method and a digital stereomicroscope. The Kruskal-Wallis test was used to analyze data.

RESULTS

The studied groups differed significantly (p<0.001). G2 (130.31±7.87 μm) and G3 (48.43±19.14 μm) showed the largest and smallest mean vertical marginal gap, respectively. G2 and G3 led to the highest and lowest internal gaps in all regions, respectively. With significant differences among the internal regions (p<0.001), the pulpal area demonstrated the most considerable misfit in all groups.

CONCLUSIONS

Scanning the impression using an extraoral scanner showed smaller marginal and internal gaps.

Effect of printing layer thickness on the trueness of 3-unit interim fixed partial dentures

STATEMENT OF PROBLEM

Three-dimensional printing has facilitated the fabrication processes in dentistry. However, knowledge on the effect of layer thickness on the trueness of 3D printed fixed partial dentures (FPDs) is lacking.

PURPOSE

The purpose of this in vitro study was to compare the effect of printing layer thickness on the trueness of 3-unit interim FPDs fabricated by using additive manufacturing with that of those fabricated by subtractive manufacturing.

MATERIAL AND METHODS

The right first premolar and first molar teeth of a dentate mandibular model were prepared for a 3-unit restoration and then digitized by using an intraoral scanner. A 3-unit interim FPD was designed to fabricate 40 restorations by using either the additive (NextDent C&B MFH) with layer thicknesses of 20 μm (n=10), 50 μm (n=10), and 100 μm (n=10) or subtractive manufacturing technique (Upcera) (milled, n=10). After fabrication, the interim FPDs were digitized by using the same intraoral scanner and were superimposed over the design data by using a 3D analysis software program. Root mean square (RMS) was used to analyze the trueness of the restorations at 4 different surfaces (external, intaglio, marginal area, and intaglio occlusal) and as a complete unit (overall). Data were analyzed with the Kruskal-Wallis and Wilcoxon tests with Bonferroni correction (α=.05).

RESULTS

The 100-μm-layer thickness interim FPDs showed the greatest overall (P≤.015), external (P≤.021), and intaglio occlusal (P≤.021) deviations, whereas the milled interim FPDs showed the lowest (P=.001). No significant differences were found among the test groups for marginal RMS (P≥.108). The differences between the 50-μm-layer thickness and 100-μm-layer thickness interim FPDs for the intaglio surface deviations (P=.064) and between the 20-μm-layer thickness and 50-μm-layer thickness interim FPDs for each surface tested were not statistically significant (P≥.108).

CONCLUSIONS

The printing layer thickness had a significant effect on the trueness of the additively manufactured interim FPDs. However, subtractively manufactured interim FPDs presented higher trueness than those additively manufactured, regardless of the printing layer thickness.

Positional trueness of abutments by using a digital die-merging protocol compared with complete arch direct digital scans and conventional dental impressions

STATEMENT OF PROBLEM

Complex prosthodontic treatments frequently require capturing an accurate impression of abutment teeth throughout the dental arch. Intraoral digital scanning has been reported to be accurate within single dental quadrants; however, the positional trueness of complete arch intraoral digital scans is not well understood.

PURPOSE

The purpose of this in vitro study was to compare the positional trueness of a complete arch digital scan generated by digitally merging portions of a direct digital scan from an intraoral scanner (IOS) with a digitized polyvinyl siloxane (PVS) complete arch impression.

MATERIAL AND METHODS

A 3D printed reference cast was scanned with a desktop scanner, and reference standard tessellation language (STL) data sets were obtained. The reference cast was used to generate 4 nonmerged (NM) groups and 2 die-merged (DM) groups. In the NM groups (n=10), a direct digital scan of the reference cast was made with an IOS (NM-IOS), the PVS impression of the reference cast was digitized by using a cone beam computed tomography (CBCT) scanner (NM-PVS-CBCT) or a desktop scanner (NM-PVS-DESK), and the gypsum cast made from the PVS impression was digitized by using a desktop scanner (NM-STONE). In the DM groups (n=10), individual dies were cropped from the complete arch digital scan from the NM-IOS group and merged with the digital scans from the NM-PVS-DESK and NM-PVS-CBCT groups to generate the DM-PVS-DESK and DM-PVS-CBCT groups, respectively. Deviation was measured as the absolute value of the distance from a reference position on the reference cast. The Kruskal-Wallis and Dunn pairwise comparison tests were used to compare the difference in deviation between the groups (α=.05).

RESULTS

The NM-STONE and NM-PVS-DESK groups demonstrated the highest positional trueness, with global deviations of 19.6 and 17.7 μm, respectively, with no statistically significant difference (P>.999). However, both the NM-IOS and NM-PVS-CBCT groups differed significantly from the NM-STONE group (P<.001 and P=.003, respectively) and the NM-PVS-DESK group (P<.001 and P=.004, respectively). In the DM groups, the DM-PVS-CBCT group presented a higher deviation than the DM-PVS-DESK group.

CONCLUSIONS

Complete arch digital scans of PVS impressions digitized with a desktop scanner exhibited less positional deviation than those digitized with a CBCT scanner or complete arch digital scans generated with an IOS. Complete arch digital scans generated with an IOS and CBCT scanner result in more deviations in the posterior regions, and their positional trueness may not be sufficient to construct an accurate digital scan. Generating a complete arch digital scan by digitally merging portions of a direct digital scan from an IOS with a digitized PVS complete arch impression is a suitable alternative to the contemporary workflow of digitizing a stone cast with a desktop scanner.

A guide for selecting the intraoral scan extension when fabricating tooth- and implant-supported fixed dental prostheses

OBJECTIVES

To describe a new classification for intraoral scans based on the scan extension and to introduce a decision guideline to choose the scan extension for fabricating tooth- and implant-supported fixed dental prostheses (FDPs).

OVERVIEW

Multiple operator- and patient-related factors have been identified that can decrease the scanning accuracy of intraoral scanners (IOSs), including scan extension. However, the decision criteria for selecting scan extension for fabricating tooth- and implant-supported restorations is unclear. Based on the extension of the intraoral digital scans, three types of scans can be defined: half-arch (anterior or posterior), extended half-arch, and complete-arch scan. Variables to consider when choosing the scan extension include the number and location of units being restored, as well as the extension and location of edentulous areas. Additionally, the accuracy of the virtual definitive cast and the accuracy of the maxillomandibular relationship captured by using IOSs should be differentiated.

CONCLUSIONS

A decision tree for selecting the scan extension is presented. The decision is based on the number and location of units being restored, and the extension and location of edentulous areas. Intraoral scans with reduced scan extension are indicated when fabricating tooth- and implant-supported crowns or short-span fixed prostheses, when the patient does not have more than one missing tooth in the area of the dental arch included in the scan. For the remaining clinical conditions, complete-arch intraoral scans are recommended.

CLINICAL SIGNIFICANCE

Scan extension is a clinician's decision that should be based on the number and location of units being restored and the extension and location of edentulous areas. Intraoral scans with a reduced scan extension is recommended, when possible.

Accuracy of intraoral scanning versus conventional impressions for partial edentulous patients with maxillary defects

This study aimed to evaluate the accuracy of digital dental impressions obtained by intraoral scanning (IOS) for partial edentulous patients with maxillary defects by comparing them with conventional impression techniques. Ten subjects underwent an experimental procedure where three ceramic blocks were affixed to the healthy palate mucosa. Digital dental impressions were captured using IOS and subsequently imported into software. Conventional impressions obtained by silicone rubber were also taken and scanned. Linear distance and best-fit algorithm measurements were performed using conventional impression techniques as the reference. Twenty impressions were analyzed, which included 30 pairs of linear distances and 10 best-fit algorithm measurements. Regarding linear distance, paired two-sample t-test demonstrated no significant differences between IOS and model scanning in groups A and C, whereas significant differences were found in group B (P < 0.05). Additionally, ANOVA revealed significant differences among the groups (P < 0.05). No significant differences were found for the best-fit algorithm measurement of the dentition. IOS can provide accurate impressions for partial edentulous patients with maxillary defects and its accuracy was found to be comparable with conventional impression techniques. A functional impression may be needed to ensure accurate reproduction of soft and hard tissues in defect or flap areas.

Evaluation of marginal and internal fit of single crowns manufactured with an analog workflow and three CAD-CAM systems: A prospective clinical study

PURPOSE

This prospective clinical study evaluated and compared the marginal and internal fit of crowns fabricated with an analog workflow and three different computer-aided design and computer-aided manufacturing (CAD-CAM) systems.

MATERIALS AND METHODS

Twenty-five participants in need of a single complete-coverage molar or premolar crown were recruited in the study. Twenty-two completed the study, and three participants dropped out. Teeth were prepared according to a standardized protocol by one operator. For each participant, one final impression was made with polyether material (PP) and three intraoral scanners: CEREC Omnicam (C), Planmeca Planscan (PM), and True Definition (TR). For the PP group, crowns were fabricated with a pressable lithium disilicate ceramic, whereas for the other three groups (C, PM, and TR), crowns were designed and milled with dedicated CAD-CAM systems and materials. Marginal (vertical and horizontal) and internal discrepancies between the crowns and tooth preparation were measured at various locations with digital superimposition software. Data was analyzed for normality with Kolmogorov-Smirnov and Shapiro-Wilk tests and then compared with one-way ANOVA and Kruskal-Wallis tests.

RESULTS

Mean vertical marginal gap values were 92.18 ± 141.41 μm (PP), 150.12 ± 138.06 μm (C), 129.07 ± 109.96 μm (PM), and 135.09 ± 112.03 μm (TR). PP group had statistically significantly smaller vertical marginal discrepancy (p = 0.001) than all other groups, whereas no significant difference was detected among the three CAD-CAM systems (C, PM, and TR). Horizontal marginal discrepancies were 104.93 ± 111.96 μm (PP), 89.49 ± 119.66 μm (C), 113.36 ± 128.49 μm (PM), and 136.39 ± 142.52 μm (TR). A significant difference was detected only between C and TR (p < 0.0001). Values for the internal fit were 128.40 ± 49.31μm (PP), 190.70 ± 69.79μm (C), 146.30 ± 57.70 μm (PM), and 168.20 ± 86.67 μm (TR). The PP group had a statistically significant smaller internal discrepancy than C (p < 0.0001) and TR groups (p = 0.001), whereas no significant difference was found compared to the PM group.

CONCLUSION

Posterior crowns fabricated with CAD-CAM systems showed vertical margin discrepancy greater than 120 μm. Only crowns fabricated with the conventional methodology had vertical margins below 100 μm. Horizontal marginal discrepancy was different among all groups, and only CEREC CAD-CAM was below 100 μm. Internal discrepancy was less for crowns fabricated with an analog workflow.

Fibre-reinforced Cad/CAM post and cores: The new "gold standard" for anterior teeth with extensive coronal destruction?-A fully digital chairside workflow

Objectives

Since one-third of persons suffer a dental trauma, treatment of anterior teeth using post and core (PC) is becoming important. In teeth with extensive destruction, cast PC (CPC) remain the "gold standard", even though they lead to aesthetic impairment and have a mismatching elastic modulus to that of dentin. Prefabricated fibre-reinforced posts have elastic modulus similar to that of dentin but the accuracy of fit and mechanical stability are worse. This study was aimed to evaluate the deviation and mechanical performance of fibre-reinforced CAD/CAM PC (FRPC) fabricated in a fully digital chairside workflow, compared to those of CPC.

Methods

On 30 teeth, a PC preparation was conducted, and a conventional and digital post impression were taken with an intraoral scanner. Fifteen teeth each were treated with CPC and FRPC, respectively. The deviation was evaluated by superimposing the datasets of the digitalised stone models and digital post impressions. Decementation and root fracture during chewing simulation were analysed by microscopy and X-ray. Statistical analysis was performed by pairwise comparison and Kaplan-Meier analysis.

Results

The median deviation for the "coronal", "middle" and "apical" were 14.5, 18.0 and 113.7 μm, respectively. The pairwise comparison for "coronal"/"middle" showed no significance (p = 0.465), whereas that for "coronal"/"apical" and "middle"/"apical" showed highly significant differences (p < 0.001). After chewing simulation, five decementations and two root fractures were detected for CPC. For FRPC, neither decementation nor root fracture were documented.

Significance

Within the limitations of this study, FRPC performed significantly better than CPC.

Comparing the accuracy of distinct scanning systems and their impact on marginal/internal adaptation of tooth-supported indirect restorations. A scoping review

OBJECTIVE

To summarize the existing scientific evidence on the effect of distinct intraoral (IOS) and extraoral (EOS) scanners in terms of their accuracy for image acquisition and the marginal/internal adaptation of indirect restorations.

METHODS

The protocol of this scoping review is available online (https://osf.io/cwua7/). A structured search, with no date restriction, was performed in LILACS, MEDLINE via Pubmed, EMBASE, Web of Science, and Scopus, for articles written in English. The inclusion criteria were studies that considered at least two scanners, regardless of method (intra or extraoral), for the production of tooth-supported restorations. Two independent and blinded researchers screened the studies, collected and analyzed the data descriptively.

RESULTS

103 studies were included (55 on marginal/internal adaptation, 33 on accuracy, 5 on both outcomes, and 10 reviews). Most of them, shown clinically acceptable adaptation (<120 μm). Factors commonly related to the performance of scanners are: use of anti-reflection powders, method of image acquisition, and restoration/tooth characteristics. The need of anti-reflection powders was controversial. Different scanning principles seems to result on similar performance; IOS that combine them could be promising. The most explored systems were Omnicam - IOS, and inEos X5 - EOS, which showed similar performance on marginal/internal adaptation. Scarce studies explored the performance of EOS systems, especially in terms of accuracy. Different restoration designs as single-unit seemed not to modify the performance of scanners. Limited information is available regarding the planned cement space, restorative material and design (multi-unit restorations), as also techniques to measure adaptation.

CONCLUSIONS

Digital scanners are valid approaches to obtain accurate impressions resulting in clinically acceptable restorations. Systems that uses combined principles of image acquisition seems promising for optimal performance. Based on high discrepancy, the quality of evaluated evidence is low, and well-designed studies are still encouraged, especially considering validated IOS/EOS as a control comparison condition.

Evaluating the accuracy of CAD/CAM optimized stones compared to conventional type IV stones

This study compared the accuracy (trueness and precision) of stone models fabricated using two brands of CAD/CAM optimized stones Cerec Stone (BC) and Elite Master (EM), and a conventional type IV stone Elite Rock Fast (ERF). 30 conventional Type IV and scannable stone complete-arch models were scanned with a blue LED extraoral scanner, and root mean square values were obtained. 6 abutments were used in complete-arch models. The digital models were compared with the master model to evaluate their trueness using model superimposition with Geomagic software. Precision was determined for each case by superimposing combinations of the 10 datasets in each group. The point cloud density of each model was calculated with MeshLab software. Kruskal-Wallis and Mann-Whitney non-parametric tests were used for the statistical analysis. The trueness of the stone models was 96 μm for the BC, 88.2 μm for the EM, and 87.6 μm for the ERF. There were no significant differences between the tested dental stones (p = .768). However, the EM models (35.6 μm) were more precise than the BC (46.9 μm) and ERF (56.4 μm) models (p = .001, p < .001). EM models also showed the highest point cloud density. There were significant differences in point cloud density (p = .003). The EM models showed significant differences in precision but no significant differences in terms of trueness. Although EM was more precise and had the highest point cloud density, all models were within the clinically acceptable limit.

Accuracy of Additively Manufactured Dental Casts Compared with That of Virtual Scan Data Obtained with an Intraoral Scanner: An In Vitro Study

The study aimed to evaluate the time-related accuracy of additively manufactured dental casts and to compare it with scan data obtained with an intraoral scanner in vitro. Twenty-eight markers were attached to a set of dentiforms as reference model, and the distances between the markers were measured using a digital caliper. An intraoral scanner was used to obtain the virtual scan data of the reference model with a total of 30 scans per arch. The distances between markers were measured using a three-dimensional inspection software for all scans (group IOS). Scan data were additively manufactured using a 3D printer, and the distances between markers were measured as in the reference model immediately after post-polymerization (group PPIA), 1 day (group PP1D), 7 days (group PP7D), and 30 days after post-polymerization (group PP30D). The linear deviation in group IOS was 199.74 ± 11.14 μm, PPIA was 242.88 ± 49 μm, PP1D was 259.9 ± 42.59 μm, PP7D was 289.82 ± 39.74 μm, and PP30D was 315.8 ± 33.28 μm, in comparison with the reference model, with significant differences among all groups (all p < 0.05). When additively manufacturing casts from scan data to verify the quality of dental prostheses designed virtually, the prostheses should be adapted to casts manufactured within one week.

Accuracy of full-arch digitalization for partially edentulous jaws - a laboratory study on basis of coordinate-based data analysis

Objectives

To compare the accuracy (trueness and precision) of direct digitization of four different dental gap situation with two IOS (intraoral scanner).

Materials and methods

Four partially edentulous polyurethane mandible models were used: (1) A (46, 45, 44 missing), (2) B (45, 44, 34, 35 missing), (3) C (42, 41, 31, 32 missing), and (4) D (full dentition). On each model, the same reference object was fixed between the second molars of both quadrants. A dataset (REF) of the reference object was generated by a coordinate measuring machine. Each model situation was scanned by (1) OMN (Cerec AC Omnicam) and (2) PRI (Cerec Primescan AC) (n = 30). Datasets of all 8 test groups (N = 240) were analyzed using inspection software to determine the linear aberrations in the X-, Y-, Z-axes and angular deviations. Mann–Whitney U and two-sample Kolmogorov–Smirnov tests were used to detect differences for trueness and precision.

Results

PRI revealed higher trueness and precision in most of the measured parameters (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\overrightarrow{V}}_{E}$$\end{document}V→E 120.95 to 175.01 μm, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overrightarrow{V}_{E}$$\end{document}V→E(x) − 58.50 to − 9.40 μm, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overrightarrow{V}_{E}$$\end{document}V→E (z) − 70.35 to 63.50 μm), while OMN showed higher trueness for \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overrightarrow{V}_{E}$$\end{document}V→E (y) regardless of model situation (− 104.90 to 34.55 μm). Model D revealed the highest trueness and precision in most of the measured parameters regardless of IOS (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overrightarrow{V}_{E}$$\end{document}V→E 120.95 to 195.74 μm, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overrightarrow{V}_{E}$$\end{document}V→E (x) − 9.40 to 66.75 μm,\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overrightarrow{V}_{E}$$\end{document}V→E (y) − 14.55 to 51.50 μm, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overrightarrow{V}_{E}$$\end{document}V→E (z) 63.50 to 120.75 μm).

Conclusions

PRI demonstrated higher accuracy in the X- and Z-axes, while OMN depicted higher trueness in the Y-axis. For PRI, Model A revealed the highest distortion, while for OMN, Model B produced the largest aberrations in most parameters.

Clinical relevance

Current results suggest that both investigated IOS are sufficiently accurate for the manufacturing of tooth-borne restorations and orthodontic appliances. However, both hardware specifications of IOS and the presence of edentulous gaps in the dental model have an influence on the accuracy of the virtual model dataset.

Accuracy of intraoral scans of edentulous jaws with different generations of intraoral scanners compared to laboratory scans

PURPOSE

Purpose of this in vitro study was to determine the accuracy of different intraoral scans versus laboratory scans of impressions and casts for the digitization of an edentulous maxilla.

MATERIALS AND METHODS

A PEEK model of an edentulous maxilla, featuring four hemispheres on the alveolar ridges in region 13, 17, 23 and 27, was industrially digitized to obtain a reference dataset (REF). Intraoral scans using Cerec Primescan AC (PRI) and Cerec AC Omnicam (OMN), as well as conventional impressions (scannable polyvinyl siloxane) were carried out (n = 25). Conventional impressions (E5I) and referring plaster casts were scanned with the inEOS X5 (E5M). All datasets were exported in STL and analyzed (Geomagic Qualify). Linear and angular differences were evaluated by virtually constructed measurement points in the centers of the hemispheres (P13, P17, P23, P27) and lines between the points (P17–P13, P17–P23, P17–P27). Kolmogorov-Smirnov test and Shapiro-Wilk test were performed to test for normal distribution, Kruskal-Wallis-H test, and Mann-Whitney-U test to detect significant differences in trueness, followed by 2-sample Kolmogorov-Smirnov test to detect significant differences in precision (P < .008).

RESULTS

Group PRI showed the highest trueness in linear and angular parameters (P < .001), while group E5I showed the highest precision (P < .001).

CONCLUSION

Intraoral scan data obtained using Primescan showed the highest trueness while the indirect digitization of impressions showed the highest precision. To enhance the workflow, indirect digitization of the impression itself appears to be a reasonable technique, as it combines fast access to the digital workflow with the possibility of functional impression of mucosal areas.

Fit of zirconia fixed partial dentures fabricated from conventional impressions and digital scans: A systematic review and meta-analysis

STATEMENT OF PROBLEM

Available studies comparing fit accuracy of zirconia fixed partial dentures (FPDs) fabricated from conventional impressions and digital scans provide contradictory results. In addition, studies have been heterogeneous and of a limited number to provide conclusive evidence.

PURPOSE

The purpose of this systematic review and meta-analysis was to compare the marginal and intaglio fit of tooth-supported zirconia FPDs fabricated from conventional impressions and digital scans and to investigate the effect of different variables on the fit results.

MATERIAL AND METHODS

An electronic search was performed on the National Library of Medicine (NLM), Cochrane Central Register of Controlled Trials, and Scopus databases. In addition, a manual search was carried out. Studies comparing the fit of tooth-supported zirconia FPDs fabricated from conventional impressions and digital scans and reporting sufficient data for qualitative and quantitative analysis were included. Standard mean differences (SMDs) and 95% confidence intervals (CI) were calculated for meta-analysis. Subgroup analysis was performed to study the effect of variables including restoration form (monolithic or framework), units number, intraoral scanner (IOS) type, conventional impression material, spacer thickness, and abutments region.

RESULTS

The initial search resulted in a total of 608 articles. Nine articles were included in the analysis (1 clinical and 8 in vitro) evaluating 118 restorations. Digital scan displayed significantly better marginal fit (P<.001; SMD: -0.68; 95% CI: -0.92, -0.09) and intaglio fit (P=.020; SMD: -0.51; 95% CI: -0.94, -0.42). Test for subgroup difference showed a significant influence of only impression material type (P=.008) and units number (P=.030) on marginal fit. Digital scan showed significantly better marginal accuracy for 3-unit FPDs than 4-unit FPDs (P<.001; SMD: -1.02; 95% CI: -1.41, -0.63). In addition, digital scanning had significantly better marginal fit with polyvinyl siloxane than polyether (P<.001; SMD: -0.98; 95% CI: -1.32, -0.64). A cement spacer ≤50 μm improved both marginal and intaglio fit in the digital group. The TRIOS scanner resulted in the best performance in the digital group for marginal fit.

CONCLUSIONS

Digital scanning provides significantly better marginal and intaglio fit than conventional impression making for fabricating zirconia FPDs up to 4 units, either in monolithic form or frameworks and at any region of the arch. However, further clinical studies are recommended to obtain more substantial results.

Comparison of marginal and internal fit of three-unit implant-supported fixed prosthetic substructures fabricated using CAD/CAM systems

OBJECTIVE

This study compared the marginal and internal fit of implant-supported fixed dentures fabricated using CAD/CAM systems.

MATERIALS AND METHODS

A lower jaw model representing partial edentulism was produced. Two dental implants were inserted in the area of teeth 35 and 37, onto which cemented abutments were screwed. The model was scanned using a laboratory scanner and transferred to a design software program for substructure fabrication. Sixty substructures were fabricated out of each group for six substructure types (n = 10), cast Co-Cr (control), milling Co-Cr, laser sintering Co-Cr, titanium (Ti), zirconium, and polyetheretherketone (PEEK) substructures. The marginal and internal fit was evaluated using a silicone replica viewed under a stereomicroscope. The data were analyzed using the statistical package program for social sciences (SPSS, Chicago, IL, USA, v. 17) at a significance level of 0.05. Marginal and internal gaps were compared using the one-way ANOVA test and Tukey's post hoc test. The differences between abutment teeth were determined using the independent sample t-test.

RESULTS

There was a significant difference in the marginal gap between PEEK and Ti groups (p < 0.05) but no difference between other groups (p > 0.05). There was a significant difference in the internal gap between PEEK, laser sintering Co-Cr, and milling Co-Cr groups (p < 0.05) but no difference between other groups (p > 0.05). The PEEK group had a higher marginal gap than the Ti group and a higher internal gap than the DMLS Co-Cr group (p < 0.05).

CONCLUSION

All substructures have a marginal and internal fit within acceptable clinical limits.

CLINICAL RELEVANCE

This in vitro study suggests that materials and techniques used in CAD/CAM systems improve the fitting accuracy of implant-supported fixed restorations.

Trueness and precision of digital implant impressions by intraoral scanners: a literature review

Background

With the development of intraoral scanners, their trueness and precision have been evaluated in various studies. Through these studies, the amount of accuracy that can be expected from intraoral scanners has gradually been disclosed, at the same time, it was difficult to integrate the results of individual studies due to differences in evaluation methods between studies. The purpose of this article was to review the currently available evidence, summarise what is currently known about IOS, analyse the evaluation methods of each study, and list points to note when interpreting the results.

Main text

Most of the studies were conducted in vitro. The accuracy is evaluated in situations such as single missing teeth, partially edentulous ridges with multiple missing teeth, and fully edentulous jaws. To evaluate the accuracy, direct measurement of distance or angle by coordinate measuring machines and calculation of surface deviation by superimposing surface data were predominantly performed. The influence of parameters such as the number of implants, distance between implants, angle between implants, and experience of the operator was evaluated. Many studies have shown that trueness tends to decrease as the distance between the implants and the scan range increases. It was agreed that the implant angle did not affect either trueness or precision. Regarding other factors, the results varied among studies. Therefore, the effects of these parameters are not clear.

Conclusions

Heterogeneity in the research methodology was prevalent among the studies considered in this review. Therefore, we cannot make a decisive statement regarding the trueness and precision of digital implant impressions by IOSs. So far, the comparison of the numerical values of error between studies has yet to elucidate any clear answers, despite small methodological differences.

Applications of three-dimensional printers in prosthetic dentistry

This narrative review aims to provide an overview of recent studies and case reports on three-dimensional (3D) printing, and to verify the applicability of 3D printers in the field of dental prostheses. This review was performed by conducting a search of PubMed. The clinical application of fabricating a prosthesis made with cobalt-chromium is considered possible depending on the material and hardware of the 3D printer. However, it is currently difficult to assess the clinical use of 3D-printed zirconia crowns. Further research is required, such as verification of materials used, margin morphology, and hardware. Clinically acceptable results have been reported for patterns using 3D printers. Interim restorations made using a 3D printer have been reported with good results that are considered clinically usable. Dentures made with 3D printers need further verification in terms of strength and deformation. Custom trays made with 3D printers are clinically useful, however, issues remain with design time and effort. Although several studies have reported the usefulness of 3D printers, further verification is required since 3D printers are still considered new technology.

3D Virtual Patient Representation for Guiding a Maxillary Overdenture Fabrication: A Dental Technique

This report describes a technique to obtain a 3D virtual representation of a maxillary edentulous patient guided by an additively manufactured intraoral scan body. The intraoral scan body incorporated a custom tray and occlusion rim which facilitated the acquiring of a digital definitive cast, maxillary occlusion rim position, interocclusal registration, and guided the integration of the facial scans. The technique simplified the design and manufacturing of the maxillary overdenture.

Comparison of CAD-CAM and traditional chairside processing of 4-unit interim prostheses with and without cantilevers: Mechanics, fracture behavior, and finite element analysis

STATEMENT OF PROBLEM

How processing by computer-aided design and computer-aided manufacturing (CAD-CAM) or traditional chairside fabrication techniques affects the presence of defects and the mechanical properties of interim dental prostheses is unclear.

PURPOSE

The purpose of this in vitro study was to compare the effects of CAD-CAM versus traditional chairside material processing on the fracture and biomechanical behavior of 4-unit interim prostheses with and without a cantilever.

MATERIAL AND METHODS

Two types of 4-unit interim prostheses were fabricated with abutments on the first premolar and first mandibular molar, one from a prefabricated CAD-CAM block and one with a traditional chairside polymer-monomer autopolymerizing acrylic resin (n=10). Both groups were assessed by compressive strength testing and additionally with or without a cantilevered second molar by using a universal testing machine with a 5-kN load cell. A finite element model (FEM) was built by scanning both prosthesis designs. Finite element analysis (FEA) replicated the experimental conditions to evaluate the stress distribution through the prostheses.

RESULTS

Interim fixed prostheses manufactured by CAD-CAM showed significantly higher mean fracture loading values (3126 N to 3136 N) than for conventionally made interim fixed prostheses (1287 N to 1390 N) (P=.001). The presence of a cantilever decreased the fracture loading mean values for CAD-CAM (1954 N to 2649 N), although the cantilever did not influence the traditional prostheses (1268 N to 1634 N). The highest von Mises stresses were recorded by FEA on the occlusal surface, with the cantilever design, and at the transition region (connector) between the prosthetic teeth.

CONCLUSIONS

Interim partial prostheses produced by CAD-CAM had a higher strength than those manufactured traditionally. The presence of a cantilever negatively affected the strength of the prostheses, although the structures manufactured by CAD-CAM still revealed high strength and homogenous stress distribution on occlusal loading.

Influence of intraoral scanning on the quality of preparations for all-ceramic single crowns

Objectives

To evaluate the influence of intraoral scanning on the quality of preparations for all-ceramic single crowns.

Material and methods

A total of 690 randomly selected and anonymized in vivo single crown preparations were examined. Three hundred twenty-three preparations were directly recorded with an intraoral scanner (group IS). Data from plaster casts digitized by a laboratory scanner (group ID; N = 367) served as control. Comparisons included convergence angle, marginal design, marginal substance reduction, homogeneity of the finish line, and undercuts. Evaluation was performed using fully automated specialized software. Data were analyzed applying Kolmogorov-Smirnov, Mann-Whitney U test, and Fisher’s exact test. Level of significance was set at p < 0.05.

Results

Convergence angle was above optimum in both groups, but significantly larger for group IS (p < 0.001). Marginal design was more ideal in group IS concerning the absence of featheredge design (p < 0.001) and reverse bevel (p = 0.211). Marginal substance reduction was closer to prerequisites for all-ceramic restorations in group IS (p < 0.001). Finish lines were more homogeneous in group IS regarding the uniformity of their course (p < 0.001). Undercuts were more frequently found in group ID than in group IS (p < 0.001).

Conclusions

Intraoral scanning of prepared teeth has positive impact on the quality of preparations for all-ceramic single crowns regarding marginal substance reduction, marginal design, homogeneity of the finish line, and undercuts.

Clinical relevance

Accurate preparation design represents a fundamental condition for success of ceramic crowns. Since there is potential for optimization, intraoral scanning might enhance preparation quality providing instant visual feedback.

Combination of Digital and Conventional Workflows in the CAD/CAM-Fabrication of an Implant-Supported Overdenture

Completely digital workflows for the fabrication of implant-supported removable restorations are not yet common in clinical dental practice. The aim of the current case report is to illustrate a reliable and comfortable workflow that reasonably merges conventional and digital workflows for the CAD/CAM-fabrication of implant-supported overdentures. The 53-year old patient was supplied with a digitally processed complete denture in the upper jaw and, simultaneously, with an overdenture supported by four interforaminal implants in the lower jaw. The overdenture included a completely digitally processed and manufactured alloy framework that had been fabricated by selective laser sintering. The case report indicates that digital manufacturing processes for extensive and complex removable restorations are possible. However, as it is currently not yet possible to digitally obtain functional impressions, future developments and innovations might focus on that issue.

Comparison of clinical fit of three-unit zirconia fixed prostheses fabricated using chairside and labside CAD/CAM systems

The purpose of this study was to assess the clinical fit provided by EZIS system, the newly commercialized chairside CAD/CAM system. Prostheses were fabricated with the chairside CAD/CAM system (CS) and labside CAD/CAM system (LS) and marginal, axial, and occlusal fit of the prostheses were compared and analyzed by using replica technique. CS group presented significantly lower fit in all the three fits compared to LS group. Differences in marginal fit, axial fit, and occlusal fit were 12.57 μm (P < 0.001), 3.32 μm (P < 0.05), and 17.20 μm (P < 0.05), respectively. Newly commercialized EZIS system yielded clinically feasible fit; however, further researches covering its biomechanical, physiological, stability aspects are required to promote active clinical use.

Dentistry 4.0 Concept in the Design and Manufacturing of Prosthetic Dental Restorations

The paper is a comprehensive but compact review of the literature on the state of illnesses of the human stomatognathic system, related consequences in the form of dental deficiencies, and the resulting need for prosthetic treatment. Types of prosthetic restorations, including implants, as well as new classes of implantable devices called implant-scaffolds with a porous part integrated with a solid core, as well as biological engineering materials with the use of living cells, have been characterized. A review of works on current trends in the technical development of dental prosthetics aiding, called Dentistry 4.0, analogous to the concept of the highest stage of Industry 4.0 of the industrial revolution, has been presented. Authors’ own augmented holistic model of Industry 4.0 has been developed and presented. The studies on the significance of cone-beam computed tomography (CBCT) in planning prosthetic treatment, as well as in the design and manufacture of prosthetic restorations, have been described. The presented and fully digital approach is a radical turnaround in both clinical procedures and the technologies of implant preparation using computer-aided design and manufacturing methods (CAD/CAM) and additive manufacturing (AM) technologies, including selective laser sintering (SLS). The authors’ research illustrates the practical application of the Dentistry 4.0 approach for several types of prosthetic restorations. The development process of the modern approach is being observed all over the world. The use of the principles of the augmented holistic model of Industry 4.0 in advanced dental engineering indicates a change in the traditional relationship between a dentist and a dental engineer. The overall conclusion demonstrates that it is inevitable and extremely beneficial to implement the idea of Dentistry 4.0 following the assumptions of the authors’ own, holistic Industry 4.0 model.

Marginal and internal fit of three-unit zirconia fixed dental prostheses: Effects of prosthesis design, cement space, and zirconia type

PURPOSE

The purpose of this study was to compare the marginal and internal fit of three-unit fixed dental prostheses (FDPs) fabricated using CAD/CAM with two designs, two cement space (CS), and two zirconia types.

METHODS

A master model with two zirconia abutments and a missing tooth was scanned with an intraoral scanner. FDPs were fabricated with two designs (Full contour: FC, Framework: FW), two zirconia types (multi-layer: L, single-layer: W), and two CS values (30 and 45 μm for L and 30 μm for W). There were six experimental groups. The fit of the FDPs was evaluated using the replica method. The space between an abutment and the FDPs in the marginal (MO), chamfer (CH), axial (AX), and occlusal (OC) areas was measured under an optical microscope and the data was statistically analyzed using three-way ANOVA and Bonferroni test (p < 0.05).

RESULTS

FW-l-45 μm showed a significantly smaller space than those for the FC in MO (p = 0.011), CH (p = 0.001) and AXE (p = 0.003). FW-l-30 μm showed a significantly smaller space than that for the 45 µm in AXE (p = 0.000) and OC (p = 0.016). FW-W-30 µm showed a significantly smaller space than that for the L in MO (p = 0.000), CH (p = 0.000), AXE (p = 0.000), and OC (p = 0.002).

CONCLUSIONS

The design and CS of the FDPs affected the fit. FDPs with single-layer zirconia showed better fit than that obtained with multi-layer zirconia.

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 manufacturing techniques for cobalt chromium fixed dental prostheses

Purpose

To compare the fit and assess the accuracy of tooth-supported single and multi-unit FDPs in cobalt chromium fabricated using different manufacturing techniques.

Materials and methods

A systematic search was performed in three databases; PubMed, Scopus, and Web of Science, using clearly specified search terms and inclusion criteria. The search yielded 1071 articles and included 18 articles in the analysis. Data regarding the fit analyses and the methods of manufacturing were extracted and the accuracy was defined as the fit result minus the pre-set cement spacer. Internal gap (IntG) was the mean of all the internal measuring points and total gap (TotG) was the mean of all measuring points (marginal, cervical, chamfer, axial, occlusal).

Results

The total gap results for fit and accuracy irrespective of manufacturing technique were 96 μm and 54 μm for single crowns, 107 μm and 54 μm for multi-unit FDPs, and 98 μm and 54 μm for both single crowns and multi-unit FDPs combined. For total gap of single crowns soft milling had the highest accuracy, for multi-unit FDPs additive manufactured restorations had the highest accuracy. With the results grouped by impression technique, the accuracy for total gap was highest for digital impressions and lower for conventional impressions.

Conclusions

Due to the inherent limitations of this systematic review, it still remains unclear what effect the manufacturing technique has on the fit of FDPs. However, the descriptive results suggest that the marginal fit of cobalt chromium FDPs is not negatively affected by the manufacturing technique.

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.

Accuracy of an intraoral digital impression: A review

Intraoral scanners (IOSs) are used for capturing the direct optical impressions in dentistry. The development of three-dimensional technology and the trend of increasing the use of IOSs in dental office routine lead to the need to assess the accuracy of intraoral digital impressions. The aim of this review was to assess the accuracy of the different IOS and the effect of different variables on the accuracy outcome. An electronic search using PubMed with specific keywords to obtain potential references for review. A search of MEDLINE (PubMed) identified 507 articles. After title and abstract screening, 412 articles were excluded for not meeting the inclusion criteria and discarding duplicate references. Ninety-five articles were followed for full screening; only 24 articles were included in the final analysis. The studies indicated a variable outcome of the different IOS systems. While the accuracy of IOS systems appears to be promising and comparable to conventional methods, they are still vulnerable to inaccuracies.

Trueness of CAD/CAM digitization with a desktop scanner - an in vitro study

BACKGROUND

Desktop scanners are devices for digitization of conventional impressions or gypsum casts by indirect Computer-Aided Design/Computer-Assisted Manufacturing (CAD/CAM) in dentistry. The purpose of this in vitro study was: 1, to investigate whether virtual models produced by the extraoral scanner have the same trueness as sectioned casts; and 2, to assess if digitization with an extraoral scanner influences the surface information.

METHODS

A polimethyl-methacrilic acid (PMMA) cast and a reference scanner (TwoCam 3D, SCAN technology A/S, Ringsted, Denmark; field of view 200 mm, resolution 0.1 mm ± 0.025 mm) were used to create the reference data in standard tessellation format (STL). According to the extraoral CAD/CAM digitization steps, impressions, mastercasts, and sectioned casts were made, and STL files were generated with the reference scanner. The pivotal point of the study was to digitalize these sectioned casts with the extraoral scanner (Straumann CARES Scan CS2 Visual 8.0 software, InstitutStraumann AG, Basel, Switzerland) and STL files were exported. Virtual caliper measurements were performed. Absolute deviations were compared using multilevel mixed-effects linear regression. Relative distortions were calculated with mean absolute errors and reference values.

RESULTS

Differences were observed in measurements of tooth sizes. All four prepared teeth were affected. No relationship was observed in relative deviations. Absolute differences between all the indirect digitization steps considering arch distances were: impressions, - 0.004 mm; mastercasts, 0.136 mm; sectioned casts, - 0.028 mm; and extraoral scanner, - 0.089 mm. Prepared dies on the virtual casts (extraoral scanner) were closer to each other than those on the sectioned gypsum casts. Relative deviation calculations revealed no relationship with the position of the dies in the arch.

CONCLUSION

The trueness of the virtual models generated by the extraoral scanner system used in this study was different from the dimensions of the sectioned casts. The digitization of gypsum casts changes both the dimensions of dies and the distances between the dies. The virtual casts had smaller distances than any distances measured at previous steps. Either bigger dies or longer distances did not result in greater distortions. We cannot, however, generalize our results to all scanners available on the market, because they might give different results.

Evaluation of marginal adaptation in three-unit frameworks fabricated with conventional and powder-free digital impression techniques

PURPOSE

The purpose of this in vitro study was to evaluate the marginal misfits of three-unit frameworks fabricated with conventional and digital impressions techniques.

MATERIALS AND METHODS

Thirty brass canine and second premolar abutment preparations were fabricated by using a computer numerical control machine and were randomly divided into 3 groups (n=10) as follows: conventional impression group (Group Ci), Cerec Omnicam (Group Cdi), and 3shape TRIOS-3 (Group Tdi) digital impression groups. The laser-sintered metal frameworks were designed and fabricated with conventional and digital impressions. The marginal adaptation was assessed with a stereomicroscope at ×30 magnification. The data were analyzed with 1-way analysis of variances (ANOVAs) and the independent simple t tests.

RESULTS

A statistically significant difference was found between the frameworks fabricated by conventional methods and those fabricated by digital impression methods. Multiple comparison results revealed that the frameworks in Group Ci (average, 98.8 ± 16.43 µm; canine, 93.59 ± 16.82 µm; premolar, 104.10 ± 15.02 µm) had larger marginal misfit values than those in Group Cdi (average, 63.78 ± 14.05 µm; canine, 62.73 ± 13.71 µm; premolar, 64.84 ± 15.06 µm) and Group Tdi (average, 65.14 ± 18.05 µm; canine, 70.64 ± 19.02 µm; premolar, 59.64 ± 16.10 µm) (P=.000 for average; P=.001 for canine; P<.001 for premolar). No statistical difference was found between the marginal misfits of canine and premolar abutment teeth within the same groups (P>.05).

CONCLUSION

The three-unit frameworks fabricated with digital impression techniques showed better marginal fit compared to conventional impression techniques. All marginal misfit values were clinically acceptable.

Variables affecting the fit of zirconia fixed partial dentures: A systematic review

STATEMENT OF PROBLEM

Different parameters affect the marginal and internal fit of zirconia fixed partial dentures (FPDs) on natural teeth. Determining a way to optimize these restorations is essential.

PURPOSE

The purpose of this systematic review was to determine the variables affecting the marginal fit and internal accuracy of zirconia FPDs on natural teeth.

MATERIAL AND METHODS

An electronic search was conducted by 2 independent reviewers by using the MEDLINE, Cochrane, Web of Science, and Scopus databases, as well as Google Scholar, for studies published up to July 2018, and a manual search was conducted from the reference lists of related articles. Eligibility criteria included articles in English published in peer-reviewed journals that assessed the marginal and/or internal adaptation of zirconia FPDs on teeth with 3 or more units, with at least 1 of the experimental groups being frameworks or FPDs fabricated from zirconia. Risk of bias was assessed with the aid of the Cochrane Handbook for Systematic Reviews of Interventions.

RESULTS

The search provided 418 records, with 41 fulfilling the inclusion criteria. The selected studies showed considerable heterogeneity regarding materials, state of sintering, manufacturer and computer-aided design and computer-aided manufacturing (CAD-CAM) system, experimental methodology, sample size, and span length. Of the included articles, 36 were in vitro studies and 5 were clinical studies, most of which exhibited high-performance and detection biases. CAD-CAM systems provided more precise marginal and internal fit than CAM systems. An increase of framework span length to 6 or more units decreased both marginal and internal fit. The reported marginal gap tended to increase after the veneering process. The introduction of a conventional impression into an otherwise digital workflow seems to have a negative effect on the marginal fit.

CONCLUSIONS

The accuracy of zirconia FPDs or frameworks is considerably influenced by the processing procedure used and the choice of CAD-CAM system.

Chairside measurement of the marginal and internal fit of crowns: a new intraoral scan-based approach

OBJECTIVES

To investigate the marginal and internal fit of crowns, a new intraoral scanner-based digital approach for chairside measurement (D-IOS) was systematically analysed and compared with the conventional silicone replica technique (CV-SR) and digital 3D analysis software (D-GOM).

MATERIALS AND METHODS

Two models, representing different clinical situations, were constructed, and the first molar was prepared for a full-coverage crown. On the basis of an intraoral scan (Trios 3), copings of three different materials (non-precious alloy, zirconium dioxide, and resin composite) with two different cement spaces (80 μm, 50 μm) were manufactured. The fit of the copings was investigated by all three methods (CV-SR, D-IOS, D-GOM). Therefore, the cement space was visualized with low-viscosity silicone and digitalized with a second intraoral scan. Evaluation of fit by the D-IOS-method was measured in the intraoral scanner software, whereas for analysis by D-GOM, both intraoral scan datasets were transferred to 3D analysis software (GOM Inspect). The CV-SR-method was used as a control group. For all copings, the measurements were repeated five times. The data were analysed with ANOVA.

RESULTS

No significant differences between the three evaluation methods and the coping materials were shown. However, in the occlusal area, the internal gap was significantly higher compared to the internal gap in the marginal and axial areas regardless of the cement space setting (p < .05). The target parameter of the cement spaces did not match the actual measured internal gaps.

CONCLUSIONS

All three evaluation methods and coping materials can be used for the measurement of fit within different clinical situations.

CLINICAL RELEVANCE

The digital chairside measurement implemented in the intraoral scanner software enables an easy, applicable evaluation of fit of crowns without additional laboratory devices or special software applications.

A clinical comparison of digital and conventional impression techniques regarding finish line locations and impression time

OBJECTIVE

This study compared digital and conventional impression techniques regarding impression time, frequency of adjustments, and adaptation of cobalt-chromium (Co-Cr) copings with supragingival and subgingival finish lines.

MATERIALS AND METHODS

Thirty premolars prepared for single-unit metal-ceramic restorations with supragingival and subgingival finish lines (n = 15). Conventional impression and digital scan of prepared teeth were made. Using computer aided design/computer aided manufacturing (CAD/CAM) system the copings were produced by a milling machine from Co-Cr blocks and internal and marginal discrepancies were measured using silicone replica technique. Data were analyzed using repeated measures ANOVA and Mann-Whitney test (alpha = .05).

RESULTS

The impression technique had a significant effect on the magnitude of gap (P < .001). The internal and marginal gaps in the digital technique (49.43 μ and 60.07 μ, respectively) were significantly lower than the values in the conventional method (91.88 μ and 96.96 μ, respectively-P < .001). Finish line positions had no significant effect on the fit and marginal gap of copings (P = .54 and .243, respectively). The mean impression time (19':27″ in conventional technique and 10':31″ in digital technique) was significantly shorter (P < .001) and the mean frequency of adjustments (2.2 times for conventional and 1.3 times for digital technique) was significantly lower in the digital technique (P < .001). The gingival biotype (thick or thin) had no significant effect on marginal and internal fit (P = .052 and .319, respectively).

CONCLUSION

The digital technique was superior in terms of fit, impression time, and frequency of adjustments. Finish line positions had no significant effect on the fit of copings.

CLINICAL SIGNIFICANCE

Using intraoral scanner promotes the fits of restorations in supragingival and subgingival finish lines.

Accuracy and practicality of intraoral scanner in dentistry: A literature review

PURPOSE

The digitization of the dental field has been vigorously promoted in recent years. An impression using an intraoral scanner is considered to significantly change future dental treatment. The purpose of this review is to evaluate accuracy and practicality of various intraoral scanners and verification method of intraoral scanners.

STUDY SELECTION

This review was based on articles searched through the MEDLINE and PubMed databases. The main keywords that were employed during the search were "Oral Scanner, Intraoral Scanners, Desktop Scanner, and Digital Impression".

RESULT

It was reported that illuminance and color temperature affected trueness and precision of intraoral scanners. The repeatability of intraoral scanners indicated the possibility of producing fixed prostheses within the range of being partially edentulous. It is considered difficult to use intraoral scanners in fabricating cross-arch fixed prostheses. However, with intraoral scanners, it may be considered possible to fabricate mouth guards and dentures equivalent to those of desktop scanners. Current intraoral scanner scans are considered more comfortable than traditional impressions that use irreversible hydrocolloid and elastomeric impression materials.

CONCLUSION

Since the intraoral scanner is an evolving device, further improvement in accuracy is expected in the future. In addition, verification of the accuracy of intraoral scanners must be conducted accordingly.

Intrasubject comparison of digital vs. conventional workflow for screw-retained single-implant crowns: Prosthodontic and patient-centered outcomes

OBJECTIVES

The aim of this intrasubject clinical study was to measure and compare prosthodontic and patient-reported outcome measures (PROMs) in the fabrication of implant-supported, all-ceramic single crowns with a full digital workflow and a conventional workflow.

MATERIALS AND METHODS

Thirty-one patients were subjected to first a digital (test group) and then a conventional impression (control group) at the same visit. From the intraoral optical scanner (IOS), a screw-retained, monolithic crown was delivered according to a complete digital workflow (no cast), whereas a veneered crown on a zirconia (Zi) frame was provided as a control treatment. Both crowns were assessed during the clinical stages of try-in. Prosthodontic outcomes (contact points, occlusion, PROMs, and esthetic results using the white esthetic score [WES]) were assessed.

RESULTS

Occlusion and interproximal contacts showed comparable results for the two workflows (p = 0.37 and p = 0.36, respectively), whereas the global WES was significantly higher (p < 0.0001) in the control group. Patient satisfaction scores, using visual analog scales (VAS), were significantly better for IOS than for conventional impressions (p = 0.0098). On the contrary, patients' perception of the esthetic outcomes showed significantly higher value (p < 0.0001) in the control group.

CONCLUSIONS

Both workflows allowed the delivery of ceramic crowns within two appointments. The clinical fit was acceptable in both groups. A better esthetic outcome, in both patients' and clinicians' opinions, was found in the control group. PROMs showed higher satisfaction with the IOS.

A Comparison Study of Marginal and Internal Fit Assessment Methods for Fixed Dental Prostheses

Numerous studies have previously evaluated the marginal and internal fit of fixed prostheses; however, few reports have performed an objective comparison of the various methods used for their assessment. The purpose of this study was to compare five marginal and internal fit assessment methods for fixed prostheses. A specially designed sample was used to measure the marginal and internal fit of the prosthesis according to the cross-sectional method (CSM), silicone replica technique (SRT), triple scan method (TSM), micro-computed tomography (MCT), and optical coherence tomography (OCT). The five methods showed significant differences in the four regions that were assessed (p < 0.001). The marginal, axial, angle, and occlusal regions showed low mean values: CSM (23.2 µm), TSM (56.3 µm), MCT (84.3 µm), and MCT (102.6 µm), respectively. The marginal fit for each method was in the range of 23.2-83.4 µm and internal fit (axial, angle, and occlusal) ranged from 44.8-95.9 µm, 84.3-128.6 µm, and 102.6-140.5 µm, respectively. The marginal and internal fit showed significant differences depending on the method. Even if the assessment values of the marginal and internal fit are found to be in the allowable clinical range, the differences in the values according to the method should be considered.

Comparison of marginal and internal fit of 3-unit zirconia frameworks fabricated with CAD-CAM technology using direct and indirect digital scans

STATEMENT OF PROBLEM

Accurate marginal and internal fit of dental restorations are essential for their long-term success. The fit of zirconia restorations prepared using digital scan systems has not been fully evaluated.

PURPOSE

The purpose of this in vitro study was to compare the marginal and internal fit of 3-unit zirconia frameworks fabricated using direct and indirect digital scans.

MATERIAL AND METHODS

In a maxillary model, the left first premolar and first molar were prepared to receive 3-unit zirconia fixed dental prostheses. Conventional impressions were made using stock trays and 2-step putty/wash polyvinyl siloxane material and were scanned using laboratory scanner (Conventional Impression-Laboratory scanner [CIL] group). The impressions were then poured, and the stone casts were scanned (Dental Cast-Laboratory scanner [DCL] group). Digital scans were made using TRIOS (TRIOS Intraoral scanner [TRI] group) and CS3600 (CS3600 Intraoral scanner [CSI] group) scanners (n=10). Zirconia copings were designed and milled from presintered blocks and subsequently sintered. Marginal, mid-axial, axio-occlusal, and mid-occlusal discrepancies were measured using the silicone replica technique with stereomicroscopy at ×50 magnification. The data were analyzed using 1-way ANOVA (α=.01).

RESULTS

The ANOVA revealed significant differences among the studied groups in terms of all studied characteristics (P≤.01). Marginal gap was significantly higher in the DCL group (106 ±45 μm) compared with all other groups (P≤.01). However, no significant differences were observed in marginal gap between the TRI (60 ±15 μm) and CSI (55 ±13 μm) groups (P>.01). Internal gap in the mid-occlusal and axio-occlusal regions were significantly higher in the CIL (238 ±92 μm and 227 ±95 μm) and DCL (248 ±71 μm and 216 ±68 μm) groups than those recorded in the TRI (104 ±27 μm and 126 ±31 μm) and CSI (128 ±16 μm and 147 ±28 μm) groups (P≤.01). Internal discrepancies in the mid-axial position were similar between the TRI (70 ±15 μm) and CSI (72 ±23 μm) groups (P>.01), but these values were significantly lower than those recorded in the CIL (88 ±31 μm) and DCL (85 ±30 μm) groups (P≤.01).

CONCLUSIONS

Within the limitations of this study, zirconia frameworks in the TRI and CSI groups had lower marginal and internal gaps compared with those in the DCL and CIL groups. Marginal gap in all groups was within a clinically acceptable range.

Can lithium disilicate ceramic crowns be fabricated on the basis of CBCT data?

OBJECTIVES

Evaluating the fit of CAD/CAM lithium disilicate ceramic crowns fabricated on basis of direct and indirect digitalization of impressions by CBCT or of dental casts.

MATERIAL AND METHODS

A metal model with a molar chamfer preparation was digitized (n = 12 per group) in four ways: IOS-direct digitalization using an Intra-Oral scanner (CS3600), cone-beam computed tomography scan (CBCT 1)-indirect digitalization of impression (CBCT-CS9300), CBCT 2-indirect digitalization of impression (CBCT-CS8100), and Extra-Oral scanner (EOS)-indirect digitalization of gypsum-cast (CeramillMap400). Accuracy of 3D datasets was evaluated in relation to a reference dataset by best-fit superimposition. Marginal fit of lithium disilicate crowns after grinding was evaluated by replica technique. Significant differences were detected for 3D accuracy by Mann-Whitney U and for fit of crowns by One-way ANOVA followed by Scheffe's post hoc (p = 0.05).

RESULTS

3D analysis revealed mean positive and negative deviations for the groups IOS (- 0.011 ± 0.007 mm/0.010 ± 0.003 mm), CBCT 1 (- 0.046 ± 0.008 mm/0.093 ± 0.004 mm), CBCT 2 (- 0.049 ± 0.030 mm/0.072 ± 0.015 mm), and EOS (- 0.023 ± 0.007 mm/0.028 ± 0.007 mm). Marginal fit presented the results IOS (0.056 ± 0.022 mm), CBCT 1 (0.096 ± 0.034 mm), CBCT 2 (0.068 ± 0,026 mm), and EOS (0.051 ± 0.017 mm).

CONCLUSIONS

The marginal fit of EOS and IOS, IOS and CBCT 2, and CBCT 2 and CBCT 1 showed statistical differences. The marginal fit of CBCT 1 and CBCT 2 is within the range of clinical acceptance; however, it is significant inferior to EOS and IOS.

CLINICAL RELEVANCE

The use of a CBCT enables clinicians to digitize conventional impressions. Despite presenting results within clinical acceptable levels, the CBCT base method seems to be inferior to Intra-Oral scans or to scanning gypsum models regarding the resulting accuracy and fit.

Impression of Subgingival Dental Preparation Can Be Taken with Ultrasound

Because of its ability to capture hard structures behind soft tissue, ultrasound-based micro-scanning may be a promising alternative for taking digital impressions of teeth, especially in the case of subgingival margin preparations. The aim of this study was to assess the accuracy of ultrasound impressions taken of subgingivally prepared teeth compared with digital optical impressions. Ten extracted human teeth (7 pre-molars, 3 molars) were prepared for crowns with chamfer finish line and then digitized using two different intra-oral scanners (Cara Trios, 3 Shape, Heraeus Kulzer, Hanau, Germany; and Lava COS; 3M ESPE, Seefeld, Germany) and one extra-oral scanner (Cares CS2, Straumann, Basel, Switzerland). Afterward, the preparation margin was covered with porcine gingiva (thickness ranged between 0.3 and 0.9 mm), and every sample was scanned with a high-frequency ultrasound scanner under experimental subgingival conditions. Optical scanning processes were performed without gingiva. The data sets were superimposed on each other for pairwise comparisons, and deviations between different scans were determined using a 3-D evaluation software (CloudCompare). Kruskal-Wallis and post hoc tests (Dunn-Bonferroni) were applied to detect significant differences at p ≤ 0.05. The ultrasound scanner was able to detect subgingival preparation margins. Mean deviations for all comparisons ranged from 12.34 to 46.38 µm. There were no statistically significant differences between superimpositions of intra-oral and extra-oral scans (Trios-Lava, Lava-CS2, Trios-CS2), whereas in comparisons between intra-/extra-oral scans and ultrasound scans, mean deviations were statistically significantly higher. There were no significant differences with respect to type of tooth (pre-molar and molar). However, gingiva thickness was significantly correlated with the quality of the ultrasound scan; thin layers had better image quality than thicker layers. Ultrasound was able to scan tooth preparation margins covered with gingiva, although with less accuracy than achieved by conventional optical scanners (non-covered margins). Gingiva thickness may play an important role in ultrasound scan accuracy.

Accuracy of single crowns fabricated from ultrasound digital impressions

OBJECTIVE

This in vitro study aimed to evaluate marginal and internal fit of single crowns produced from high-frequency ultrasound based digital impressions of teeth prepared with finish lines covered by porcine gingiva, in comparison with those obtained by optical scanners with uncovered finish lines.

METHODS

Ten human teeth were prepared and forty zirconia crowns were fabricated from STL-datasets obtained from four dental scanners (n=10): extraoral CS2 (Straumann), intraoral Lava COS (3M), intraoral Trios (3Shape) and extraoral ultrasound scanner. The accuracy of the crowns was compared evaluating marginal and internal fit by means of the replica technique with measurements in four areas; P1: occlusal surface; P2: transition between occlusal and axial surfaces; P3: middle of axial wall; and P4: marginal gap. Restoration margins were classified according to their mismatch as regular, underextended or overextended. Kruskal-Wallis one-way ANOVA and Mann-Whitney U test were used to evaluate the differences between groups at p<0.05.

RESULTS

The median value of marginal gap (P4) for Ultrasound (113.87μm) differed statistically from that of CS2 (39.74μm), Lava COS (41.98μm) and Trios (42.07μm). There were no statistical differences between ultrasound and Lava COS for internal misfit (P1-P3), however there were statistical differences when compared with the other two scanners (Trios and CS2) at P1 and P2.

SIGNIFICANCE

The ultrasound scanner was able to make digital impressions of prepared teeth through porcine gingiva (P4), however with less accuracy of fit than that of conventional optical scanners without coverage of the finish lines. Where no gingiva was available (P1-P3), the ultrasound accuracy of fit was similar to that of at least one optical scanner (Lava COS).

Comparison of the marginal fit of milled yttrium stabilized zirconium dioxide crowns obtained by scanning silicone impressions and by scanning stone replicas

PURPOSE

To determine the discrepancy in monolithic zirconium dioxide crowns made with computer-aided design and computer-aided manufacturing (CAD/CAM) systems by comparing scans of silicone impressions and of master casts.

MATERIALS AND METHODS

From a Cr-Co master die of a first upper left molar, 30 silicone impressions were taken. The 30 silicone impressions were scanned with the laboratory scanner, thus obtaining 30 milled monolithic yttrium stabilized zirconium dioxide (YSZD) crowns (the silicone group). They were poured and the working models were scanned, obtaining 30 milled monolithic yttrium stabilized zirconium dioxide (YSZD) crowns (the plaster group). Three predetermined points were analyzed in each side of the crown (Mesial, Distal ,Vestibular and Palatal), and the marginal fit was evaluated with SEM (×600). The response variable is the discrepancy from the master model. A repeated measures ANOVA with two within subject factors was performed to study significance of main factors and interaction.

RESULTS

Mean marginal discrepancy was 22.42±35.65 µm in the silicone group and 8.94±14.69 µm in the plaster group. The statistical analysis showed significant differences between the two groups and also among the four aspects. Interaction was also significant (P=.02).

CONCLUSION

The mean marginal fit values of the two groups were within the clinically acceptable values. Significant differences were found between the groups according to the aspects studied. Various factors influenced the accuracy of digitizing, such as the design, the geometry, and the preparation guidance, as well as the texture, roughness and the color of the scanned material.