Master Model Research Articles

Fracture load of 4-unit interim fixed partial dentures using 3D-printed and traditionally manufactured materials

Statement of problemHow the fracture strength of recently introduced 3-dimensionally (3D) printed interim materials compares with that of conventional materials is unclear. PurposeThe purpose of this in vitro study was to compare the fracture load of 4-unit interim fixed partial dentures made from 3 different materials before and after mastication simulation. Material and methodsBased on a master model of a 4-unit fixed partial denture with maxillary left first premolar and second molar abutment teeth, interim restorations were fabricated from 3 different materials (3D-printed, Temporary CB Resin, milled, PMMA for brain, and manually manufactured, Luxatemp Plus). The fixed partial dentures (n=30 for each material) were cemented on 3D-printed model abutment teeth that were connected via a thin latex layer to a polyurethane base block. The fracture load of 15 fixed partial dentures of each material was tested without aging. Another 15 fixed partial dentures of each material were tested after thermomechanical aging. ResultsThe mean fracture load was between 186 N and 661 N, and all materials showed significant lower fracture loads after aging. Before and after aging (before/after ±standard deviation) milled (661 ±59/568 ±52 N) achieved the highest loads before manually manufactured (621 ±100/478 ±96 N) and 3D-printed (294 ±83/186 ±70). ConclusionsThe 3D-printed interim restoration material and the inherent manufacturing process show significant lower fracture loads than the tested alternatives. However, as the influence of geometric differences could not be quantified, whether this remains true after correcting for geometric differences remains unclear. For the tested interim materials, thermocycling and mastication simulation significantly reduced fracture loads over time, even at loads as low as 50 N.

Comparison of the Accuracy of Two Transfer Caps in Positional Transmission of Palatal Temporary Anchorage Devices: An In Vitro Study.

The aim of this study was to compare the positional information transfer accuracy of palatal temporary anchorage devices (TADs) of two different brands of transfer caps: PSM and Leone. Thirty plaster casts of maxillary dental arches were chosen for master models. A couple of Leone TADs were inserted in each master model. For each master model, two analysis models were created: using two transfer caps, Leone and PSM, the impressions were taken, the analogues were connected on the transfer caps, and the casts were poured. Using digital methods and equipment, such as a 3D scanner, a 3D analysis and a comparison of the accuracy of the two transfer caps in transferring the positional information of the TADs was then made. The data obtained were analyzed using the Mann-Whitney U-test at a significance level of α = 0.05. PSM transfer caps showed higher error frequency in almost all measurements. Only two measurements had a larger error in the analysis models made with Leone transfer caps. The Mann-Whitney U-test found a significant difference between the error levels of TADs found in the analysis models created with PSM transfer caps. Leone transfer caps showed greater reliability in TADs positional information transmission.

Graphene-Doped Polymethyl Methacrylate (PMMA) as a New Restorative Material in Implant-Prosthetics: In Vitro Analysis of Resistance to Mechanical Fatigue

Provisional prostheses in restorations over several implants with immediate loading in completely edentulous patients increase the risk of frequent structural fractures. An analysis was performed of the resistance to fracture of prosthetic structures with cantilevers using graphene-doped polymethyl methacrylate (PMMA) resins and CAD-CAM technology. A master model was produced with four implants measuring 4 mm in diameter and spaced 3 mm apart, over which 44 specimens representing three-unit fixed partial prostheses with a cantilever measuring 11 mm were placed. These structures were cemented over titanium abutments using dual cure resin cement. Twenty-two of the 44 units were manufactured from machined PMMA discs, and 22 were manufactured from PMMA doped with graphene oxide nanoparticles (PMMA-G). All of the samples were tested in a chewing simulator with a load of 80 N until fracture or 240,000 load applications. The mean number of load applications required for temporary restoration until the fracture was 155,455 in the PMMA-G group versus 51,136 in the PMMA group. Resistance to fracture under cyclic loading was three times greater in the PMMA-G group than in the PMMA group.

Comparison of 3D positional accuracy of implant analogs in printed resin models versus conventional stone casts: Effect of implant angulation.

To study the effect of implant angulation on 3D linear and absolute angular distortions of implant analogs in printed resin models and conventional stone casts. Three sectional master models with two implants with total inter-implant angulations of 0°, 10°, and 20° were fabricated. For each master model, five conventional stone casts (CS) and printed resin models (PM) were fabricated (n=5). Test models were made with nonsplinted impression copings and open tray polyether impressions for the CS groups and scan bodies scanned using an intraoral scanner for the PM groups. The physical positions of the implants and implant analogs were measured with a coordinate measuring machine. 3D linear distortion (ΔR) and absolute angular distortion (Absdθ) defined the 3D positional accuracy of the analogs in the test models. Univariate ANOVA was used to analyze data followed by post hoc tests (Tukey HSD, α=0.05). Mean ΔR was significantly greater for PM10 (73.5±8.9µm) and PM20 (65.5±33.3µm) compared to CS0 (16.8±14.1µm), CS10 (22.2±13.0µm), CS20 (15.6±19.9µm), and PM0 (23.9±16.1µm). For Absdθ, there were no significant differences between test groups. With conventional stone casts, implant angulation had no significant effect on 3D linear and absolute angular distortions. Amongst printed resin models test groups, angulated implants had significantly greater ΔR. Amongst angulated implants test groups, printed resin models had significantly greater ΔR than conventional stone casts. Compared to the master model, all test groups, regardless of inter-implant angulation, produced greater inter-analog distances.

The Effect of Master Model To Students Understanding of Mathematical Concepts

Understanding of mathematical concepts is one of the abilities that must be possessed by students, because it’s the basic to achieve the aims of further mathematics learning. However, the fact is that the understanding of mathematical concepts of grade 8 students of Junior High School 1 2x11 Enam Lingkung is still low, so it needs to be improved. The learning is still teacher-centered in the classroom with the result that the students were not able to construct their knowledge. One of the learning models that can support students to actively construct their knowledge is MASTER learning model. This kind of research is both descriptive and quasi experiment, with Static Group Design. Based on the results of data analysis it can be concluded as follows: the first is the activites of students who learn with MASTER learning model is better than those who learn with conventional learning. The second is obtained P- values = 0.024 < α = 0.05, so that understanding the mathematical concepts of students who learn with MASTER learning model is better than those who learn with conventional learning.

Accuracy of digital impressions for implant-supported complete-arch prosthesis when using an auxiliary geometry device

Background/purposeDigital impressions using intraoral scanners have recently gained popularity. The aim of the present study was to evaluate the fit of full-arch screw-retained cobalt-chromium frameworks fabricated via two different digital impression methods. Materials and methodsAn edentulous resin master model with four dental implants was fabricated. Forty cobalt-chromium superstructures were fabricated and evaluated according to four groups. In Group 1, the superstructures were evaluated using an intraoral scanner to generate digital impressions. Group 2 relied on the help of an auxiliary geometric appliance in generation of digital impressions via intraoral scanner. The traditional method of splinted open-tray conventional impressions was designated for Group 3. Finally, the control group (Group 4) relied on scanning of the master model directly with a laboratory scanner. Vertical marginal discrepancy was evaluated, and data obtained were statistically analyzed. ResultsThe highest mean vertical marginal gap value (80.86 ± 50.06 μm) was observed for Group 1 and statistically higher than Group 2, 3, and 4 (P < 0.05). The lowest mean vertical marginal gap value (41.98 ± 26.33 μm) was measured from Group 4 and statistically similar to Group 2 and 3 (P > 0.05). ConclusionIt has been suggested that the use of auxiliary geometric appliances yields increased scanning accuracy. Frameworks fabricated using the traditional splinted open-tray technique were more reliable compared to those frameworks from digital impressions.

Marginal and internal fit of five-unit zirconia fixed dental prostheses fabricated with digital scans and conventional impressions: A comparative in vitro study.

This study aimed to compare the marginal and internal fit of five-unit zirconia fixed dental prostheses fabricated using digital scans and conventional impressions. Nine master models with three zirconia abutments were scanned with an intraoral scanner (test group), and nine conventional impressions (control group) of these same models were also made. The stone casts from theses impressions were scanned with a laboratory extraoral scanner (D700, 3Shape, Copenhagen, Denmark). A total of 18 five-unit zirconia fixed dental prostheses frameworks (test group, n = 9; control group, n = 9) were manufactured. Marginal and internal fit (in μm) were evaluated using the replica method under micro-computed tomography. Analysis of variance (one-way ANOVA) and Kruskal Wallis tests were used to compare continuous variables across two groups. A level of P <0.05 was accepted as statistically significant. The mean ±standard deviation of the marginal fit was 95.03 ±12.74 μm in the test group and 106.02 ±14.51 μm in the control group. The lowest marginal mean value was observed in the test group, with a statistically significant difference comparing to the control group (F = 14. 56, P <0.05). The mean ±standard deviation of the internal fit was 103.61 ±9.32 μm and 106.38 ±7.64 μm, respectively, in the test and control groups, with no statistically significant difference (F = 1.56, P >0.05). The mean values of both groups were clinically acceptable. The five-unit zirconia fixed dental prostheses fabricated with digital scans showed better fit than conventional impressions group. Within the limitations of this study, these results are encouraging and continued progress in the digital field should allow for more accurate long-span restorations. This article is protected by copyright. All rights reserved.

Fit analysis of stereolithography-manufactured three-unit resin prosthesis with different 3D-printing build orientations and layer thicknesses

Statement of problemPrinting conditions can affect the fit of a 3-dimensionally (3D) printed prosthesis. Therefore, it is important to determine the optimal printing conditions for stereolithography (SLA)-manufactured prostheses. PurposeThe purpose of this study was to analyze the fit according to the build orientations and layer thicknesses in SLA-manufactured 3-unit resin prostheses. Material and methodsSLA 3D printed prostheses were produced in 5 build orientations (0, 30, 45, 60, and 90 degrees) and 2 layer thicknesses (50 and 100 μm). Milled prostheses were fabricated from the same design. The mounted prostheses on the master model were scanned with microcomputed tomography (μCT). Data were processed with the NRecon software program. For quantitative analysis, marginal and internal fits were measured by using the imageJ software program in terms of the following metrics: absolute marginal discrepancy, marginal gap, cervical area, midaxial wall area, line-angle area, and occlusal area. Internal gap volume was also measured with the CTAn software program. For statistical analysis, ANOVA and Tukey HSD tests were used (α=.05). For qualitative analysis, μCT cross-sections were compared among groups, and intaglio surfaces were imaged with a scanning electron microscope. ResultsA layer thickness of 50 μm with build orientations of 45 and 60 degrees exhibited smaller mean gap values (P<.05) than the other conditions for all measurements except line-angle area and occlusal area. The scanning electron microscope images showed voids on the intaglio surfaces for the 0- and 90-degree groups. ConclusionsFor SLA 3D printed resin prostheses, a difference in fit occurred based on the printing conditions, although both 3D printed and milled prostheses showed a clinically acceptable fit. When an SLA 3D printed prosthesis is manufactured under appropriate conditions, a clinically acceptable fit can be obtained.

In Vitro Trueness and Precision of Intraoral Scanners in a Four-Implant Complete-Arch Model

(1) Background: New intraoral (IOS) and laboratory scanners appear in the market and their trueness and precision have not been compared. (2) Methods: Seven IOS and two laboratory scanners were used to scan a mandibular edentulous model with four parallel internal hexagon implant analogues and PEEK scan bodies. Digital models in Standard Tessellation Language (STL) were created. The master model with the scan bodies was scanned (×10) with a computerized numerical control 3D Coordinate Measuring Machine (CMM). The short (distances of adjacent scan posts) and long distances (distances of the scan posts with non-adjacent sites in the arch) among the centroids of the four analogues were calculated using CMM special software. Trueness (comparisons with the master model) and precision (intragroup comparisons) were statistically compared with ANOVA, chi-square and Tukey tests. (3) Results: Laboratory scanners had the best trueness and precision compared to all IOSs for long distances. Only iTero (Align Technologies Inc., Milpitas, CA, USA) had comparable trueness with one laboratory scanner in short and long distances. For short distances, CS3600 (Carestream Health, Inc., Rochester, NY, USA), Omnicam, Primescan (Sirona Dental Sys-tems GmbH, Bens-heim, Germany) and TRIOS 4 (3Shape A/S, Copen-hagen, Denmark) had similar trueness to one laboratory scanner. From those, only Omnicam and Primescan had similar precision as the same laboratory scanner. Most IOSs seem to work better for smaller distances and are less precise in cross-arch distances. (4) Conclusions: The laboratory scanners showed significantly higher trueness and precision than all IOSs tested for the long-distance group; for the short distance, some IOSs were not different in trueness and precision than the laboratory scanners.

The influence of 3D-printing technological conditions on the performance properties of master models

The influence of 3D-printing technological conditions on the performance properties of master models has been investigated. It is shown that strength properties of master models depend significantly on two parameters: layer thickness and percentage of filling. Recommendations onthe choice of 3D-printing conditions for manufacturing master models, as well as products based on master models, are presented.

Intelligent Print Circuit Board Defect Detection

During the manufacturing process of electronic products, one of the most critical stages is the soldering of components onto the printed circuit board (PCB). Even a minor defect in the PCB can lead to significant issues in the final product. Therefore, a rigorous\ndefect inspection process is employed during manufacturing, which can be categorized into manual inspection and automated optical inspection (AOI). Manual inspection suffers from drawbacks such as slow speed and the expenditure of manpower and costs. Hence, most manufacturers opt for automated optical inspection to expedite production. However, most current automated optical inspection systems rely on traditional optical inspection algorithms. These computational methods are susceptible to variations in lighting conditions caused by slight differences in the placement of PCBs or the amount of solder. Consequently, these variations often result in misjudgments, where qualified PCBs are mistakenly categorized as defective, leading to high false positive rates in AOI systems.\nThis paper presents a deep learning based method for PCB defect detection. The proposed approach involves the creation of two separate models for classifying defective components individually. Once both models demonstrate a basic recognition capability, they are combined into a master model using the method proposed in this study to enhance overall recognition accuracy. The model has\nbeen trained on datasets for capacitors and resistors, and the experimental results indicate an accuracy of over 99% for both component types.

Alteração dimensional linear de modelos edêntulos fabricados com silicones laboratoriais de alta densidade em diferentes tempos de armazenagem

ABSTRACT Objective: To evaluate the dimensional change of edentulous models made of high density laboratory silicones at different storagetimes. Methods: A metallic master model simulating an edentulous maxilla was used. The model had projections of 1.8 cm located in the regions of canines (A and B) and molars (C and D) allowing the linear measurement of distances AB, BC, CD, DA, AC and BD. A laboratory silicone mold was made for duplication of master model in the following materials (n = 10): G1: Zetalabor 85, G2: Titanium 95, G3: Platinum 95 and G4: Gypsum type III (control). The samples were photographed and measured using a software (Image J) at times T1 (baseline) and T2 (after one week of models fabrication). The data were statistically analyzed using Kruskal- Wallis and Dun non-parametric tests (α = 0.05). Results: The storage time influenced the behavior of the materials evaluated. All groups presented dimensional changes in both times and the group Tit95 presented the best results. Only Zet85 group showed a different behavior related to the region of the model. Conclusions: The high density laboratory silicones showed satisfactory results when compared to the gypsum group. Tit95 was the most stable material and it can be recommended as an edentulous model for total protheses.

Application of additive technologies for master model creating at porcelain ware production

The article considers the prospects of application of additive technologies in porcelain production by the example of creating a master model of a porcelain coffee pot. The results of printing a master model of the product obtained using a 3D printer with FDM printing technology are analyzed. The possible defects of 3D-printing that may occur during modelling and printing of models with complex configuration and fine plasticity are considered.

ГЛИНЯНЫЕ ПРЯСЛА ТЕТЮШСКОГО-II ГОРОДИЩА ИМЕНЬКОВСКОЙ КУЛЬТУРЫ И ИХ АРХЕОЛОГИЧЕСКИЙ КОНТЕКСТ

The article deals with clay spindle whorls, special weights for spindles, necessary for spinning threads from various materials — wool, vegetable fibers (nettle, flax). They were found at the Tetyushy-II hillfort of the Imenkovo culture, in the Republic of Tatarstan. The hillfort was studied by K.A. Rudenko in 2007–2013. It differs from many other sites of the Imenkovo culture in its clear stratigraphy with dated layers. A total of 186 spindle whorls were found. This is currently one of the most representative collections of these artifacts from archaeological excavations at the settlements of the Imenkovo culture in the Kazan Volga region. According to the complex of features, 6 types of spindle whorls were distinguished. The typology is based on the shape of the product. Three types of these products, the shape of which is truncated-biconical, are the most common in the Imenkovo settlements. They differ in their sizes: small (diameter up to 2.6 cm), medium (diameter up to 3.5 cm) and large (diameter up to 5 cm). The objectivity of such a grouping is also confirmed by the weight parameters of these sections: small — up to 7 g, medium — up to 11 g, and large — up to 25 g. The dependence of the weight of the spindle whorls on the diameter of the channel through which it was put on the spindle whorls was revealed. At Tetyushy-II fortified hillfort, fragments of spindle whorls make up 33.8% of their total number and most often they are found in the lower horizon of the III — upper horizon of the IV layer, which were formed at the end of the 6th — the first half of the 7th century. There are few spindle whorls decorated with ornaments — 16% of the total. The most frequently decorated with ornaments (dots, crests, etc.) were medium-sized spindle whorls. Based on the materials of the Tetyushy-II hillfort and finds from the Imenkovo settlements located in the lower reaches of the Kama: Shcherbet’-I (island), the settlement, the settlements of “Kurgan” and “Devichiy Gorodok” and a number of others in the amount of 375 copies, methods for making Imenkovo spindle whorls. These products were made in 4 ways: from a blank in the form of a finished product; from a cylindrical billet with further sculptural refinement; from a ring blank with sculptural refinement; of three bundles, by winding onto a rod. For the first method, master models were probably used. Clay with an admixture of sand, sometimes fine chamotte and organic matter, and in some cases crushed shells of river mollusk shells was used for the manufacture of spindle whorls. It was found that in most cases the spinners were associated with buildings and were used in household crafts (spinning). Since the weight of the spindle whorls is small, then, apparently, several of them were put on the spindle, depending on the raw material for spinning. Thus, according to the materials of the Tetyushy-II hillfort, the systematization of the Imenkovo culture was carried out, for the first time methods of manufacturing were identified, the most characteristic types of these products for the 6th–7th centuries in the Kazan Volga region were determined.

Comparison of accuracy of hexed and nonhexed pickup impression copings in a multiple variable impression setup for recording multiple straight and angulated implant positions: An in vitro study.

The aim of this study was to evaluate and compare the accuracy of hexed and nonhexed pickup impression copings with and without splinting using polyether (PE) and polyvinyl siloxane (PVS) impression materials in open-tray technique in recording multiple straight and angulated implant positions. An accurate impression results in an accurate definitive cast, thus minimizing the incidence of prosthesis misfit. The critical aspect is to record the three-dimensional location of the implant in bone rather than reproducing fine surface details. Precise fit of a fixed implant-supported prosthesis depends on the accuracy of the implant analog location within the definitive cast. Factors which affect impression accuracy include implant angulation, impression material, impression copings, technique, and splinting. A sample size of 80 study models fabricated from the impression of different groups was included. A reference master model based on All-on-4 implant concept with two parallel (implants 1 and 2) and two angulated (implant 3 at 17° and implant 4 at 30°) was fabricated using implant angulation guide. All impressions were recorded using open-tray impression technique. The groups were divided into two main groups of 40 samples each. Group A used hexed open-tray impression copings and Group B used nonhexed open-tray impression copings. Both the groups involved impression recording using splinted (Subgroup I) and nonsplinted impression copings (Subgroup II). Further, impressions in each subgroup were made using PE (Subsubgroups a) and PVS (Subsubgroup b). A total of eight subsubgroups with ten samples each were included. Impressions were recorded for each group and poured into Type IV die stone for fabrication of study models. After 24 h, the study models and reference master model were fitted with implant abutments for measurement with coordinate measuring machine. The mean differences of the interimplant distance R1 (1-2), R2 (1-3), R3 (2-4), and R4 (3-4) between the reference model and sample models in different subsubgroups were calculated and three-way analysis of variance test was applied with Tukey's post hoc tests. No significant difference was found in mean coronal deviations for distance R1, R2, and R3 (P > 0.05) between different study groups. P = 0.02 for R4 (distance between 17° and 30° implants) between impression materials subsubgroups suggested that significantly less distortion was created in location of highly angulated implants (>30°) using PVS impression material. Splinting and type of coping did not have a significant influence on impression accuracy. Increasing angulation decreased the accuracy. PVS was found equivalent in accuracy to rigid PE for recording parallel or angulated implants. Impressions of implants with higher angulations were recorded more accurately with PVS. The study found no difference in accuracy with or without splinting. Furthermore, nonhexed impression copings facilitate easier and accurate recording of multiple angulated implant location in bone.

Use of scanning electron microscope to evaluate the marginal fit of protocol bars obtained through benchtop or intraoral digital scanners

Aim: To evaluate the marginal fit of protocol bars milled from digital models obtained by conventional molding followed by bench scanning or digital molding with an intraoral scanner. Methods: Four morse-cone implants and the mini-pillars were installed in a 3D printed mandible model (master model). Digital models of the master model were obtained by (n=10): (Group A - Conventional) conventional (analog) molding of the master model followed by bench scanning or (Group B - Digital) molding of the master model with an intraoral scanner. All-on-four protocol bars were designed and milled from the digital models for both groups and screwed into the master model. Scanning electron microscopy (SEM) images from the distal, central, and mesial regions of each implant were obtained and the implant-protocol bar marginal fit was measured in an image software (Image J). The mean misfit of each region was analyzed by two-factor ANOVA, Tukey test, and Student’s t-test (0,05 = 0.05). Results: The digital approach (B) showed higher misadaptation than the conventional approach (A, p &lt; 0.05), regardless of the region evaluated. In group A, the central region showed higher maladjustment than the mesial region (p&lt;0.05), however, there were no differences among regions of group B (p&gt;0.05). Conclusion: The conventional method of acquiring digital models using the bench scanner produced bars for the All-On-Four protocol with better marginal fit than the digital models obtained with an intraoral scanner.

Trueness and Precision of Eight Intraoral Scanners with Different Finishing Line Designs: A Comparative In Vitro Study.

This study aimed to evaluate the accuracy in terms of trueness and precision of eight intraoral scanners (IOS) and the effect of different finishing line designs on the IOS's accuracy. Three printed models of the maxillary arch with maxillary right first molar virtually prepared with chamfer, shoulder, and vertical preparation designs were used as master models in this study. Each model was scanned 30 times with each IOS: Medit i700, Planscan Emerald S, CEREC Primescan, TRIOS 3, CS3600, MEDIT i500, Heron 3Disc, and Cerec Omnicam. The trueness was measured by superimposition of the scanned dataset made with IOS and the scanned dataset made with a lab scanner (In Lab Medit T710) that was used as a reference and the deviation was measured and expressed as a color-coded map by the metrology program (Medit compare, version 2.3.5.892), while precision was measured by the superimposition of the scans of each IOS on each other.The data were analyzed statistically using repeated measure analysis of variance (ANOVA) test, one-way ANOVA test, and Bonferroni test at significance level of 0.05. The tested IOS showed significant differences in trueness and precision. Medit i700 and CEREC Primescan recorded the highest precision with no significant difference between them, while Medit i700 recorded the highest trueness as compared to other IOS. Each IOS showed significant differences in trueness and precision with the three finishing line designs except CEREC Primescan and Heron 3 disc that showed no significant difference in trueness with the three finishing line designs and CS3600 that showed no significant difference in precision with the three finishing line designs. A significant difference in accuracy was found among the tested IOS and the type of finishing line design had a significant effect on IOS's accuracy.

Application of 3D Printing Technologies for the Manufacture of Master Models in Mechanical Engineering

Application of 3D Printing Technologies for the Manufacture of Master Models in Mechanical Engineering

Comparison of the accuracy of resin-composite crowns fabricated by three-dimensional printing and milling methods.

This study aimed to compare the dimensional accuracies of three-dimensional (3D)-printed and milled resin-composite crowns, and to determine acceptable abutment-tooth shapes for printing. Four first-molar abutment models were prepared: the master model form and three models with sharp occluso-axial line angles. Crowns were designed on each abutment using computer-aided design software. The drill-offset value was set at 0.0 or 0.5 mm to evaluate the effect on the dimensional accuracy of milling. A digital light processing-based 3D printer was used to fabricate 3D-printed crowns. Milled crowns were fabricated by wet-milling. The trueness was evaluated by superimposing the design data. Regardless of the abutment form, 3D-printed crowns showed higher accuracy with fewer marginal discrepancies than milled crowns. Milled crowns showed significant dimensional deviations, especially at cusps. Moreover, offset correction resulted in grooves on the internal surface of milled crowns with negative deviations, which were especially evident in crowns for the sharp models.

Comparison of Digital and Conventional Impressions Based on the 3D Fit of Crowns.

To evaluate intraoral scanners, scannable impression materials, and conventional methods for impression-taking with regard to precision and accuracy. Ten impressions per technique were initially taken from a cobalt-chromium (Co-Cr) master model (chamfer preparation for the maxillary right first molar) for fabricating Co-Cr crown copings. The test specimens, their respective metal master model, and the plaster casts from the conventional impressions were then digitized with the light-optical Atos Triple Scanner. The fit of the dental crown copings was measured in two and three dimensions using computer-aided design software. Global differences between the methods were determined using Kruskal-Wallis test, and pairwise comparisons were performed with Mann-Whitney U test. The significance level was set at .05. The 2D analysis showed that the average absolute marginal distance of the crown copings was 0.026 mm when fabricated with the digital impression method and 0.038 mm when fabricated with the conventional method (P = .028). However, the 3D analysis revealed that the conventional group had a smaller marginal gap (0.028 mm) compared to the digital group (0.06 mm; P = .015). This study showed that, in the field of single-crown prosthetics, digital impressions and the use of scannable impression material could serve as alternatives to conventional methods in the future.