Accuracy of printed models obtained from intraoral scanning

Objectives: To compare the accuracy of two methods for the manufacturing of physical models: I) intraoral scanning and resin-printed models; and II) addition silicone impression and gypsum model. Materials and methods: A dental manikin was used as the master model and compared with five gypsum models (g1) and five resin printed models (g2) by analyzing linear measurements at four sites (M1, M2, M3, and M4) using an image measuring instrument. The mean values of the experimental models were compared to those of the master model using one-sample t-test. The samples of each group at the same site were compared with an independent t-test. For all tests, a significance level of 5% (0.05) was considered. Results: The confidence intervals from M1, M2, and M4 sites for both gypsum and resin models presented statistically lower linear distance when compared to the reference values. At m3, the mean value for the gypsum models was not statistically different from the reference mean value (p > 0.05); however, resin-printed models presented a statistically different mean value (p < 0.05), as well as lower values of linear distance. Conclusions: When compared to gypsum models, resin- printed models differed greatly from the master model, indicating the need for standardizing the printing protocol, for its variables may influence printed models accuracy.

Influence investigation of technological conditions of 3D-printing on antiadhesion properties of master-model surfaces

It is shown that one of the promising methods to prepare a master-model for the casting production of engineering industry products is FDM 3D-printing. The influence of technological conditions of 3D-printing on antiadhesion properties of surfaces has been studied. By experiments it was found out that for 3D-printing of master-models it was necessary to have conditions in which the parameter of filling percent was more than 60%. Recommendations for the use of 3D-printing methods for production of casting molds are given.

Application of 3D-printing technologies for production of master-model in engineering industry

Analysis of 3D-printing methods used in the molding production to manufacture master-models has been carried out. The technology was selected, which allowed one to make high-precision parts, combining the molding and the 3D-printing. Factors effecting on the quality of 3D-models printed by this technology were analyzed. Experimental studied for determination of the printing parameter influence (layer thickness, filling percentage, printing velocity) on ultimate strength of specimens made of ABS-plastic were carried out.

The Influence of Hard- and Software Improvement of Intraoral Scanners on the Implant Transfer Accuracy from 2012 to 2021: An In Vitro Study

This study aimed to investigate the transfer accuracy (trueness and precision) of three different intraoral scanning families using different hardware and software versions over the last decade from 2012 to 2021, compared to a conventional impression. Therefore, an implant master model with a reference cube was digitized and served as a reference dataset. Digital impressions of all three scanning families (True definition, TRIOS, CEREC) were recorded (n = 10 per group), and conventional implant impressions were taken (n = 10). The conventional models were digitized, and all models (conventional and digital) were measured. Therefore, it was possible to obtain the deviations between the master model and the scans or conventional models in terms of absolute three-dimensional (3D) deviations, deviations in rotation, and angulation. The results for deviations between the older and newer scanning systems were analyzed using pairwise comparisons (p < 0.05; SPSS 26). The absolute 3D deviations increased with increasing scan path length, particularly for the older hardware and software versions (old vs. new (MW ± SD) True Definition: 355 ± 62 µm vs. 483 ± 110 µm; TRIOS: 574 ± 274 µm vs. 258 ± 100 µm; and CEREC: 1356 ± 1023 µm vs. 110 ± 49 µm). This was also true for deviations in rotation and angulation. The conventional impression showed an advantage only regarding the absolute 3D deviation compared to the older systems. Based on the data of the present study, the accuracy of intraoral scanners is decisively related to hardware and software; though, newer systems or software do not necessarily warrant improvement. Nevertheless, to achieve high transfer accuracy, regular updating of digital systems is recommended. The challenge of increasing errors with increasing scan paths is overcome in the most recent systems. The combination of two different scanning principles in a single device seems to be beneficial.

Assessment of Fit on Ten Screw-Retained FrameworksRealized through Digital Full-Arch Implant Impression

Background: Discordant opinions have emerged among clinicians and researchers regarding a digital impression for full-arch implant-supported fixed dental prostheses (FDPs). The purpose of this study was to assess the fit of screw-retained milled frameworks on six implants realized from digital impressions through the Sheffield test. Methods: One patient received a maxillary full-arch implant-supported FDP. Six months after the surgical procedure, ten intraoral full-arch digital impressions were performed to mill ten frameworks. To clinically assess the fit, the Sheffield test was applied for all frameworks. The gaps among the frameworks and the implant analogs were measured using a microscope on the master model realized with a traditional impression. The Wilcoxon sum-rank test was used to compare the misfit value among the different implant positions. Results: The Sheffield test did not show gaps in the framework–implant interfaces when the screw was completely tightened on the more distal implant for all the milled frameworks. The mean misfit value calculated after microscope examination was 38 ± 5 μm. Differences that were statistically significant emerged when the misfit values of central positions were compared with other values. Conclusions: The use of full-arch implant digital impressions represents a viable alternative to traditional impressions for the fabrication of implant-supported FDPs.

Can transfer type and implant angulation affect impression accuracy? A 3D in vitro evaluation

Impression accuracy is fundamental to achieve a passive fit between implants and the superstructure. Three transfer types were tested to evaluate the differences in impression accuracy and their efficiency in case of different implant angles. A master model with four implant analogues placed at 0°, 15° and 35° was used. 27 impressions were taken with three different types of impression coping: closed tray technique coping (CT), open tray technique coping (COT) and telescopic open tray coping (TOT). The impressions were poured. Analogues were matched with scan bodies to be scanned and exported in STL. An implant bar was designed from each STL and another one from the master model. A comparison between these bars was obtained. Linear and angular measurements for every type of coping were calculated for different angulations. The collected data were analyzed with ANOVA test (95% of confidence). Student’s t test showed a significative discrepancy (p ≤ 0.001) on linear and angular measurements on Δx, Δy, Δz with different transfer types as well as diverse implant positioning angles (p ≤ 0.001). Within the limitations of this study, it can be concluded that the coping type and the implants divergence may be significant parameters influencing the impression accuracy.

A New Method to Evaluate Trueness and Precision of Digital and Conventional Impression Techniques for Complete Dental Arch

Purpose: The aim of this study was to present a new method to analyze the three-dimensional accuracy of complete-arch dental impressions and verify the reliability of the method. Additionally, the accuracies of conventional and intraoral digital impressions were compared using the new method. Methods: A master model was fabricated using 14 milled polyetheretherketone cylinders and a maxillary acrylic model. Each cylinder was positioned and named according to its corresponding tooth position. Twenty-five definitive stone casts were fabricated using conventional impressions of the master model. An intraoral scanner was used to scan the master model 25 times to fabricate 25 digital models. A coordinate measuring machine was used to physically probe each cylinder in the master model and definitive casts. An inspection software was used to probe cylinders of digital models. A three-dimensional part coordinate system was defined and used to compute the centroid coordinate of each cylinder. Intraclass correlation coefficient (ICC) was evaluated to examine the reliability of the new method. Independent two sample t-test was performed to compare the trueness and precision of conventional and intraoral digital impressions (α = 0.05). Results: ICC results showed that, the new method had almost perfect reliability for the measurements of the master model, conventional and digital impression. Conventional impression showed more accurate absolute trueness and precision than intraoral digital impression for most of the tooth positions (p < 0.05). Conclusions: The new method was reliable to analyze the three-dimensional deviation of complete-arch impressions. Conventional impression was still more accurate than digital intraoral impression for complete arches.

Comparison of implant placement accuracy in two different preoperative digital workflows: navigated vs. pilot-drill-guided surgery

Background The aim of the study is to evaluate the accuracy of a new implant navigation system on two different digital workflows. Methods A total of 18 phantom jaws consisting of hard and non-warping plastic and resembling edentulous jaws were used to stimulate a clinical circumstance. A conventional pilot-drill guide was conducted by a technician, and a master model was set by using this laboratory-produced guide. After cone beam computed tomography (CBCT) and 3D scanning of the master models, two different digital workflows (marker tray in CBCT and 3D-printed tray) were performed based on the Digital Imaging Communication in Medicine files and standard tessellation language files. Eight Straumann implants (4.1 mm × 10 mm) were placed in each model, six models for each group, resulting in 144 implant placements in total. Postoperative CBCT were taken, and deviations at the entry point and apex as well as angular deviations were measured compared to the master model. Results The mean total deviations at the implant entry point for MTC (marker tray in CBCT), 3dPT (3d-printed tray), and PDG (pilot-drill guide) were 1.024 ± 0.446 mm, 1.027 ± 0.455 mm, and 1.009 ± 0.415 mm, respectively, and the mean total deviations at the implant apex were 1.026 ± 0.383 mm, 1.116 ± 0.530 mm, and 1.068 ± 0.384 mm. The angular deviation for the MTC group was 2.22 ± 1.54°. The 3dPT group revealed an angular deviation of 1.95 ± 1.35°, whereas the PDG group showed a mean angular deviation of 2.67 ± 1.58°. Although there were no significant differences among the three groups (P > 0.05), the navigation groups showed lesser angular deviations compared to the pilot-drill-guide (PDG) group. Implants in the 3D-printed tray navigation group showed higher deviations at both entry point and apex. Conclusions The accuracy of the evaluated navigation system was similar with the accuracy of a pilot-drill guide. Accuracy of both preoperative workflows (marker tray in CBCT or 3D-printed tray) was reliable for clinical use.

Using the “One Shot” Concept for Immediate Loading Implant Protocol in Edentulous Patient Rehabilitation with a Fixed Prosthesis: A 6-Year Follow-Up

Immediate-loaded implants with a fixed prosthesis are a viable option for the restoration of edentulous ridges. Several procedures now allow for the fabrication of immediate-loading provisional and definitive prostheses. However, this complex treatment is not accessible to all patients with budget restrictions. By using a unique master model with a single titanium framework prosthesis can simplify and shorten the treatment, as well as reduce costs. After surgical placement of implant fixtures, an interim prosthesis was fabricated using a laser-welded definitive titanium framework. The prosthesis was fitted intraorally following the immediate loading protocols. The master cast model used to fabricate interim prosthesis was conserved and subsequently used in modifying the final prosthesis. After the healing process and complete soft tissue stability, an impression was made to register the clearance between the gingiva and resin. The light silicone material was directly injected under the prosthesis screwed in the mouth. In the master cast model, the stone was eliminated between the implants and a new plaster was poured to modify the crest profile with the posthealing new shape. With this modified model, it is possible to rehabilitate the denture to the new gingival anatomy in 3 to 4 hours and, if necessary, the tooth rearrangement. This “one shot” concept combines the single definitive titanium welded framework and limited laboratory work with a unique master model thereby decreasing the cost and the time of treatment.

Experimental validation of finite element simulation of a new custom-designed fixation plate to treat mandibular angle fracture

Background The objective of the study was to validate biomechanical characteristics of a 3D-printed, novel-designated fixation plate for treating mandibular angle fracture, and compare it with two commonly used fixation plates by finite element (FE) simulations and experimental testing. Methods A 3D virtual mandible was created from a patient’s CT images as the master model. A custom-designed plate and two commonly used fixation plates were reconstructed onto the master model for FE simulations. Modeling of angle fracture, simulation of muscles of mastication, and defining of boundary conditions were integrated into the theoretical model. Strain levels during different loading conditions were analyzed using a finite element method (FEM). For mechanical test design, samples of the virtual mandible with angle fracture and the custom-designed fixation plates were printed using selective laser sintering (SLS) and selective laser melting (SLM) printing methods. Experimental data were collected from a testing platform with attached strain gauges to the mandible and the plates at different 10 locations during mechanical tests. Simulation of muscle forces and temporomandibular joint conditions were built into the physical models to improve the accuracy of clinical conditions. The experimental vs the theoretical data collected at the 10 locations were compared, and the correlation coefficient was calculated. Results The results show that use of the novel-designated fixation plate has significant mechanical advantages compared to the two commonly used fixation plates. The results of measured strains at each location show a very high correlation between the physical model and the virtual mandible of their biomechanical behaviors under simulated occlusal loading conditions when treating angle fracture of the mandible. Conclusions Based on the results from our study, we validate the accuracy of our computational model which allows us to use it for future clinical applications under more sophisticated biomechanical simulations and testing.