International Journal of Computerized Dentistry, 01/2019

Objective: Intraoral scanners (IOSs) are widely used for obtaining digital dental models directly from the patient. Additionally, improvements in IOSs are made from generation to generation. The aim of this study was to evaluate the accuracy of new and actual IOS devices for complete- and partial-arch dental impressions in an in vitro setup. Materials and methods: A custom maxillary complete-arch cast with teeth made from feldspar ceramic material was used as the reference cast and digitized with a reference scanner (ATOS III Triple Scan MV60). One conventional impression technique using polyvinylsiloxane (PVS) material (President) served as the control (CO), and eight different IOS devices comprising different hardware and software configurations (TRn: Trios 3; TRi: Trios 3 insane; CS: Carestream Dental CS 3600; MD: Medit i500; iT: iTero Element 2; OC4: Cerec Omnicam 4.6.1; OC5: Cerec Omnicam 5.0.0; PS: Primescan) were used to take complete-arch impressions from the reference cast. The impressions were repeated 10 times (n = 10) for each group. Conventional impressions were poured with type IV gypsum and digitized with a laboratory scanner (inEos X5). All datasets were obtained in standard tessellation language (STL) file format and cut to either complete-arch, anterior segment, or posterior segment areas for respective analysis. Values for trueness and precision for the respective areas were evaluated using a three-dimensional (3D) superimposition method with special 3D difference analysis software (GOM Inspect) using (90-10)/2 percentile values. Statistical analysis was performed using either one-way analysis of variance (ANOVA) or Kruskal-Wallis test (α = 0.05). Results are given as median and interquartile range [IQR] values in µm. Results: Statistically significant differences were found between test groups for complete- and partial-arch impression methods in vitro (p 0.05). Values ranged from 16.3 [2.8] µm (CO) up to 89.8 [26.1] µm (OC4) for in vitro trueness, and from 10.6 [3.8] µm (CO) up to 58.6 [38.4] µm (iT) for in vitro precision for the complete-arch methods. The best values for trueness of partial-arch impressions were found for the posterior segment, with 9.7 [1.2] µm for the conventional impression method (CO), and 21.9 [1.5] µm (PS) for the digital impression method. Conclusion: Within the limitations of this study, digital impressions obtained from specific IOSs are a valid alternative to conventional impressions for partial-arch segments. Complete-arch impressions are still challenging for IOS devices; however, certain devices were shown to be well within the required range for clinical quality. Further in vivo studies are needed to support these results. Keywords: intraoral scanner, digital impression, conventional impression, accuracy, precision, trueness

Aim: Deformation of the mandible presents a major challenge for many dentists, both in conventional prosthetic supraconstructions and in complex implant restorations. This study aimed to evaluate the three-dimensional (3D) deformation of the mandible in vivo with scannable impression material and an industrial optical scanner. Materials and methods: In the present study, 20 female and 20 male subjects were examined. In each case, two impressions were made with polyvinylsiloxane: one with the mouth slightly open, and a second with the mouth wide open. The impressions were digitized with an industrial optical scanner and transformed into a virtual model. The two corresponding models were digitally superimposed over all the teeth. Then, an individual local coordinate system was assigned to each individual tooth. Subsequently, a best-fit procedure was performed for each individual tooth. Finally, the open- and closed-mouth models were compared by calculating the differences and rotations in the individual axes. This procedure was performed individually for each tooth. Results: The mean deviations in the x-, y-, and z-coordinates ranged from 0.011 mm at the canines to 0.232 mm at the molars. Larger discrepancies were observed in the female subjects than in the male subjects; however, these differences were not statistically significant. Conclusion: The results demonstrated that the posterior region of the mandible deformed when the mouth was maintained in a wide-open position. Therefore, this position should be avoided when performing dental impressions. Moreover, potential negative consequences of this mandibular deformation should be taken into consideration when planning wide-span fixed dental restorations. Keywords: mandible, deformation, flexure, impression, three-dimensional (3D), prosthetic

Purpose: To evaluate the masking ability of computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia-reinforced lithium silicate (ZLS) glass-ceramic under the different material configurations of thickness, translucency, and finishing protocol as well as significance of the color difference due to the manufacturer's one-firing protocol. Materials and methods: Ninety high-translucency (HT) and low-translucency (LT) ZLS glass-ceramic discs of different thicknesses (1.0, 1.5, and 2.0 mm) were evaluated as a monolithic structure with and without the use of a one-firing protocol. Disc samples were placed onto the substrates for measurement; a spectrophotometer measured the L*, a*, and b* color attributes of each specimen. ∆E value was calculated for determining color differences in tooth-colored substrate specimens (shade B1) compared with three darker backgrounds (shade C2, and two metal substrates - gold and silver). ∆E values were then compared against clinically acceptable (∆E = 5.5) and ideal (∆E = 2.6) thresholds. Color differences between the control and test groups were evaluated under different effects using a series of one-sided paired t tests (P 0.01). The 99% confidence interval (CI) for the true ∆E mean and P values are reported and discussed. A complementary regression analysis depicts the effect size of translucency and firing protocol. Results: Over C2, a 1-mm thickness demonstrated P 0.01 for the clinically acceptable threshold, whereas the ideal threshold was ensured only with P 0.01 under a 2-mm thickness. Over silver, only the clinically acceptable standard was met with P 0.01 under a 2-mm thickness. Over gold, a 1-mm thickness was clinically acceptable with P 0.01, and the ideal standard was met with P 0.01 under a 1.5-mm thickness. These results remained valid regardless of the firing protocol or translucency; however, significant (P 0.01) yet small-sized effects were found for translucency and firing protocol over gold, and for translucency over silver, through multiple regression analysis. Conclusions: To achieve ideal masking, the minimum thickness of CAD/CAM ZLS glass-ceramic should be 1.5 mm over a gold background, and 2 mm over a C2 background. The silver background did not achieve ideal masking in any situation. The one-firing protocol did not affect the final color and can be used to increase restoration strength. Keywords: color, spectrophotometry, computer-aided design/computer-aided manufacturing (CAD/CAM), zirconia-reinforced lithium silicate (ZLS) glass-ceramic, visual perception

Purpose: To compare the failure loads of teeth restored with endocrowns, post-core retained crowns without a ferrule, and post-core retained crowns with a ferrule provided after crown lengthening. Materials and methods: 27 mandibular molar teeth were collected, sectioned 1.5 mm above the cementoenamel junction (CEJ), and endodontically treated. Teeth were randomly assigned into three groups according to the type of final restoration (n = 9): endocrown (EC) group, post-core retained crowns without ferrule (CNF) group, and post-core retained crowns with ferrule provided following crown lengthening (CF) group. Lithium disilicate crowns and endocrowns were designed and fabricated using the Cerec system. Teeth were mounted in acrylic resin and subjected to thermocycling and oblique compressive loading until failure. Results: Mean fracture loads of the CF, CNF, and EC groups were 491.13 (± 6.93) N, 458.57 (± 5.26) N, and 584.48 (± 5.8) N, respectively. One-way ANOVA showed statistically significant differences between the groups (P 0.05). Fracture of the root was the dominant mode of failure in all groups. Conclusion: Molar teeth restored with endocrowns have superior fracture strength compared with those restored with post-core retained crowns. Keywords: endocrown, failure mode, fracture resistance, mandibular molar

Aim: To evaluate the marginal adaptation and internal fit of milled fiber post and cores using different scanning methods. Materials and methods: Thirty typodont tooth models (Nissin) with pulp cavity were endodontically treated and prepared to receive 30 fabricated fiber post and cores. Three different methods of scanning were used (n = 10): an intraoral scanner (IOS) (Trios 3; 3Shape) to directly digitalize the post space (Group T) and a laboratory scanner to indirectly digitalize the resin pattern (Group RP) and the silicone impression (Group S) of the post space. All the specimens were examined using an optical microscope for the measurement of the vertical marginal discrepancy (VMD), and five in each group were scanned using microcomputed tomography (µCT) for the assessment of the VMD, the internal fit at the corner (IFC), post apex (PA), and at four horizontal cross-sections (CS1-4) inside the canal. All data were analyzed using mixed-design ANOVA, followed by pairwise testing to identify the differences (α = 0.05). Results: Statistical analysis revealed that Group T was associated with the smallest cement space compared with Group RP (P = 0.001) and Group S (P 0.001) for VMD using µCT or direct microscopy (OM) (P 0.001). Similarly, the cement space for Group T was smaller than that of Group S (P = 0.039) when measured at the IFC (µCT), and smaller than Group RP (P = 0.025) when measured at CS1-4 (µCT), with CS1 larger than CS3 (P = 0.015). There was no significant difference at PA (P = 0.271). Conclusion: Better adaptation was achieved with a complete digital workflow. Scanning the resin pattern or the silicone impression introduced more variables in the digital process or milling of a one-piece fiber post and core. Keywords: CAD/CAM, fiber post, post and core, intraoral scanner (IOS), extra-fine milling, prosthodontics

Objectives: To review the current metal-based additive manufacturing (AM) technologies, namely powder bed fusion (PBF) technologies, and their current prosthodontic applications. The PBF technologies reviewed are selective laser sintering (SLS), selective laser melting (SLM), and electron beam melting (EBM). Materials and methods: The literature on metal AM technologies was considered, and the AM procedures and their current applications in prosthodontics were collated and described. Published articles about AM metal in dental care were searched (MEDLINE, EMBASE, EBSCO, and Web of Science). All studies related to the description, analysis, and evaluation of prosthodontic applications using metal AM technologies. Results and conclusions: AM technologies are reliable for many applications in dentistry, including metal frameworks for removable partial dentures (RPDs), overdentures, tooth- and implant-supported fixed dental prostheses (FDPs), and metal frameworks for splinting implant impression abutments. However, further studies are needed in future to evaluate the accuracy, reproducibility, and clinical outcome throughout function of AM technologies. Keywords: 3D printing, additive manufacturing technologies, electron beam melting, metal, selective laser melting, selective laser sintering, prosthodontics

Aim: This article introduces and evaluates Dentsply Sirona's new intraoral scanner Cerec Primescan AC and Cerec 5 software. The article uses multiple clinical examples to discuss all the new features, applications, and accuracy of this new system. Materials and methods: The Cerec Primescan AC scanner comes with a touchscreen, touchpad, and new Cerec 5 software. To evaluate this scanner and software, multiple full-arch scans and clinical cases were completed to show the new and improved clinical applications and efficiency of this workflow. Results: The Cerec Primescan AC allows full-arch scans to be completed with incredible efficiency and accuracy. The scanner and software allow for the scanning of restorations, metal, and teeth with the exact same efficiency and accuracy. This new scanning capability allows both full-arch and individual restorations to be completed with minimal user effort. The new Cerec 5 software has perfected the so-called 5-click workflow, allowing almost complete automation of the Cerec workflow. Conclusion: By combining excellent accuracy in measuring teeth, restorations, and metal with efficiency and automation, Dentsply Sirona's new Cerec Primescan AC scanner and Cerec 5 software are quite possibly a revolutionary step forward in both scanning and restoration fabrication. Keywords: Cerec Primescan AC, Cerec 5 software, full-arch, automation, clarity, accuracy, efficiency

An entirely digital concept has previously been proposed for the reconstruction of the occlusal plane in the case of wear-induced loss of the vertical dimension of occlusion (VDO). The concept, however, calls for a face scan. Since this technology is less frequently available than a facebow, the concept discussed in this article proposes a combination of analog and digital techniques. It takes into account the problem of redefining the occlusal plane in the case of occlusal alteration, and tries to avoid a situation where the chairside digital design of the occlusal surfaces is performed without any anatomical references. Such a situation poses a significant risk if the treatment indication for bite elevation exists in both the maxilla and the mandible. Keywords: vertical relation, bite raising, chairside, CAD/CAM, planes, facebow, alternating, ceramic, composite

The digital inhouse workflow consists of the components optical impression, computer-aided design (CAD) and machine manufacturing. In the sense of a time-optimized workflow, coordinated, closed systems prove to be the better solution. The company 3Shape (Copenhagen, Denmark) started with the existing Trios Intraoral Scanner and added both the software component Trios Design Studio and a number of 'trusted connection mills.' In combination with a collection of 'trusted materials,' a fast workflow with high clinical safety can ultimately be guaranteed. In order for a single-stage in-house restoration to be successfully completed, it is advisable to carry out thorough diagnostics and pretreatment; prepare the restoration by machine with a clear representation of the margin lines; organise the manufacturing process in a competent manner; and use an adhesive, target-oriented fastening strategy. Individual sections of the workflow can be delegated to specially and comprehensively trained medical staff. The increasing networking of digital processes creates very useful synergy effects such as the visualization of possible therapy results, follow-up, smile design, and the planning of implant restorations. A clinical case of a single-stage, in-house restoration with three posterior crowns is presented. Keywords: intraoral scanners, CAD/CAM, chairside, in-house, digital dentistry, milling