International Journal of Computerized Dentistry, 02/2021

Aim: A technique for merging digital intraoral and CBCT scans for implant-supported complete-arch fixed dental prostheses (FDPs) is described. The aim is to improve the dimensional accuracy of intraoral scans in edentulous arches. Materials and method: Two files are recorded: an intraoral scan and a CBCT scan, both obtained with scan bodies connected to the implants in the same position. The intraoral scan is then divided into several fragments and realigned, taking as reference the position of the implants recorded in the CBCT file. Results: An improved intraoral digital model with corrected implant positions appropriate for complete-arch implant FDPs is generated. Conclusion: The methodology proposed can minimize possible intraoral scanning error and deliver more reliable digital impressions for implant-supported complete-arch FDPs. Keywords: fixed dental prosthesis (FDP), dental implants, complete-arch rehabilitation, passive fit, intraoral scanners (IOSs), CBCT

Aim: The aim of the present study was to verify the possibility of obtaining an optimized prosthetic substructure using generic software, respecting the distribution loads and forces involved. What is considered to be original and innovative in this study is the possibility of designing the prosthetic substructure on the basis of the individual patient’s chewing biomechanics, with the purpose of obtaining an even greater efficiency than a prosthesis designed according to a traditional method. Materials and methods: The starting standard triangulation language (STL) file was processed with Rhinoceros software and the tOpos plugin. It was decided to submit the entire prosthetic solution, intended as total volume, to structural analysis and topological optimization because the entire prosthesis is subjected to load during the chewing act. The software program was provided with information on the material, modulus, and direction of the applied forces. The objective was to optimize stiffness by maximizing volume. Results: The volume of the final structure was 2% compared with the starting model and was a completely different design compared with the traditional model. This new design was characterized by trabeculations that reflect the normal bone architecture. The material was distributed on the basis of the load points as well as the direction and modulus of the applied force. Conclusions: After assessing the applicability of the proposed workflow and the results obtained thus far, the most important clinical implication is represented by the greater efficiency and the same resistance of the prosthesis obtained with topological optimization compared with that obtained with the traditional method. Keywords: prosthetic substructure, structural analysis, finite element method (FEM), finite element analysis (FEA), chewing biomechanics, prosthetic complications, CAD/CAM technology

Aim: The positional accuracy of bracket placement planned through tooth setup vs actual placement was evaluated by means of conventional thermoplastic indirect bonding trays and customized 3D-printed indirect bonding trays. Materials and methods: A total of 280 bracket positions placed on the crowns of 10 dental plaster models were evaluated. The manual setup method and a thermoplastic indirect bonding tray were used for the manual group. For the CAD/CAM group, the bracket was positioned using a digital setup and a corresponding 3D-printed tray. The positional accuracy of the bracket placement on the duplicated gypsum model using the trays was evaluated by means of 3D software. Six errors of bracket position (height, depth, mesiodistal, torque, rotation, and tip errors), including linear and angular errors, were measured. Differences in variables were compared across subgroups using the independent t test or the Mann-Whitney U test. Results: Only the height error differed significantly (P < 0.05) between groups (manual: 0.2 mm; CAD/CAM: 0.12 mm). For both incisors and molars, the manual group showed significantly greater height errors than the CAD/CAM group (P < 0.05). The analysis of variance of the position error to the whole bracket showed statistically significant differences between tooth positions, linear measurements, and angular measurements (P < 0.05). Conclusion: A 3D-printed indirect bonding tray showed accuracy similar to that of conventional methods for bracket placement, with slightly greater bracket height accuracy. Further studies should strive to improve accuracy in terms of tooth positions. Keywords: 3D-printed tray, accuracy of bracket placement, customized orthodontic bracket, indirect bracket bonding, manual tooth setup, digital tooth setup

Background: The esthetic outcome of a dental restoration largely depends on the translucency of the materials used, especially for monolithic restorations. Research has been published reporting a correlation between translucency and material thickness. However, no mathematical formula has been described yet. The aim of the present study was to determine the mathematical relationship between material thickness and translucency of three dental ceramic materials. Material and methods: Three representative all-ceramic materials were taken out of the group of silicate ceramics (IPS Empress CAD LT), lithium X-silicate ceramics (IPS e.max CAD LT), and oxide ceramics (Lava Plus HT). Sixty specimens with five different thicknesses (0.4, 0.7, 1.0, 1.3, and 1.6 mm; N = 60, n = 12) were produced out of each ceramic (N = 180). A spectrophotometer was used to measure the transmittance coefficient tc[%] for each wavelength within the visible light spectrum, and the total light transmittance (T%) was calculated for each specimen. Linear, exponential, and logarithmic regression curves were fitted to the results. Results: The logarithmic regression curves exhibited the best correlation (R2; IPS Empress CAD LT, R2 = 0.996; IPS e.max CAD LT, R2 = 0.987; Lava Plus HT, R2 = 0.907) to the transmittance values. Conclusion: Within the limitations of the present study, the transmittance behavior of silicate ceramics, lithium-X-silicate ceramics, and oxide ceramics can be described by a logarithmic equation. The findings of this study therefore suggest that the optical behavior might be calculable by a mathematical approach. Keywords: silicate ceramics, oxide ceramics, translucency, translucency equation, CAD/CAM, digital workflow

Aim: Dental research involves variations between actual and reference datasets of master models to determine the metric accuracy through transfer accuracy tests. Various methods of measurement are used to analyze the results, which are often subjected to direct comparisons. Hence, the aim of the present study was to analyze the influence and effect on results of different methods of digital data analysis, being coordinate-based analysis (CBA) and best-fit superimposition analysis. Materials and methods: A model with four implants and a reference cuboid was digitized through computed tomography (CT), which served as the master model. Ten implant impressions were made using a Trios (3Shape) intraoral scanner, and three different scan bodies (nt-trading, Kulzer, and Medentika) were used. The deviations between the master model and the digital impressions were analyzed using CBA and best-fit superimposition analysis. Statistical analysis was performed using SPSS 25. Results: The deviations in the CBA and best-fit superimposition analysis ranged from 0.088 ± 0.012 mm (mean ± SE; Medentika, 14) to 0.199 ± 0.021 mm (Kulzer, 26), and from 0.042 ± 0.010 mm (Medentika, 16) to 0.074 ± 0.006 mm (Kulzer, 16), respectively. Significant differences were observed between the implant positions in the CBA and the digital measurements at each implant position, whereas the best-fit analysis showed no significant difference between the scan bodies and implant positions. Conclusion: CBA displays an advantage over best-fit superimposition analysis in the detection of possible influencing factors for primarily scientific purposes. However, a global analysis and visualization of angles and torsions is difficult, for which a best-fit evaluation is needed. However, a best-fit analysis better represents the clinical try-in. It is associated with the risk that possible disturbing factors and resulting errors might be leveled out and their identification camouflaged. Keywords: dimensional measurement accuracy, accuracy, trueness, precision, intraoral scanner, digital dentistry, implant impression, best-fit analysis

Computer-assisted implant surgery is one of the techniques that has gained much popularity over the past years. The amount of information that can be managed in a virtual environment allows for a faster, safer, and more precise implant placement. In certain cases, an appropriate implant-supported rehabilitation is accompanied by the need for complementary surgical procedures. The present technique report describes a clinical situation in which a bone reduction template and a stackable implant placement guide were digitally designed and 3D printed for a simultaneous ridge ostectomy and computer-assisted implant placement. Keywords: computer-assisted, computer-guided, 3D printing, implant surgery, implant placement, bone reduction

Aim: The present clinical case reports on the workflow of a multidisciplinary treatment including both orthodontic and esthetic procedures for the rehabilitation of a young patient with severe wear in the anterior area of both the maxillary and mandibular arches due to malocclusion. The described workflow comprises a digital step-by-step process that involves 3D printing, intraoral scanners, and CAD/CAM milling systems. Results: Accurate diagnostic and treatment planning were paramount when different specialties needed to combine and work together. For that purpose, different digital procedures helped to improve the predictability and the dynamic of the orthodontic and restorative treatments. Conclusion: The present multidisciplinary clinical case was executed with a digital approach that assisted to speed things up and achieve a predictable treatment option. Keywords: CAD/CAM, 3D printing, digital wax-up, orthodontics, ceramic veneers

Aim: The aim of the present study was to compare the marginal gap of teeth restored with crowns using six different CAD/CAM materials with two different milling units. Materials and methods: Ten mandibular molar teeth were collected after surgical extractions and prepared with two different diamond-coated instruments to receive full veneer crowns. The teeth were optically scanned, designed in CAD/CAM software, and milled in two different milling units. The marginal gap was measured using an optical microscope at 200x magnification. The restricted maximum likelihood (REML) method was used to estimate unknown parameters, and the statistical calculation was performed using R software. Results: The model used to answer the primary study question involved a significant (P < 0.001) instrument versus material interaction. No other interaction was statistically significant (P = 0.146). Finally, significant within-crown heteroscedasticity was found (P < 0.001) for the two different diamond-coated instruments and was taken into account in the model used. Conclusions: The marginal gaps achieved by the crowns across all groups were within a clinically acceptable range. Keywords: crowns, marginal gap, CAD/CAM, MC XL, Primemill, fine instrument, coarse instrument

Aim: The aim of the present study was to compare inlay and onlay restorations fabricated from conventional impressions and two different digital impression systems in terms of clinical features and marginal fit. Materials and methods: Participants were randomly assigned to three groups according to the type of impression system used. The impressions were taken with polyvinyl siloxane silicone material for the control group (CON). For the digital impressions, Trios Pod Scanner (3Shape) was used for the TRIOS group and Cerec AC Omnicam (Sirona) for the CEREC group. A total of 40 IPS e.max CAD and 20 IPS e.max Press (both Ivoclar Vivadent) inlay and onlay restorations were then placed in 24 participants. Clinical evaluations, Plaque Index, Gingival Index, and pocket probing depth measurements were taken at baseline, 6 months, and 12 months using FDI criteria. The continuous margin percentages were quantitatively examined by scanning electron microscopy at baseline and 12 months. Results: All the restorations showed clinically acceptable measurements at baseline, 6 months, and 12 months. The continuous margin evaluations showed no statistically significant difference between the groups. Conclusions: Based on the 12-month follow-up results, inlay and onlay restorations fabricated with digital impressions were found to be a reliable alternative to conventional impressions. Keywords: Trios, Cerec, clinical follow-up, in vivo marginal adaptation, randomized controlled clinical trial