International Journal of Computerized Dentistry, 02/2023

Aim: The purpose of the present investigation was to evaluate the accuracy of root canal length (RCL) determination according to CBCT acquisition protocol and evaluate the influence of additional superimposed computerized optical impressions. Materials and methods: CBCT scans with low-dose (LD) and high-definition (HD) protocols as well as computerized optical impressions of 30 extracted human molars were acquired. Sicat Endo software (Sicat) was used for CBCT RCL measurements with (LD+, HD+) and without (LD-, HD-) a superimposed optical impression. To evaluate the accuracy, absolute differences between test groups and the actual root canal length (ARCL) were calculated and statistically analyzed using the Wilcoxon rank sum test. Results: Absolute differences between the ARCL and the tested measurement methods varied significantly (P < 0.05). Both higher resolution and additionally superimposed computerized optical impression improved measurement accuracy. Mean differences compared with the ARCL were 0.26 mm (HD+), 0.34 mm (HD-), 0.43 mm (LD+), and 0.66 mm (LD-). 93.4% of all measurements in the HD+ group were within the limits of ± 0.5 mm. Conclusion: Both resolution and superimposition of additional computerized optical impressions have a significant influence on RCL measurements using CBCT. Keywords: CBCT, computerized optical impression, root canal length determination, Sicat Endo

Aim: Orthodontic treatments with custom-made active elements may lead to more efficient treatment with fewer side effects. The objective of the present in vitro study was to determine whether individually constructed, mathematically simulated, and 3D-printed power chains could generate adequate forces for orthodontic tooth movement. Materials and methods: An individual measurement device was developed using a high-precision load cell, amplifier, and microcontroller for signal processing. Elastic chains were designed and subsequently printed from two different thermoplastic polyurethane (TPU) filaments and a thermoplastic elastomer (TPE) filament. With the CAD data, a finite element analysis (FEA) was performed to calculate the reactive forces to be expected at different activation levels. The measured force development of the test objects was compared with the results from the FEA. Results: The results showed a high precision of the measurement device, with an intraclass correlation coefficient (ICC) of 0.999 and a Dahlberg error of 0.05 N. The measured forces ranged from 196 to 681 g. There was a significant correlation between the measured and calculated forces (R 0.91 to 0.98). Discussion: In the present study, the fully digital workflow of producing an individualized active orthodontic treatment element, which developed almost exactly the force values calculated in the FEA, was shown. Future clinical use seems promising, in combination with fully individualized and digitally planned treatment approaches. This offers the possibility to integrate these insights from exemplary applications into patient-specific digital planning in orthodontics. The combination of CBCT root reconstruction, intraoral scans with customized brackets, and wires is the perfect starting point to add mechanical and numerical simulations. This would be the next step from shape-driven planning to force-driven planning. The goal is to reduce treatment time and negative side effects, eg, root resorption. Conclusion: The present in vitro study is the first to show the possible individualized construction and 3D printing of elastic chains exhibiting reproducible, predefined forces. Keywords: rubber chain, power chain, custom active element, orthodontics, CAD/CAM, 3D printing, finite element analysis

Aim: To compare the planned implant position (PIP) with the transferred implant position (TIP) after fully guided implant placements in single-tooth gaps. Materials and methods: Dental implant placements were planned using two different implant systems (Camlog Screw-Line [C-SL] and Straumann Bone Level Tapered [S-BLT]), and two different planning software programs (SMOP and coDiagnostiX). All implants were placed according to fully guided protocols, and intraoral scans were performed intraoperatively. For the comparison of PIP and TIP, scan data were imported to Geomagic Control X (GCX) software and accuracies were evaluated. Deviations were reported in a coordinate system (x- [mesiodistal], y- [vestibulo-oral], and z- [vertical] axis) at entry points and apices. Total deviations, including angular deviations, were calculated with GCX. For statistical analysis, the level of significance was set to P < 0.05. Results: Twenty-six patients received 26 implants. Mean 3D deviation at the implant’s entry point was 0.61 mm ± 0.28 for C-SL and 0.63 mm ± 0.24 for S-BLT. For the implant’s apex, mean 3D deviation of 0.96 mm ± 0.41 was documented for C-SL and 1.04 mm ± 0.34 for S-BLT. Mean angular deviation was 2.58 degrees ± 1.40 for C-SL and 2.89 degrees ± 1.12 for S-BLT. Statistical analysis revealed no significant differences between implant systems, but showed significant deviations regarding the z-axis, both at entry point and apex (P < 0.05). Conclusions: Fully guided implant placements in single-tooth gaps provide accurate results. Due to significant vertical deviations, reevaluation of both drilling and insertion depths prior to implant installation should be considered. Maintenance of 1.5- to 2-mm safety distances to critical structures was confirmed. Keywords: dental implants, static navigation, CAD/CAM, computer-assisted, computer-assisted implant surgery, backward planning

Aim: The CAM of esthetically pleasing monolithic dental restorations presents with specific challenges. One vital parameter to consider is the translucency of the materials. Previous studies have proven a correlation between translucency and material thickness for various all-ceramic materials. The aim of the present study was to assess and define the relationship between thickness and translucency in modern resin-based restorative materials. Materials and methods: Specimens fabricated from two resin nano-ceramics (Cerasmart, Lava Ultimate), a polymer-infiltrated ceramic network (Vita Enamic), and a polymethyl methacrylate (Telio CAD) were examined, representing these different material classes. For each material, 12 specimens (n = 12) were fabricated in five thicknesses (0.4, 0.7, 1.0, 1.3, and 1.6 mm; N = 240). The translucency was measured with a spectrophotometer. The total light transmittance for each specimen was calculated applying specialized software. Regression curves were fitted to the results and their coefficient of determination (R2) fit was determined. Results: Logarithmic regression curves showed the best R2 approximation (Cerasmart: R2 = 0.994; Vita Enamic: R2 = 0.978; Lava Ultimate: R2 = 0.997; Telio CAD: R2 = 0.997) to the light transmission values. Conclusions: The results of the present study indicate that the translucency of resin-based materials can be calculated using a mathematic approach to estimate their optical behavior. Cerasmart, Lava Ultimate, Vita Enamic, and Telio CAD exhibit a logarithmic relationship between material thickness and translucency. By determining material-specific coefficients for this logarithmic function, the resulting translucency can be computed for any given material thickness. Keywords: hybrid materials, PMMA, polymer-infiltrated ceramic network, resin nano-ceramics, translucency, translucency equation, mathematic analysis, CAD/CAM, digital workflow

Aim: The aim of the present study was the evaluation of the in vitro performance and fracture force of 3D-printed anterior implant-supported temporary partial dentures (TPDs) with different filler content. Materials and methods: Identical anterior resin-based TPDs (tooth sites 11 to 13; n = eight per material) were 3D printed from methacrylate resins with different filler content. A cartridge polymethyl methacrylate (PMMA) material was used as a reference. After temporary cementation, combined thermal cycling and mechanical loading (TCML) was performed on all the restorations to mimic clinical application. Behavior during TCML and fracture force was determined, and failures were analyzed. Data were statistically investigated (Kolmogorov-Smirnov test, one-way ANOVA; post hoc Bonferroni, Kaplan-Meier survival; α = 0.05). Results: Failure during TCML varied between three failures and total failure during loading time. Mean survival time varied between 93 ± 206 x 103 cycles and 329 ± 84 x 103 cycles. Significantly different survival cycles between the individual materials could be determined (Mantel Cox log-rank test: chi-square: 21,861; degrees of freedom (df) = 4, P < 0.001). A correlation between filler level and survival cycles could be found (Pearson: 0.186, P = 0.065). Fracture values of the surviving TPDs varied between 499 and 835 N. Failures were characterized by fracture of the connector (n = 24) followed by fractures at the abutment (n = 10). Conclusions: TDPs showed different filler-dependent survival. Individual 3D-printed materials provided comparable or even better performance than a standard cartridge system and might be sufficient for temporary application of at least half a year. Keywords: rapid prototyping, 3D printing, temporary dentures, thermal cycling and mechanical loading (TCML), finite element analysis (FEA), temporary partial denture (TPD), implant

Aim: The aim of the present study was to compare the performance of a tactile collaborative robot programmed by a dental professional (DP) with that of a DP in the removal of surrogate plaque in vitro. Materials and methods: Six typodont teeth in articulated jaws were covered with surrogate plaque and cleaned by a DP with the help of a manual toothbrush (DP/manual) and an electric toothbrush (DP/electric). The experiment was repeated with the help of a collaborative seven-axis tactile robot programmed by a DP handling a manual toothbrush (robot/manual) and an electric toothbrush (robot/electric). All experiments were repeated five times, resulting in a total of N = 30 teeth in each group. Cleaning results were reported as the percentage of surface area with residual plaque. Results: The cleaning results of the DP and the robot showed no significant differences. However, electric toothbrushing was significantly less effective compared with manual toothbrushing (P < 0.05). Conclusion: The present in vitro study indicates that current robot technology may perform the removal of surrogate plaque as efficiently as a DP. In future, this may be helpful to release nursing staff from this time-demanding task that could possibly cause contagion or to support people with reduced motor skills or impaired vision in performing daily oral hygiene. Keywords: dentronics, robotics, dentistry, dental robots, oral hygiene, electric toothbrush, manual toothbrush, human-machine interaction, human-robot interaction

Surgical crown lengthening is one of the most common surgical procedures in periodontal practice. It is divided into functional and esthetic surgical crown lengthening. In general, surgical crown lengthening is a predictable periodontal surgical procedure. Its most common complication is excessive regression of the dentoalveolar complex coronally. Esthetic surgical crown lengthening can be performed predictably through prior digital planning, minimizing the risk of potential complications such as excessive regression of the dentoalveolar complex coronally. The present study reported in this article is a clinical case of surgical crown lengthening with digital planning to derive practical recommendations. Keywords: surgical crown lengthening, digital planning, esthetics