International Journal of Computerized Dentistry, Pre-Print

Purpose: Endodontically treated teeth are more susceptible to fractures than vital teeth because of significant coronal and radicular dentin loss during endodontic therapeutic procedures. The objective of this study was to estimate and compare the influence of length and post type on the fracture strength of endodontically treated maxillary central incisors. Material and methods: In this in vitro study, sixty extracted human maxillary central incisors were decoronated 2 mm above the cemento-enamel junction.They were selected and subjected to standard endodontic treatment ,resulting in preparation with lengths of 5 mm (group 5mm),7,5 mm (group 7,5 mm) and 10 mm (group 10mm). Each group was randomly divided into 2 subgroups according to the post type , zirconia and fiber post. After appropriate surface treatment,they were cementet with resin adhesive cement and restored with zirconia crowns. Thermocycling (5 -55°C, 60 seconds, 1500 cycles) was performed after cementing the zirconia crowns on each tooth. Prepared samples were subjected to compresive static load of 0.5mm / min, at an angle of 130° to the long axis of the roots, using Universal Testing Machine (Matest ) at an cross head speed of 0.5 mm / min, until fracture.The significance of the results was assessed using 2-way ANOVA and the Tukey-Kramer test (α=0.05) Results:The ANOVA analysis indicated significant differences (P<0.05) between the groups. Tukey test revealed no significant difference among the zirconia posts of 5-mm length (26.5 N ±13.4) 7,5-mm length (25.2 N ±13.9), and 10-mm length (17.1 N ±5.2). Also, in the fiber post group, there was no significant difference when posts of 7.5-mm length (13.4 N ±11.0) were compared with the 5-mm (6.9 N ±4.6) and 10-mm (31.7 N ±13.1) groups. The 10-mm long post displayed superior fracture strength, and the 5mm-long post showed significantly lower mean values (P<0.001). Conclusion: The fracture strength of zirconia posts (5-mm and 7,5- mm length)was found to be significantly higher than those of fiber posts (5-mm and 7,5- mm length). The 10-mm long fiberpost group demonstrated significantly higher values of fracture strengths and the 5-mm long fiberpost group showed the lowest values for the force resulting in root fracture; these groups were significantly different from each other (P<.001).The fracture strength analysis with Universal Testing Machine is the only method that enables us to estimate the differences between zirconia and fiber posts with different lengths on endodontically treated teeth. Schlagwörter: Endodontically treated teeth, fiber post, fiberpost, fracture strength, universal testing machine, zirconia post

Aim: This in vitro study aimed to evaluate the depth of reading of intraoral scanners (IOSs) inside the gingival sulcus. Materials and methods: A knife-edge preparation for a full crown was performed on a Frasaco model. The gingival sulcus of the scanned model was modified using a dedicated software (Model Creator, Exocad DentalCAD 2.4 Plovdiv) by setting the coronal (CW) and apical (AW) widths and sulcus depths (D). Two dental models with different sulcus depths (1 mm or 2 mm) were printed using the digital light processing (DLP) technique. Each model was scanned ten times with seven IOSs: Emerald, Trios3, Carestrem 3600, Dentalwings, Condor, True Definition Scanner (TDS), and Omnicam. Measurements of D values were performed using 3Shape 3D viewer software. The normality of the data distribution was evaluated using the Shapiro–Wilk test (P<.05). A nonparametric Levene test was performed to check for homoscedasticity. The data were statistically analyzed with Kruskal–Wallis test (α=.05) and Nemenyi’s test. Result: All IOSs were able to read within the 1 mm-deep gingival sulcus, albeit with some statistically significant differences (P<.001). Only Trios3 was able to read the 2 mm-deep gingival sulcus (P<.001). Conclusion: The depth of reading of different IOSs can vary significantly. In the model with a 2-mm sulcus, even in the absence of oral fluids, the depth of reading is incomplete, suggesting that deep preparations into the sulcus are difficult to detect with IOSs. Schlagwörter: Depth of reading, Digital light processing, Gingival sulcus, IOS, Knife-edge preparation

Ausgeprägte Zahnhartsubstanzdefekte können durch unterschiedliche ätiologische Faktoren ausgelöst werden und sind zumeist mit einer Veränderung in der Vertikaldimension der Okklusion verknüpft, die auch die Kondylenposition beeinflussen kann. Diese Auswirkungen, die zum irreversiblen Verlust der Zahnhartsubstanz führen, können dramatische funktionelle und ästhetische Konsequenzen für den Patienten haben und erfordern häufig komplexe Rehabilitationskonzepte. Vor diesem Hintergrund hat sich der Einsatz zahnfarbener CAD/CAM-gefertigten Okklusionsschienen aus Polycarbonat als ästhetisch-funktionell, vorteilhaftes und sicheres Vorbehandlungskonzept erwiesen. Grundvoraussetzung für eine nachhaltige und funktionelle restaurative Intervention ist es, die verlorengegangene Zahnhartsubstanz in einer Weise wieder aufzubauen, die die Vertikaldimension und Okklusion in adäquater Kondylenposition wiederherstellt. Digitale Systeme sollen diesen komplexen Ablauf in Zukunft vereinfachen, unterstützen, individualisieren und präziser gestalten. Das hier verwendete DMD-System® (Ignident GmbH, Ludwigshafen, Deutschland), liefert patientenindividuelle Bewegungsdaten zur Optimierung dieses Workflows. Mit diesem System lassen sich reale Bewegungsmuster digitalisieren und hinsichtlich ihrer Funktion und therapeutischen Konsequenz analysieren sowie in den zahnmedizinischen und zahntechnischen Workflow integrieren. Die bereits bekannte Herstellung einer zahnfarbenen CAD/CAM-Okklusionsschiene, wird im vorliegenden Fallbericht durch eine digital ermittelte zentrische Kieferrelationsbestimmung und individuellen patientenspezifische Bewegungsdaten ergänzt. Schlagwörter: Vertikaldimension der Okklusion (VDO), instrumentelle zahnärztliche Funktionsanalyse, maximale Interkuspitation (IKP), zentrische Kondylenposition (ZKP), zahnfarbene Okklusionsschiene, digitaler Workflow

Statement of the Problem: Occlusion is associated with all disciplines of dentistry and plays a major role in the longevity of both implant and tooth borne restorations. Achieving occlusal harmony ensures balance is established between the dental and myofascial structures, which can be measurably established to high numerical tolerances with the T-Scan digital occlusal analysis system. Purpose: To describe and evaluate the known and proven applications of T-Scan digital occlusal analysis in various dental practice disciplines, with a systematic review of the literature. Materials and Methods: An electronic English language Medline/PubMed and Cochrane central library database search using key words “T-Scan”, “TMD”, “Occlusion”, “Implant Protected Occlusion”, “Orthodontics”, was conducted without any date restrictions. The related journal findings were hand searched to determine studies that met a systematic review’s inclusion. Results: The PubMed/MEDLINE identified 423 articles. After removing duplicates the titles and abstracts of the 421 studies were screened. 274 ineligible articles were excluded leaving 147 articles. Of those, 33 articles were not in English, 27 full text articles were not available, 4 were comments and Letter to the Editors, and 2 articles described techniques. 86 articles total met the eligibility criteria for inclusion. Conclusion: Much scientific evidence supports the use of T-Scan, as it measures relative occlusal contact forces and occlusal contacts time-sequence durations objectively, accurately, and repeatedly for improved treatment outcomes. It’s hardware, sensor, and software evolution from T-Scan I up to today’s T-Scan10 Novus system, has overcome early sensor and system drawbacks to improve T-Scan’s clinical performance in many disciplines of Dental Medicine. Schlagwörter: digital, occlusal Equilibrium, occlusion, Quantitative analysis, T-scan

Aim: The aim of this in vivo study was to compare the clinical trueness of primary mucostatic impressions obtained either by a classical alginate technique or by an optical intraoral scanner of fully maxilla edentulous patients. Materials and methods: 30 patients with fully edentulous maxilla were included and underwent conventional impressions as well as intraoral optical impressions (TRIOS 3®, 3Shape®). The conventional impressions were casted and the resulting stone models were digitized using a desktop scanner (Iscan D104i®, Imetric®). These digitized impressions were superimposed over the optical impressions to compare differences between the two datasets. Statistical analyses were performed to identify relevant deviations. Result: For the 30 intraoral impressions, 80.88% of the surface areas were below the tolerance threshold of 25 μm and thus considered similar to the area scanned with the desktop scanner from the reference stone model. Interestingly, the differences (19.12% of the surfaces) were localized in depressible areas like vestibule, soft palate, incisal papilla and flabby ridge. These locations were coherent with the positive mean of differences of +22.8μm, indicating deformation or less compression using the intraoral scanner. Conclusion: Digital primary impression of the fully edentulous maxilla can be considered as similar to the conventional alginate impression, except in the depressible areas. Considering the mucostatic objective of such a primary impression, one may consider optical impression as more accurate than the conventional one. Schlagwörter: clinical trial, conventional impression, digital impression, edentulous patients, intraoral scanner, maxilla

Aim: To summarize the features of condylar kinematics in patients with condylar reconstruction using a mandibular motion simulation method based on intraoral scanning registration. Materials and methods: Patients undergoing unilateral segmental mandibulectomy and autogenous bone reconstruction, as well as healthy volunteers were enrolled in the study. Patients were grouped based on whether the condyles were reconstructed. Mandibular movements were recorded using a jaw-tracking system and kinematic models were simulated after registration. The path inclination of the condyle point, margin of border movement, deviation and chewing cycle were analyzed. A t-test and one-way analysis of variation were carried out. Results: Twenty patients, including six patients with condylar reconstruction, fourteen patients with condylar preservation, and ten healthy volunteers were included. The patients with condylar reconstruction showed flatter movement paths of the condyle points. The mean inclination angle of the condylar movement paths of the patients with condylar reconstruction (0.57°  12.54°) was significantly smaller than that of the patients with condylar preservation (24.70° ± 3.90°, P= 0.014) during maximum opening, as well as protrusion (7.04°  12.21° and 31.12°  6.79°, P= 0.022). Healthy volunteers’ inclination angle of the condylar movement paths was 16.81±3.97° during maximum opening and 21.54±2.80° during protrusion, no significant difference compared to patients. The condyles of the affected-side tended to deviate laterally in all patients during mouth opening and protrusion. Patients with condylar reconstruction showed more severe symptoms of mouth opening limitation and mandibular movement deviation, and showed shorter chewing cycles than patients with condylar preservation. Conclusion: Patients with condylar reconstruction showed flatter movement paths of the condyle points, greater lateral motion range, and shorter chewing cycles than patients with condylar preservation. The method of mandibular motion stimulation based on intraoral scanning registration was feasible to simulate condylar movement. Schlagwörter: Digital technology, Electromyography, Joint range of motion, Mandibular condyle, Mandibular neoplasms, Patient-Specific modeling

Purpose: A reference method for quantifying contaminations on two-piece abutments manufactured using CAD/CAM (Computer-Aided Design/Computer-Aided Manufacturing) has not yet been established. In this in vitro study, a pixel-based machine learning method for detecting contamination on customised two-piece abutments was investigated and embedded in a semi-automated quantification pipeline. Material and Methods: Forty-nine CAD/CAM zirconia abutments were fabricated and bonded to a prefabricated titanium base. All samples were analysed for contamination by scanning electron microscopy (SEM) imaging followed by pixel-based machine learning (ML) and thresholding (SW) for contamination detection; quantification was performed in the post-processing pipeline. Wilcoxon signed-rank test and Bland-Altmann plot were applied to compare both methods. The contaminated area fraction was recorded as a percentage. Results: There was no statistically significant difference between the percentages of contamination areas (median = 0.004) measured with ML (median = 0.008) and with SW (median = 0.012), asymptotic Wilcoxon-test: p = 0.22. The Bland-Altmann plot demonstrated a mean difference of -0,006% (95% confidence interval, CI from -0.011% to 0.0001%) with increased values from a contamination area fraction > 0.03% for ML. Conclusion: Both segmentation methods showed comparable results in evaluating surface cleanliness; pixel based machine learning is a promising assessment tool for detecting external contaminations on zirconia abutments; Further studies must investigate its clinical performance. Schlagwörter: Computer-Aided Design, Dental Implant Abutments, Hygiene, Machine Learning, Scanning Electron Microscopy, Ultrasonics

Aim: The aim of this in vitro study was to assess and compare the accuracy of 2 best-fit alignment strategies with different reference areas for wear measurement with an intraoral scanner. Materials and methods: 8 anatomic-contour zirconia crowns were fabricated and scanned twice with an intraoral scanner. One of the scan data (Data Trueness) was duplicated and wear facets were simulated (Data Wear). The other scan data (Data Baseline) was aligned to Data Wear by 2 best-fit alignment strategies with different reference areas (the occlusal surface with no signs of wear and the axial surface), and 3D deviation analysis was performed to detect the wear loss. The 3D deviation between Data Trueness and Data Wear was calculated as the truth-value for accuracy evaluation. Results: Color-difference map showed Group Occlusal had a similar wear-facet distribution to Group Trueness, while Group Axial showed an obvious tilting position and the obtained height loss values were larger and with large standard deviations. Both Group Occlusal and Group Axial showed significant differences from Group Trueness in maximum height loss and mean height loss(P<.05), while no significant difference in mean distance(P>.05). Paired t test showed significant differences between Group Occlusal and Group Axial in maximum height loss and mean height loss(P<.05), while no significant difference in mean distance (P>.05). Conclusions: Best-fit alignment with the occlusal reference area produces a better alignment result than that with the axial reference area. Wear measurement with an intraoral scanner is potential but prone to overestimate the height loss. Schlagwörter: ccuracy, best-fit alignment, digital, In vitro , intraoral scanner, wear measurement

Aim: To evaluate the effect of cement gap and drill offset on the marginal and internal fit discrepancies of crowns designed with different tooth preparations. Materials and methods: Five tooth preparations were constructed, and crowns with different cement gaps and drill offset were obtained. Then, best-fit-alignment was performed on the crowns with the corresponding tooth preparations, and the fit discrepancies were expressed by the color-code difference images and root mean square (RMS) values. The RMS values of each group were analyzed by the rank-based Scheirer-Ray-Hare test (α=0.05). Result: The color segments in the sharp line angles area of the Sharp line angles group changed significantly before and after the drill offset. The cement gap had a significant effect on the marginal, internal, or overall fit discrepancies of the five design groups (P<0.001), while the drill offset had a significant effect on the marginal fit discrepancies of the Shoulder-lip group and the internal or overall fit discrepancies of the Sharp line angles group (P<0.001). Additionally, the interaction effect between cement gap and drill offset was significant for the marginal fit discrepancies of the Shoulder-lip group and the internal or overall fit discrepancies of the Sharp line angles group (P<0.01). Conclusion: The cement gap and drill offset had a significant adverse effect on the marginal or internal fit discrepancies in the crowns designed with the shoulder-lip and sharp line angles designs. Designs of tooth preparation with intense curvature changes such as shoulder-lip and sharp line angles should be avoided clinically. Schlagwörter: Cement gap, computer-aided design, drill offset, fit discrepancies, fixed crown, tooth preparation design

Aim: This study aimed to evaluate the accuracy of automated detection of preparation finish lines in teeth with defective margins. Materials and methods: An extracted first molar was prepared for a full veneer crown, and marginal defects were created and scanned (discontinuity of finish line: 0.5, 1.0, and 1.5 mm; additional line angle: connected, partially connected, and disconnected). Six virtual defect models were loaded in computer-aided design (CAD) software, where the preparation finish line was designated by 20 clinicians (CAD-experienced group: n = 10 and CAD-inexperienced group: n = 10) using the automated margin detection method. The accuracy of automatic detection was evaluated by calculating the three-dimensional deviation of the registered finish line. The Kruskal–Wallis and Mann–Whitney U tests were used for between-group comparisons (α = 0.05). Result: The deviation values of the registered finish lines were significantly different according to the conditions with different amounts of finish line discontinuity (P < 0.001). There was no statistical difference in the deviation of the registered finish line between models with additional line angles around the margin. Moreover, no statistical difference was found in the results between CAD-experienced and CAD-inexperienced operators. Conclusion: The accuracy of automated finish line detection for tooth preparation could differ when the finish line was discontinuous. The presence of an additional line angle around the preparation margin and prior experience in dental CAD software did not affect the accuracy of automated margin detection. Schlagwörter: automated detection, computer algorithm, computer-aided design, finish line, marginal defect, tooth preparation

Aim: This study aimed to evaluate the intaglio surface trueness and fit of zirconia crowns depending on the different machining strategies used with the CEREC system. Materials and methods: Thirty duplicate tooth models for a single zirconia crown were randomly assigned to the three groups (n = 10) according to the machining mode used for fabrication: grinding, wet milling, and dry milling. The scan data of the final crowns were compared to their design data to evaluate the intaglio surface trueness. The marginal and internal fits were evaluated using the cross-sectional method. The time required for the machining and sintering processes was measured for each group. Result: The wet milling group showed better trueness (RMS, 13.8 ± 1.0 μm) than the grinding and dry milling groups (p < 0.001). The marginal gap was greater in the grinding group (58.6 ± 28.9 μm) than that in the wet milling and dry milling groups (p < 0.001). The dry milling group required the shortest time for the manufacturing process. Conclusion: All machining modes fabricated crowns with a clinically acceptable trueness and fit. However, the dry milling mode was advantageous for the chairside CAD/CAM system with respect to time efficiency. Schlagwörter: 3D printing, CEREC, comparative 3D analysis, dry milling, grinding, marginal gap

Aim: Although many studies in various fields employ deep learning models, only few such studies exist in dental imaging. This paper aims to evaluate the effectiveness of Convolutional Neural Network (CNN) algorithms for the detection and diagnosis of the quantitative level of dental restorations using panoramic radiographs by preparing a novel dataset. Materials and methods: 20,973 panoramic X-ray radiographs, all labeled into five distinct categories by three dental experts, were used. AlexNet, VGG-16 and variants of ResNet models were trained with the dataset and evaluated for the classification task. Additionally, 10-fold cross-validation (i.e. nine-folds were separated for training and one-fold for validation) and data augmentation were carried out for all experiments. Result: The most successful result came from ResNet-101 with 92.7% accuracy. Its macro-average AUC was also the highest with 0.989. Other accuracy results obtained for the dataset were 75.5% for AlexNet, 85.0% for VGG-16, 92.1% for ResNet-18, 91.7% for ResNet-50 and 92.1% for Inception ResNet V2. Conclusion: Accuracy of 92.7% is a very promising result for a computer-aided diagnosis system. This result proved that the system could assist dentists in providing supportive preliminary information the moment they first take a panoramic X-ray radiograph of a patient. Furthermore, as the introduced dataset is powerful enough, it can be re-labeled for different problems and used in different studies. Schlagwörter: artificial intelligence, computer aided diagnosis, convolutional neural networks, deep learning, dental restoration, panoramic radiographs

Objective: To develop a Deep Learning (DL) Artificial Intelligence (AI) model for the instance segmentation and numbering of teeth on Orthopantomograms (OPGs). Methods: Forty OPGs were manually annotated to lay down the ground truth for training two Convolutional Neural Networks (CNNs), U-net, and Faster RCNN. These algorithms were concurrently trained and validated on a dataset of 1,280 teeth (40 OPGs) each. The U-net algorithm was trained on OPGs specifically annotated with fluid margins to label all 32 teeth via instance segmentation allowing each tooth to be denoted as a separate entity from the surrounding structures. Simultaneously, teeth were also numbered as per the Fédération Dentaire Internationale (FDI) numbering system, using bounding boxes to train Faster RCNN. Consequently, both trained CNNs were combined to develop an AI model capable of segmenting and numbering all teeth on an OPG. Results: The performance of the U-net algorithm was determined using various performance metrics including precision=88.8%, accuracy=88.2%, re-call=87.3%, F-1 score=88%, dice index=92.3% and Intersection over Union (IoU)=86.3%. The performance metrics of the Faster RCNN algorithm were determined using overlap accuracy=30.2 bounding boxes (out of a possible of 32 boxes) and classifier accuracy of labels=93.8%. Conclusions: The instance segmentation and teeth numbering results of our trained AI model were close to the ground truth, holding a promising future for its incorporation into clinical dental practice. The ability of an AI model to automatically identify teeth on OPGs will aid dentists with diagnosis and treatment planning thus increasing efficiency. Schlagwörter: Artificial Intelligence, Convolutional Neural Network, Deep Learning, Dentistry, Intraoral Radiography, Neural Networks

Aim: The aim of this paper was to describe a new method to reduce the unwanted reduction of material thickness resulting from overmilling due to the tool diameter compensation correction of common CAD/CAM software. Materials and methods: Today's CAD/CAM software (e.g. 3-Shape or Exocad) specifies the same tool diameter compensation for different ceramics. In the case of zirconia ceramics milled in the raw state, this leads to excessive milling of the inner surfaces of crowns. This results in unnecessary large cementation gaps and a restoration that is thinned out from the inside. By manually reducing the preset correction in the digital design process by the volumetric sintering shrinkage factor specified by the manufacturer, excessive thinning of the zirconia can be avoided. Results: The inner geometry of the restorations changes only slightly after reducing the preset tool diameter compensation correction manually. Consequently, a design of the restoration with the required minimum interocclusal thickness, yet with accurate passive seating and marginal fit is possible without any further interventions. Conclusions: Understanding the specifics of the subtractive fabrication process as well as the properties of the restorative materials is a key factor in achieving optimal clinical outcomes with all-ceramic restorations fabricated with the CAD/CAM technology. The use of monolithic zirconia combined with a calculated reduction in the preset tool diameter compensation correction might be beneficial in cases with thin or uneven geometry. Schlagwörter: All-ceramic restorations, CAD/CAM, tool diameter compensation, monolithic zirconia, minimum thickness, subtractive manufacturing

Aim: To compare the accuracy of three impression methods by comparing the distance between the reference points of the implant fixture, especially in curved maxillary anterior teeth. Materials and methods: Implant fixtures were placed on the maxillary central incisor and canine areas. A maxillary master cast was made using a model scanner and 3D printer. Ten impressions were taken from the three experimental groups constructed (group P: pick-up impression coping; group I: scan body with an intraoral scanner; and group B: bite impression coping). The distance between the reference points, the angle between the scan bodies, and displacement of the 3D surface area were measured. Results: The distance between reference points were significantly different between group I and group B in the maxillary incisors and between group P and the other two groups in the maxillary canines. Group P had the least amount of displacement in both fixtures. Both fixtures showed the highest displacement in group B. Displacement of the 3D surface area in the maxillary incisors showed no significant difference between the groups. There was a significant difference in the maxillary canines between groups P and I. Conclusions: All three implant impression methods showed changes in the position and angle of the fixture compared with the master cast. In this study, the impression method using the pick-up impression coping showed the highest accuracy, but the impression method using the intraoral scanner also showed clinically acceptable accuracy. It should be noted that errors may occur when taking impressions using bite coping. Schlagwörter: bite impression coping, implant angulation, implant impression, intraoral scanner, scan body

Die chirurgische Kronenverlängerung stellt einen der häufigsten operativen Eingriffe in der parodontologischen Praxis dar. Sie kann grundsätzlich in eine funktionale und eine ästhetische chirurgische Kronenverlängerung unterteilt werden. Generell stellt die chirurgische einen vorhersagbaren parodontalchirurgischen Eingriff dar. Die typische Komplikation liegt in einer übermässigen Rückbildung des dentoalveolären Komplexes nach koronal. Die ästhetische chirurgische Kronenverlängerung kann durch eine vorherige digitale Planung vorhersagbar durchgeführt werden, das Risiko möglicher Komplikationen wie eine übermässige Rückbildung des dentoalveolären Komplexes nach koronal kann dadurch minimiert werden. Ziel dieses Beitrags ist es nun, ein klinisches Fallbeispiel zur chirurgischen Kronenverlängerungen mit digitaler Planung zu präsentieren und daraus praktische Empfehlungen abzuleiten. Schlagwörter: chirurgische Kronenverlängerung, digitale Planung, Ästhetik

Aim: This study’s purpose was to evaluate the long-term clinical survival and success rate of veneered zirconia crowns with a modified anatomical framework design after 10 years in function. Materials and Methods: In total, 36 zirconia crowns were fabricated for 28 patients. An anatomically modified framework design was developed. Crowns were inserted between the years 2008 and 2009. A follow-up of 19 patients with 28 crowns was conducted in 2020 to document mechanical and biologic parameters. Additionally, a modified version of the pink esthetic score (PES) was collected. Patient satisfaction was assessed using United States Public Health Service (USPHS) criteria. The success and survival rates were calculated using the Kaplan–Meier analysis. Results: After more than 10 years of clinical service, the zirconia crowns’ survival rate was 92.9%. Biological complications occurred in 12% of crowns, whereas technical complications occurred in 54% of the examined crowns. Mostly, chippings (50%) and insufficient marginal gaps (50%) were observed. Most crowns were positively evaluated for more than one technical complication. Periodontal conditions with probing depths up to 3 mm were comparable to measured values before crown delivery (73–75%). Most of the crowns had modified PES values of 10 or higher. Patients’ satisfaction was high. Conclusion: The modified framework design leads to crowns’ high survival rate but relatively low success rate. High patient satisfaction and inconspicuous periodontal conditions were demonstrated. Biological complications occur far less frequently than technical complications. Schlagwörter: All-ceramic crown, framework design, clinical study, chipping, complications

Aim: To evaluate the fracture load and the type of failure of two different monolithic restorative materials bonded to standardized titanium bases and fabricated by two different procedures regarding the bonding-interface. Materials-Methods: All screw-retained implant-crown specimens (n=40), subjected to fatigue by thermomechanical loading, differed in the restorative material (lithium disilicate-LDS or polymer infiltrated ceramic network (PICN), referred to as “hybrid ceramic”-HYC) and the interface type between the restorative material and the titanium base abutment (prefabricated ex-factory or produced during the CAM-milling procedure). This resulted in the following groups (n=10/group): (1) LDS-M: lithium disilicate crown with a CAM-milled interface, (2) LDS-P: lithium disilicate crown with a prefabricated interface, (3) HYC-M: PICN crown with a CAM-milled interface and (4) HYC-P: PICN crown with a prefabricated interface. Aged specimens underwent static fracture load testing. The load (N) at which the initial crack occurred was denoted as Finitial, and the maximal load (N) at which the restorations fractured as F_max. All specimens were examined under a stereomicroscope to determine the failure mode. Results: The median F_initial values were 180 N for LDS-M, 343 N for LDS-P, 340 N for HYC-M and 190 N for HYC-P. The median F_max values were1822 N for LDS-M, 2039 N for LDS-P, 1454 N for HYC-M and 1581 N for HYC-P. The intergroup differences were significant for F_initial (KW: p = 0.0024) and for F_max (KW: p = 0.0010). The failure types also showed differences between the restorative groups. Conclusion: The choice of restorative material had a stronger influence on the fracture load than the abutment interface workflow. Lithium disilicate showed the highest load for initial crack appearance (F_initial) and for complete fracture of the restoration (F_max). Schlagwörter: abutment interface, dental materials, failure mode, fracture load, lithium disilicate, polymer infiltrated ceramic network, prosthetic dentistry, restorative material, thermomechanical aging

Aim: To evaluate CAD-CAM milling vibrations related to zirconia disk design, framework and location of digital crown nesting during zirconia soft milling. Materials and methods: In this in-vitro study, 25, 98 mm round (R group) and 15, 71 mm D-shape (D group) zirconia disks were placed in a 5-axis CAD-CAM milling unit. The R group had 3 crown milling sites (n = 75) and the D group had 2 crown milling sites (n = 30). In the R group, site A was located 57 mm from the machine holder. Site B was 92 mm and C was 123 mm from the machine holder. In the D group, site A was 57 mm and site C was 123 mm from the machine holder attachment. A vibration meter (VB-8200; Lutron) was connected to the disk holder and data (mm/seconds) were collected during the milling process at the different nesting locations. One-way ANOVA with post-hoc tests and Bonferroni correction for multiple tests were used to compare the groups (α = 0.05). Results: In the R group, site C exhibited the highest mean vibration values compared to site A (P = 0.001). The first and second cutter tools (2.5 and 1 mm) exhibited statistically significant difference between the D and R groups, at milling sites A and C (P < 0.001/ P = 0.003, respectively). Conclusions: Milling vibration increased as the distance between the machine holder arm and a digitally nested site increased. Round zirconia disks induced higher vibration values, as compared to D-shape disks. Schlagwörter: CAD-CAM, Digital nesting, Milling vibration, Zirconia

Aim: The aim of this study was to compare the load bearing capacity of monolithic or bilayered single crowns with zirconia or polyetherketoneketone frameworks designed and fabricated using computer-aided design/computer-aided manufacturing (CAD/CAM) systems. Materials and methods: Cr–Co -based metal dies (N=60) were duplicated from an extracted and prepared premolar and then restored with different CAD/CAM materials. The specimens were divided into five groups (n= 12 per group) according to the type of materials: Group S: monolithic zirconia-reinforced lithium silicate; group ZI: bilayered zirconia framework with lithium disilicate; group ZE: bilayered zirconia framework with resin-infiltered hybrid ceramic; group PI: bilayered polyetherketoneketone (PEKK) framework with lithium disilicate; and group PE: bilayered PEKK framework with resin-infiltered hybrid ceramic. The crown specimens were cemented on Cr-Co metal dies with a resin cement (Multilink N). The specimens were subjected to cyclic mechanical loading followed by load bearing testing. Data were analyzed using Kruskall-Wallis and Mann-Whitney U tests (α=0.05). Results: The monolithic crowns in group S (1930±452.18 N) presented significamtly higher load bearing capacity than those of other groups (p <0.05). This was followed by group ZI (1165.41±264.04 N). The remaining groups demonsrated comparable results. Failure types were more frequent in all zirconia specimens that included veneering ceramic. Conclusions: Monolithic zirconia-reinforced lithium silicate CAD/CAM ceramics showed superior load bearing capacity compared to all other bilayered counterparts. All CAD/CAM materials tested remarkably exceeded the average occlusal force in the posterior region. Schlagwörter: bilayered, CAD/CAM, load bearing capacity, monolithic, PEKK

Aim: The accuracy of 3-dimensional images produced by intraoral-scanner (IOS) is affected by the optical characteristic of restorative materials such as metal, ceramic, and resin. This in-vitro study aimed to investigate the impact of core build-up resin composite translucency on IOS’s accuracy. Material and methods: A core build-up procedure was performed on a proprietary 3D-printed model using injectable composites with 4 levels of translucency (highest to lowest: GC AE, A3, AO3, and EX). Ten experimental scans/group were operated using IOS Medit i700 on the phantom head-mounted model. Reference scans were obtained by an industrial scanner (Solutionix C500). Values of accuracy (trueness and precision) for the respective groups were evaluated using mean deviation values following 3D superimposition. Results: Composite translucency caused scale reduction of optical impression. Values of trueness showed the highest scale reduction in the AE group significantly, followed by A3, AO3, and EX. Considering the cut-off value of deviations as 50μm for clinical acceptability, the analysis elucidated the most deviations in AE and A3. Similar results were found in precision where AE showed the highest deviation value statistically, then A3, AO3, and EX. Conclusions: Composite translucency affects the accuracy of optical impression, causing the fitting error of CAD/CAM prosthesis. The more translucent the composite, the less accurate the optical impression. This suggests the proper compensation during prosthesis designing for an optimal clinical result. Besides, practitioners should indicate the proper restorative materials regarding not only the aesthetics and mechanical properties but also the optical characteristics in the digital workflow. Schlagwörter: Accuracy, CAD/CAM, digital dentistry, intraoral-scanner, precision, resin composite, trueness

Aim: This in-vitro study aimed to compare the accuracy of the implant position inserted by surgical guides manufactured by three different 3D Printers (one SLA and two DLP printers) and subtractive technique for a free-end situation. Material and Methods: Surgical guides have been manufactured using three different 3D printing devices, one SLA (Form 2, Formlabs) and two DLP Printers (D20II, Rapidshape; Solflex 350, Voco). Surgical guides manufactured using the conventional CAD/CAM based subtractive method served as controls. In total 48 guides were printed and assessed for accuracy. The surgical guides were used for the placement of implants at tooth position no. 37. The postoperative implant position has been digitally scanned for metric comparison with the preoperatively planned implant position. Results: Significant differences have been found comparing the SLA and the DLP printers. While showing that SLA in comparison to DLP had a significant lower accuracy in implant displacement at crest (p = 0.032) and angular displacement (p = 0.049). DLP showed comparable values as the control group. The results were within an acceptable clinical range. Conclusion: DLP technology seems to be superior to conventional SLA technology, in terms of accuracy of 3D printed surgical guides when used for placement of implants in free-end situations. Schlagwörter: 3D printing, accuracy, dental materials, free-end situation, guided surgery, milling, oral implantology

Aim: The computer-aided manufacture 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 polymethylmethacrylate (TelioCAD) were examined, representing these different material classes. For each material, 12 specimens (n=12) were fabricated in five thicknesses (0.4 mm, 0.7 mm, 1.0 mm, 1.3 mm, 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 determined. Results Logarithmic regression curves showed the best R² approximation (Cerasmart, R² = 0.994; Vita Enamic, R² = 0.978; Lava Ultimate, R² = 0.997; TelioCAD, R² = 0.997) to the light transmission values. Conclusion The results of this study indicate that the translucency of resin-based materials can be calculated using a mathematical approach to estimate their optical behavior. Cerasmart, Lava Ultimate, Vita Enamic, and TelioCAD 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. Schlagwörter: CAD-CAM, digital workflow, hybrid materials, mathematical analysis, PMMA, polymer infiltrated ceramic network, resin nano ceramics, translucency, translucency equation

Aim: To compare the planned implant position (PIP) to the transferred implant position (TIP) after fully guided implant placements in single-tooth gaps. Materials and methods: Dental implant placements were planned using different implant systems (Camlog Screw Line [C-SL], Straumann Bone Level Tapered [S-BLT]) and planning software (SMOP and coDiagnostiX). All implants were placed according to full-guided protocols and intraoral scans were performed intraoperatively. For comparison of PIP and TIP scan data were imported to a software (Geomagic Control X [GCX]) and accuracies were evaluated. Deviations were reported in a coordinate system (x-, y- and z-axis) at entry points and apices. Total deviations including the angular deviations were calculated with GCX. For statistical analysis, level of significance was set to p < 0.05. Results: Twenty-six patients received twenty-six implants. Mean three-dimensional (3D) deviation at implant’s entry point was 0.61mm ± 0.28 for C-SL and 0.63mm ± 0.24 for S-BLT. For implant’s apex, mean 3D deviation of 0.96mm ± 0.41 was documented for C-SL and 1.04mm ± 0.34 for S-BLT. Mean angular deviation was 2.58° ± 1.40 for C-SL and 2.89° ± 1.12 for S-BLT. Statistical analysis revealed no significant differences between implant systems, but significant deviations regarding z-axis, both at entry point and apex (p < 0.05). Conclusion: 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 1.5mm safety distances to critical structures was confirmed. Schlagwörter: dental implants, static navigation, CAD/CAM, computer-assisted, backward planning, digital workflow

Aim: The aim was to compare the performance of a collaborative tactile robot programmed by a dental professional (DP) with the performance of a DP in removal of surrogate plaque In vitro. Materials and methods: Six teeth of typodonts in articulated jaws were covered with surrogate plaque and cleaned by a DP with 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 experiment 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 robot and the DP showed no significant differences. However, electric toothbrushing was significantly less effective compared to manual toothbrushing (p<0.05). Conclusion: This In vitro study indicates that current robot technology may perform removal of surrogate plaque as efficient as a DP. In future this may be helpful to release nursing staff from this time-demanding and possibly contagious task or support humans with reduced motor skills or impaired vision in performing daily oral hygiene. Schlagwörter: Dental robots, Dentistry, Dentronic, electric toothbrush, human-machine-interaction, human-robot-interaction, manual toothbrush, Oral hygiene, Robotics

Objective: Orthodontic treatments with custom-made active elements may lead to more efficient treatment with fewer side effects. The objective of this in vitro study was to determine whether individually constructed, mathematically simulated and 3D printed power chains can generate adequate forces for orthodontic tooth movement. 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 Polyurethan (TPU) filaments and thermoplastic elastomer (TPE) filament. With the CAD-data a finite elemente 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 ICC of 0.999 and a Dahlberg error of 0.05 N. The measured forces ranged from 168 g to 680 g. There was a significant correlation between measured and calculated forces (R 0.91 to 0.98). Discussion: In this 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 examplary 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, e.g., root resorption. Conclusion: This in vitro study is the first to show the possible individualized construction and 3D printing of elastic chains exhibiting reproducible, predefined forces. Schlagwörter: force measurement, 3D printing, digital workflow, finite elemente, orthodontics

Aim: The purpose of this investigation was to evaluate the accuracy of root canal length determination in dependence of CBCT acquisition protocol and evaluating the influence of additional superimposed computerized optical impressions. Materials and Methods: CBCT scans with low-dose (LD) and high-definition (HD) protocols and computerized optical impressions of thirty extracted human molars were acquired. The Sicat Endo software (Sicat, Bonn, Germany) was used for CBCT root canal length (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 to the ARCL were 0.26 mm (HD+), 0.34 mm (HD-), 0.43 (LD+) and 0.66mm (LD-). 93.4% of all measurements in the HD+ group were within the limits of ±0.5 mm. Conclusions: Both resolution and superimposition of additional computerized optical impressions have a significant influence on root canal length measurements using CBCT. Schlagwörter: CBCT, computerized optical impression, root canal length determination, SICAT Endo

Aim: The aim of this in vitro study was the evaluation of the in-vitro performance and fracture force of 3D-printed anterior implant-supported temporary partial dentures (TPD) with different filler content. Materials and Methods: Identical anterior resin-based TPDs (tooth situation 11-13; n=8 per material) were 3D-printed of methacrylate resins with different filler content. A cartridge polymethacrylate (PMMA) material was used as a reference. After temporary cementation, combined thermal cycling and mechanical loading (TCML) was performed on all 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). Result: Failure during TCML varied between three failures and total failure during loading time. Mean survival time varied between 93±206 x10³ cycles and 329±84 x10³ cycles. Significant different survival cycles between individual materials could be determined (Log Rank test Mantel Cox: Chi2 21,861, 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 N and 835 N. Failures were characterized by fracture of the connector (n=24) followed by fractures at the abutment (n=10). Conclusion: 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. Schlagwörter: rapid prototyping, 3D printing, temporary dentures, TCML, FEA, TPD, Implant

Aim: The accuracy and reproducibility of occlusal contact points visualized by articulation foil (AF) should be investigated and then compared with contact points calculated by three different intraoral scanners (IOS). Materials and Methods: Occlusal contact points were visualized on a standardized resin dental tooth model using AF 50 times with maximum intercuspidation and constant biting force. The points were photographed from a vertical position above the model and superimposed on a screen in order to test the reproducibility of the model. This was followed by fifty-fold repetition by scans and computation of the occlusal contact points by the respective IOS CS3600 (CS ScanFlow v.1 4th version), TRIOS 3 (Basic 2019), and CEREC Omnicam (Software version 5.1). The results of computation were captured with screenshots, and were then overlaid with the photographs of the AF. The image overlays were classified into five categories: category 1 = total overlapping of contact points, category 2 = partly overlapping, category 3 = adjacent contact points without overlapping, category 4 = contact points identified only by IOS, category 5 = contact points identified only by AF. All data were statistically evaluated (95% CI). Results: In total, the visualisation of the occlusal contact points by the IOS were significantly less accurate and less reproducible compared to the AF (p < 0.05). In the combination of sensitivity and accuracy, the TRIOS3 by 3Shape showed significantly better results than the other IOS tested (p < 0.05). Conclusion: In vitro, AF displayed a significantly more accurate visualisation of the occlusal contact points than IOS. Schlagwörter: articulating foil, digital intraoral scanners, occlusion, occlusal contact point, reproducibility, visualisation