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BACKGROUND/PURPOSE: Clenching is a dental parafunctional disorder that jeopardizes the life of teeth and/or dental prostheses. Computer-aided design and computer-aided manufacturing (CAD/CAM)–fabricated or 3-dimensional-printed dental prostheses are aesthetic, strong, and of good quality, but noticeable damage can still be observed after clenching. Stress analysis of synthetic ceramic assemblies with various parameters was conducted to provide data that may be used to improve the fabrication of CAD/CAM–fabricated dental prostheses. MATERIALS AND METHODS: Abaqus software was used to run the simulations. A total of 96 axisymmetric finite element ceramic assembly models were simulated under 800 N vertical loading and different contact radii (0.25, 0.5, 0.75, 1.0 mm), materials (IPS e.max CAD and Vita Enamic), layer thicknesses and combinations. RESULTS: Four-layered ceramic assembly models produced promising results with the following parameters: contact radius of at least 0.5 mm, total thickness of at least 0.5 mm, and use of IPS e.max CAD as the first layer and Vita Enamic as the second layer without cement. CONCLUSION: The ideal four-layered assembly model design uses 0.25-mm-thick IPS e.max CAD as its outer layer to simulate enamel binding and 0.25-mm-thick Vita Enamic as its inner layer to imitate the natural tooth. This design may be used as reference for prosthodontic treatment.

BACKGROUND/PURPOSE: Palladium-silver (Pd–Ag) alloys are important as an alternative to gold-based alloys. The purpose of this study was to investigate the effect of an argon-arc vacuum pressure casting process on the recasting of the Pd–Ag alloy. MATERIALS AND METHODS: The recasting Pd–Ag alloys were compared with conventional horizontal centrifugal (HC) casting to an argon (Ar)-arc vacuum pressure (Ar-arc/VP) casting. The first-generation castings were made from a Pd–Ag alloy purchased from a supplier. Next-generation castings were made from 50 wt% Pd–Ag alloy before casting and 50 wt% from previous castings. This sequence was repeated over three generations to form the 2nd, 3rd and 4th recasting ingots. The ingots were then measured for marginal accuracy, interfacial oxidation, hardness and phase identification. RESULTS: The recasting success rate of recastibility reached 100%. Compared with the HC group, the Ar-arc/VP group had better edge precision, smaller oxide layer thickness and lower hardness. The comparison of X-ray diffraction intensity showed that the relative intensities of Pd and Ag in the first, second and third generations recasting of the Ar-arc/VP group were significantly higher than those of the HC group. Phase analysis showed that the trace elements of indium and tin contents in the Pd–Ag recasting ingots of the Ar-arc/VP group were higher than those of the HC group. CONCLUSION: The results showed that the casting process used for recasting affected the quality of the Pd–Ag alloy. Therefore, Ar-arc/VP casting process could improve the effect of Pd–Ag recasting and maintain the alloy properties in comparison with HC casting.

Cone beam computed tomography (CBCT) is frequently used in dental diagnosis and treatment. Comparative studies of the effects of CBCT on implant navigation, however, are still limited. The objective of this study was to evaluate whether the computed tomography images of the four commercial brands will affect the accuracy of the new version of IRIS implant navigation system.In the first part, the accuracy of the IRIS implant navigation system was evaluated by a precision confirmation jig whose position is confirmed. In the second part, the IRIS implant navigation system was used in conjunction with 4 brands of CBCT scans analyzed by its effect on accuracy.The results showed that the mean deviation of the new version of IRIS-100 system accuracy was less than 1 mm. Among the four groups, the overall average deviation caused by CBCT images showed that the 3D eXam group had the smallest error of approximately 0.94 ± 0.12 mm and the AZ 3000 CT group had the largest error of approximately 1.34 ± 0.10 mm.Based on the study, the accuracy of the IRIS implant navigation system will vary with the CBCT image resolution and the status of the CBCT machine.

BACKGROUND/PURPOSE: The SimEx is dental training system that applies new technology in a computerized dental simulator. The purpose of this study was to understand the usability satisfaction of the SimEx dental education and evaluation system by dental students and dentists at Tohoku University. MATERIALS AND METHODS: In this study, the Tohoku University IRB execution number was 2020-3-33. The number of subjects accepted was 59 at Tohoku University and divided into 4 groups based on years of clinical experience (Group A: 0 years; Group B: 1–2 years; Group C: 2–5 years; Group D: at least 5 years), and a total of 58 usability questionnaires were collected. Subjects completed the SimEx Usability Satisfaction Questionnaire after operating the SimEx (EPED Inc., Kaohsiung, Taiwan) course, which contained 16 questions. RESULTS: Among the 58 questionnaires collected by Tohoku University, there were 19 undergraduate students (4th∼6th grade), 12 post-graduate students, 14 residents, and 13 dentists. Significant differences between Group A and Group B, and between Group A and Group D were found (P

BACKGROUND/PURPOSE: The optimal strategy for scanning removable partial dentures remains unknown. This study investigated scanning strategies for patients with a maxillary Kennedy Class I arch as well as the measurement deviations of three scanning strategies. MATERIALS AND METHODS: A standard maxilla model was positioned with a holder in a dental chair to simulate a natural patient position and posture. Standard Tessellation Language files for reference models were formatted with a desktop scanner, and model operation files were obtained with a TRIOS 3 Pod intraoral scanner and superimposed using Exocad computer-aided design software. The three scanning strategies evaluated in this study (Strategy M, T-R, and R-T) were used for nine scans each, and the resulting data were recorded. The deviation of the three strategies was statistically analyzed through one-way ANOVA and Tukey post hoc testing. RESULTS: The trueness of Strategy M, T-R, and R-T was 52.6 ± 31.0, 54.9 ± 27.6, and 50.1 ± 22.3 μm, respectively. No statistically significant differences in trueness were detected among the three groups (P > 0.05). However, Strategy T-R had the evenest distribution of all measuring points. The deviations of the measurements obtained by three scanning strategies were mostly between 30 and 70 μm. The precision of the three strategies was similar as well. CONCLUSION: Trueness did not differ significantly among the three strategies. However, Strategy T-R is recommended for use with a TRIOS 3 Pod scanner because of its reduction of the seesaw effect and high stabilization of the RPD framework.

Background This study evaluated the operating performance of an implant navigation system used by dental students and dentists of prosthodontic background with varying levels of experience. A surgical navigation system and optical tracking system were used, and dentists’ accuracies were evaluated in terms of differences between the positions of actually drilled holes and those of the holes planned using software before surgeries. Methods The study participants were 5 dental students or dentists who had studied in the same university and hospital but had different experience levels regarding implants. All participants were trained in operating the AqNavi system in the beginning of the study. Subsequently, using 5 pairs of dental models, each participant drilled 5 implant holes at 6 partially edentulous positions (11, 17, 26, 31, 36, and 47). In total, each participant conducted 30 drilling tests. Results In total, 150 tests among 5 dentists at 6 tooth positions (11, 17, 26, 31, 36, and 47) were conducted. Although a comparison of the tests revealed significant differences in the longitudinal error (P P = .0011), no significant difference was observed in the total error among the dentists. Conclusions A relatively long operating time was associated with relatively little implant experience. Through the dental navigation system, dental students can be introduced to dental implant surgery earlier than what was possible in the past. The results demonstrated that the operational accuracy of the dental implant navigation system is not restricted by participants’ implant experience levels. The implant navigation system assists the dentist in the ability to accurately insert the dental implant into the correct position without being affected by his/her own experience of implant surgery.

OBJECTIVES To determine the minimum thickness required for a monolithic hybrid ceramic crown on different substrates (soft vs stiff) used in posterior dentition for bruxism. METHODS 80 polymer-infiltrated ceramic networks Vita Enamic (PICN VE) disc specimens with four different occlusal thicknesses (0.8, 1.2, 1.6 and 2.0 mm), were produced using a computer-aided design/manufacturing system, and cemented on a stiff (zirconia) or soft (polyamide) substrate of 4-mm thickness. The ten specimens, in soft or stiff groups, were subjected to compressive loading by a MTS machine until fracture or maximum load (4500 N) was reached. The unbroken specimens were examined using optical coherence tomography. Eight axisymmetric finite element models and eight 3D models comprising the four different occlusal thicknesses and two substrates under different vertical loads and sliding movements were constructed. The maximum principal stress was selected to evaluate the stress distribution in this study. RESULTS The fracture resistance of the specimens was significantly different between the two substrates (P

Background/purpose Among the ceramic materials used for all-ceramic crowns, zirconia has high biocompatibility and favorable mechanical properties, but its main drawbacks include low translucency and stress-induced phase transformation. To stabilize high-strength tetragonal zirconia polycrystal (TZP), 3–5 mol% yttria is usually added to prepare yttria-stabilized TZP (Y-TZP). In this study, the optical properties of three commercial Y-TZP ceramics were compared with those of the clinically available glass-ceramic material of lithium disilicate, and the relationship between translucency and crystal properties was analyzed in vitro. Materials and methods Twelve 5-mm-thick standardized disks were prepared from three Y-TZP ceramics and one lithium disilicate block. Absolute translucency was measured using a spectrophotometer with an integrating sphere. X-ray diffraction was used to quantify the main structural parameters (i.e., preferred plane, quantitative phase, and grain size) of Y-TZP crystals. Results The product-dominated phase of Y-TZP exhibited a tetragonal lattice pattern, and the preferred planes had minor variations. The diffraction patterns of the three Y-TZP ceramics demonstrated minor effects on translucency, without significant differences (p > 0.05). The grain size of 54–70 nm was negatively related to translucency in Y-TZP. Lithium disilicate specimens had significantly higher translucency than the three Y-TZP specimens (p Conclusion Grain size reduction played an essential role in developing highly translucent Y-TZP ceramics. The three Y-TZP ceramics were essentially opaque but exhibited poorer translucency than lithium disilicate in terms of esthetics.

Cleidocranial dysplasia (CCD) is an autosomal-dominant malformation syndrome affecting bones and teeth. The most common skeletal and dental abnormalities in affected individuals are hypoplastic/aplastic clavicles, open fontanelles, short stature, retention of primary teeth, delayed eruption of permanent teeth, supernumerary teeth, and multiple impacted teeth. Treatment of CCD requires a multidisciplinary approach that may include dental corrections, orthognathic surgery and cranioplasty along with management of any complications of CCD. Early diagnosis of this condition enables application of the treatment strategy that provides the best quality of life to such patients. Notably, Runx2 gene mutations have been identified in CCD patients. Therefore, further elucidation of the molecular mechanism of supernumerary teeth formation related to Runx2 mutations may improve understanding of dental development in CCD. The insights into CCD pathogenesis may assist in the development of new treatments for CCD. Keywords: cleidocranial dysplasia, mutation, Runx2, supernumerary teeth