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We considered the possibility of reducing industrial waste by fabricating and reusing dental models prepared using a fused deposition modeling (FDM) 3D printer and polylactic acid (PLA) filaments. The purpose of this study was to verify the accuracy of models fabricated using FDM and PLA.The same provisional crown was used to check the marginal fit on PLA models prepared using an intraoral scanner (IOS) and FDM, plaster models made with silicone impression material and plaster, and resin models prepared using an IOS and stereolithography apparatus (SLA) 3D printer. The marginal fit was measured using micro-computed tomography at four points on the tooth: the buccal center (B), palatal center (P), mesial center (M), and distal center (D) points.At point B, the marginal gaps were 118 ± 21.7, 62 ± 16.4, and 50 ± 26.5 μm for the PLA, resin, and plaster models, respectively, with a significant difference between the PLA model and the other two. However, the marginal gap at all other measurement points was not significantly different between the models (P0.05).We compared the accuracy of the models fabricated using the FDM, SLA, and conventional methods. The combination of FDM and PLA filaments showed no significant differences from the other models, except at point B, indicating its usefulness. Therefore, FDM and PLA may become necessary materials for dental treatment in the future.

Polylactic acid (PLA) has gained considerable attention as an alternative to petroleum-based materials due to environmental concerns. We fabricated implant models with fused filament fabrication (FFF) 3D printers using PLA, and the accuracies of these PLA models were compared with those of plaster models made from silicone impressions and resin models made with digital light processing (DLP). A base model was obtained from an impact-training model. The scan body was mounted on the plaster, resin, and PLA models obtained from the base model, and the obtained information was converted to stereolithography (STL) data by the 3D scanner. The base model was then used as a reference, and its data were superimposed onto the STL data of each model using Geomagic control. The horizontal and vertical accuracies of PLA models, as calculated using the Tukey–Kramer method, were 97.2 ± 48.4 and 115.5 ± 15.1 μm, respectively, which suggests that the PLA model is the least accurate among the three models. In both cases, significant differences were found between PLA and gypsum and between the PLA and resin models. However, considering that the misfit of screw-retained implant frames should be ≤150 µm, PLA can be effectively used for fabricating implant models.

Background The use of intraoral scanners (IOS) has facilitated the use of digital workflows for the fabrication of implant-supported prostheses not only for single missing teeth, but also for multiple missing teeth. However, the clinical application of IOS and computer-aided design/manufacturing (CAD/CAM) in implant-supported prosthodontics remains unclear. This study aimed to compare the accuracy of digital and silicone impressions for single-tooth implants for bounded edentulous spaces and two-unit and three-unit implant-supported fixed dental prostheses for free-end edentulous spaces. Methods This study enrolled 30 patients (n = 10 for each of the three groups) with an average age of 61.9 years. Conventional silicone-based and digital IOS-based impressions were made for all patients, and the implant superstructures were fabricated. We measured the scan-body misfit and compared the accuracy of the impressions for single-unit, two-unit, and three-unit implant prostheses with a bounded edentulous space by superimposing the standard triangulated language (STL) data obtained from IOS over the STL data of the plaster model used for final prosthesis fabrication. The scan bodies of the superimposed single-molar implant, two-unit implant prosthesis without teeth on the mesial side, two-unit implant prosthesis without teeth on the distal side, three-unit implant prosthesis without teeth on the mesial side, and three-unit implant prosthesis without teeth on the distal side were designated as A, B1, B2, C1, and C2, respectively. The misfit for each scan body was calculated and the accuracies were compared using the Tukey–Kramer method. Results The average scan-body misfit for conditions A, B1, B2, C1, and C2 was 40.5 ± 18.9, 45.4 ± 13.4, 56.5 ± 9.6, 50.7 ± 14.9, and 80.3 ± 12.4 μm, respectively. Significant differences were observed between the accuracies of A and B2, A and C2, and C1 and C2 (P Conclusions IOS and CAD/CAM can find clinical applications for implant-supported prostheses of up to three units for a bounded edentulous saddle. The use of IOS could render implant treatment easier, benefiting both the surgeons and patients. Prosthesis maladjustment may lead to peri-implantitis and prosthetic fracture. Therefore, further validation of the accuracy of IOS impressions is required in patients with multiple missing teeth in long-span implant prostheses.

Background In locations where the alveolar bone height is low, such as at the maxillary molars, implant placement can be difficult, or even impossible, without procedures aimed at generating new bone, such as sinus lifts. Various types of bone graft materials are used after a sinus lift. In our study, a three-dimensional image analysis using a volume analyzer was performed to measure and compare the volume of demineralized bovine bone mineral (Bio-Oss®) and carbonate apatite (Cytrans®) after a sinus lift, as well as the amount of bone graft material resorption. Patient data were collected from cone-beam computed tomography images taken before, immediately following, and 6 months after the sinus lift. Using these images, both the volume and amount of resorption of each bone graft material were measured using a three-dimensional image analysis system. Results The amount of bone resorption in the Bio-Oss®-treated group was 25.2%, whereas that of the Cytrans®-treated group was 14.2%. A significant difference was found between the two groups (P < 0.001). Conclusions Our findings indicate that the volume of bone resorption was smaller in the Cytrans®-treated group than in the Bio-Oss®-treated group, suggesting that Cytrans® is more promising for successful implant treatments requiring a sinus lift.

Background Implant treatment using guided surgery is becoming widespread in clinical dental practice. Furthermore, the development of digital technology has enabled the use of intraoral scanners (IOSs) to fabricate surgical guide plates. The objective of this study was to compare the accuracy of guided surgery using the silicone impression method with a three-dimensional (3D) scanner and the digital impression method with IOS for one side of the mandibular free end. In addition, we compared the accuracy of tooth-supported vs tooth/mucosa-supported surgical guide plates. Results The accuracy of the tooth-supported surgical guide plate using the new IOS method instead of the method of obtaining impressions with conventional silicone resulted in better measurements of 3D deviation at the crest, 3D deviation at the apex, and angular deviation. In terms of the accuracy of the tooth/mucosa-supported surgical guide plate, there were no significant differences in all measurements. The surgical guide plate using an IOS and the tooth/mucosa-supported surgical guide plate may enable more accurate guided surgery. Conclusion Tooth/mucosa-supported guided surgery involving preparation with an IOS may result in more accurate implant surgery.

Based on the hypothesis that the fabrication of dental models using fused deposition modeling and poly-lactic acid (PLA), followed by recycling and reusing, would reduce industrial waste, we aimed to compare the accuracies of virgin and recycled PLA models. The PLA models were recycled using a crusher and a filament-manufacturing machine. Virgin PLA was labeled R, and the first, second, and third recycles were labeled R1, R2, and R3, respectively. To determine the accuracies of the virgin and reused PLA models, identical provisional crowns were fitted, and marginal fits were obtained using micro-computed tomography. A marginal fit of 120 µm was deemed acceptable based on previous literature. The mesial, distal, buccal, and palatal centers were set at M, D, B, and P, respectively. The mean value of each measurement point was considered as the result. When comparing the accuracies of R and R1, R2, and R3, significant differences were noted between R and R3 at B, R and R2, R3 at P, and R and R3 at D (p < 0.05). No significant difference was observed at M. This study demonstrates that PLA can be recycled only once owing to accuracy limitations.

Background The vertical thickness of the peri-implant mucosa is associated with the amount of post treatment marginal bone loss. However, the variations in mucosal thickness at the different edentulous sites have been sparsely documented. The purpose of the study was to conduct a survey of the frequency distribution of variations in mucosal thickness at the different sites of the edentulous alveolar ridge and to compare them according to gender. Our study included 125 partially edentulous patients having a total of 296 implant sites. Cone-beam computed tomography (CBCT) scans were obtained by placing a diagnostic template with a radiopaque crown indicator on the ridge to determine the mucosal thickness at the crest of the alveolar ridge. Results The mucosal thickness was 3.0±1.3 mm in the maxilla, which was significantly greater than the mucosal thickness of 2.0±1.0 mm in the mandible (p Conclusions Although this study was a limited preoperative study, the vertical mucosal thickness at the edentulous ridge differed between the maxillary and mandibular regions. The majority of sites in the mandibular molar region had a mucosal thickness of less than 2 mm. Practitioners might be able to develop an optimal dental implant treatment plan for long-term biologic and esthetic stability by considering these factors.

Background The purpose of this study was to assess the cortical-level sensory differences between natural teeth with a periodontal membrane and dental implants. Material and methods We used functional near-infrared spectroscopy (fNIRS) to measure brain activity in the cerebral cortex of 12 patients who had both natural teeth and dental implants in the lower molar region. Painless vibratory tactile stimulation was performed on both the natural teeth and the dental implants. Results Activation was seen in the somatosensory cortex during stimulation of both natural teeth and dental implants. A comparison of cortical activation showed no significant differences between natural teeth and dental implants. Conclusions These results indicate the possible existence of sensory input to the cerebral cortex via dental implants as well as natural teeth, and thus suggest that may not only the periodontal membrane be involved in the signaling pathway. The data from this experiment may help us for understanding the neural mechanisms underlying natural teeth and dental implants. Key words:fNIRS, natural teeth, implants, brain activity, somatosensory cortex.

An epithesis using osseointegrated implants as an anchorage has been proven and established as an effective means for maxillofacial rehabilitation. In this paper, we describe the basic techniques of auricular epithesis and the applications of computer technology to its execution, ranging from diagnosis to surgery, and superstructure fabrication to maintenance. The key steps of this treatment are conducting Computed Tomography (CT ) diagnosis before the operation to avoid implant penetration through the skull during the operation, embedding two implants into the section that represents the antihelix, and if possible, preserving or forming the tragus so that the edge of the epithesis is not close to the temporomandibular joint region to ensure mandibular movements are not restricted. We also discuss the applications of navigation surgery, which we are currently investigating, as well as the future prospect of augmented reality and mixed reality surgeries.

連続乳化重合プロセスの強化の観点から，撹拌・混合操作条件および，反応溶液のpHが粒子の反応・凝集に及ぼす効果を調べた．実験は乳化剤濃度を低くすることを目的として臨界ミセル濃度以下で行った．撹拌条件を変化させる実験では，半月型2枚翼の回転数が200 rpm未満で撹拌の影響を受け，重合率および，凝集による粒子成長は抑制された．一方，回転数が200 rpm以上では重合速度に対して重合反応が律速となり，高い重合率が得られた．撹拌速度の増加に伴い，粒子の凝集による成長速度も速くなり，大きい粒子が得られた．反応溶液のpH条件を変化させた実験では，反応溶液のpHが6，7と大きい場合は平均粒子径の最大値は3 μmと増加し，粒子径が10 μm以上のものが観察された．この場合，平均粒子径が最大値に達するまでの粒子径分布はバイモーダルとなり，平均粒子径がピークを過ぎ減少しはじめると粒子径分布は単分散となることがわかった．