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Background and Objective: Complete denture is a common restorative treatment in dental patients and the design of the core components (major connector and retentive mesh) of complete denture metal base (CDMB) is the basis of successful restoration. However, the automated design process of CDMB has become a challenging task primarily due to the complexity of manual interaction, low personalization, and low design accuracy., Methods: To solve the existing problems, we develop a computer-aided Segmentation Network-driven CDMB design framework, called CDMB-SegNet, to automatically generate personalized digital design boundaries for complete dentures of edentulous patients. Specifically, CDMB-SegNet consists of a novel upright-orientation adjustment module (UO-AM), a dental feature-driven segmentation network, and a specific boundary-optimization design module (BO-DM). UO-AM automatically identifies key points for locating spatial attitude of the three-dimensional dental model with arbitrary posture, while BO-DM can result in smoother and more personalized designs for complete denture. In addition, to achieve efficient and accurate feature extraction and segmentation of 3D edentulous models with irregular gingival tissues, the light-weight backbone network is also incorporated into CDMB-SegNet., Results: Experimental results on a large clinical dataset showed that CDMB-SegNet can achieve superior performance over the state-of-the-art methods. Quantitative evaluation (major connector/retentive mesh) showed improved Accuracy (98.54 ± 0.58 %/97.73 ± 0.92 %) and IoU (87.42 ± 5.48 %/70.42 ± 7.95 %), and reduced Maximum Symmetric Surface Distance (4.54 ± 2.06 mm/4.62 ± 1.68 mm), Average Symmetric Surface Distance (1.45 ± 0.63mm/1.28 ± 0.54 mm), Roughness Rate (6.17 ± 1.40 %/6.80 ± 1.23 %) and Vertices Number (23.22 ± 1.85/43.15 ± 2.72). Moreover, CDMB-SegNet shortened the overall design time to around 4 min, which is one tenth of the comparison methods., Conclusions: CDMB-SegNet is the first intelligent neural network for automatic CDMB design driven by oral big data and dental features. The designed CDMB is able to couple with patient's personalized dental anatomical morphology, providing higher clinical applicability compared with the state-of-the-art methods., Competing Interests: Declaration of competing interest The authors report no conflicts of interest., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Volatile organic compounds (VOCs) undergo substantial photochemical losses during their transport from emission sources to receptor sites, resulting in serious implications for their source apportionment and ozone (O 3 ) formation. Based on the continuous measurements of VOCs in suburban Jinan in August 2022, the effects of photochemical losses on VOC source contributions and O 3 formation were evaluated in this study. The observed and initial concentrations of total VOCs (TVOC) were 12.0 ± 5.1 and 16.0 ± 7.4 ppbv, respectively. Throughout the observation period, alkenes had the most prominent photochemical losses (58.2%), followed by aromatic hydrocarbons (23.1%), accounting for 80.6% and 6.9% of the total losses, respectively. During high O 3 episodes, the photochemical loss of VOCs was 6.9 times higher than that during the cleaning period. Alkene losses (exceeding 67.3%), specifically losses of isoprene, propylene, ethylene, and n-butene, dominated the total losses of VOCs during the O 3 increase period. Eight sources of VOCs were identified by positive matrix factorization (PMF) based on the observed and initial concentration data (OC-PMF and IC-PMF, respectively). Concentrations of all emission sources in the OC-PMF were underestimated by 2.4%-57.1%. Moreover, the contribution of each emission source was over- or underestimated compared with that in case of the IC-PMF. The contributions of biogenic and motor vehicle exhaust emissions were underestimated by 5.3 and 2.8 percentage points, respectively, which was associated with substantial oxidation of the emitted high-reactive species. The contributions of coal/biomass burning and natural gas were overestimated by 2.4 and 3.9 percentage points, respectively, which were related to the emission of low-reactive species (acetylene, ethane, and propane). Based on our results, the photochemical losses of VOCs grossly affect their source apportionment and O 3 formation. Thus, photochemical losses of VOCs must be thoroughly accounted to establish a precise scientific foundation for air-pollution control strategies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Objectives: This study evaluated the accuracy of digital implant impressions with or without prefabricated landmarks compared with the conventional method in the edentulous mandible., Methods: An edentulous mandibular stone cast with implant abutment analogs and scan bodies in FDI #46, #43, #33, and #36 served as the master model. The scans captured with intraoral scanners (IOS) were divided into four groups: IOS-NT (no landmarks + Trios 4 scanner), IOS-NA (no landmarks + Aoralscan 3 scanner), IOS-YT (landmarks + Trios 4 scanner), and IOS-YA (landmarks + Aoralscan 3 scanner) (n=10). Landmarks were attached to the scan bodies with resin to improve scanning fluency. Conventional open-trayed technique (CNV) was performed with the 3D-printed splinting frameworks (n=10). The master model and conventional castings were scanned using a laboratory scanner, and the former served as the reference model. Overall distance and angle deviations between scan bodies were measured to determine trueness and precision. The ANOVA or Kruskal-Wallis test compared CNV group to scans without landmarks, while a generalized linear model analyzed scan groups with and without landmarks., Results: Compared to the CNV group, the IOS-NA and IOS-NT groups showed higher overall distance trueness (p=0.009), and precision (distance, p<0.001 and angular, p<0.001). With landmarks, the IOS-YA group had higher overall trueness (distance, p<0.001 and angular, p<0.001) than the IOS-NA group, and the IOS-YT group has higher distance trueness (p=0.041) than the IOS-NT group. Moreover, the precision in distance and angle was significantly improved for IOS-YA and IOS-YT groups, compared with the IOS-NA (p<0.001) and IOS-NT (p<0.001) groups separately., Conclusions: Digital scans were more accurate than conventional splinting open-trayed impressions. Prefabricated landmarks significantly improved the accuracy of full-arch implant digital scans, regardless of the scanner used., Clinical Significance: Prefabricated landmarks can enhance the accuracy of intraoral scanners for full-arch implant rehabilitation, improving scanning efficiency and clinical outcomes., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

Objectives: To evaluate the effect of a nanosilica-lithium spray coating on the internal and marginal fit of high translucent zirconia crowns using a digital evaluation method., Methods: A three-dimensional analysis model of a zirconia abutment was digitally scanned using a dental scanner, and 30 monolithic high translucent zirconia crowns were designed and fabricated. They were divided into groups (n = 10) according to the surface treatment method: (1) no treatment: as-sintered zirconia; (2) airborne-particle abrasion with 50 μm Al 2 O 3 particles; and (3) nanosilica-lithium spray coating. Three-dimensional data for the abutment, crown, and crown seated on the abutment were obtained using a dental scanner. The three-dimensional seated fit between the crown and abutment was reconstructed using registration technology, and a three-dimensional (3D) deviation analysis was used to evaluate the effect of different modification methods on the internal and marginal fit of the crowns using root mean square (RMS) values., Results: The 3D deviation analysis of all groups conformed to a normal distribution (P > 0.05), and the variance was homogeneous (P > 0.05). The different surface treatments had no significant effect on the RMS values in the occlusal, axial, and marginal regions of the high translucent zirconia crowns (P > 0.05)., Conclusions: Nanosilica-lithium spray coating for the modification of as-sintered zirconia is clinically feasible and does not affect the internal or marginal fit of high translucent zirconia crowns., Clinical Significance: Nanosilica-lithium spray coating does not affect the adaptation of zirconia crowns and is a clinically feasible surface treatment method for zirconia. It is unnecessary to add the setting values of the internal and marginal fit when fabricating nanosilica-lithium-sprayed zirconia crowns., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

Background and Objective: The retention of selective laser melting (SLM)-built denture clasps is inferior to that of cast cobalt-chromium (Co-Cr) clasps engaging 0.01-in undercuts, which are commonly used in clinical practice. Either the clasps engage in excessively deep undercuts or inappropriate printing process parameters are applied. With appropriate undercut engagement and levels of process parameters, the retention of SLM-built clasps (including Co-Cr, commercially pure titanium [CP Ti], and Ti alloy [Ti-6Al-4V] ones) may be comparable to that of cast Co-Cr clasps. Therefore, this feasibility study aimed to evaluate their retention to guide dentists during material selection for the powder-bed fusion process during the printing of denture clasps., Methods: We engaged the clasp arm at an appropriate undercut depth (0.01 or 0.02 in), built clasps at the orientation of their longitudinal axes approximately parallel to the build platform, generated square prism support structures at a critical overhang angle of 30°, applied optimized laser parameters (laser power, scan speed, and hatch space), and adopted annealing treatment for Co-Cr, CP Ti, and Ti-6Al-4V clasps. After postprocessing and accuracy measurement, an insertion/removal test of the clasps for 15,000 cycles was performed to simulate 10 years of clinical use, and the retentive force was recorded every 1500 cycles. Permanent deformation of the retentive arms of the clasps was measured. Cast Co-Cr clasps engaging 0.01-in undercuts were designated the control group., Results: The initial retentive forces of the SLM-built Co-Cr clasps engaging 0.01-in undercuts and CP Ti and Ti-6Al-4V clasps engaging 0.02-in undercuts were comparable to those of the control group. SLM-built Co-Cr clasps engaging 0.01-in undercuts and Ti-6Al-4V clasps engaging 0.02-in undercuts had similar final retentive force and less permanent deformation compared with those of the control group; SLM-built CP Ti clasps engaging 0.02-in undercuts had lower final retentive force and greater permanent deformation., Conclusions: Considering the long-term retention and permanent deformation of the retentive arms, Co-Cr and Ti-6Al-4V alloys, except CP Ti, are recommended for printing denture clasps. SLM-built Co-Cr clasps should engage 0.01-in undercuts, and Ti-6Al-4V clasps should engage 0.02-in undercuts., Competing Interests: Declaration of competing interest None Declared., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Purpose: In this study, we propose a 3D printing-aided method for manufacturing complete dentures and evaluate its accuracy of artificial tooth positioning., Methods: Complete dentures were designed and 3D printed and put on a plaster cast; and pack and press technique was used to fabricate the final denture during which artificial teeth were inserted in the teeth holes formed by the printed denture. In this study, fused deposition moulding (FDM) and stereolithography (SLA) techniques were used to fabricate complete dentures (10 pairs of maxillary and mandibular dentures each). After 3D scanning the final dentures, 3D comparison between the scanned teeth on the denture and its computer-aided design (CAD) data was made and single-tooth deflection angles were measured to evaluate the tooth position. Values were compared using independent-sample t-tests or the Mann-Whitney U test., Results: In the result of 3D comparison, the root mean square values of artificial teeth were 0.107 ± 0.018 mm (SLA group) and 0.136 ± 0.023 mm (FDM group; P < 0.05). In the result of single-tooth deflection angles, the mandibular anterior teeth demonstrated the maximum deflection angle, followed by the molars, premolars, and maxillary anterior teeth., Conclusions: It is feasible to fabricate complete dentures using 3D-printed complete dentures as prototypes and combine conventional methods. The accuracy of the final denture fabricated using SLA printing was better than that of dentures produced using the FDM method., Clinical Significance: The 3D printing-aided manufacturing for complete dentures refers to using the 3D-printed dentures as a prototype along with the traditional process to fabricate final dentures and is an effective alternative when the dentures cannot be directly processed using computer-aided manufacturing (CAM)., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Tumor grading and interpretability of laryngeal cancer is a key yet challenging task in the clinical diagnosis, mainly because of the commonly used low-magnification pathological images lack fine cellular structure information and accurate localization, the diagnosis results of pathologists are different from those of attentional convolutional network -based methods, and the gradient-weighted class activation mapping method cannot be optimized to create the best visualization map. To address this problem, we propose an end-to-end depth domain adaptive network (DDANet) with integration gradient CAM and priori experience-guided attention to improve the tumor grading performance and interpretability by introducing the pathologist's a priori experience in high-magnification into the depth model. Specifically, a novel priori experience-guided attention (PE-GA) method is developed to solve the traditional unsupervised attention optimization problem. Besides, a novel integration gradient CAM is proposed to mitigate overfitting, information redundancies and low sparsity of the Grad-CAM graphs generated by the PE-GA method. Furthermore, we establish a set of quantitative evaluation metric systems for model visual interpretation. Extensive experimental results show that compared with the state-of-the-art methods, the average grading accuracy is increased to 88.43% (↑4.04%), the effective interpretable rate is increased to 52.73% (↑11.45%). Additionally, it effectively reduces the difference between CV-based method and pathology in diagnosis results. Importantly, the visualized interpretive maps are closer to the region of interest of concern by pathologists, and our model outperforms pathologists with different levels of experience., Competing Interests: Declaration of competing interest The authors declared no conflict of interest., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Background: The authors of this study aimed to compare the treatment outcomes and time efficiency between digital and conventional complete denture restorations and propose suggestions for clinical use., Methods: The authors used digital (functionally suitable digital complete denture [FSD]) and conventional complete denture restorations to make 2 dentures each for 10 edentulous patients. All the operations of both techniques before denture delivery were completed in the first 4 visits, and then 2 dentures were delivered successively for the patients. The clinical and laboratory times were recorded to evaluate the time efficiency; treatment outcomes were evaluated via scoring the denture satisfaction of the dentist and patients in a double-blind manner., Results: The satisfaction scores of FSDs (7.6-9.6 [dentist's scores], 8.4-10 [patients' scores]) were higher than those of conventional dentures (7.2-9.7 [dentist's score], 7.4-9.8 [patients' scores]), but there were no significant differences. The clinical and laboratory operation times of the FSD group were less than those of the conventional group, saving an average of 28.0 minutes and 64.3 minutes in the clinic and laboratory, respectively., Conclusions: FSD technology can improve the efficiency of clinical and laboratory operations and shorten the manufacturing cycle of dentures. The occlusion stability of FSDs was statistically better than that of traditional dentures, but there was no statistical difference in other clinical indicators., Practical Implications: FSD technology is low cost and easy to operate and has several applications. Compared with conventional complete denture restoration technology, FSDs can save time and have a comparable clinical effect. This clinical trial was registered at the Chinese Clinical Trial Registry. The registration number is ChiCTR1900021722., (Copyright © 2023 American Dental Association. Published by Elsevier Inc. All rights reserved.)

Purpose: The purpose of this study was to evaluate a novel 3D-printed custom tray for impressions of edentulous jaws, and to compare it with conventional impression trays., Methods: Fifteen edentulous patients were enroled to evaluate the accuracy and border extension of a novel custom tray in the shape of a complete denture. Four impressions were made for each patient. Impressions made using novel custom trays were considered the experimental group, impressions made using conventional custom trays were considered the control group, and impressions made using final dentures and non-pressure custom trays were considered the reference groups. The experimental and control groups were compared with the reference groups using three-dimensional (3D) comparison analysis, and the impressions were further divided into regions. The root mean square (RMS) value was calculated to analyse the differences in impression morphology. Additionally, the experimental and control groups were compared to analyse border extension at standard locations., Results: Compared to the final denture impression as a reference, the diagnostic denture impression (RMS:0.146 ± 0.024 mm) was closer to the reference than the conventional impression (RMS:0.176 ± 0.047 mm), with a significant difference only in the secondary stress-bearing area. The border extension of the diagnostic denture impression was slightly longer than the conventional impression; however, the difference was not statistically significant., Conclusions: The impressions made using the novel custom tray were similar to those made with a definitive complete denture. However, no significant differences were noted when compared with the conventional impressions., Competing Interests: Declaration of Competing Interest The authors have no financial conflicts of interest., (Copyright © 2022. Published by Elsevier Ltd.)

Objectives: To compare the trueness of computer-aided design and computer-aided manufacturing (CAD-CAM) assisted procedure and freehand procedure for preparing guiding planes for removable partial dentures (RPDs)., Methods: Forty identical mandibular resin casts were divided into two groups in which the guiding planes of two abutment teeth were prepared freehand (control group, n = 20) and using rigidly constrained templates (test group, n = 20). The template was designed on a digital cast of virtually prepared guiding planes and fabricated by selective laser melting using cobalt-chromium alloy. To assess the 3D trueness, all prepared guiding planes (Test data) were digitized using a laboratory scanner and compared to the virtually designed guiding planes (Reference data). The angle deviation between the Test data and the designed direction of the path of placement was measured for assessing the direction trueness of guiding plane preparation., Results: The 3D trueness of guiding plane preparation was significantly better in the Test group (48.4 ± 12.9 μm) than in the Control group (128.5 ± 37.6 μm, p < 0.01). The direction trueness of guiding plane preparation was also significantly better in the Test group (1.20 ± 0.55°) than in the Control group (7.68 ± 3.00°, p < 0.01)., Conclusions: The CAD-CAM template assisted procedure can significantly improve tooth preparation of the guiding planes compared to the freehand preparation. The CAD-CAM template could help clinicians prepare parallel guiding planes in a predictable manner., (Copyright © 2022. Published by Elsevier Ltd.)

Background and Objective: To evaluate the effect of guiding structure and 3D-printing material of CAD-CAM guides on the accuracy of guiding planes preparation., Methods: Four types of computer-aided design and computer-aided manufacturing (CAD-CAM) guides for preparing guiding planes of removable partial denture (RPD) were designed in two types of guiding structures (triple-constraint and single-plane constraint) and were 3D printed using resin and cobalt-chromium (Co-Cr) alloy. Guiding plane preparation of identical resin casts was performed using CAD-CAM guides (resin template, metal template, resin guided device, and metal guide device) in four test groups and by freehand in the control group (n = 22 per group). All prepared casts were then scanned (Test) and aligned to the reference cast with designed guiding planes. 3D compare analysis was performed and root-mean-square (RMS) values were calculated for assessing the 3D trueness and 3D precision of guiding plane preparation. The angle between the prepared guiding plane (Test) and the designed path of placement of RPD (Reference) was measured for evaluating the direction trueness., Results: RMS values of the metal template group for 3D trueness (39.7 ± 14.6 μm) and 3D precision (28.6 ± 6.8 μm) were significantly lower than that of other groups (p < .05). For direction trueness, the metal template group showed the least angle deviation (1.09 ± 0.56°), and the freehand group demonstrated the largest angle deviation (7.03 ± 2.83°)., Conclusions: The Co-Cr alloy guides with triple-constraint guiding structure can assist to prepare accurate guiding planes of RPD., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

With the development of three-dimensional (3D) scanning and measurement technologies, the internal adaptation of restorations was measured by the 3D analysis method. The purpose of this study was to explore a novel 3D digital evaluation method to assess the intraoral fitness of removable partial dentures (RPDs) and evaluate the accuracy of this novel digital method in vitro. A 3D digital method to evaluate the clinical fitness of RPD was introduced. A standard stone cast of a partially edentulous mandible simulating the oral tissues and a corresponding RPD were used to evaluate the accuracy of this novel digital method (3D analysis on duplicated polyether cast) and another reported 3D digital evaluation method (3D analysis on RPD directly) for intraoral fitness of RPD in vitro. 12 polyvinyl siloxane (PVS) replica specimens were fabricated in each method in vitro, and the thicknesses of these PVS replicas were measured by 3D analysis on duplicated polyether cast (named Polyether group), 3D analysis on RPD directly (named Denture group), and 3D analysis on the stone cast (named Stone group), respectively. The thicknesses of PVS replicas were compared with analyses of variance (ANOVA) to evaluate the accuracy of these methods (α = 0.05). The accuracy based on the mean thickness of the PVS replicas of Polyether group were better than that of Denture group (P < 0.05) and had no statistical difference with that of Stone group (P > 0.05). 3D analysis on duplicated polyether cast has comparable trueness and precision to 3D analysis on the stone cast and is feasible for evaluating clinical fitness of RPD., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Subtractive manufacturing has become the dominant method in fabricating zirconia dental restorations while additive manufacturing is emerging as a potential alternative. The aim of this in vitro study was to investigate the performance of stereolithography (SLA) and milling in fabricating monolithic zirconia crowns with different finish line designs. Full-contour crowns with three finish lines (chamfer, rounded shoulder, knife-edge) were designed and fabricated by SLA and milling. Fabrication accuracy was accessed by 3D deviation analysis and margin quality was characterized under microscopes. The obtained root mean square value was significantly influenced by finish line design (P < 0.05) but not by fabrication method (P＞0.05). However, the color-difference map showed crowns fabricated by SLA and milling had different error distribution in external surfaces. SLA-printed crowns exhibited margins of rounded line angle and without small flaws, although large chippings were found in knife-edged crowns. In milling group, crowns showed margins of sharp line angle and with separate chippings. More and larger margin chippings were found in knife-edged crowns by milling. The results indicate that SLA and milling can fabricate monolithic zirconia crowns of comparable accuracy and knife-edged crowns are prone to large margin chippings by either of the two manufacturing methods., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Purpose: To compare the accuracy of a chairside fused deposition modeling (FDM) 3D-printed surgical template with that of a light-cured template for implant placement., Materials and Methods: Twenty standard mandibular resin models with missing teeth 36 and 46 were selected. Surgical templates were fabricated using a chairside FDM 3D-printer (test group) or a light-curing 3D printer (control group) (n = 20/group). Forty implants were placed by a clinician blinded to group allocation. The angular, 3D, mesiodistal, buccolingual, and apicocoronal deviations at the implant base and tip between preoperative design and postoperative implant position were recorded., Results: The mean angular (test vs control groups: 3.22° ± 1.55° vs 2.74° ± 1.24°, p = 0.343) and 3D deviations at the implant base (test vs control groups: 0.41 ± 0.13 mm vs 0.35 ± 0.11 mm, p = 0.127) and tip (test vs control groups: 0.91 ± 0.34 mm vs 0.75 ± 0.28 mm, p = 0.150) were similar. The mesiodistal, buccolingual, and apicocoronal deviations at the implant base and tip also did not differ significantly between groups (p > 0.05)., Conclusions: For single tooth gap indications, implant placement with an FDM 3D-printed surgical template was as accurate as that with a light-cured template, and more efficient., (Copyright © 2019 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.)

Objectives: The effects of different surface treatments on cyclic fatigue strengths of computer-aided design and computer-aided manufacturing (CAD/CAM) zirconia implants and its mechanisms were evaluated., Material and Methods: One-piece cylindrical screw-type zirconia (Y-TZP) implants with diameters of 4.1-mm were fabricated using CAD/CAM technique; they were divided into four groups according to the type of surface treatment: (i) sintering (control group, CTRL), (ii) sandblasting (SB), (iii) sandblasting and etching with an experimental hot etching solution (SB-ST), and (iv) sandblasting and etching with hydrofluoric acid (SB-HF). The surface morphology and roughness of the implants were evaluated. Tetragonal to monoclinic transformation was measured on the surface by micro Raman spectroscopy. Static and fatigue tests were carried out at room temperature following the ISO 14801:2014 Standard. The cyclic fatigue strength of each group was determined using the staircase method. Specimens that survived the fatigue test were statically loaded to measure the residual fracture strength., Results: Among the four groups, SB-HF exhibited the highest surface roughness. Compared with the CTRL group, the surface monoclinic content was higher after all three types of surface treatments, amongst which, SB-HF had the highest content (39.14%), significantly more than the other three groups (P < 0.01). The cyclic fatigue strengths of CTRL, SB, SB-ST, and SB-HF implants were 530 N, 662.5 N, 705 N, and 555 N, respectively. The fracture strength after fatigue loading was higher than that before fatigue loading with no significant difference (P＞0.05)., Conclusions: SB and SB-ST remarkably enhanced the fatigue resistance of zirconia implants, while SB-HF did not. One-piece 4.1-mm diameter CAD/CAM zirconia implants have sufficient durability for application in dental implants., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A dental defect is one of the most common oral diseases, and it often requires a full crown restoration. In this clinical operation, the dentist must manually prepare the affected tooth for the full crown so that it has a convergence angle between 4° and 10°, no undercuts, and uniform and even shoulder widths and depths using a high speed diamond bur in the patient׳s mouth within one hour, which is a difficult task that requires visual-manual operation. The quality of the tooth preparation has an important effect on the success rate of the subsequent prosthodontic treatment. This study involved research into digital modeling technology for full dental crown tooth preparation. First, the margin line of the tooth preparation was designed using a semi-automatic interactive process. Second, the inserting direction was automatically computed. Then, the characteristic parameters and the constraints on the tooth preparation were defined for the model. Next, the shoulder and axial surface of the tooth preparation were formed using parametric modeling. Finally, the implicit surface of a radial basis function was used to construct the tooth preparation׳s occlusal surface. The experimental results verified that the method of digital modeling for full crown preparation proposed in this study can quickly and accurately implement personalized designs of various parameters, such as the shoulder width and the convergence angle; it provides a digital design tool for full crown preparation., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

With the accelerated aging of world population, complete denture prosthesis plays an increasingly important role in mouth rehabilitation. In addition to recovering stomatognathic system function, restoring the appearance of a third of the area under the face has become a great challenge in complete denture prosthesis. This study analyzes the interactive relationship between the appearance of a third of the area under the face and complete denture, and proposes a new method to predict facial deformation after complete denture prosthesis. Firstly, to improve computational efficiency, the feature template is constructed to replace the deformed facial region. Secondly, a forecast model of elastic deformation is constructed using BP neural network and predicts elastic deformation amount because of the inhomogeneous, anisotropic and nonlinear material properties of soft tissue. Finally, a new feature template is calculated using deformation amount, and the deformation of preoperative model is simulated using Laplacian deformation technique. The average error rates of different hidden layer nodes in the neural network are analysed. Deformation and postoperative models are superimposed for match analysis. Experimental results show that this method can predict facial soft tissue deformation quickly and accurately., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Background: This paper introduces a method to digitally design a virtual model of a tooth preparation of the mandibular first molar, by using the commercial three-dimensional (3D) computer-aided design software packages Geomagic and Imageware, and using the model as an input to automatic tooth preparing system., Methods: The procedure included acquisition of 3D data from dentate casts and digital modeling of the shape of the tooth preparation components, such as the margin, occlusal surface, and axial surface. The completed model data were stored as stereolithography (STL) files, which were used in a tooth preparation system to help to plan the trajectory. Meanwhile, the required mathematical models in the design process were introduced., Results: The method was used to make an individualized tooth preparation of the mandibular first molar. The entire process took 15min., Discussion: Using the method presented, a straightforward 3D shape of a full crown can be obtained to meet clinical needs prior to tooth preparation., (© 2013 Published by Elsevier Ltd.)