Yuchun Sun

Study on CAD&RP for removable complete denture

This study explored a method for fabricating removable complete denture aided by CAD&RP technology. 3D crossing section scanner and laser scanner were respectively applied to obtain the surface data of artificial teeth, edentulous models and rims made in clinic. The vertical and horizontal relations of models were recorded before scanning with a special device. A 3D graphic database of artificial teeth, which can be aligned with parameters, was established. Special CAD software developed by ourselves was applied to the 3D integrated design process including automatic setting up artificial teeth, semiautomatic designing aesthetic and individualized artificial gingiva and base plate, automatic constructing individualized virtual flasks according to the finished CAD digital models of removable complete denture. At last, 3DP technology was used to make the individualized physical flasks. In this study, AMT and classic denture materials were effectually combined to achieve making removable complete denture aided by CAD/RP technology.

Nano hydroxyapatite particles promote osteogenesis in a three-dimensional bio-printing construct consisting of alginate/gelatin/hASCs

To design a hydrogel material containing nano hydroxyapatite particles for three-dimensional (3D) bio-printing of human adipose-derived stem cells (hASCs) and to explore whether nano hydroxyapatite particles can promote osteogenic differentiation of a 3D bio-printing construct consisting of hASCs in vivo and in vitro. A 3D reticular printing structure was designed. Sodium alginate/gelatin/hASCs (AG group) was considered as the control group, and sodium alginate/gelatin/nano hydroxyapatite/hASCs (AGH group) was considered as the experimental group. Immunofluorescence microscopy was used to observe the cell viability and cell adhesion, and cell proliferation was analyzed by comparison of viable cell numbers in printed constructs at 1 day and 7 days after printing. After 14 days of osteogenic induction for the AG group and AGH group, real-time quantitative PCR and immunofluorescence were used to analyse the expression of the osteogenesis-related genes Runt-related transcription factor 2 (RUNX2), osterix (OSX), and osteocalcin (OCN). New bone formation in printed constructs was observed using micro-CT, HE staining, Masson trichrome staining, and OCN immunohistochemical staining 8 weeks after being implanted. The cells in the AG group and AGH group were evenly distributed in the 3D printed constructs. The number of viable cells and cell viability both in the AG group and AGH group at 7 days after printing were higher than those at 1 day after printing (p < 0.05); however, the difference between the AG group and AGH group was not significant. At 14 days after osteogenic induction in vitro, real-time PCR results showed that the expression of osteogenesis-related genes in the AGH OM group was significantly higher than that in the AGH PM group, AG PM group, and AG OM group (p < 0.05). At 8 weeks after bio-printed construct implantation, the results of micro-CT, HE staining, Masson trichrome staining, and OCN immunohistochemical staining showed that the new bone formation in the AGH group was higher than that in the AG group (p < 0.05). The in vivo and in vitro results demonstrated that nano hydroxyapatite particles dispersed in a sodium alginate/gelatin matrix could promote osteogenic differentiation of hASCs in a 3D bio-printed construct, and this scaffold material could be considered to repair large bone tissue defects.

Osteogenic Differentiation of Three-Dimensional Bioprinted Constructs Consisting of Human Adipose-Derived Stem Cells In Vitro and In Vivo.

Here, we aimed to investigate osteogenic differentiation of human adipose-derived stem cells (hASCs) in three-dimensional (3D) bioprinted tissue constructs in vitro and in vivo. A 3D Bio-plotter dispensing system was used for building 3D constructs. Cell viability was determined using live/dead cell staining. After 7 and 14 days of culture, real-time quantitative polymerase chain reaction (PCR) was performed to analyze the expression of osteogenesis-related genes (RUNX2, OSX, and OCN). Western blotting for RUNX2 and immunofluorescent staining for OCN and RUNX2 were also performed. At 8 weeks after surgery, osteoids secreted by osteogenically differentiated cells were assessed by hematoxylin-eosin (H&E) staining, Masson trichrome staining, and OCN immunohistochemical staining. Results from live/dead cell staining showed that most of the cells remained alive, with a cell viability of 89%, on day 1 after printing. In vitro osteogenic induction of the 3D construct showed that the expression levels of RUNX2, OSX, and OCN were significantly increased on days 7 and 14 after printing in cells cultured in osteogenic medium (OM) compared with that in normal proliferation medium (PM). Fluorescence microscopy and western blotting showed that the expression of osteogenesis-related proteins was significantly higher in cells cultured in OM than in cells cultured in PM. In vivo studies demonstrated obvious bone matrix formation in the 3D bioprinted constructs. These results indicated that 3D bioprinted constructs consisting of hASCs had the ability to promote mineralized matrix formation and that hASCs could be used in 3D bioprinted constructs for the repair of large bone tissue defects.

Influence of object translucency on the scanning accuracy of a powder-free intraoral scanner: A laboratory study

Statement of problem. Limited information is available regarding the influence of object translucency on the scanning accuracy of a powder‐free intraoral scanner. Purpose. The purpose of this in vitro study was to evaluate the scanning accuracy of a confocal microscopy principle powder‐free intraoral scanner on ceramic copings and to analyze the relationship between scanning accuracy and object translucency. Methods. Six slice specimens (12×10 mm) and 6 offset copings (1.00‐mm thickness) were made from different translucent homogeneous ceramic blocks (CEREC Blocs, S0‐M to S5‐M, highest to lowest translucency). The primary sintered zirconia offset coping was produced in the same way as the control. Optical parameters related to the translucency of each slice were measured with a spectrophotometer. Three‐dimensional (3D) datasets of the surface morphology of offset copings were obtained by using the intraoral scanner. The same white wax resin bases were used for registration. Quantitative parameters of scanning trueness and precision were measured. One‐way ANOVA was used to analyze the values of each parameter among the 6 ceramic blocks. Bivariate correlation was used to analyze the relationships between each parameter of scanning accuracy and translucency (&agr;=.05). Results. Translucent copings showed a positive 3D bias (S0‐M to S5‐M: 0.149 ±0.038 mm to 0.068 ±0.020 mm), a narrower collar diameter (Dd=−0.067 mm), larger convergence angle (&Dgr;&PHgr;=2.79 degrees), and larger curvature radius of the internal gingivoaxial corner (&Dgr;&rgr;=0.236 mm). The smaller the percentage sum of scattering and absorption, the greater was the occurrence of scanning bias (r=−0.918) and curvature (r=−0.935) decrease. Conclusions. Use of the tested powder‐free intraoral scanner, higher translucency objects (greater translucency than S1‐M/A1C) resulted in lower scanning accuracy and morphological changes. Therefore, more suitable methods of measurement are still required.

A Method of Three-Dimensional Recording of Mandibular Movement Based on Two-Dimensional Image Feature Extraction.

Background and Objective To develop a real-time recording system based on computer binocular vision and two-dimensional image feature extraction to accurately record mandibular movement in three dimensions. Methods A computer-based binocular vision device with two digital cameras was used in conjunction with a fixed head retention bracket to track occlusal movement. Software was developed for extracting target spatial coordinates in real time based on two-dimensional image feature recognition. A plaster model of a subject’s upper and lower dentition were made using conventional methods. A mandibular occlusal splint was made on the plaster model, and then the occlusal surface was removed. Temporal denture base resin was used to make a 3-cm handle extending outside the mouth connecting the anterior labial surface of the occlusal splint with a detection target with intersecting lines designed for spatial coordinate extraction. The subjects head was firmly fixed in place, and the occlusal splint was fully seated on the mandibular dentition. The subject was then asked to make various mouth movements while the mandibular movement target locus point set was recorded. Comparisons between the coordinate values and the actual values of the 30 intersections on the detection target were then analyzed using paired t-tests. Results The three-dimensional trajectory curve shapes of the mandibular movements were consistent with the respective subject movements. Mean XYZ coordinate values and paired t-test results were as follows: X axis: -0.0037 ± 0.02953, P = 0.502; Y axis: 0.0037 ± 0.05242, P = 0.704; and Z axis: 0.0007 ± 0.06040, P = 0.952. The t-test result showed that the coordinate values of the 30 cross points were considered statistically no significant. (P<0.05) Conclusions Use of a real-time recording system of three-dimensional mandibular movement based on computer binocular vision and two-dimensional image feature recognition technology produced a recording accuracy of approximately ± 0.1 mm, and is therefore suitable for clinical application. Certainly, further research is necessary to confirm the clinical applications of the method.

Femtosecond laser ablation of dentin and enamel: relationship between laser fluence and ablation efficiency

Abstract. The objective was to study the relationship between laser fluence and ablation efficiency of a femtosecond laser with a Gaussian-shaped pulse used to ablate dentin and enamel for prosthodontic tooth preparation. A diode-pumped thin-disk femtosecond laser with wavelength of 1025 nm and pulse width of 400 fs was used for the ablation of dentin and enamel. The laser spot was guided in a line on the dentin and enamel surfaces to form a groove-shaped ablation zone under a series of laser pulse energies. The width and volume of the ablated line were measured under a three-dimensional confocal microscope to calculate the ablation efficiency. Ablation efficiency for dentin reached a maximum value of 0.020  mm3/J when the laser fluence was set at 6.51  J/cm2. For enamel, the maximum ablation efficiency was 0.009  mm3/J at a fluence of 7.59  J/cm2. Ablation efficiency of the femtosecond laser on dentin and enamel is closely related to the laser fluence and may reach a maximum when the laser fluence is set to an appropriate value.

Surface roughness and wettability of dentin ablated with ultrashort pulsed laser

Abstract. The aim of this study was to evaluate the surface roughness and wettability of dentin following ultrashort pulsed laser ablation with different levels of fluence and pulse overlap (PO). Twenty-five extracted human teeth crowns were cut longitudinally into slices of approximately 1.5-mm thick and randomly divided into nine groups of five. Samples in groups 1 to 8 were ablated with an ultrashort pulsed laser through a galvanometric scanning system. Samples in group 9 were prepared using a mechanical rotary instrument. The surface roughness of samples from each group was then measured using a three-dimensional profile measurement laser microscope, and wettability was evaluated by measuring the contact angle of a drop of water on the prepared dentin surface using an optical contact angle measuring device. The results showed that both laser fluence and PO had an effect on dentin surface roughness. Specifically, a higher PO decreased dentin surface roughness and reduced the effect of high-laser fluence on decreasing the surface roughness in some groups. Furthermore, all ablated dentin showed a contact angle of approximately 0 deg, meaning that laser ablation significantly improved wettability. Adjustment of ultrashort pulsed laser parameters can, therefore, significantly alter dentin surface roughness and wettability.

Effects of different surface treatments on the cyclic fatigue strength of one-piece CAD/CAM zirconia implants

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.

Assessment of CAD-CAM zirconia crowns designed with 2 different methods: A self-controlled clinical trial

Statement of problem. In computer‐aided design and computer‐aided manufacturing (CAD‐CAM) dentistry, the correlation method is an efficient way to design complete crowns. However, the occlusal relationship and patient satisfaction with prostheses fabricated using this method remain unclear. Purpose. The purpose of this clinical trial was to compare the occlusion of monolithic zirconia crowns designed using the correlation and library methods. Material and methods. Twenty‐three teeth of 21 participants received 2 monolithic zirconia crowns designed by using the correlation or the library method. Defective teeth were scanned using an intraoral scanner to obtain references and working casts from before and after the preparation. Before cementation, the occlusal relationship of both crowns and patient satisfaction were evaluated, and the occlusal adjustment time was recorded. Results. The correlation method resulted in less lateral occlusal interference of the crowns than the library method (P<.01). The occlusal adjustment times of the correlation and library conditions were 455.8 ±357.1 seconds and 575.3 ±488.0 seconds, respectively (P>.05). Relative occlusal force was significantly higher in the correlation than in the library condition and was related to before preparation relative occlusal force (r=0.706, P<.01). The visual analog score before occlusal adjustment was higher in the correlation than in the library condition (P<.05). The occlusal contacts, occlusal contact distributions, and number of occlusal contacts did not differ between conditions (P>.05). Conclusions. Better eccentric occlusion and reduced lateral occlusal interference were obtained when the correlation method was used to design crowns. The correlation method yielded higher relative occlusal force, which helped to restore the original occlusal force.

Evaluation of the accuracy of three-dimensional reconstruction of edentulous model jaw relation based on dental articulator positioning

A dental articulator and three-dimensional (3D) scanner were utilized to reconstruct the spatial relationship between upper and lower edentulous jaw gypsum models made from five patients. The 7-axis Faro Edge contact measurement system was used to evaluate the vertical and horizontal distances between jaws. Paired t-test results of vertical distance (0.089±0.428 mm) and horizontal distance (-0.082±0.221 mm) between points on the jaws showed no significant differences (P>0.05). One-Way ANOVA of the same measurement data for the five models also showed no significant differences (P>0.05). With an error of less than 0.1 mm, these measurements met clinical requirements. In conclusion, 3D reconstruction of edentulous jaw gypsum models with accurate jaw relation was made possible by scanning the models in centric relation on a dental articulator.