Objective·To fabricate a 3D-printed dental crown and bridge resin slurry using digital light processing(DLP)technology,investigate the influence of different printing parameters on its mechanical properties,determine the optimal printing parameters,and optimize the composition ratio of DLP-printed crown and bridge resin.Methods·Based on the viscosity characteristics of the mixture,the optimal ratio of urethane dimethacrylate(UDMA)to poly(propylene glycol)dimethacrylate(PPGDMA)was explored.After silanizing silicon dioxide(SiO2),it was mixed with UDMA,PPGDMA,and 2,4,6-trimethylbenzoyl bis(p-tolyl)phosphine oxide(TMO)to prepare DLP-printed dental crown and bridge resin slurries with different solid contents,and their rheological properties were tested.The Beer-Lambert equation was used to calculate the light penetration depth and critical exposure energy of the printing slurry.Based on these values,different exposure intensities,exposure times,post-curing times,and layer thicknesses were set respectively to carry out a series of printing experiments.By comparing and analyzing the flexural strength of the products under different printing parameters,the optimal printing parameter combination was screened out.Results·Viscosity tests showed that the optimal UDMA-to-PPGDMA ratio was 6∶4.The rheological behavior of printing slurries with different solid contents was tested,and the results showed that the DLP-printed dental crown and bridge resin with a solid content of 22%exhibited the best printing performance.According to the Beer-Lambert analysis,the light penetration depth Dp of the printing slurry was 119.79 μm,and the critical exposure energy Ec was 25.54 mJ/cm2.When the exposure intensity was 20 mW/cm2,the flexural strength reached a maximum of(132.39±8.92)MPa,and the difference was statistically significant(P<0.05).The flexural results of different exposure times showed that the flexural strength could reach(131.73±9.43)MPa when the single-layer exposure time was 3.0 s,and there was no significant difference when the exposure time was further increased.The flexural results of different post-curing times showed that when the post-curing time reached 30 min,there was no significant relationship between the flexural strength value and the increase in post-curing time.Regarding the influence of different layer thicknesses on the flexural performance,the test results showed that when the layer thickness was 50 μm,the result was the best,and the difference was statistically significant(P<0.001).Conclusion·Based on viscosity and rheological tests,a DLP-printable crown and bridge resin slurry was successfully developed.The optimal printing parameters were determined through statistical analysis of flexural strength:exposure intensity of 20 mW/cm2,exposure time of 3.0 s,post-curing time of 30 min,and a layer thickness of 50 μm.

Objective·To fabricate a 3D-printed dental crown and bridge resin slurry using digital light processing(DLP)technology,investigate the influence of different printing parameters on its mechanical properties,determine the optimal printing parameters,and optimize the composition ratio of DLP-printed crown and bridge resin.Methods·Based on the viscosity characteristics of the mixture,the optimal ratio of urethane dimethacrylate(UDMA)to poly(propylene glycol)dimethacrylate(PPGDMA)was explored.After silanizing silicon dioxide(SiO2),it was mixed with UDMA,PPGDMA,and 2,4,6-trimethylbenzoyl bis(p-tolyl)phosphine oxide(TMO)to prepare DLP-printed dental crown and bridge resin slurries with different solid contents,and their rheological properties were tested.The Beer-Lambert equation was used to calculate the light penetration depth and critical exposure energy of the printing slurry.Based on these values,different exposure intensities,exposure times,post-curing times,and layer thicknesses were set respectively to carry out a series of printing experiments.By comparing and analyzing the flexural strength of the products under different printing parameters,the optimal printing parameter combination was screened out.Results·Viscosity tests showed that the optimal UDMA-to-PPGDMA ratio was 6∶4.The rheological behavior of printing slurries with different solid contents was tested,and the results showed that the DLP-printed dental crown and bridge resin with a solid content of 22%exhibited the best printing performance.According to the Beer-Lambert analysis,the light penetration depth Dp of the printing slurry was 119.79 μm,and the critical exposure energy Ec was 25.54 mJ/cm2.When the exposure intensity was 20 mW/cm2,the flexural strength reached a maximum of(132.39±8.92)MPa,and the difference was statistically significant(P<0.05).The flexural results of different exposure times showed that the flexural strength could reach(131.73±9.43)MPa when the single-layer exposure time was 3.0 s,and there was no significant difference when the exposure time was further increased.The flexural results of different post-curing times showed that when the post-curing time reached 30 min,there was no significant relationship between the flexural strength value and the increase in post-curing time.Regarding the influence of different layer thicknesses on the flexural performance,the test results showed that when the layer thickness was 50 μm,the result was the best,and the difference was statistically significant(P<0.001).Conclusion·Based on viscosity and rheological tests,a DLP-printable crown and bridge resin slurry was successfully developed.The optimal printing parameters were determined through statistical analysis of flexural strength:exposure intensity of 20 mW/cm2,exposure time of 3.0 s,post-curing time of 30 min,and a layer thickness of 50 μm.

Objective: To fabricate Ti alloy frameworks for a maxillary complete denture with three-dimensional printing (3DP) technique, such as selective laser melting (SLM) and electron beam melting (EBM), and to evaluate the microstructure of these frameworks and their adaptation to the die stone models. Methods: Thirty pairs of edentulous casts were divided into 3 groups randomly and equally. In each group, one of the three techniques (SLM, EBM, conventional technique) was used to fabricate Ti alloy frameworks. The base-cast sets were transversally sectioned into 3 sections at the distal of canines, mesial of first molars, and the posterior palatal zone. The gap between the metal base and cast was measured in the 3 sections. Stereoscopic microscope was used to measure the gap. Three pieces of specimens of 5 mm diameter were fabricated with Ti alloy by SLM, EBM and the traditional casting technology (as mentioned above). Scanning electron microscope (SEM) was used to evaluate the differences of microstructure among these specimens. Results: The gaps between the metal base and cast were (99.4±17.0), (98.2±26.1), and (99.6± 16.1) μm in conventional method; (99.4 ± 22.8), (83.1 ± 19.3), and (103.3 ± 13.8) μm in SLM technique; (248.3±70.3), (279.1±71.9), and (189.1±31.6) μm in EBM technique. There was no statistical difference in the value of gaps between SLM Ti alloy and conventional method Ti alloy group (P>0.05). There was statistical difference among EBM Ti alloy, conventional method Ti alloy and SLM Ti alloy group (P<0.05). The SLM Ti alloy showed more uniform and compact microstructure than the cast Ti alloy and EBM Ti alloy did. Conclusions SLM technique showed initial feasibility to manufacture the dental base of complete denture. The mechanical properties and microstructure of the denture frameworks prepared by SLM indicate that these dentures are appropriate for clinical use. EBM technique is inadequate to make a complete denture now.

Three-dimensional printing (3DP) forming technology can shape personalized porous implant material with complex shape and fine structure to meet the various needs of different patients. In this paper, the green parts of porous titanium implants with diameter 25 mm x 20 mm were prepared using 3DP, and then debinded at 500 degrees C under vacuum. Finally they were sintered in the argon gas at 1 300 degrees C. The pore sizes were observed, and they were between 50-150 microm under SEM. The results of porosity, bulk density, Vickers hardness, compressive strength and elastic modulus were (44.26% +/- 2.43)%, (2.59 +/- 0.81)g/cm3, 134.2-151.6 (61.2 +/- 3.2) MPa, (3.25 +/- 1.08) GPa, respectively. That shows excellent biomechanical compatibility. It is concluded that 3DP has wide application for fabrication of personalized porous titanium implant.
Biocompatible Materials ; chemistry ; Bone Substitutes ; chemistry ; Computer-Aided Design ; Materials Testing ; Porosity ; Prostheses and Implants ; Stress, Mechanical ; Tensile Strength ; Titanium ; chemistry

Objective The aim of this study was to evaluate the feasibility of three-dimensional printing (3DP) for the preparation of porous titanium implant and to investigate the impacts on microstructure and mechanical properties with different sintering temperatures.Methods The CAD model of the specimens was designed to be 25 mm in diameter,20 mm in height,and with 0.5 mm pore size mesh.On every cross-section,80％ bonding area was designed.Titanium powder (purity of 98.5％,75 μm diameter) was selected as raw material.Polyvinyl alcohol powder (160 μm diameter) was selected as a binder,and polyvinylpyrrolidone powder was selected as an auxiliary binder.The green porous titanium implants were fabricated by 3DP followed by sintering at 1 200,1 300,1 400 ℃,separately,under the protection of argon gas.After sintering,the properties of porous titanium implants were evaluated,including the porosity,microstructure,microhardness,compressive strength and elastic modulus.Results After sintering,the specimen had uniform contraction and no obvious distortion.The specimen sintered at 1 200,1 300 and 1 400 ℃ sintering temperatures had porosity of (65.01±1.03)％,(46.73±0.73)％ and (41.06±0.31)％,hardness of 115.2±0.6,148.6±1.1 and 182.8±2.1,elastic modulus of (5.9±0.5),(16.2±0.9) and (34.8±1.5) GPa,compressive strength of (81.3±4.3),(135.4±8.5) and (218.6±7.1) MPa,respectively.A porous structure with three-dimensional network of connected pores was observed under scanning electron microscope.Conclusion It is feasible to fabricate porous titanium implants by three dimensional printing technique.The mechanical properties of the porous titanium implants match well with bone tissue which has excellent biomechanical compatibility.

Objective To investigate the accuracy of three dimensional facial measurement system based on structured light projection, and explore the methods to reduce noise of the output images. Methods The known object for calibration was measured by the measurement system to correct the parameters of the system and enhance the measurement accuracy. The mechanism of noise was analysed, and the noise and sundry of the images were eliminated. Results The parameters of each assembly of system were obtained by calculation and calibrated, and the measurement accuracy (0.028 mm) of three dimensional facial measurement system based on structured light projection was increased. Application of image processing technology reduced the noise and sundry of output images. Conclusion The accuracy of three dimensional facial measurement system based on structured light projection is high. The image output is reliable, and can be clinically used in facial scanning and three dimensional reconstruction.

Objective To investigate the relationship between interpersonal acceptance and loneliness of college students.Methods 510 college students were administered by interpersonal acceptance scale(IASCS)and UCLA loneliness scale.Results (1)As a whole,there exists great capable difference of interpersonal acceptance according their genders,grades(t=5.37,P＜0.01,t=12.56,P＜0.01).(2)Significant negative correlation exist great capable difference about the scores of loneliness between the higher and lower acceptance of college students(P＜0.01).(4)Analysis of regression indicates that interpersonal acceptance has significant predictable effects on loneliness.Conclusion Interpersonal acceptance is the important factor influencing loneliness in college students.