Cho-Pei Jiang

Subgingival calculus imaging based on swept-source optical coherence tomography

We characterized and imaged dental calculus using swept-source optical coherence tomography (SS-OCT). The refractive indices of enamel, dentin, cementum, and calculus were measured as 1.625 ± 0.024, 1.534 ± 0.029, 1.570 ± 0.021, and 2.097 ± 0.094, respectively. Dental calculus leads strong scattering properties, and thus, the region can be identified from enamel with SS-OCT imaging. An extracted human tooth with calculus is covered with gingiva tissue as an in vitro sample for tomographic imaging.

The Osteogenesis of Bone Marrow Stem Cells on mPEG-PCL-mPEG/Hydroxyapatite Composite Scaffold via Solid Freeform Fabrication

The study described a novel bone tissue scaffold fabricated by computer-aided, air pressure-aided deposition system to control the macro- and microstructure precisely. The porcine bone marrow stem cells (PBMSCs) seeded on either mPEG-PCL-mPEG (PCL) or mPEG-PCL-mPEG/hydroxyapatite (PCL/HA) composite scaffold were cultured under osteogenic medium to test the ability of osteogenesis in vitro. The experimental outcomes indicated that both scaffolds possessed adequate pore size, porosity, and hydrophilicity for the attachment and proliferation of PBMSCs and the PBMSCs expressed upregulated genes of osteogensis and angiogenesis in similar manner on both scaffolds. The major differences between these two types of the scaffolds were the addition of HA leading to higher hardness of PCL/HA scaffold, cell proliferation, and VEGF gene expression in PCL/HA scaffold. However, the in vivo bone forming efficacy between PBMSCs seeded PCL and PCL/HA scaffold was different from the in vitro results. The outcome indicated that the PCL/HA scaffold which had bone-mimetic environment due to the addition of HA resulted in better bone regeneration and mechanical strength than those of PCL scaffold. Therefore, providing a bone-mimetic scaffold is another crucial factor for bone tissue engineering in addition to the biocompatibility, 3D architecture with high porosity, and interpored connection.

Grain Size Effect on the Springback Behavior of the Microtube in the Press Bending Process

One of the most troublesome problems facing the tubing production industry is springback in the press bending process. With the ongoing miniaturization of products, springback is a dominant effect because material behavior greatly varies in the microtube press bending process. The present investigation numerically and experimentally addresses the effect of grain size on the press bending process of seamless stainless microtubes. The problem was approached in three stages. First, the microtubes were annealed to examine the grain size effect on mechanical properties by performing a tensile test. Second, a microtube press bending system was developed to observe springback behavior. Third, the press bending process was simulated by a conventional finite element model to predict the springback amount and make comparisons with the experimental result. Consequently, the experimental springback result was higher than that of the prediction made by the simulation. The occurrence of grain subdivision, induced by strain hardening, reduced the springback amount. The criterion of grain subdivision occurrence may be determined by observing the reaction force with respect to the stroke of the press and bending angle.

Finite Element Analysis of Dental Implant Neck Effects on Primary Stability and Osseointegration in a Type IV Bone Mandible

The purpose of this study is to investigate the effect of implant neck design and cortical bone thickness by means of 3-D linearly elastic finite element analysis and to analyze primary and secondary stability of clinical evidence based on micromotion and principal stress. Four commercial dental implants, comparable in size, for a type IV bone and mandibular segments were created. Various parameters were considered, including the osseointegration condition (non- and full bonded), force direction (vertical and horizontal) and cortical bone thickness (0.3, 0.5 and 1mm). The force was considered a static load applied at the top of the platform. The magnitudes of the vertical and horizontal loading direction were 500 N and 250 N. Micromotion and principal stresses were employed to evaluate the failure of osseointegration and bone overloading, respectively. The results show that Maximum stress of the peri-implant bone decreased as cortical bone thickness increased. The stress concentration regions were located at the implant neck between the cortical bone and cancellous bone. The micromotion level in full osseointegration is less than that in non-osseointegration and it also decreases as a increasing of cortical bone thickness. Consequently, cortical bone thickness is a key factor for primary stability.

Development of a Three-Dimensional Slurry Printing System Using Dynamic Mask Projection for Fabricating Zirconia Dental Implants

This study aims to develop a three-dimensional slurry printing system (3DSP) and to use a two-stage sintering process for the fabrication of zirconia dental implants. Solvent-soluble slurry which is composed of zirconia powder, visible light-curable resin, and methanol is prepared. During layer casting, the liquid slurry penetrates into the pores of the subjacent layers. The fresh layer and the subjacent layer tightly connect when the solvent dries. The mask pattern for the sliced layers is then exposed on a solvent-soluble slurry, for solidification and to form the green part that is embedded in the green block, layer-by-layer. The green block is immersed in a methanol solution, which causes the collapse of the un-exposed part. As a result, the rigid green part is obtained. Two-stage sintering is used to heat the rigid green part to 600°C to produce binder burnout and to 1450°C to sinter the zirconia dental implant part. The results show that sintered parts have an average flexural strength and micro-hardness of 539.1 MPa and 1556 HV, respectively. The zirconia dental implant is successfully fabricated using the 3DSP system developed. The proposed fabrication method using a 3DSP system is briefly described and it is proven that there is a good capacity to fabricate zirconia dental implants.

Design improvement and dynamic finite element analysis of novel ITI dental implant under dynamic chewing loads

The main aim of this article was to introduce the application of a uniform design for experimental methods to drop the micromotion of a novel ITI dental implant model under the dynamic loads. Combining the characteristics of the traditional ITI and Nano-Tite implants, a new implant with concave holes has been constructed. Compared to the traditional ITI dental implant model, the micromotion of the new dental implant model was significantly reduced by explicit dynamic finite element analysis. From uniform design of experiments, the dynamic finite element analysis method was applied to caluculated the maximum micromotion of the full model. Finally, the chief design in all the experiment simulations which cause the minimum micromotion is picked as the advanced model of the design. Related to the original design, which was associated with a micromotion of 45.11 μm, the micromotion of the improved version was 31.37 μm, for an improvement rate of 30.5%.

Effects of implant neck design on primary stability and overload in a type IV mandibular bone

This study investigates the effect of implant neck design on primary stability and overload using 3D finite element analysis. Four commercial dental implants and mandibular segments are created. Various parameters including the osseointegration condition (non-osseointegration and full osseointegration), force direction (vertical and horizontal), and cortical bone thickness (Tc = 0.3, 0.5, and 1 mm) are considered. The vertical and horizontal forces, 500 N and 250 N, are statically applied at the top of the platform, respectively. Micromotion and von Mises stress are employed to evaluate the risk of osseointegration and bone fatigue before osseointegration condition. After osseointegration, the principal stress is used to analyze the bone overload. Maximal von Mises stress and micromotion of the peri-implant bone decreased as cortical bone thickness increased. Horizontal force induces stress concentration in the bone around the implant neck easier than that of vertical force, and it may result in crestal bone loss. Thinner cortical bone should avoid dental implantation because it causes a noteworthy larger micromotion and stress concentration in cortical bone in particular Tc less than 0.3 mm.

Characterization of tooth structure and the dentin-enamel zone based on the Stokes–Mueller calculation

Abstract. This is the first study of dentin-enamel zone (DEZ) identification with tooth structure characterization based on the optical Stokes–Mueller measurement. Stokes vectors of a cross-sectional tooth slice were measured using various polarization inputs. The direction of the DEZ is different in enamel and dentin structures; therefore, the Stokes profiles can specifically characterize the structures based on the DEZ. This optical method, using polarimetry, provides a useful tool for characterizing tooth.

Application of uniform design to improve dental implant system

This paper introduces the application of uniform experimental design to improve dental implant systems subjected to dynamic loads. The dynamic micromotion of the Zimmer dental implant system is calculated and illustrated by explicit dynamic finite element analysis. Endogenous and exogenous factors influence the success rate of dental implant systems. Endogenous factors include: bone density, cortical bone thickness and osseointegration. Exogenous factors include: thread pitch, thread depth, diameter of implant neck and body size. A dental implant system with a crest module was selected to simulate micromotion distribution and stress behavior under dynamic loads using conventional and proposed methods. Finally, the design which caused minimum micromotion was chosen as the optimal design model. The micromotion of the improved model is 36.42 μm, with an improvement is 15.34% as compared to the original model.

Effects of titanium dioxide and tartrazine lake on Z-axis resolution and physical properties of resins printed by visible-light 3D printers

Purpose The aim of this paper is to examine the effects of light controlling system that combined high refractive particles (n-TiO2 [titanium dioxide – TiO2]) and tartrazine lake dye (TL dye) on thickness, flexural strength, flexural modulus and surface details of the 3D-printed resin. Design/methodology/approach Influences of different concentrations of n-TiO2 and TL dye in light-cured resin formulations for 3D printing (3DP) application were evaluated, including curing thickness, flexural strength and surface details under scanning electron microscopy. Findings The polymerization thickness of samples containing both n-TiO2 and TL dye was lower compared to samples with TL dye solely. Samples containing more n-TiO2 and more TL dye exhibited lower flexural strength and modulus. Ramp models showed that for samples containing 1 per cent TL dye, when their n-TiO2 content increased from 1 to 5 per cent, surface laminate structures became sharper. However, when the TL dye content doubled to 2 per cent, the surface laminate structures were indefinite compared to 1 per cent TL dye-containing counterparts. Originality value In visible-light 3DP, light controlling system in cooperate dye with high refractive particles provides better energy distribution and scattering control. High refractive particles, dyes and light exposure time had influenced the surface resolution and mechanical properties of the 3DP products.