Browsing by Author "Chu, Tien-Min"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Laser-treated stainless steel mini-screw implants: 3D surface roughness, bone-implant contact, and fracture resistance analysis
    (Oxford University Press, 2016-04) Kang, He-Kyong; Chu, Tien-Min; Dechow, Paul; Stewart, Kelton; Kyung, Hee-Moon; Liu, Sean Shih-Yao; Department of Orthodontics and Oral Facial Genetics, School of Dentistry
    BACKGROUND/OBJECTIVES: This study investigated the biomechanical properties and bone-implant intersurface response of machined and laser surface-treated stainless steel (SS) mini-screw implants (MSIs). MATERIAL AND METHODS: Forty-eight 1.3mm in diameter and 6mm long SS MSIs were divided into two groups. The control (machined surface) group received no surface treatment; the laser-treated group received Nd-YAG laser surface treatment. Half in each group was used for examining surface roughness (Sa and Sq), surface texture, and facture resistance. The remaining MSIs were placed in the maxilla of six skeletally mature male beagle dogs in a randomized split-mouth design. A pair with the same surface treatment was placed on the same side and immediately loaded with 200 g nickel-titanium coil springs for 8 weeks. After killing, the bone-implant contact (BIC) for each MSI was calculated using micro computed tomography. Analysis of variance model and two-sample t test were used for statistical analysis with a significance level of P <0.05. RESULTS: The mean values of Sa and Sq were significantly higher in the laser-treated group compared with the machined group (P <0.05). There were no significant differences in fracture resistance and BIC between the two groups. LIMITATION: animal study CONCLUSIONS/IMPLICATIONS: Laser treatment increased surface roughness without compromising fracture resistance. Despite increasing surface roughness, laser treatment did not improve BIC. Overall, it appears that medical grade SS has the potential to be substituted for titanium alloy MSIs.
  • Thumbnail Image
    Item
    Modeling Progressive Damage Accumulation in Bone Remodeling Explains the Thermodynamic Basis of Bone Resorption by Overloading
    (Springer, 2020-10-10) Sego, T. J.; Hsu, Yung-Ting; Chu, Tien-Min; Tovar, Andres; Cariology, Operative Dentistry and Dental Public Health, School of Dentistry
    Computational modeling of skeletal tissue seeks to predict the structural adaptation of bone in response to mechanical loading. The theory of continuum damage-repair, a mathematical description of structural adaptation based on principles of damage mechanics, continues to be developed and utilized for the prediction of long-term peri-implant outcomes. Despite its technical soundness, CDR does not account for the accumulation of mechanical damage and irreversible deformation. In this work, a nonlinear mathematical model of independent damage accumulation and plastic deformation is developed in terms of the CDR formulation. The proposed model incorporates empirical correlations from uniaxial experiments. Supporting elements of the model are derived, including damage and yielding criteria, corresponding consistency conditions, and the basic, necessary forms for integration during loading. Positivity of mechanical dissipation due to damage is proved, while strain-based, associative plastic flow and linear hardening describe post-yield behavior. Calibration of model parameters to the empirical correlations from which the model was derived is then accomplished. Results of numerical experiments on a point-wise specimen show that damage and plasticity inhibit bone formation by dissipation of energy available to biological processes, leading to material failure that would otherwise be predicted to experience a net gain of bone.
  • Thumbnail Image
    Item
    Optimizing light-cured composite through variations in camphorquinone and butylhydroxytoluene concentrations
    (2016-05) Nassar, Hani; Chu, Tien-Min; Platt, Jeffrey; Biomedical and Applied Sciences, School of Dentistry
    The use of a free-radical polymerization inhibitor, butylhydroxytoluene (BHT), and a common photo-initiator, camphorquinone (CQ), to reduce polymerization stress in dental composite was investigated in this study. Samples were prepared by mixing Bis-GMA, UDMA, and TEGDMA at a 1:1:1 ratio (wt%), and silanized borosilicate glass fillers at 70 wt% were added to form the composite. Sixteen groups of resin composite were prepared using combinations of four CQ (0.1%, 0.5%, 1.0%, and 1.5%) and four BHT (0.0%, 0.5%, 1.0%, and 1.5%) concentrations. For each group, six properties were tested, including flexural strength (FS), flexural modulus (FM), degree of conversion (DC), contraction stress (CS), stress rate, and gel point (GP). The effects of CQ and BHT combinations on each of these properties were evaluated using two-way analysis of variance (ANOVA) and Fisher’s Protected Least Significant Differences test at the 5% significance level. Groups with low CQ and BHT showed moderate values for FS, FM, and CS with a 70% DC. Increasing the BHT concentration caused a decrease in CS and DC with an increase in GP values. Increasing the CQ content led to a steady increase in values for FS and FM. High CQ and BHT combinations showed the most promising values for mechanical properties with low stress values.
  • Thumbnail Image
    Item
    Physicomechanical properties of a zinc-reinforced glass ionomer restorative material
    (2014) Al-Angari, Sarah S.; Hara, Anderson T.; Chu, Tien-Min; Platt, Jeffrey; Eckert, George; Cook, N. Blaine; Department of Restorative Dentistry, School of Dentistry
    We compared a zinc-reinforced glass ionomer restorative material (ChemFil Rock) with three commercially available glass ionomer cements (GICs), namely, Fuji IX GP Extra, Ketac Molar Quick Aplicap, and EQUIA Fil, with respect to fracture toughness, microhardness, roughness, and abrasive wear. Fracture toughness (KIC) was tested according to ISO 13586 (n = 10). Hardness, roughness, and abrasive wear were also tested (n = 9). Data were analyzed using the Wilcoxon rank-sum test with adjustment for multiple comparisons (α = 0.05). As compared with the other GICs ChemFil Rock exhibited a greater increase in surface roughness (P < 0.05) and lower microhardness (P < 0.01). The wear resistance of ChemFil Rock was comparable to that of the other GICs (P > 0.05). ChemFil Rock had significantly lower fracture toughness as compared with EQUIA Fil (P = 0.01) and significantly higher fracture toughness as compared with the other GICs (P < 0.02). In conclusion, as compared with the three other commercially available GICs, ChemFil Rock had intermediate fracture toughness, the lowest microhardness, and the greatest change in surface roughness.
  • Thumbnail Image
    Item
    Visible Light Cured Thiol-vinyl Hydrogels with Tunable Gelation and Degradation
    (2014) Hao, Yiting; Berbari, Edward J.; Lin, Chien-Chi; Xie, Dong; Chu, Tien-Min
    Hydrogels prepared from photopolymerization have been widely used in many biomedical applications. Ultraviolet (200-400 nm) or visible (400-800 nm) light can interact with light-sensitive compounds called photoinitiators to form radical species that trigger photopolylmerization. Since UV light has potential to cause cell damage, visible light-mediated photopolymerization has attracted much attention. The conventional method to fabricate hydrogels under visible light exposure requires usage of co-initiator triethanolamine (TEA) at high concentration (∼200 mM), which reduces cell viability. Therefore, the first objective of this thesis was to develop a new method to form poly(ethylene glycol)-diacrylate (PEGDA) hydrogel without using TEA. Specifically, thiol-containing molecules (e.g. dithiothreitol or cysteine-containing peptides) were used to replace TEA as both co-initiator and crosslinker. Co-monomer 1-vinyl-2-pyrrolidinone (NVP) was used to accelerate gelation kinetics. The gelation rate could be tuned by changing the concentration of eosinY or NVP. Variation of thiol concentration affected degradation rate of hydrogels. Many bioactive motifs have been immobilized into hydrogels to enhance cell attachment and adhesion in previous studies. In this thesis, pendant peptide RGDS was incorporated via two methods with high incorporation efficiency. The stiffness of hydrogels decreased when incorporating RGDS. The second objective of this thesis was to fabricate hydrogels using poly(ethylene glycol)-tetra-acrylate (PEG4A) macromer instead of PEGDA via the same step-and-chain-growth mixed mode mechanism. Formation of hydrogels using PEGDA in this thesis required high concentration of macromer (∼10 wt.%). Since PEG4A had two more functional acrylate groups than PEGDA, hydrogels could be fabricated using lower concentration of PEG4A (∼4 wt.%). The effects of NVP concentration and thiol content on hydrogel properties were similar to those on PEGDA hydrogels. In addition, the functionality and chemistry of thiol could also affect hydrogel properties.