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Biomedical subjects

Chung-Ju Hwang

Publications and source records attributed to Chung-Ju Hwang.

9 recordsLinked to original sources
PubMed2007

Friction of conventional and silica-insert ceramic brackets in various bracket-wire combinations.

OBJECTIVE: To compare the level of friction resistance (FR) of conventional and silica-insert ceramic brackets using various bracket-wire combinations and angulations. MATERIALS AND METHODS: Four types of ceramic brackets were examined: (1) polycrystalline alumina bracket (PCA-C), (2) polycrystalline alumina bracket with a stainless steel (SS) slot (PCA-M), (3) polycrystalline alumina bracket with a silica layer (PCA-S), and (4) monocrystalline sapphire bracket (MCS). A conventional SS bracket was used as the control. The static and kinetic FR in four bracket-wire angulations (0 degrees, 5 degrees, 10 degrees, and 15 degrees) was examined using SS and beta-titanium (beta-Ti) orthodontic wires, 0.019 x 0.025 inches in size, under elastic ligature in the dry state. RESULTS: The FR generated by the PCA-S bracket was significantly lower than that generated with the other ceramic brackets, and was similar to that of the SS bracket. The PCA-S bracket showed the lowest FR with both the SS and the beta-Ti wires at zero bracket angulation. The FR to sliding increased rapidly and nonlinearly when the bracket wire angulation was >5 degrees. The PCS-S bracket showed the lowest FR from 5 degrees to 15 degrees of angulation. The MCS bracket demonstrated the highest increase in FR from 0 degrees to 15 degrees of angulation, showing the highest FR at 15 degrees of angulation. CONCLUSION: PCA-S showed minimal FR among the ceramic brackets, and was comparable to the conventional SS bracket. The silica layer and rounded edges of the ceramic slot lowered FR considerably.

Aluminum Oxide↗
PubMed2006

Effect of silver addition on the properties of nickel-titanium alloys for dental application.

Equiatomic and near-equiatomic nickel-titanium alloys exhibit a shape-memory effect and superelasticity. However, the properties of such alloys are extremely sensitive to the precise nickel-titanium ratio and the addition of alloying elements. High corrosion resistance is necessary for biomedical applications, especially orthodontic. The purpose of this study was to investigate the effect of silver addition to nickel-titanium alloys for dental and medical application. Arc melting, homogenization, hot rolling, and solution heat treatment were performed to prepare the nickel-titanium-silver (NiTi-Ag) specimens. The properties of the ternary NiTi-Ag alloys such as phase-transformation temperature, microstructure, microhardness, corrosion resistance, and cytotoxicity were investigated. The NiTi-Ag alloys showed low silver recovery rate for the cast alloy, due to silver's low evaporation temperature, and low silver solubility in nickel-titanium. Silver addition to nickel-titanium increased the transition temperature range to 100 degrees C and stabilized the martensitic phase (monoclinic structure) at room temperature, because the martensitic transformation starting temperature (Ms) was above room temperature. Martensitic and austenitic phases existed in X-ray diffraction patterns of solution-annealed NiTi-Ag alloys. The silver addition was considered to improve the corrosion resistance and form a stable passive film. Significantly, the mechanical properties of the silver-added alloys were dependent upon the amount of alloying addition. There was no toxicity in the NiTi-Ag alloys, as the response index showed none or mild levels.

Animals↗
PubMed2006

Lateral cephalometric characteristics of malocclusion patients with temporomandibular joint disorder symptoms.

INTRODUCTION: There is much controversy about the relationship between temporomandibular joint (TMJ) disorders and the skeletal structures of the lower face. It is not clear whether the disharmony of the facial skeletal structure is caused by the TMJ disorder or vice versa. The aim of this study was to determine the relationship between craniofacial skeletal structures and TMJ disorders by using lateral cephalogram measurements to examine the characteristics of the facial profile of patients with TMJ disorders. METHODS: Of 111 patients over 18 years of age from the Department of Orthodontics, Dental Hospital, Yonsei University, those showing symptoms of TMJ disorders were chosen as the experimental group (56 patients), and patients without TMJ disorders were chosen as the control group (55 patients). A lateral cephalogram of each subject was taken and traced to confirm the significance of the craniofacial measurements between the experimental group and the control group of Class I (mean ANB angle, 2.89 degrees), Class II (mean ANB angle, 6.32 degrees), Class III (mean ANB angle, -2.02 degrees) patients, who were grouped according to ANB-angle difference. RESULTS: Each experimental subject with a TMJ disorder had a hyperdivergent facial profile, more lingual tilting of the maxillary incisors, and a steeper inclined occlusal plane. CONCLUSIONS: There was a significant correlation between the structure of the lower face and the temporomandibular disorder.

Adult↗
PubMed2006

Customized three-dimensional computational fluid dynamics simulation of the upper airway of obstructive sleep apnea.

OBJECTIVE: To use computer simulations to describe the role of fluid dynamics in the human upper airway. MATERIALS AND METHODS: The model was constructed using raw data from three-dimensional (3-D) computed tomogram (CT) images of an obstructive sleep apnea (OSA) patient. Using Bionix software (CantiBio Inc., Suwon, Korea), the CT data in DICOM format was transformed into an anatomically correct 3-D Computational fluid dynamic (CFD) model of the human upper airway. Once constructed, the model was meshed into 725,671 tetra-elements. The solution for testing was performed by the STAR-CD software (CD adapco group, New York, NY). Airflow was assumed to be turbulent at an inspiration rate of 170, 200, and 230 ml/s per nostril. The velocity magnitude, relative pressure, and flow distribution was obtained. RESULTS: High airflow velocity predominated in medial and ventral nasal airway regions. Maximum air velocity (15.41 m/s) and lowest pressure (negative 110.8 Pa) were observed at the narrowest portions of the velopharynx. Considering differences in model geometry, flow rate, and reference sections, when airflow patterns in nasal cavity were compared, our results were in agreement with previous data. CONCLUSIONS: CFD analyses on airway CT data enhanced our understanding of pharyngeal aerodynamics in the pathophysiology of OSA and could predict the outcome of surgeries for airway modification in OSA patients.

Adult↗
PubMed2005

Corrosion resistance of titanium-silver alloys in an artificial saliva containing fluoride ions.

Dental gels and rinses for caries prophylactic contain fluoride at concentrations ranging from 0.1 to 1%. In addition, many types of fluoride-releasing materials have been used in dental applications. The purpose of the study was to investigate the addition effect of fluoride into artificial saliva on the corrosion resistance of pure titanium and titanium-silver alloys. Titanium and titanium-silver alloys were arc melted, homogenized at 950 degrees C for 72 h, hot rolled, and solution heat treated and quenched. In order to investigate the effect of the fluoride ions on the corrosion resistance, potentiodynamic polarization testing, potentiostatic testing, and open-circuit potential measurements were performed in plain artificial saliva and 0.1 and 1% NaF-added artificial saliva. The passive current densities of titanium and titanium-silver alloys increased with increasing fluoride-ion concentration. Ti2.0Ag and Ti3.0Ag exhibited a low current density relatively and showed a stable behavior compared to titanium. The open-circuit potential of titanium decreased and current density at 250 mV (SCE) potentiostatic testing reacted sensitively with increasing fluoride concentration. On the other hand, the open-circuit potential of titanium-silver alloys with a high silver content (3.0-4.0 at %) reacted less sensitively to the fluoride-ion concentration. Among titanium-silver alloys, Ti3.0Ag alloy had a higher resistance against the attack of fluoride ions and showed a more stable open-circuit potential and current density than titanium in the fluoride-containing solution. It is concluded that they are electrochemically stable and maintained good corrosion resistance in fluoride-containing artificial saliva.

Biocompatible Materials↗
PubMed2004

Orthodontic treatment with growth hormone therapy in a girl of short stature.

The purpose of this article is to review the characteristics of craniofacial morphology in children of short stature and the effects of human growth hormone (HGH) therapy on the craniofacial complex. Changes in body height, facial growth, and dental maturity of a 9-year-old girl who received HGH therapy during orthodontic treatment were observed. Orthodontists need to understand the skeletal characteristics of the craniofacial complex of short-stature patients before beginning orthodontic treatment and consider how the differences between chronologic and skeletal ages affect the timing and method of orthodontic treatment. If short-stature children are undergoing HGH therapy, its cranioskeletal effect should be considered; if possible, it is better to delay orthodontic treatment until HGH is finished. However, if orthodontic treatment is performed, the following should be considered: (1) HGH therapy affects the growth of the mandible more than the growth of the maxilla, (2) the amount and pattern of growth during HGH administration are unpredictable, and (3) HGH therapy rarely affects dental maturity.

Adolescent↗
PubMed2003

Mechanical and biological comparison of latex and silicone rubber bands.

Latex rubber bands are routinely used to supply orthodontic force. However, because the incidence of allergic reactions to latex is rising, the use of nonlatex alternatives is increasing, and assessing the mechanical properties of the replacement products is becoming more important. The purposes of this study were to compare the mechanical properties of latex and silicone orthodontic rubber bands through static testing under dry and wet conditions, and to compare their biologic (cytotoxic) properties. Three brands of latex and 1 brand of silicone rubber bands were tested. When extended to 300% of the lumen diameter, the silicone group had an initial force equal to 83% of the product specifications; this was the lowest of the 4 groups. All 4 brands showed notable amounts of force degradation at the 300% extension when subjected to saliva immersion; this approximated a 30% force decay over 2 days. The latex bands all followed a similar pattern of force degradation, whereas the silicone bands showed a greater increase in force decay as the extension length increased. The silicone bands were less cytotoxic than 2 of the 3 types of latex. Although the silicone bands showed the least discrepancy of force degradation between air and saliva conditions, the amount of the force decay was the greatest. Therefore, great improvements in the physical properties of the silicone band are required before they can be considered an acceptable replacement for latex.

Analysis of Variance↗
PubMed2003

In vitro surface corrosion of stainless steel and NiTi orthodontic appliances.

Simulated fixed orthodontic appliances were constructed, immersed and incubated in artificial saliva for periods up to three months. Two types of stainless steel archwires and two types of NiTi wires were used. The surface corrosion of the archwires was determined macroscopically, with scanning electron microscopy, and with spectrophotometry. The deposits on the wires were identified with X-ray diffraction. Uniform corrosion was observed on stainless steel wires, and a slight colour change was detected on the NiTi wires beneath stainless steel ligatures. The corrosion product on the stainless steel wires increased with immersion time, and the surface oxide films were easily detached from the underlying matrix. Crevice corrosion was observed under deposits of oxide, and at the interface between bracket and band. Such corrosion may weaken a wire or weld leading to fracture. In contrast, the NiTi archwires did not corrode, and there was no significant difference in surface morphology. The stainless steel archwires showed a significant loss of reflectance after heat treatment and immersion in artificial saliva. The NiTi archwires had the same reflectance before and after the immersion test. NiTi archwires are significantly more stable and resistant to corrosion than stainless steel archwires.

Color↗