Doug Youn Lee

Bioactive Cyanoacrylate-Based Filling Material for Bone Defects in Dental Applications

We tried to prepare a new filling material for bone defects using β-Tricalcium phosphate (β-TCP) particles and Histoacryl®. The aim of this study was to evaluate physical and bioactive properties of cyanoacrylate-based filling materials for bone defects in the dental field. The shear bond strength values of the Histoacryl® and β-TCP/ Histoacryl® compounds stored in double-distilled water decreased with the increase of the amount of added β-TCP. The temperature change of the β-TCP/ Histoacryl® compounds during polymerization decreased compared to that of the Histoacryl®. The cytotoxicity of the filling materials decreased when the amount of added β-TCP was increased. In the evaluation of bioactivity, hydroxyapatite (HA) was precipitated on the surface and inner space of the porous filling material 4 weeks after immersion in SBF. This precipitation of HA on the surface of the filling material was also confirmed in the XRD result. These results indicate that our novel β-TCP/Histoacryl® compounds have the potential to serve as filling materials for bone defects in the dental field.

Synthesis and performance of magnetic composite comprising barium ferrite and biopolymer

The purpose of this study was to prepare the magnetic polymer composite particles with high ferrite content by encapsulating barium ferrite powders with alginate and investigate their physical and biological properties. The magnetic Ca-alginate composite particles were manufactured by adding barium ferrite-alginate slurry dropwise to a CaCl/sub 2/ solution. The final product was then completely cleaned and dried. Average size (0.1/spl sim/1 mm in diameter) of magnetic composite particles was dependent on the ratio of barium ferrite to alginate. The degree of swelling of magnetic Ca-alginate particles was increased as pH increased in aqueous media. The magnetic polymer composite particle was found to maintain high coercivity. The saturation magnetization for the magnetic Ca-alginate composites increased with the increase in the barium ferrite/alginate ratio. The self-heating induced by hysteresis loss under an alternating magnetic field was measured as a function of barium ferrite/alginate ratio in distilled water. The agar overlay test indicated a relatively high cell viability for the L929 cell line upon contact with the magnetic composite particles.

A Histological Evaluation of Novel Cyanoacrylate-Based β-TCP Composite in Rat Calvarial Defects

In this study, the osteoconductive properties of novel cyanoacrylate-based filling materials for bone defect were evaluated. A new filling material was prepared by mixing Histoacryl® and acid-treated -tricalcium phosphate ( -TCP). Mixing weight ratio of acid-treated -TCP to Histoacryl® was 5:1. 12 male Spraque-Dawley rats were used in this study. The animals were divided into 4 groups. Critical-sized calvarial defects (8 mm) were created in 9 animals, and then the defects were treated with dense pellet specimen, porous cement-like specimen, and untreated defect for surgical control group. Augmentation treatments were carried out in 3 animals. Histological analysis revealed excellent ostgeoconductive properties of new filling materials. But, some of -TCP particle in the cement-like group were encapsulated by fibrous connective tissue. For the dense pellet group and augmentation treatment group, shape and stability were better maintained during the implantation time than cement like group. These results indicate that our novel -TCP/Histoacryl® composite have the potential to serve as filling materials for bone defects in the dental and plastic surgery.

Physical and Adhesive Properties of Cyanoacrylate-Based β-TCP Composites

Histoacryl® (N-butyl-2-cyanoacrylate) has been widely utilized as a tissue adhesive. The aim of this study was to evaluate the physical and adhesive properties of newly developed cyanoacrylate-based β-TCP composite systems. The β-TCP powder was modified on the surface with citric acid to make this material mixed with cyanoacrylate easily. The setting time of acidtreated β-TCP/ Histoacryl® systems was dramatically prolonged and the polymerization heat was significantly decreased compared to that of untreated β-TCP/Histoacryl® system. The shear bond strength of cyanoacrylate-based β-TCP composites decreased with addition of acid-treated β-TCP filler. The compressive strength of β-TCP/Histoacryl® composites increased strongly with increasing the amount of acid-treated β-TCP filler. The cytotoxicity of the β-TCP/Histoacryl® composites decreased with the increasing of the amount of added β-TCP. These results indicated that our novel β-TCP/Histoacryl® composites had the great potential to serve as adhesives or filling materials in the dental field.

The sustaining effect of three polymers on the release of chlorhexidine from a controlled release drug device for root canal disinfection

ABSTRACT Ⅰ. Introduction Complete debridement and thorough disinfection ofinfected root canals are considered mandatory for thesuccess of root canal treatment 1) . However, canalpreparation and irrigation are not always effective ineliminating total microflora from the root canal sys-tem 1-3) . Traditionally, calcium hydroxide has provento be an excellent intracanal medicament for infectedroot canals 4,5) . However, it is known to be less effec-tive against the therapy-resistant flora such likeEnterococcus facecalis, Actinomycesand Candidathat are frequently isolated in persistent root canals 6) .This is because of dilution of calcium hydroxide astime passes or dentin buffering effects 7) . Therefore,alternative medicaments should be explored thatwould maximize microbial eradication when used asintracanal disinfection. Intracanal disinfection of infected root canal is one of important treatment procedure. This in vitrostudyaimed to evaluate whether the surface polymers of controlled release drug (CRD) can effectively control therelease rate of chlorhexidine for root canal disinfection. Four CRD prototypes were prepared: Group A(n=12); The core device (absorbent paper point) was loaded with 40% CHX solution as control. Group B(n=12); same as group A, but the device was coated with chitosa n. Group C (n=12); same as group Aand then coated three times with 5% PMMA. Group D (n=12); same as group A and then coated threetimes with 3% PLGA. All CRD prototypes were soaked in 3 mL dist illed water for experimental periodsand the concentrations of released CHX from each CRD prototype were determined using a UV spectropho-tometer. Results showed that release rate of CHX were the greatest in the non-coated group (controlgroup), followed by the chitosan-coated group, the PLGA-coated group, and the PMMA-coated group (P <0.05). This data indicate that surface polymers can control the release rate of CHX from the CRD proto-types.

Effect of Cyanoacrylate-Based β-TCP Adhesive on Pullout Strength of Orthodontic Mini-Screw

In this study, the effect of cyanoacrylate-based β-tricalcium phosphate (β-TCP) on pullout strength of orthodontic mini-screw was evaluated. New cements were prepared by mixing Histoacryl® (n-butyl cyanoacrylate) and acid-treated β-tricalcium phosphate. The ratios of β-TCP to Histoacryl® were 0, 0.5, 1.0, and 2.0. Artificial bone blocks were used as a substrate for the miniscrew implantation. The test groups were divided into three groups (one solid bone block [group 1] and a bone block with a 0.9 mm hole [group 2], and a bone block with a 2.5 mm hole [group 3]). And each group was divided into subgroups according to cement usage and non-usage. The used artificial bone density was 0.64g/cm2. Pullout strengths were determined using a universal testing machine. Statistical analysis was performed using the SPSS 9.0 for Windows program. Paired samples t-tests and ANOVA were used with p<0.05. The maximum pullout strengths were 295.9 ± 3.8 N for group 1, 261.1±15.0 N for group 2, and 273.2±20.0 N for group 3. In group 1 and 2, the pullout strength in the subgroup using cement was higher than that of the subgroup of not using cement (p<0.05). In group 3, the pullout strength in the subgroups using cyanoacrylate-based β- TCP cement was higher than that of the subgroup using conventional glass ionomer cement (GC Fuji-I, GC Co., Tokyo, Japan) (p<0.05). These results indicate that our β-TCP/Histoacryl® cements have the potential to enhance pullout strength of the orthodontic mini-screw.

Early Volumetric Change and Treatment Outcomes After Palliative Radiation Therapy for Brain Metastasis

Purpose/Objective(s): Although brain metastasis is the most common type of brain malignancy, standard treatment scheme still remains uncertain. In this retrospective study, we analyzed early volumetric change and treatment outcomes after radiation therapy (RT) for metastatic brain tumors at our single institution. Materials/Methods: A total of 242 targets (metastatic brain lesions) out of 37 patients were analyzed for this study. We performed co-registration and image fusion of serial MRI on planning CT, and contoured each metastatic lesion to evaluate time-dependent volumetric changes. Influencing factors on local tumor control and dose-response relationship for volumetric reduction of targets were evaluated. RT was delivered by one of the following regimens: Whole brain radiation therapy (WBRT) alone; WBRT+3-dimensional conformal (3D-CRT) boost; Local RT alone; and Tomotherapy-based simultaneous integrated boost (SIB) technique. Most common dose prescription schedule for WBRT was 25 Gy in 10 fractions, and normalized total dose of 1.8 Gy to the target by a/b ratio 10 was 45 (range, 27-64.8) Gy. Most common primary origins were lung followed by breast cancer. Results: Median age of the entire cohorts was 53 (range, 15-82) years. Median number of metastatic lesion was 5 (range, 1-37). Majority of the patients had ECOG performance status scale of 0 to 1 (83.8%) and 24 (64.9%) patients were male. Twenty-three targets out of 16 patients were surgically removed before RT. Among 219 lesions primarily treated with RT, 93.6% of the lesions were controlled at the time of analysis. Six-month local control rate of primary target was 93.4%. CR after RT was achieved in 118 (53.9%) lesions with median 2.8 (range, 0.8-17.1) months. Intracranial progression in other sites developed in nine patients with median 6.9 (range, 1.1-17.5) months. Among 26 patients who had presented with mild to moderate neurologic symptoms, 21 (80.8%) patients improved either by RT or surgery. Tumor volume, initial tumor diameter and tumor histology were major determinants for local control rates. Dose-response analysis revealed that 37 Gy of normalized total dose of 1.8 Gy is required to achieve CR in tumors with less than 1cm in diameter (p < 0.001). Median volume reduction rate at first and second follow-up was 65 and 73.3%, respectively. Conclusions: Palliative RT for brain metastasis is still valuable treatment option in terms of effective tumor control and symptomatic recovery. Our data warrant a larger randomized study to develop more optimized dose prescription schedules depending on tumor size and histology in the radiotherapeutic management of brain metastasis. Author Disclosure: D. Lee: None. Y. Kim: None. C. Lee: None. C. Suh: None. J. Lim: None. H. Kim: None. J. Cho: None.

Novel Antibacterial Calcium Phosphate Cement

The antibacterial brushite-forming calcium phospahte cements (CPC) were prepared using an equimolar mixture of β-tricalcium phosphate (β-TCP) and monocalcium phosphate monohydrate (MCPM) with chlorine dioxide (ClO2) generating powders (sodium chlorite and mixed acid activator). The effect of ClO2 on cement setting time, compressive strength, and antibacterial property of novel antibacterial CPC was investigated. The use of 0.3M citric acid solutions as liquid phase enabled final setting times of 5~10 min. The setting time of antibacterial cement systems was prolonged with increasing the amount of antibiotic used. Dry compressive strength was found to be in the range between 9~15 MPa and increased with addition of ClO2 generating powders. Wet compressive strength was slightly decreased compared to dry compressive strength after immersion of cement samples in water for 24 h. The antimicrobial potency of the different cement formulations was investigated using the agar diffusion method. The acidic brushite cement itself showed the inhibitory effect for Streptococcus mutans. The inhibition zone was increased with the amount of ClO2 generating powders. These results indicate that our novel antibacterial CPC have the great potential to avoid the development of infections for preventive antibiotic therapy.

In Vitro Cytotoxicity of Alginate-Encapsulating Ferrite Particles Using WST-1

The purpose of this study was to evaluate the cytotoxicity of alginate-encapsulting ferrite particles in vitro. Various ferrite particles such as Ba-ferrite, Sr-ferrite, Co-ferrite, Co/Ni-ferrite were prepared by sol-gel process. Ferrite particles were encapsulated via calcium alginate process with different alginate contents ranged from 10 to 100 wt%. Mouse-fibroblastic NCTC L-929 cells were cultured in RPMI-1640 medium with 10% fetal bovine serum. The alginate-encapsulating ferrites were extracted in 5 ml of distilled water under pH 6.5 at 121°C for 1 h in accordance with ISO 10993-12. In vitro cytotoxicity was evaluated by WST-1. The results of this study indicated that the alginate-encapsulting ferrite particles affected cell viability by increasing alginate contents. Especially, alginate-encapsulating process were enhanced cell viability of ferrites such as Sr-ferrite, Co/Ni-ferrite, and Ba-Ferrite when alginate content was 10 wt%.

Aqueous-Based Alumina Tape Casting for 3-Dimensional Forming

Aqueous-based alumina tapes were prepared using polyvinyl pyrrolidone and acrylate, respectively, as binders. 3-unit all-ceramic dental bridges with a marginal gap of 42 μm were fabricated utilizing the tape containing the acrylic binder. Asymmetric ceramic membranes were formed by a single-step process, which consisted of wrapping tapes for support and intermediate layer in sequence onto a plaster preformer for the membrane.