Key Engineering Materials Vols. 330-332

Abstract: Our previous study showed that synthetic octacalcium phosphate (OCP) enhanced bone regeneration more than hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP). Recently, we have engineered a composite of synthetic OCP and collagen (OCP/Collagen), which improved the handling performance and synergistically enhanced bone regeneration up to eight weeks after implantation. The present study investigated whether the regenerated bone by OCP/Collagen could be stable for long period. OCP/Collagen sponge was prepared from pepsin-digested atelocollagen isolated from the porcine dermis and OCP granules. A standardized critical-sized defect was made in the rat calvarium, and an OCP/Collagen was implanted into the defect. Five rats were fixed at twenty-four weeks after implantation and examined radiographically and histologically. Radiographic examination showed that radiopaque figure was occupied throughout the defect, whereas OCP/Collagen itself was no radiopacity before implantation. Histological examination showed that newly formed bone was observed throughout the defect in OCP/Collagen. The implanted OCP/Collagen tended to be resorbed and was replaced by newly formed bone. The regenerated bone was stable and matured. The present study indicated that bone regeneration by the implantation of OCP/Collagen was stable for long-term periods. Application of OCP/Collagen without both cell transplantation and exogenous osteogenic cytokines would result in cost-effective bone regenerative therapy in the future.

Abstract: The objectives of this study are to investigate the influence of class III orthopedic forces generated by repelling rare earth magnets of class III magnetic orthopedic appliance (MOA-III) on the zygmaticomaxillary suture of Rhesus monkeys. Six male Rhesus monkeys in the stage of mixed dentition were used in this study. Fluorescent dyes were injected intravenously in each animal before and during the experimental period. Distinct changes from physiologic growth remodeling were observed in some sutures but not in the control groups. No inflammation was noted in both experimental and control monkeys. The results show that MOA-III is a small intraoral appliance to treat class III malocclusion, and the 300gm per side heavy orthopedic forces are safe and effective for Rhesus monkey.

Abstract: Beneficial properties of room temperature processed silica sol-gels as resorbable and biocompatible materials for the controlled release of drugs and macromolecules have been described before. Recently, it was shown that a thin sol-gel film can be used for the controlled delivery of antibiotics such as vancomycin. It was also demonstrated that the release and degradation properties of the sol-gel films can be tailored via processing parameters. In this work, we evaluated the in vitro and in vivo bactericidal effects of vancomycin-containing thin sol-gel films applied on Ti-alloy intramedullary nails. Both the in vitro and the in vivo results demonstrate a pronounced bactericidal effect of the sol-gel/antibiotic films. This study suggests that thin antibiotic-containing sol-gel film holds great promise for the prevention and treatment of bone infections.

Abstract: This study evaluated the efficacy of periodontal tissue regeneration using guided tissue regeneration (GTR) with a mixture of tooth ash and plaster as a bone substitute material in the treatment of class II furcation defects in dogs. GTR was performed at the site of a surgically formed mandibular premolar bifurcation area in dogs. Four adult dogs were used in the animal study. The animals were in a good periodontal state without any systemic disease. A resorbable membrane (Bio-Gide®, Swiss) and bone graft material using a mixture of tooth ash and plaster were used to examine the biological activity. The defect in the control group was filled a Bio-Gide® only. For the experimental group, the defects were filled with a mixture of tooth ash and plaster and covered by a Bio-Gide®. Oral rinsing with 0.12% chlorhexidine was performed twice a day for 2 weeks. In control group, new bone formation was observed adjacent to the preexisting bone. Soft tissue ingrowth was also noted. In experimental group, new lamellar type trabecular bone formation as well as centum and PDL regeneration was observed in the base of the infrabony pocket. More bone regeneration would be expected when GTR is performed using a mixture of human tooth-ash and plaster of Paris as a bone graft material.

Abstract: This study evaluated the histology results of surgically created bone cavities in the calvaria of rabbits that were subsequently filled with a HA/ß-TCP composite powder developed in Korea (Dentium, Korea). Ten young adult rabbits were used. Four defects were surgically produced in the calvaria of each rabbit. These defects were classified into 4 groups: the control group, no graft materials; experimental group I, normal saline + graft materials; experimental group II, venous blood + graft materials; and experimental group III, graft materials only. The defects were randomly filled with the graft materials. The rabbits were sacrificed with at 1-, 2-, 4-, 6- and 8- weeks after surgery. The histology specimens were prepared using the general method with H & E staining at a 6 ㎛ thickness. Histologically, the degree of new bone formation was similar in all experimental groups. However, for experimental group II, many cells had gathered around the graft materials 1-week after surgery, and new bone formed slightly faster and than in the other groups. No bone formation was observed in the control group. Based on histology findings, the new HA/ß- TCP composite powders appeared to act as a scaffolding material for the regeneration of osseous defects.

Abstract: In an effort to investigate the growth mechanism of nacre, a conventional vapor diffusion method for CaCO3 crystal precipitation was applied to in vitro growth of calcium carbonate on freshwater H. cumingii Lea shell. In a 10mM/L CaCl2 solution without any additives, aragonite deposit was obtained on the nacre surface, specifically at the edges of nacreous tablets. At the early stage of the deposition (up to 4 hr), the deposit did not take any specific form. After 12hr of deposition, the deposit exhibited faceted morphology characteristic of crystalline. Further increasing the deposition time resulted in the formation of well-faceted crystals of tower-like shape. Both Raman spectra and X-ray diffraction patterns showed that the deposit consists of aragonite polymorph of calcium carbonate.

Abstract: A biocompatible glue consisting of human serum albumin (HSA) and citric acid derivative (CAD), named CAD-A glue was developed. CAD was successfully synthesized by the reaction between citric acid and N-hydroxysuccinimide in the presence of 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride. When the CAD-A glue was applied to the collagenbased casings, it took 7 min to obtain half of maximum bonding strength (760 g/cm2). The bonding strength of this glue to collagen-based casings increased with increasing of HSA concentration.The bonding strength of CAD-A glue increased with increasing CAD concentration up to 200 mM, and then decreased with increasing CAD concentration under the fixed HSA concentration (50 w/w%). The CAD-A glue showed excellent wound closure ability rather than fibrin glue when applied to the mouse skin. These results suggested that this developed glue had both tissue compatibility and bonding strength for use in clinical field.

Abstract: The extent of osseous involvement, particularly spinal cord compression, is directly correlated with patient survival. To treat metastatic spine cancer, we have developed novel paclitaxel-loaded hydroxyapatite-alginate gels. In this study, an intraosseous spinal cancer model in rats was used to investigate the efficacy of local treatment. Ten rats were randomized into two groups, a local treatment group and a control group. Disease-free time and survival rate in the local treatment group were significantly longer in this model. (p<0.05)

Abstract: A previous study reported that many supplements have been added to NaF mouthrinses to improve the remineralization potential. Nano-hydroxyapatite (nano-HA) might also be suitable to this purpose because these nano-size particles can penetrate the enamel pores. Moreover, hydroxyapatite is similar to the inorganic component of teeth and is both bioactive and biocompatible. The aim of this study was to evaluate the combined effects of a nano-HA and fluoride mouthrinse on an early caries lesion in human enamel using an in vitro cycle remineralization and treatment model. Forty-eight human enamel specimens, which had a Vickers Hardness Number (VHN) of 25~45 were artificially demineralized for 48h. There were 8 treatment groups (0%, 1%, 5%, 10% nano-HA in distilled water and the same concentrations of nano-HA in a 0.05% NaF solution). The specimens were incubated in an in vitro remineralization model. After immersing the specimens into the treatment and remineralization solution for 12 hours each, the VHN of each specimen was evaluated for total 24 hours. This step was repeated once again for total 48 hours. The enamel surfaces of all specimens were examined by Confocal Laser Scanning Microscopy (CLSM) and SEM. The statistical significance of the data was identified by one-way ANOVA followed by a Duncan’s studentized range test. A p value < 0.05 was considered significant. The results showed that the degree of remineralization, as revealed by the VHN values, was higher in the NaF groups than in the distilled water groups. The VHNs of the remineralized enamel specimens for 48 hours were higher than after the 24 hours treatment. In addition, the level of remineralization increased with increasing concentration of nano-HA and was more pronounced in the NaF groups than the distilled water groups (p<0.05). The CLSM and SEM images nano-sized particles attached to the enamel in the nano-HA treated groups. Nano-HA might play a synergistic role in remineralization with a fluoride mouthrinse. However, more study will be needed to determine the optimal condition of nano-HA and NaF mouthrinse for human use. In conclusion, nano-HA in a 0.05% NaF mouthrinse can help remineralize an early caries lesion.

Abstract: In this study, the effects of bracket designs and force direction on fracture strength of alumina bracket were evaluated. Two differently designed alumina brackets (MISO, HT Co., Ltd., Seoul, Korea) were tested. Each bracket was bonded with orthodontic adhesive to stainless steel cylinder. Compressive force was applied to the tie wing of bracket at 30°, 60°, and 90° to the long axis of the test device. Fracture strengths were assessed by using a universal testing machine (Instron 3366, Instron Co., Ltd., U.S.A.). Fractured bracket surfaces were examined using SEM. Statistical analysis was performed by using SPSS 9.0 for Windows program. Paired samples t-tests and Kruskal-wallis tests were used at P<0.05. The fracture strength ranged from 150 N with the occlusal wing to 63 N with the cervical wing in bracket A. A significant difference was founded in fracture strength between the bracket designs and force directions. Based on this result, it could be concluded that bracket designs and force direction was important rule to improve fracture strength of ceramic bracket.