Papers by Author: Hwan Kim

Abstract: The sliding wear of four different compositions of novel low temperature degradation-free zirconia/alumina (LTD-free Z/A) composites were characterized in a ceramicceramic point contact pair. The wear tests were performed by a pin-on-disk type wear tester in a linear reciprocal sliding motion with a point contact in both dry and bovine serum lubricated conditions at room temperature. For the dry sliding wear tests, AZ-2 (20 vol% (Y,Nb,Ce)-TZP/ 80 vol% Al2O3) showed the best wear resistance among four kinds of LTD-free Z/A composites. For the bovine serum lubricated sliding wear tests, wear was too little to be measured for all kinds of Z/A composites. These novel LTD-free Z/A composites having excellent wear resistance demonstrated a potential as the alternative materials for the ceramic- ceramic contact pairs of femoral head and acetabular liner in total hip replacement.

Abstract: The sliding wear behaviors of three different compositions of novel low temperature degradation-free zirconia/alumina (LTD-free Z/A) composites were examined in a ceramicceramic contact pair. The wear tests were performed by using a pin-on-disk type wear tester in a linear reciprocal sliding motion with a line contact in both dry and bovine serum lubricated conditions at room temperature. From the results of dry sliding wear tests, Z/A#1 ((5.3Y,4.6Nb)-TZP/80 vol% Al2O3) showed the best wear resistance among three kinds of LTD-free Z/A composites. For the bovine serum lubricated sliding wear tests, wear was too little to be measured for all kinds of Z/A composites. These novel LTD-free Z/A composites having excellent wear resistance demonstrated a potential as the alternative materials for the ceramicceramic contact pairs of femoral head and acetabular liner in total hip replacement.

Abstract: In this study, the wear characteristics of five different dental composite resins cured by conventional halogen light and LED light sources were investigated. Five different dental composite resins of Surefil, Z100, Dyract AP, Fuji II LC and Compoglass were worn against a zirconia ceramic ball using a pin-on-disk type wear tester with 15 N contact force in a reciprocal sliding motion of sliding distance of 10 mm/cycle at 1Hz under the room temperature dry condition. The wear variations of dental composite resins were linearly increased as the number of cycles increased. It was observed that the wear resistances of these specimens were in the order of Dyract AP > Surefil > Compoglass > Z100 > Fuji ı LC. On the morphological observations by SEM, the large crack formation on the sliding track of Fuji ıLC specimen was the greatest among all resin composites. Dyract AP showed less wear with few surface damage. There is no significant difference in wear performance between conventional halogen light curing and light emitting diodes curing sources. It indicates that a light emitting diodes (LED) source can replace a halogen light source as curing unit for composite resin restorations.

Abstract: The sliding wear behavior of ultra high molecular weight polyethylene (UHMWPE) was examined on a novel low temperature degradation-free zirconia/alumina composite material and on the conventional ceramics (alumina and zirconia) used for a femoral head in total hip joint replacement. The wear of UHMWPE pins against these ceramic disks was evaluated by performing linear reciprocal sliding and repeat pass rotational sliding tests for one million cycles in a bovine serum. The weight loss of polyethylene against the novel low temperature degradation-free zirconia/alumina composite disks was much less than conventional ceramics for all tests. The mean weight loss of the polyethylene pins was more in the linear reciprocal sliding test than in the repeat pass rotational sliding test for all kinds of disk materials. Neither the coherent transfer film nor the surface damage was observed on the surface of the novel zirconia/alumina composite disks during the test. In conclusion, the novel zirconia/alumina composite leads the least wear of polyethylene among the tested ceramics and demonstrates the potential as the alternative materials for femoral head in total hip joint replacement.

Abstract: The sliding wear behavior of ultra high molecular weight polyethylene (UHMWPE) was examined on four different compositions of novel low temperature degradation-free zirconia/alumina (Z/A) composite material used for a femoral head in total hip joint replacement. The wear of UHMWPE pins against these Z/A composite disks were evaluated by performing the linear reciprocal sliding and repeat pass rotational sliding tests for one million cycles in a bovine serum. The novel low temperature degradation (LTD)-free tetragonal zirconia polycrystal (TZP)/alumina composite (90(5.3Y, 4.6Nb)-TZP/10Al2O3) induced the less wear amount of UHMWPE than the other Z/A composites. Linear reciprocal motion wore more the UHMWPE pin than did repeat pass rotational motion for all disk materials. It was observed that few transfer film on the sliding track of Z/A composite disks and the matching contact surfaces of pins had relatively less scratch. Getting rid of transfer film, there is no change of surface roughness on the sliding track of Z/A composite disks. This novel Z/A composite (90(5.3Y, 4.6Nb)-TZP/10 Al2O3) demonstrates the potential as an alternative material for the femoral head in total hip replacement.

Abstract: The purpose of our study is to compare the biodegradation and osteoconduction between CaO-SiO2-B2O3 glass-ceramics(CS10B) and hydroxyapatite(HA), tricalcium phosphate(TCP). Porous CS10B implants were prepared by polymer sponge method. Single-level posterolateral spinal fusions were performed on thirty rabbits. The animals were divided into three groups by implant material: HA, TCP and CS10B. Radiographs checked every two weeks. All animals were sacrificed 12 weeks after surgery. The proportion of the area occupied by ceramics in final radiography on the initial radiography was calculated. Uniaxial tensile strength was measured on 7 cases in each group. The proportion of the area of HA(88.7%±16.1) was significantly higher than those of the others(p<0.05), and the proportion of the area of CS10B(28.2%±9.3) was significantly lower than those of HA and TCP(37%±9.6)(p<0.05). The mean values of tensile strength of the HA(191.4±33.5 N) and CS10B(182.7±19.9 N) were significantly higher(p<0.05) than those of the TCP(141.1±28.2 N). CS10B showed the tensile strength of fusion masses similar to those of the HA, however, more rapid biodegradation than HA and TCP. These findings suggest that CS10B grafts have the possibility as a bone graft substitute.

Abstract: Three types of calcium phosphate ceramics, i.e. tricalcium phosphate, biphasic calcium phosphate and near stoichiometric hydroxyapatite, were prepared by sintering at 1200oC for 2 h in air with moisture protection. Their dissolution processes were investigated by taking microstructural observations after immersion in distilled water for 3 or 7 days. It was found that the surface dissolution of the ceramics was initiated at grain boundaries and generated many separated grains. In case of the materials with high porosity, the residual pores on the surface appeared to be a primary defect site where the dissolution starts although the soluble compound was existed on the matrix.