Key Engineering Materials Vols. 330-332

Abstract: Alumina and zirconia have been used in joint prostheses for decades. With mixtures of both materials (ZTA and ATZ) mechanical strength can be increased. The wear behaviour was investigated using standard and microseparation conditions. Both materials ZTA and ATZ showed similar or better wear resistance compared to alumina.

Abstract: Alumina and zirconia have been used for hip joint prostheses for decades. With mixtures of both materials (ZTA and ATZ) mechanical strength can be increased. The resistance against damaging of the surface of the ceramic articulation partners head and liner was investigated using a special luxation apparatus (PI-3:1997-07, Endolab GmbH, Thansau, Germany). Both new ceramic materials ZTA and ATZ showed a better resistance against roughening and damaging of the stressed surface areas during the luxation test compared to alumina.

Abstract: Wear is the primary cause of failure of joint replacement prostheses. Poly(ether-ether-ketone)(PEEK) was reinforced with nano-Al2O3 particals of various mass fractions in this study. The effect of nanometer Al2O3 mass fractions on the contacted angle of the reinforced PEEK composites was investigated. Tribological properties of composites under distilled water and physiological saline lubrication condition was measured. And the morphologies of the worn surfaces were observed with optical microscope. The results shows that the wettability and wear resistance were all improved with appropriate nano-Al2O3.The wear resistance of composites filled with 7% nano-Al2O3 was the best under both distilled water and physiological saline lubrication. In addition, it can be found that there is serious plough on the surface of pure PEEK. This indicated that serious fatigue wear occurred on the worn surface of pure PEEK. Moreover, there are only light fatigue wear on the worn surfaces of PEEK composites filled with nano-Al2O3.

Abstract: Medial placement of a cementless acetabular component into or beyond the medial wall of a shallow, dysplastic acetabulum is a technique to enhance its coverage during difficult total hip arthroplasty (THA). Dysplastic hips almost always need small size of acetabular component, so an accelerated polyethylene wear can occur when a conventional bearing surface is used. Modern alumina-on-alumina couplings can be an alternative for these patients. We evaluated the clinical results of 43 medially placed cementless acetabular components (PLASMACUP®SC) incorporating a modern alumina bearing surface (BIOLOX® forte). Acetabular components were inserted medially beyond the ilioischial line and, therefore, beyond the level of the cortical bone of the cotyloid notch, and followed up for more than 5 years (range, 60 – 93 months). In 14 hips, the medial acetabular wall was perforated purposefully and the medial aspect of the cup was placed beyond both the ilioischial and the iliopubic line on radiographs. The mean Harris hip score improved from 55.3 points preoperatively to 94.5 points postoperatively. Postoperatively, the hip center migrated 12.1 mm medially and 1.5 mm inferiorly. The average amount of cup protrusion beyond the ilioischial and the iliopubic line was 3.1 mm and 1.9 mm, respectively. The average superolateral coverage of the cup was 98.5 percent. During follow-up, no osteolysis or loosening of acetabular components was observed and no revision was required. Medial placement of a cementless acetabular component into or beyond the medial acetabular wall offers predictable clinical results and durable fixation in modern alumina-on-alumina THA.

Abstract: Total hip arthroplasty (THA) in patients with sequelae of the hip joint infection is a technically challenging procedure. In addition, the majority of such patients are less than fifty years old, so it has been reported that they have higher prevalence of complication and failure of component fixation. Alumina-on-alumina couplings are an attractive alternative and may offer a promising option for such young active patients. We analyzed 33 primary cementless alumina-onalumina THAs (PLASMACUP®SC-BiCONTACT® system incorporating BIOLOX® forte) that had been performed in patients who had sequelae of the hip joint infection. The average age of the patients was 37.8 years (range, 19-68 years) and 26 patients were younger than 50 years old. They were followed-up for more than 5 years (average, 74 months; range, 60-93 months). All hips had no recurrence of hip joint infection. The mean Harris hip score improved from 59.8 points to 93.5 points. All of the implants had radiographic evidence of a bone ingrowth and no radiological loosening was found. During the follow-up period, no cup or stem was revised and no periprosthetic osteolysis was observed. Nonunion of the osteotomized greater trochanter occurred in one hip, but no postoperative infection or ceramic failure was observed. The 5-year minimum follow-up clinical results of modern alumina-on-alumina THAs performed in patients with sequelae of the hip joint infection were encouraging with regard to osteolysis and implant stability. Our findings show that this alternative articulation offers a reliable solution for these young patients with long-standing anatomic abnormalities of the bone and soft tissues.

Abstract: This in vitro study compared the wear behavior between the enamel/dentine, two types of dental veneering ceramics for all-ceramic restorations (Vita-alpha，Vintage -AL ). A variety of factors including hardness, fracture toughness, flexural strength, frictional coefficients, wear scar width, element concentrations were considered. The wear scars of the samples were characterized by dynamic atomic force microscopy (DFM). The element concentrations of the surface before/after the wear test were determined with energy dispersion spectrometry (EDS). In this study Enamel/dentine, Vita-alpha and Vintage-AL have showed good wear resistance. The results also showed that there were statistical significance in samples. The friction coefficient varied from time in each kind of materials. The analytical differences between materials were observed in wear width and properties of materials (p<0.05). The wear ability among four materials ranked from highest to lowest as follows, Vintage-AL, Vita-alpha, enamel and dentine. DFM results demonstrated the wear patterns of natural tooth detected as abrasive and denaturation of dental texture. Wear patterns of tested veneering ceramics consisted mainly of abrasive wear, adhesion and fatigue wear and the different pattern plays different roles in Vita-alpha and Vintage-AL. The EDS results showed the element concentration of Fe was obviously found on the samples. Resistance ability against wear of veneering ceramics is better than that of natural human teeth. And the ability may have some correlation with the ceramics mechanical properties.

Abstract: The friction and wear behavior of dental ceramics (Vita VMK95) against uniform Si3N4 balls has been investigated using a small amplitude reciprocating apparatus under simulated oral conditions. The variables of ball radii (2mm, 6 mm, 13mm, and 21mm), load (10N, 20N, 30N, and 40N), reciprocating amplitude (200(m), frequency (2Hz) and use of artificial saliva lubrication or no lubrication were selected. Tests lasting up to 10,000 cycles were conducted. The wear scars of the samples were characterized with 3-D con focused laser-scanning microscope. The wear depths were analyzed statistically. The correlations between the wear behaviors and antagonist radii were also compared. The results show the friction coefficient of dental porcelain goes up with the decreasing of antagonist radii, and the wear depth decreases with the antagonist diameters. Load and lubrication effect is significant for friction coefficient and wear depth. The friction and wear mechanism of dental ceramics was characterized by abrasive wear and delaminating.

Abstract: Wear debris contributes to the development of granulomatous debris disease and loosening. It is accepted that hydroxyapatite ceramic (HA) will bond a prosthesis to bone.[1,2] Osteolysis has not been seen for several years after implantation but cases are now emerging [3]. Is HA still working Should we use hard on hard bearings Should we abandon polythene liners With a modular hip system, patients with polythene acetabular liners have been compared with those with ceramic liners. Polythene liners wear out and patients with a life expectancy of more than ten years should have ceramic/ceramic bearings.

Abstract: This study was aimed to investigate the effect of grinding, sandblasting by alumina and SiC, and heat treatment on the phase transformation from tetragonal to monoclinic zirconia on the surface of yttria stabilized tetragonal zirconia (Y-TZP) and zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al2O3 nanocomposite). The monoclinic phase content of both materials increased with the grinding and the sandblasting, while it decreased with the heat treatment. The monoclinic content sequentially increased with the sandblasting and decreased with the heat treatment to each specific value. The SiC-sandblasting produced the larger monoclinic content than alumina-sandblasting. Furthermore, the content changes of the nanocomposite were larger than Y-TZP.

Abstract: The JMM-ZTA, a kind of zirconia-toughened alumina, is a bearing ceramic newly developed for artificial joints. Although it has already been reported that mechanical strength and fracture toughness are higher in the JMM-ZTA than in alumina, the stability of the JMM-ZTA has not been studied in detail yet. In the present study, the stability of the JMM-ZTA with respect to mechanical strength and crystalline phases was examined under hydrothermal environment, and the results were compared with those of alumina. Both the 4-point bending strength and the fraction of monoclinic zirconia unchanged even after the aging test at 121°C for 300 h. These results indicate that the JMM-ZTA possesses quite excellent stability to be used as bearing material of artificial joints.