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Particulate wear debris in totally replaced hips causes adverse local host reactions. The extreme form of such a reaction, aggressive granulomatosis, was found to be a distinct condition and different from simple aseptic loosening. Reactive and adaptive tissues around the totally replaced hip were made of proliferation of local fibroblast like cells and activated macrophages. Methylmethacrylate and high-molecular-weight polyethylene were shown to be essentially immunologically inert implant materials, but in small particulate form functioned as cellular irritants initiating local biological reactions leading to loosening of the implants. Chromium-cobalt-molybdenum is the most popular metallic implant material; it is hard and tough, and the bearings of this metal are partially self-polishing. In total hip implants, prerequisites for longevity of the replaced hip are good biocompatibility of the materials and sufficient tribological properties of the bearings. The third key issue is that the bearing must minimize frictional shear at the prosthetic bone-implant interface to be compatible with long-term survival. Some of the approaches to meet these demands are alumina-on-alumina and metal-on-metal designs, as well as the use of highly crosslinked polyethylene for the acetabular component. In order to avoid the wear-based deleterious properties of the conventional total hip prosthesis materials or coatings, the present work included biological and tribological testing of amorphous diamond. Previous experiments had demonstrated that a high adhesion of tetrahedral amorphous carbon coatings to a substrate can be achieved by using mixing layers or interlayers. Amorphous diamond was found to be biologically inert, and simulator testing indicated excellent wear properties for conventional total hip prostheses, in which either the ball or both bearing surfaces were coated with hydrogen-free tetrahedral amorphous diamond films. Simulator testing with such total hip prostheses showed no measurable wear or detectable delamination after 15,000,000 test cycles corresponding to 15 years of clinical use. The present work clearly shows that wear is one of the basic problems with totally replaced hips. Diamond coating of the bearing surfaces appears to be an attractive solution to improve longevity of the totally replaced hip.

Butyl-methylmethacrylate resin mixtures were tested for brittleness-inducing factors in polymerised resin using a rapid quantitative scoring technique. The major source of brittleness was identified as the reducing agent dithiothreitol, which is commonly included in resin mixtures at 10 mM, to protect against tissue oxidation. Lowering the dithiothreitol content to 5 mM substantially reduced brittleness. Changing the 4:1 ratio of butyl- to methylmethacrylate to 9:1 or 3:2, and reducing the concentration of the catalyst, benzoin ethyl ether, to 0.25% also reduced dithiothreitol-induced brittleness. Polymerisation at temperatures close to 0 degrees C increased dithiothreitol-induced brittleness, but this was controlled in the 4:1 and 9:1 resin mixtures by lowering the catalyst concentration from 0.5 to 0.25%. Degassing the resin mixture with nitrogen gas prior to polymerisation did not reduce brittleness. Immunolabelled onion roots which were embedded using the 3:2 resin mixture ratio, 5 mM dithiothreitol and the 0.25% catalyst concentration, showed excellent preservation of cortical microtubule arrays.

We developed a prepacked mixing system for the preparation of bone cement. The system is based on mixing and collection of bone cement under a vacuum and serves as both the storage and mixing device for the cement components, thereby minimizing the exposure of the operating staff to the monomer and the risk for contamination of the cement during preparation. We evaluated the system using Palacos R and Simplex P. The cement produced was compared with cement obtained from a commercially available mixing system. Temperature evolution during curing, handling characteristics, density, and porosity of the cement obtained were analyzed. The results showed that the experimental system produces cement with physical properties (i.e., setting times and temperature, porosity, and density) equal to or better than those obtained with commercially available systems. Reducing the amount of monomer in the experimental system led to a reduction of the curing temperature without compromising the physical properties of the cements.

Aims/background: To clarify whether intraocular lens (IOL) implantation in the human eye affects the durability of polymethylmethacrylate over an average period of 10.9 years., Methods: Shearing stress and extent of damage following neodymium (Nd):YAG laser application to 18 study and 12 control optics were examined., Results: No significant difference was found between the study and the control IOLs in shearing stress and extent of damage following Nd:YAG., Conclusion: An average 10.9 years' implantation in humans does not affect either the shearing stress or extent of damage following Nd:YAG shots of polymethylmethacrylate.

BOP (biocompatible osteoconductive polymer) is a material proposed for osteosyntheses and for filling of bone defects in orthopaedics, neurosurgery and stomatology. It is a composite made of a copolymer of N-vinylpyrrolidone and methylmethacrylate, of polyamide-6 fibers and of calcium gluconate. The histological investigation includes the study of 30 intact rabbit femurs instrumented with a BOP rod, as well as the study of organs of the reticuloendothelial system. The currently available results show the absence of toxicity on hematopoietic tissue. Zones of osteoblastic activity surround the rods, coupled with an osteoclastic reaction which may result in the partial fragmentation of the polyamide fibers and its incorporation in the newly formed bone. We also observed the encapsulation of the material. The biomechanical approach investigated the mechanical properties of the material in bending and in shear. The radiological aspects of the investigation consisted of computerized axial tomography of the implanted femurs to measure density at the bone-implant interface.

A recent case-control study indicated that the insertion of an intraocular lens with polypropylene (Prolene) haptic materials was a significant risk factor for postoperative endophthalmitis (odds ratio = 4.5, P < .01). In the present study, we used quantitative techniques to evaluate adherence of Staphylococcus epidermidis to two intraocular lens types--lenses with polypropylene haptic materials and all-polymethyl methacrylate optic and three-piece all-polymethyl methacrylate lenses--using a quantitative culture method, a radioisotope technique, and scanning electron microscopy. All three methods demonstrated approximately twice as many bacteria adherent to lenses with polypropylene haptic materials as to all-polymethyl methacrylate lenses. Scanning electron microscopy showed preferential bacterial adherence to the polypropylene haptic materials. These data provide a pathogenic mechanism to explain our epidemiologic findings of an increased risk of postoperative endophthalmitis associated with implantation of intraocular lenses with polypropylene haptic materials.

Historical and modern advances in the development of an injectable soft tissue substitute are reviewed. Nonbiologic alloplastic and biologic injectables are described. The authors' experiences, as well as those of others, employing presently available materials in terms of specific indications and special techniques are delineated. The search for a safe, effective, easy-to-use, and long-lasting soft tissue substitute continues.

A revision of the ISO-standard for bone cement testing has been proposed to include compressive strength after 24 hours in air and 4-point bending testing after 50 hours in a 37 degrees water bath. Nine commercially available bone cements were tested in accordance with the new program. Compressive strength varied from 78 to 100 MPa, bending strength from 48 to 74 MPa and bending modulus from 2.2 to 2.8 GPa. The highest strengths, but also the highest stiffness, were encountered with Simplex brands and low-viscosity cements.

We fabricated batches of cement containing 0.5 gm, 1.0 gm, and 2.0 gm vancomycin and one with 1.0 gm tobramycin and shaped them into cylinders. They were immersed into 0.5 L of normal saline and the fluid volume was changed daily. Samples of fluid were obtained on days 1, 2, 3, 5, 7, 14, and 28. All fluid samples had antibiotic assays performed to quantitate the amount of elution for vancomycin or tobramycin. Vancomycin elution from PMMA occurred under our study conditions in similar quantities to that measured for tobramycin controls. Vancomycin-loaded PMMA cement may have a clinical role in the treatment of musculoskeletal sepsis caused by gram-positive bacteria, particularly if organisms resistant to the usual antibiotic agents are identified.

Variations in the atomic composition, and mass and electron densities of polystyrene and polymethylmethacrylate (PMM) plastics were assessed from experimentally determined mass attenuation coefficients for 125I and 137Cs gamma rays. The means and standard deviations in the mass densities of 16 samples of PMM and 10 samples of polystyrene were found to be 1.174 +/- 1.4% and 1.042 +/- 0.6% g/cm3, respectively. Based upon transmission measurements on various solutions of ethyl alcohol in water, the standard deviations in the effective atomic numbers of PMM and polystyrene were determined to be 0.77% and 1.3%, respectively. Based upon experimentally determined mass attenuation coefficients for 137Cs, the standard deviations in electron density for PMM and polystyrene were 0.5% and 1.2% respectively. Similar measurements on tap water and two grades of distilled water failed to detect any differences in atomic composition.

Mechanics can be understood in non-mathematical terms. Two important kinds of strength are ultimate or breaking strength, and yield strength--the stress which will cause a permanent deformity (e.g., bending a bone plate). Stress, like pressure, is measured in pounds per square inch. Strain is the percentage "gain in length." The strength of bone is roughly comparable to oak wood. With hyperemia and resorption of bone substance, this strength can fall drastically in a matter of weeks. Bone cement is well named; like cement it has almost no useful tensile strength. Its compressive strength is roughly comparable to bone. Doubling the depth of a beam quadruples its strength

A new method enables the dimensional changes of a range of anterior restorative materials to be demonstrated in an artificial cavity. The cavity wall-restoration interspace was incorporated into an electrochemical cell and the changes in the current passing through this cell reflected changes in the dimensions of the interspace.

We evaluated a new compound of polymethylmethacrylate (PMMA) that effectively blocks radiation below 380 nm, while maintaining nearly ideal transmittance characteristics above this wavelength. Our in vitro studies demonstrated no toxicity from this compound. Comparisons in primate eyes showed the standard and ultraviolet (UV)-absorbing plastic to be equally well tolerated.

For the biological examination of dental resin filling materials, a solubility and hemolysis test is recommended as an in-vitro testing method. Solubility and degree of hemolysis were examined in various filling materials based on MMA and BIS-GMA. It was found that, at the beginning, solubility was considerably higher in MMA-containing materials than in the BIS-GMA systems, and that after a while the conditions were reversed. The degree of hemolysis decreased in the following order with the individual materials: 1. Posite, Sevriton, Adatpic, 2. Epoxylite, Smile, Palakav, 3. MMA-BPO/Amin and MMA-TBBO. Comparison between the MMA and BIS-GMA monomers showed that corresponding to the same molar amounts, BIS-GMA materials developed a higher degree of hemolysis.

The fatigue response of PMMA-specimen was tested under cyclic bending of 1.5 Hz in a particularly designed testing device. Specimen were tested that a "Wöhler" curve and the corresponding fatigue strength could be evaluated. The fatigue strength was reached after a comparatively short time and ranged in the order of 33 per cent of static breaking strength.

Tensile and fatigue studies were performed on four different preparations of acrylic bone cement: (1) surgical Simplex-P inserted into molds in the dough stage, (2) Zimmer Low Viscosity Cement (LVC) inserted in the liquid phase, (3) an experimental cement inserted in the dough phase, and (4) the same experimental cement inserted in the liquid phase. The void characteristics of the cements appeared to dictate their mechanical performance. While tests revealed no difference in the tensile strengths of the four cement preparations, small but statistically significant differences in mean fatigue life were observed. The experimental cement used in the dough stage exhibited superior fatigue characteristics when compared with Simplex and LVC. LVC had the poorest mechanical properties of the four cement groups. Since the specimen preparation procedures can markedly influence the cement void characteristics and, consequently, the mechanical properties, general statements about different cement types are offered with considerable reservations.

The minimum corneal oxygen need varies between 2 and 5% depending on individual characteristics. The tear pump alone is not sufficient to provide the corneal oxygen needs of many PMMA wearers. Hard permeable contact lenses may provide oxygen to the cornea by the tear pump and/or direct transmission through the lens. The relationship between the various oxygen permeable hard materials and the oxygen provided at the corneal surface is shown in this paper.

Mechanical testing of specimen from fresh acrylic cement and from lossened prostheses between one and two years after implantation shows difference in compressive strength. Air bubbles, blood particles, and folds distinctly influence mechanical properties. Therefore, care should be taken to avoid these enclosures during implantation. But it is not the aging of the acrylic cement which presents the main problem in endoprosthetic fixation, but the cement-bone interface. Clinical experience and this mechanical study show that fracture of the acrylic cement is not due to primary fatigue of the material, but occurs secondarily after loosening of the bonding between bone and cement.

Three cement systems are favored for permanent luting of cast restorations. These include zinc phosphate, reinforced zinc oxide-eugenol, and polycarboxylate cements. Although others have been used in the past and new luting media are anticipated for the future, the status of currently used cement for luting is based mainly on the results of laboratory research and on clinical experience. Zinc phosphate cement, with an impressive 100-year history, currently holds the advantage. Future comprehensive clinical studies, correlated with results of physical and biological testing, may eventually direct the clinican's preference to another, newer material. It is hoped that properties and strength values that are clinically significant also will be identified, so that laboratory tests can be more predictive of clinical success.

Strength characteristics of dental poly(methyl methacrylate) were studied in terms of the fracture surface energy and inherent flaw size, using the methods of Berry.2-9 Dental poly(methyl methacrylate) is weaker than the corresponding bulk polymer because the former has a lower energy and higher inherent flaw size.

Intraocular lens (IOL) implants of polymethyl methacrylate (PMMA) lack an important yellow pigment useful as a filter in the visual process and in the protection of the retina from short-wavelength radiant energy. The ability to produce a yellow pigment in the PMMA used in IOL implants by exposure to near-ultraviolet (UV) light was tested. It was found that the highly cross-linked material in Copeland lens blanks was tinted slightly because of this exposure. The absorptive properties of lens blanks treated with near-UV light in this way approached that of the absorptive properties of human lenses. This finding shows that it is possible to alter IOL implants simply so as to induce a pale-yellow pigment in them to improve the visual process and to protect the retinas of IOL users.

The physical properties of thermosetting methacrylic resins contain a kind or more than two kinds of cross linking agents were investigated. Knoop hardness and bending strength after drying, water sorption and thermal cycling were listed in table 4 and 5. Hydrophilic resins absorbed water about 3 times as much as hydrophobic resins. The materials contain a small amount of hydrophobic cross linking agents in MMA indicate comparatively excellent properties after drying, water sorption and thermal cycling. Knoop hardness of resins generally reduced by water sorption, especially in the case of the resin contains a large amount of triethylene glycol dimethacrylate.

Previous investigators have shown that thin polymethyl methacrylate (PMMA) contact lenses (less than or equal to 0.12 mm) flex on toric corneas, thereby altering the residual astigmatism. The present study was designed to evaluate the flexure and residual astigmatism of gas permeable Polycon contact lenses on toric corneas and compare the results with those obtained with PMMA lenses on the same corneas. Eight subjects (16 eyes) with corneal toricities ranging from 1.25 to 4.25 D wore four pairs of identical Polycon and PMMA lenses. The only lens parameter that varied was center thickness, which ranged from 0.07 to 0.16 mm. Flexure and residual astigmatism were measured on all corneas with all lenses in a double-masked fashion. Our results indicate that Polycon lenses undergo significantly more flexure and alter residual astigmatism more on toric corneas than PMMA lenses at all center thicknesses evaluated. For both materials, flexure and residual astigmatism increased as center thickness decreased. The clinical implications of these findings are discussed.

The flexure fatigue properties of 10 denture base resins (four different types) were tested. Each specimen underwent two-way testing in a water bath maintained at 37 degrees +/- 1 degree C. A load of 3,650 gm was applied a 342 flexures per minute until the specimen broke. The resin types listed in order of increasing resistance to flexure fatigue are polymethylmethacrylate (PMM) pour resins, PMM thermosetting resins, vinyl resins, and a PMM grafted resin. Although small samples size and scatter of results limit broad application of this data, it is of some significance that the grafted resin Lucitone 199 tended to withstand repeated flexure when compared to the other resins.

We measured the effects of pH changes after water washings of polymethylmethacrylate (PMMA) intraocular lenses sterilized in 10% sodium hydroxide (NaOH). Whereas inserting the base-sterilized lens directly into the eye causes a large pH change in the local area of the implant, three separate washings of the NaOH-treated implant in 15 ml of water eliminates this change. No buffer is required.

A proposed specification covering handling characteristics and physical and chemical properties of bone cement composed primarily of methyl methacrylate has been prepared on the basis of data from the authors' studies and from various other sources. Under handling characteristics, requirements included relate to dough, handling and setting time, proper plasticity for insertion and temperature rise on setting. Mechanical properties specified include compressive strength and indentation and recovery characteristics. Maximum limits are proposed for water sorption and solubility. Suggested packaging requirements are also included.

The tensile strength of the bond formed between etched bovine enamel and selected resin systems was evaluated; also, the need for a resin pulpal barrier was examined. Results indicate that the BIS-GMA unfilled primer is unnecessary for strength or as a pulpal protectant. The large scatter of results substantiates the clinical hypothesis that the effectiveness of the acid etch is highly variable.

Assessments of the practical deficiencies of polymethylmethacrylate in service have been carried out by several workers. Some of these studies and one further one have been compared so as to seek any common factors, especially those concerned with the age of the appliance at failure. Times of vulnerability for different types of dentures have been demonstrated, and the scope for time-based studies in the laboratory and in service has been discussed.