Tinting of intraocular lens implants.

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.

Influence of haptic materials on the adherence of staphylococci to intraocular lenses.

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.

Current status of biomaterials in ophthalmology.

The artificial materials currently used in ophthalmology are reviewed. Those include poly(methyl methacrylate) in contact lenses, keratoprostheses, and intraocular lenses; cellulose acetate butyrate and the siloxane-containing polymethacrylates in contact lenses; the silicones in contact lenses, scleral buckling materials, and drainage implants in glaucoma; the hydrogels for contact lenses and retinal surgery implants; and the cyanoacrylate adhesives for corneal perforations and ulcers. The properties of the materials and their relationship to ocular tissues, as well as the advantages and disadvantages of their use in the eye are discussed. Probable future advances of biomaterials in ophthalmology are also discussed.

Fracture mechanics of dental poly (methyl methacrylate).

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.

Assessment of microleakage using a conductimetric technique.

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.

Selection of a resin system for anterior fracture treatment.

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.

On the constancy in composition of polystyrene and polymethylmethacrylate plastics.

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.

Consideration of physical parameters to predict thermal necrosis in acrylic cement implants at the site of giant cell tumors of bone.

In the previous paper we had developed a general thermodynamic equation describing a polymethylmethacrylate implant at the site of giant cell tumors. In this paper we consider various characteristics of bone and methylmethacrylate crucial to the analysis such as thermal conductivity, specific heat, density, and heat generation. Also, an estimation of the temperature at which adjacent cells die is analyzed from literature. Finally, using the physical constants measured in laboratory situations a temperature profile is developed at various depths of bone that could facilitate predicting the zone of necrosis. These analyses show the maximum temperature attained in the acrylic cement-bone system depends primarily on the volume of the implant, the relative proportion of polymerization of the monomer, the temperature at which the monomer and polymer are mixed together, and the time lapse between the beginning of polymerization and implantation into the bone cavity. The temperature profile is shown to be relatively insensitive to the geometry of the system, greatly simplifying the analysis.

Intraocular lens durability after a mean of 10.9 years' implantation in humans.

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.

Injectable soft tissue substitutes.

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.

Compatibility of the totally replaced hip. Reduction of wear by amorphous diamond coating.

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.

Cements for permanent luting: a summarizing review.

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.

High vacuum as a method of reducing porosity of polymethylmethacrylate.

In total hip arthroplasty, fracture and subsequent premature loosening are directly related to the strength of the cement mantle serving as an interface between bone and prosthesis. The cement has been shown to be weakened by its porosity, which enhances the formation of microfractures that contribute to crack propagation. By means of a vacuum mixing method for preparing the cement, nearly all the porosity can be removed and cement strength enhanced by about 17%.

Vancomycin vs tobramycin elution from polymethylmethacrylate: an in vitro study.

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.

Additional mechanical tests of bone cements.

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.