Lawrence Gettleman

Effect of rapid curing procedures on polymer implant materials

This investigation of standard curing methods for PMMA implants has demonstrated that alternate means of using the air oven may produce good strength properties along with a considerable degree of porosity, when desired, in a relatively short period of time. Curing of polymers in a pressure pot offers few advantages owing to the length of time required to produce, at best, equivalent strength for the porous materials. The method also poses dangers inherent in the use of superheated salt solution or hot glycerin. The autoclave is widely used in dental offices for sterilizing and will fully and consistently cure polymers within 30 minutes. The best properties for the PMMA resin were achieved with this method (61 MPa or 9,130 p.s.i., tensile strength). The microwave oven has become relatively inexpensive in recent years, and it offers time savings of up to 90 per cent which would be beneficial in implant dentistry or in dental laboratory procedures in general. The exact condition for curing particular polymers must be carefully determined to adjust the time of irradiation in order not to under- or overcure the polymer object. Curing polymers which contain intrinsic foaming agents under pressure conditions slightly reduced the total pore volume. But, pore volume and pore diameter in the large-bead polymers are determined predominantly by packing conditions, not curing conditions. Biologic tolerance to materials cured by these methods in primates is presently being evaluated.

Structure and Microdistribution of Components of Gold Alloys

SYNOPSIS IN INTERLINGUA STRUCTURA E MICRODISTRIBUTION DEL COMPONENTES DE ALLIGATOS DE AURO.-Specimens de fusible alligatos de auro dental esseva subjicite a un varietate de analyses, incluse le sondage electronic e le quantitative microscopia televisional. Esseva trovate que certe areas de inclusion esseva componite de oxydos de metallo, durante que alteres consisteva de materiales de investimento o de politura. Es postulate que inhomogeneitates contribue possibilemente al migration de iones metallic ad in dur e molle tissus oral.

Effect of Metal Surface Treatment on the Masking Power of Opaque Porcelain

Spectral reflectance was determined as a function of incremental thickness of opaque porcelain applied to precious metal alloy surfaces treated in three ways. Sandblasted and fine-ground surfaces required comparable thicknesses of porcelain to achieve the same degree of opacity at selected wavelengths, whereas specimens conditioned with a gold flashing agent required 40 to 60% less opaque porcelain to achieve the same result. A logarithmic model for predicting reflectance as a function of porcelain thickness was applicable for gold-flashed surfaces at wavelengths greater than 550 nm.

Microhardness of Human Apical Cementum Related to Fluoride Exposure and Age

Many investigations have been done on the microhardness of enamel or dentin, but few studlies have been donie on cementum (NIKE, j Osalka U Dent Sc/I 4: 1, 1959; RAUTIOLA and CRAIG, J Peuiodontol 32: 113, 1961; and WARREN FT AL, J Periodontol 35: 505, 1964). Cementum has )eels shown to have a higher concen-tration of fluoride tbhan any other calcified tissue (YARDENI ET AL, Arch Oral Biol 8: 697, 1963; YOON ET At, JADA 61: 565, 1960; and NAKATA FT AL, J Periodontol 43: 115, 1972). The addition of fluoridle to a cavity liner has been shown to increase the fluoride content and microhardness of unclerlying dentin (WOLF ET AL, J Dent Res 52: 467, 1973), whereas extensive studies have shown that fluoride accelerates the rehardening of enamel artificially softened by acids (KOULOURIDES, Art and Science of Dental Caries Researchi, Newv York: Academic Press, Inc, 1968). The purpose of this study was to determine any differences in the microhardness of human cementum in the teeth of residents from areas of different fluoride exposure. Ninety periodontally healthy teeth were collected from lifetime residents of low, optimal, or high natural fluoride areas and were separated into three age groups as shown in the table. Ground sections (750-micrometers [gim] thick) from the apical third of the root were embedded in acrylic and polished using S.C. papers followed by 0.02 gm levigated alumina. The testing apparatusa used a Knoop diamond indenter, 50-gm load, and 15-second dwell time (RYGE ET AL, J Dent Res 40: 1116, 1961). All hardness testing was done by one operator (L.G.) and values were recorded

Polyphosphazine Fluoroelastomer (PNF) As a Permanent Soft Liner for Removable Dentures

A semi-organic elastomer, polyphosphazine fluoroelastomer, has been compounded to make it bond to hard dental acrylic resins for use as a liner for removable dentures. The material retains its elastic properties indefinitely, resists swelling, can be machined and polished, and is opaque to X rays. It is cured in gypsum flasks against old or new denture bases using ordinary dental laboratory techniques at no more than boiling water conditions. The PNF material is undergoing a controlled clinical trial at the present time.

Themoplastic Chlorinated Polyethylene for Maxillofacial Prostheses

Portions of the face such as ears, noses, eyes and chins are most often lost due to skin cancers, with trauma and birth defects secondary in incidence. Such devastating losses can be replaced by the use of elastomeric materials by specially trained prosthodontists to make removable prostheses for rehabilitation. Because conventional silicone rubbers often fray, tear, or absorb coloring agents, multiple prostheses are usually made. Such thermosetting materials allow for few corrections after molding; chlorinated polyethylene has been chosen for further development because of its excellent mechanical properties, coloring ability, and the possibility of repeated molding until perfection is achieved. Gypsum molds have been found to be useful when heated in a steam autoclave for 30 minutes. Coloring has been achieved by applying pigment or fibers to the CPE surface and laminating beneath a thin sheet of CPE, followed by cycling in the autoclave once more. Clinical trials are now underway, alternating CPE prostheses with identically-shaped ones made from medical-grade silicone rubbers.

Strength and biocompatibility of polymethacrylate-silica composite dental implant materials

A study was made of the strength properties of several composite dental implant materials composed of silica microspheres (6%, 24%, and 48% by weight) and PMMA. Prepared specimens of the materials were tested for compressive strength and tensile strength as a function of the curing methods. Compressive strength was reduced only slightly when the 6% mixture was used, as compared to 100% PMMA, but the compressive strengths of the 12% and 24% mixtures were reduced by approximately 30% when compared to 100% PMMA. The compressive strengths of these materials were reduced even further after curing in a microwave oven, and the tensile strengths decreased to a greater degree. The 6% mixture was reduced by 38% in the heat-cured specimens and was reduced by 27% in the microwave-cured specimens. Tooth replica implants were placed in baboons and the peri-implant tissues were studied histologically after 6 months. Inflammation was minimal. Peri-implant alveolar bone was viable and active, and both connective tissue and epithelial attachment to the implant surface was evident.