George C. Paffenbarger

Clinical Evaluation of a Radiopaque Composite Restorative Material After Three and a Half Years

A clinical comparison was made of an experimental radiopaque composite restorative material and Addent 35. The radiopaque experimental formulation contained a novel ternary eutectic dimethacrylate as the resin binder and fused silica and a novel BaF2 containing glass as the reinforcing fillers. Evaluation of restorations indicate that the experimental material compared favorably with the commercial material.

The Role of Zinc in Dental Amalgams

Twenty-five Ag-Sn alloys containing various additions of Zn were amalgamated and the amalgams tested for physical properties pertinent to dental restoration use. The mercury retained, dimensional change, compressive strength, and creep were all functions of the Zn content.

Dental cements, direct filling resins, composite and adhesive restorative materials: A resume

This resume concerns experimental and commercial dental cements and restorative and adhesive materials usually containing nonmetallic inorganic components, the biocompatibility of the above with oral tissues, proposed methods of bioevaluation, the oral environment, the nature of the hard tooth tissue, cavity treatment, agents for bonding the restorative material to the tooth, and 112 references. The cements include those based on (C-1) zinc oxide-eugenol with additives such as zinc acetate, rosin, polymers and most important o-ethoxybenzoic acid (EBA); (C-2) metallic oxides-phosphoric acid; (C-3) acid phosphate salts-water; (C-4) aluminosilicate glass-phosphoric acid; (C-5) zinc oxide-polyacrylic acid; (C-6) methyl methacrylate-poly-(methyl methacrylate) with or without inorganic fillers. Direct filling resins (C-6) without filler and composite restorative materials (C-6) with filler are based on acrylic resins or reaction products of acrylic (methacrylates) with other resins. Coupling agents include cyanoacrylates, epoxy-acrylic adducts and polyurethanes. The 10 tables give composition, values for pertinent physical properties or dental requirements. (C-2) Dominates the cements but (C-1) with (EBA) and (C-5) which has some adhesion to hard tooth tissues and stainless steel may displace (C-2). (C-4) Restorative materials are anticariogenic and widely used but are being supplanted by composite restorative materials.

Dimensional Changes of Four Amalgams After Five Years of Storage in Air at 60, 37, and 23°C:

Amalgam cylinders, 4 mm in diameter and 8 mm long, made from four alloys, expanded lengthwise from 204 to 220 at 60°C, 18 to 46 at 37°C, and 6 to 35 at 23°C, μm/cm, respectively, after storage in air at the indicated temperatures for five yr.

Metals in Solution in Mercury Expressed from Copper-rich Dental Amalgams

Metals dissolved in excess mercury expressed from copper-rich amalgams ranged from 0.06 to 0.63 wt %. Such small percentages are not likely to affect pertinent properties. The solubility data may assist in explaining the kinetics of hardening of amalgams.

Copper-free Amalgams: Dimensional Change After Approximately Five Years at 60, 37, and 23°C

Two copper-free amalgams expanded excessively after storage in air at 60°C for about five yr. One expanded significantly at 37°C and slightly at 23°C. High silver content, absence of copper, and presence of small amounts of zinc, or all three, seemed to promote very high expansions at 60° C.

Fifty Years of Cooperative Research Between the American Dental Association and the National Bureau of Standards: A Historical Perspective 1928-1978

Today, March 15, 1978, marks within a few days the fiftieth anniversary of the beginning of cooperative dental research between the American Dental Association and the National Bureau of Standards. On April 2, 1928, Assistant Professor Norris Onslow Taylor of the Chemistry Department of the University of Iowa reported for duty as the first Research Associate from the American Dental Association at the National Bureau of Standards. How fitting it is that his son, Dr. Duane Francis Taylor, Professor of Dentistry at the University of North Carolina, is the moderator of this 50th Anniversary Symposium. He literally followed in his fathers footsteps in more ways than one, as he was a metallurgist in the Dental Research Section of the National Bureau of Standards from 1954 to 1961. So here is an example where we have two generations in the science of dental materials. But one cannot stop there, as Duane Taylor tells me he has a son who also is employed in dental research. Thus this Taylor family has been able to sustain itself biologically and scientifically for five decades in dental materials research. The American Dental Association has long been interested in conducting and in financing research on, and testing of, dental materials, because of their role in dental health service. What spurred the Association to initiate this activity? -a personality, of course. Dr. Weston A. Price of Cleveland, Ohio, almost singlehandedly founded the Scientific Foundation and Research Commission of the National Dental Association and established its research institute in 1913.

Early strength, flow and dimensional changes obtained on amalgam prepared with a standardized mechanical technic: : progress report

The rate of hardening of five amalgams was nearly linear with time during the first hours, as shown by the increase in compressive strength or the decrease in flow. There were large differences in strength and in flow among the alloys. The data indicate that an early flow test should be given consideration as a method of specifying the setting time of amalgam. The magnitude of initial shrinkage during hardening appears to be directly related to strength and flow. The time of maximum shrinkage occurs at about the same time for all five amalgams but there are large differences in the dimensional changes which occur during the hardening of the five amalgams. The relation of the dilatometric and flow data is linear up to the time of maximum shrinkage. Specimens were prepared by an allmechanical method so that observations could begin within three minutes from the end of trituration. 1.

Pertinent data on some physical properties of different investments used in the casing of gold alloys: : progress report

Fineness, time of setting, compressive strength, linear thermal expansion, hygroscopic expansion, normal setting expansion, and surface defects of alloy castings were determined using casting investments of three types thermal inlay, hygroscopic inlay, and thermal partial denture. The use of the normal setting expansion combined with either the hygroscopic or thermal expansion to compensate for the shrinkage of casting gold alloys is discussed .

Dental research at the national bureau of standards in relation to orthodontia

George Colby Paffenbarger was a man of considerable insight. Nearing the end of his life as a result of prostate cancer, he perceived a need to educate the dental profession and the public about the enormous benefits to dentistry and public health that were being wrought through the cooperative research of the American Dental Association (ADA) and the National Bureau of Standards. Tax dollars, allocations from ADA dues, and funding from the National Institute of Dental Research were being used to support this work, and it was important for everyone to know that this investment was yielding benefits which far exceeded costs. Elsewhere, an oversupply of graduating practitioners and a reduced demand for dental care was leading to the closing of some dental schools and an attendant pressure to reduce all sources of funding for dental research. What George Paffenbarger saw, and others did not, was the continued evolution of (then unappreciated) dramatic benefits from dental research, even as the primary emphasis for research began to shift away from treatments for caries (the incidence of which had already declined) to treatments for other oral diseases and conditions. Paffenbarger’s solution to this problem was to publish a paper [1] that would place the ADA/ NBS dental research program into a clear and succinct context. Paffenbarger undertook this project in collaboration with John A. Tesk and W. E. Brown at NBS. Together, they documented the development of modern dental materials research, beginning with the inception of a dental research program at NBS in 1919. The beginning can be traced to a request by the U.S. Army to develop a bid specification for the purchase of dental amalgam. That effort, headed and championed by Dr. Wilmer Souder, focused on the properties of amalgams, including their compositions, dimensional changes on setting, compressive strengths, and flow characteristics [2]. That work led to the collaboration between NBS and the Weinstein Research Laboratory to measure the physical properties of the whole range of materials being used by dentists, for which the literature of the day was rather scant and often controversial [3]. The impact of that eight-year study is credited with the development of the cooperative program of the ADA and NBS, which continues to this day. The review by Paffenbarger, Tesk, and Brown paints a picture of a remarkable and far-reaching program that touches on every aspect of dentistry and, hence, public health. The thrust of the program was not simply the measurement of properties or even the development of standards and certification programs. Dental professionals and the public needed to be informed about the significance of the results, particularly with respect to self-serving promotions of products that had been propagated unchecked early in the century. “Aside from probable deceptive claims (for the exploitation of dental materials) exposed in the individual surveys, reports were published by the Association at NBS showing the fraudulent nature of some of the deceptions.” [1] Dental practices were also an important part of the program. As the ADA/NBS program began to understand more about the physical and chemical properties of amalgams, the influence of impurities and contaminants on the degradation of restorations also began to be understood. In one case, the practice of dentists mulling the amalgam mix in the palms of their hands was found to add moisture and sodium chloride to the mix, which subsequently led to severe corroding of zinc-bearing amalgams [4]. Fig. 1. George C. Paffenbarger.