MSEL: DENTAL AND MEDICAL MATERIALS

1996 Annual Report

Technical Activities: DENTAL AND MEDICAL MATERIALS

The Dental and Medical Materials Program provides basic materials science, engineering, test methods, and standards to sectors of the health-care industry for the development of new or improved materials and delivery systems. The focus of this program is the development of improved dental restorative materials with greater durability, wear resistance and clinical acceptability.

Dental restorative composites are heterogeneous materials having three essential phases: (1) a polymeric matrix which comprises the continuous phase, (2) fillers of various types, sizes, shapes and morphologies which constitute the disperse phase and (3) an interfacial phase that, in varying degree, bonds the continuous and disperse phases into a unitary material rather than a simple admixture. While all three phases are important in determining the properties of the composites, this program is focused primarily on the interfacial and polymer matrix phases. Since the polymerization shrinkage that occurs in the matrix phase is one of the most commonly cited deficiencies of dental restorative composites, resources are allocated to develop high conversion, durable, low shrinkage polymeric materials for use in dental resin and composite applications. The polymeric matrix of a dental composite typically is formed by free radical polymerization of a resin which is one or more vinyl monomers, usually of the methacrylate class. Polymerization is started either by the formation of initiating radicals from chemical reduction-oxidation( redox) reactions or by photochemical redox reactions.

Although only a minor component of these composites, the interfacial phase that develops from the interaction of the silane coupling agent with the polymer matrix and the siliceous filler exerts a profound effect on the properties of the composites. Because these composites are used in an aggressive, aqueous environment that constantly challenges the vulnerable silane mediated polymer-filler bond, understanding of this critical interfacial phase is being acquired so that strategies can be developed for its improvement.

The occupational and environmental hazards associated with the use of mercury-containing dental alloys are a recurring source of public concern. Since dental amalgams have performed exceedingly well over more than one hundred years, the development of a direct filling material still based on the common constituents of dental amalgams, other than mercury, is desirable. The approach is based on three main premises: (1) the cold-welding of oxide-free silver; (2) the in situ formation of Ag_xSn_y intermetallics by the room temperature fast diffusion of silver and tin; and (3) the homogeneous precipitation of silver by Sn(II) in solution. This project is focused on acid-assisted consolidation of chemically precipitated silver powders and property measurements of hand consolidated test compacts prepared with the tools and procedures normally employed by dentists. The observed values of flexural strength for the silver compacts were equal or superior to mercury amalgams. Corrosion resistance, microleakage and marginal toughness values of the compacts were found to be superior to those of amalgams. Wear and biocompatibility studies on the hand consolidated compacts are in progress.

Dental research directions in support of the goals are established in collaboration with the American Dental Association(ADA), the National Institute of Dental Research, and guest scientists from the U.S. Navy and the U.S. Public Health Service. NIST has hosted research associates from ADA since 1928. Currently, the ADA Health Foundation sponsors 32 research associates at NIST. The collaborative relationship between that professional association and the federal government is unique, and continues to develop and transfer important new technologies to dentistry and medicine.

Significant Accomplishments

Low shrinkage interpenetrating polymer networks were formed by coincident free- radical methacrylate polymerization and cationic double ring-opening polymerization.
Demonstrated that the addition of urethane functional groups to fluorinated methacrylate monomers can provide polymers with significantly improved strength and minimal water uptake.
An efficient method was developed to prepare hydroxy-functionalized methacrylates that can be used directly as dental bonding agents or further derivatized to give highly reactive crosslinkable monomers.
Demonstrated that the microbond test could be used as a durability test for monitoring polymer-glass interfacial adhesion.
Demonstrated by mass spectrometry that N-aryl--amino acids act as polymerization initiators for acrylic monomers.
Demonstrated the feasibility of developing stress-bearing craniofacial implants from hydroxyapatite and bioresorbable polymers.
Cooperative Research and Development Agreements were signed with six orthopaedic companies to evaluate the wear properties of orthopaedic joint materials.

Dental Polymers Designed with Minimal Polymerization Shrinkage, Residual Vinyl Content and Water Sorption.

Jeffrey W. Stansbury

Objective

The objective is to develop dental composite restoratives that provide improved performance in specific areas where current dental materials have acknowledged deficiencies. Deficiencies include excessive polymerization shrinkage, the lack of long term durability, and susceptibility to moisture.

Technical Description

Through appropriate monomer design, the resin phase of the dental composites can undergo efficient photopolymerization with minimal shrinkage. A reduction in the volume contraction associated with polymerization is necessary to avoid excessive internal stresses that result in both micro and macro defects in dental composites. The lack of long-term durability of dental composites compared with amalgam restorations requires that material modifications be made in the polymeric and interfacial phases of composites, which are the weak links in this regard.

There is need for more hydrophobic, more hydrolytically stable polymers and interfacial layers to enhance the resistance of composite restoratives to the challenging oral environment.

The use of ring-opening spiro orthocarbonate (SOC) monomers, which can produce expansion during polymerization, and monomers with bulky spacer groups that limit the density of reactive groups can provide photocurable resins that offer low shrinkage and good mechanical strength properties. The introduction of organofluorine substituents in the monomers allows the formation of inert polymers that repel not only water, but a wide range of chemicals that can potentially degrade or stain polymer-based dental restorations. Structural alterations to increase the hydrophobicity of the coupling agent used to fuse the resin matrix with the reinforcing filler particles can improve the strength and stability of dental composites.

External Collaborations

Dr. Kyung Choi is actively advancing the work with fluorinated resins and modified coupling agents under a NIDR-supported contract between NIST and the University of California, Irvine.

Planned Outcomes

Development of visible light photocurable dental resins with less than half the polymerization shrinkage of conventional materials. Expect these new monomers to provide low shrinkage polymers with less residual stress and minimized polymerization-induced defects.

Development of organofluorine containing dental composites with less than 1/10th the water uptake of conventional materials. Expect more durable composites that retain their excellent initial properties during prolonged exposure to challenging environments.
Development of more hydrolytically stable coupling agents for use in dental composite restoratives. Expect more inert composites with improved initial properties and better retention of these properties upon long-term storage in water.

Accomplishments

An examination of the photopolymerization of SOC monomers (cured by a cationic mechanism) with methacrylate-based comonomers (cured by a free radical process) has provided details on the simultaneous formation of very low shrinkage interpenetrating polymer networks. Multifunctional SOC oligomers were used to produce highly crosslinked, ring-opened polymers with expansion.

A computer modeling study has been conducted to screen prospective monomers for predicted shrinkage based on the solvent excluded molecular volume of the monomers. Large differences in molecular volumes were found for monomers with very similar molecular weights. The predicted monomeric molecular volume proved to be a better indicator of actual polymerization shrinkage than monomer molecular weight.

A previous investigation demonstrated that very high strength, hydrophobic polymers can be prepared from urethane-based fluorinated monomers. The role of the urethane functionality to promote polymer mechanical strength (via extended hydrogen bonding networks) while minimizing the hydrophilic tendency of these polar groups was examined. A new coupling agent, which is more compatible with the fluorinated resins, was evaluated and found to provide surface coverage that is more hydrophobic and more durable than that obtained with the conventional silane coupling agent used in dental composites.

An efficient method to produce functionalized methacrylates was developed. The monomers obtained can be used directly as bonding agents for the adhesion of dental restoratives to dentin or they can be further modified through the hydroxy functional groups to produce new crosslinkable monomers that exhibit unusually high reactivity during photopolymerization.

Outputs

Publications

J.W. Stansbury, J.M. Antonucci, K.M, Choi, High Strength Hydrophobic Composites from Urethane-containing Fluorinated Resins. Proceedings of the International Association of Dental Research Meeting, J. Dent. Res., 75, 145 (1996).

K.M. Choi, J.W Stansbury, New Families of Photocurable Oligomeric Fluoromonomers for Use in Dental Composites. Chem. Mater. (in press).

Presentations

J.W. Stansbury, J.M. Antonucci, K.M. Choi, High Strength, Hydrophobic Composites from Urethane-containing Fluorinated Resins. IADR meeting, San Francisco, CA, March 1996.

J.W. Stansbury, Dental Resins Based on Alternative Monomers and Polymerization Pathways. Advances in Materials Science: New approaches and developments symposium. IADR meeting, San Francisco, CA, March 1996.

J.W. Stansbury, Current Dental Materials Research at NIST. ASME Applied Mechanics Division and Materials Division Meeting at Johns Hopkins University, Biomaterials symposium, June 1996.

J.W. Stansbury, Evaluation of Cross-linkable Double Ring-opening Monomer and Oligomer Systems. The Science of Adhesion Gordon Conference, Tilton, NH, August 1996.

Dental Composites With Improved Interfaces

Joseph M. Antonucci

Objective

The objective is to develop polymeric dental composites with enhanced interfacial strength and durability.

Technical Description

It is expected that improvements in the quality of the interfacial phase along with similar improvements in the polymer matrix and filler phases will result in dental composites of improved performance and service life. In addition to the use of traditional mechanical tests as a means of measuring interfacial strength, two single-fiber tests, the single-fiber fragmentation and the microbond test, have also been used to assess interfacial behavior. Attempts to utilize the single-fiber fragmentation test to determine the strength and durability of the interface derived from dental polymers and variously treated glass fibers have generally met with limited success due to the premature fracture of the brittle polymeric matrices. By contrast, the microbond test has proved to be a useful method for assessing polymer-fiber shear bond strengths and, generally, for exploring the interaction of dental polymers and silane coupling agents with silica surfaces. Recent studies indicate that the microbond test can also be used as a durability test and can be adapted for use with substrates other than fibers.

Accomplishments

It was demonstrated that 10-methacryloxydecyltrimethoxysilane, a more hydrophobic silane coupling agent than the widely used 3-methacryloxypropyltrimethoxysilane (MPTMS), generates a more durable interface than MPTMS.

The microbond test was adapted for use with flat glass surfaces that are potentially more amenable for surface analysis than fiber glass substrates.

Facile methods for the synthesis of multifunctional acrylic substituted silsesquioxanes were developed. These novel hybrid organic-inorganic resins are expected to find use in composite, sealant and adhesive dental applications.

Outputs

Publications

W.G. McDonough, J.M. Antonucci, J. P. Dunkers, Interfacial Shear Strengths of Dental Composites by the Microbond Test, J. Dent. Res., 75,14 Abstract 1026 (1996).

Presentations

W. G. McDonough, J. M. Antonucci, J. P. Dunkers, Interfacial Shear Strengths of Dental Composites by the Microbond Test. IADR Meeting, San Francisco, CA, March 1996.

Improved Adhesive Systems for Bonding to Tooth Structure

Joseph M. Antonucci

Objectives

The overall objective of this project is to develop effective, less technique- sensitive adhesive systems for bonding to dentin and other dental substrates. An ancillary objective is to elucidate the mechanisms involved in bonding to dentin by means of N-aryl--amino acids and N-arylimino acids.

Technical Description

Previously, it was shown that the application of aqueous acetone solutions of N-phenyliminodiacetic acid (PIDAA) to dentin both etches and activates the dentinal surface for subsequent polymerization of photoactivated adhesive resins. With this simple two-step bonding protocol strong composite-to-resin bonds were routinely obtained. Recent studies indicate that this unique adhesive system can be modified by the addition of silane coupling agents without adversely affecting its adhesion to dentin. The presence of silane coupling agents has potential for mediating adhesion to other dental substrates such as porcelain. In a related study, the mechanism of initiating polymerization with N-aryl--amino acids was investigated by mass spectrometry. In addition, a study was initiated to investigate the mechanism of diffusion of primers into demineralized dentin and their role in dentin bonding.

External Collaboration

Drs. G. E. Schumacher and J. E. Code of the U. S. Public Health Service and P. S. Bennett of the American Dental Association Health Foundation's Paffenbarger Research Center collaborated in the bonding study. The mechanism study involved collaboration with Dr. M. Farahani of the Paffenbarger Research Center. Dr. T. Nikaido, a guest researcher from the Tokyo Medical and Dental University, also participated in the dentin bonding studies.

Accomplishments:

Demonstrated that silane agents such as 3-methacryloxypropyltrimethoxysilane can be successfully incorporated in the two component PIDAA adhesive system to yield high composite-to-dentin shear bond strengths.
Demonstrated by mass spectrometric analysis techniques that N-aryl--amino acids act as polymerization initiators when dissolved in acrylic monomers.
Demonstrated the N-aryl--amino acids such as N-phenylglycine prevent the collapse of demineralized dentinal collagen, thereby promoting enhanced interfacial diffusion on adhesive resins.

Impacts

A patent has been issued based on self-etching primers of the N-aryliminodiacetic acid type. The American Dental Association has licensed this invention and several companies have shown interest in this technology.

Outputs

Publications

J.E. Code, J.M. Antonucci, G.E. Schumacher, P.S. Bennett, Silane-Modified Dentin Bonding Systems, J. Dent. Res., 75, 126 Abstract #870 (1996).

G.E. Schumacher, J.M. Antonucci, T. Nikaido, J.E. Code, Molar Efficiency of N-Phenyliminodiacetic Acid in Dentin Bonding, J. Dent. Res., 75, 348 Abstract #2641 (1996).

J.M. Antonucci, G.E. Schumacher, J. E. Code, T. Nikaido. Efficacy of N-Aryl and N-Alkyliminodiacetic Acids in Dentin Bonding, J. Dent. Res., 75, 348 Abstract #2644 (1996).

T. Nikaido, J. M. Antonucci, Stabilization Effect of NPG on Demineralized Dentin and Its Mechanism, J. Dent. Res., 75, 126 Abstract #871 (1996).

M. Farahani, J.M. Antonucci, L.R. Karam, Initiation of Methacrylate Polymerization by N-Aryl--amino acids. A Mass Spectrometric Study, J. Dent. Res., 75, 46 Abstract #1032 (1996).

J.M. Antonucci, G.E. Schumacher, P.S. Bennet, N-Phenyliminodiacetic Acid as an Etchant/Primer for Dentin Bonding, J. Dent. Res., (in press).

Patents

J.M. Antonucci, P.S. Bennett, A Method and Composition for Promoting Improved Adhesion to Substrates. U.S. Patent #5498643, March 12, 1996.

Presentations

J.E. Code, J.M. Antonucci, G.E. Schumacher, P.S. Bennett, Silane-Modified Dentin Bonding Systems, IADR meeting, San Francisco, CA, March 1996.

G.E. Schumacher, J.M. Antonucci, T. Nikaido, J.E. Code, Molar Efficiency of N-Phenyliminodiacetic Acid in Dentin Bonding, IADR meeting, San Francisco, CA, March 1996.

J.M. Antonucci, G.E. Schumacher, J. E. Code, T. Nikaido. Efficacy of N-Aryl and N-Alkyliminodiacetic Acids in Dentin Bonding, IADR meeting, San Francisco, CA, March 1996.

T. Nikaido, J. M. Antonucci, Stabilization Effect of NPG on Demineralized Dentin and Its Mechanism, IADR meeting, San Francisco, CA, March 1996.

M. Farahani, J.M. Antonucci, L.R. Karam, Initiation of Methacrylate Polymerization by N-Aryl--amino acids. A Mass Spectrometric Study, IADR meeting, San Francisco, CA, March 1996.

J.M. Antonucci, N-Phenyliminodiacetic Acid as an Etchant/Primer for Dentin Bonding, Generic/Pentron, Wallingford, CT, April 1996.

Polymer-Modified Porous Ceramics: Interpenetrating Phase Composites for Dental Applications

Joseph M. Antonucci

Objective

The objective is to develop strong, tough interpenetrating phase composites by the in situ polymerization of resin-infiltrated porous ceramic structures that are easily formed by low temperature pyrolysis of ceramic powders coated with pre-ceramic polymers such as polysiloxanes.

Technical Description

Conceptually, interpenetrating phase composites are expected to have enhanced properties compared to either dental ceramics or traditional dental composites. Previously, it was shown that a polymer-reinforced interpenetrating composite (IPC) with high strength properties could be prepared by the in situ polymerization of methyl methacrylate (MMA) within a silanized, porous ceramic network formed by the low temperature pyrolysis (<750C) of feldspathic porcelain or alumina powders that had been coated with a poly(dimethylsiloxane) binder. During the current phase of this research, the effects of silanization versus no silanization of the porous ceramic and the influence of resin composition on the biaxial tensile strength of the IPCs were investigated.

External Collaboration

Dr. J. R. Kelly, of the Naval Dental Research Institute and the Naval Dental School, Bethesda, MD

Accomplishments:

The use of the silane agent 3-methacryloxypropyltrimethoxysilane had a positive effect on the biaxial tensile strength of the IPCs, a result similar to that found with traditional dental composites.
The polymerization of infiltrated thermosetting resin systems based on MMA and cross-linking difunctional methacrylates did not generally enhance the strength of alumina-polymer-based IPCs. (This suggests that the role of the polymer phase in IPCs and in conventional particulate-filled composites may not be equivalent.)

Impacts

Two patent applications have been filed and several companies have shown interest in the technology.

Outputs

Publications

M.G. Marks, J.R. Kelly, J.M. Antonucci, Effect of Resin Composition on Polymer-Reinforced Ceramics, J. Dent. Res., 75, 148 Abstract #1041 (1996).

Patents

J.R. Kelly, J.M. Antonucci, U. S. Patent Applications - 08,487,557 and 08,660,000.

Presentations

M.G. Marks, J.R. Kelly, J.M. Antonucci, Effect of Resin Composition on Polymer-Reinforced Ceramics, IADR meeting, San Francisco, CA, March 1996.

Bioresorbable Polymer-Reinforced Calcium Phosphate Cements

Joseph M. Antonucci

Objective

The object is to improve the load-bearing behavior of a biocompatible, self-setting calcium phosphate cement by the inclusion in its structure of a bioresorbable polymer in fiber mesh form.

Technical Description

Hydroxyapatite-forming calcium phosphate cements (CPC) derived from the reaction of tetracalcium phosphate and dicalcium phosphate in aqueous media have proven successful in healing small, non-stress bearing skeletal defects. However, because of its low tensile strength, CPC is not an appropriate cement for stress-bearing applications. Polyglactin (a copolymer of glycolic and lactic acids of the type used in resorbable sutures) in knitted fiber mesh form was incorporated into the tensile surface of CPC discs during the setting process. Two sets of control discs were prepared: (1) unreinforced CPC and (2) heat cured PMMA, i.e., poly(methyl methacrylate) cements of the type used for ocular prostheses. The three types of discs were loaded in biaxial flexure (ring-on-ring) to simulate blunt loading of an edge-supported cranial prosthesis (mesh surfaces placed in tension). Work-to-fracture was measured for the discs at a defined strain following storage in artificial serum for 0-28 days at 37C.

External Collaborations

This project involved collaboration with Dr. Ann Sue von Gonten of the U. S. Army Dental Corps and Dr. J. Robert Kelly of the U. S. Navy Dental Corps, both of the Naval Dental School in Bethesda, MD.

Planned Outcomes

The technology developed in this study has the potential for extending the biomedical use of the highly biocompatible CPC developed at the American Dental Association Health Foundation Paffenbarger Research Center (ADAHF/PRC). A company involved in the commercialization of CPC has shown interest in this technology and, in part, because of the promising results of this study, has agreed to provide some financial assistance (through the ADAHF/PRC) for this type of research.

Accomplishments

The results of this study demonstrated the compatibility of polyglactin fibers with CPC. The 2-D oriented polyglactin fibers exhibited good adhesion to CPC and resisted biaxial tensile stresses prior to their hydrolytic degradation. Thus, CPC reinforced with polyglactin fiber mesh progressed to failure in a manner consistent with the inelastic behavior of oriented fiber composites, holding relatively high loads despite the occurrence of innumerable fracture events. Unreinforced CPC behaved as a simple brittle material with low fracture toughness. Not surprisingly the PMMA cement exhibited only minimal change in its work-to-fracture value after 28 days of immersion. For at least seven days the fiber mesh-reinforced CPC performed as well as PMMA. Thus, bioresorbable polymeric fiber-reinforced CPCs show potential for use in stress-bearing as well as non-stress bearing biomedical applications.

Outputs

Publications

A.S. Von Gonten, J.R. Kelly, J.M. Antonucci, Load-bearing Behavior of a Simulated Craniofacial Structure Fabricated from Hydroxyapatite Cement and Bioresorbable Fiber Mesh, J. Prosth. Dent. (Submitted).

Presentations

A.S. Von Gonten, J.R. Kelly, J.M. Antonucci, Load-bearing Behavior of a Simulated Craniofacial Structure Fabricated from Hydroxyapatite Cement and Bioresorbable Fiber Mesh, Winner: Graduate Student Research Award, American Academy of Maxillofacial Prosthodontists, Kansas City, MO, October 1996.

Measurement Methods for Process Control of Cell Encapsulation

Francis W. Wang

Objective

The objective is to develop measurement methods for monitoring the encapsulation of cells and enzymes.

Technical Description

In a commonly used process for encapsulating cells with sodium alginate, reaction conditions, such as temperature, reaction time, and amounts of reactants, are controlled to produce functionalized alginate with varying degrees of attachment of photopolymerizable functional groups. In addition, the extent of photo-induced cross-linking of the functionalized alginate is controlled to produce microcapsules of required porosity. The method of wavelength-shift fluorescence is used in this project to monitor the degree of functionalization. This is accomplished by: (1) synthesizing a mobility-sensitive fluorescent probe which becomes covalently attached to sodium alginate at a reaction rate similar to the rate for the attachment of photopolymerizable functional groups to sodium alginate; (2) adding a trace amount of the probe to the reaction mixture containing sodium alginate and other reactants; and (3) measuring the fluorescence spectrum of the probe as a function of the reaction time. Since the mobility of the probe molecules decreases upon their attachment to sodium alginate, the fluorescence wavelength of the probe decreases with the increase in the attachment of the probe molecules to sodium alginate. Consequently, the change in the fluorescence wavelength of the probe is a measure of the degree of attachment of the photopolymerizable functional groups to sodium alginate, if the probe has been designed such that its reactivity with the secondary hydroxy groups of sodium alginate is comparable to the reactivity of the reactant for attaching photopolymerizable functional groups to the secondary hydroxy groups of sodium alginate. Once a correlation is established between the change in the fluorescence wavelength and the degree of attachment determined by H-NMR, an absolute value for the degree of attachment can be obtained from the change in the fluorescence wavelength. Alternatively, the measured value of the fluorescence wavelength can be used to compare or maintain the degree of attachment throughout the functionalization process.

Photo-induced crosslinking of the functionalized alginate can be monitored in the manner similar to the method described for monitoring the functionalization. This will be accomplished by: (1) synthesizing a mobility-sensitive fluorescent probe with a photopolymerizable moiety which has the same reactivity as the photopolymerizable functional groups covalently attached to sodium alginate; (2) adding a trace amount of the fluorescent probe to the reaction mixture containing the photo-crosslinkable alginate and other reactants; and (3) measuring the fluorescence spectrum of the probe as a function of the reaction time. Since the mobility of the probe molecules is reduced due to their reaction with the functional groups on sodium alginate, the fluorescence wavelength of the probe decreases with the increase in the degree of crosslinking of the alginate. Consequently, the change in the fluorescence wavelength of the probe is a measure of the degree of crosslinking. Once a correlation is established between the change in the fluorescence wavelength and the porosity of the microcapsules, the porosity can be obtained from the change in the fluorescence wavelength. Alternatively, the measured value of the fluorescence wavelength can be used to compare or maintain the porosity throughout the photo-induced crosslinking process.

External Collaboration

VivoRx

Planned Outcomes

Technology transfer to VivoRx of process control methods for functionalization and cross-linking of sodium alginate for cell encapsulation.

Accomplishments

Mobility-sensitive fluorescent probes for monitoring functionalization and cross-linking of sodium alginate have been synthesized. It was demonstrated that, when the mobility-sensitive probe was dissolved in the reaction mixture for functionalization of sodium alginate, the peak fluorescence wavelength of the fluorescent probe decreased with the extent of functionalization.

Outputs

Patents

F.W. Wang, K.F. Lin, and R.E. Lowry, Non-destructive Method for Determining the Extent of Cure of a Polymerizing Material and the Solidification of a Thermoplastic Polymer Based on Wavelength Shift of Fluorescence, U.S. Patent Application Serial No. 08/389,823, allowed for July, 1996.

Bioactive Polymeric Dental Materials with Remineralization Potential Based on Amorphous Calcium Phosphate.

Joseph M. Antonucci

Objective

The objective of this project is to develop bioactive polymeric composites with remineralization potential using various forms of amorphous calcium phosphates (ACP) as the filler phase.

Technical Description

Two modified ACP fillers were prepared by sol-gel precipitation techniques using tetraethoxysilane (silica modified ACP) and zirconyl chloride (zirconia modified ACP). Visible light activated acrylic composites based on these fillers prepared and compared with similar composites based on unmodified ACP as a filler. In vitro release of calcium and phosphate ions from the modified ACP composites was monitored by atomic absorption and UV spectroscopic methods respectively. Mechanical strength was evaluated by the biaxial flexure test.

Remineralizing polymer based ACP systems are expected to find use as adhesives, sealants and as base and lining materials.

External Collaborations

Dr. E.D. Eanes, Dr. D. Skrtic, Mr. A.W. Hailer of NIDR and Dr. S. Takagi of ADAHF/PRC.

Accomplishments

Demonstrated that glass forming agents such as tetraethoxysilane and zirconyl chloride can be used to modify ACP fillers for bioactive composite applications.
The new biactive composites exhibited adequate release of calcium and phosphate ions for remineralization on exposure to oral-simulative environments.

The biaxial tensile strengths of the modified ACP composites exceeded that of an unmodified ACP composite control.

Impacts

A patent has been issued based on the use of amorphous calcium phosphate as a bioactive filler, and several companies have expressed interest in this technology.

Outputs

Publications

D. Skrtic, J.M. Antonucci, E.D. Eanes, Modified Amorphous Calcium Phosphate Fillers for Bioactive Composite Applications, J. Dent. Res., 75, 145 Abstract #1017 (1996).

J.M. Antonucci, D. Skrtic, E.D.Eanes, Bioactive Polymeric Materials Based on Amorphous Calcium Phosphate - effect of coupling agents, Chapter 20 in: Hydrogels and Biodegradable Polymers for Bioapplications (R. Ottenbrite, S. Huang and K. Park eds.); ACS Symposium Series 627, Washington, DC, pp.243-254 (1996).

D. Skrtic, A.W. Hailer, S. Takagi, J.M. Antonucci and E.D. Eanes, Quantitative Assessment of the Efficacy of Amorphous Calcium Phosphate/Methacrylate Composites in Remineralizing Caries-like Lesions Artificially produced in Bovine Enamel, J. Dent. Res. (in press).

Patents

J.M. Antonucci, D. Skrtic and E.D. Eanes, Polymeric Amorphous Calcium Phosphate Compositions. Patent issued April 16, 1996, (US Patent 5508342).

Presentations

D. Skrtic, J.M. Antonucci, E.D. Eanes, Modified Amorphous Calcium Phosphate Fillers for Bioactive Composite Applications, IADR meeting, San Francisco, CA, March 1996.

J.M. Antonucci, D. Skrtic, E.D.Eanes, Bioactive Polymeric Materials Based on Amorphous Calcium Phosphate - effect of coupling agents, Generic/Pentron, Inc., Wallingford, CT., April 1996.

Support for the Biomaterials Integrated Products Industries

J.A. Tesk, Steve Hsu¹

¹ Ceramics Division

Objective

The objective is to assess the standards and measurement needs of the U.S. industries that manufacture biomaterial integrated products.

Technical Description

Objectives will be met by forming cooperative relationships between industry, NIST, other government agencies (NIH and FDA), and standards bodies to identify needs and develop strategies to meet needs. This is done by sponsoring of workshops, development of CRADAs and other agreements, and active support of standards related activities.

External Collaborations

Biomet Inc. (Warsaw Ind.), Johnson & Johnson Professional, Inc. (Raynham, Mass.), Ostenoics Inc. (Allendale, N.J.), Smith & Nephew Richards, Inc. (Memphis, Tenn.), Wright Medical Technology, Inc. (Arlington, Tenn.), and Zimmer, Inc., (Warsaw, Ind.), Poly Hi Solidur (Fort Wayne, Ind) Teledyne Allvac/Vasco (Monroe,NC), Polymer Technology Group (Emeryville, Ca.) American Association of Orthopaedic Surgeons, Hip and Knee Society, Ohio State University Department of Orthopaedic Surgery, Massachusetts General Hospital Department of Orthopaedic Surgery, Rush-Presbyterian - St Luke's Hospital Department of Orthopaedic Surgery, National Heart, Lung, & Blood Institute, Medical Devices Standards Board, Leadership roles with the Biomaterials Society.

Planned Outcomes

Accelerated tests for evaluation of wear of orthopaedic joint materials.
Reference materials for implantable materials and explanted devices.
National and international standards for medical devices.

Accomplishments

Cooperative Research & Development Agreements (CRADAs) were signed with six (6) orthopaedic companies to form a consortium to identify accelerated methods for evaluation of the wear properties of orthopaedic joint materials.

Facilitating NIST-NIH-FDA-Private Industry collaboration for NIST dissemination of industry developed Polyetherurethane Reference Materials, useful in the development of cardiovascular devices.

Coordinating development of a memorandum of understanding between NIST, NIH & FDA for future development of reference materials for biomedical devices.

Outputs.

Publications

J. Tesk, What is a Standard Reference Material, What is any Reference Material?,Biomaterials Newsletter "The Forum", April 1996.

J. Tesk, International Standards and Reference Materials, Proceedings of Workshop On Implant Retrieval and Analysis; Buffalo NY., June 1996.

Presentations

J. Tesk, International Standards and Reference Materials, Workshop on Implant Retrieval and Analysis, Buffalo, NY, June 1996.

Durability Assessment of Biomedical Materials/ Prostheses

John A. Tesk; J. Stansbury, J. Lechner (retired, Division 882); Collaborators: S.C. Saunders; H. Morris; K.Asaoka.

Objectives

The objectives are to explore the following: employment of cyclopolymerizable monomers as substitutes for poly(methyl methacrylate) in orthopaedic bone cement, models of the mechanical behavior of dental/medical materials, probabilistic methods which may be useful in the prediction of clinical survivability of biomedical implants and prostheses based on early time survival data, and screening tests for nanosized filler dental restoratives for which the coupling agents to the filler acts as the resin matrix.

Technical Description

Evaluate properties of mixtures of poly(methyl methacrylate) and cyclopolymerizable monomers; explore with NIH, NIST and Washington State University the feasibility/interest in workshop on implant reliability predictions using engineering statistical approaches; continue modeling collaborations with Tokushima University.

External Collaborations

J. Lechner (retired, Division 882); S.C. Saunders, Washington State University; H. Morris, Veterans Administration; K.Asaoka, Tokushiima University.

Accomplishments

Established informal collaboration with Ohio State University Department of Orthopaedic Surgery for evaluation of experimental bone cement formulations.

Outputs

Publications

J.A. Tesk, and Asaoka, On Computer Simulation of Stresses developed in Dental Investments During Burnout, Prior to Casting, Dent. Mater. (submitted).