The research on dental materials that is described in this report is a part of a larger total effort that is carried out in collaboration with the American Dental Association Health Foundation. The U. S. Army and Navy Medical R&D Command and the School of Dentistry, Georgetown University are also part of this collaborative effort through support funding and/or assignment of research personnel.While the bulk of the research progress in this report represents only the efforts of NBS staff supported under the Interagency Agreement with NIDR, there will of necessity be a degree of contribution that originates through the intentionally strong interaction among all persons participating in this collaborative dental program.The objective is to effect improved dental health through development of new knowledge and better understanding of the mechanical, chemical, and physical properties of restorative and caries-preventive materials and the mechanisms by which clinical performance is governed.A wide variety of techniques has been brought to bear to generate approaches to new and improved adhesive restorative dental materials These include: syntheses of components to improve current composite restorative materials and pit and fissure sealants and development of techniques that can be used to examine the extent of the polymerization reaction in dental resins and components, investigation of new approaches to bonding restorations to tooth surfaces, determination of the mechanisms by which composite systems wear and degrade in clinical use coupled with production of accelerated laboratory wear test data, and development of characterization methods and data for analyzing the compatibility of dental porcelains for base metal alloys.

New polymeric formulations designed to reduce curing shrinkage, residual unsaturation and hydrophi 1 icity in dental composite restorations have been developed and evaluated. To reduce polymerization shrinkage emphasis has been placed on high molecular weight bulky monomers such as blends of BIS-GMA and diurea dimethacrylate types. While typically moderate to fast-acting accelerators such as bis(N ,N-2-hydroxypropyl )ptoluidine or p -tert-butyl -N ,N-dimethylani 1 ine could not be used with such formulations, substitution of slower acting accelerators such as ethyl -4-dimethyl ami nobenzoate or ascorbyl palmitate yielded formulations that set in clinically acceptable times.Powder/liquid, paste/paste or single paste/visible light cured formulations produced composites with

Significant accomplishments during the FY84 are itemized as follows:(1) Synthesis of syringate esters and of polymerizable vanillates was achieved.Properties of cement composites were determined and found to hold potential as intermediate restorative materials. Formulations which adhered well to porcelains, composites, and metals were developed.(2) 27 PETMP, etc.) for the peroxide. These systems yield composites with higher and more unifrom degrees of cure versus depth, minimal air inhibition and enhanced strength.3.Halotopolymer Cements Based on Dimer and Trimer Acids.

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The research program described herein is designed to achieve a number of objectives leading to improved dental restorative materials, techniques, and applications of dental materials science for improved dental health care in general.Some of the research in dental composites is directed toward developing generic polymer science potentially useful for composite applications, e.g., durable resin matrices and stronger more durable coupling between fillers and resins.Improved reinforcement is sought by defining the type, and percentages of fillers which will result in improved performance of composites.Methods for reducing polymerization shrinkage and attendant stress and marginal leakage are also explored.Cements are investigated and basic formulations developed for lower solubility, higher biocompatibility, higher strength, greater toughness and adhesion to various substrates including enamel and dentin.Analysis techniques include IR spectroscopy, chromatography, x-ray analysis, mechanical testing, and dilatometry.Another major effort is directed at elucidating the fundamentals involved in wear and degradation of dental composites and restoratives.Wear and hardness measurement techniques are used as well as identification of the origins and sources of flaws leading to failure.Weibull statistical analysis is expected to provide useful information for this task.In this regard an objective is to investigate improved correlations between clinical results of wear and failure with laboratory test data.Metrology and analysis constitutes the underlying theme of investigations into porcelain-metal systems, casting of dental alloys and the expansion of dental casting investments."The activity covered by this agreement consists of work which requires the definition of measurement methods, materials property data, and standards of basic scientific and engineering units and the application of primary standards to insure equity and comparability in U.S. commerce, international trade, and technical activities.As such it complies with OMB Circular A-76, revised under paragraph 5f (Activities classified as Government responsibilities or are intimately related to the public interest)."