MATRIX AND FILLER ON COMPOSITE RESIN PROPERTIES

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Recent improvements in materials and techniques have given today's dentist an ability to provide quality esthetic dentistry at an unprecedented level. The materials most used for this purpose are composite resins, which consist of small inorganic filler particles embedded in a polymer matrix. The dramatic increase in popularity for these materials has been accompanied by a couple of noteworthy problems. First of all, the number of composite resin products currently available to the dentist are virtually countless and are continually changing in composition. This has resulted in a wide range of formulations differing from each other with respect to polymer chemistries, filler particle sizes and fractions of filler introduced into the polymer matrix. The effects of varying these parameters are largely unknown. A second problem is the increased patient demand for dentists to place these materials not only in highly visible anterior teeth, but posterior teeth as well. Unfortunately, clinical data on older formulations indicate that a rapid wearing away of material occurs when they are subjected to heavy chewing forces. Furthermore, clinical data on present day composites are limited since a considerable investment in time, manpower and money is required to keep pace with these rapidly changing materials. In an attempt to gain some insight into these problems, one goal of this investigation is to evaluate a number of physical properties in a group of experimental composite resins in which the polymer chemistries, filler particle sizes and filler volume fractions are controlled. A second major objective is to study the sliding wear process on these materials when they are worn in a laboratory pin-on-disc machine. To date, data has been collected on a group of unfilled polymers with controlled chemistries. Resistance to sliding wear increases when the number of functional carbons present in the monomer increases from 2 to 4 and when the fraction of a crosslinking agent is increased from 15% to 30%. These changes in chemistry do not appear to greatly affect strength, stiffness or water absorption of the polymers.