RELATIONSHIP BETWEEN FILLER AND MATRIX RESIN CHARACTERISTICS AND THE PROPERTIES OF UNCURED COMPOSITE PASTES

The relationships between filler type, filler content, matrix resin co mposition and viscosity and the flow characteristics of composite past e formulations have been investigated. BIS-GMA and 10 experimental BIS -GMA analogues were diluted as needed with TEGDMA to produce 1000 and 2000 cp solutions corresponding to the viscosity range of commercial c omposite matrices. All of these resins were mixed with a silanated hyb rid-filler and a silanated micro-filler. For each combination the maxi mum filler content was determined, as well as the paste consistencies (plasticities) at a series of filler contents. Paste consistencies wer e measured by a modification of the ADA specification methods develope d for determining standard test consistencies for zinc phosphate and s ilicate cements. For each monomer-filler combination increasing filler contents resulted in monotonically reduced plasticities. The maximum filler contents appeared to be an attribute of the particular filler r ather than matrix resin characteristics. For the materials used, the m aximum contents were approximately 86 wt% (83 vol%) filler for the hyb rid filler, and 36% wt% (24 vol%) for the microfilled material. At low er filler contents, plasticity differences unexpectedly existed even a t equal filler contents and matrix viscosities. Evidence was found tha t the plasticity varied both with the base monomer composition and the amount of TEGDMA present. The results imply that compositional intera ctions between the filler and matrix influence the results when all kn own mechanical factors are controlled. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.