1. INFLUENCE OF THE CHEMICAL COMPOSITION UPON THE PROPERTIES OF SOME EXPERIMENTAL DENTAL INDIRECT RESIN COMPOSITES C. Prejmerean, M. Moldovan, L. Vezsenyi, D. Borzea, C. Nicola, S. Sava, & A. Farcas 21 emes Journ e es Scientifiques du Coll e ge Francais de Biomat e riaux Dentaires 10-11 Juin 2004, Neuch a tel, SUISSE “ Raluca Ripan” Chemistry Research Institute, Department of Polymeric Composites, Cluj-Napoca, ROMANIA “Iuliu Hatieganu”University of Medicine and Pharmacy, Faculty of Dentistry, Department of Propaedeutics and Dental Materials, Cluj-Napoca, ROMANIAICCRR

2. Purpose and materials purpose The purpose of the present study was focused on obtaining a series of experimental indirect resin composites based on different resin matrix and on investigating the effect of post-curing upon the degree of conversion of the resin and respectively on the mechanical properties of the cured experimental indirect composites. Materials Materials: The resins were prepared from (Bis-GMA) 0-2 aromatic dimethacrylic oligomers synthesized in our laboratory, having 39 mol % Bis-GMA 0 monomer - 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy) phenyl]-propane, 60 mol % Bis- GMA 1 dimer and 1 mol % Bis-GMA 2 trimer; and aliphatic monomers TEGDMA, EGDMA, and HEMA. The inorganic filler consisted of 90% silanized SrO glass and 10% silanized colloidal silica. The powder/liquid ratio was 4/1. For the obtaining of specimens, the resin composites were light-cured by exposing to a visible radiation for 40 sec (Optilux stomatological lamp). After initial polymerization, the specimens were postcured by barro-thermic treatment at 135 0 C temperature and 60 psi pressure, for 20 minutes, using a “belleGlass” warmer.

3. Determination of the residual double bonds (RDB) Schematic representation of the crosslinked polymer network in diacrylic resins Composition of the resin matrix in the experimental indirect composites (%) The RDB values for the light-cured and postcured resin composites The RDB values for the light-cured  and postcured  resin composites

4. Determination of the mechanical properties The compressive strength values for the light-cured and postcured resin composites The compressive strength values for the light-cured  and postcured  resin composites The diametral tensile strength values for the light- cured and postcured resin composites The diametral tensile strength values for the light- cured  and postcured  resin composites The flexural strength values for the light-cured and postcured resin composites The flexural strength values for the light-cured  and postcured  resin composites

5. CONCLUSIONS  All the values obtained for the RDB in the case of post-cured resin composites were lower than the RDB values recorded for the corresponding untreated materials.  The decrease of RDB quantity was maximum for the Bis-GMA 0-2 / HEMA/ TEGDMA matrix (45% from RDB of untreated copolymer polymerized after post-curing), followed by the Bis-GMA 0-2 /HEMA copolymer (42% RDB).  The lowest RDB value (14,8%) was recorded for the post-cured Bis-GMA 0-2 / HEMA based resin composite.  The values for the mechanical properties are increased in the case of resin composites subjected to the barro-thermic treatment compared to the corresponding untreated materials. The increase of compressive strength was maximum in the case of Bis-GMA 0-2 /HEMA/TEGDMA based composite (21,5%). Diametral tensile strength has a higher increase, approximately 30% in the case of the same composite, and the increase of flexural strength was maximum for the Bis-GMA 0-2 /HEMA composite (18%).  Taking into consideration the quantity of RDB and the values obtained for the mechanical properties in the case of post-cured resins, the Bis-GMA 0-2 /HEMA based experimental resin composite was proposed for further investigations, toxicological and clinical tests, in order to be used as restorative material in indirect tecniques.