Aspects of water sorption from the air, water and artificial saliva in resin composite restorative materials

Objectives. Primarily to establish whether artificial saliva (AS) at 37 degreesC is essential as a clinically relevant environment for testing filled, resin composite restorative materials. The effect of other storage conditions was also investigated for comparison and controls: desiccation, exposure to the laboratory atmosphere, high humidity cabinet, saturated water vapor, and deionized water. Methods. Two visible light-cured products were used: Heliomolar Radiopaque (HR) and Tetric Ceram (TC) (Ivoclar, Schaan, Liechtenstein). Bar specimens (26 X 1.5 X 1.0 mm(3)) were cured at five overlapping spots for 60 s per spot and randomly distributed into groups of six. Trial 1: one group of each material was exposed first to atmospheric air at 24 degreesC, similar to50% RH ((WV50)-W-24), then to water vapor at 37 C, similar to97% RH ((WV97)-W-37), and then immersed in deionized water at 37 degreesC ((DW)-D-37). Trial 2 used three groups of each material, one first exposed to (WV97)-W-37 followed by (DW)-D-37, the other two were immediately immersed in (DW)-D-37 or artificial saliva ((37)AS). Trial 3: two groups of each material were vacuum desiccated at 37 degreesC, then exposed to 37 C, similar to100% RH ((WV100)-W-37), then immersed in (DW)-D-37 or (37)AS. Trial 4: four groups of HR were treated similarly to Trial 3; one was left under desiccation, and another in (WV100)-W-37 for the remaining period. Three-point bend tests for flexural strength (F), flexural modulus (E), and total energy to failure (W) were performed at the end of Trials 2-4. Results. Environmental moisture absorption was substantial at (WV50)-W-24(c. 0.2%), at least 40% of that in (DW)-D-37 (HR:. c-0:7%, TC: c. 0.5%). Saturation was achievable in (WV100)-W-37. Mass loss on desiccation (HR: c. 0.4-0.5%, TC: c. 0.25%) was reversible in (WV100)-W-37. There were some significant effects of exposure conditions on mechanical properties (e.g. F for HR: after desiccation, 85.7 +/- 1.4 MPa; after (WV100)-W-37, 73.2 +/- 3.6 MPa; difference: p < 0.0002), but overall the results were unclear. After a rapid gain in mass, there was a gradual loss in both (DW)-D-37 and (37)AS for both materials, slightly: more in (37)AS than (DW)-D-37. Significance. Water vapor absorption is substantial, hence attention must be paid to the laboratory working environment and conditions of storage and testing, i.e. temperature and RH must be stated to assist interpretation of data and comparisons between studies. Test conditions need to be standardized and with reference to normal oral conditions, immediate immersion in artificial saliva at 37 degreesC is the preferred treatment for these materials, whatever time of testing is chosen. (C) 2003 Academy of Dental Materials. Published by Elsevier Science Ltd. All rights reserved.