Cements based on resin technology are available for lining a cavity preparation with various modifications containing active agents. These cements need to support the overlying restoration long term without losing their properties. Objectives: The goal of this investigation was to determine the effects of wet environment on the mechanical properties of liner cements.
Method: The six lining cements investigated were resin based cements: Aegis Liner (AL), Lime-Lite (LL), Prisma VLC Dycal (PVD), and Ultra-Blend Plus (UBP); resin modified glass ionomers: Fuji LC Lining Cement (FL), and Vitrebond (VB); and conventional glass ionomer: GC Lining Cement (GCL). Standard methods for resin (ISO 4049) were used to determine water sorption and solubility (N=5). Initial flexural strength and modulus (Xhead speed=1mm/min) were obtained at 2 days after storage at 37oC, dry, of 2x2x25mm specimens that were light cured, 40s, 500mW/cm2 (N=5). Specimens were stored either dry or wet at 37oC until the wet specimens were totally saturated with water, determined by constant weight of all wet specimens (45 days). All flexural specimens were tested at 23oC, in air or water, respective to their storage conditions. All data were statistically analyzed (p≤0.05).
Result: Statistical comparisons: water sorption, VB>FL=PVD>AL>LL=GCL>UBP; water sorption, GCL>AL=UBP>PVD=LL=VB=FL; initial flexural strength, UBP=LL=PVD=AL≥VB≥FL=GCL, initial flexural moduli, VB=AL≥FL=LL>UBP=GCL≥PDL. Initial flexural strengths (MPa) were: UBP=59.5, LL=56.1, PVD=52.3, AL=44.6, VB=29.6, FL=17, GCL=3.2. The 45d means stored dry were not significantly different from the initial values. The 45d means stored dry decreased significantly for most of the cements. The dry cements did not increase in strength significantly over time, but resins did show a trend to increase, probably due to continued conversion.
Wet storage decreases the flexural strength of most of these materials. These decreases would suggest that these materials may not work as well clinically as indicated by initial dry strengths.
Keywords: Cements, Dental materials and Stress
See more of: Dental Materials 7: Polymer-based Materials-Physical Properties and Performance