The effect of monomer to powder ratio on polymerization shrinkage-strain kinetics of polymer-based provisional crown and fixed partial denture materials

Kim, Sung Hun

Abstract

STATEMENT OF PROBLEM: Although a number of previous investigations have been carried out on the polymerization shrinkage-strain kinetics of provisional crown and fixed partial denture (FPD) materials, the effect of the changes of liquid monomer to powder ratio on its polymerization shrinkage-strain kinetics has not been reported. PURPOSE. The purpose of this study was to investigate the influence of liquid monomer to powder ratio of polymer-based provisional crown and FPD materials on the polymerization shrinkage-strain kinetics. MATERIAL AND METHODS: Chemically activated acrylic provisional materials (Alike, Jet, Snap) were investigated. Each material was mixed with different liquid monomer to powder ratios by volume (1.0:3.0, 1.0:2.5, 1.0:2.0, 1.0:1.5, 1.0:1.0). Time dependent polymerization shrinkagestrain kinetics of all materials was measured by the bonded-disk method as a function of time at 23 degrees C. Five recordings were taken for each ratio. The results were statistically analyzed using one-way ANOVA and the multiple comparison Scheffe test at the significance level of 0.05. Trends were also examined by linear regression.
RESULTS
At 5 minutes after mixing, the polymerization shrinkage-strains of all materials ranged from only 0.01percent to 0.49 percent. At 10 minutes, the shrinkage-strain of Alike was the highest, 3.45 percent (liquid monomer to powder ratio = 1.0:3.0). Jet and Snap were 2.69 percent (1.0:2.0) and 1.58 percent (1.0:3.0), respectively (P > 0.05). Most shrinkage (94.3 percent - 96.5 percent) occurred at 30 minutes after mixing for liquid monomer to powder ratio, ranging from 1.0:3.0 to 1.0:1.0. The highest polymerization shrinkage-strain values were observed for the liquid monomer to powder ratio of 1.0:3.0. At 120 minutes after mixing, the shrinkage-strain values were 4.67 percent, 4.18 percent, and 3.07 percent for Jet, Alike, and Snap, respectively. As the liquid monomer to powder ratio increased, the shrinkage- strain values tend to be decreased linearly (r = - 0.769 for Alike, - 0.717 for Jet, - 0.435 for Snap, r2 = 0.592 for Alike, 0.515 for Jet, 0.189 for Snap; P < 0.05).
CONCLUSION
The increase of the liquid monomer to powder ratio from 1.0:3.0 to 1.0:1.0 had a significant effect on the shrinkage-strain kinetics of polymer-based crown and FPD materials investigated. This increased the working time and decreased the shrinkage-strain during polymerization.