Objectives: To evaluate the effect of different propionaldehyde ratios on the degree of conversion (DC%), microhardness (H) and glass transition temperature (Tg) of copolymers based on Bis-GMA diluted with propoxylate BisGMA (CH3BisGMA).
Methods: Five experimental comonomers were prepared combining BisGMA, CH3BisGMA, and the following propionaldehyde ratios: G1- (0mol%), G2- (2mol%), G3- (8mol%), G4- (16mol%), G5- (24mol%). Photopolymerization was effected by using camphorquinone (0.2wt%) and N,N-dimethyl-p-toluidine (0.2wt%). DC% (n=3) was investigated by FT-IR. H measurements (n=5) were performed for dry and wet samples (7 days in distilled, 37oC) using Knoop microindenter (5gf/15s). Tg was evaluated by Differential Scanning Calorimetry. Data (table 1) were analyzed by ANOVA and Tukey-Kramer test (α=0.05).
Results:
Table 1: Results for copolymers DC%, H and Tg
| DC%(s.d.) | H (KHN)(s.d.) Dry specimens | H (KHN)(s.d.) Wet specimens | Tg (oC) |
G1 | 38.0 (±2.6)a | 13.3(±1.2)d | 12.6(±0.8)f | 48 |
G2 | 38.6(±3.0)a | 14.0(±0.7)d | 13.3(±0.6)fg | 48 |
G3 | 40.0(±1.7)ab | 14.2(±1.0)d | 14.0(±0.7)g | 49 |
G4 | 44.3(±1.5)b | 14.6(±0.6)d | 14.1(±0.3)g | 49 |
G5 | 53.3(±1.5)c | 17.2(±0.9)e | 16.5(±0.8)h | 50 |
s.d.: standard deviation; same letters indicate no statistical differences.
Incorporation of propionaldehyde produced significant increase in the DC% and H for G5 (p≤0.0001). No remarkable variation on Tg was noted among the evaluated groups.
Conclusion: The ability of propionaldehyde to improve copolymer DC% probably led to an enhancement of G5 surface hardness.