Effect Of Methyl Formate-Methyl Acetate Treatment On Flexural Strength Between Denture Base And Self-Cured Hard Reline Materials

The purpose of this study was to evaluate the effect of methyl formate-methyl acetate (MF-MA) surface treatment on the flexural strength between denture base and hard reline materials. 180 heat-cured acrylic denture base (Meliodent®) specimens were prepared according to ISO 20795-1 (2013) and divided into 18 groups with various autopolymerizing hard reline materials. Group I-III: relined with Unifast Trad®, Group IV-VI: relined with Kooliner® Group VII-IX: relined with Tokuyama® Rebase II Fast (without adhesive, with hardener), Group X-XII: relined with Tokuyama® Rebase II Fast (with adhesive and hardener), Group XIII-XV: relined with Tokuyama® Rebase II Fast (without adhesive and hardener), Group XVI-XVIII: relined with Tokuyama® Rebase II Fast (with adhesive, without hardener).  Group I, IV ,VII and  XIII were untreated surface (control groups), Group II, V, VIII and XIV were surface treated with methyl methacrylate (MMA) for 180 s and Group III, VI, IX and XV  were surface treated with MF-MA solution for 15 s. Group X and XVI were surface treated with the manufacturer adhesive,  Group XI and XVII were surface treated with MMA 180 s and the manufacturer adhesive, Group XII and XVIII were surface treated with MF-MA 15 s and the manufacturer adhesive. The flexural strength was measured using a Universal Testing Machine. The data were analyzed using two-way ANOVA (group I-IX) and one-way ANOVA (group I-XVIII).  If the significant differences in the groups were found, the mean flexural strengths of the groups were compared using Tukey’s test at a 95 % confidence level. For Tokuyama® Rebase II Fast, the data were analyzed using three-way ANOVA (Hardener, Manufacturing Adhesive, Surface treatment). The reline material type and surface treatments significantly affected on the flexural strength (p<0.05). For each reline material, the flexural strength of the MF-MA treated group was significantly higher compared with that of the MMA treated group and the MMA treated group had higher flexural strength than the untreated group (p<0.05).  For Tokuyama® Rebase II Fast, the surface treatment and manufacturing adhesive affected on the flexural strength (p< 0.05), but the hardener did not affected on the flexural strength (p> 0.05). Groups of additional surface treatment (MMA, and MF-MA) after applied with the adhesive significantly increased the flexural strength compared with the groups with only using the manufacturing adhesive (p<0.05). For the same surface treatment, the flexural strength of Unifast Trad® was significantly higher compared with Kooliner® (p<0.05). The flexural strength of Kooliner® was higher than that of Tokuyama® Rebase II Fast (p<0.05). This study suggests the application of MF-MA solutions for 15 s before relining procedure can increase the flexural strength between denture base and hard reline materials.