Evaluation of the frequency and temperature dependence of the dynamic mechanical properties of acetal resins.

The purpose of this study was to evaluate and compare the dynamic mechanical properties of two acetal resins (different colored samples of the same resin), an autopolymerized reline resin, and a heat-polymerized denture base resin. Measurements were obtained in two conditions, the frequency- and temperature-dependent conditions, using a dynamic viscoelastometer. The acetal resins exhibited lower loss tangent values than the autopolymerized reline resin and heat-polymerized denture base resin. With respect to temperature dependence, all of the materials displayed stable viscoelastic properties in the temperature range found in the oral environment. The acetal resin had both a glass transition temperature and a melting point, whereas the autopolymerized reline resin and heat-polymerized denture base resin had only glass transition temperatures. The results of this study suggest that acetal resin displays elastic properties when compared with the other 2 materials.

The effect of length parameter on the repair strength of acrylic resin using fibers or metal wires.

Fractures of acrylic resin dentures occur quite often in prosthodontic practice. Autopolymerized acrylic resin is the most popular material for denture repair; however, it is significantly weaker than the intact heat-polymerized resin. Metal strengtheners or fibers have been used to reinforce the resin. This study investigated the fracture force, deflection, and toughness of a heat-polymerized denture resin that had been repaired either with autopolymerized resin alone or with autopolymerized resin that had been reinforced with metal wire or woven glass fibers. This study also investigated how these qualities were affected when the length of the strengthener was reduced. Sixty specimens were divided into six groups of ten (depending on the repair method), together with a control group of intact heat-polymerized resin specimens. The group repaired with autopolymerized resin alone reported significantly lower (p < 0.05) fracture force, deflection at fracture, and toughness when compared to the control. When metal wire or glass fiber at full or half-length was used for reinforcement, only the original fracture force was restored; deflection and toughness remained significantly lower (p < 0.05). Based on this study, it appears that the group reinforced with full lengths of metal wire offered the best potential for reinforcement.

Fracture force, deflection, and toughness of acrylic denture repairs involving glass fiber reinforcement.

PURPOSE: Fractures in acrylic resin dentures occur quite often in the practice of prosthodontics. A durable repairing system for denture base fracture is desired to avoid recurrent fracture. The purpose of this study was to evaluate the fracture force, deflection, and toughness of a heat-polymerized denture base resin repaired with autopolymerized resin alone (C), visible light-polymerizing resin (VLC), or autopolymerizing resin reinforced with unidirectional (Stick) (MA-FS) and woven glass fibers (StickNet) (MA-SN). Another group was repaired with autopolymerized resin after wetting the repair site with methyl methacrylate (MA-MMA) for 180 seconds. A group of intact specimens was used as control. MATERIALS AND METHODS: Heat-polymerizing acrylic resin was used to fabricate the specimens. The specimens (10 per group) were sectioned in half, reassembled with a 3-mm butt-joint gap, and repaired. A cavity was included when glass fibers were used. Three-point bending was used to test the repaired site, and data were analyzed with one-way ANOVA and the Tukey's post hoc test (alpha < or = 0.05). RESULTS: Fracture force, deflection, and toughness for the repaired groups without reinforcement (MA: 46.7 +/- 8.6 N, 2.6 +/- 0.3 mm, 0.08 +/- 0.001 J; MA-MMA: 41.0 +/- 7.2 N, 2.7 +/- 0.4 mm, 0.07 +/- 0.002 J) were significantly lower (p < 0.05) than the control group (C: 78.6 +/- 9.6 N, 5.9 +/- 0.4 mm, 0.27 +/- 0.003 J). Repair with visible light-polymerizing resin (VLC, 15.0 +/- 4.0 N, 1.2 +/- 0.4 mm, 0.02 +/- 0.0001 J) resulted in significant reduction of mechanical properties (p < 0.05). Reinforcement with glass fibers restored (MA-SN: 75.8 +/- 9.2 N) or increased (MA-FS: 124.4 +/- 12.5 N) the original strength. CONCLUSION: The most effective repair method was the use of autopolymerized resin reinforced with unidirectional glass fibers.

Dynamic mechanical properties of hard, direct denture reline resins.

STATEMENT OF PROBLEM: Dynamic mechanical properties of hard, direct reline resins are important factors in the clinical success of dentures. However, little information is available on the nature of these properties. PURPOSE: This study evaluated the dynamic mechanical properties of a variety of hard, direct reline resins: (1) visible light-polymerized, powder-liquid type, (2) visible light-polymerized, paste-type, (3) autopolymerized, powder-liquid type, as classified by component composition and mode of polymerization activation, namely, type of delivery system, and (4) heat-polymerized denture base materials. MATERIAL AND METHODS: The dynamic mechanical analysis (DMA) of 8 commercial hard denture reline materials (HDR) (2 visible light-polymerized, powder-liquid type, 4 visible light-polymerized, paste-type, and 2 autopolymerized, powder-liquid type), and 2 heat-polymerized denture base materials was obtained at a frequency of 1 Hz at 37 degrees C. Five specimens of each material, 40.0 x 7.0 x 2.0 mm, were made to measure the elastic (storage) (E') and inelastic (loss) (E'') moduli, and loss tangent (tan delta). These parameters were compared with MANOVA and Student-Newman-Keuls test (alpha =.05). RESULTS: The E' values of 3 visible light-polymerized, paste-type reline resins were significantly higher than those of the other 5 reline resins. However, the E' values of all reline resins were significantly lower than those of the 2 heat-polymerized denture base resins. Except for 1 autopolymerized reliner, all reline materials had significantly lower E'' than the heat-polymerized denture base resins. The tan delta values of all but 1 visible light- and autopolymerized reliners were significantly higher than those of the heat-polymerized denture base materials. CONCLUSIONS: Three visible light-polymerized, paste-type reline resins showed greater stiffness than the visible light- or autopolymerized, powder-liquid type reline resins. However, all of the hard, direct reline resins, including the 3 paste-type materials, exhibited greater flexibility compared to the heat-polymerized denture base resins.

Bonding of silicone extra-oral elastomers to acrylic resin: the effect of primer composition.

Silicone elastomer is bonded to acrylic resin in many facial or oro-facial prostheses. The silicone elastomer/acrylic resin bond has been reported to be insufficient and primers have been used to enhance the bond. This study investigated the bond strength of silicone elastomer to acrylic resin using different types of primers. The extra-oral silicone elastomers studied were Cosmesil and Ideal. The "overlap-joint" model was used to evaluate the bond strength and the samples were stretched until fracture. The bonding surfaces were treated with a primer. The control primer was Cosmesil and the others a mixture of Cosmesil/Z-6020 and Cosmesil/A-174 in 50/50 v/v ratio. The bond strength ranged from 0.026 MPa to 0.219 MPa. The results obtained in this work led to the conclusion that the most critical parameter allowing the efficient performance of a primer is the compatibility and affinity of its composition with the selected silicone elastomer.

Bonding of silicone prosthetic elastomers to three different denture resins.

PURPOSE: The aim of this study was to evaluate the interfacial bond strength between different types of silicone facial elastomers and denture resins. MATERIALS AND METHODS: The facial materials studied were Cosmesil and Ideal, whereas SR 3/60, SR 3/60 Quick, and Triad were included in the denture resins group. The "overlap-joint" model was used to evaluate the bond strength, and the samples were placed in tension until failure. The bonding surfaces were treated with a primer. Ten samples for each silicone/resin group were tested. The results were subjected to two-way analysis of variance and Tukey's test for comparison. RESULTS: The bond strength was affected by the type of silicone elastomer and denture resin. An interaction between them was also noted. The bond strength ranged from 0.03 to 0.23 MPa. CONCLUSION: Cosmesil condensation-type silicone always showed higher bond strength with the three different types of denture resins compared to Ideal addition silicone, keeping other variables associated with the silicone-resin bond fixed.