Plasticizer effect on network structure and hydrolytic degradation

Assessing the effect of chemical surface treatment and joint surface preparations on transverse strength of repaired denture base resin

The present study was conducted to assess the effect of chemical surface treatment and joint surface preparations on transverse strength of repaired denture base resin. The study included 120 specimens divided into 8 groups of 15 samples each based on the combination of chemical surface treatment with either methyl methacrylate, ethyl acetate, or methylene chloride and chemical surface treatment of rounded joint, 45° bevel, and butt joint. Following surface treatment, dentures were repaired with self-cure resin. After treatment, to assess the transverse strength, they were subjected to a 3‑point bending test. Surfaces that were fractured were assessed under the microscope and were analyzed to AutoCAD for assessing cohesive or adhesive failure type and the area was measured. The study results showed that a statistically significant difference was seen in most of the comparisons done. Specimens with rounded joints and methylene chloride used for 60 seconds showed the gain of strength of 60%-70& in the present study. The present study concludes that to attain better bond strength in a specimen repaired, the fractured segments of the specimens should be etched with methylene chloride for 60 s and should be given the rounded joints.

Influence of Various Chemical Surface Treatments, Repair Materials, and Techniques on Transverse Strength of Thermoplastic Nylon Denture Base

The process of repairing the fractured nylon denture bases and addition of acrylic teeth to the previously worn nylon denture bases has not been widely studied. This study aims to assess the transverse strength of nylon denture bases repaired by various resin materials, different curing techniques, and types of surface treatments. Materials and Methods. One hundred fifty thermoplastic nylon denture base samples were fabricated using plastic patterns measuring 65 × 10 × 2.5 mm (length, width, and thickness, respectively). These samples were then divided into three equal groups. Fifty samples were repaired by microwave heat-polymerization, fifty samples were repaired using the Ivomate autopolymerization, and the other fifty were repaired using light-polymerized acrylic resin. Each of these three groups was further divided into five subgroups of ten samples based on the type of surface treatment. The samples in the control group did not undergo any surface treatment, and the other four groups were chemically surface treated with monomer, acetone, ethyl acetate, and isopropanol, respectively. A three-point bending test was used to calculate the transverse strength values of the samples. Fourier transform infrared (FTIR) analysis was conducted to determine the component of functional groups between the polyamide nylon base and poly(methyl-methacrylate) PMMA repair materials. A polarizing microscope was utilized to investigate the mode of failure at the fracture surfaces. Results. The collected data were analyzed with one-way ANOVA and Sidak's multiple comparison test to show the differences among different groups. For surface treatments, the highest transverse strength values were obtained by monomer-treated samples (18.29 N/mm²); however, the lowest values were obtained in non-surface treated samples (5.58 N/mm²). While for repair techniques, the highest transverse strength values were obtained by microwave processing, followed by Ivomate and then the light-cured polymerization. The means were found to be significant (p < 0.001). FTIR analysis shows the presence of hydrogen bonding which is due to the ester and amid groups which enhance the bond strength of the surface-treated samples. The interface of the polarizing microscope images revealed a cohesive fracture within repair materials rather than the adhesive nature. Conclusion. The microwave-polymerized resin was considered as the most effective repair technique along with monomer chemical etchant which creates a tight adhesion between PMMA and nylon denture base in comparison to other groups.

Effect of surface treatment methods on the shear bond strength of auto-polymerized resin to thermoplastic denture base polymer

PURPOSE

Polyamide polymers do not provide sufficient bond strength to auto-polymerized resins for repairing fractured denture or replacing dislodged denture teeth. Limited treatment methods have been developed to improve the bond strength between auto-polymerized reline resins and polyamide denture base materials. The objective of the present study was to evaluate the effect of surface modification by acetic acid on surface characteristics and bond strength of reline resin to polyamide denture base.

MATERIALS AND METHODS

84 polyamide specimens were divided into three surface treatment groups (n=28): control (N), silica-coated (S), and acid-treated (A). Two different auto-polymerized reline resins GC and Triplex resins were bonded to the samples (subgroups T and G, respectively, n=14). The specimens were subjected to shear bond strength test after they were stored in distilled water for 1 week and thermo-cycled for 5000 cycles. Data were analyzed with independent t-test, two-way analysis of variance (ANOVA), and Tukey's post hoc multiple comparison test (α=.05).

RESULTS

The bond strength values of A and S were significantly higher than those of N (P<.001 for both). However, statistically significant difference was not observed between group A and group S. According to the independent Student's t-test, the shear bond strength values of AT were significantly higher than those of AG (P<.001).

CONCLUSION

The surface treatment of polyamide denture base materials with acetic acid may be an efficient and cost-effective method for increasing the shear bond strength to auto-polymerized reline resin.