Evaluation of hard direct reline resins

Peak curing temperatures of hard, direct, autopolymerizing reline resin materials tested were all within ADA specification guidelines. A temperature range of 10 degrees C was demonstrated among materials, with the highest polymerization temperatures recorded for Perm and Lang's Self-Curing Rebase Acrylic, and the lowest for KOOLiner, Flexacryl, and COE-Rect. This temperature difference is probably clinically detectable. However, intraoral testing of polymerization temperatures yielded lower peak values than those observed with specification testing, and the temperature peaks occurred earlier with intraoral conditions. There were significant color changes with simulated aging for three of the products tested: Flexacryl, COE-Rect, and Lang's Self-Curing Rebase Acrylic. The color changes occurred after only 24 hours of accelerated aging. Although there was only a small change in color with aging for Perm and KOOLiner, there was a moderate shift in the color of KOOLiner (delta E = 2.2) before aging. Thus only Perm demonstrated little color change with simulated aging. Of the reline products, one material, KOOLiner, demonstrated lower bond tensile strengths to denture base materials. However, the clinical significance of this was not known. One denture base material (Astron) recorded significantly higher bond strength values for all reline products and failure always took place within the denture base.     

Basic studies on hard direct reline resins. Part 1. Adhesive strength

Direct relining methods has come to occupy an important position in removable denture prosthodontics. The purpose of this study was to investigate the effect of various experimental conditions on the adhesive strength of hard direct reline resins to denture base resin. The experimental conditions were as follows: 1) immersion time of denture base resin before relining, 2) amount of load at relining, 3) roughness of adhesive surface, 4) immersion time of relined resin. The following results were obtained: 1. The adhesive strength of Rebaron was the highest, followed by that of TRIAD and KOOLiner. 2. The immersion times of denture base resin did not appreciably affect the adhesive strength. 3. With the rougher adhesive surface, Rebaron and KOOLiner showed a tendency to increase adhesive strength. 4. The adhesive strength was not appreciably affected by load. 5. We did not find a definitive correlation between adhesive strength and immersion times of relined resin.     

Effect of water-bath post-polymerization on the mechanical properties,degree of conversion,and leaching of residual compounds of hard chairside reline resins

ObjectivesThis study evaluated the effect of water-bath post-polymerization at 55 °C for 10 min (WB) on the content and leaching of residual compounds, degree of conversion, flexural strength, and hardness of hard chairside reline resins (Kooliner: K, New Truliner: N, Ufi Gel hard: U, and Tokuso Rebase Fast: T).MethodsLeaching experiments were made by storing specimens (n = 48) in artificial saliva at 37 ± 1 °C and analyzing residual monomers and plasticizer by HPLC. Analysis of residual monomer and plasticizer content (n = 48) was also made by HPLC. Degree of conversion (n = 40) was analyzed by using FT-Raman spectroscopy. A 3-point loading test was used to evaluate the flexural strength of the specimens (n = 80). One fragment of each flexural test specimen was then submitted to Vickers microhardness test.ResultsWB produced a significant decrease (p < 0.050) in the amount of residual compounds eluted from the materials within the first hour of immersion. With the exception of material U, WB decreased the duration of release of the residual compounds evaluated. All materials evaluated exhibited significantly (p < 0.050) lower values of residual monomer and plasticizer (material N) after WB compared with the control groups. WB increased the degree of conversion of K and T resins and the hardness of N, K, and T resins (p < 0.050). Only material K showed an increase in flexural strength after WB (p < 0.050).SignificanceImmersion of relined dentures in water at 55 °C for 10 min can be used to reduce the amounts and duration of release of residual compounds and improve mechanical properties of some of the materials evaluated.     

Analysis of composition and structure of hard autopolymerizing reline resins

summary The authors investigated the composition and structure of six hard auto-polymerizing reline resins. The chemical compositions, glass transition temperatures, molecular weights and particle size distributions of the powders, and the chemical compositions of the liquids were examined. The powder compositions were classified into three groups. The first group contained poly(methyl methacrylate). The second contained poly (ethyl methacrylate) and poly(methyl methacrylate/ethyl methacrylate) and the third contained poly(ethyl methacrylate). The average molecular weights of these powders was about 2 × 105. The indexes of molecular weight dispersion suggested that all powders contained polymers that had a narrow molecular weight distribution. The particle size distribution of these powders was classified into two groups. The first group was mainly in the range of 50–100 μm and the second mainly between 20 and 50 μm. The composition of the liquids was classified into three groups. The first group contained a monofunctional methacrylate monomer. The second contained a monofunctional methacrylate monomer and a plasticizer and the third contained monofunctional methacrylate monomers and cross-linking agents. The results of this experiment showed the differences in composition among the products. This will be useful for examining the relationship between the composition and mechanical properties of hard autopolymerizing reline resins.     

Effectiveness of microwave sterilization on three hard chairside reline resins

PURPOSE: The aim of this study was to evaluate the effectiveness of microwave irradiation sterilization on hard chairside reline resins. MATERIALS AND METHODS: Specimens of three reline resins (Kooliner, Tokuso Rebase, and Ufi Gel Hard) were fabricated and subjected to ethylene oxide sterilization. The specimens were then individually inoculated (10(7) cfu/mL) with Tryptic Soy Broth media containing one of the tested microorganisms (C albicans, S aureus, B subtilis, and P aeruginosa). After 48 hours at 37 degrees C, the samples were vortexed for 1 minute and allowed to stand for 9 minutes, followed by a short vortex to resuspend any organisms present. After inoculation, 40 specimens of each material were immersed in 200 mL of water and subjected to microwave irradiation at 650 W for 6 minutes. Forty non-irradiated specimens were used as positive controls. Replicate specimens (25 microL) of suspension were plated at dilutions of 10(-3) to 10(-6) on plates of selective media appropriate for each organism. All plates were incubated at 37 degrees C for 48 hours. After incubation, colonies were counted, and the data were statistically analyzed by the Kruskal-Wallis test. Twelve specimens of each material were prepared for SEM. RESULTS: All immersed specimens showed consistent sterilization of all the individual organisms after microwave irradiation. SEM examination indicated an alteration in cell morphology after microwave irradiation. CONCLUSION: Microwave sterilization for 6 minutes at 650 W proved to be effective for the sterilization of hard chairside reline resins.     

Flexural strength of autopolymerizing denture reline resins with microwave postpolymerization treatment

STATEMENT OF PROBLEM: Microwave postpolymerization has been suggested as a method to improve the mechanical strength of repaired denture base materials. However, the effect of microwave heating on the flexural strength of the autopolymerizing denture reline resins has not been investigated. PURPOSE: This study analyzed the effect of microwave postpolymerization on the flexural strength of 4 autopolymerizing reline resins (Duraliner II, Kooliner, Ufi Gel Hard, and Tokuso Rebase Fast) and 1 heat-polymerized resin (Lucitone 550). MATERIAL AND METHODS: For each material, 80 specimens (64 x 10 x 3.3 mm) were polymerized according to the manufacturer's instructions and divided into 10 groups (n = 8). Control group specimens remained as processed. Before testing, the specimens were subjected to postpolymerization in a microwave oven using different power (500, 550, or 650 W) and time (3, 4, or 5 minutes) settings. Load measurements (newtons) were made at a crosshead speed of 5 mm/min using a 3-point bending device with a span of 50 mm. The flexural strength values were calculated in MPa. Data analyses included 3-way and 2-way analysis of variance and the Tukey Honestly Significant Difference test (alpha = .05). RESULTS: The flexural strengths of resins Duraliner II and Kooliner were significantly increased (P = .0015 and P = .0046, respectively) with the application of microwave irradiation using different time/power combinations. The materials Lucitone 550, Tokuso Rebase Fast, and Ufi Gel Hard demonstrated no significant strength improvement compared to the corresponding control. Only after microwave postpolymerization irradiation for 3 minutes at 550 W did Lucitone 550 show significantly higher flexural strength (P =.001) than Tokuso Rebase Fast and Ufi Gel Hard relining resins. CONCLUSION: Microwave postpolymerization irradiation can be an effective method for increasing the flexural strength of Duraliner II (at 650 W) and Kooliner (at 550 W and 650 W for 5 minutes).     

A comparison of physical characteristics of six hard denture reline materials

Six rigid autopolymerizing acrylic resins were examined to determine and compare the cost per reline, the curing temperatures, the setting times, and the porosity of each material. The cost per reline ranged from $0.63 to $1.55. Three product groups had significantly different mean setting times, and two groups had significantly different mean setting temperatures. SEM cross-sections of each product revealed an apparently porous-free solid mass of acrylic resin, which in two products was overlayed by a thin porous surface layer. The physical characteristics of any one product did not indicate clinical superiority.     

Correlation in the mechanical properties of acrylic denture base resins

The aim of the present study was to measure various mechanical properties of acrylic denture base resins, including flexural modulus, flexural strength, fracture toughness, Barcol and Vickers hardness and their related properties, and to investigate correlations between different mechanical properties. Resin specimens were prepared according to manufacturers' recommended instructions. The mechanical properties were measured under specified standards. Data from the mechanical tests were examined using correlation tests. In general, the mean results for mechanical properties of each specimen group were differently ranked depending on the tested mechanical property. The flexural modulus value showed strong or reasonable positive correlation with those of proportional limit, flexural strength, and surface hardness. In contrast, fracture toughness revealed strong negative correlations with the flexural parameters and hardness values. Results of correlation tests for the different parameters can be used for estimation of mechanical performance of acrylic denture bases in clinical situation and for quality control purposes.     

Effect of microwave disinfection on the flexural strength of hard chairside reline resins

OBJECTIVES: This study investigated the effect of microwave disinfection (650W/6 min) on the flexural strength of five hard chairside reline resins (Kooliner, Duraliner II, Tokuso Rebase Fast, Ufi Gel Hard, New Truliner) and one denture base resin (Lucitone 550). METHODS: Thirty-two specimens (3.3x10x64 mm) from each acrylic resin were produced and divided into four groups of eight specimens each. The flexural test was performed after polymerization (G1), after two cycles of microwave disinfection (G2), after 7 days storage in water at 37 degrees C (G3) and after seven cycles of microwave disinfection (G4). Specimens from group G4 were microwaved daily being stored in water at 37 degrees C between exposures. The specimens were placed in three-point bend fixture in a MTS machine and loaded until failure. The flexural values (MPa) were submitted to ANOVA and Tukey's test (p=0.05). RESULTS: Two cycles of microwave disinfection promoted a significant increase in flexural strength for materials Kooliner and Lucitone 550. After seven cycles of microwave disinfection, materials Kooliner and New Truliner showed a significant increase (p<0.05) in flexural values. The flexural strength of the material Tokuso Rebase was not significantly affected by microwave irradiation. Seven cycles of microwave disinfection resulted in a significant decrease in the flexural strength of material Duraliner II. Material Ufi Gel Hard was the only resin detrimentally affected by microwave disinfection after two and seven cycles. CONCLUSIONS: Microwave disinfection did not adversely affect the flexural strength of all tested materials with the exception of material Ufi Gel Hard.     

Tensile bond strengths of hard chairside reline resins as influenced by water storage

Due to gradual resorption of the edentulous ridge bone, removable prostheses often require denture base relines to improve fit and stability. This research evaluated the bond strength between one heat-cured acrylic resin (Lucitone 550(R)) and two hard chairside reline resins, after two different periods of storage in water (50 h and 30 days). The bond strength was evaluated using a tensile test. The mode of failure, adhesive or cohesive, was also recorded. The results submitted to the Kruskal-Wallis test indicated that the highest tensile strengths were achieved with intact Lucitone 550(R) denture base resin in both periods of storage in water. After 50 h of storage in water, Duraliner II(R) reline material exhibited the highest bond strength to the denture base resin. After 30 days of storage in water, Duraliner II(R) reline resin demonstrated a significant reduction in adhesion, showing lower tensile bond strength than Kooliner(R) material. Both hard chairside reline materials failed adhesively across Lucitone 550(R) denture base resin, in both periods of time.     

Impact strength of denture base and reline acrylic resins subjected to long-term water immersion

Water may influence the mechanical properties of the acrylic resins. Thus, the effect of water storage on the impact strength (IS) of one denture base (Lucitone 550 - L) and four reline resins (Tokuyama Rebase II - T; UfiGel Hard - U; Kooliner - K; New Truliner - NT) was evaluated. Bars of L were made (60 x 6 x 2 mm) and relined (2 mm) with T, U, K, NT and L. Intact specimens of each material (60 x 6 x 4 mm) were also fabricated for comparative purposes. Specimens were submitted to Charpy impact tests without water storage (control) and after immersion in water for 7, 90 and 180 days. Data (kJ/m(2)) analyzed by two-way ANOVA and Tukey's test (p=0.05) revealed that after 90 days, U exhibited an increase in the IS (0.93) compared to 7 days (0.58). K (1.48) and L/K (7.21) exhibited a decrease at the 7-day period (1.01 and 3.23, respectively). NT (0.60) showed an increase in the IS after 180 days (1.52), whereas L/NT (7.70) showed a decrease (3.17). Water immersion improved the IS of U and NT, and decreased the IS of K, L/K, and L/NT. Water may affect differently the IS of acrylic resins and, consequently, the resistance to fracture of relined denture bases.     

义齿基托树脂的力学性能研究

通过测试４种商品义齿基托树脂的弯曲强度，冲击强度，挠度及弹性模量，评价了采用可见光，热和微波聚合的基托树脂的力学性能，结果显示：热处理效果优于光和自凝处理，在热处理中，水热优于热压，热压优于微波加热。     

Antimicrobial efficacy and mechanical properties of BAC-modified hard and soft denture liners

This study investigated the antimicrobial efficacy and mechanical strength of hard and soft denture liners modified with benzalkonium chloride (BAC). The specimens (1 mm thickness, 8 mm diameter) were prepared by mixing 0.5, 1, 2 and 5 wt% BAC with soft (Sofreliner Medium, Tokuyama) and hard (Rebase II, Tokuyama) denture liners (n = 5/group). BAC was not added to the controls. Candida albicans ATCC 28366 (A ₅₅₀ = 0.5) and Streptococcus mutans Ingbritt suspensions (A ₅₅₀ = 0.35) were pipetted onto the specimens, and incubated for 4 h. The viable cells were collected, and determined by plate-culturing (CFU). The tests were repeated after the specimens were soaked in distilled water for 7 days. The mechanical strengths were evaluated by tear and 4-point flexural strength tests for soft and hard liners, respectively. The data were analyzed with ANOVA and Tukey’s HSD tests at p = 0.05. C. albicans viability was lost in all groups of BAC-modified soft liners (p < 0.001), and S. mutans viability was reduced (p < 0.01), except of soaked BAC 0.5 wt% group (p > 0.05). For the hard liner, BAC 5 wt% killed the C. albicans and S. mutans cells both before and after soaked in water (p < 0.001). BAC 2 wt% showed comparable tear strength with the soft liner control (p > 0.05). BAC did not reduce the flexural strength of the hard liner (p > 0.05), except of BAC 5 wt% group (p < 0.01). BAC can be a promising agent reducing the C. albicans and S. mutans viability on the soft and hard denture liner surfaces.     

Influence of water sorption on mechanical properties of injection-molded thermoplastic denture base resins

Objective. This study investigated the influence of water sorption on certain mechanical properties of injection-molded thermoplastic denture base resins. Materials and methods. Six thermoplastic resins (two polyamides, two polyesters, one polycarbonate, one polymethylmethacrylate) and a polymethylmethacrylate (PMMA) conventional heat-polymerized denture-based polymer, selected as a control, were tested. Specimens of each denture base material were fabricated according to ISO 1567 specifications and were either dry or water-immersed for 30 days (n = 10). The ultimate flexural strength, the flexural strength at the proportional limit and the elastic modulus of the denture base materials were calculated. Results. Water sorption significantly decreased the ultimate flexural strength, the flexural strength at the proportional limit and the elastic modulus of one of the polyamides and the PMMAs. It also significantly increased the ultimate flexural strength of the polycarbonate. Conclusion. The mechanical properties of some injection-molded thermoplastic denture base resins changed after water sorption.     

Evaluation of mechanical and thermal properties of commonly used denture base resins.

PURPOSE: The purpose of this investigation was to evaluate and compare the mechanical and thermal properties of 6 commonly used polymethyl methacrylate denture base resins. MATERIALS AND METHODS: Sorption, solubility, color stability, adaptation, flexural stiffness, and hardness were assessed to determine compliance with ADA Specification No. 12. Thermal assessments were performed using differential scanning calorimetry and dynamic mechanical analysis. Results were assessed using statistical and observational analyses. RESULTS: All materials satisfied ADA requirements for sorption, solubility, and color stability. Adaptation testing indicated that microwave-activated systems provided better adaptation to associated casts than conventional heat-activated resins. According to flexural testing results, microwaveable resins were relatively stiff, while rubber-modified resins were more flexible. Differential scanning calorimetry indicated that microwave-activated systems were more completely polymerized than conventional heat-activated materials. CONCLUSION: The microwaveable resins displayed better adaptation, greater stiffness, and greater surface hardness than other denture base resins included in this investigation. Elastomeric toughening agents yielded decreased stiffness, decreased surface hardness, and decreased glass transition temperatures.