Gülay Uzun

Color stability of denture base acrylic resins in three food colorants

STATEMENT OF PROBLEM Three commonly used artificial dyes in food technology are erythrosine, tartrazine, and sunset yellow. PURPOSE The color stability of 5 commercially available denture base acrylic resins (QC-20, Meliodent, Trevalon, Trevalon High, and Lucitone) was studied in vitro. METHODS The specimens were exposed to 3% erythrosine, tartrazine, and sunset yellow solutions at 23 degrees C +/- 1 degrees C. Color changes were determined with a computer-controlled spectrophotometer. Five specimens from each material were processed, and initial color measurements were made after 1, 3, and 6 months of exposure to the staining solutions. Finally, the color stability was quantitatively measured again, and color differences (DeltaE) were calculated. RESULTS For the observations made in 1, 3, and 6 months intervals, the specimens that exhibited the least color change were in the sunset yellow solution. The greatest color changes observed according to the National Bureau of Standards unit system were Lucitone (2.71) in erythrosine solution, Lucitone (2.54), QC-20 (1.71) in tartrazine solution, and QC-20 (1.66) in sunset yellow solution. The changes in the other acrylic resins in the 3 solutions were slight and at trace level. CONCLUSIONS All materials tested were acceptable from the standpoint of color stability for long-term exposure to these food colorants.

Comparison of the Fracture Resistance of Six Denture Base Acrylic Resins

Fracture strength of denture base resins is of great concern, and many approaches have been used to strengthen acrylic resin dentures. Fracture resistance of six commercially available acrylic resin denture base materials were compared, through impact and transverse strength tests. Three rapid heat-polymerised resins (QC 20, Meliodent and Trevalon), two high-impact strength resins (Trevalon Hi and Lucitone 199) and a strengthened injection-moulded acrylic resin (SR Ivocap plus) were included in the study. Twenty acrylic resin test specimens were fabricated from each resin. For impact strength test, ten notched specimens were tested in a Charpy-type impact tester. The other ten specimens were used for transverse strength tests, deflection and modulus of elasticity values were also determined, which were assessed with three-point bending tests using an Universal Testing Machine. Impact test values showed significant differences among acrylic resins (F = 4.817 p = 0.0). SR Ivocap resin showed the highest impact strength values, followed by Trevalon Hi and Lucitone 199. The transverse strength test values were not significant when six acrylic resins were compared (F = 1.705 p = 0.151). High-impact resins can be recommended to increase the impact strength of denture base. If the cause of fracture is mechanical or anatomical, strengthened acrylic resins and conventional acrylic resins have similar fracture resistance.

Effect of muscle relaxation splint therapy on the electromyographic activities of masseter and anterior temporalis muscles.

The purpose of this study was to compare the effectiveness of splint therapy on the electromyographic activity of masticatory muscles (anterior temporalis and masseter) before and after the application of a muscle relaxation splint. Electromyography recordings from the masseter and anterior temporalis muscles were analyzed quantitatively during maximal biting in the intercuspal position both before and after treatment without a splint. Fourteen patients whose chief complaint was masticatory muscle pain were selected for the study. After the initial evaluations muscle relaxation splints were applied, and the patients were instructed to use the splints for 6 weeks. Surface electromyographic recordings were taken from each patient before the beginning of clinical therapy and after 6 weeks of wearing the splints. The data obtained were analyzed through paired sample t tests and Wilcoxons signed rank tests. The results of the study were as follows: (1) the electromyographic activity of the two muscles during maximal biting was not markedly changed after the muscle relaxation splint was used; and (2) the changes observed in electromyographic activity of the involved and noninvolved sides were insignificant as well.

The Effect of Fiber Reinforcement Type and Water Storage on Strength Properties of a Provisional Fixed Partial Denture Resin

Fracture resistance of provisional restorations is an important clinical concern. This property is directly related to transverse strength. Strengthening of provisional fixed partial dentures may result from reinforcement with various fiber types. This study evaluated the effect of fiber type and water storage on the transverse strength of a commercially available provisional resin under two different conditions. The denture resin was reinforced with either glass or aramid fiber or no reinforcement was used. Uniform samples were made from a commercially available autopolymerizing provisional fixed partial denture resin. Sixteen bar-shaped specimens (60 × 10 × 4 mm) were reinforced with pre-treated epoxy resin-coated glass fibers, with aramid fibers, or with no fibers. Eight specimens of each group, with and without fibers, were tested after 24 h of fabrication (immediate group), and after 30-day water storage. A three-point loading test was used to measure the transverse strength, the maximal deflection, and the modulus of elasticity. The Kruskal-Wallis Analysis of Variance was used to examine differences among the three groups, and then the Mann-Whitney U Test and Wilcoxon Signed Ranks Test were applied to determine pair-wise differences. The transverse strength and the maximal deflection values in the immediate group and in the 30-day water storage group were not statistically significant. In the group tested immediately, the elasticity modulus was found to be significant (P = 0.042). In the 30-day water storage group, all the values were statistically insignificant. The highest transverse strength was displayed by the glass-reinforced resin (66.25 MPa) in the immediate group. The transverse strength value was 62.04 MPa for the unreinforced samples in the immediate group. All the specimens exhibited lower transverse strength with an increase in water immersion time. The transverse strength value was 61.13 MPa for the glass-reinforced resin and was 61.24 MPa for the unreinforced resin. The aramid-reinforced resin decreased from 62.29 to 58.77 MPa. The addition of fiber reinforcement enhanced the physical properties (the transverse strength, the maximal deflection, the modulus of elasticity) of the processed material over that seen with no addition of fiber. Water storage did not statistically affect the transverse strength of the provisional denture resin compared to that of the unreinforced resin. The transverse strength was lowered at water storage but it was not statistically significant. The transverse strength was enhanced by fiber addition compared to the unreinforced resin. The glass fiber was superior to the other fiber. Also the modulus of elasticity was enhanced by fiber addition compared to the unreinforced resin.

The Effect of Woven, Chopped and Longitudinal Glass Fibers Reinforcement on the Transverse Strength of a Repair Resin

Fracture resistance of prosthesis is an important clinical concern. This property is directly related to transverse strength. Strengthening of prostheses may result from reinforcement with various fiber types. This study evaluated the effect of fiber type on the transversestrength of a commercially available autopolymerizing resin that is used for repairing prosthesis. The resin was reinforced with woven form, chopped form and longitudinal form, and no reinforcement was used.Uniform samples were made from autopolymerizing resin. In total, twenty-four bar-shaped specimens (60 × 10 × 4 mm) were reinforced with glass fibers. Nine specimens were prepared without fiber. Athree-point loading test was used to measure transverse strength, maximal deflection, and modulus of elasticity. The Kruskal-Wallis analysis of variance was used to examine differences between the four groups. Although the results of the analysis between these groups showed no statistical significances, the transverse strength, maximal deflection and modulus of elasticity increased more with fiber than without the fiber group. This finding may be of clinical significance. Because the addition of fiber reinforcement enhanced the physical properties of the processed material, specially woven form glass fiber was superior to the other forms.

Effect of Anterior Repositioning Splints on the Electromyographic Activities of Masseter and Anterior Temporalis Muscles

The effect of anterior repositioning (AR) splint therapy on masticatory muscle activity was investigated in seventeen patients with internal derangement; disk displacement with reduction in particular. Integrated electromyography (EMG) recordings from the masseter and anterior temporalis muscles were analyzed quantitatively during maximal biting in intercuspal position before and after eight week treatment period, EMG recordings were taken for each subject prior to the beginning of clinical therapy and final EMG recordings were made without AR splint to provide a standard for comparison. The results of the investigation revealed the following: 1. AR splint therapy did not cause any significant modification of the EMG activity in the recorded muscles during maximal biting in intercuspal position; 2. Before and after treatment the EMG activity from the masseter muscle was less than from the temporal muscle; 3. AR splint therapy resulted in reduction of the pain (88.2%) and jaw joint sounds (64.7%) and mean vertical opening which was 42.17 mm before treatment increased to 45.06 mm.

The effects of glass fiber reinforcement at different concentrations on the transverse strength, deflection and modulus of elasticity of a provisional fixed partial denture resin

This study focused on some mechanical properties such as the transverse strength, maximal deflection and modulus of elasticity of a resin reinforced with untreated, chopped form glass fibers at different concentrations. A Teflon mould was used to prepare four groups of specimens. The specimens were prepared with different concentrations of the glass fiber to the mass of the powder/liquid mix (0.5, 1, 1.5%), and a mix without fiber was used as the control group. All the specimens were subjected to transverse testing with a cross-head speed of 5 mm/min. The load to fracture for each specimen with the maximum deflection at the point of loading in a three-point load test was recorded. The transverse strength of 0.5% fiber concentration was 54.45 MPa. The lowest value was 49.67 MPa for the 1% fiber concentration. The highest mean strength was for the specimens reinforced with 0.5% glass fiber. This mean was higher than for the mean of the control “without fiber” specimens. The specimens demonstrated an insignificant decrease in the transverse strength and the maximum deflection when the fiber concentration was increased. The inclusion of 1% glass fiber reduced the transverse strength, although the result was not statistically significant.

The effect of curing time and immersion solutions on discoloration of hybrid composites and nanocomposites

Objectives: The purpose of this study was to evaluate the color change of six esthetic dental composite materials immersed in various solutions for 7 days, and determine the effect of curing time on color change. Materials and Methods: Disk-shaped samples of six types of light curing composite were prepared, and all samples were divided into two groups that were light cured for 20 s and 40 s (n = 7). After 24 h, color measurements were performed with a digital spectrophotometer. Samples were immersed in a solution (coffee, tea, Coke; , cherry juice and distilled water) for 7 days. The discoloration of each specimen was measured and statistically analyzed with a statistics software SPSS Version 17.0 (Released 2008. SPSS Statistics for Windows, Chicago: SPSS Inc.). Results: The discoloration of Filtek™ and Ceram.X was significant. The highest color change values were in Filtek™ group. The lowest color change values were in Herculite classic group. Coffee (ΔE = 12.27) showed the highest influence on color change. There was no effect of curing time on the discoloration of the composites. Significance: The color differences (ΔE) ranged from 3.23 to 12.48. There was no significant difference in color change between two curing times, and coffee was the immersion medium that promoted the highest color change on the tested composite resin.