Effect of Home Bleaching Agents on Color Stability and Surface Roughness of Hybrid Ceramics: An in vitro study.

PURPOSE: To evaluate the effect of two different home bleaching agents on the color stability and surface roughness of hybrid ceramics. MATERIALS AND METHODS: Three dental hybrid ceramics (Lava Ultimate, CeraSmart, and Vita Enamic) and two different home bleaching agents (hydrogen peroxide [9.5%; HP] and carbamide peroxide [22%; CP]) were used. Thirty specimens with dimensions of 12 x 14 x 1 mm were prepared for each material. Technical polishing kits were applied to one surface of the specimens for the surface finishing procedure. The color parameters (L*a*b*) of specimens were measured. Three subgroups for each ceramic were determined: control (C), HP, and CP (n = 10 each). After bleaching procedures, the color parameters were remeasured, and color differences (ΔE) were calculated. The surface roughness values of the specimens were detected using a profilometer. Surface analysis was performed with a scanning electron microscope on one specimen from each group. Data were analyzed using two-way analysis of variance and Tukey honest significant difference tests. RESULTS: There was an interaction between material and bleaching agent type (P < .05). The highest ΔE values were observed in the CP groups, and the lowest ΔE values were observed in the C groups. For surface roughness, there was no interaction between material and bleaching agent type (P > .05). Material and bleaching agent factors had a significant effect on surface roughness (P Δ .05). The highest surface roughness values were detected in the HP groups. CONCLUSION: Home bleaching agents caused clinically acceptable color differences on hybrid ceramic materials. HP increased the surface roughness of hybrid ceramics.

Evaluation of flexural properties and dynamic mechanical analysis of glass fiber-reinforced polyamide resin.

PURPOSE: The aim of this study was to evaluate flexural strength, elastic modulus and dynamic mechanical analysis (DMA) of heat-polymerized polymethyl methacrylate resin, polyamide resin and glass fiber-reinforced polyamide resin. MATERIALS AND METHODS: Three groups were determined according to denture base materials as polymethyl methacrylate resin (H), polyamide resin (P) and glass fiber reinforced polyamide resin (R). Sixteen specimens for each denture base material were prepared with dimensions of 64x10x3.3 mm for three-point bending test. Two specimens for each denture base material were prepared with dimensions of 30x10x3 mm for DMA. Polymethyl methacrylate and polyamide specimens were prepared according to the manufacturer's recommendations. The silane was applied to glass fibers (4.5 mm length) 2% by weight of the polyamide resin, they were placed in polyamide resin cartilages and injected to the mold. The thermal aging procedure was applied to half of specimens of each material (n=8). Flexural strength and elastic modulus of the specimens were determined by three-point bending test at a speed of 5 mm/ min. DMA was performed to 1 specimen from each group to evaluate viscoelastic properties. Data were analyzed with one-way ANOVA, Tukey and Paired t tests. RESULTS: A statistically significant difference was found in flexural strength and elastic modulus values of denture base materials (p=0.00). The highest flexural strength and elastic modulus values were observed in polymethyl methacrylate group. There was no significant difference between polyamide and glass-fiber reinforced polyamide groups (p=0.497). No significant difference was determined in all threedenture base materials before and after aging procedure. CONCLUSION: The reinforcement with glass-fibers did not affect the flexural strength and elastic modulus of polyamide resin.

Effect of argon plasma and Er:YAG laser on tensile bond strength between denture liner and acrylic resin.

STATEMENT OF PROBLEM: The separation of a denture liner from the denture base can be a clinical problem. Different surface treatments to increase the bond have been evaluated, but studies comparing the effect of argon plasma and erbium-doped yttrium aluminum garnet (Er:YAG) laser on the bond between acrylic resin and a denture liner are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the effect of argon plasma and Er:YAG laser treatments on the bond strengths of acrylic resin to 2 denture liners. MATERIALS AND METHODS: Heat-polymerized acrylic resin (Acron Duo) was bonded to silicone soft-liner materials (Molloplast B, n=30; Mollosil, n=30) to create control specimens (n=10), argon plasma treatment (n=10), and Er:YAG laser treatment (n=10). Silicone liners were polymerized on resin specimens. The tensile bond strength test was performed with a crosshead speed of 10 mm/min with a 10-N load until failure. Data were analyzed by using the Kruskal-Wallis test and unpaired t test (α=.05). RESULTS: The laser group showed significantly higher bond strength than the argon plasma group for both Molloplast-B (P=.001) and Mollosil (P<.001). The highest tensile bond strength values were determined in the laser-treated Molloplast-B group (1.325 ±0.119 MPa) while the lowest bond strength values were determined in the Mollosil control group (0.384 ±0.018 MPa). CONCLUSIONS: Argon plasma and Er:YAG laser applications increases the tensile bond strength between soft-liner material and resin. Er:YAG laser treatment results in higher bond strength values than treatment with argon plasma for 1 minute.

Oral health behavior differences between dental students in graduate and doctoral programs.

PURPOSE: This study aimed to compare oral health behavior between dental students in graduate programs and those in doctoral programs (PhD students) and determine the effects of parental education and occupation on these behaviors. MATERIALS AND METHODS: A questionnaire on oral health behaviors was distributed in a faculty of dentistry in Ankara, Turkey. A total of 629 questionnaires were distributed, and 528 dental graduate and 101 PhD students responded. Parental education and occupation were also recorded, and data were statistically analyzed. RESULTS: Statistically significant differences were found between the two groups with respect to the frequency of replacing toothbrush (p=0.001), use of electric toothbrush (p<0.001), frequency of brushing (p<0.001), amount of water used to rinse mouth (p<0.001), toothpaste selection criteria (p<0.001), use of dental floss (p<0.001), amount of toothpaste used for brushing (p=0.018), frequency of professional care (p<0.001), and sugar consumption (p<0.001). The PhD group showed more favorable outcomes for these behaviors except for toothpaste selection. Parental education and occupation were correlated with higher frequencies of flossing and mouth rinsing. CONCLUSION: The outcomes of this study show that the self-reported quality of overall oral health behavior is more pronounced in PhD students than in graduate students, with the exceptions of behaviors regarding the duration of brushing, toothpaste selection criteria, and use of mouth rinse. The current dental curriculum in the universities should be revisited with respect to oral health attitudes. This study also implies that educational and occupational status of parents had little effect on oral health behavior of the students, including the use of dental floss and mouth rinse.

Effect of surface treatments on shear bond strength of resin composite bonded to CAD/CAM resin-ceramic hybrid materials.

PURPOSE: The purpose of this study was to assess the effect of surface treatments on shear bond strength of resin composite bonded to thermocycled and non-thermocycled CAD/CAM resin-ceramic hybrid materials. MATERIALS AND METHODS: 120 specimens (10×10×2 mm) from each material were divided into 12 groups according to different surface treatments in combination with thermal aging procedures. Surface treatment methods were airborne-particle abrasion (abraded with 50 micron alumina particles), dry grinding (grinded with 125 µm grain size bur), and hydrofluoric acid (9%) and silane application. According to the thermocycling procedure, the groups were assigned as non-thermocycled, thermocycled after packing composites, and thermocycled before packing composites. The average surface roughness of the non-thermocycled specimens were measured after surface treatments. After packing composites and thermocycling procedures, shear bond strength (SBS) of the specimens were tested. The results of surface roughness were statistically analyzed by 2-way Analysis of Variance (ANOVA), and SBS results were statistically analyzed by 3-way ANOVA. RESULTS: Surface roughness of GC were significantly lower than that of LU and VE (P<.05). The highest surface roughness was observed for dry grinding group, followed by airborne particle abraded group (P<.05). Comparing the materials within the same surface treatment method revealed that untreated surfaces generally showed lower SBS values. The values of untreated LU specimens showed significantly different SBS values compared to those of other surface treatment groups (P<.05). CONCLUSION: SBS was affected by surface treatments. Thermocycling did not have any effect on the SBS of the materials except acid and silane applied GC specimens, which were subjected to thermocycling before packing of the composite resin.