The aim of this study was to determine the photocatalytic effect of doped-TiO 2 nanoparticles (NPs) on teeth bleaching with an aid of 3% H2O2 and laser irradiation. For the study, Mo-N-TiO2 NPs were prepared. The characteristics of the prepared NPs, NPs morphology and light absorbance, were evaluated. Photocatalytic reactions of NPs were tested using 10 ppm methylene blue (MB) solution. Extracted teeth were pasted using carbomer gel for color differences measurements. Mo-N-TiO2 NPs have close to round shape with some tens nm size. Their absorbance was higher and longer than that of TiO 2 NPs. For MB solution, Mo-N-TiO2 with 3% H2O2 condition showed much decrease in absorbance after laser irradiation for 20 min. Also, regardless of wavelength, Mo-N-TiO2 NPs produced much greater color difference (whitening) on teeth after 3 h than that by 15% H2O2 .

The purpose of the present study was to assess the temperature change and compressive property of bulk-fill composites (BFCs) by the light curing. Seven resin-based composites (RBCs), including five BFCs, were chosen to evaluate their maximum temperature rise and exothermic heat during and after light curing and compressive strength (CS) and modulus (CM) for 4-mm thick state. Light attenuation coefficients (ACs) showed reasonably high correlation with filler content (vol% and wt%).Except one resin product, AC values of BFCs were lower than those of RBCs tested. All the tested specimens showed temperature rise (9.8-23.6℃) and exothermic heat (4.2-18.3℃) for 4-mm thick case. CS and CM values of the tested specimens ranged approximately 69 to 116 MPa and 1.3 to 2.8 GPa, respectively. The difference of temperature changes and compressive properties (CS and CM) between BFCs and RBCs was not consistent and had no statistically consistent significance.

The effect of the cooling rate on changes in hardness, flexural strength, and microstructure of zirconia core ceramics was investigated during simulated porcelain firing without layering porcelain on the zirconia core ceramic. Three cooling rates were tested: 227.5 ℃/min, which is the rate suggested by the manufacturer, Stage 0 (taking the ceramic out of the firing chamber immediately after firing and bench cooling to room temperature), and Stage 3 (cooling to 600 ℃ with the firing chamber closed and then bench cooling to room temperature (33 ℃/min)). In the Stage 0 group and the group cooled at the rate suggested by the manufacturer, the hardness increased compared to the group before firing (p<0.001). The hardness of the Stage 3 group was not different from that of the group before firing (p>0.05). The grain size of the specimen groups whose hardness increased after firing was reduced by recrystallization, but the Stage 3 group had coarsened grains. In all test groups before and after firing, only the tetragonal phase was observed. In particular, a metastable phase (T’) in which the axial ratio (c/a ratio = c/√ 2a) was closer to 1 coexisted with the tetragonal phase. The flexural strength of the zirconia core did not exhibit a significant difference with respect to the cooling rate (p>0.05).

The purpose of the present study was to assess the temperature change and compressive property of bulk-fill composites (BFCs) by the light curing. Seven resin-based composites (RBCs), including five BFCs, were chosen to evaluate their maximum temperature rise and exothermic heat during and after light curing and compressive strength (CS) and modulus (CM) for 4-mm thick state. Light attenuation coefficients (ACs) showed reasonably high correlation with filler content (vol% and wt%).Except one resin product, AC values of BFCs were lower than those of RBCs tested. All the tested specimens showed temperature rise (9.8-23.6℃) and exothermic heat (4.2-18.3℃) for 4-mm thick case. CS and CM values of the tested specimens ranged approximately 69 to 116 MPa and 1.3 to 2.8 GPa, respectively. The difference of temperature changes and compressive properties (CS and CM) between BFCs and RBCs was not consistent and had no statistically consistent significance.

The effect of the cooling rate on changes in hardness, flexural strength, and microstructure of zirconia core ceramics was investigated during simulated porcelain firing without layering porcelain on the zirconia core ceramic. Three cooling rates were tested: 227.5 ℃/min, which is the rate suggested by the manufacturer, Stage 0 (taking the ceramic out of the firing chamber immediately after firing and bench cooling to room temperature), and Stage 3 (cooling to 600 ℃ with the firing chamber closed and then bench cooling to room temperature (33 ℃/min)). In the Stage 0 group and the group cooled at the rate suggested by the manufacturer, the hardness increased compared to the group before firing (p<0.001). The hardness of the Stage 3 group was not different from that of the group before firing (p>0.05). The grain size of the specimen groups whose hardness increased after firing was reduced by recrystallization, but the Stage 3 group had coarsened grains. In all test groups before and after firing, only the tetragonal phase was observed. In particular, a metastable phase (T’) in which the axial ratio (c/a ratio = c/√ 2a) was closer to 1 coexisted with the tetragonal phase. The flexural strength of the zirconia core did not exhibit a significant difference with respect to the cooling rate (p>0.05).

Flowable resins can be used as a base material during the restoration of deep tooth cavity. The purpose of the present study was to evaluate the mechanical properties of the layered specimens which have flowable resin as a base material. For the study, two composite resins and five flowable resins were chosen for the overlying and base materials, respectively. Flexural and compressive properties of each bulk and ten layered specimens were measured. Layered specimens showed high flexural strength (FS) and flexural modulus (FM) if bulk state FS and FM of the base flowable resin are high. However, compressive strength (CS) was not that case. CS of the layered specimen was not high (251.4~295.3 MPa) whether CS of the bulk state is high or not (259.8~439.8 MPa). FM showed high linear correlation with CM. After all mechanical properties of the layered specimens were not consistently influenced by the mechanical properties of the base flowable resins regardless of the overlying composite resins.
Composite Resins ; Compressive Strength ; Tooth

In this study, change of optical properties and microstructure of an Ag-Pd-In alloy according to Ag content was investigated. For this purpose, specimen alloys were prepared by adding 0–100 wt.% of Ag to the 50Pd-50In (wt.%) alloy. When the content of Ag was more than 40 wt.%, the color difference with pure gold specimen was increased(p < 0.001). L* value increased as the Ag content of the specimen increased, but a* and b* value increased until the addition of 20 wt.% Ag, and then decreased with increasing Ag content(p < 0.001). Ag-free specimen was single phase in the as-cast state, but when the content of Ag was more than 20 wt.%, the phase separation occurred and two phases of matrix and dendrite or granular structure were confirmed. The dendrite or granular structure was composed of the InPd phase, and the matrix was composed of the Ag-rich phase. From these results, it can be concluded that the specimens with Ag content of 20–70 wt.% have the Ag-rich matrix which has a high L* value and low a* and b* value, and have the dendrite structure which has a low L* value and high a* and b* value. As the content of Ag increased, the color changed from light yellow to silver white due to the increase in the ratio of the matrix to the dendrite or granular structure.
Alloys ; Dendrites ; Silver

The aim of this study was to determine if a 457 nm blue laser could effectively polymerize dental composite resins. After light curing 6 dental composite resins using a laser or a LED light-curing unit at 530 mW/cm2 and 900 mW/cm2, respectively, degree of conversion and microhardness were evaluated. Degree of conversion of specimens by the laser and LED was similar (on top surface 54.4–67.7% and 55.2–67.1%, respectively; on bottom surface 35.1–53.8% and 45.4–53.1%, respectively). Microhardness was also similar (on top surface 28.5–83.6 Hv and 19.1–82.4 Hv, respectively; on bottom surface 22.5–65.4 Hv and 16.8–74.4 Hv, respectively), although, in some cases, laser-treated specimens showed slightly lower microhardness than the LED-treated on bottom surface. The present study shows that the 457 nm laser can polymerize dental composite resins to the same level as LED achieved.
Composite Resins ; Polymerization ; Polymers

There has been increasing use of the H₂O₂-based teeth bleaching agents. The purpose of this study was to evaluate the bleaching effectiveness of the laser irradiation combined with nitrogen doped-TiO₂ nanoparticles (NPs) on the stained resin. Nitrogen (N) doped-TiO₂ NPs were prepared under sol-gel method. Light absorbance, X-ray diffraction patterns of NPs, and bleaching of methylene blue and stained resins were evaluated. For bleaching of stained resin, NPs-containing gel was used. For irradiation, light of two different wavelengths was used. Unlike TiO₂, N-TiO₂ showed high absorbance after 400 nm. N-TiO₂, which have used TiN as a precursor, showed a new rutile phase at the TiN structure. For methylene blue solution, N-TiO₂ with 3% H₂O₂ resulted in the greatest absorbance decrease after laser irradiation regardless of wavelength. For stained resin test, N-TiO₂ with 3% H₂O₂ resulted in the greatest color difference after laser irradiation, followed by group that used N-TiO₂ without 3% H₂O₂.
Methods ; Methylene Blue ; Nanoparticles ; Nitrogen ; Tin ; Tooth Bleaching Agents ; X-Ray Diffraction

The pH of the oral cavity can dynamically change due to diverse foods and beverages served. The purpose of the present study was to evaluate flexural and compressive properties of composite resins after immersion in solutions of different pHs. Four composite resins were cured and immersed in test solutions of different pHs (3, 7.1, and 9) for 2 weeks. Flexural and compressive properties (strength and modulus) were evaluated using universal test machine. After immersion, initial flexural and compressive strength significantly changed to 1.5–30.0% and 0.3–19.6%, respectively; flexural and compressive modulus significantly changed to 4.4–29.0% and 3.5–21.5%, respectively. However, the values obtained from solutions of different pHs were not significantly and consistently different to each other.
Beverages ; Composite Resins ; Compressive Strength ; Hydrogen-Ion Concentration ; Immersion ; Mouth