Effect of superspeed sintering on translucency, opalescence, microstructure, and phase fraction of multilayered 4 mol% yttria-stabilized tetragonal zirconia polycrystal and 6 mol% yttria-stabilized partially stabilized zirconia ceramics.

STATEMENT OF PROBLEM: The optical properties of recently developed multilayer zirconia have mainly been studied for the effects of conventional sintering and speed sintering but not as much for the effect of superspeed sintering. As superspeed sintering protocols typically require a higher sintering temperature and higher heating and cooling rates than speed- and conventional sintering protocols, the optical properties of superspeed sintered zirconia may be affected differently. PURPOSE: The purpose of this in vitro study was to investigate the effect of superspeed sintering on the optical properties, microstructure, and phase fraction of multilayered 4 mol% yttria-stabilized (4Y-) and 6 mol% yttria-stabilized (6Y-) zirconia. MATERIAL AND METHODS: Multilayered 4Y- and 6Y-zirconia were sectioned. After conventional and superspeed sintering, the translucency parameter (TP), and opalescence parameter (OP) were measured with a spectrophotometer (n=10). To obtain the grain sizes from the field emission scanning electron microscopy (FE-SEM) images for each layer (n=2), more than 500 (6Y-zirconia) and 800 grains (4Y-zirconia) were measured by linear intercept methods. The phase fractions were obtained through X-ray diffraction (XRD) analysis by using the Rietveld method (n=1). The results were analyzed by 3-way ANOVA and post hoc Tukey honest significant difference tests (TP and OP) and by 3-way ANOVA and post hoc Scheffé tests (grain size) (α=.05). RESULTS: No layers exhibited a significant difference in TP after superspeed sintering, except the dentin layer (DL) and transition layer 2 (T2) of 4Y- and 6Y-zirconia, respectively. The TP increased (P<.05) in DL for superspeed sintered 4Y-zirconia and decreased (P<.05) in T2 for the superspeed sintered 6Y-zirconia. However, the difference in TP by superspeed sintering was lower than the perceptibility thresholds of 50:50%. The OP decreased (P<.05) in the DL and T2 of 4Y-zirconia after superspeed sintering. For 6Y-zirconia, the OP decreased (P<.05) in all layers except for the transition layer 1 (T1) after superspeed sintering. However, the difference in OP values was minimal, with only a 1.1 difference observed for Zolid Gen-X (4Y) and a range of 1.22 to 1.62 for Katana UTML (6Y) when using superspeed sintering. No significant change was found in the grain size after superspeed sintering of either zirconia. Regardless of the sintering speed, the average grain size of the 6Y-zirconia (conventional: 2.09 to 2.21 µm; superspeed: 2.11 to 2.20 µm) was larger than that of the 4Y-zirconia (conventional: 0.50 to 0.52 µm; superspeed: 0.52 to 0.54 µm). Owing to superspeed sintering, the metastable tetragonal (T') phase content increased while the tetragonal (T) phase decreased in 4Y-zirconia; in 6Y-zirconia, the cubic (C) phase content increased, while the T'-phase content decreased. CONCLUSIONS: Superspeed sintering did not result in any clinically significant changes in the translucency and opalescence of 4Y- or 6Y-zirconia.

Autofluorescence spectra and image to differentiate restorative dental resins from the tooth.

PURPOSE: To compare the autofluorescence (AF) spectra of resin products with teeth to determine if this type of non-invasive testing is feasible for differentiating resin products from teeth during resin repair. METHODS: For the study, 11 methacrylate-based resin products were chosen. A 405 nm laser was used to induce AF, and a spectrophotometer and a qualitative laser-induced fluorescence (QLF) camera were used to obtain AF spectra and images, respectively. RESULTS: Resin products and teeth showed one or two emission peak(s) at 435-465 nm and 475-480 nm, respectively. Other resin constituents produced weak emission peaks beyond the 435-475 nm range. Resin products with high emission intensities produced bright images. When layered, surface resins (0.2 mm-thick) were different from underlying base resins and teeth. CLINICAL SIGNIFICANCE: During resin repair, a restored resin can be readily removed if AF spectroscopy is used alone or in combination with QLF imaging.

Bactericidal effect on S. mutans using N-TiO2 with combined treatment of low concentration H2O2 and visible light.

PURPOSE: To test the feasibility of nitrogen-doped TiO2 nanoparticles in the killing of Streptococcus mutans (S. mutans) for short term treatment. METHODS: For the study, S. mutans were treated with the combinations of N-TiO2, visible light, and without/with 0.5% H2O2 inclusion. Visible light was irradiated for 3 minutes one time. RESULTS: Methylene blue solution was degraded (bleached) 5-30% by one of N-TiO2 (or TiO2) + visible laser (405 or 660 nm) +0.5% H2O2 conditions owing to almost linearly producing free radicals through photocatalysis. Antibacterial outcomes treated with N-TiO2 were slightly better than those by TiO2 regardless of test condition. Also, killing of S. mutans treated with 405 nm laser was slightly better than those by 660 nm laser. CLINICAL SIGNIFICANCE: S. mutans can be eliminated using N-TiO2 with clinically acceptable light (wavelength, intensity) and low concentration H2O2 condition under short term treatment.

Teeth whitening using nitrogen doped-TiO2 nanoparticles and hydrogen peroxide under visible light irradiation.

PURPOSE: To test the efficacy of nitrogen doped-TiO2 (N-TiO2) nanoparticles (NPs) on teeth whitening under visible light irradiation. METHODS: N-TiOV2 NPs were prepared by the sol-gel method, using TiN as a precursor. Their light absorbance and crystal structures were characterized. Photocatalytic reactions were tested using methylene blue (MB) and extracted teeth. For the extracted teeth, carbomer gel, without or with 3% H2O2, and light irradiated, with subsequent evaluation of the color differences. RESULTS: Unlike ordinary TiO2, N-TiO2 showed high absorbance after 400 nm. N-TiO2 prepared with TiN as a precursor showed rutile phase over the TiN structure. For MB solution, N-TiO2 with 3% H2O2 showed the maximum decrease in absorbance after laser irradiation. Observing the effect on teeth, N-TiO2+3% H2O2+405 nm laser treatment achieved approximately 25% higher whitening than that by 15% H2O2 during the same treatment time. Higher H2O2 concentrations may offer faster results. CLINICAL SIGNIFICANCE: N-TiO2 nanoparticles (without or with 3% H2O2) show better whitening of teeth as compared to 15% H2O2, if used with a visible laser for 5 hours. The potential on N-TiO2 nanoparticles to be used as a tooth whitener needs to be further explored to reduce its application time.

Difference assessment of composite resins and sound tooth applicable in the resin-imbedded tooth for resin repair using fluorescence, microhardness, DIAGNOdent, and X-ray image.

OBJECTIVE: Visual differentiation of resin and tooth in a tooth cavity is not simple due to their highly similar shade. The purpose of the present study was to find any noninvasive method which can effectively differentiate resin from sound tooth in a resin-imbedded tooth for resin repair. MATERIALS AND METHODS: For the study, various resin products were imbedded into the cavity of sound tooth. By applying laser of different wavelengths, autofluorescence (AF) of sound tooth and resin products were obtained. Microhardness, X-ray radiograph, and DIAGNOdent were tested for each tooth, resin product, and resin-imbedded tooth. RESULTS: For the AF spectra obtained using the 405-nm wavelength, sound tooth has emission peak at 440-470 nm and near 490 nm. Sound tooth has several times higher microhardness than resin products regardless of position in tooth subsurface. Due to the difference of radiopaque fillers' composition and concentration, resin products have different brightness in the X-ray radiograph. DIAGNOdent readings for tooth and resin products were inconsistently different, and the difference of obtained values was slightly not to be applicable for the differentiation. CONCLUSION: Among the tested methods, with noninvasive treatment, AF spectrum by the 405-nm wavelength showed the apparent difference between resin and tooth. CLINICAL SIGNIFICANCE: For the resin repair in a resin-imbedded tooth cavity, AF spectrum produced by 405-nm wavelength could be a useful method in tracing the resin-tooth boundary if combined with conventional X-ray radiography.

Dentin sealing and antibacterial effects of silver-doped bioactive glass/mesoporous silica nanocomposite: an in vitro study.

OBJECTIVES: To synthesize a silver-doped bioactive glass/mesoporous silica nanoparticle (Ag-BGN@MSN), as well as to investigate its effects on dentinal tubule occlusion, microtensile bond strength (MTBS), and antibacterial activity. MATERIALS AND METHODS: Ag-BGN@MSN was synthesized using a modified "quick alkali-mediated sol-gel" method. Demineralized tooth disc models were made and divided into four groups; the following treatments were then applied: group 1-no treatment, group 2-bioglass, group 3-MSN, group 4-Ag-BGN@MSN. Next, four discs were selected from each group and soaked into 6 wt% citric acid to test acid-resistant stability. Dentinal tubule occlusion, as well as the occlusion ratio, was observed using field-emission scanning electron microscopy. The MTBS was also measured to evaluate the desensitizing effect of the treatments. Cytotoxicity was examined using the MTT assay. Antibacterial activity was detected against Lactobacillus casei, and ion dissolution was evaluated using inductively coupled plasma optical emission spectrometry. RESULTS: Ag-BGN@MSN effectively occluded the dentinal tubule and formed a membrane-like layer. After the acid challenge, Ag-BGN@MSN had the highest rate of dentinal tubule occlusion. There were no significant differences in MTBS among the four groups (P > 0.05). All concentrations of Ag-BGN@MSN used had a relative cell viability above 72%. CONCLUSIONS: Ag-BGN@MSN was successfully fabricated using a modified sol-gel method. The Ag-BGN@MSN biocomposite effectively occluded dentinal with acid-resistant stability, did not decrease bond strength in self-etch adhesive system, had low cytotoxicity, and antibacterial effect. CLININAL RELEVANCE: Dentinal tubule sealing induced by Ag-BGN@MSN biocomposite with antibacterial effect is likely to increase long-term stability in DH.

Effect of different sizes of bioactive glass-coated mesoporous silica nanoparticles on dentinal tubule occlusion and mineralization.

OBJECTIVES: To synthesize two different sizes of bioactive glass-coated mesoporous silica nanoparticles (BGN@MSNs) and to investigate their effects on dentinal tubule occlusion and remineralization. MATERIALS AND METHODS: Two different sizes of mesoporous silica nanoparticles (MSNs) were synthesized using the Stöber method (368A, 1840A) and coated with bioactive glass nanoparticles (BGNs) using a modified quick alkali-mediated sol-gel method (368B, 1840B). Sensitive tooth disc models were prepared and divided into six groups and the following treatments were applied: group 1-no treatment, group 2-bioglass, group 3-368A, group 4-368B, group 5-1840A, and group 6-1840B. Then, five discs were selected from each group and soaked in 6 wt% citric acid to test acid resistance. Dentinal tubule occlusion and occlusion ratio were observed using field-emission scanning electron microscopy. In vitro mineralization tests using simulated body fluid solution were performed to evaluate the remineralization effect of the treatment. RESULTS: All samples effectively occluded the dentinal tubule and formed a membrane-like layer. After acid treatment, 1840B (group 6) exhibited the highest rate of dentinal tubule occlusion. Remineralization was observed in 368B and 1840B, and 1840B exhibited the fastest remineralization. CONCLUSIONS: Dentinal tubule remineralization induced by the BGN@MSN biocomposite can be used to stabilize long-term prognosis in dentin hypersensitivity. The 1840B induced the most efficient remineralization, and its smaller size and larger surface area were effective for remineralization. CLINICAL RELEVANCE: The BGN@MSN biocomposite with its smaller size and larger surface area was more effective for remineralization and dentinal tubule sealing.

How light attenuation and filler content affect the microhardness and polymerization shrinkage and translucency of bulk-fill composites?

OBJECTIVES: The purpose of this study was to investigate the microhardness, polymerization shrinkage, and translucency of bulk-fill composites (BFCs) which have different light attenuation properties and filler contents. MATERIALS AND METHODS: Five BFCs [Filtek Bulk Fill (FB), SureFil SDR (SS), Venus Bulk Fill (VB), SonicFill (SF), and Tetric N-Ceram Bulk Fill (TB)] and two resin-based composites (RBCs) [Tetric N-Ceram (TN) and Filtek Z350XT Flowable (ZF)] were chosen. Numbers of transmitted photons, refractive index, microhardness at different thicknesses, polymerization shrinkage, and translucency parameter (TP) were evaluated. RESULTS: Attenuation coefficients (ACs) based on measured photons ranged from -0.88 to -1.90. BFCs, except SF, had lower AC values than TN or ZF, and BFCs, except TN, had smaller refractive index decreases between top and bottom surfaces. Regardless of an exponential decrease in photon counts, microhardness decreased linearly as specimen thickens. Moreover, microhardness of BFCs showed smaller top-to-bottom decreases (11.5-48.8 %) than TN or ZF (57.3 and 71.5 %, respectively). BFCs with low filler contents showed lower microhardness and higher polymerization shrinkage than those of high filler contents. Also, BFCs had significantly higher (p < 0.001) TP values than TN or ZF. CONCLUSION: BFCs attenuated light less than RBCs. However, some BFCs had much lower top surface microhardness and higher polymerization shrinkage than tested RBCs. CLINICAL RELEVANCE: Despite the convenience of bulk filling, careful selection of BFC is advised because some BFCs have worse microhardness and polymerization shrinkage than RBCs due to their lower filler contents.

Effect of two lasers on the polymerization of composite resins: single vs combination.

The selection of a light-curing unit for the curing composite resins is important to achieve best outcomes. The purpose of the present study was to test lasers of 457 and 473 nm alone or in combination under different light conditions with respect to the cure of composite resins. Four different composite resins were light cured using five different laser combinations (530 mW/cm(2) 457 nm only, 530 mW/cm(2) 473 nm only, 177 mW/cm(2) 457 + 177 mW/cm(2) 473 nm, 265 mW/cm(2) 457 + 265 mW/cm(2) 473 nm, and 354 mW/cm(2) 457 + 354 mW/cm(2) 473 nm). Microhardness and polymerization shrinkage were evaluated. A light-emitting diode (LED) unit was used for comparison purposes. On top surfaces, after aging for 24 h, microhardness achieved using the LED unit and the lasers with different conditions ranged 42.4-65.5 and 38.9-67.7 Hv, respectively, and on bottom surfaces, corresponding ranges were 25.2-56.1 and 18.5-55.7 Hv, respectively. Of the conditions used, 354 mW/cm(2) 457 nm + 354 mW/cm(2) 473 nm produced the highest bottom microhardness (33.8-55.6 Hv). On top and bottom surfaces, microhardness by the lowest total light intensity, 354 (177 × 2) mW/cm(2), ranged 39.0-60.5 and 18.5-52.8 Hv, respectively. Generally, 530 mW/cm(2) at 457 nm produced the lowest polymerization shrinkage. However, shrinkage values obtained using all five laser conditions were similar. The study shows the lasers of 457 and 473 nm are useful for curing composite resins alone or in combination at much lower light intensities than the LED unit.

In Vitro Evaluation of Speed Sintering and Glazing Effects on the Flexural Strength and Microstructure of Highly Translucent Multilayered 5 mol% Yttria-Stabilized Zirconia.

This study aimed to investigate the impact of speed sintering and glazing on the flexural strength and microstructure of multilayered 5 mol% yttria-stabilized (5Y-) zirconia, which remains unknown. Bar-shaped specimens (N = 600) were fabricated from 5Y-zirconia (FX; Ceramill Zolid FX ML, ST; Katana STML) by cutting, polishing, sintering (conventional and speed sintering), and then glazing. A flexural strength test (n = 30/group), field emission scanning electron microscopy (FE-SEM) observation (n = 2/group), and an X-ray diffraction (XRD) study with Rietveld refinement (n = 1/group) were performed. The flexural strength was analyzed using three-way ANOVA and a post hoc Scheffé test. The grain size was analyzed using the Kruskal-Wallis H test and Bonferroni-Dunn post hoc test. Flexural strength slightly decreased in the nonglazed FX after speed sintering (p < 0.05). Glazing with and without glazing paste did not affect flexural strength at both sintering speeds (p > 0.05). Speed sintering and glazing minimally changed the Weibull modulus and phase fraction, and did not affect grain size (p > 0.05). ST had a larger grain size and lower tetragonal phase content than FX and had a lower flexural strength than FX in most groups (p < 0.05). Overall, the multilayered 5Y-zirconia is considered suitable for dental application using speed sintering and glazing.

Effect of a DPSS laser on the shear bond strength of ceramic brackets with different base designs.

This study evaluated the shear bond strength (SBS) and adhesive remnant index (ARI) of ceramic brackets with different base designs using a 473-nm diode-pumped solid-state (DPSS) laser to test its usefulness as a light source. A total of 180 caries-free human premolars were divided into four groups according to the base designs: microcrystalline, crystalline particle (CP), dovetail, and mesh. For each base design, teeth were divided into three different subgroups for light curing using three different light-curing units (LCUs) (quartz-tungsten-halogen unit, light-emitting diode unit, and a DPSS laser of 473 nm). Applied light intensities for the DPSS laser and the other LCUs were approximately 630 and 900 mW/cm(2), respectively. Stainless steel brackets with a mesh design served as controls. The failure modes of debonded brackets were scored using ARI. As a result, brackets bonded using the DPSS laser had the highest SBS values (16.5-27.3 MPa) among the LCUs regardless of base design. Regarding base designs, the CP groups showed the highest SBS values (22.9-27.3 MPa) regardless of LCU. Furthermore, stainless steel brackets with a mesh design had the lowest SBS values regardless of LCU. In many cases, brackets bonded using the DPSS laser had higher ARI scores and had more adhesive on their bases than on tooth surfaces. The study shows that the 473-nm DPSS laser has considerable potential for bonding ceramic brackets at lower light intensities than the other light-curing units examined.

Mechanical properties of composite resins light-cured using a blue DPSS laser.

Lasers have many favorable features as a light source owing to their monochromaticity and coherence. This study examined the mechanical properties of composite resins that were light-cured using a diode-pumped solid state (DPSS) laser. Eight composite resins were light-cured using four different light sources (one quartz-tungsten-halogen (QTH), two light-emitting diodes (LEDs), and one DPSS laser with a wavelength of 473 nm). The light intensity of the DPSS laser and remaining light-curing units were approximately 500 and 900 mW/cm(2), respectively. The microhardness, flexural properties, and compressive properties were evaluated using the Vickers hardness test, three-point bending test, and compression test, respectively. In most cases, the microhardness, flexural properties, and compressive properties of the specimens light-cured using the DPSS laser were similar to those obtained using the other light-curing units. Within the limits of the study, the microhardness, flexural modulus, and compressive strength were linearly correlated with the filler content (in weight percent). The flexural modulus and compressive modulus were also linearly correlated with the microhardness. Even with a much lower light intensity, the DPSS laser with a wavelength of 473 nm can polymerize composite resins and give comparable mechanical properties to those obtained using the other light-curing units.

Microhardness and polymerization shrinkage of flowable resins that are light cured using a blue laser.

This study evaluated the microhardness and polymerization shrinkage of flowable resins that are cured using different light sources. Seven flowable resins and two light sources (diode-pumped solid-state (DPSS) laser (LAS) and Optilux 501 (OP)) were chosen for the study. To evaluate the microhardness, a mold (height: 2 mm, inner diameter: 4 mm) was filled with resin and then light cured. The microhardness was measured at the top and bottom surfaces after aging for 24 h. The level of polymerization shrinkage was evaluated for 130 s (during and after the light curing) by measuring the dimensions of the cylindrical shape resin filling. The light intensity of the LAS and OP was approximately 520 mW/cm(2) and 800 mW/cm(2), respectively. The data for the microhardness and polymerization shrinkage were analyzed statistically. The microhardness (Hv) of the specimens at the top and bottom surface ranged from 25.3 ± 0.6 to 55.3 ± 1.0 and 28.0 ± 2.6 to 63.0 ± 2.3, respectively. Admira flow, Grandio flow, and Filtek Z350 flow showed a slightly higher microhardness at the bottom surface than that at the top surface. The degree of polymerization shrinkage (µm) of the specimens ranged from 30.5 ± 1.3 to 45.9 ± 0.6 for LAS and from 35.1 ± 1.5 to 47.1 ± 1.0 for OP. The values obtained using LAS and OP showed a statistical difference, but in many cases, the difference between the absolute values was minor.

Effect of Cooling Rate on Mechanical Properties, Translucency, Opalescence, and Light Transmission Properties of Monolithic 4Y-TZP during Glazing.

A standard cooling rate has not been established for glazing; therefore, the effects of the cooling rate on the properties of zirconia need to be evaluated to predict outcomes in clinical practice. 4Y-TZP glazed at three different cooling rates was analyzed to estimate the effect of cooling rate during glazing on the mechanical and optical properties. Hardness tests, field-emission scanning electron microscopy analysis, X-ray diffraction analysis, flexural strength measurement, and optical property evaluations were performed. When 4Y-TZP was glazed at a higher cooling rate (Cooling-1) than the normal cooling rate (Cooling-2), there was no significant difference in grain size, flexural strength, average transmittance, and translucency parameters. The hardness was slightly reduced. The opalescence parameter was reduced for the 2.03 mm thick specimens. When 4Y-TZP was glazed at a lower cooling rate (Cooling-3) than the normal cooling rate, there was no significant difference in hardness, grain size, flexural strength, and translucency parameters. In addition, the average transmittance and opalescence parameters were slightly reduced for the 0.52 and 2.03 mm specimens, respectively. The effects of the cooling rate during glazing on the mechanical and optical properties of 4Y-TZP appear to be minimal and clinically insignificant. Therefore, even if the cooling rate cannot be strictly controlled during glazing, the clinical outcomes will not be significantly affected.

Diode-pumped solid-state laser for bonding orthodontic brackets: effect of light intensity and light-curing time.

This study evaluated the shear bond strength (SBS) of orthodontic brackets bonded to teeth using a diode-pumped solid state (DPSS) laser of 473 nm with various light intensity and light-curing settings. For the study, a total of 150 extracted human teeth were divided into ten groups. In the control group, the brackets were bonded to the teeth using a quartz-tungsten-halogen (QTH) light with an intensity of 900 mW/cm(2). In the experimental groups, the brackets were bonded using a DPSS laser with three different light intensities and light-curing times. The same bracket type and adhesive were used in all groups throughout the study. Statistical analysis was performed to compare the SBS, and adhesive remnant index (ARI) among the groups. As results, brackets bonded using the DPSS laser with an intensity of 700 mW/cm(2) for 40 s (totally) showed a slightly higher SBS (12.2 ± 1.8 MPa) than that of those bonded using a QTH light (control; 11.6 ± 1.6 MPa). The SBS values linearly increased with increasing energy density (light intensity × light-curing time) of the DPSS laser (R = 0.95, p < 0.001). However, the SBS values among the test groups were similar regardless of the difference in light-curing conditions. A comparison of the ARI scores among the groups suggested a similar bracket failure mode.

Effect of diode-pumped solid state laser on polymerization shrinkage and color change in composite resins.

A diode-pumped solid state (DPSS) laser emitting at 473 nm was used to test its influence on the degree of polymerization of composite resins. Eight composite resins were chosen and light cured with three different light-curing systems [a quartz-tungsten-halogen (QTH) lamp-based unit, a light-emitting diode (LED) unit, and a DPSS laser]. Polymerization shrinkage and color change in specimens were measured. According to the statistical analysis, each light-curing system produced a significantly different value of maximum polymerization shrinkage. In most specimens, the DPSS laser induced the least polymerization shrinkage. After being immersed in distilled water for 10 days, specimens light-cured by the DPSS laser had undergone less color change than those cured by the other units. In conclusion, the DPSS laser induced better or similar polymerization in terms of polymerization shrinkage and color change in composite resins compared with those of the QTH lamp-based and LED units.

Effect of DPSS laser on the shear bond strength of orthodontic brackets.

PURPOSE: To test the bonding of orthodontic brackets to teeth using a diode-pumped solid state (DPSS) laser. METHODS: A total of 60 extracted human teeth were divided randomly into four groups: Group 1 (control)--he brackets were bonded to teeth using the quartz-tungsten-halogen (QTH) light (800 mW/cm2) for 40 seconds; Groups 2-4--the brackets were bonded to teeth using the DPSS laser (500 mW/cm2) for 40 seconds, 20 seconds, and 10 seconds, respectively. The teeth were debonded using shear force in a universal testing machine, and the amount of residual adhesive remaining on each tooth was evaluated. Statistical analysis was carried out for the shear bond strength (SBS) and Adhesive Remnant Index (ARI). RESULTS: The brackets bonded using the DPSS laser for 40 seconds showed the highest mean SBS (13.1 +/- 1.2 MPa) among the groups. Furthermore, the DPSS laser with 10 seconds light-curing could achieve 83% of the mean SBS obtained using the QTH light for 40 seconds. The ARI scores showed no differences among all four groups suggesting a similar failure mode.

Effect of light-curing units on the thermal expansion of resin nanocomposites.

PURPOSE: To examine the thermal expansion of resin nanocomposites after light-curing using different light-curing units. METHODS: Four different resin nanocomposites and four different light-curing units [quartz-tungsten-halogen (QTH), light emitting diode (LED), laser, and plasma arc] were chosen. Metal dies were filled with resin to make specimens and light-cured. The light intensity and light-curing time of the QTH and LED light-curing units were 1000 mW/cm2 and 40 seconds, 700 mW/cm2 and 40 seconds for the laser, and 1600 mW/cm2 and 3 seconds for the plasma arc. The coefficient of thermal expansion (CTE) was evaluated using a thermomechanical analyzer (TMA) at temperatures ranging from 30-80 degrees C. RESULTS: The CTE of the resin nanocomposites tested ranged from 28.5 to 65.8 (x 10(-6)/ degrees C), depending on the product and type of light-curing unit used. Among the specimens, Grandio showed the lowest CTE. The specimens cured using the plasma arc unit (Apollo 95E) showed the highest CTE. There was a linear correlation between the CTE and filler content (vol%) (R: -0.94-0.99 depending on the light-curing unit). The results may suggest a careful selection of the light-curing unit because there was more expansion in the specimens cured using the plasma arc unit than those cured by the other units.

Effect of hydrogen peroxide on microhardness and color change of resin nanocomposites.

PURPOSE: To examine the effect of hydrogen peroxide on the microhardness and color change of resin composites containing nanofillers. METHODS: Three resin nanocomposites with three different shades and two different tooth whitening agents were used. The specimens were given a 3-week treatment with one of three protocols: (1) 7 hours/day treatment of carbamide peroxide (CP) + 17 hours/day immersion in distilled water (DW); (2) 1 hour/week treatment of hydrogen peroxide (HP) + immersion in DW for the rest of the week; and (3) immersion in DW for 24 hours/day. The microhardness and color changes were measured after treatment. RESULTS: After treatment with the whitening agents, there was an 8.1-10.7% decrease in the original microhardness. These values were similar to those obtained from the samples treated with distilled water. In the same resin product, the decrease was similar regardless of the test agents used. In most cases, the color change was only slight (deltaE*=0.5-1.4). Hydrogen peroxide enhanced the color change but the absolute color change values were similar in the same product and shade, regardless of the test agent used.

Effect of staining solutions on discoloration of resin nanocomposites.

PURPOSE: To examine the effect of staining solutions on the discoloration of resin nanocomposites. METHODS: Three resin nanocomposites (Ceram X, Grandio, and Filtek Z350) were light cured for 40 seconds at a light intensity of 1000 mW/cm2. The color of the specimens was measured in %R (reflectance) mode before and after immersing the specimens in four different test solutions [distilled water (DW), coffee (CF), 50% ethanol (50ET) and brewed green tea (GT)] for 7 hours/day over a 3-week period. The color difference (deltaE*) was obtained based on the CIEL*a*b* color coordinate values. RESULTS: The specimens immersed in DW, 50ET and GT showed a slight increase in L* value. However, the samples immersed in CF showed a decrease in the L* value and an increase in the b* value. CF induced a significant color change (deltaE*: 3.1-5.6) in most specimens but the other solutions induced only a slight color change. Overall, coffee caused unacceptable color changes to the resin nanocomposites.