This study investigated temperature rises caused by different light curing units (LCUs) in dentin of different thicknesses. The different LCUs tested in this study were namely: quartz-tungsten-halogen (QTH) (Heliolux DLX) LCU, plasma arc (PAC) (Apollo 95E Elite) LCU, and light emitting diode (LED) (Mini LED) in standard curing mode as well as pulse and soft-start modes. One hundred and forty dentin disks of 0.5, 1, 1.5, and 2 mm thickness were prepared from mandibular molars (n=7). Temperatures were recorded using a L-type thermocouple in direct contact with the light guide tip. For all curing units/modes, dentin thickness was inversely proportional to temperature rise and that QTH light gave significantly higher values compared to PAC and LED in all the test conditions. The highest temperature rise was observed under 0.5-mm-thick dentin disk with QTH, whereas the lowest temperature rise was registered with LED light in pulse mode under 2-mm-thick dentin.

View full abstract

PEMA- and eugenol-based trial agents (PE 1.0, PE 1.6) possessed the requisite dental engineering properties that satisfied the requirements for temporary luting agents. To assess their clinical applicability, this study examined the following properties after the trial agents were removed: their residue ratios on the abutment surface and the bond strengths of resin-modified glass ionomer cement and resin cement for the abutment materials. The residue ratio of PE 1.0 on the abutment material after temporary restoration removal was lower than those of comparable temporary luting agents (polycarboxylate cement type, zinc oxide-eugenol cement type), and no residue was recognized for PE 1.6. On bond strength, those of the resin-modified glass ionomer cement and resin cement for the resin core and bovine dentin surface after the removal of trial agents tended to be the same or increase in comparison to commercial temporary luting agents. In conclusion, results of this study suggested that the trial agents were suitable for clinical use.

View full abstract

The behavior of water-soluble photoinitiators with crown ethers in dental adhesives is unknown. This study investigated the effect of sodium acylphosphine oxide (APO-Na) with crown ether in a hydrophobic adhesive on adhesion to teeth. Sodium 2,4,6-trimethylbenzoyl-phenylphosphine oxide (TMPO-Na = APO-Na) was synthesized in 67.1% yield and identified by ¹H NMR. APO-Na was dissolved in hydrophobic resins in the presence of a crown ether (ionophore effect). Thirty kinds of experimental single-step adhesives comprising APO-Na, CE, Bis-GMA, 6-methacryloyloxyhexyl phosphonoacetate (6-MHPA), and 4-methacryloyloxyethyl trimellitic acid (4-MET) were thereby prepared. Shear bond strength to unetched ground teeth was measured at a crosshead speed of 1.0 mm/min, and the data were analyzed by ANOVA. The shear bond strength results of bonding resins containing APO-Na with 18-crown-6-ether (CE-6) were significantly higher than that without CE-6 (control) (p<0.05). Higher bond strength values [for enamel: BR24 at 19.3 (3.2) MPa; for dentin: BR29 at 20.2 (4.7) MPa] were achieved with the adhesives containing APO-Na, CE-6, 6-MHPA, and 4-MET. Therefore, it was found that APO-Na with CE-6 contributed to the efficient bonding performance of single-step adhesive to teeth. However, in view of the biosafety hazard posed by crown ethers, the search is still on for reagents that are biologically safer than crown ethers — but with ionophor effects — to be used in dental adhesives.

View full abstract

This study evaluated the surface roughness and morphological changes of various flowable resins after long-term storage in a phosphate-buffered saline (PBS) or surface polishing with a mini-brush. The tested products were Beautifil Flow BF02 and BF10, Clearfil Majesty LV, Filtek^TM Supreme XT, and UniFil LoFlo Plus. A paste-type resin composite, Filtek^TM Supreme, was used as a control. The prepared specimens were 10 mm in diameter and 1 mm in height. The standard surfaces were polished with #600–1200 diamond disks and kept in deionized water for 24 hours. Surface roughness was detected after storage in PBS (pH 7.4) for either 2 weeks or 6 months, or after polishing with a mini-brush.
Results of this study demonstrated that the surface roughness of the standard specimens had a lower value as compared to those after storage in PBS for 2 weeks and 6 months, or after polishing with a mini-brush.

View full abstract

The aim of this study was to investigate and compare the temperature rises which occurred during the setting reactions of different permanent cements used to lute fixed partial prosthodontics.
In this study, four cements were used. They were mixed in three different proportions: according to manufacturers' recommendations, at doubled powder ratio, and at doubled liquid ratio. With a thermocouple, the temperature rises which occurred during the setting reactions were measured. For each proportion, the measurement was repeated five times such that a total of 60 measurements were done for the four different cements. Data were analyzed using analysis of variance (ANOVA).
ANOVA results showed that cement type and the interaction between cement type and the powder-liquid ratio were statistically significant factors (p<0.001). Similarly, the powder-liquid ratio was a statistically significant (p<0.01) factor.
Among the dental cements tested, zinc phosphate cement showed the highest temperature rise during setting reaction, whereas glass ionomer cement showed the lowest.

View full abstract

This study compared the effectiveness of three obturation techniques for oval-shaped canals. Roots of 42 extracted teeth with oval canals were randomly divided into three groups: (1) ProTaper canal preparation and single cone obturation with matching gutta-percha point; (2) ProTaper preparation plus thermoplastic obturation (Thermafil); (3) Profile .06 taper and matching master cone with lateral condensation. Cross-sectional area of the canal space occupied by sealer cement and gutta-percha was measured in the coronal, middle, and apical thirds using an image analysis software. The percentage of the crosssectional shape occupied by sealer cement was calculated. The Thermafil group was significantly lower than the single cone group or the lateral condensation group in the middle third (p<0.01) and lower than the single cone group in the coronal third (p<0.05). There were no significant differences between the single cone obturation group and the lateral condensation group in each level.

View full abstract

This study investigated the hardness and Young's modulus of coronal and radicular intertubular dentin. Ten bovine teeth were each divided into coronal and radicular groups, and the flat surfaces of the coronal and radicular dentin were subsequently processed along the tooth axis. The hardness and Young's modulus of the coronal and radicular intertubular dentin were evaluated using nanoindentation tests, at two locations per tooth. Mean hardness and Young's modulus values were statistically compared by one-way ANOVA and Fisher's PLSD test. The hardness of coronal intertubular dentin was 0.81±0.05 GPa and that of radicular dentin was 0.55±0.02 GPa. Additionally, the Young's modulus of coronal intertubular dentin was 26.60±2.19 GPa and that of radicular dentin was 20.89±1.10 GPa. Findings of this study revealed that the hardness and Young's modulus of coronal intertubular dentin were greater than those of radicular intertubular dentin.

View full abstract

The purpose of the study was to investigate the effects of a K₂SO₄ solution on the improvement of the properties of an experimental magnesia-based gypsum-bonded investment.
The characteristics of the experimental investment with different ratios of a K₂SO₄solution were as follows: setting time ranged from 34 to 152 minutes, green and fired compressive strengths were approximately 2.15 to 5.81 MPa and 1.63 to 2.45 MPa, respectively; thermal expansion was 0.38 to 0.47% at 700°C, which did not show any significant differences due to the concentration of the K₂SO₄ solution. Titanium casting could be obtained using the experimental investment mixed with a 1% K₂SO₄ solution, and the reaction layer thickness of the casting was less than 200 μm.
The results suggest that the experimental investment mixed with 1% K₂SO₄ showed acceptable physical properties and casting characteristics for titaniumcasting.

View full abstract

The bactericidal efficacy of 1.00–4.50% glycine-type amphoteric surfactant (Gly) was evaluated by measuring its microorganism removal rate in denture plaque. Physical and mechanical properties such as surface roughness, color difference, and bending strength of two different denture base resins were determined before and after cleaning in Gly solutions, a commercial denture cleaner, and tap water. The microorganism removal rates of all the Gly solutions were higher than those of a commercial enzymatic denture cleaner (Polident) (p<0.05). The removal rate of Candida spp. by Polident was not significantly different from the removal rate using water. Changes in the surface roughness and color difference among the specimens were slight. There were no significant differences in the bending strengths of the two resins for all concentrations of Gly solution (p<0.05). These results suggested that glycine-type amphoteric surfactant solution may be effective as a denture cleaner in conjunction with an ultrasonic cleaning device.

View full abstract

Carbamide peroxide and hydrogen peroxide are used as the main agents in vital tooth bleaching. In this study, the influence of peroxide treatment on cross-sectional morphology and mechanical property was investigated. A 3×5-mm window of enamel on the labial surface of a bovine tooth was exposed to immersion in 10% or 30% carbamide peroxide or hydrogen peroxide for 30 or 180 min. After immersion, the cross-sectional structure of each specimen was examined by nanoindentation and SEM. Nanohardness in the enamel showed a decrease at 2 μm below the surface, but none at 50 μm. High concentrations of peroxide caused erosion to a depth of 5 μm below the surface. In conclusion, decrease in nanohardness and change in morphology were limited to an area less than 50 μm below the surface, regardless of either concentration of peroxide or period of immersion.

View full abstract

We synthesized silver methacrylate, added it to resin for dental use, and observed color changes in the resin from colorless to red-purple following light irradiation. Therefore, 0.01-0.10 wt% silver methacrylate was added to two types of resin powder, i.e., self-curing resin produced by the polymerization of a barbituric acid derivative, quaternary ammonium, and an organometallic compound (Type I), and BPO-tertiary amine resin (Type II), and samples were produced by polymerization with the attached monomer. Changes with time in the color of samples from 3 hours (new samples) to 16 days (old samples) after polymerization and also color changes of old and new samples after heating were evaluated. Subsequently, changes in color with variations in the light intensity, irradiation time, and wavelength were evaluated in terms of color differences.

View full abstract

The purpose of this in vitro investigation was to study the effects of coffee and tea immersion on surface discoloration of one commercial temporary resin coating material, White Coat (WHC; Kuraray Medical Inc., Tokyo, Japan), and an experimental one, SI-R20209 (SIR; Shofu Inc., Kyoto, Japan). Disk-shaped specimens were prepared, their colors were determined at baseline, and after immersion in water (control), tea and coffee solutions for 24, 48, and 72 hours. Very little discoloration was found with the water-stored specimens. Staining response was most pronounced after coffee immersion for White Coat and after tea immersion for the experimental material, exceeding the clinically acceptable discoloration threshold value of ΔΕ=3.3. However, most of the resin shades tested are likely to be sufficiently safe against heavy discoloration when used for short-term restoration only.

View full abstract

In this study, the surface hardness of five light-cured composite resins were evaluated, namely: filled (Estelite), nanofil (Ælite), unfilled (Valux Plus), hybrid (Tetric ceram), and Ormocer-based (Admira) composite resins. The microhardness values of composite specimens were measured at the top and bottom surfaces after 24 hours or 30 days of immersion in different solutions (tea, coffee, Turkish coffee, mouthwash, cola, and distilled water). Comparisons were made with univariate analysis of variance and Duncan's multiple range test. It was found that rough specimens of reinforced nano-hybrid composite material immersed in cola for 30 days had the lowest surface hardness (33.20), whereas rough specimens of hybrid composite material immersed in cola for 24 hours had the highest surface hardness (156.00). In both tea and coffee, the top surfaces tended to be harder than the bottom ones. In conclusion, the five different materials exhibited different hardnesses, and that the hardness values of composite materials were statistically different in different immersion solutions.

View full abstract

The aim of this study was to evaluate and clarify the various mechanical properties and behavior of layering porcelains (Tokuyama Dental Ceramic, IPS Empress 2, Cerabien, Vitadurα, Creation) used for veneering high-strength ceramic core materials. The layering porcelains studied exhibited the following range of mechanical properties: compressive strength at 586–1091 MPa, bending strength at 30–97 MPa, diametral tensile strength at 16–28 MPa, Vickers hardness at 481–647 Hv, and fracture toughness at 1.36–2.05 MPa·m^1/2. Results of this study indicated that the mechanical shortcomings of conventional porcelain, such as brittleness and hardness, have been overcome by the enhanced mechanical properties of layering porcelain, resulting in improved fracture toughness.

View full abstract

The purpose of this study was to investigate the effects of food-simulating liquids (FSL) on the hardness and flexural strength (FS) of a new silorane-based composite and to compare it with methacrylate-based composites (MBCs). Four restorative materials (Filtek Silorane, P60, Z250, and Supreme XT) were used. Specimens for the FS and hardness measurements were fabricated in customized molds. Immediately after polymerization, the materials were stored in the following dietary simulating solvents at 37°C for 1 week: distilled water, 0.02 N citric acid, heptane, and 75% aqueous ethanol solution. After conditioning, the FS and hardness values were measured. Data were subjected to ANOVA/Scheffé's test at a significance level of 0.05. The hardness and FS of Filtek Silorane were not significantly affected by FSL (p>0.05). Conversely, the hardness of MBCs significantly decreased after conditioning in water and ethanol (p<0.05). Similarly, the FS values of MBCs were significantly affected after conditioning in ethanol.

View full abstract