Kuraray Noritake Dental Research Articles

Interfacial Adaptation of Composite Restorations Before and After Light Curing: Effects of Adhesive and Filling Technique.

To investigate the effects of placement technique and adhesive material on adaptation of composites before and after light curing. Cylindrical cavities (3 mm diameter, 1.7 mm depth) in extracted human molars were restored in 6 groups (n=5) using 2 adhesives--two-step self-etching Clearfil SE Bond 2 (SE2) and all-in-one Clearfil Tri-S Bond Plus (TSP) (Kuraray Noritake Dental)--and 2 composites--Estelite Sigma Quick (ESQ) and Estelite Flow Quick (FLQ) (Tokuyama Dental)--placed with three different techniques: ESQ bulk placed, FLQ lining followed by ESQ and FLQ bulk placed. Specimens were scanned twice using swept-source optical coherence tomography (SS-OCT) before and after photopolymerization of the composite. Gap formation during polymerization or the difference in floor interface (DFI%) and final unsealed interface (USI%) were measured by image coregistration and subtraction on 6 diametrical planes across each scan. Two-way ANOVA suggested that both factors (adhesive and filling technique) and their interaction were significant (p<0.001). SE2 showed significantly lower DFI% than did TSP when the composites were placed in bulk, but no difference was found when flowable lining was applied (p<0.05). Within TSP, all filling techniques were significantly different and the lining group showed the lowest values, followed by ESQ-bulk. Overall, SE2 always showed lower UFI% than did TSP, while there was no difference among different techniques within SE2. SS-OCT is a unique method to observe the pre-existing interfacial defects and gaps developed during polymerization, which were found to depend on both placement technique and applied adhesive.

In situ characterization of resin–dentin interfaces using conventional vs. cryofocused ion-beam milling

ObjectiveThe introduction of focused ion beam (FIB) milling has facilitated preparation of hard tissue samples for transmission electron microscope (TEM). However, this technique generates high temperature that may alter or damage morphological features in biological tissue. Therefore, the aim of this study was to determine the effects of cryogenic cooling on the morphological features of dentin interfaces with dental restorative materials in samples prepared by FIB for TEM examination. MethodsAfter preparation of a cylindrical-shaped cavities in extracted, non-carious premolar teeth, the specimens were restored with dental adhesive/composite and categorized into two restorative materials groups; (PB) a combination of Clearfil Protect Bond (Kuraray Noritake Dental, Japan)/Estelite Sigma Quick composite (Tokuyama Dental, Japan), and (SB) Filtek Silorane restorative system (3M ESPE, USA). The specimens were subjected to interfacial cross-sectioning, followed by observation and area selection using confocal laser microscopy. Later, ultrathin sections were prepared using FIB with cryogenic cooling (PB-C) and (SB-C), or without cooling (PB-NC) and (SB-NC) that all were examined under TEM. ResultsResulting TEM images of the ultra-morphological features at the resin–dentin nano-interaction zone were improved when FIB preparation was conducted in the cryogenic condition and no sign of artifacts were detected. SignificanceConducting ion beam milling with cryogenic cooling was advantageous in minimizing the elevation in specimen temperature. This led to preservation of dentin microstructures that revealed additional information about substrates that are necessary for advanced characterization of tooth–biomaterial interactions.

Evaluation of experimental phosphate and sulfur-based primer bonding to metal casting alloys

The aim of this study was to evaluate the effect of three experimental primers prepared with synthesized phosphorous and sulfur monomers (HEMA-P, ETMA and the mixture of HEMA-P/ETMA) on bonding to nickel–chromium (NiCr), silver–palladium (AgPd) and silver–gold (AgAu) metal alloys. The specimens were treated with experimental primers: HEMA-P, ETMA, HEMA-P/ETMA and Alloy Primer (Kuraray Noritake Dental Inc., Okayama, Japan) was used as commercial reference. Resin cement cylinders were built-up after application of tested primers on different alloy surfaces. Samples were stored in distilled water at 37°C for 24h before being subjected to shear bond tests using a mechanical testing machine. Shear bond strength (SBS) was recorded in MPa. Failure modes were classified under magnification as adhesive and mixed failure. Data were submitted to a two-way ANOVA and Student–Newman–Keuls׳ test. The statistically highest shear bond strength was observed with commercial primer to the AgPd alloy while the lowest value was shown with commercially available primers and experimental HEMA-P/ETMA to the NiCr alloy (p<0.05).There was a predominance of adhesive failure, with the exception of commercially available primer, for which mixed failures were predominant. It could be concluded that formulations of metal primers containing HEMA-P or ETMA primers should be considered for use in the bonding protocol of NiCr alloys.

Microtensile bond strength of a newly developed resin cement to dentin.

The purpose of this study was to evaluate the microtensile bond strength (µTBS) of a newly developed resin cement, ECD-89 (ECD, Tokuyama Dental, Tokyo, Japan) to dentin and to observe the interfacial micromorphology by comparing with two commercial resin cements, Multilink Automix (MA, Ivoclar Vivadent AG, Schaan, Liechtenstein) and Panavia F2.0 (PF, Kuraray Noritake Dental, Tokyo, Japan). Flat dentin surfaces of human third molars were exposed using #600 SiC. After application of primer and cement to the dentin surface, each cement was applied and cured with light (light condition) or without light (dark condition). The teeth were sectioned to obtain beams (1 mm×1 mm) after 24 h of water storage. The mean bond strengths and SDs (MPa) were: ECD: 68.6±14.9, MA: 39.2±18.9, PF: 39.4±18.5 and ECD: 54.5±22.4, MA: 36.7±15.6, PF: 13.4±4.46 when cured in light and dark condition, respectively. In both conditions, ECD-89 showed statistically higher µTBS than the others.

Bonding property of resin cement to composite resin crown

Purpose:Direct Crownsmade of a composite resinmaterial recently developed by 3M ESPE. These crowns maintain the coronal morphology even in an uncured state. The advantage is that the entire process of crown fabrication until cementing and delivery can be completed chairside on the same day. There has not been a detailed study on how adhesion with resin cement is affected by bonding performed immediately after polymerization of composite resin. Thus, this study examined the effects of time period after crown fabrication on the bonding property. Methods and materials: This study used a combination of composite resin and resin cement from the same manufacturer. The following items were used: 3M ESPE Direct Crowns with RelyX Unicem 2 Automix self-adhesive resin cement and Kuraray Noritake Dental Estenia C&B with Panavia F 2.0. Discs of Estenia C&B and Direct Crowns were fabricated (10mm diameter and 3mm thickness). They were divided into groups with bonding performed immediately after fabrication of discs (0h-Direct Crown group and 0h-Estenia C&B group) and groups with bonding performed 48h later (48h-Direct Crown group and 48h-Estenia C&B group). Amicrotensile bond strength test was performed after bonding. Subsequently, fracture surface morphology of samples was examined by scanning electronmicroscopy. ATR-FTIR (Attenuated total reflection-Fourier transform infrared spectroscopy) analysis was performed on Direct Crowns. Results: The adhesive strength was significantly higher in the 0h-Direct Crown group (76.6± 13.4MPa) compared with the 0h-Estenia C&B group (60.9± 14.8MPa), the 48h-Direct Crown group (45.8± 9.7MPa), and the 48h-Estenia C&B group (53.7± 12.5MPa). When fracture surfaces were examined after the microtensile bond strength test, the 0h-Direct Crown group had many mixed fractures but no fracture at the interface between composite resin and resin cement. The other three groups had mainly mixed fractures and fractures at the interface between composite resin and resin cement. The results of ATR-FTIR analysis suggest that the degree of surface polymerization was low for Direct Crowns immediately after fabrication compared with Direct Crowns 24h later. Conclusion: The results of this study suggest that Direct Crowns are effective in clinical use with their high adhesion due to bonding immediately after fabrication.

Efficiency of dual-cured resin cement polymerization induced by high-intensity LED curing units through ceramic material.

This study aimed to evaluate the ability of high-intensity light-emitting diode (LED) and other curing units to cure dual-cured resin cement through ceramic material. A halogen curing unit (Jetlite 3000, Morita), a second-generation LED curing unit (Demi, Kerr), and two high-intensity LED curing units (PenCure 2000, Morita; Valo, Ultradent) were tested. Feldspathic ceramic plates (VITABLOCS Mark II, A3; Vita Zahnfabrik) with thicknesses of 1.0, 2.0, and 3.0 mm were prepared. Dual-cured resin cement samples (Clearfil Esthetic Cement, Kuraray Noritake Dental) were irradiated directly or through one of the ceramic plates for different periods (5, 10, 15, or 20 seconds for the high-intensity LED units and 20, 40, 60, or 80 seconds for the others). The Knoop hardness test was used to determine the level of photopolymerization that had been induced in the resin cement. Data were analyzed by one-way analysis of variance and Dunnett's post-hoc test to identify test-control (maximum irradiation without a ceramic plate) differences for each curing unit (p<0.05). For all curing units, the curing conditions had a statistically significant effect on the Knoop hardness numbers (KHNs) of the irradiated cement samples (p<0.001). In general, the KHN decreased with increasing plate thickness and increased as the irradiation period was extended. Jetlite 3000 achieved control-level KHN values only when the plate thickness was 1.0 mm. At a plate thickness ≥2.0 mm, the LED units (except for PenCure 2000 at 3.0 mm) were able to achieve control-level KHN values when the irradiation time was extended. At a plate thickness of 3.0 mm, irradiation for 20 seconds with the Valo or for 80 seconds with the Demi were the only methods that produced KHN values equivalent to those produced by direct irradiation. Regardless of the type of curing unit used, indirect irradiation of dual-cured resin cement through a ceramic plate resulted in decreased KHN values compared with direct irradiation. When the irradiation period was extended, only the LED units were able to achieve similar KHN values to those observed under direct irradiation in the presence of plates ≥2.0-mm thick. High-intensity LED units require a shorter irradiation period than halogen and second-generation LED curing units to obtain KHN values similar to those observed during direct irradiation.

Nondestructive observation of teeth post core space using optical coherence tomography: a pilot study

Coronal tooth lesions, such as caries, enamel cracking, and composite resin restoration cavities, have been observed by optical coherence tomography (OCT). This pilot study was performed to verify whether OCT could reveal details of root canals filled with resin core build-up. A dual-cure, one-step, self-etch adhesive system-bonding agent (Clearfil Bond SE ONE, Kuraray Noritake Dental) and dual-cure resin composite core material (Clearfil DC Core Automix ONE, Kuraray Noritake Dental) were used according to the manufacturer's instructions in root canals. OCT was performed at three stages of the core build-up: after the post space preparation, after bonding application, and after resin core fabrication. The cementum was removed in the cementum absent group and the root was left untreated in the cementum present group. Bubbles were observed in the resin cores and gaps formed between the resin core and dentin. In the cementum absent group, the internal structure of the root could be visualized clearly compared with the cementum present group. The root internal structure could be observed by OCT and the image became clearer when cementum was removed.

The effect of atmospheric plasma treatment of dental zirconia ceramics on the contact angle of water

The purpose of this study was to investigate the effect of atmospheric pressure plasma application on the water contact angle (CA) of zirconia ceramics. Two zirconia ceramics (Katana, Kuraray Noritake Dental and Lava, 3 M ESPE) were used to test the plasma treatment (SAP, surface) with argon gas for one minute (1 L/min). To measure the CA, a drop of water was placed on a zirconia surface, which was observed under optical microscopy, and images were used to calculate the CA (n = 5). The dynamic behavior of the surface wettability was analyzed by collecting the CA data over a 70-hour period. CA data were analyzed by two-way ANOVA and the Tukey test (5%). The CA baseline values were 66° and 68° for Katana and Lava, respectively. After the application of plasma, the CA was reduced significantly to 36° and 31°, respectively. The CAs for Lava zirconia and Katana returned to baseline values after 5 and 15 hours, respectively. The plasma treatment improved the wettability of the zirconia surface, decreasing the CA approximately 50%. The duration of the effect of plasma on zirconia surfaces was at least 5 hours and material-dependent.

Novel Fluoro-carbon Functional Monomer for Dental Bonding

Among several functional monomers, 10-methacryloxydecyl dihydrogen phosphate (10-MDP) bonded most effectively to hydroxyapatite (HAp). However, more hydrolysis-resistant functional monomers are needed to improve bond durability. Here, we investigated the adhesive potential of the novel fluoro-carbon functional monomer 6-methacryloxy-2,2,3,3,4,4,5,5-octafluorohexyl dihydrogen phosphate (MF8P; Kuraray Noritake Dental Inc., Tokyo, Japan) by studying its molecular interaction with powder HAp using solid-state nuclear magnetic resonance (1H MAS NMR) and with dentin using x-ray diffraction (XRD) and by characterizing its interface ultrastructure at dentin using transmission electron microscopy (TEM). We further determined the dissolution rate of the MF8P_Ca salt, the hydrophobicity of MF8P, and the bond strength of an experimental MF8P-based adhesive to dentin. NMR confirmed chemical adsorption of MF8P onto HAp. XRD and TEM revealed MF8P_Ca salt formation and nano-layering at dentin. The MF8P_Ca salt was as stable as that of 10-MDP; MF8P was as hydrophobic as 10-MDP; a significantly higher bond strength was recorded for MF8P than for 10-MDP. In conclusion, MF8P chemically bonded to HAp. Despite its shorter size, MF8P possesses characteristics similar to those of 10-MDP, most likely to be associated with the strong chemical bond between fluorine and carbon. Since favorable bond strength to dentin was recorded, MF8P can be considered a good candidate functional monomer for bonding.

Effects of curing mode and moisture on nanoindentation mechanical properties and bonding of a self-adhesive resin cement to pulp chamber floor

ObjectiveThis study aimed to investigate the effect of dentin surface moisture and curing mode on microtensile bond strength (MTBS) and nanoindentation characteristics of a self-adhesive resin cement. MethodsForty-four extracted human molars were distributed into four groups according to dentin surface moisture (dry or wet) and curing mode of the resin cement (light or chemical). Clearfil SA Cement (Kuraray Noritake Dental, Japan) was used for cementation of composite cores to the pulp chamber dentin. The specimens were sectioned into beams for MTBS test at the pulpal floor. Nanoindentation hardness and creep of the cement layer were measured under 100mN load with 30s hold segment. Data were statistically analyzed using two-way ANOVA and Weibull distribution of MTBS (α=0.05). ResultsMoisture, curing mode or their interaction did not significantly affect mean MTBS values that ranged 17.6–22.6MPa (p>0.05); however, the lowest characteristic strength was found in moist chemically cured group. Hardness ranged 437–512MPa, and was not affected by the experimental factors (p>0.05). Nanoindentation creep ranged 9.3–10.9% with the chemically cured groups showing the highest values, indicating lower cross-linking and deformation resistance of their polymer network. SignificanceAdditional moisture on dentin surface did not contribute to adhesion of the anhydrous self-adhesive resin cement to dentin. Light-curing, despite attenuation through the composite core, was beneficial and improved nanoindentation creep resistance of the cement. The difference was not, however, reflected in the mean bond strength or hardness values.

Effect of solvent evaporation strategies on regional bond strength of one‐step self‐etch adhesives to root canal dentine

To evaluate the efficacy of different solvent evaporation strategies on bonding of one-step self-etch adhesives to root canal dentine. Two dual-cure resin core systems (Clearfil DC Bond/Clearfil DC Core Automix and Clearfil Tri-S Bond Plus/Clearfil DC Core Plus; Kuraray Noritake Dental, Tokyo, Japan) were equally applied in 24 post spaces from extracted human mandibular premolars. After the adhesive application, specimens were randomly assigned into four water/solvent evaporation strategies as follows (I) insertion of absorbent paper point for 10s: P, (II) 10s air-blowing: A, (III) as (II) followed by insertion of absorbent paper point: AP, (IV) as (III) followed by 10s additional air-blowing: APA. Then, the adhesives were light cured, and resin core materials were placed into the post space, followed by light curing for 60s. After water storage for 24h, 0.6×0.6mm-thick beams were prepared to measure the regional μTBS. The mode of failure was also observed. The μTBS values were statistically analysed using three-way anova and Duncan HSD test (α=0.05). In the coronal region, there were no significant differences in μTBS between each evaporation strategy (P>0.05), except P group. However, in the apical region, APA and AP groups significantly increased in μTBS compared with A and P groups (P<0.05). Only in the APA group of Clearfil Tri-S Bond Plus/Clearfil DC Core Plus, was there no significant difference in μTBS between the coronal and apical regions (P>0.05). The use of paper points with additional air-blowing for removing excessive adhesive and evaporating residual water/solvent would be effective in producing higher bond strength for the tested one-step self-etch adhesives and fewer blister formations in deeper regions of the post space.