Masaomi Ikeda

Effect of primer treatment on bonding of resin cements to zirconia ceramic

OBJECTIVES To evaluate and compare bond strengths of different primers and resin cements to silica-based and zirconia ceramics. METHODS Silica-based and zirconia ceramic specimens were ground flat with #600-grit SiC paper. The ceramic surfaces were airborne-particle abraded and then divided into 11 groups of seven each: untreated (control); and conditioned with one of the six primers in combination with a resin cement from the same manufacturer as follows: Bistite II/Tokuso Ceramic Primer, Linkmax/GC Ceramic Primer, RelyX ARC/RelyX Ceramic Primer, Panavia F 2.0/Clearfil Ceramic Primer, and Resicem/Shofu Porcelain Primer and Resicem/AZ Primer. Stainless steel rods were bonded to the ceramic surfaces using one of the five resin cements. After 24-h water storage, the tensile bond strengths were tested using a universal testing machine and failure modes were examined. RESULTS Conditioning with primers containing a silane coupling agent (all the primers except AZ Primer) significantly enhanced bond strengths of resin cements to silica-based ceramic. For zirconia ceramic, Resicem/AZ Primer exhibited significantly higher bond strength than the other groups except Panavia F 2.0/Clearfil Ceramic Primer. The predominant failure mode of the groups conditioned with primers containing a phosphonic acid monomer (AZ Primer) or a phosphate ester monomer (Clearfil Ceramic Primer and Tokuso Ceramic Primer) was cohesive failure in cements whereas that with the other primers was adhesive failure at the zirconia surfaces. SIGNIFICANCE The use of primers containing a silane coupling agent improved resin bonding to silica-based ceramic. On the other hand, the use of primers containing a phosphonic acid monomer or a phosphate ester monomer improved resin bonding to zirconia ceramic.

Long-term evaluation of water sorption and ultimate tensile strength of HEMA-containing/-free one-step self-etch adhesives

OBJECTIVE The objective of this study was to evaluate the water sorption (Wsp) and ultimate tensile strength (UTS) of HEMA-containing/free one-step self-etch adhesives after long-term water-storage. METHODS Three HEMA-containing one-step self-etch adhesives (Bond Force (BF), Clearfil S(3) Bond (S3) and OptiBond All-In-One (OP)), and one HEMA-free one-step self-etch adhesive, G Bond (GB) was used. After the solvents of each adhesive were evaporated, polymerised adhesive disks and dumbbell-shaped specimens of thirty-two each were prepared and divided into four groups of 14-, 90-, 180- and 360-day water-storage. After immersion in water for the designated storage periods, the disks were subjected to measurement of Wsp, and the dumbbell-shaped specimens were subjected to measurement of UTS. The data of Wsp and UTS were statistically analysed using a two-way ANOVA and Bonferroni test. RESULTS Wsp of BF, S3 and OP increased over time, whereas for GB, there were no significant differences in Wsp among all the storage periods. Wsp of GB was lower than those of BF, S3 and OP in each period. The UTS of BF, S3 and OP decreased over time, whereas for GB, there were no significant differences in UTS among all storage periods. The highest UTS was initially seen in BF>GB=S3=OP, and after 360-day water-storage, seen in BF=GB>OP=S3. CONCLUSIONS For the HEMA-containing adhesives, Wsp increased and UTS decreased over time. On the other hand, for the HEMA-free adhesive, Wsp and UTS did not significantly change even after 360-day water-storage.

Relationship between mechanical properties of one-step self-etch adhesives and water sorption

OBJECTIVES The purpose of this study was to evaluate the relationship between changes in the modulus of elasticity and ultimate tensile strength of one-step self-etch adhesives, and their degree of water sorption. METHODS Five one-step self-etch adhesives, Xeno IV (Dentsply Caulk), G Bond (GC Corp.), Clearfil S3 Bond (Kuraray Medical Inc.), Bond Force (Tokuyama Dental Corp.), and One-Up Bond F Plus (Tokuyama Dental Corp.) were used. Ten dumbelled-shaped polymers of each adhesive were used to obtain the modulus of elasticity by the three-point flexural bending test and the ultimate tensile strength by microtensile testing. The modulus of elasticity and the ultimate tensile strength were measured in both dry and wet conditions before/after immersion in water for 24h. Water sorption was measured, using a modification of the ISO-4049 standard. Each result of the modulus of elasticity and ultimate tensile strength was statistically analyzed using a two-way ANOVA and the result of water sorption was statistically analyzed using a one-way ANOVA. Regression analyses were used to determine the correlations between the modulus of elasticity and the ultimate tensile strength in dry or wet states, and also the percent decrease in these properties before/after immersion of water vs. water sorption. RESULTS In the dry state, the moduli of elasticity of the five adhesive polymers varied from 948 to 1530 MPa, while the ultimate tensile strengths varied from 24.4 to 61.5 MPa. The wet specimens gave much lower moduli of elasticity (from 584 to 1073 MPa) and ultimate tensile strengths (from 16.5 to 35.0 MPa). Water sorption varied from 32.1 to 105.8 g mm(-3). SIGNIFICANCE The moduli of elasticity and ultimate tensile strengths of the adhesives fell significantly after water-storage. Water sorption depended on the constituents of the adhesive systems. The percent decreases in the ultimate tensile strengths of the adhesives were related to water sorption, while the percent reductions in the moduli of elasticity of the adhesives were not related to water sorption.

Translucency, opalescence and light transmission characteristics of light-cured resin composites.

OBJECTIVES To evaluate the translucency, opalescence and light transmission characteristics of resin composites with different thicknesses. METHODS Disks of three resin composites (Estelite∑, Beautifil II, Clearfil Majesty) of A2 shade were prepared in diameter of 10mm with various thicknesses (0.5mm, 1.0mm and 2.0mm). Color was measured according to CIELAB color scale on a reflection spectrophotometer and a color haze meter, and translucency parameter (TP) and opalescence parameter (OP) were calculated. Using the distribution graphs of transmitted light intensity on a goniophotometer, diffusion factor (DF) as an indicator for a diffuse transmission property and peak gain (G0) for a straight-line transmission property were calculated. RESULTS The TP and G0 values significantly decreased in the order: 0.5mm>1.0mm>2.0mm thickness (p<0.05). The OP value increased as the thickness of resin composite increased from 1.0mm to 2.0mm (p<0.05), while was similar for the 0.5mm- and 1.0mm-thick groups. The DF value increased from 0.5mm to 1.0mm, but was similar for the 1.0mm- and 2.0mm-thick groups. There was a significant correlation between TP and DF (R(2)=0.96, p<0.001). On the other hand, there was a weak correlation between OP and DF (R(2)=0.21, p<0.005), however within the values of the 0.5mm-thick group, OP was highly correlated with DF (R(2)=0.84, p<0.001). SIGNIFICANCE At the 0.5mm thickness, the translucency (TP) and opalescence (OP) of resin composites had a significant correlation with a diffuse transmission property (DF). When more than 1.0mm thickness of resin composites, translucency and opalescence were influenced by the thickness, in which translucency significantly decreased and opalescence significantly increased.

Pulpal responses to bacterial contamination following dentin bridging beneath hard-setting calcium hydroxide and self-etching adhesive resin system.

To evaluate the pulp healing to bacterial contamination beneath a hard-setting calcium hydroxide (DY: Dycal, L.D. Caulk Co.) and a self-etching adhesive resin (2V: Clearfil Liner Bond 2V, Kuraray Medical Inc.) following dentin bridge formation. Class V cavities were prepared on 30 monkey teeth, and the pulps were exposed with a carbide bur through the cavity floor. Each exposed pulp was capped with either DY or 2V. The cavities were restored with a hybrid resin composite. The resin composite was removed at 180 days after capping, and then cavities were left open to the oral environment for 2 weeks to obtain bacteria contamination DY (BDY) and 2V (B2V; n = 10). A non-bacterial-contaminated group capped with DY was used as control. After bacterial challenges, inflammatory cell infiltration, incidence and differentiation of dentin bridges were evaluated histologically. There were significant differences in the presence of inflammatory cell infiltration among all groups (P < 0.05). No moderate or severe inflammatory reaction was found in Group DY. Group BDY showed moderate or severe inflammatory cell infiltration in 50%, and showed four necrotic specimens. Although no statistically significant difference was found in the formation and differentiation of dentin bridges among all groups, tunnel defects in dentin bridges were detected in 70% (DY), 80% (BDY), and 50% (B2V). Group B2V showed a significantly lower presence of inflammatory cell infiltration than Group BDY (P < 0.05). Bonding agent is supposed to seal the exposure site, and the remaining bonding agent on the cavities was effective as the barrier in the dentin bridges after bacterial challenges.

Internal coating of zirconia restoration with silica-based ceramic improves bonding of resin cement to dental zirconia ceramic

Resin bonding to zirconia ceramic cannot be established by standard methods that are utilized for conventional silica-based dental ceramics. This study was aimed to examine the tensile bond strength of resin cement to zirconia ceramic using a new laboratory technique. Sixty-four zirconia ceramic specimens were air-abraded using Al2O3 particles and divided into two groups; the control group with no pretreatment (Control), and the group pretreated using the internal coating technique (INT), in which the surface of the zirconia specimens were thinly coated by fusing silica-based ceramic and air-abraded in the same manner. The specimens in each group were further divided into two subgroups according to the silane coupling agents applied; a mixture of dentin primer/silane coupling agent (Clearfil SE Bond Primer/Porcelain Bond Activator) or a newly developed single-component silane coupling agent (Clearfil Ceramic Primer). After bonding with dual-cured resin cement (Panavia F 2.0), they were stored in water for 24 h and half of them were additionally subjected to thermal cycling. The tensile bond strengths were tested using a universal testing machine. ANOVAs revealed significant influence of ceramic surface pretreatment (p<0.001), silane coupling agent (p<0.001) and thermal cycling (p<0.001); the INT coating technique significantly increased the bond strengths of resin cement to zirconia ceramic, whereas thermal cycling significantly decreased the bond strengths. The use of a single-component silane coupling agent demonstrated significantly higher bond strengths than that of a mixture of dentin primer/silane coupling agent. The internal coating of zirconia dental restorations with silica-based ceramic followed by silanization may be indicated in order to achieve better bonding for the clinical success.

Gum Containing Calcium Fluoride Reinforces Enamel Subsurface Lesions in situ

The aim of this study was to assess the effect of chewing gum containing phosphoryl oligosaccharides of calcium (POs-Ca) and a low concentration of fluoride (F) on the hardness of enamel subsurface lesions, utilizing a double-blind, randomized, and controlled in situ model. Fifteen individuals wore removable lingual appliances with 3 bovine-enamel insets containing subsurface demineralized lesions. Three times a day for 14 days, they chewed one of the 3 chewing gums (placebo, POs-Ca, POs-Ca+F). After the treatment period, cross-sectional mineral content, nanoindentation hardness, and fluoride ion mapping by time-of-flight secondary ion mass spectrometry (TOF-SIMS) were evaluated. Although there were no statistical differences in overall mineral content and hardness recovery rates between POs-Ca and POs-Ca+F subsurface lesions (p > 0.05), nanoindentation at 1-μm distance increments from the surface showed statistical differences in hardness recovery rate between POs-Ca and POs-Ca+F in the superficial 20-μm region (p < 0.05). Fluoride mapping revealed distribution of the ion up to 20 μm from the surface in the POs-Ca+F group. Nanoindentation and TOF-SIMS results highlighted the benefits of bioavailability of fluoride ion on reinforcement of the superficial zone of subsurface lesions in situ (NCT01377493).

In vitro evaluation of dentinal hydraulic conductance and tubule sealing by a novel calcium–phosphate desensitizer†

In the current trend of materials used for dentin hypersensitivity treatment, calcium-phosphate-containing desensitizers are expected to have advantages in oral environment. A newly formulated desensitizer containing tetracalcium phosphate and dicalcium phosphate anhydrous (CPD-100) was evaluated in comparison to oxalate containing desensitizer (SS) regarding permeability reduction (PR%) by measuring hydraulic conductance on the etched dentin discs in vitro. CPD-100 exhibited mean PR% of 91%, which significantly increased to 98% after immersion in artificial saliva (AS) for 4 weeks (p < 0.001), while SS showed a significant decrease from 99% to 93% (p < 0.01). SEM observation showed newly formed crystallites on CPD-100 treated dentin, which did not exist in SS treated dentin after AS immersion, suggesting that calcium oxalate inhibited formation of new calcium-phosphate minerals. Five-minute acid challenge did not significantly affect PR% of dentin treated by any of the desensitizers. The energy dispersive X-ray spectroscopy (EDS) analysis indicated that the formed layer of CPD-100 were minerals with similar Ca/P ratio to hydroxyapatite. In conclusion, the newly developed calcium-phosphate desensitizer has the potential to exhibit long-term stability in the oral environment, owing to its chemical properties that promote the crystal growth in salivary fluid.

Effects of a chewing gum containing phosphoryl oligosaccharides of calcium (POs-Ca) and fluoride on remineralization and crystallization of enamel subsurface lesions in situ

OBJECTIVES Manufacturers are adding fluoride (F) to calcium-containing chewing gums to further promote enamel remineralization. The aim of this study was to assess the effect of a chewing gum containing phosphoryl oligosaccharides of calcium (POs-Ca) and fluoride on remineralization of enamel subsurface lesions, in a double-blind, randomized controlled in situ trial. METHODS Thirty-six volunteer subjects wore removable buccal appliances with three different insets of bovine enamel with subsurface demineralized lesions. For 14 days the subjects chewed one of the three chewing gums (placebo, POs-Ca, POs-Ca+F), three times a day. After each treatment period, the insets were removed from the appliance, embedded, sectioned, polished and then subjected to laboratory tests; mineral level was determined by transverse microradiography (TMR; n=36), and hydroxyapatite (HAp) crystallites were assessed by synchrotron radiation wide-angle X-ray diffraction (WAXRD; n=13). Data were analysed by t-test or Wilcoxon rank-sum test with Bonferroni corrections at 0.05 significance level. RESULTS Chewing POs-Ca and POs-Ca+F gums resulted in 21.9±10.6 and 26.3±9.4 (mean±SD) percentage mineral recovery, which was significantly higher than that of placebo gum (15.0±11.4) (p<0.05). Chewing POs-Ca+F gum resulted in 24.9±5.4 (mean±SD) percentage HAp crystallites recovery, which was significantly higher compared to POs-Ca (16.0±4.1%) or placebo (11.1±4.8%) gums (p<0.05). CONCLUSIONS Addition of POs-Ca to the chewing gum resulted in significant remineralization of enamel subsurface lesions. Although POs-Ca+F gum was not superior in TMR recovery rate when compared with POs-Ca gum, WAXRD results highlighted the importance of fluoride ion bioavailability in the formation of HAp crystallites in enamel subsurface lesions in situ (NCT01377493).

The role of MDP in a bonding resin of a two-step self-etching adhesive system.

The purpose of this study was to evaluate the role of 10-methacryloyloxydecyl dihydrogen phosphate (MDP) contained in the bonding resin of a two-step self-etch adhesive system. An experimental adhesive (M0) containing MDP only in the primer, but not in the bonding resin was prepared. Clearfil SE Bond (MM) and M0 were compared in terms of microtensile bond strength to dentin, ultimate tensile strength of the bonding resin, and dentin-resin bonding interface morphology under SEM and TEM. The immediate µTBS values of MM significantly decreased after thermal cycles while M0 were stable even after 10,000 cycles. In the SEM observations, formation of erosion was observed beneath the acid-base resistant zone only in M0. The results suggested that MDP in the bonding resin of the two-step self-etching system; 1) improved the immediate bond strength, but caused reduction in long-term bond durability; 2) offered the advantages of acid-base resistance at the ABRZ forefront area.