This paper reviews our recent studies on fluoride-releasing adhesives and the related studies in this field based on information from original research papers, reviews, and patent literatures. A revolutionary PRG (pre-reacted glass ionomer) filler technology—where fillers were prepared by the acid-base reaction of a fluoroaluminosilicate glass with polyalkenoic acid in water, was newly developed, and a new category as “Giomer” was introduced into the market. On fluoride release capability, SIMS examination revealed in vitro fluoride ion uptake by dentin substrate from the PRG fillers in dental adhesive. On bonding durability, it was found that the improved durability of resin-dentin bonds might be achieved not only via the strengthened dentin due to fluoride ion uptake from the PRG-Ca fillers, but also due to retention of relatively insoluble 4-AETCa formed around remnant apatite crystallites within the hybrid layer in 4-AET-containing self-etching adhesives. On ultramorphological study of the resin-dentin interface, TEM images of the PRG-Ca fillers revealed that the dehydrated hydrogel was barely distinguishable from normal glass fillers, if not for the concurrent presence of remnant, incompletely reacted glass cores. In conclusion, it was expected that uptake of fluoride ions with cariostatic effect from PRG-Ca fillers would endow dentin substrates with the benefit of secondary caries prevention, together with an effective and durable adhesion to dentin.

View full abstract

To improve the bioactivity of titanium surfaces, glow discharge was used to facilitate collagen grafting on titanium disks. Titanium test specimens were pre-treated by glow discharge fed with a mixture of argon and allylamine (AA) gases. Treated titanium disks were then grafted with type I collagen using glutaraldehyde (GA) as a crosslinking agent. The surfaces of collagen-grafted titanium disks were evaluated using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). MG-63 osteoblast-like cells were cultured on the grafted titanium surfaces to examine the effect of collagen grafting in terms of cell morphology. Our results demonstrated that collagen component elements could be detected on the titanium surfaces. Morphology of the cells on the surfaces of collagen-grafted titanium disks indicated differentiation. These findings showed that type I collagen could be successfully grafted onto titanium surfaces using glow discharge technology, with enhanced biofunctionality demonstrated on osteoblastic cells.

View full abstract

The present study aimed to investigate the effects of SiO₂ polymorphism on the mechanical properties of feldspathic porcelains. Seven kinds of experimental feldspathic porcelains were prepared using chemical reagents; three types of low-fusing feldspathic glasses and four types of two-phase porcelains by adding 10 or 20 mass% of fused silica (T-F) or cristobalite (T-C). Flexural strength and fracture toughness of these porcelains were evaluated. Flexural strengths of two-phase porcelains did not show any significant increase when compared with those of single-phase glasses. On the other hand, fracture toughnesses of porcelains with cristobalite showed a significant increase when compared with those of single-phase glasses. Circumferential cracks were observed in the porcelains with cristobalite. These results suggested that cristobalite could strengthen fracture toughness of feldspathic porcelains, but not flexural strength.

View full abstract

From a selection of four kinds of post and core systems, including a fiber post and composite resin core, the purpose of this study was to determine the most effective system for the restoration of endodontically treated teeth with 0 mm of coronal tooth structure. For experimental abutment teeth, typical human maxillary central incisor teeth were modeled using bovine mandibular incisor teeth. By means of a static loading test, the four restoration systems were evaluated and compared in terms of failure load and failure mode. Further, by means of a cyclic loading test, these systems were assessed in terms of durability.
For fiber post and composite resin core, it excelled from the standpoints of failure load and failure mode, and fared favorably too in durability after cyclic loading test. For composite resin post-and-core, it also showed excellent results for both failure load and failure mode in static loading test, but durability significantly decreased with cyclic loading. Taken together, the fiber post and composite resin core was found to be most effective from the standpoints of failure load, failure mode, and durability.

View full abstract

The aim of this in vitro study was to evaluate the effects of different preparation designs on the fracture resistance of single-crown zirconia frameworks. To this end, maxillary molar dies of CrCo alloy were fabricated with five different preparation designs: shoulderless, slight and pronounced deep chamfer, beveled and non-beveled shoulder. Ten zirconia copings with a wall thickness of 0.4 mm were fabricated for each type of preparation. After cementation by glass ionomer cement, they were loaded until fracture.
There were significant differences in the breaking load of the experimental groups (ANOVA, p<0.01). The shoulder preparation had a mean breaking load of 2286 N, the shoulderless preparation 2041 N, the beveled shoulder 1722 N, the pronounced deep chamfer 1752 N, and the slight chamfer 1624 N.
Based on the results of this study, a shoulder preparation is highly recommended whenever possible. Moreover, for endodontically treated teeth that are structurally compromised or which have anatomically limited areas, the slight chamfer preparation is an optimal recommendation.

View full abstract

Previously, we developed a poly(lactide-co-glycolide)/nano-hydroxyapatite (PLGA/HA) composite that overcame the limitations of conventional ceramic bone substitutes. This was achieved by introducing a bone-like apatite layer on the composite to further enhance its osteogenic potential. In this study, we compared the osteogenic potential of the apatite-coated PLGA/HA particulates to that of Bio-Oss^®, a deproteinized bovine bone material. A mixture of fibrin gel and either apatite-coated PLGA/HA particulates or Bio-Oss^® was implanted into critical-size rat calvarial defects. As a control, fibrin gel was implanted alone into the defects. At eight weeks after treatment, histological examination showed new bone formation around the grafting materials, and bone formation was similar between the two groups. In the control group, bone was not regenerated and the defects were filled with fibrous tissues. This study showed that a synthetic bone graft material, apatite-coated PLGA/HA particulates, had a comparable bone regeneration potential to the bovine-derived bone graft material, Bio-Oss^®.

View full abstract

The aim of this study was to evaluate the influence of different polymerization modes on degree of conversion and micropush-out bond strength of dual-polymerized resin core systems to dentin by using two different adhesive systems. Two resin core systems, Rebilda DC and Build-It FR, were used in combination with total-etch (Adper Scotchbond Multi-Purpose) and self-etch (Clearfil SE Bond) adhesive systems. After treatment of dentin surfaces, resin core systems were applied into the cavities and subjected to different polymerization modes as follows: (1) chemical polymerization; (2) dual polymerization with standard mode of LED (Elipar FreeLight 2 LED); or (3) dual polymerization with exponential mode of LED. The cavities (n=10 per group) were tested in a universal testing machine. Degree of monomer conversion (DC%) was determined by Fourier transform infrared spectroscopy (n=5 cavities per group). ANOVA revealed that resin core (p=0.002), adhesive system (p<0.001), and polymerization mode (p<0.001) had significant effects on bond strength values. The degree of conversion for resin cores decreased significantly (p<0.001) when only chemical polymerization was employed.

View full abstract

This study determined the bond strengths to Er:YAG laser-irradiated and non-irradiated bovine enamel of three one-step self-etch adhesives (AQ Bond Plus (AQP), G-Bond (GB), and Clearfil Tri-S Bond (TS)) and one two-step self-etch adhesive (Clearfil Megabond (MB)). Eighty SiC paper-ground bovine enamel surfaces were used, of which half were laser-irradiated. The enamel surfaces were bonded to a resin composite with each adhesive, and tensile bond strengths were determined after 24 hours. For non-irradiated enamel groups, MB achieved greater bond strength to enamel than GB and TS (p<0.05), but no significant difference was found between MB and AQP (p>0.05). For laser-irradiated enamel groups, no significant differences were found among the four adhesives (p>0.05). Additionally, for each adhesive, no significant differences were found between laser-irradiated and non-irradiated enamel. It was thus concluded that Er: YAG laser irradiation of enamel did not affect the tensile bond strength of one-step and two-step self-etch adhesives.

View full abstract

This study sought to assess the efficacy of two self-etching primer systems (Transbond Plus and Beauty Ortho Bond) on orthodontic brackets. Therefore, shear bond strengths and bracket-adhesive failure modes (ARI scores) were determined and compared against an etch-and-rinse adhesive system (Transbond XT) under two experimental conditions (dry and saliva application). Shear bond strength test was performed at a crosshead speed of 0.5 mm/min, while enamel surfaces and enamel-adhesive interfaces were examined with SEM. There were no significant differences between Transbond XT (9.15 MPa) and Transbond Plus (9.74 MPa) under the dry condition, whereas that of Beauty Ortho Bond (6.47 MPa) was significantly lower than these two systems. Under SEM examination, both self-etching primers showed a milder etching effect and decreased depth of resin penetration into intact enamel than Transbond XT. In conclusion, results of this study showed that both self-etching systems seemed to offer more merits than conventional acid etching because of fewer irreversible changes to enamel.

View full abstract

The purpose of this study was to evaluate the effect of resin coating on the microtensile bond strength (MTBS) of indirect composite cores to pulpal floor dentin. Thirty extracted human molars with root canal fillings were used. After post space preparation, dentin surface was coated with either Clearfil SE Bond (SE) or SE with Clearfil Flow FX (SE+FX) for the resin-coated groups, while dentin was treated with ED Primer II (ED) for the non-coated group. Indirect composite cores were cemented with either Panavia F2.0 (PA) or Clearfil DC Core Automix (DC). After 24-hour storage, MTBSs were measured at a crosshead speed of 1 mm/min. Two-way ANOVA indicated that the MTBSs of resin-coated groups were significantly higher than those of the non-coated groups. In particular, the SE+FX/DC group exhibited the highest MTBS. It was thus concluded that resin coating enhanced the dentin bond strength of indirect composite cores to pulpal floor dentin.

View full abstract

Two types of tetragonal zirconia polycrystals (TZP), a ceria-stabilized TZP/Al₂O₃ nanocomposite (CZA) and a conventional yttria-stabilized TZP (Y-TZP), were sandblasted with 70-μm alumina and 125-μm SiC powders, then partially annealed at 500—1200°C for five minutes. Monoclinic ZrO₂ content was determined by X-ray diffractometry and Raman spectroscopy. Biaxial flexure test was conducted on the specimens before and after the treatments. Monoclinic ZrO₂ content and biaxial flexure strength increased after sandblasting, but decreased after heat treatment. However, in both cases, the strength of CZA was higher than that of Y-TZP. Raman spectroscopy showed that a compressive stress field was introduced on the sample surface after sandblasting. It was concluded that sandblasting induced tetragonal-to-monoclinic phase transformation and that the volume expansion associated with such a phase transformation gave rise to an increase in compressive stress on the surface of CZA. With the occurrence of such a strengthening mechanism in the microstructure, it was concluded that CZA was more susceptible to stress-induced transformation than Y-TZP.

View full abstract

The purpose of this study was to evaluate the effects of acid-etched titanium on the biological responses of osteoblast-like MC3T3-E1 cells. Four types of treatments (polishing, sandblasting, concentrated H₂SO₄ etching, and concentrated H₂SO₄ etching with vacuum firing) were carried out on the surfaces of commercially pure titanium (cpTi) disks. MC3T3-E1 cells were then cultured on the treated cpTi surfaces. Through surface roughness measurement and SEM analysis, it was found that the acid-etched surfaces showed higher roughness values than the sandblasted ones. Scanning electron microscope analysis showed that the cells on the disks treated with acid-etching and acid-etching with vacuum firing spread as well as the sandblasted ones. There were no significant differences in cell proliferation and collagen production on cpTi among the four different surface treatments. Based on the results of this study, it was concluded that etching with concentrated sulfuric acid was a simple and effective way to roughen the surface of titanium without compromising its biocompatibility.

View full abstract

This study evaluated the accuracy of marginal and internal fit between the all-ceramic crowns manufactured by a conventional double-layer computer-aided design/computer-aided manufacturing (CAD/CAM) system and a single-layer system. Ten standardized crowns were fabricated from each of these two systems: conventional double-layer CAD/CAM system (Procera) and a single-layer system (Cerec 3D). The copings and completed crowns were seated on the abutments by a special device that facilitated uniform loading, and the marginal discrepancies were measured. Internal gaps were also measured using a low-viscosity silicone material. Marginal discrepancies of Procera copings were significantly smaller than those of Procera crowns and Cerec 3D crowns (p<0.05), but Procera crowns and Cerec 3D crowns did not differ significantly from each other (p>0.05). On internal gaps, Cerec 3D crowns showed significantly larger internal gaps than Procera copings and crowns (p<0.05). Within the limitations of this study, the single-layer system demonstrated acceptable marginal and internal fit.

View full abstract

This study examined the effects on the bond durability of resins arising from the application of adhesive agent on porcelain surface, silanated by a ceramic primer consisting of γ-methacryloxypropyltrimethoxysilane (γ-MPTS), by comparing shear bond strengths before and after thermocycling.
When an adhesive agent was applied to a porcelain surface which had been silanated by a ceramic primer for 10 seconds, a significant reduction in resin bonding durability was observed. Extending the silanating period of the ceramic primer to 60 minutes resulted in an increase in resin bonding durability to the porcelain surface. However, the effect on resin bonding durability resulting from the application of adhesive agent was nearly the same as that without adhesive agent application, even though the porcelain surface was silanated for 60 minutes. In other words, positive effects arising from adhesive agent application on resin bonding durability were not observed.

View full abstract

The present study examined the effects on dentin ablation efficiency arising from various pulse durations of Er: YAG laser at a fixed energy fluence. Ten flat human dentin disks were prepared and exposed to an Er: YAG laser at 1 pps for three seconds at pulse durations of 100—500 μsec with 150 mJ/pulse (40.0 J/cm²•pulse). The depth and diameter of the ablated dentin were measured and the ablation volume was estimated. Irradiated surfaces and cross-sections were observed using a SEM. Depth of the removed dentin increased and the diameter of the spot decreased without a change in the estimated volume at increased pulse durations. SEM observation of the irradiated surfaces revealed that there were no morphological differences when the pulse duration was changed. When the specimens were cross-sectioned, the ablated dentin had a dome shape and there was a dark layer under the irradiated surface.

View full abstract

Objective: The aim of the present study was to evaluate the clinical performance of four denture soft liners up to 12 months. Materials and methods: Thirty-three edentulous patients who experienced difficulties when using hard denture bases because of changes in denture-supporting tissues were accepted for the study and randomly received Molloplast B, GC Reline Soft, Silagum Comfort, or Mollosil Plus relines. Performance of the materials was evaluated using nine criteria at 3, 6, and 12 months: physical integrity, surface detail, adhesion, color, odor, plaque accumulation, resilience, hygiene, and mucosal condition. A four-point categorized scale (1=poor, 2=fair, 3=good, 4=excellent) was used. Unscheduled maintenance events and the presence of fungal colonization were also recorded. Results: The percentage of patients available at 3, 6, and 12 months were 91%, 91%, and 66%. Main reasons for dropouts and discontinuation were fractured dentures and patient dissatisfaction. At 6 months, 96% of the performance scores were good or excellent and the largest changes were observed for physical integrity, surface detail, color, and fungal colonization. Fungal colonization was the most commonly observed problem and was the only reason of failure at 12 months. Conclusions: The clinical performance of all soft liners was slightly impaired over the 12-month observation. Except for cases showing extensive fungal colonization, the observed changes in clinical performance did not necessitate remaking of the dentures. Mollosil Plus showed a performance comparable to that of Molloplast B, and the other materials had slightly lower performance especially in terms of fungal colonization.

View full abstract

Aim of the investigation was to assess the effect of different surface treatments on the bond strength of veneering ceramics to zirconia.
In a shear test, the influences of polishing, sandblasting, and silica-coating of the zirconia surface on bonding were assessed with five different veneering ceramics. In addition the effect of liner application was examined. With one veneering ceramic, the impact of regeneration firing of zirconia was also evaluated. Statistical analysis was performed with one-way ANOVA and post hoc Scheffé' test.
Failure in every case occurred in the veneering ceramic adjacent to the interface with a thin layer of ceramic remaining on the zirconia surface, indicating that bond strength was higher than the cohesive strength of the veneering ceramic. Shear strength ranged from 23.5±3.4MPa to 33.0±6.8MPa without explicit correlation to the respective surface treatment. Regeneration firing significantly decreased the shear strength of both polished and sandblasted surfaces.
Findings of this study revealed that bonding between veneering ceramics and zirconia might be based on chemical bonds. On this note, sandblasting was not a necessary surface pretreatment to enhance bond strength and that regeneration firing was not recommended.

View full abstract

The purpose of this study was to evaluate the morphological changes of the surfaces of flowable resins eroded by orange juice and alcohol drinks. The tested products were Beautifil Flow BF02 and BF10, Clearfil Majesty LV, Filtek^TM Supreme XT Flowable Restorative, Unifil LoFlo Plus and Filtek^TM Supreme. Filler percentages of flowable resins were calculated after the latter were incinerated at 750°C. Specimens were shaped into a disk form with a diameter of 10 mm and a thickness of 1 mm. Morphological changes were evaluated for the following types of flowable resin surfaces: polished surface, surfaces eroded by 100% orange juice, wine and whisky. Filler percentages of the tested flowable resins ranged between 42 and 78%. Surface degradation was observed for the specimens immersed in acidic and alcoholic drinks, and it was thought that the lower the filler percentage, the greater was the surface degradation. Decomposition of the matrix resin and fallout of the fillers were observed in flowable resins that eroded with acidic and alcoholic drinks.

View full abstract

The purpose of this study was to compare the temperature rise under normal and caries-affected primary tooth dentin during photopolymerization of two adhesives and resin-containing restorative materials.
Caries-affected and normal dentin disks were prepared from extracted primary molars with only mesial or distal approximal caries (4 mm in diameter, 1 mm in height). Temperature rise during photopolymerization of adhesive materials was measured with a J-type thermocouple wire that was connected to a data logger. Data were analyzed with two-way ANOVA and independent samples t-test.
Temperature rise under caries-affected primary tooth dentin disks was higher than that of normal primary tooth dentin disks during polymerization of both adhesive systems and resin-containing dental materials (p<0.05). It was found that adhesive systems induced a higher temperature rise during polymerization as compared to the resin-containing restorative materials (p<0.05). In particular, temperature rise during polymerization of adhesive materials exceeded 5.5°C under caries-affected primary tooth dentin.

View full abstract

The two-fold aims of this study were: (1) to evaluate the microtensile bond strengths of different adhesive systems to sclerotic and sound palatal dentin; and (2) to observe the respective resin-dentin interfaces. Thirty extracted human incisor teeth were divided into two groups. Group I comprised sclerotic defects in the palatal zone. Group II comprised sound palatal dentin surfaces as control. Each group (n=15) was divided into three subgroups according to dentin adhesive systems: self-etch (Clearfil SE Bond), total-etch (Scotchbond Multi-Purpose Plus), and glass ionomer (Reactmer Bond) adhesive systems. The specimens were subjected to tensile forces. Obtained data were analyzed by two-way ANOVA and post hoc Duncan's test. Fracture sites and resin-dentin interfaces were observed using a light microscope and SEM. With sound dentin, Clearfil SE Bond showed a significantly higher bond strength than the other adhesives (p<0.05). With sclerotic dentin, although there were no significant differences in bond strength among the adhesives groups (p>0.05), the bond strength values of Clearfil SE Bond and Scotchbond Multi-Purpose Plus were significantly decreased. On resin-dentin interface observation, different images were presented by different bonding systems.

View full abstract