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. Key words: Pre-reacted glass ionomer (PRG) technology, Giomer, Fluoride-releasing adhesiveReceived May 30, 2007: Accepted Nov 2, 2007 In 1955, Dr. Michael Buonocore 1) first demonstrated the bonding of acrylic resin to etched enamel. This success has since opened a new vista in the field of adhesive dentistry, and so-called acid-etching technique is ubiquitous in today's dental clinics. The field of adhesive dentistry has made a significant progress over the past decade. A large part of this success is attributed to the major advances in a bonding technology 2) . On dental adhesives, most of the developed products are biologically evaluated by means of in vivo histopathological studies and clinical trial investigations. INTRODUCTIONResults obtained thus far, when measured against stringent clinical demands, point to the need for further research and improvement. The ultimate goal in the design and development of dental adhesives is to render a material that is relatively easy to apply, less technique-sensitive, and which inhibits the formation of secondary caries. To achieve these targets through the development of more advanced adhesives, numerous challenges have been continuously performed by rigorous chemical-approach studies with the aim of tackling research problems and speculations that are regularly encountered in the course of exploration and development. In addition, to understand the mechanism of adhesion to dental hard tissues or its degradation at the resin-dentin interface, numerous ultramorphological studies are undertaken, and made valuable ...

To develop a multipurpose dental adhesive resin, the effects of polymerization initiator systems comprising 5-monosubstituted barbituric acid (5-MSBA), aromatic sulfinate amide (ASA), and tert-butyl peroxymaleic acid (t-BPMA) with 4-acryloxyethyltrimellitic acid (4-AET) or its anhydride (4-AETA) on adhesion and curing time were investigated. Tensile bond strength values of a NiOCr alloy are affected by the inclusion of t-BPMA, and the optimum concentration of t-BPMA in a 5-MSBA-ASA-t-BPMA-type initiator system was found to be 0.5-2.0 wt %, and it was noteworthy that the correlation between the tensile bond strength and curing time on the t-BPMAconcentration showed a highly negative correlation of a benzenesulfinate morphoride (BSMo) series adhesive: r ϭ Ϫ0.957, and a p-toluenesulfinate morphoride (p-TSMo) series adhesive: r ϭ Ϫ0.949. The combination of 1-cyclohexyl-5-ethylbarbiturioc acid (CEBA) with ASA provides a high level of tensile bond strength to the NiOCr alloy, and the optimum concentration of CEBA in a CEBA-ASA-t-BPMA-type initiator and the bond strength values were found to be 0.75 wt % CEBA: 52.3 MPa (with BSMo), and 1.0 wt % CEBA: 50.9 MPa (with p-TSMo), respectively. It was suggested that 5-MSBA, ASA, and t-BPMA and their combinations provided the environment where 4-AETA exhibited good bonding performance with increasing wettability to metal without interference of a charge-transfer complex derived from a polymerization initiator system such as benzoyl peroxide (BPO)-amine.

This paper reviews our recent studies on radical photopolymerization initiators, which are used in the design of light-curing dental adhesives and resin composites, by collating information of related studies from original scientific papers, reviews, and patent literature. The photopolymerization reactivities of acylphosphine oxide (APO) and bisacylphosphine oxide (BAPO) derivatives, and D,L-camphorquinone (CQ)/tertiary amine were investigated, and no significant differences in degree of conversion (DC) were found between BAPO and CQ/amine system (p>0.05). In addition, a novel 7,7-dimethyl-2,3-dioxobicyclo[2.2.1]heptane-1-carbonyldiphenyl phosphine oxide (DOHC-DPPO=CQ-APO) was synthesized and its ultraviolet and visible (UV-VIS) spectral behavior was investigated. CQ-APO possessed two maximum absorption wavelengths (λmax) at 350-500 nm [372 nm (from APO group) and 475 nm (from CQ moiety)], and CQ-APO-containing resins exhibited good photopolymerization reactivity, excellent color tone, relaxed operation time, and high mechanical strength. It was also found that a newly synthesized, water-soluble photoinitiator (APO-Na) improved adhesion to ground dentin.

The aims of this study were to synthesize new phosphonic acid monomers, and to examine their bonding performance. Four kinds of newly designed phosphonic acid monomers were synthesized, and seven experimental composite-type adhesive resins comprising the synthesized monomers(3 wt％) , with BPO/DEPT/BPBA initiator were prepared. Tensile bond strengths of the adhesive resins to enamel and metal were measured with a universal testing machine at a crosshead speed of 1.0 mm/ min. The synthesized adhesive monomers were light yellow viscous liquids with 32.5％-49.3％ yields, and identified by 1 H NMR, IR and elemental analysis to be(meth) acryloxyalkyl 3-phosphonopropionates［R-P (＝O) (OH) 2 ］ (5-MPPP, 6-MHPP, 6-AHPP, 10-MDPP). It was found that the newly developed phosphonic acid monomers with BPO/DEPT/BPBA initiator attained strong adhesion to both unetched, ground enamel and sandblasted Ni-Cr alloy with good durability. They exhibited significantly higher bond strengths than conventional phosphorous-containing monomers such as MEPP and VBPA (p ＜0.01). These findings indicate that the experimental phosphonic acid monomer-containing adhesive resins have potential prosthodontic and orthodontic applications, especially as self-etching, non-rinsing orthodontic adhesive resins.

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The aims of this study were to investigate the photoinitiation behaviors of acylphosphine oxide (APO) and bisacylphosphine oxide (BAPO) derivatives in comparison to D,L-camphorquinone (CQ)/tertiary amine (EDAB) system. Fifty six kinds of experimental unfilled, light-cured resins were prepared using APO, BAPO, CQ, EDAB, resin monomers, and adhesive monomers. The measurements of ultraviolet-visible (UV-VIS) spectroscopy, photopolymerization with differential scanning calorimeter (photo-DSC) and degree of conversion (DC) determination were performed. Results showed that the UV-VIS spectra of all APO and BAPO derivatives possessed λmax ranging between 365 and 416 nm. Their photoinitiation behaviors were not influenced by acidic adhesive monomers formulated in unfilled Bis-GMA-based resins (p<0.05). Although BAPO exhibited higher reactivity than CQ/EDAB in unfilled 6-methacryloyloxyhexcyl phosphonoacetate (6-MHPA)/ 2-hydroxyethyl methacrylate (HEMA) and 6-MHPA/glycerol monomethacrylate (GM)-based resins, it was found that there were no statistically significant differences in DC (％) between BAPO [44.2(6.5)-51.2(4.3)] and CQ/EDAB [42.4(4.4)-47.5(3.7)] (p<0.05). It was concluded that APO and BAPO photoinitiators exhibited reactivity comparable to that of CQ/tertiary amine system.

Water is required to ionize acid resin monomers for demineralization of tooth substrates. We tested the null hypothesis that altering the water concentration in two-step self-etching primers has no effect on their aggressiveness and bonding efficacy to dentin. Five experimental self-etching primers were prepared with resin-water-ethanol volume ratios of 9-0-1, 8-1-1, 7-2-1, 5-4-1, and 3-6-1. They were applied to smear-layer-covered dentin, followed by a bonding resin and composite build-ups for microtensile bond testing and TEM examination of tracer penetration. Increasing water concentration from 0-60 vol% improved acidic monomer ionization that was manifested as increasing hybrid layer thickness. However, significantly higher bond strength was observed in the 7-2-1 group, with minimal nanoleakage in the corresponding hybrid layer. When self-etching primers are formulated, a balance must be achieved to provide sufficient water for adequate ionization of the acidic monomers, without lowering the resin concentration too much, to optimize their bonding efficacy to dentin.

Multi-purpose bonding performance of three kinds of newly synthesized phosphonic acid monomers was investigated. Methacryloxyalkyl or acryloxyalkyl phosphonoacetates of 6-MHPA, 6-AHPA, 10-MDPA were synthesized in 42.8-51.9％ yields with a light yellow viscous liquid, and identified as new compounds by 1 H NMR, IR, and elemental analysis. Conventional adhesive monomers, namely VBPA, 4-META, and 4-AETA, and CEBA-p-TSMo-t-BPMA initiator were also used. Seven experimental composite-type adhesive resins comprising these six kinds of adhesive monomers and None (control) with the initiator were prepared. Tensile bond strengths of adhesive resins to unetched ground enamel and dentin, ground porcelain, and sandblasted Ni-Cr alloy were measured at a crosshead speed of 1.0 mm/min. Results showed that except with VBPA, there were no significant differences among 6-MHPA, 6-AHPA, 10-MDPA, 4-AETA, and 4-META in bonding performance to the adherends (p<0.01). It was found that the new phosphonic acid monomers provided good multipurpose adhesion to all adherends tested.