A review of our development of dental adhesives--effects of radical polymerization initiators and adhesive monomers on adhesion.

This paper reviews the development of dental adhesives by collating information of related studies from original scientific papers, reviews, and patent literatures. Through our development, novel radical polymerization initiators, adhesive monomers, and microcapsules were synthesized, and their effects on adhesion were investigated. It was found that 5-monosubstituted barbituric acid (5-MSBA)-containing ternary initiators in conjunction with adhesive monomers contributed to effective adhesion with good polymerization reactivity. Several kinds of novel adhesive monomers bearing carboxyl group, phosphonic acid group or sulfur-containing group were synthesized, and investigated their multi-purpose bonding functions. It was suggested that the flexible methylene chain in the structure of adhesive monomers played a pivotal role in their enhanced bonding durability. It was found that the combination of acidic monomers with sulfur-containing monomer markedly improved adhesion to enamel, dentin, porcelain, alumina, zirconia, non-precious metals and precious metals. A new poly(methyl methacrylate) (PMMA)-type adhesive resin comprising microencapsulated polymerization initiators was also found to exhibit both good formulation stability and excellent adhesive property.

Synthesis of a novel camphorquinone derivative having acylphosphine oxide group, characterization by UV-VIS spectroscopy and evaluation of photopolymerization performance.

Camphorquinone (CQ) derivatives having acylphosphine oxide (APO) group are unknown. This study synthesized such a novel 7,7dimethyl-2,3-dioxobicyclo[2.2.1]heptane-1-carbonyldiphenyl phosphine oxide (DOHC-DPPO = CQ-APO). Ultraviolet and visible (UVVIS) spectra of CQ-APO, CQ, and APO were measured. Photopolymerization performances of experimental light-cured resins comprising these photoinitiators were investigated. Newly synthesized CQ-APO showed as a pale yellow crystal (mp 365K). UV-VIS spectrum of CQ-APO showed two maximum absorption wavelengths (lambda(max)) [372 nm (from APO group) and 475 nm (from CQ moiety)] within 350-500 nm. Unfilled resin containing CQ-APO exhibited good photopolymerization time (9.6 sec) and relaxed operation time (50 sec), as well as a pronouncedly lower b value (4.0) in the CIELab color specification system than that containing CQ (84.0). Resin composites containing CQ-APO, exhibited high flexural strength (114.3-133.8 MPa). It was concluded that CQ-APO possessed two lambda(max )peaks within 350-500 nm, and that CQ-APO-containing resins exhibited excellent color tone, good photopolymerization reactivity, relaxed operation time, and high mechanical strength.

Design of a new self-etching HEMA-free adhesive.

The effect of the pH value of single-bottle, self-etching 2-hydroxyethyl methacrylate (HEMA)-free adhesives on their shelf lives with bonding ability was investigated. Two experimental adhesives [SA-1 (pH=3.0); SA-2 (pH=2.1)] comprising 6-methacryloyloxyhexyl phosphonoacetate (6-MHPA), 4-acryloyloxyethyltrimellitic acid (4-AET), Bis-GMA, water, and acetone, in which the pH values were controlled with 1N NaOH, were stored for 6 weeks at 50 degrees C in air. Shear bond strengths of aged adhesives to ground and unetched enamel and dentin were measured at a crosshead speed of 1.0 mm/min, and the data were analyzed by ANOVA. The resin-tooth bonding interfaces were further observed with SEM. With SA-1, the bond strengths to the tooth substrates were maintained throughout the 6 weeks. However, with SA-2, bond strength significantly degraded from weeks 4 to 6 (p<0.05). Based on SEM observation, non-aged and 6-week-aged adhesive SA-1 appeared to be strongly adhered to both enamel and dentin. It was found that the stability of the self-etching adhesive was influenced by its pH value.

Design of a new dental adhesive--effect of a water-soluble sodium acylphosphine oxide with crown ether on adhesion to dental hard tissues.

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.

Novel, multi-purpose, PMMA-type adhesive resin with newly synthesized microcapsule of radical polymerization initiators.

The behavior of microencapsulated polymerization initiators in dental adhesives is unknown. This study investigated the effects of new microencapsulated initiators in novel, multi-purpose, PMMA-type adhesive resin on the bonding performance and polymerization reactivity. Microencapsulated BPO and 1,3,5-trimethylbarbituric acid (TMBA) with PEMA as a shell polymer were quantitatively synthesized at 97-98% yield with 30-54 microm diameter. Adhesive-MC (comprising the synthesized microcapsules) and Adhesive-BR (comprising bare BPO and bare TMBA) were prepared and stored at 5 degrees C, 23 degrees C, and 40 degrees C for two months. MMA monomer was used as a solvent for the microcapsules. At the starting period, there were no significant differences between Adhesive-MC and Adhesive-BR in shear bond strength to enamel or dentin treated with or without surface treatment agent (p<0.05); moreover, their curing times (tc=304 seconds) were almost the same. After two months' storage at 40 degrees C, Adhesive-BR degraded in bond strength and showed markedly delayed polymerization reactivity as storage period progressed. In direct contrast, it was found that Adhesive-MC still retained its capabilities for adhesion to gold alloy and initiation of radical polymerization (p<0.05).

A review of chemical-approach and ultramorphological studies on the development of fluoride-releasing dental adhesives comprising new pre-reacted glass ionomer (PRG) fillers.

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.

UV-VIS spectra and photoinitiation behaviors of acylphosphine oxide and bisacylphosphine oxide derivatives in unfilled, light-cured dental resins.

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 lambda max 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.

Multi-purpose bonding performance of newly synthesized phosphonic acid monomers.

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 1H 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.

Design of new phosphonic acid monomers for dental adhesives--synthesis of (meth) acryloxyalkyl 3-phosphonopropionates and evaluation of their adhesion-promoting functions.

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 1H 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.

Bonding mechanism and ultrastructural interfacial analysis of a single-step adhesive to dentin.

OBJECTIVES: to characterize the interaction of 4-acryloxyethyltrimellitic acid (4-AET), a key ingredient in a commercial all-in-one adhesive (Reactmer Bond) with dentin apatite, to measure the solubility of 4-AET calcium (4-AETCa), and to examine the ultrastructure of the resin-dentin interface bonded by this adhesive. METHODS: solubility of synthesized 4-AETCa in several solutions was measured. Flattened bovine dentin blocks were treated with 0.1wt% NaOCl for 10 min, or 5.0wt% NaOCl for 10 min, or 30 min. Fourier transform infrared analysis using attenuated total reflection (FT-IR/ATR) was performed on these four substrates before and after treatment with a 4-AET mixture (4-AET/HEMA: 40/60wt%). Undemineralized, unstained sections of human sound dentin that were bonded with the same comonomers were examined by transmission electron microscopy (TEM). RESULTS: the respective solubilities of the 4-AETCa in water, 2-hydroxyethyl methacrylate (HEMA; 100wt%) and HEMA/water (70/30wt%) were 0.023, 0.003 and 0.014 mol/l after 2 min. The IR analysis indicated that Ca-carboxylate (new bands: nuCz.dbnd6;O:1580 and 1413 cm(-1)) was formed on all dentin specimens following application of 4-AET, with or without NaOCl pretreatment. TEM showed a 1 micro m thick hybrid layer with some remnant apatite crystallites that were encapsulated by a layer of less electron-dense material. SIGNIFICANCE: the results suggest that ionized carboxyl groups in 4-AET may interact with Ca(2+) from apatite crystallites within the partially demineralized hybrid layer to form an insoluble calcium salt (4-AETCa) that may aid in bonding this resin system to dentin.

[Mandibular anterior alveolar osteotomy and patient with malocculusion and facial deformity after healed mandibular fracture; report of a case].

Recent advances in orthognatic surgery have been remarkable. Among the surgical procedures, sagital ramus osteotomy has been often used for mandibular protrusion. Causes of dentofacial deformities include not only congenital but also acquired ones, which are caused by trauma or resection of tumor in the maxillofacial region. In all cases, functional and psychological disorders would often occur in the patient with these dentofacial deformities. We report a favorable result of anterior alveolar osteotomy of the mandible, which was applied to a patient complaining of malocculusion and facial deformity developed from a healed fracture of the mandible treated at another hospital.

A review of the developments of multi-purpose primers and adhesives comprising novel dithiooctanoate monomers and phosphonic acid monomers.

This paper reviews the developments of dithiooctanoate monomers and acidic adhesive monomers, and their roles in multi-purpose primers and adhesives in promoting adhesion to multiple substrate materials. Novel dithiooctanoate monomers exhibited excellent bonding to precious metals and alloys when compared against conventional sulfur-containing monomers. Newly developed phosphonic acid monomers, endowed with a water-soluble nature, enabled sufficient demineralization of dental hard tissues and thus improved bonding to both ground enamel and dentin. The optimal combination for bonding to dental hard tissues and precious and non-precious metals and alloys was 5.0 wt% 10-methacryloyloxydecyl 6,8-dithiooctanoate (10-MDDT) and 1.0 wt% 6-methacryloyloxyhexyl phosphonoacetate (6-MHPA). For bonding to dental porcelain, alumina, zirconia, and gold (Au) alloy, a ternary combination of silane coupling agent, acidic adhesive monomers, and dithiooctanoate monomers seemed promising. The latest development was a single-bottle, multi-purpose, self-etching adhesive which contained only acidic adhesive monomers and dithiooctanoate monomers but which produced strong adhesion to ground enamel and dentin, sandblasted zirconia, and Au alloy.

A review of the developments of self-etching primers and adhesives -Effects of acidic adhesive monomers and polymerization initiators on bonding to ground, smear layer-covered teeth.

This paper reviews the developments of self-etching primers and adhesives, with a special focus on the effect of acidic adhesive monomers and polymerization initiators on bonding to ground, smear layer-covered teeth. Ionized acidic adhesive monomers chemically interact with tooth substrates and facilitate good bonding to ground dentin. Polymerization initiators in self-etching primers further promote effective bonding to ground dentin. To promote bonding to both dentin and enamel, phosphonic acid monomers such as 6-methacryloyloxyhexyl phosphonoacetate (6-MHPA) were developed. These novel adhesive monomers also have a water-soluble nature and are hence endowed with sufficient demineralization capability. A new single-bottle, self-etching, 2-hydroxyethyl methacrylate (HEMA)-free adhesive comprising 6-MHPA and 4-acryloyloxyethoxycarbonylphthalic acid (4-AET) was developed. This novel adhesive enabled strong adhesion to both ground enamel and dentin, but its formulation stability was influenced by pH value of the adhesive. To develop hydrolytically stable, single-bottle, self-etching adhesives, hydrolytically stable, radical-polymerizable acidic monomers with amide or ether linkages have been developed.

Synthesis of novel acryloyloxyalkyl and methacryloyloxyalkyl 6,8-dithiooctanoates and evaluation of their bonding performances to precious metals and alloys.

This study investigated the bonding effectiveness of novel acryloyloxyalkyl and methacryloyloxyalkyl 6,8-dithiooctanoates (dithiooctanoate monomers) to precious metals and alloys. Eight kinds of dithiooctanoate monomers were synthesized in 16.09-39.34% yields. They were characterized and confirmed as new compounds using (1)H- and (13)C-NMR spectroscopy and mass spectral analysis. Eight experimental primers each containing 5.0 wt% of a novel dithiooctanoate monomer in acetone were prepared. After primer treatment and 2,000 thermal cycles, tensile bond strengths of MMA-PMMA/TBBO resin to seven metal adherends were measured. Results were as follows: 17.2-29.3 MPa (Au), 41.9-49.6 MPa (Ag), 36.8-47.6 MPa (Pt), 36.7-47.5 MPa (Pd), 34.0-48.9 MPa (Au alloy), 24.3-49.6 MPa (Ag alloy), 35.0-48.8 MPa (Au-Ag-Pd alloy). 10-Methacryloyloxydecyl 6,8-dithiooctanoate exhibited the highest mean bond strength to gold (29.3 MPa) and 12-methacryloyloxydodecyl 6,8-dithiooctanoate to Au alloy (48.9 MPa). Therefore, it was found that the novel dithiooctanoate monomers synthesized in this study exhibited excellent bonding to precious metals and alloys.

Effect of the combination of dithiooctanoate monomers and acidic adhesive monomers on adhesion to precious metals, precious metal alloys and non-precious metal alloys.

This study investigated the effect of the combination of a dithiooctanoate monomer and an acidic adhesive monomer on adhesion to precious metals, precious and non-precious metal alloys. From a selection of four dithiooctanoate monomers and six acidic adhesive monomers, 14 experimental primers containing a combination of 5.0 wt% of a dithiooctanoate monomer and 1.0 wt% of an acidic adhesive monomer in acetone were prepared. Tensile bond strengths (TBSs) of MMA-PMMA/TBBO resin to nine kinds of precious metals, precious metal alloys, and non-precious metal alloys after 2,000 thermal cycles were measured. Results showed that there were no significant differences in TBS among the primers to all the precious and non-precious metal adherends tested (p>0.05). Highest TBS values (46.5-55.8 MPa) for bonding to Au alloy, Au-Ag-Pd alloy, Co-Cr alloy, and Ni-Cr alloy were achieved with the primer which contained 5.0 wt% 10-methacryloyloxydecyl 6,8-dithiooctanoate (10-MDDT) and 1.0 wt% 6-methacryloyloxyhexyl phosphonoacetate (6-MHPA). Therefore, 5.0 wt% 10-MDDT and 1.0 wt% 6-MHPA was determined as the optimal combination for bonding to precious metals, precious and non-precious metal alloys.

Effect of novel dithiooctanoate monomers, in comparison with various sulfur-containing adhesive monomers, on adhesion to precious metals and alloys.

This study investigated the effect of novel dithiooctanoate monomers, in comparison with conventional sulfur-containing monomers, on adhesion to precious metals and alloys. Nine experimental primers containing 5.0 wt% 2-methacryloyloxyethyl 6,8-dithiooctanoate (2-MEDT), 6-methacryloyloxyhexyl 6,8-dithiooctanoate (6-MHDT), 10-methacryloyloxydecyl 6,8-dithiooctanoate (10-MDDT), bis(2-methacryloyloxyethyl) disulfide (BMEDS), bis(5-methacryloyloxypentyl) disulfide (BMPDS), bis(10-methacryloyloxydecyl) disulfide (BMDDS), 6-(4-vinylbenzyl-n-propyl) amino-1,3,5-triazine-2,4-dithione (VBATDT), N-(4-mercaptophenyl)methacrylamide (MPMA), or 4-methacryloyloxyethoxycarbonylphthalic anhydride (4-META; control) were prepared. After primer pretreatment and bonding using modified MMA-PMMA/BPO-DEPT resin, tensile bond strengths to precious metals and alloys after 2,000 thermal cycles were measured. For bonding to Au or Ag, novel 2-MEDT, 6-MHDT, and 10-MDDT exhibited significantly higher tensile bond strengths than conventional BMEDS, BMPDS, BMDDS, VBATDT, MPMA, and 4-META (p<0.05). For bonding to Au alloy, Ag alloy, and Au-Ag-Pd alloy, all the novel dithiooctanoate monomers showed significantly higher tensile bond strengths than conventional BMEDS, BMPDS, VBATDT, MPMA, and 4-META (p<0.05). It was found that novel dithiooctanoate monomers exhibited excellent bonding to precious metals and alloys when compared with conventional sulfur-containing monomers.

Effects of a newly designed HEMA-free, multi-purpose, single-bottle, self-etching adhesive on bonding to dental hard tissues, zirconia-based ceramics, and gold alloy.

This study investigated the bonding effectiveness of newly designed self-etching adhesives to four types of adherends--enamel, dentin, zirconia, and gold (Au) alloy. Five experimental adhesives were prepared, which contained 3.0-5.0 wt% 6-methacryloyloxyhexyl phosphonoacetate (6-MHPA) or 6-methacryloyloxyhexyl 3-phosphonopropionate (6-MHPP), 3.0 wt% 4-acryloyloxyethoxycarbonylphthalic acid (4-AET) or 17.0 wt% 4-methacryloyloxyethoxycarbonylphthalic acid (4-MET), 0-0.5 wt% 6-methacryloyloxyhexyl 6,8-dithiooctanoate (6-MHDT) or 10-methacryloyloxydecyl 6,8-dithiooctanoate (10-MDDT), and varying contents of Bis-GMA, dimethacrylate monomers, water, acetone, and a photoinitiator system. After 2,000 times of thermal cycling, shear bond strengths (SBSs) between a resin composite (Beautifil II, Shofu Inc., Japan) and the four adherends, bonded using the experimental adhesives, were measured at 1.0 mm/min. No statistically significant differences in SBS for bonding to ground enamel, dentin, sandblasted zirconia and Au alloy (p>0.05) were found between experimental adhesives which contained 6-MHPA and/or 6-MHPP, 4-MET or 4-AET, 6-MHDT and/or 10-MDDT, Bis-GMA, and dimethacrylates. An adhesive layer of less than 5.0 µm thickness, by scanning electron microscopy observation, revealed strong adhesion to the four adherends. Therefore, the newly designed multi-purpose, self-etching adhesive strongly adhered to all the four adherend materials tested.

Development of a new single-bottle multi-purpose primer for bonding to dental porcelain, alumina, zirconia, and dental gold alloy.

This study investigated the bonding efficacy of a combined primer application which comprised a silane coupling agent, an acidic adhesive monomer, and a dithiooctanoate monomer, as well as the influence of shelf life on bonding. Five experimental primers (coded as Si-P-SS-1 to Si-P-SS-4, and Si-SS as the control) were prepared using 20.0-40.0 wt% 3-methacryloyloxypropyltriethoxysilane (3-MPTES), 0-7.44 wt% 6-methacryloyloxyhexyl phosphonoacetate (6-MHPA), and 0.50 wt% 10-methacryloyloxydecyl 6,8-dithiooctanoate (10-MDDT). After 24-hour storage at 23°C (Initial) and 2-month storage at 50°C (Aged), tensile bond strengths (TBSs) of a resin cement (ResiCem, Shofu Inc., Kyoto, Japan) to primer-treated porcelain, alumina, zirconia, and Au alloy were measured. With the Initial and Aged primers of Si-P-SS-1 to Si-P-SS-3, there were no statistically significant differences in the mean TBSs (MPa) [porcelain: 21.7-29.2; alumina: 21.4-25.3; zirconia: 20.3-24.5; and Au alloy: 23.4-27.6] among these three primers (p>0.05), but they were significantly higher than that of the control primer (p<0.05). The experimental primers Si-P-SS-1 to Si-P-SS-3 demonstrated good potential as multi-purpose primers: they had good shelf lives as single-bottle primer systems and were thus able to exhibit good bond strength to all the adherends tested after 2-month storage under accelerated aging conditions.

Design of a metal primer containing a dithiooctanoate monomer and a phosphonic acid monomer for bonding of prosthetic light-curing resin composite to gold, dental precious and non-precious metal alloys.

The effect of metal primers on adhesion of a resin composite to dental metal alloys was investigated. Experimental primers containing a dithiooctanoate monomer [10-methacryloyloxydecyl 6,8-dithiooctanoate (10-MDDT) or 6-methacryloyloxyhexyl 6,8-dithiooctanoate (6-MHDT)] and a phosphonic acid monomer [6-methacryloyloxyhexyl phosphonoacetate (6-MHPA) or 6-methacryloyloxyhexyl 3-phosphonopropionate (6-MHPP)] were prepared. After treating Au, Au alloy, Ag alloy, Au-Ag-Pd alloy, and Ni-Cr alloy with the experimental primers, their shear bond strengths (SBSs) with a prosthetic light-curing resin composite (Solidex, Shofu Inc., Japan) were measured after 1-day storage followed by 5,000 thermal cycles. The SBSs between Solidex and the primer-treated metals which were incubated in air at 50°C for 2 months were further measured. Results showed that the SBSs [mean (SD)] of all metal adherends treated with primer DT-PA-1 (5.0 wt% 10-MDDT, 1.0 wt% 6-MHPA) ranged between 31.2 (5.2) and 34.5 (5.8) MPa. The SBSs of the primer-treated metals did not degrade after 2-month incubation at 50°C. Therefore, a combined primer application consisting of a dithiooctanoate monomer and a phosphonic acid monomer provided efficacious bonding to Au as well as precious and non-precious metal alloys.

Design of a new, multi-purpose, light-curing adhesive comprising a silane coupling agent, acidic adhesive monomers and dithiooctanoate monomers for bonding to varied metal and dental ceramic materials.

A newly designed, light-curing adhesive was investigated for its bonding effectiveness to porcelain, alumina, zirconia, Au, Au alloy, Ag alloy, Au-Ag-Pd alloy, and Ni-Cr alloy. Four experimental adhesives were prepared using varying contents of the following: a silane coupling agent [3-methacryloyloxypropyltriethoxysilane (3-MPTES)], acidic adhesive monomers [6-methacryloyloxyhexyl phosphonoacetate(6-MHPA),6-methacryloyloxyhexyl3-phosphonopropionate(6-MHPP)and 4-methacryloyloxyethoxycarbonylphthalic acid (4-MET)], and dithiooctanoate monomers [6-methacryloyloxyhexyl 6,8-dithiooctanoate (6-MHDT) and 10-methacryloyloxydecyl 6,8-dithiooctanoate (10-MDDT)]. After all adherend surfaces were sandblasted and applied with an experimental adhesive, shear bond strengths (SBSs) of a light-curing resin composite (Beautifil II, Shofu Inc., Kyoto, Japan) to the adherend materials after 2,000 times of thermal cycling were measured. For the experimental adhesive which contained 3-MPTES (30.0 wt%), 6-MHPA (1.0 wt%), 6-MHPP (1.0 wt%), 4-MET (1.0 wt%), 6-MHDT (0.5 wt%) and 10-MDDT (0.5 wt%), it consistently yielded the highest SBS for all adherend surfaces in the range of 20.8 (4.8)-30.3 (7.9) MPa, with no significant differences among all the adherend materials (p>0.05). Therefore, the newly designed, multi-purpose, light-curing adhesive was able to deliver high SBS to all the adherend materials tested.