Thebehaviorofwater-solublephotoinitiatorswithcrownethersindentaladhesivesisunknown.Thisstudyinvestigatedthe effectofsodiumacylphosphineoxide(APO-Na)withcrownetherinahydrophobicadhesiveonadhesiontoteeth.Sodium 2,4,6-trimethylbenzoyl-phenylphosphine oxide (TMPO-Na = APO-Na) was synthesized in 67.1% yield and identified by 1 H NMR. APO-Na was dissolved in hydrophobic resins in the presence of a crown ether (ionophore effect). Thirty kinds of experimentalsingle-stepadhesivescomprisingAPO-Na,CE,Bis-GMA,6-methacryloyloxyhexylphosphonoacetate(6-MHPA), and4-methacryloyloxyethyltrimelliticacid(4-MET)weretherebyprepared.Shearbondstrengthtounetchedgroundteeth wasmeasuredatacrossheadspeedof1.0mm/min,andthedatawereanalyzedbyANOVA.Theshearbondstrengthresults 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).Higherbondstrengthvalues[forenamel:BR24at19.3(3.2)MPa;fordentin:BR29at20.2(4.7)MPa]wereachieved 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 posedbycrownethers,thesearchisstillonforreagentsthatarebiologicallysaferthancrownethers-butwithionophor effects-tobeusedindentaladhesives.
In dentistry, a wide range of materials is available for restorative treatment; a typical product of such restorative materials mainly consists of radically polymerizable monomer(s) and inorganic filler(s) (for added physical strength), as well as a surface modifier (e.g. silane coupling agent) for improved affinity between monomer and filler. It is favorable to use an optimal surface modifier depending on the respective restorative materials. However, commercially available surface modifiers, which are synthesized by the ton, are not always suited for what is required for properties of the many different dental restorative materials. As a potential solution to such a problem, we focused on the latest technology, "micro flow reactors" that enabled an on-demand low-volume synthesis of many types of surface modifiers. Using micro reaction fields of such flow reactors, we synthesized a novel long-chain silane coupling agent. Compared to the control system synthesized using a conventional reaction flask, the novel system enabled significant reduction in reaction time without inducing any major side reactions. A dental composite resin that was treated with the novel coupling agent exhibited higher toughness, suggesting that such a silane coupling agent was an effective surface modifier.
It was tried to microencapsulate erythritol as a phase change material with the interfacial polycondensation reaction method by using the (W/O) emulsion and to characterize the microcapsules prepared. In the experiment, toluene diisocyanate, diphenyl methane diisocyanate and hexamethylenediisocyanate were used to form the polyurethane shell and the effects of them on the heat storage density and the microencapsulation efficiency were investigated. Furthermore, the effect of supercooling prevention agent on the phase change behavior of erythritol was investigated. The microcapsules prepared with toluendiisocyanate monomer showed the highest heat storage density and the higher microencapsulation efficiency. Considerable supercooling phenomenon in the microcapsule was observed and prevented to a certain degree by addition of potassium dihydrogen phosphate and calcium sulfate as the supercooling prevention agent.
It was tried to prepare hybrid microcapsules composed of porous inorganic particles and epoxy resin shell and to apply to the self-healing agent. A water soluble imidazole of gelation promoting agent as the core material was microencapsulated in the porous inorganic particles, which were coated with epoxy resin. The porous inorganic particles were prepared with the interfacial reaction between sodium silicate and calcium ion in the (W/O) dispersion. In the experiment, the concentration of sodium silicate and the mixing speed to form the (W/O) dispersion were mainly changed. The porous inorganic particles were immersed in the aqueous solution dissolving imidazole and then, added in the corn oil dissolving epoxy resin to be microencapsulated with gelated epoxy resin. The hybrid microcapsules containing imidazole with the mean diameters from 200 to 400 μm were able to be prepared and to induce the gelation reaction of epoxy resin by breaking the hybrid microcapsule shell due to heating.
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 μm diameter. Adhesive-MC (comprising the synthesized microcapsules) and Adhesive-BR (comprising bare BPO and bare TMBA) were prepared and stored at 5℃, 23℃, and 40℃ 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℃, 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).
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