Etching Efficacy of Self-Etching Functional Monomers.

Besides chemically interacting with hard tooth tissue, acidic functional monomers of self-etch adhesives should etch the prepared tooth surface to dissolve the smear layer and to provide surface micro-retention. Although the etching efficacy of functional monomers is commonly determined in terms of pH, the pH of adhesives cannot accurately be measured. Better is to measure the hydroxyapatite (HAp)-dissolving capacity, also considering that functional monomers may form monomer-Ca salts. Here, the etching efficacy of 6 functional monomers (GPDM, phenyl-P, MTEGP, 4-META, 6-MHP and 10-MDP) was investigated. Solutions containing 15 wt% monomer, 45 wt% ethanol, and 40 wt% water were prepared. Initially, we observed enamel surfaces exposed to monomer solution by scanning electron microscopy (SEM). X-ray diffraction (XRD) was employed to detect monomer-Ca salt formation. Phenyl-P exhibited a strong etching effect, while 10-MDP-treated enamel showed substance deposition, which was identified by XRD as 10-MDP-Ca salt. To confirm these SEM/XRD findings, we determined the etching efficacy of functional monomers by measuring both the concentration of Ca released from HAp using inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and the amount of monomer-Ca salt formation using 31P magic-angle spinning (MAS) nuclear magnetic resonance (NMR). ICP-AES revealed that the highest Ca concentration was produced by phenyl-P and the lowest Ca concentration, almost equally, by 4-META and 10-MDP. Only 10-MDP formed 10-MDP-Ca salts, indicating that 10-MDP released more Ca from HAp than was measured by ICP-AES. Part of the released Ca was consumed to form 10-MDP-Ca salts. It is concluded that the repeatedly reported higher bonding effectiveness of 10-MDP-based adhesives must not only be attributed to the more intense chemical bonding of 10-MDP but also to its higher etching potential, a combination the other functional monomers investigated lack.

Novel fluoro-carbon functional monomer for dental bonding.

Among several functional monomers, 10-methacryloxydecyl dihydrogen phosphate (10-MDP) bonded most effectively to hydroxyapatite (HAp). However, more hydrolysis-resistant functional monomers are needed to improve bond durability. Here, we investigated the adhesive potential of the novel fluoro-carbon functional monomer 6-methacryloxy-2,2,3,3,4,4,5,5-octafluorohexyl dihydrogen phosphate (MF8P; Kuraray Noritake Dental Inc., Tokyo, Japan) by studying its molecular interaction with powder HAp using solid-state nuclear magnetic resonance ((1)H MAS NMR) and with dentin using x-ray diffraction (XRD) and by characterizing its interface ultrastructure at dentin using transmission electron microscopy (TEM). We further determined the dissolution rate of the MF8P_Ca salt, the hydrophobicity of MF8P, and the bond strength of an experimental MF8P-based adhesive to dentin. NMR confirmed chemical adsorption of MF8P onto HAp. XRD and TEM revealed MF8P_Ca salt formation and nano-layering at dentin. The MF8P_Ca salt was as stable as that of 10-MDP; MF8P was as hydrophobic as 10-MDP; a significantly higher bond strength was recorded for MF8P than for 10-MDP. In conclusion, MF8P chemically bonded to HAp. Despite its shorter size, MF8P possesses characteristics similar to those of 10-MDP, most likely to be associated with the strong chemical bond between fluorine and carbon. Since favorable bond strength to dentin was recorded, MF8P can be considered a good candidate functional monomer for bonding.

Flavonol-containing phosphorylated pullulan may attenuate pulp inflammation.

AIM: To find possible reagents to minimize inflammatory responses by using an established pulpitis models for the purpose of developing new pulp-capping materials, and to test the possible use of phosphorylated pullulan as a carrier for such an anti-inflammatory reagent. METHODOLOGY: Co-culturing was performed using transwell systems. Inflammatory responses were evaluated by measuring cytokines produced by the cells. The effects of two flavonoids, luteolin and quercetin, as anti-inflammatory reagents, and phosphorylated pullulan, which potentially achieves a sufficient marginal sealing to hydroxyapatite and slowly releases luteolin, as a carrier for flavonoids, were tested. RESULTS: Flavonols, particularly luteolin, dramatically attenuated inflammatory cytokine production, which was augmented by co-cultures. Luteolin was successfully enclosed by phosphorylated pullulan. Finally, it was confirmed that luteolin released from phosphorylated pullulan was effective in reducing cytokine production by co-cultures. CONCLUSIONS: Combination of phosphorylated pullulan and luteolin could be potentially used in the treatment of dental pulp inflammation.

HEMA inhibits interfacial nano-layering of the functional monomer MDP.

Previous research showed that the functional monomer 10-methacryloxydecyl dihydrogen phosphate (MDP) ionically bonds to hydroxyapatite (HAp) and forms a nano-layered structure at the interface with HAp-based substrates. Such hydrophobic nano-layering is considered to contribute to the long-term durability of the bond to tooth tissue. However, dental adhesives are complex mixtures usually containing different monomers. This study investigated the effect of the monomer 2-hydroxyethylmethacrylate (HEMA) on the chemical interaction of MDP with HAp by x-ray diffraction (XRD), nuclear magnetic resonance (NMR), and quartz crystal microbalance (QCM). We examined the chemical interaction of 5 experimental MDP solutions with increasing concentrations of HEMA. XRD revealed that addition of HEMA inhibits nano-layering at the interface, while NMR confirmed that MDP remained adsorbed onto the HAp surface. QCM confirmed this adsorption of MDP to HAp, as well as revealed that the demineralization rate of HAp by MDP was reduced by HEMA. It was concluded that even though the adsorption of MDP to HAp was not hindered, addition of HEMA inhibited interfacial nano-layering. Potential consequences with regard to bond durability necessitate further research.

Establishment of an ex vivo pulpitis model by co-culturing immortalized dental pulp cells and macrophages.

AIM: To establish an ex vivo pulpitis model by co-culturing dental pulp cells with macrophages. METHODOLOGY: As dental pulp cells, immortalized human dental pulp cells, named DP-1, were used, whilst as macrophage cell lines, the differentiated human monocytic cell line, THP-1, was used. In some experiments, primary dental pulp cells were isolated and used to confirm the results obtained in the experiments using immortalized cells. Co-culturing was performed using transwell systems. Inflammatory responses were evaluated by measuring cytokines produced by the cells. RESULTS: Co-culturing both cell types markedly up-regulated inflammatory cytokine production as compared with the cells cultured independently, suggesting that both cell types interact with each other to synergistically produce higher amounts of inflammatory cytokines. Interestingly, both DP-1 and primary dental pulp cells appeared to produce molecules stimulating macrophages to produce tumour necrosis factor-α-. CONCLUSION: Co-culturing immortalized dental pulp cells and macrophages may be a new ex vivo model for studying the pathophysiology of reversible pulpitis.