Effect of 2-hydroxyethyl methacrylate pre-treatment on micro-tensile bond strength of resin composite to demineralized dentin.

The purpose of this study was to evaluate the effect of 2-hydroxyethyl methacrylate (HEMA) application on the micro-tensile bond strength of resin composite to demineralized dentin. Artificially demineralized lesions were formed on bovine dentin surfaces and treated with 10, 30, 50, 70 and 100 wt% HEMA aqueous solution. The surfaces were then applied and covered with SE Bond and AP-X according to the manufacturer's instruction. After immersion in 37 degrees C water for 24 h, bond strength were measured using a universal testing machine. Bond strengths to both demineralized dentin and normal dentin, without HEMA application, were also measured. Scanning electron microscopic (SEM) observation and confocal laser scanning microscopy (CLSM) analysis at the resin-dentin interface were also performed. The bond strength data were statistically compared with anova and Scheffe's test (P < 0.05). Bond strength to demineralized dentin treated with over 30 wt% HEMA aqueous solution were significantly higher than that to demineralized dentin without HEMA application, but significantly lower than that to normal dentin. SEM observation revealed that the hybrid layer and resin-tags thickened and lengthened with HEMA application. In CLSM, the diffusion of adhesive primer into demineralized dentin increased with HEMA application. These results indicated that HEMA application might increase the bond strength to demineralized dentin by the enhancement of resin monomer penetration of HEMA.

Micro-tensile bond strength of self-etching primer adhesive systems to human coronal carious dentin.

The aim of this study was to evaluate the micro-tensile bond strengths of three self-etching primer adhesive systems to normal dentin (ND), caries-affected dentin (CAD) and caries-infected dentin (CID). Human extracted molars with caries were used, and flat dentin surfaces ground by 600-grit SiC paper were prepared. The surfaces were dyed using Caries-Detector solution, treated with Clearfil SE Bond, Mac-Bond II and UniFil Bond, and then covered with resin composites according to manufacturer's instructions. After immersion in 37 degrees C water for 24 h, the teeth were serially sectioned into multiple slices. Each slice was distinguished into ND, CAD and CID groups by the degree of staining, and the bond strength was measured in a universal testing machine. Scanning electron microscopic (SEM) observation was also performed. For statistical analysis, anova and Scheffe's test were used (P < 0.05). The bond strengths of the three adhesive systems to CAD and CID were significantly lower than those to ND. There was significant difference in the bond strength to ND between Clearfil SE Bond and UniFil Bond, but no significant differences to CAD and CID among the three adhesive systems. On SEM, the hybrid layers in CAD and CID showed more porous structures compared with ND. The results indicated that the bond strengths to CAD and CID were not affected by a variety of self-etching primer adhesive systems because of the porous hybrid layer formation in carious dentin.

Effect of fluoride-releasing adhesive system on decalcified dentin.

The aim of this study was to evaluate the effect of fluoride-releasing adhesive systems on human decalcified dentin in vitro. Two fluoride-releasing adhesive systems, Reactmer bond (RB, Shofu) and ABF (AF, Kuraray), an experimental system, and a commercial adhesive system without fluoride release, SE bond (SE, Kuraray), were used in this study. The amount of fluoride release from adhesive in deionized water was measured every week for 10 weeks. Class V cavities were prepared on extracted human pre-molars and decalcified dentin was promoted by using a bacterial caries induction system at the cavity floor. The cavities preserving decalcified dentin were restored with resin composite (AP-X, Kuraray) after treatment by each adhesive system. The specimens without treatment by adhesive system and restoration were used for control. The specimens with restoration were then incubated for 4 weeks at 37 degrees C, 100% humidity. Microradiographs of the specimens showed that the radiopacities of the decalcified dentin layers in RB and AF groups with fluoride release were significantly higher than those in SE or control groups without fluoride release. This result suggested that the fluoride-releasing adhesive systems enhanced mineralization of decalcified dentin.

Regulation of fluoride ion release from Na2SiF6 contained in resin based on hydrophobic siloxane layer coating.

Regulation of fluoride release from restorative resin or sealant is beneficial to patients as it will prevent the occurrence of the secondary caries. In this study, we evaluated whether or not the formation of a hydrophobic polysiloxane layer on the surface of the fluoride compound could contribute to the regulation of fluoride release from resin. First, sodium hexafluorosilicate (Na2SiF6) powder was treated with gamma-methacryloxypropyltrimethoxysilane (gamma-MPTS) and analysed with scanning electronmicroscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR) and electron spectroscopy for chemical analysis (ESCA). Analysis revealed that a hydrophobic polysiloxane layer was formed on the surface of Na2SiF6 powder. Heat treatment commonly used during gamma-MPTS treatment was not necessary for the polysiloxane layer formation on the surface of Na2SiF6 powder. Then Na2SiF6 powder treated with gamma-MPTS was loaded in bis-GMA/TEGDMA resin, immersed in distilled water and fluoride release was measured using a fluoride electrode. We found that the rate of fluoride release was significantly lower from the resin containing Na2SiF6 powder treated with c-MPTS. We concluded, therefore, that c-MPTS treatment and the resulting hydrophobic polysiloxane layer formation are very effective for the regulation of fluoride release from resin.

Inhibition of artificial secondary caries by fluoride-releasing adhesives on root dentin.

Fluoride-releasing materials can be expected to inhibit the secondary caries. The aim;of this study was to evaluate the effect of fluoride-releasing adhesives on inhibition of secondary caries in outer and wall lesions. Two commercial fluoride-releasing adhesives, Reactmer bond (RB) and One-up bond F (OB), and a commercial adhesive without fluoride release, Mac-bond II (MB), were used prior to placement of restorative materials without fluoride release, Lite-fil II A (LF) and Estelite (EL), and a fluoride-releasing restorative material, Reactmer paste (RP). Class V cavities prepared on extracted human premolars were restored with various combinations of the materials: MB/EL, OB/EL, RB/LF and RB/RP. The restored teeth were incubated in bacterial medium containing sucrose with Streptoccus mutans for 14 days. Microradiographs of specimens showed no wall lesions in all groups and an acid-resistant layer adjacent to the restoration in the caries-like lesion. OB/EL, RB/LF and RB/RP groups showed thicker layers than the MB/EL group. The RB/RP group formed the shallowest outer lesion among all groups. These results indicate that fluoride-releasing adhesives are effective in the prevention of wall lesions but exhibit little outer lesion inhibition. Therefore, combined restoration using a fluoride-releasing adhesive and fluoride-releasing restorative material should be selected to inhibit secondary caries.

Effect of adhesives on the inhibition of secondary caries around compomer restorations.

This study evaluated the effect of adhesives on the inhibition of secondary caries around compomer restorations in vitro. Two adhesive systems with a Bis-GMA resin, Scotch bond Multi-purpose (MP) and Single Bond (SB), and one adhesive system with no Bis-GMA resin, F2000 compomer primer/adhesive (PA), were used prior to placement of the compomer (F2000), and non-fluoride releasing resin composite (Z100) was used as a control. Class V cavities prepared on extracted human premolars were restored with various combinations of materials: F2000/MP, F2000/SB, F2000/PA, Z100/MP, Z100/SB and Z100/PA. The restored teeth were incubated in bacterial medium containing sucrose with Streptococcus mutans for two weeks after storage for 14 days. On microradiographs, the radio-opaque layers adjacent to the F2000 restorations were thick and clear, while the layers in the Z100 restorations were unclear. In the F2000 restorations, the mean thickness of the radio-opaque layers in the PA group was significantly greater than that of the MP and SB groups. In fluoride-releasing measurement, F2000 coated with PA showed a significantly higher amount of fluoride release than MP and SB, and no significant difference in the amount of fluoride release from uncoated F2000. These results indicated that applying an adhesive without Bis-GMA resin to compomer restoration has no suppressive effect on the fluoride release from compomer and might be beneficial for inhibiting secondary caries in vitro.

Effects of polysiloxane coating of NaF on the release profile of fluoride ion from Bis-GMA/TEGDMA resin containing NaF.

The aim of this study was to regulate fluoride release from restorative resin containing NaF using N-(beta-aminoethyl)-gamma-aminopropylmethyldimethoxysilane (AMMS) and evaluate factors that regulate fluoride release from the resin. ESCA analysis, FT-IR measurements along with SEM observations demonstrated that a polysiloxane layer was formed on the surface of NaF treated with AMMS. Bis-GMA/TEGDMA resin containing NaF powder treated with AMMS released lower concentrations of fluoride for longer periods when compared with that containing untreated NaF. However, AMMS treatment of NaF was less effective for the regulation of fluoride released from the resin than gamma-methacryloxypropyltrimethoxysilane (gamma-MPTS) treatment, despite its higher hydrophobic polysiloxane layer formation. These findings may have been caused by the higher density of polysiloxane prepared with gamma-MPTS than that prepared with AMMS. The present findings suggested, therefore, that alkoxysilane should be chosen based not only on hydrophobicity but also the density of polysiloxane to effectively regulate fluoride release from the restorative resin containing NaF.

Inhibition of artificial secondary caries in root by fluoride-releasing restorative materials.

This investigation evaluated the fluoride-releasing properties of various fluoride-releasing restorative materials, including resin-modified glass-ionomer cements (Fuji ionomer TypeII LC, Photac-Fil Aplicap, Vitremer), compomers (Ionosit FIL, Compoglass, Dyract) and fluoride-releasing resin composites (Heliomolar radiopaque, Degufill mineral). The study also estimated the effects of those materials on the inhibition of artificial secondary caries around restorations using a bacterial caries-inducing system. The amount of fluoride released from the materials in deionized water was measured every one week for 10 weeks. Class V cavities with the gingival margin located in the root were prepared in extracted human premolars and restored with each of the materials. The restored teeth were incubated in the bacterial artificial caries chamber, and the artificial lesion created around the restoration was observed microradiographically. The resin-modified glass-ionomer cements released the largest amount of fluoride and created a thick radio-opaque zone in the artificial lesion along the restoration-dentin interface. These results indicated that the fluoride-releasing restorative materials have the potential to inhibit secondary caries formation around restorations. Resin-modified glass-ionomer cements presented a particularly strong effect, compared with compomers and fluoride-releasing resin composites.

Adhesion in vitro of oral streptococci to porcelain, composite resin cement and human enamel.

We investigated the initial adhesion in vitro of oral streptococci to porcelain inlays. Four strains of streptococci, Streptococcus mitis NCTC12261, Streptococcus oralis ATCC9811, Streptococcus sanguis ATCC10556 and Streptococcus sobrinus OMZ176, were used in this study. The disc specimens were made of porcelain, composite resin cement and human enamel. These specimens, with or without a saliva-coat, were immersed in a suspension of each streptococci strain at 37 degrees C for 1 hr, and the numbers of cells adhering to specimens were counted after staining. The saliva-coat significantly decreased the numbers of adhering cells in all strains tested (t-test, p < 0.05). The adhesion to the porcelain and resin cements could be explained by a thermodynamic approach, although the adhesion to enamel could not be explained. These results indicated the possibility that the mechanism is different in initial adhered strains of streptococci between enamel and dental restorative materials.

Release and recharge of fluoride by restorative materials.

This study investigated the release and recharge of fluoride by restorative materials. Resin-modified glass ionomers (RGIs), polyacid-modified composite resins (PMCRs) and resin composite containing fluoride were used for comparison of fluoride release. Non-fluoride-releasing resin composite was used as a control. The amounts of fluoride release from RGIs and PMCRs remarkably increased in the citrate-phosphate acid buffer compared with distilled water. The amounts of fluoride recharged in RGIs increased with the concentration of NaF solution, but those of PMCRs exposed to all concentrations of NaF solutions were less than 1.5 ppm. Neither resin composite containing fluoride and non-fluoride-releasing resin composite gave any evidence of recharge. RGIs and PMCRs affected by acid buffer solution could not recharge much fluoride even if they were immersed in the 1000 ppmF NaF solution. The results suggested that the matrix of RGIs and PMCRs functioned as a reservoir of fluoride, but the functions were lost by acid attack.