Kou Fujita

Hydrolysis of Functional Monomers in a Single-bottle Self-etching Primer—Correlation of 13C NMR and TEM Findings

Self-etching primers/adhesives that combine acidic methacrylate monomers with water in a single bottle are hydrolytically unstable and require refrigeration to extend their shelf-lives. This study tested the null hypothesis that one year of intermittent refrigeration of a 4-MET-containing simplified self-etching primer does not result in hydrolytic changes that are identifiable by transmission electron microscopy and 13C NMR spectroscopy. Human dentin was bonded with UniFil Bond immediately after being unpacked, or after one year of intermittent refrigeration at 4°C. Fresh and aged primers were analyzed by NMR for chemical changes. Ultrastructural observations indicated that there was an augmentation in etching capacity of the aged adhesive that was not accompanied by resin infiltration or effective polymerization. New NMR peaks detected from the aged ethanol-based primer confirmed that degradation occurred initially via esterification with ethanol, followed by hydrolysis of both ester groups in the 4-MET. Hydrolysis of functional methacrylate monomers occurs despite intermittent refrigeration.

Effects of particle size of silica filler on polymerization conversion in a light-curing resin composite

OBJECTIVES The effect of visible light passing through a resin composite with different particle sizes of spherical silica filler on the curing depth and Knoop hardness of the resin composite was examined. The null hypotheses tested were that the particle size of silica filler has no effect on (1) the transmitted amount of visible light passing through the resin composite, (2) the curing depth of the resin composite, and (3) the ratio of the Knoop hardness of the hardened resin composite. METHODS A series of different experimental resin composite pastes with different particle sizes of silica filler were prepared. The amount of visible light passing through each of the experimental resin pastes during the hardening process was determined. The curing depth and Knoop hardness of the resin composites were measured. Further, to characterize the polymerization conversion, the ratio of the Knoop hardness of the bottom surface against the irradiated surface of the hardened resin composites was determined. RESULTS Increases in the particle size of the silica filler resulted in decreases in the transmitted amount of visible light, curing depth, and ratio of the Knoop hardness of the resin composite. The rate of polymerization conversion of the resin composite occurring deep within the cavity was found to be less than the rate of polymerization conversion occurring at the upper surface. SIGNIFICANCE To increase the rate of polymerization conversion deep within the resin composite, it is important to reduce the particle size of the silica filler.

Effect of Reacted Acidic Monomer with Calcium on Bonding Performance

We determined the number of reacted and unreacted 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) molecules with calcium during the demineralization process of hydroxyapatite or dentin by 10-MDP-based one-step (Clearfil Tri-S Bond, TS) or two-step self-etch adhesive (Clearfil SE Bond Primer, SE). We then examined the effects of the number of reacted and/or unreacted 10-MDP molecules on the initial bond strength and bond durability of the resultant adhesive layer. The null hypotheses were that (1) the etching efficacy of tooth apatite by 10-MDP used in TS was the same as that in SE, and (2) the unreacted 10-MDP polymer included within the adhesive layer does not affect bond durability. Addition of hydroxyapatite or dentin to the TS and SE resulted in decreases in the NMR peak intensities for 10-MDP. The peak intensity for 10-MDP showed a greater reduction in SE than in TS, consistent with the observation that SE provided significantly higher initial mean bond strengths than TS. Further, the unreacted 10-MDP polymer within the adhesive layer did not decrease the mean bond strength, despite the application of 20,000x thermo-cycling.

Degradation-stage Effect of Self-etching Primer on Dentin Bond Durability

It is well-known that self-etching primers can be altered. However, the effects from altered primers on the dentin bond durability have yet to be thoroughly identified. In this study, we examined the effects from 5 altered Liquid A primers in different stages of degradation—where 2-hydroxyethylmethacrylate (HEMA) and 10-methacryloyloxydecyl dihydrogen phosphate (MDP), used in Liquid A primers, were altered by the hydrolysis of the methacryloxy ester portion in the HEMA and MDP—on the hybrid layer’s quality and dentin bond durability. The hypothesis was that degradation stages of altered Liquid A primers have no effect on the hybrid layer’s quality and on dentin bond durability. Bond strengths, obtained after thermo-cycling, were strongly dependent on the degradation stage of the altered Liquid A primer. Alterations of self-etching primers reduced dentin bond durability and decreased the created hybrid layer’s quality.

Quantitative Evaluation of MDP-Ca Salt and DCPD after Application of an MDP-based One-step Self-etching Adhesive on Enamel and Dentin.

PURPOSE To investigate the effects of an experimental 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-based one-step self-etching adhesive (EX adhesive) applied to enamel and dentin on the production of calcium salt of MDP (MDP-Ca salt) and dicalcium phosphate dehydrate (DCPD) at various periods. MATERIALS AND METHODS The EX adhesive was prepared. Bovine enamel and dentin reactants were prepared by varying the application period of the EX adhesive: 0.5, 1, 5, 30, 60 and 1440 min. Enamel and dentin reactants were analyzed using x-ray diffraction and solid-state phosphorus-31 nuclear magnetic resonance (31P NMR). Curvefitting analyses of corresponding 31P NMR spectra were performed. RESULTS Enamel and dentin developed several types of MDP-Ca salts and DCPDs with amorphous and crystalline phases throughout the application period. The predominant molecular species of MDP-Ca salt was determined as the monocalcium salt of the MDP monomer. Dentin showed a faster production rate and greater produced amounts of MDP-Ca salt than did enamel, since enamel showed a knee-point in the production rate of the MDP-Ca salt at the application period of 5 min. In contrast, enamel developed greater amounts of DCPD than did dentin and two types of DCPDs with different crystalline phases at application periods > 30 min. The amounts of MDP-Ca salt developed during the 30-s application of the EX adhesive on enamel and dentin were 7.3 times and 21.2 times greater than DCPD, respectively. CONCLUSION The MDP-based one-step adhesive yielded several types of MDP-Ca salts and DCPD with an amorphous phase during the 30-s application period on enamel and dentin.

Differentiation of banding patterns between Streptococcus mutans and Streptococcus sobrinus isolates in rep-PCR using ERIC primer

Background Streptococcus mutans and Streptococcus sobrinus are considered to be important bacterial species in the initiation of human dental caries. Therefore, the establishment of a reliable genotyping method to distinguish S. mutans from S. sobrinus is of central importance. Objective We assessed the usefulness of repetitive extragenic palindromic polymerase chain reaction (rep-PCR) using ERIC primer banding patterns in differentiating S. mutans and S. sobrinus. Design Five S. mutans and two S. sobrinus prototype strains and 50 clinical isolates (38 S. mutans serotype c, 4 S. sobrinus serotype d, and 8 S. sobrinus serotype g) were examined. The banding patterns of amplicons generated were compared among the prototype strains and clinical isolates, to find common bands that distinguish S. mutans and S. sobrinus. Results Multiple banding patterns were seen with all strains tested. The representative strains of S. mutans tested revealed six unique, strong bands at 2,000 bp, 1,700 bp, 1,400 bp, 1,100 bp, 850 bp, and 250 bp, whereas S. sobrinus had seven strong bands at 2,000 bp, 1,800 bp, 1,100 bp, 900 bp, 800 bp, 600 bp, and 550 bp. The band at 1,100 bp was the only band that was observed in both S. mutans and S. sobrinus. Furthermore, most clinical S. mutans isolates revealed identical banding patterns. All S. mutans had amplicons at 1,700 bp, 850 bp, and 250 bp, whereas those of S. sobrinus were at 1,100 bp, 900 bp, and 800 bp. Conclusions These results indicate that using rep-PCR with the ERIC primers can distinguish between S. mutans and S. sobrinus.

Effect of the demineralisation efficacy of MDP utilized on the bonding performance of MDP-based all-in-one adhesives

OBJECTIVES The amounts of calcium salt of 10-methacryloyloxydecyl dihydrogen phosphate (MDP-Ca salt) and dicalcium phosphate dihydride (DCPD) with an amorphous phase produced by the demineralisation of enamel and dentin were determined using commercial MDP-based 2-hydroxyethyl methacrylate (HEMA)-containing and HEMA-free all-in-one adhesives. The effect of the amount of MDP-Ca salt produced on bonding performance to enamel and dentin was then characterized. METHODS Three types of commercial HEMA-containing adhesives (Scotchbond Universal Adhesive, Clearfil Tri-S Bond ND, Clearfil Tri-S Bond ND Quick), a commercial HEMA-free adhesive (G-Bond Plus) and an experimental HEMA-free adhesive were used. The reactant residues of each adhesive were prepared after interacting with enamel and dentin samples for 60 s. The amounts of MDP-Ca salt and amorphous DCPD produced were determined using a phosphorous-31 nuclear magnetic resonance technique. Enamel and dentin bond strengths were measured for each adhesive, with and without thermocycling. RESULTS The amounts of MDP-Ca salt and amorphous DCPD formed after interacting with enamel and dentin differed among the five adhesives and were independent of their pH values. Enamel showed a strong positive-correlation of the bond strength of the all-in-one adhesives to the amount of MDP-Ca salt produced, however, the dentin showed a weak negative-correlation. CONCLUSION The HEMA-free all-in-one adhesives showed a greater efficacy to demineralise the enamel and dentin than the HEMA-containing all-in-one adhesives. The dentin showed a different effect of the amount of MDP-Ca salt produced on the bonding performance compared with enamel. CLINICAL SIGNIFICANCE The enamel bond strength of MDP-based all-in-one adhesives strongly contributes to the demineralisation efficacy by the incorporation of MDP, in contrast to the dentin bond strength. However, the efficacy of MDP-based all-in-one adhesives to demineralise the enamel and dentin is not directly related to the pH value of the MDP-based all-in-one adhesive.

Demineralization capacity of commercial 10-methacryloyloxydecyl dihydrogen phosphate-based all-in-one adhesive

OBJECTIVE We determined the amounts of calcium salt of 10-methacryloyloxydecyl dihydrogen phosphate (MDP-Ca salt) and dicalcium phosphate dihydride (DCPD) with an amorphous phase developed during the application of commercial MDP-based all-in-one adhesives to enamel and dentin. This is because the demineralization by MDP and following calcium salt formation of MDP may be limited by an ionic bond formation of MDP to hydroxyapaptite in the enamel and dentin and following intermediary layer formation of MDP, since MDP forms a chemically-stable adsorption layer. METHODS Scotchbond Universal Adhesive, Clearfil Tri-S Bond ND, Clearfil Tri-S Bond ND Quick, G-Bond Plus and our designed MDP-based all-in-one adhesive were used. Enamel and dentin reactant residues of each adhesive were prepared by varying the adhesive application periods: 1, 30 and 60min, and were analyzed using phosphorous-31 nuclear magnetic resonance and X-ray diffraction. RESULTS Increasing the adhesive application period to enamel and dentin led to the increased amount of MDP-Ca salt in contrast to amorphous DCPD. In the dentin, each adhesive showed a saturated value on the production amount of MDP-Ca salt when the adhesive was applied more than 30min. In contrast, in the enamel, each adhesive showed an intermediate value on the saturated production amount of MDP-Ca salt that the respective adhesive exhibited. This is due to MDP employed demineralizes the enamel and dentin until MDP was completely consumed yielding MDP-Ca salt. CONCLUSION Commercial MDP-based all-in-one adhesives would not form an intermediary layer of MDP on hydroxyapatite throughout their application period to enamel and dentin. CLINICAL RELEVANCE The rate of MDP-Ca salt produced by the demineralization of enamel and dentin depends on the components that constitute commercial adhesive more strongly than on the concentrations of MDP and water in the respective adhesive. This is because HEMA-containing adhesive shows a slower production rate of MDP-Ca salt than HEMA-free adhesive in the enamel and dentin samples.