In vitro demineralization of tooth enamel subjected to two whitening regimens.

BACKGROUND: The resistance of bleached enamel to demineralization has not been elucidated fully. In this study, the authors aimed to examine the level of in vitro demineralization of human tooth enamel after bleaching by using two common bleaching regimens: home bleaching (HB) and office bleaching (OB) with photoirradiation. METHODS: The authors bleached teeth to equivalent levels by means of the two bleaching regimens. They used fluorescence spectroscopy to measure the reduction in enamel density and the release of calcium into solution after storing the treated teeth in a demineralizing solution for two weeks. They also visualized and quantified mineral distribution in demineralized bleached enamel over time by using a desktop microcomputed-tomographic analyzer. RESULTS: Enamel subjected to HB or to photoirradiation without bleaching showed increased demineralization. In contrast, enamel treated with OB was more resistant to demineralization. This resistance to demineralization in teeth treated with OB presumably is due to peroxide's permeating to deeper layers of enamel before being activated by photoirradiation, which enhances mineralization. CONCLUSIONS: The mineral distribution pattern of enamel after treatment plays a critical role in providing resistance to demineralization in whitened teeth. PRACTICAL IMPLICATIONS: OB confers to enamel significant resistance to in vitro demineralization. Dentists should supervise the nightguard HB process.

Adhesiveness of various glass ionomer cements in cavities treated with Carisolv.

OBJECTIVE: The purpose of this study was to investigate the adhesion of glass ionomer cements to dentin and the effect of pretreatment using Carisolv. STUDY DESIGN: Forty extracted permanent teeth with caries were used for this study. All lesions were removed using the Carisolv system and teeth were divided into eight groups. Groups 1 to 4 were filled with three types of conventional glass ionomer cements and a resin modified glass ionomer cement. Group 8 was restored with composite resin. In the remaining three groups (Groups 5 to 7), several pretreatment procedures, including EDTA and dentin primer application and a combination of these, were performed before restoring with resin modified glass ionomer cement. All restorations were thermocycled, and microleakage tests were performed on all teeth. RESULTS: There were no statistical differences among Groups 1, 2 and 3 or between Groups 4 and 8. However Groups 1 to 3 had higher microleakage levels than Groups 4 and 8. Groups 5 to 7 showed similar leakage levels as Group 4. CONCLUSION: Pretreatment with EDTA or dentin primer did not improve bonding ability. Combination of caries removal using Carisolv and a resin modified glass ionomer cement restoration without pretreatment seems to be an acceptable method for caries treatment.

In situ proliferation and differentiation of macrophages in dental pulp.

The presence of macrophages in dental pulp is well known. However, whether these macrophages proliferate and differentiate in the dental pulp in situ, or whether they constantly migrate from the blood stream into the dental pulp remains unknown. We have examined and compared the development of dental pulp macrophages in an organ culture system with in vivo tooth organs to clarify the developmental mechanism of these macrophages. The first mandibular molar tooth organs from ICR mice aged between 16 days of gestation (E16) to 5 days postnatally were used for in vivo experiments. Those from E16 were cultured for up to 14 days with or without 10% fetal bovine serum. Dental pulp tissues were analyzed with immunohistochemistry to detect the macrophages and with reverse transcription and the polymerase chain reaction (RT-PCR) for the detection of factors related to macrophage development. The growth curves for the in vivo and in vitro cultured cells revealed similar numbers of F4/80-positive macrophages in the dental pulp. RT-PCR analysis indicated the constant expression of myeloid colony-stimulating factor (M-CSF) in both in-vivo- and in-vitro-cultured dental pulp tissues. Anti-M-CSF antibodies significantly inhibited the increase in the number of macrophages in the dental pulp. These results suggest that (1) most of the dental pulp macrophages proliferate and differentiate in the dental pulp without a supply of precursor cells from the blood stream, (2) M-CSF might be a candidate molecule for dental pulp macrophage development, and (3) serum factors might not directly affect the development of macrophages.

Water evaporation from substrate tooth surface during dentin treatments.

The purpose of this study was to evaluate changes in the quantity of water evaporation from tooth surfaces. The amount of water evaporation was measured using Multi probe adapter MPA5 and Tewameter TM300 (Courage+Khazaka Electric GmbH, Köln, Germany) after acid etching and GM priming of enamel; and after EDTA conditioning and GM priming of dentin. The results indicated that the amount of water evaporation from the enamel surface was significantly less than that from the dentin. Acid etching did not affect the water evaporation from enamel, though GM priming significantly decreased the evaporation (83.48 ± 15.14% of that before priming). The evaporation from dentin was significantly increased by EDTA conditioning (131.38 ± 42.08% of that before conditioning) and significantly reduced by GM priming (80.26 ± 7.43% of that before priming). It was concluded that dentin priming reduced water evaporation from the dentin surface.

Diffusion of GM primer and dentin adhesive into EDTA-conditioned dentin.

The aim of this study was to investigate the diffusion of red-stained experimental GM primer and blue-stained dentin bonding agent into EDTA-conditioned dentin and the effect of GM priming on contraction gap formation. After GM priming at 0, 35, 70, or 100 vol%, marginal adaptation was evaluated by measuring the wall-to-wall contraction gap width of a light-activated resin composite (Palfique Estelite, Tokuyama Dental, Japan) mediated with a commercial dentin bonding agent (Clearfil Photo Bond, Kuraray Medical, Japan). Contraction gap formation was completely prevented when treated with 35 vol% GM primer. Moreover, after treatment with 35 vol% GM, the red and blue dyes of stained GM primer and dentin bonding agent diffused up to a depth of 40 µm into the dentin surface. The diffusion of primer and bonding agent into EDTA-conditioned dentin was essential for bonding efficacy although SEM observation revealed an absence of hybrid layer formation.

Measurement of shear bond strength to intact dentin.

Previously, we reported that the integrity of a resin composite restoration deteriorated when the dentin cavity wall was decalcified by conditioning. In this study, to evaluate the bonding between dentin adhesive and non-decalcified dentin surface, we experimented with a novel method of using a high-pressure water spray device to prepare smear layer-free dentin surfaces. When the smear layer was removed, shear bond strength significantly increased regardless of the removal method employed. Further, with glyceryl monomethacrylate (GM) priming, no significant differences in bond strength were observed among these smear layer removal methods: ethylenediamine tetraacetic acid (EDTA) conditioning, phosphoric acid conditioning, and removal by water spray. It was also found that GM priming was key to achieving marginal integrity, whereas contraction gap width increased with phosphoric acid conditioning. It was thus concluded that the efficacy of a dentin adhesive should be evaluated by consistently observing the contraction gap in three-dimensional cavities rather than by mere measurement of bond strength to a flat dentin surface.

Resistance of nanofill and nanohybrid resin composites to toothbrush abrasion with calcium carbonate slurry.

The aim of this study was to investigate the wear of four nanofilled resin composites using simulated toothbrushing for 50,000 cycles with calcium carbonate slurry. The depth of abrasion and roughness (Ra) were measured after each 10,000 brushing cycle. The surface texture of the worn samples was examined by SEM.The wear depths of the nanofill Filtek Supreme XT (FIL), the nanohybrides Grandio (GRA), Tetric EvoCeram (TET), and Venus Diamond (VED) increased linearly with numbers of brushing cycles or approximately 80, 12, 600, and 60 mum, respectively after 50,000 strokes. Surface roughness showed virtually no change between 10,000 and 50,000 brushing cycles; the ranking order was TET < FIL < GRA < VED. FIL showed rather uniform abrasion with nanoclusters protruding from the surface. TET was very smoothly abraded without signs of debonding of the prepolymerized particles, whereas GRA and VED showed pronounced wear of the matrix polymer surrounding larger glass filler particles.

Effects of opacity and oxygen inhibition of coating resin composites on bond strength to enamel.

The purpose of this in vitro investigation was to study the effects on bond strength to primed human enamel stemming from opacity and polymerization inhibition by oxygen due to two coating resins. The coating resins and primers used were White Coat and an experimental material, SIR. The bond strengths on fine-ground enamel were evaluated for three shades of each of these coating resins after 24-hour storage in water. In addition, their degrees of opacity and oxygen inhibition depths were measured. The mild self-etch primer solutions produced very shallow but distinct etching patterns for micromechanical retention of the coating resin. Significant linear relationships between bond strength on the one hand and opacity and oxygen inhibition depth on the other were found for the three shades of each coating resin. Generally, the bond strength mediated on enamel is sufficiently high when these resins are combined with their proprietary adhesives. Therefore, the decrease in bond strength with increasing opacity of the coating resin shades has to be taken into account during application and light-curing.

In vitro comparison of three caries dyes.

PURPOSE: To evaluate the efficacy of a conventional and newly-developed caries detector (Caries Check) by measuring the Vickers microhardness (VMH) and DIAGNOdent value of the dentin cavity wall of extracted human teeth after removing carious dentin that was stained by the caries detector. METHODS: 30 human teeth with coronal dentin caries extending halfway through the dentin were sectioned and extracted for use in this study. As a control, the longitudinal section of a caries-free extracted human tooth was prepared. The VMH and DIAGNOdent values were measured and the microstructure of the dentin cavity wall was examined using a scanning electron microscope (SEM). RESULTS: When Caries Check was employed as a guide for carious dentin removal, the microhardness of the cavity wall was significantly lower than the normal dentin and the DIAGNOdent value indicated that the dentin may have recalcified. SEM observations of the stained regions revealed that Caries Check did not stain the sclerotic dentin. Based on these findings, Caries Check may be a useful modality because the excavation of the dentin structure was shallower and the sclerotic dentin was preserved.

Priming effects of triethylene glycol and triethylene glycol monomethacrylate on dentin bonding.

The objective of this study was to evaluate the effects of triethylene glycol (TEG) and triethylene glycol monomethacrylate (TEGMA) solutions as dentin primers on dentin bonding. To this end, wall-to-wall polymerization contraction gap width of a resin composite in a cylindrical dentin cavity and shear bond strength to a flat dentin surface were measured. Dentin was pretreated with an experimental dentin bonding system - consisting of 0.5 M ethylenediaminetetraacetic acid conditioner, TEG or TEGMA primer, and Clearfil Photo Bond bonding agent - prior to resin composite filling. When the cavity was primed with an aqueous solution of 35 vol% TEG, 35 or 45 vol% TEGMA for a few seconds, contraction gap formation was prevented completely. Then, among these three gap-free groups, there were no significant differences in shear bond strength. It was thus shown that both TEG and TEGMA were highly effective dentin primers, completely preventing contraction gap formation even when they were applied for only a few seconds.

Guinea Pig Maximization Test of tri-ethylene glycol mono-methacrylate.

The aim of this study was to evaluate tri-ethylene glycol mono-methacrylate (TEGMA) in terms of dermatological allergic reaction using a Guinea Pig Maximization Test. Skin reaction was evaluated according to the criteria of International Contact Dermatitis Research Group. TEGMA, as a constituent in new primers, has been reported to contribute to a priming ability similar to that of highly purified glyceryl mono-methacrylate (GM). In this study, it was found that its adverse effect was less than that of 2-hydroxy ethyl methacrylate (2-HEMA), but similar to that of highly purified GM. In conclusion, it was anticipated that TEGMA would hereafter replace 2-HEMA as a primer, as it posed a lower risk of triggering dermatological allergic reaction.

Contraction gap versus shear bond strength of dentin adhesive in sound and sclerotic dentins.

To evaluate the effect of a dentin adhesive on sclerotic dentin, contraction gap width and shear bond strength were measured. Dentin cavity wall was pretreated with an experimental dentin bonding system with and without a dentin primer, or with a commercial dentin bonding system. In the experimental dentin bonding groups, contraction gap width of sclerotic dentin was significantly smaller than that of sound dentin when the cavity was not primed with glyceryl monomethacrylate. For each individual tooth, the correlation between contraction gap width and shear bond strength was insignificant. In conclusion, the bonding efficacy of dentin bonding systems to sclerotic dentin was superior to that of sound dentin. Further, it was determined that it was impossible to detect the interaction between the polymerization contraction stress of resin composites and the efficacy of dentin adhesives by measuring bond strength.

Efficacy of a self-etching dentin primer composed of TEGMA and phenyl-P.

The purpose of the present study was to evaluate the efficacy of an experimental self-etching dentin primer composed of TEGMA and phenyl-P using primary and young permanent teeth. The efficacy of the self-etching dentin primer was evaluated by measuring the wall-to-wall polymerization contraction gap width and the shear bond strength to the flat dentin surface. The contraction gap formation was prevented completely in the specimens primed with the 35 vol% TEGMA and 20% phenyl-P for 30 sec.

Effect of multiple application of a dentin adhesive on contraction gap width of a resin-based composite.

PURPOSE: To test the efficacy of the multiple application of a total-etch dentin adhesive was investigated by measuring (1) the contraction gap width of a light-activated resin-based composite in a cylindrical dentin cavity and (2) the early tensile bond strength to a flat dentin surface with the Single Bond Dental Adhesive System. MATERIALS AND METHODS: Contraction gap width was measured in a cylindrical dentin cavity (3 mm x 1.5 mm) treated with a single coat or double coats of the Single Bond adhesive and restored with Silux Plus or Z-100. As control, the cavity was treated with an experimental dentin bonding system consisting of EDTA, 35% GM and Clearfil Photo Bond. Early tensile bond strengths of Silux Plus or Z-100 were measured on the flat dentin surface treated with the three bonding procedures as in the contraction gap study within 10 min. after final cure. RESULTS: The contraction gap of Silux Plus and Z-100 was prevented with the double coats of the Single Bond adhesive, whereas the contraction gap of Z-100 was not prevented with the single coat of the Single Bond and the experimental system. When the film thickness of the Single Bond system was less than 2 microm, the gap could not be prevented. The tensile bond strengths of Silux Plus and Z-100 to flat dentin mediated with the three bonding procedures were not significantly different (P>0.05).

The efficacy of dentine adhesive to sclerotic dentine.

OBJECTIVE: To evaluate the effect of a dentine bonding system to sclerotic dentine in comparison with normal dentine. METHODS: The efficacy of the dentine bonding system to sclerotic dentine was examined by measuring wall-to-wall polymerization contraction gap width. The dentine cavity wall was pretreated with an experimental dentine bonding system with and without a dentine primer. The dentine primer was glyceryl mono-methacrylate (Blemmer GLM, NOF Corp., Tokyo, Japan) (GM), which contained esterified methacrylate with a polyvalent alcohol, which is similar to 2-HEMA. The structure of sclerotic dentine and the changes to that structure caused by etching were observed using a scanning electron microscope (SEM). RESULTS: With GM priming, complete marginal integrity was obtained regardless of the type of dentine. Without GM priming, complete marginal integrity was obtained in half of the specimens of the sclerotic dentine, and was not obtained in any of the specimens of normal dentine. In the SEM study, the structure of sclerotic dentine was considered to be viable for adhesion. However, this was not the case when etched with phosphoric acid. CONCLUSION: It was concluded that sclerotic dentine had a clear advantage over normal dentine with regard to the adaptation of resin composites. Therefore the structure of sclerotic dentine possesses a naturally derived structure to which a primer may attach. Sclerotic dentine is part of the body's natural defenses and should be preserved. It should not be exposed to acid etching which would damage its structure.

Raman and IR studies on adsorption behavior of adhesive monomers in a metal primer for Au, Ag, Cu, and Cr surfaces.

6-[N-(4-vinylbenzyl)propylamino]-1,3,5-triazine-2,4-dithione (VBATDT) and 10-methacryloyloxydecyl dihydrogen phosphate (M10P) are functional monomers used for the surface treatment of dental alloys. The aim of our study was to clarify the role of a commercial metal primer containing both the monomers in adhesion between resin and various dental metals on a molecular level. We used surface-enhanced Raman scattering (SERS) and infrared reflection absorption (IRA) spectroscopy. An SERS measurement was performed with a 647 nm laser line for a mixture of aqueous Au colloid and the primer. IRA spectra were taken for cast films of the primer on Au, Ag, Cu, and Cr surfaces as a function of rinse time, and for self-assembled monolayer (SAM) films from dilute mixed solution of VBATDT and M10P. These spectra indicate that VBATDT in the primer is mainly chemisorbed on Au, Ag, and Cu surfaces with respect to thickness, whereas only M10P is adsorbed on Cr. We also examined the tensile bond strengths between resin and Au, Ag, Cu, and Cr plates treated by VBATDT, with and without M10P, and found that VBATDT effectively promotes the bond strength between resin and the metals except for Cr, whereas M10P is effective only for Cr. These adhesion characteristics are consistent with the chemisorbed species on each metal surface as shown in the spectroscopic evidence.