Electric-current-assisted application of self-etch adhesives to dentin.

The use of electric current during the application of etch-and-rinse adhesive systems has been recently claimed to increase bonding of etch-and-rinse adhesives by enhancing substrate impregnation. The null hypothesis tested in this study was that electrically assisted application has no effect on bond strength of self-etching bonding systems. Three self-etch adhesives (Protect-Bond, Xeno III, and Prompt L-Pop) were applied with the aid of an electric signal-generating device (ElectroBond) and tested vs. controls prepared with the same disposable sponges but without electric current. Specimens bonded under the influence of electric current exhibited increased microtensile bond strength compared with the controls (p<0.05). High-resolution SEM analysis showed that bonding under the influence of electricity reduced interfacial nanoleakage. It is speculated that resin infiltration may be improved by the attraction of polar monomers by an electric current or by modification of the dentin surface charges, resulting in better water substitution or evaporation.

Reduced antigenicity of type I collagen and proteoglycans in sclerotic dentin.

Antigenic alterations to the dentin organic matrix may be detected by an immunohistochemical approach. We hypothesized that alterations in the antigenicity of type I collagen and proteoglycans occur in sclerotic dentin under caries lesions. Transverse sections were prepared from carious teeth in the sclerotic zone and normal hard dentin. A double-immunolabeling technique was performed on these sections, with anti-type I collagen and anti-chondroitin 4/6 sulfate monoclonal primary antibodies. We used gold-conjugated secondary antibodies to visualize the distribution of intact collagen fibrils and proteoglycans by high-resolution SEM. For sclerotic dentin, labeling densities were 19.57 +/- 3.01/microm2 for collagen and 9.84 +/- 2.62/microm2 for proteoglycans. For normal hard dentin, values were 35.20 +/- 2.73/microm2 and 17.03 +/- 1.98/microm2, respectively. Distribution of intact collagen fibrils and proteoglycans in sclerotic dentin was significantly lower than in normal hard dentin. Reductions in antigenicity from the organic matrix of sclerotic dentin under caries lesions raise concern about the potential of intrafibrillar remineralization.

Cyclosporin A specifically affects nuclear PLCbeta1 in immunodepressed heart transplant patients with gingival overgrowth.

One of the most commonly observed adverse effects of cyclosporin A (CsA) is the development of gingival overgrowth (GO). Fibroblasts are involved in GO, but the question why only a percentage of patients undergoing CsA treatment shows this side-effect remains unanswered. In a previous study, CsA has been demonstrated to induce over-expression of phospholipase C (PLC) beta(1) in fibroblasts of patients with clinical GO, in cells from both enlarged and clinically healthy gingival sites. In this work, we assessed the expression of PLCbeta isoforms to investigate whether the exaggerated fibroblast response to CsA related to increased PLCbeta(1) expression could also be detected in CsA-treated patients without clinical signs of GO. Our results support the hypothesis of a multi-factorial origin of gingival overgrowth, including specific changes within the gingival tissues orchestrating fibroblastic hyper-responsiveness as a consequence of a long-term in vivo exposure to cyclosporin A.

In vivo and in vitro permeability of one-step self-etch adhesives.

Adhesive dentistry should effectively restore the peripheral seal of dentin after enamel removal. We hypothesize that non-rinsing, simplified, one-step self-etch adhesives are effective for minimizing dentin permeability after tooth preparation procedures. Crown preparations in vital human teeth were sealed with Adper Prompt, Xeno III, iBond, or One-Up Bond F. Epoxy resin replicas were produced from polyvinyl siloxane impressions for SEM examination. Dentin surfaces from extracted human teeth were bonded with these adhesives and connected to a fluid-transport model for permeability measurements and TEM examination. Dentinal fluid droplets were observed from adhesive surfaces in resin replicas of in vivo specimens. In vitro fluid conductance of dentin bonded with one-step self-etch adhesives was either similar to or greater than that of smear-layer-covered dentin. TEM revealed water trees within the adhesives that facilitate water movement across the polymerized, highly permeable adhesives. Both in vitro and in vivo results did not support the proposed hypothesis.

Osmotic blistering in enamel bonded with one-step self-etch adhesives.

One-step self-etch adhesives behave as permeable membranes after polymerization, permitting water to move through the cured adhesives. We hypothesize that osmotic blistering occurs in bonded enamel when these adhesives are used without composite coupling. Tooth surfaces from extracted human premolars were bonded with 5 one-step self-etch adhesives. They were immersed in distilled water or 4.8 M CaCl(2), and examined by stereomicroscopy, field-emission/environmental SEM, and TEM. Water blisters were observed in bonded enamel but not in bonded dentin when specimens were immersed in water. They collapsed when water was subsequently replaced with CaCl(2). Blisters were absent from enamel in specimens that were immersed in CaCl(2) only. Water trees were identified from adhesive-enamel interfaces. Osmotic blistering in enamel is probably caused by the low water permeability of enamel. This creates an osmotic gradient between the bonded enamel and the external environment, causing water sorption into the interface.

Resistance of marginal enamel to acid solubility is influenced by restorative systems: an in vitro scanning electron microscopic study.

The aim of this study was to evaluate the morphology of the enamel surface along margins of class V restorations following exposure to cariogenic solution. Restorations were placed in vitro in human third molars. The specimens were divided into groups according to resin composition: (1) Scotchbond 1 + Filtek Flow, (2) Scotchbond 1 + F2000, and (3) Prompt L-Pop + experimental flowable composite. Samples were stored in a demineralizing solution (lactic acid, pH 4.5, 0.1 M) at 37 degrees for 1-4 weeks or in deionized water (control group). The solution was changed every day. Replicas of the specimens were obtained in order to exclude drying artifacts. Scanning electron microscopy (SEM) of original and replica specimens identified a distinct enamel zone, defined as perimarginal enamel showing numerous fractures, porosities, voids, and pits. After the 4-week treatment, perimarginal prismatic enamel was greatly removed, while interprismatic enamel was still in place and only partially dissolved. Enamel not in relation with composite/compomer margins (0.5-1 mm away) showed minor alterations. Perimarginal enamel fractures probably due to composite/compomer shrinkage or the bur preparation may greatly contribute to this marginal enamel demineralization by increasing the number and size of porosities, that enhance the penetration and diffusion of cariogenic solution and create a sort of demineralized enamel subsurface. Only compomer restorations revealed a thin caries inhibition zone (1-2 micro m) probably related to fluoride release. Below this protected area, we observed the typical alterations of the other samples. These morphological alterations are probably related to secondary demineralization lesions and may affect the clinical life of restorations.