Bonding of self-etch and total-etch adhesives to carious dentin

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Nanoleakage types and potential implications: evidence from unfilled and filled adhesives with the same resin composition.

PURPOSE: To compare nanoleakage patterns of an unfilled (OS; One-Step), a 6 wt% spherical silica-filled (OSs; One-Step Plus) and a 15 wt% glass-filled (OSg) version of a two-step, acetone-based self-priming adhesive. Permeability of bonded dentin treated with OS and OSs was also examined. METHODS: Deep, coronal dentin from extracted third molars were etched and bonded using these adhesives. One-mm thick sections were immersed in 50 wt% ammoniacal silver nitrate (pH 9.5) for 24 hours. Unstained, undemineralized sections were examined by TEM. The permeability of dentin bonded with OS and OSs were investigated at 20 cm of H2O hydrostatic pressure and compared with the osmotic conductance determined with 4.8 M CaCl2 at zero hydrostatic pressure. Composite-dentin beams bonded with OS, OSs and OSg that were fractured after microtensile bond testing were examined by SEM. RESULTS: Two types of nanoleakage patterns were recognized along the resin-dentin interfaces. The reticular type consisted of discontinuous islands of silver deposits and was exclusively seen in hybrid layers. The spotted type consisted of isolated silver grains and was evident throughout the hybrid and adhesive layers in OS. These two patterns were seen to variable extents in the two filled adhesive versions OSs and OSg and their distribution was independent of one another. OS and OSs bonded dentin were permeable to fluid filtration. However, part of this fluid movement was due to the permeability of the adhesive layer, as demonstrated by osmotic fluid conductance in the absence of hydrostatic pressure. Fractographic analysis revealed denuded collagen fibrils within fractured hybrid layers that were indicative of incomplete resin infiltration.link_to_subscribed_fulltex

Use of Hoy's solubility parameters to predict water sorption/solubility of experimental primers and adhesives

Self-etching primers and adhesives contain very hydrophilic acidic monomers that result in high water sorption/solubilities of their polymers. However, the chemical composition of these products varies widely. The purpose of this work was to vary the chemical composition of experimental self-etching primers and adhesives to determine if the water sorption/solubility of the polymers were affected in a predictable manner. The Hoy's solubility parameters of these mixtures were calculated to permit ranking of the degree of hydrophilicity of the polymers. Water sorption/solubility was measured according to ISO 4049. The results showed highly significant (R-2 = 0.86, P < 0.001) correlations between water sorption and Hoy's solubility parameter for polar forces (delta(p)) of the polymers. Similar correlations were obtained between polymer solubility and dp. When these results were compared with previously published results obtained with more hydrophobic resins, excellent correlations were obtained, indicating that Hoy's dp values may be used to predict the water sorption behavior of methylmethacrylate polymers.1151818

Effects of resin hydrophilicity on water sorption and changes in modulus of elasticity

As acidic monomers of self-etching adhesives are incorporated into dental adhesives at high concentrations, the adhesive becomes more hydrophilic. Water sorption by polymers causes plasticization and lowers mechanical properties. The purpose of this study was to compare the water sorption and modulus of elasticity (E) of five experimental neat resins (EX) of increasing hydrophilicity, as ranked by their Hoy's solubility parameters and five commercial resins. Methods: After measuring the initial modulus of all resin disks by biaxial flexure, half the specimens were stored in hexadecane and the rest were stored in water. Repeated measurements of stiffness were made for 3 days. Water sorption and solubility measurements were made in a parallel experiment. Results: None of the specimens stored in oil showed any significant decrease in modulus. All resins stored in water exhibited a time-dependent decrease in modulus that was proportional to their degree of water sorption. Water sorption of EX was proportional to Hoy's solubility parameter for polar forces (δp) with increasing polarity resulting in higher sorption. The least hydrophilic resin absorbed 0.55 wt% water and showed a 15% decrease in modulus after 3 days. The most hydrophilic experimental resin absorbed 12.8 wt% water and showed a 73% modulus decrease during the same period. The commercial resins absorbed between 5% and 12% water that was associated with a 19-42% reduction in modulus over 3 days. © 2005 Elsevier Ltd. All rights reserved.link_to_subscribed_fulltex

Advances in in vitro testing techniques for dentine hypersensitivity

Dentine hypersensitivity (DH) is a common clinical condition that is responsible for pain and/or discomfort in response to various stimuli \u2013 typically thermal, tactile, osmotic or chemical \u2013 not ascribed to any other tooth or oral disease (Chap. 1). The frequent use of acidic beverage and foods is considered one of the typical conditions improving discomfort and pain. Moreover, restorative procedures including periodontal therapy and hygienic professional procedures may also induce mild-to-moderate discomfort that require the use of desensitising products to reduce and remove the symptoms. It was also evident from both prevalence studies and clinical practice that DH was identified in two population groups, namely, those individuals with good oral hygiene and those with periodontal disease (or DH following periodontal therapy) (see Chaps. 1, 3 and 4). As a result of recent changes in the definitions of DH and root sensitivity (RS), we may discuss DH in the following manner: (1) a primary dentine hypersensitivity (DH) when (cervical) dentine surface is exposed as a consequence of enamel erosion and abrasion and after appearance of gingival recession and retraction and (2) a secondary dentine hypersensitivity (RS) when certain clinical periodontal procedures have been performed and the root surface has been altered with possible smear layer removal, thereby exposing a number of dentine tubules to the oral cavity (see Chap. 1). The main purpose of this chapter therefore is to review and discuss the recommended in vitro testing techniques in order to evaluate the morphological aspect of both primary and secondary DH (and some aspects of the so-called supersensitive dentine as suggested by Pashley 2013) and to test in vitro the efficacy of (new) products designed to reduce DH. The chapter will also discuss the methods currently used in the laboratory in order to detect the reduction of the functional diameter of dentine tubules and the subsequent effect on dentine fluid flow (dentine permeability)