Abstract
Objectives This study evaluated the influence of the cement composition and different polymerization protocols on the bonding chemical interaction of self-adhesive cements with synthetic hydroxyapatite. Materials and Methods Two commercial self-adhesive resin cements (RelyX U200 and Maxcem Elite) were selected, manipulated, mixed with hydroxyapatite dry powder (HAp), dispensed into molds, and distributed into three groups according to polymerization protocols: immediate photoactivation (IP); delayed photoactivation, 10 min self-curing and light-curing (DP); and chemical activation (CA, no light exposure). The detailed chemical information, at atomic scale, on the surface and deeper into the bulk of self-adhesive cement/hydroxyapatite mixtures was evaluated with X-ray photoelectron spectroscopy (XPS). Results Chemical elements were detected in both cements, such as Na, O, Ca, C, P, and Si. Other elements were detected in minor concentrations. RelyX U200 exhibited the most intense formation of calcium salts products when the cement/HAp mixtures were photoactivated (immediate or delayed). RelyX U200/HAp mixture under delayed photoactivation (DP) also exhibited higher binding energy between calcium moieties of the HAp and methacrylates in the cement. A higher energy difference in the interaction of HAp with the cement comparing the bulk and surface areas was observed when RelyX U200 underwent the delayed photoactivation protocol. Maxcem Elite exhibited an increased chemical reactivity when either chemically activated or immediately photoactivated and a higher binding energy of the carboxyl groups bonded to the calcium of HAp when chemically activated. Conclusions The interaction of cements with hydroxyapatite is chemical in nature and leads to the formation of calcium salts, which may favor better integrity and longevity of adhesive restorations. The polymerization protocol affects the chemical interaction in mixtures of self-adhesive cements and hydroxyapatite, influencing the formation of these salts and the establishment of intermolecular interactions between the HAp and the cements.
Highlights
Self-adhesive resin cements are materials with methacrylate monomers containing phosphoric acid esters that simultaneously demineralize and infiltrate both the smear layer and the underlying dental tissue, forming an interdiffusion zone [1] and providing micromechanical and chemical bonds [2].e thickness of this interfacial area reaches 2-3 μm or less, depending on the instrument used for preparation [3]
E Scientific World Journal e morphology of the interfacial area and the bonding characteristic of self-adhesive cements with dental tissues greatly depends on the functional monomers included in the adhesive formulation, on the reactants formed by the monomers-tooth reaction, and on the extent to which these monomers interact with the dental substrates [5, 6]
The material surface was covered with a Mylar strip and a glass slide and compressed to extrude excess material. e specimens of groups immediate photoactivation (IP) and delayed photoactivation (DP) were photoactivated after the working time on the top and bottom surfaces according to the exposure time recommended by the manufacturer. e specimens were removed from the molds after the photoactivation procedures (IP and DP groups). e light-curing was performed according to the manufacturer’s instructions using a polywave LED light-curing unit (Bluephase, Ivoclar Vivadent, Schaan, Liechtenstein) with a radiant emittance of 1200 mW/cm2. e light output of the unit was monitored using a handheld radiometer (Model 100, Demetron Research Corp., Danbury, CT, USA). e specimens were stored in lightproof recipients for 24 h at room temperature (22°C)
Summary
Self-adhesive resin cements are materials with methacrylate monomers containing phosphoric acid esters that simultaneously demineralize and infiltrate both the smear layer and the underlying dental tissue, forming an interdiffusion zone [1] and providing micromechanical and chemical bonds [2].e thickness of this interfacial area reaches 2-3 μm or less, depending on the instrument used for preparation [3]. E Scientific World Journal e morphology of the interfacial area and the bonding characteristic of self-adhesive cements with dental tissues greatly depends on the functional monomers included in the adhesive formulation, on the reactants formed by the monomers-tooth reaction, and on the extent to which these monomers interact with the dental substrates [5, 6]. Another characteristic that influences the quality of the interfacial area formed is the fact that the acidity of the newly manipulated self-adhesive cement needs to be neutralized to allow monomer conversion [1]. A glass ionomer concept was incorporated in the formulation of self-adhesive cements, helping to promote a shift towards pH-neutral conditions [9]. e partial surface dissolution of acid-soluble glass present in the composition helps neutralize the cement acidity and release sodium, calcium, silicate, and fluoride ions, which are nearby or take part in the cement setting reaction [8, 10]
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