Abstract
BackgroundThe purpose of this study was to evaluate nanohardness and viscoelastic behavior of dentin surfaces treated with two canal sealer cements for dentin remineralization.Material and MethodsDentin surfaces were subjected to: i) 37% phosphoric acid (PA) or ii) 0.5 M ethylenediaminetetraacetic acid (EDTA) conditioning prior to the application of two experimental hydroxyapatite-based cements, containing sodium hydroxide (calcypatite) or zinc oxide (oxipatite), respectively. Samples were stored in simulated body fluid during 24 h or 21 d. The intertubular and peritubular dentin were evaluated using a nanoindenter to assess nanohardness (Hi). The load/displacement responses were used for the nano-dynamic mechanical analysis to estimate complex modulus (E*) and tan delta (δ). The modulus mapping was obtained by imposing a quasistatic force setpoint to which a sinusoidal force was superimposed. AFM imaging and FESEM analysis were performed.ResultsAfter 21 d of storage, dentin surfaces treated with EDTA+calcypatite, PA+calcypatite and EDTA+oxipatite showed viscoelastic discrepancies between peritubular and intertubular dentin, meaning a risk for cracking and breakdown of the surface. At both 24 h and 21 d, tan δ values at intertubular dentin treated with the four treatments performed similar. At 21 d time point, intertubular dentin treated with PA+oxipatite achieved the highest complex modulus and nanohardness, i.e., highest resistance to deformation and functional mineralization, among groups.ConclusionsIntertubular and peritubular dentin treated with PA+oxipatite showed similar values of tan δ after 21 d of storage. This produced a favorable dissipation of energy with minimal energy concentration, preserving the structural integrity at the dentin surface. Key words:Dentin, fracture, hydroxyapatite, remineralization, viscoelastic, zinc.
Highlights
Self-repairing dental cements, which can promote deposition of calcium phosphate at the material-tooth interface, may have a promising preventive contribution in restorative dentistry [1]
Intertubular and peritubular dentin treated with phosphoric acid (PA)+oxipatite showed similar values of tan δ after 21 d of storage
This produced a favorable dissipation of energy with minimal energy concentration, preserving the structural integrity at the dentin surface
Summary
Self-repairing dental cements, which can promote deposition of calcium phosphate at the material-tooth interface, may have a promising preventive contribution in restorative dentistry [1]. Discrepancies in terms of viscoelastic properties at the different structures within the dentin, mean a risk for cracking, which opposed crack opening [7] and breakdown of this interface, as low modulus regions lead to energy concentration in relatively high elastic modulus regions [8] This may account for failures at the restored teeth, leading to the cracked tooth syndrome, that occurred when the crack promotes a stress intensity that reaches the local fracture toughness of the tissue [5]. Results: After 21 d of storage, dentin surfaces treated with EDTA+calcypatite, PA+calcypatite and EDTA+oxipatite showed viscoelastic discrepancies between peritubular and intertubular dentin, meaning a risk for cracking and breakdown of the surface. At 21 d time point, intertubular dentin treated with PA+oxipatite achieved the highest complex modulus and nanohardness, i.e., highest resistance to deformation and functional mineralization, among groups
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