Nanoscopic dynamic mechanical analysis of resin–infiltrated dentine, under in vitro chewing and bruxism events

Abstract

HIGHLIGHTSSustained mechanical loading promotes failures at the resin-dentine interface.Higher viscoelastic properties of tubular dentine concentrate stress at the interface.Load cycling in sine or square wave promote healing at the resin-dentine interface. 4 ABSTRACTThe aim of this study was to evaluate the induced changes in mechanical behavior and bonding capability of resin-infiltrated dentine interfaces, after application of mechanical stimuli. Dentine surfaces were subjected to partial demineralisation through 37% phosphoric acid etching followed by the application of an etch-and-rinse dentine adhesive, Single Bond (3M/ESPE). Bonded interfaces were stored in simulated body fluid during 24 h, and then tested or submitted to the mechanical loading challenge.Different loading waveforms were applied: No cycling (I), 24 h cycled in sine (II) or square (III) waves, sustained loading held for 24 h (IV) or sustained loading held for 72 h (V). Microtensile bond strength (MTBS) was assessed for the different groups.Debonded dentine surfaces were studied by field emission scanning electron microscopy (FESEM). At the resin-dentine interface, both the hybrid layer (HL) and the bottom of the hybrid layer (BHL), and both peritubular and intertubular were evaluated using a nanoindenter in scanning mode. The load and displacement responses were used to perform the nano-Dynamic Mechanical analysis and to estimate the complex and storage modulus. Dye assisted Confocal Microscopy Evaluation was used to assess sealing ability. Load cycling increased the percentage of adhesive failures in all groups.Specimens load cycled in held 24 h attained the highest complex and storage moduli at HL and BHL. The storage modulus was maximum in specimens load cycled in held 24 h at peritubular dentine, and the lowest values were attained at intertubular dentine. The storage modulus increased in all mechanical tests, at peritubular dentine. An absence of micropermeability and nanoleakage after loading in sine and square waveforms were encountered. Porosity of the resin-dentine interface was observed when specimens were load cycled in held 72 h. Areas of combined sealing and permeability were discovered 5 at the interface of specimens load cycled in held 24h. Crack-bridging images appeared in samples load cycled with sine waveform, after FESEM examination.

Ions-modified nanoparticles affect functional remineralization and energy dissipation through the resin-dentin interface

“…Concerning E* of the specimens treated with Zn-NPs after 21 d of SBFS storage, the resistance of the resin-dentin interface to dynamic deformation augmented at the adhesive and intertubular dentin layers (2.08 and 1.76 fold, respectively), in comparison with the specimens stored 24 h (Table 2). Due to the light increase in both peak and area of the phosphate group and area of the carbonate group (Table 3a), changes in the viscoelastic mechanical behavior are not unexpected (Toledano et al, 2016d). The significance of this finding lies in the weak resistance to deformation that is achieved at dentin, after 21 d of SBFS storage, due to their scarce remineralization (Balooch et al, 2008) when NPs were doped with both Ca and Zn.…”

“…Furthermore, if the bond between the adhesive tags and peritubular dentin is imperfect, as in Figures 2F and 5D, then the stress concentration zones are probably within the hybrid layer, where stresses will concentrate and the integrity of the resin-dentin interface will get damaged (Toledano et al, 2016d).…”

The peritubular reinforcement effect of porous dentine microstructure

“…This is because the needed bite force and the different function between the bovine dentine and the human dentine. Scanning of selected regions of interest enabled identification of both peritubular and intertubular dentine, it reveals that there is a significant heterogeneity in the mechanical properties in these regions [ 10 ]. Scanning based nanoscopic dynamic mechanical analysis shows that the old dentine tubules exhibit a gradient in elastic behavior, with a decrease in elastic modulus from the peritubular dentine to the center of dentine tubules [ 21 ].…”

“…There are different compositions between the peritubular and intertubular dentine and the main components of dentine as an anisotropic composite materials, which determines that the dentine is deemed as a biological composite. And the dentine tubules are also concerned as the particular characteristic [ 9 , 10 ].…”

Improved reactive nanoparticles to treat dentin hypersensitivity

“…Viscoelastic materials located at load-bearing areas, such as dentin [18] exhibit time-dependent strain [19,20]. Therefore, it is of interest to examine, with nano-dynamic mechanical analysis (nano-DMA) [21], both the complex modulus (E*) and damping or tan delta (δ) of these treated cervical dentin surfaces [22]. The aim of this study was to evaluate the ability to occlude the patent dentinal tubules measuring its effect on conductance across the dentin, and to study the viscoelastic behavior of cervical dentin surfaces treated with four different nanoparticles-based solutions for remineralizing purposes.…”