Influencia de la incorporación del copolímero del ácido polialquenoico en el comportamiento in vitro de diferentes sistemas adhesivos dentinarios

Resumen

Objective: To study the influence of polyalkenoic acid copolymer (also known as Vitrebond copolymer, VCP) on immediate (24h) and six-months (6m) bonding stability of VCP-based adhesives to dentin through micro tensile bond strength (mTBS), nanoleakage (NL) and ultra-morphological analysis of dentin-resin interfaces (UM). Also a potential chemical interaction between synthetic hydroxyapatite (HAp) and VCP-based adhesives was evaluated through Fourier Transformed InfraRed (FTIR) and Nuclear Magnetic Resonance (NMR) spectroscopy. Materials and Methods: mTBS/NL: Eighty-four extracted caries-free human molars were randomly assigned to seven dentin adhesives: 1) Clearfil SE Bond (CSE, Kuraray), a 2-step self-etch adhesive; 2) Adper Scotchbond 1XT (SB, 3M ESPE), a 2-step etch-and-rinse VCP-based adhesive; 3) Experimental SB formulation without VCP (SBnoVCP, 3M ESPE); 4) Scotchbond Universal adhesive (SBU, 3M ESPE), a universal VCP-based adhesive applied as a 2-step etch-and-rinse adhesive (SBU_ER); 5) Experimental SBU formulation without VCP (SBUnoVCP, 3M ESPE), applied as a 2-step etch-and-rinse adhesive (SBUnoVCP_ER); 6) SBU applied as a 1-step self-etch adhesive (SBU_SE); 7) SBUnoVCP applied as a 1-step self-etch adhesive (SBUnoVCP_SE). The specimens were prepared for mTBS testing: (24h) half of the beams were tested under tension after inmersion in water for 24h; and (6m) the other half was stored in distilled water (37ºC) for 6m prior to testing. For each tooth, two beams were randomly selected for NL challenge in both evaluation times. mTBS data were analyzed for each adhesive system using two-way ANOVA, Tukey's and Student t's post-hoc tests (alfa=0,05). NL data were computed with non-parametric tests (Kruskal-Wallis and Mann-Whitney followed by Wilcoxon, alfa=0,05). UM: Twenty-eight caries-free human molars were prepared for each of the referred seven experimental groups. The restored discs were cross-sectioned in two halves: for each tooth, (24h) one half was processed and the dentin-resin interface observed under a FESEM; and (6m) the other half was stored in distilled water (37ºC) for 6m prior to observation. FTIR/NMR: Additionally to SB, SBnoVCP, SBU and SBUnoVCP, Adper Easy Bond (EB, 3M ESPE), a 1-step self-etch VCP-based adhesive and an Experimental EB formulation without VCP (EBnoVCP, 3M ESPE) were analyzed. Each adhesive was mixed with HAp and polymerized. The polymerized mixtures (adhesive+HAp) were evaluated using FTIR and 13C/31P NMR spectroscopy in solid state. Results: mTBS: For both evaluation times, the highest mean mTBS was obtained with SBU_SE, remaining stable over the 6m but without significance in comparasion with SBU formulation without VCP. The lower mean mTBS was obtained with SBnoVCP. NL: None of the studied adhesives systems could avoid nanoleakage. Only SBUnoVCP_SE resulted in a significant higher silver deposition at 6m in comparison to 24h. UM: CSE and SBU_SE formed a submicron hybrid layer without signs of degradation after 6m. The formulations without VCP resulted in a ghost hybrid layer. FTIR: The SB+HAp spectra indicated the C=O stretching carbonyl group changed absorption wavenumber compared to that of SBnoVCP+HAp. No differences in C=O stretching absorption frequency were observed for EB+HAp and SBU+HAp in comparasion to EBnoVCP+HAp and SBUnoVCP+HAp, respectively. 13C NMR: The presence of methacrylated phosphoric esters in the EB and SBU formulations led to similar carbonyl resonance for the adhesives+HAp mixtures of both commercial adhesives and the experimental formulations. 31P NMR: A resonance shift at 0,5 ppm was observed for SB+HAp, EB+HAp and SBU+HAp spectra. For EBnoVCP+HAp and SBUnoVCP+HAp, it was observed a slight fade out of the referred shoulder without disappearing in comparison to EB+HAp and SBU+HAp, respectively, meaning that VCP might induce a modification of phosphorus moieties additionally to the ionic interaction between phosphate esters groups and HAp. Conclusions: VCP contributes to the long-term bonding stability of the studied VCP-based adhesives to dentin. The spectroscopy results indicate a chemical interaction between VCP and synthetic HAp for the studied adhesives systems.