Influence of hydrophobic layer of Bis-EMA with different ethoxilations on adhesive's bonding efficacy and mechanical properties

Objectives The aim of this study was to evaluate the effects of a hydrophobic layer of Bis-EMA 4 (B4, 4 ethoxilations), Bis-EMA 10 (B10, 10 ethoxilations) or Bis-EMA 30 (B30, 30 ethoxilations) on dentin adhesion and mechanical properties of a universal adhesive. Materials and methods Extracted human molars were cut and restored using self-etching mode of Ambar Universal (AU, FGM) adhesive and divided according to the hydrophobic layer employed (n = 8): only AU (Control), SBMP (Scotchbond Multi-Purpose adhesive, 3 M, Commercial Control), B4, B10 and B30. Microtensile bond strength (μTBS) and nanoleakage tests were performed after 24h and 6 months water storage. Interface micro-permeability was surveyed by confocal microscopy. Dynamic-mechanical analysis (DMA) of each adhesive combination (50 wt% Ambar + 50 wt% BisEMA or 100% Ambar) were assessed. The data were statistically analyzed using two-way ANOVA and Tukey`s test (p < 0.05). Results SBMP achieved the highest μTBS, followed by B4, B10 and Control, whilst B30 presented significantly lowest μTBS when compared with further groups (p < 0.001). After ageing, the only group depicting significant μTBS reduction was Control (p = 0,009). B4 and SBMP were almost devoid of silver deposits and did not show any signs of gaps, even after ageing. B4 presented the lowest micropermeability and the best mechanical behavior on DMA, showing the highest rubbery zone and increased glass transition temperature. Conclusions Bis-EMA-4 might be a suitable monomer for a hydrophobic layer in adhesive strategy, reducing hydrolytic degradation and increasing the durability and mechanical properties of adhesive interfaces.