Dentin wetting by three adhesive systems: influence of etching time, temperature and relative humidity

The purpose of this study was to investigate the wetting properties of three adhesives systems on etched dentin surfaces submitted to a brief air-drying procedure, as in clinical conditions. The influence of two clinical parameters (surface temperature and surrounding hygrometry) on wetting was investigated.

Two total-etch adhesives (Excite Vivapen and Adper Scothbond 1XT) and one self-etching adhesive (GC-G Bond) were used. Superficial and deep dentin slice were obtained from six caries-free extracted third molars. Before the adhesive deposition, the dentin samples were etched with 37% phosphoric acid for different time durations. The surface topography was characterised by atomic force microscopy (AFM) observations and the wetting properties of dentin were studied by contact angle measurements.

Unlike clinical expectations, the contact angles increased with the acid exposure time, and consequently with both surface roughness and the organic-mineral ratio of the dentin components. The wetting properties were clearly more sensitive to the surrounding relative humidity than the temperature. The contact angles values were reduced by about 50% when the relative humidity increased from 37% to 80% and by about 15% when the temperature was raised from 25 degrees C to 37 degrees C.

Acid-etched dentin exposed to a brief air-drying appears as the key parameter to control the wetting properties of total-etch adhesive-dentin systems. The experimental results seem to be well described by the Cassie-Baxter approach, and suggest that dentinal tubules through an adhesive repellent contribution should account for the observed wettability decreases.