Effect of acidic monomer concentration on the dentin bond stability of self-etch adhesives

摘要

This study evaluated the effect of the concentration of acidic functional monomer on the dentin bond stability of a model two-step, self-etch adhesive system. Six self-etch primers were formulated using hydroxyethyl methacrylate (HEMA), 1,3-glycerol dimethacrylate phosphate (GDMA-P), ethanol and water. Different mass concentrations of GDMA-P were tested: 0,15, 30,50, 70 or 100% (primers labeled P_(0-100)). The pH of the solutions was measured. The bonding resin was composed of (di)methacrylates. Bond strength to bovine dentin was assessed through a microtensile bond test. The beam specimens were stored in distilled water, at 37 °C, for 24 h, 6 months or 1 year. Data were statistically analyzed and failure modes classified under magnification. The increase in acidic monomer concentration was associated with an exponential decrease in pH (R~2=0.999; P< 0.001). All specimens debonded prematurely for the primers P0, P_(70) and P_(100). After 24 h, the bond strengths for P_(50)>P_(30)=P_(15). After 6 months and 1 year, P_(50)=P_(30) > P_(15). The bond strength after 6 months was similar to 24 h for P_(15) and P_(50), but significantly lower after 1 year. P_(30) showed no differences in bond strength over the 1-year storage period. A predominance of mixed failures was detected for all primers at 24 h. After 6 months, P_(30) and P_(50) showed a predominance of adhesive failures. After 1 year, the predominant failure mode for all primers was cohesive within dentin. In conclusion, a mass fraction of 50% of phosphate monomer is a limit to be added to self-etch primers; a more stable longevity of the bonds was obtained with the primer with 30% of phosphate methacrylate.