Effect of salivary esterase on the integrity and fracture toughness of the dentin-resin interface.

Human Salivary Derived Esterases (HSDE) are part of the salivary group of enzymes which show strong degradative activity toward the breakdown of one of the most common monomers used in dental composites and adhesives, 2,2-[4(2-hydroxy 3-methacryloxypropoxy)-phenyl] propane (Bis-GMA), to form the degradation product 2,2-bis [4 (2,3-hydroxy-propoxy)phenyl] propane (Bis-HPPP). This study was aimed to evaluate the effects of HSDE on the biodegradation and fracture toughness of the adhesive resin-dentin interface. Adhesive resin (Scotchbond Multi Purposes), resin composite (Z250) and mini short-rod specimens, were either not incubated; or incubated in phosphate-buffered saline (PBS) or HSDE media for up to 180 days (37 degrees C, pH 7.0). The amount of Bis-HPPP was analyzed by high performance liquid chromatography and mini-SR specimens were tested for fracture toughness using universal testing machine following 30, 90, or 180-day incubation periods. Significantly higher amounts of Bis-HPPP were produced in HSDE than in PBS incubated specimens (p < 0.05). Non-incubated mini-SR specimens had the higher fracture-toughness values, while specimens incubated for 180-days in HSDE had the lowest fracture toughness (p < 0.05). This study suggests that biodegradation is an on-going clinically relevant process that progressively compromises the integrity of the critical resin restoration-adhesive interface, as well as the resin-composite component with time.