"Human Salivary Derived Esterase" (HSDE) degrades dental composite resin restorative materials.Results and conclusions. Significantly higher amounts of methacrylic acid (MAA) and Bisphenol-A-bis [2, 3-dihydroxypropyl]-ether (Bis-HPPP) were produced in HSDE than in PBS. 180-day HSDE incubated specimens had a lower fracture toughness (KIci) than the non-incubated group (P<0.05). KIci values of PBS incubated groups were not significantly different from that of the non-incubated group. There was a significant negative correlation between the KIci values and Bis-HPPP production.Hypothesis. HSDE degrades the resin-dentin interface to produce biodegradation by-products in amounts which are negatively correlated with a reduction in the interfacial fracture toughness of the resin-dentin bond.Methods. Mini short-rod specimens (n=10/group), fabricated using composite (Z250) and adhesive system (Scotchbond Multi Purposes), were either not incubated; or incubated in Phosphate-Buffered Saline (PBS) or HSDE media. Degradation products were isolated and specimens were fracture toughness tested following 30, 90 or 180-day incubation periods.