There are concerns regarding the longevity of resin composite restorations and
the clinical relevance of in vitro bond strength testing to the durability of
dentin bonds in vivo.OBJECTIVE: The objectives of this investigation were to: (1)
develop a new method of experimental evaluation for quantifying the durability of
dentin bonds, (2) apply this method to characterize the interfacial strength of a
selected commercial system under both monotonic and cyclic loading, and (3)
distinguish mechanisms contributing to the interface degradation and failure.
METHODS: A new method for fatigue testing the resin-dentin interface was
developed based on a four-point flexure arrangement that includes two identical
bonded interfaces. Cyclic loading of specimens comprised of coronal dentin bonded
to a commercial resin composite and controls of resin composite was performed to 
failure within a hydrated environment. Scanning electron microscopy and
nanoscopic dynamic mechanical analysis were used to evaluate failure mechanisms.
RESULTS: The fatigue strength of the resin-dentin interface was significantly
lower (p≤0.0001) than that of the resin composite and reported for dentin over
the entire finite life regime. Defined at 1×10(7) cycles, the apparent endurance 
limit of the resin-dentin interface was 13MPa, in comparison to 48MPa and 44MPa
for the resin composite and dentin, respectively. The ratio of fully reversed
endurance limit to ultimate strength of the interface (0.26) was the lowest of
the three materials.
SIGNIFICANCE: The proposed approach for characterizing the fatigue strength of
resin-dentin bonds may offer new insights concerning durability of the bonded
interface.