Fatigue resistance of dentin/composite interfaces with an additional intermediate elastic layer

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According to the ‘elastic bonding’ concept, a thick intermediate layer of flexible resin has been suggested to absorb part of the polymerization shrinkage stress and to absorb shocks during function. In this study, the effect of an additional intermediate layer of a low-viscosity resin on the microrotary fatigue resistance (μRFR) of a hybrid composite bonded to dentin was evaluated. The hypotheses tested were that an intermediate layer of a low-viscosity resin (i) increases the μRFR to dentin, but (ii) has no effect on the static bond strength. Microtensile bond strength (μTBS) samples were loaded until failure or inserted in a microrotary fatigue testing device. Specimens were tested at 4 Hz until failure or until 105 cycles were reached. An additional intermediate elastic layer had no effect on the static μTBS, but significantly lowered the median μRFR from 28.4 MPa to 21.6 MPa. However, the application of an intermediate flexible layer had, no effect on the static μTBS. In conclusion, an additional elastic intermediate layer did decrease significantly the μRFR (rejection of hypothesis i), but did not alter the μTBS (acceptance of hypothesis ii). The decrease in μRFR most likely may be explained by the lower mechanical properties of the intermediary layer.

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