Determination of the elastic modulus of resin based materials as a function of resonance frequency during polymerisation

Objectives: The aim of this investigation is to describe the development of a novel non-invasive technique to measure the change in the elastic modulus of resin based restorative materials during polymerisation using resonance frequency analysis. Methods: A transducer was developed which was designed to resonate at its first natural frequency in the range 5–15 kHz. The transducer was excited electronically and the response measured using a frequency response analyser. The transducer was mounted in a specimen well containing a range of test materials including unfilled resins, composites and luting cements. Each test material was polymerised by mixing and/or exposure to a visible light source and the frequency response measured at intervals during the curing process. The resonance frequency was determined at each interval by the measurement of the signal amplitude and phase. Results: The resonance frequency of the transducer–resin system was plotted against time for the different material and curing combinations. Different sampling intervals were selected depending on the test procedure. All results showed a clear increase in resonance frequency as a function of the increase in stiffness and elastic modulus of the material during polymerisation. Significance: A new non-invasive test method is described which can measure the increase in the elastic modulus of resin based materials as a function of resonance frequency. The technique is not sensitive to temperature, exhibits no drift and does not influence the polymerisation of the test material. Further development should enable resonance frequency measurements to be directly related to elastic material coefficients.