Endodontic instruments made of fibre-reinforced polymer composites – preliminary FEM and experimental investigations

Conventional needle-shaped instrument tips under ultrasonic excitation for root canal treatment made of nickel titanium (NiTi) alloys achieve a high cleaning performance, especially when inducing the cavitation phenomenon. Nevertheless, their tendency to spontaneous material failure is disadvantageous. Monolithic polymers, e.g. polyamide (PA) significantly reduce this risk, however, instrument tips made of this material are characterised by low cleaning performance. Fibre-reinforced polymers (FRP) exhibit the possibility to bear dynamic loads at higher life cycles than conventional metallic materials. The use of endless fibre-reinforced polymers allows the realisation of instrument tips offering good damage tolerance and costefficiency as well as a high cleaning performance. This paper focusses on preliminary numerical and experimental investigations necessary to prove the suitability of fibre-reinforced materials for endodontic instrument tips. The numerical investigations conducted using a standard FE-Method contain simulations of the eigenfrequencies. The accompanying experiments were done for optical detection of the cavitation effects induced by conventional and fibre-reinforced instrument tips. The calculations and tests of the novel instruments made of PA6 reinforced with carbon fibres (CF-PA6) demonstrate a significantly higher cleaning efficiency and a clear failure tolerant structural behaviour compared to conventional polymer and nickel titanium instruments. The investigations show a large number of influencing factors on the operation of fibre-reinforced instruments under ultrasonic excitation. In this context, further tests have to be done to qualify a potential clinical relevance.