Influence of nickel-titanium rotary systems with varying tapers on the biomechanical behaviour of maxillary first premolars under occlusal forces: a finite element analysis study

AimTo evaluate the effect of three nickel-titanium (Ni-Ti) rotary systems with varying tapers on stress distribution and to analyse potential fracture patterns as well as the volume of fracture-susceptible regions in two-rooted maxillary premolars. MethodologyThe root canals of three single-rooted premolars were prepared with either HeroShaper (Micro-Mega, Besancon, France) to (size 30, .04 taper), Revo-S (Micro-Mega) to AS30 (size 30, .06 taper) or ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland) to F3 (size 30, .09 taper) Ni-Ti files. The three root canals were scanned using micro-computed tomography (CT) (Skyscan 1174, Skyscan, Kontich, Belgium) and modelled according to the CT data. An intact tooth model with a root length of 16mm was also constructed based on CT images of an extracted maxillary premolar with two roots. New models were constructed by replacing both of the original canals of the intact two-rooted premolar model with the modelled canals prepared with the HeroShaper, Revo-S or ProTaper Universal system. Occlusal forces of 200N were applied in oblique and vertical directions. Finite element analysis was performed using Abaqus FEA software (Abaqus 6.14, ABAQUS Inc., Providence, RI, USA). ResultsUpon the application of oblique occlusal forces, the palatal external cervical root surface and the bifurcation (palatal side of the buccal root) in tooth models experienced the highest maximum principal (Pmax) stresses. The application of vertical forces resulted in minor Pmax stress values. Models prepared using the ProTaper system exhibited the highest Pmax stress values. The intact models exhibited the lowest Pmax stress values followed by the models prepared with the HeroShaper system. ConclusionThe differences in Pmax stress values amongst the different groups of models were mathematically minimal under normal occlusal forces. Rotary systems with varying tapers might predispose the root fracture on the palatal side of the buccal rootand cervical palatal root surface in two-rooted premolars.