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The superelasticity of NiTi shape memory alloy has been used in endodontics since the 1990s. To study the mechanical behavior of endodontic instruments, a traditional approach consists in experimental investigations. However, finite element analysis constitutes another way to assess their mechanical behavior and to facilitate their design. The main aim of this study is to compare experimental and numerical bending results on different structures (NiTi wire, spreader, and instruments) to estimate the reliability of the finite element simulations. These investigations were carried out as follows. Firstly, experimental material parameters identification was performed using NiTi wires. These parameters were implemented in an appropriate NiTi model. Bending was numerically applied to the meshed structures generated by the finite element method. Experimental tests were performed on real structures under bending, with exactly the same loading, in order to compare experimental and numerical results. These results were in good agreement for each of the considered structures. This enabled the validation of the simulation results and the use of simulations to design new endodontic instruments.

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Superelastic NiTi SMA is the base of endodontic files. The flexibility of these instruments permits the preparation of root canals. Unfortunately the intracanal file separation can occur. To have a good idea of the mechanical behavior of these instruments, we propose in this study the finite elements simulations taking into account the real shape of root canals. This has been possible by using a well adapted model describing all the particularities of superelastic SMA and by using representative limit conditions.

Aim:The aim of this study is to evaluate the influence of final canal taper on the sealing ability of Thermafil by using microcomputed tomography (micro-CT). Materials and methods:Fifty-four single-rooted teeth were instrumented to apical size 40 taper 4, 6 and 8%. Teeth were divided into three groups. All teeth were filled with Thermafil (Dentsply,Tulsa Dental Products). Using micro-CT, roots were scanned and volume measurements of voids at 1, 3 and 5 mm from the apex were calculated using specialized CT software. Measurements were analyzed statistically with ANOVA followed by Bonferroni multiple comparison correction.Results: Data analysis showed that 0.08 preparations provided better results than 0.06 and 0.04% tapered samples especially at 1 mm from the apex. Mean percentage of voids were significantly higher with Thermafil taper 0.06% (p = 0.05). None of the root canals filled teeth were gap free. Root canal preparations with bigger taper exhibited less voids than smaller tapered preparations.Clinical significance: In our daily practice, enlarging the apical third (last 3 mm) of root canals to an 8% taper gives a better sealing ability and thus long-term success for our root canal obturations.

The 3-D representation of temporomandibular joints can be performed using magnetic resonance imaging. We carried out a MRI on an asymptomatic volunteer subject. Images were reconstructed in three dimensions. This reconstruction allowed the description of the principal anatomical elements of this joint : articular disc, condyle, bilaminar region and temporal bone. A preliminary study of articular function, in the sagittal plane was also carried out with measurement of real movements of the disc.