Tese
Efeito da sequência de processamento durante a fabricação de instrumentos endodônticos Niti em suas propriedades mecânicas
Fecha
2020-10-30Autor
Gustavo De Cristófaro Almeida
Institución
Resumen
The geometric characteristics and manufacturing techniques of endodontic
instruments affect clinical performance, fracture resistance, flexibility and other
properties. A parameter widely explored in Endodontics is the use of heat treatments,
which promote an increase in the resistance to fatigue and flexibility of these materials.
This study aimed to evaluate the effect of different heat treatment / machining
processes on the physical properties, flexibility, torsional strength and flexural fatigue
of Prodesign Logic (PDL) instruments, verifying whether the processing sequence of
the instruments would lead to different mechanical behaviors. This system is
manufactured using an innovative method that involves performing thermal treatment
to obtain shape memory in the NiTi wire prior to machining. The null hypothesis to be
tested is that the moment of application of the heat treatment and machining
procedures would not affect the physical and mechanical properties of NiTi endodontic
instruments. For comparison groups, instrument prototypes with the same geometric
and dimensional characteristics were used, being one group of instruments without
thermal treatment applied (SEP) and another with thermal treatment carried out in a
conventional manner, after machining the instrument (HTP). Physical and
microstructural characterization were performed with differential scanning calorimetry
(DSC) tests and X-ray diffractometry (XRD) tests, in addition to mechanical tests
divided into torsion tests, 45° bending and resistance to flexural fatigue. The results
showed that macroscopically there were no major change in the characteristics of the
three groups of instruments, except for color changes due to different processing
sequences. The DSC results showed that at room temperature the alloy is mainly
austenitic in the SEP group and that after the heat treatment carried out in the PDL
and HTP groups, there was a change in the transformation temperatures, with an
increase in the Af temperature and predominance of the NiTi alloy in phase R. The
XRD results confirmed the DSC findings. Differences in the parameters measured
between different types of instruments in the tests of torsional resistance, bending at
45º and flexural fatigue were always considered with a significance level of 95%. The
results for the flexibility tests showed that the HTP group proved to be the most flexible,
with the lowest values, followed by PDL and SEP. In the results of the torsion tests it
was possible to observe that SEP presented higher values of torque followed by PDL
and HTP (p <.05). Fatigue resistance tests showed higher mean NCF values for HTP,
followed by PDL and SEP. However, a worse behavior of the PDL would only be
evidenced clinically if the instruments were used several times greater than that
recommended by the manufacturer. It can be concluded that changing the
manufacturing process of endodontic instruments, inverting the machining and heat
treatment steps, led, in fact, to a change in the mechanical behavior of Prodesign Logic
instruments in relation to the prototypes.