Reciprocating kinematics in endodontics

The mechanical and biological objectives of endodontic treatment are the modeling and cleaning of the root canal system (SCR), from the removal of vital and / or necrotic pulp residues, disorganization of the bacterial biofilm, facilitating the disinfection of the canal through irrigation and providing adequate conformation for subsequent sealing.

Since mechanical preparation is an essential part of endodontic treatment, several approaches have been proposed, with the aim of improving the shape of the canal, cutting efficiency, flexibility and safety of the instrument. The new Nickel-Titanium (NiTi) systems and different activation kinematics are emerging.

For mechanized endodontic treatment, there are two types of movements or kinematics: rotational and reciprocating. And, what is the essential difference between them? The rotary rotates continuously 360 ° counterclockwise, while the reciprocating one presents an asymmetric oscillatory movement, in which the file rotates 150º counterclockwise, cutting the dentin and then, in the opposite direction, rotates 30º in the direction time to collect and loosen the dentin. Consequently, these instruments complete a complete rotation over several cycles of alternating movements, which can be defined as "partial reciprocity with a rotating effect".

The introduction of reciprocating kinematics combined with the development of NiTi files for mechanized preparation of SCR represents one of the most recent technological applications in Endodontics. Since its commercial launch in 2011, reciprocating systems have aroused great interest in clinical practice, in addition to being a recurring theme in scientific and philosophical conflicts in the academic community.

Currently, there is a solid base of scientific evidence about the benefit of reciprocating movement in relation to rotational movement, demonstrating that it is safe and effective in the preparation of curved root canals, reducing cyclic fatigue, torsional stress and working hours. The Reciproc (VDW, Munich, Germany) and WaveOne (Dentsply Maillefer, Ballaigues, Switzerland) systems are the main examples of systems for preparing root canals using reciprocating motion. Both instruments are made of M-Wire alloy.

M-Wire instruments are produced using a thermomechanical procedure developed with the objective of producing a NiTi superelastic alloy, optimizing the behavior of the microstructure and transformation of the traditional NiTi alloy. The manufacturing process of M-Wire can substantially increase flexibility and mechanical strength compared to conventional NiTi alloy.

WaveOne® Gold files (DENTSPLY-Sirona, Ballaigues, Switzerland) - a new generation of the WaveOne system - are single-use instruments and highlight the optimization of apical diameters, taper and cross section to ensure file safety, efficiency and flexibility .

WaveOne® Gold is more resistant to cyclic fatigue when compared to ordinary NiTi. Due to their functionality, they have a slightly curved shape, so that they can shape and follow the path according to the anatomy of the root canal (Dentsply, 2011). This system is made in NiTi with technology and heat treatment and Gold staining due to the thickness of the titanium oxide layer, having four different dimensions: 20.07, 25.07, 35.06 and 45.05.

The Reciproc system (VDW, Munich, Germany) is manufactured from a nickel-titanium alloy called M-Wire. During the manufacture of these instruments, the alloy undergoes a heat treatment that provides greater flexibility and resistance to cyclic fatigue. The Reciproc system consists of instruments with size 25.08.40.06 and 50.05 in the first 3 mm with an "S" shaped cross section:

These unique files in reciprocal movement represent a convenient solution to facilitate the treatment of the root canal. In fact, it has been shown that a single file, rotating at uneven angles, is four times safer and almost three times faster than several rotary files to achieve the same final shape.

The two systems of “single use” instruments, where a single instrument is used to prepare and model the root canal, even in curved or atresia channels, without requiring a pre-enlargement before instrumentation, according to the literature, indicating shorter working time, shorter learning curve, reduced number of instruments and greater safety in relation to fracture.

Therefore, the success of endodontic treatment is conditioned to the correct and harmonious execution of all stages of preparation that require biological knowledge and clinical experience from the professional, as well as constant monitoring of the evolution of the specialty in order to establish the best approach and instruments to be used. used, basing all decision making on scientific evidence, benefiting patients by reducing the risk of iatrogenesis and accidents, increasing the predictability of the proposed treatment.

Source: Sanar Saúde. Available at: https://www.sanarsaude.com/portal/carreiras/artigos-noticias/colunista-odontologia-a-cinematica-reciprocante-na-endodontia. Access on: 02/26/2021.