ABSTRACT
Objective: This study sought to assess the influence of cervical preflaring and reuse after
resterilization, on fracture strength and plastic deformation and/or surface cracking
in reciprocating nickel–titanium [NiTi] endodontic instruments after root canal instrumentation
of extracted human teeth. Materials and Methods: Forty engine-driven reciprocating NiTi instruments (20 Reciproc® [RC], VDW; 20 WaveOne® [WO], Dentsply) were used in root canal instrumentation of extracted human molars.
A total of 485 human upper molars with similar anatomical features were selected and
randomly distributed across four groups according to the instrumentation procedures
performed (G1 and G3: RC; G2 and G4: WO). Reciprocating instruments were used as per
manufacturer instructions. In groups G3 and G4, cervical preflaring was performed
prior to instrumentation. After each use of each instrument, sterilization was repeated
and scanning electron microscope (SEM) images were obtained to check for plastic deformations
and/or cracks on instrument surfaces. Each instrument was used repeatedly until fracture
occurred. Results: Regardless of flaring, RC files exhibited greater fracture strength than WO instruments
(P<0.01) with and without preflaring. Cervical preflaring significantly reduced the
risk of instrument fracture (P<0.01). No plastic deformations were observed before fracturing. However, cracks were
found on WO instruments shortly after their first use. RC and WO instruments resisted
fracturing after autoclave sterilization. Conclusions: Cervical preflaring allowed a significant increase in the number of times RC and
WO files could be reused safely.
Key words:
Dental instruments - endodontics - Reciproc - root canal preparation - WaveOne