Location of contact areas on rotary Profile¹ instruments in relationship to the forces developed during mechanical preparation on extracted teeth

Abstract

The recorded torque values and the location on the instruments of the areas of contact with dentine during this development of torque i.e. at or near the tip, indicate that great caution should be used with the rotary technique, particularly with the taper 0.04 instruments, regardless of preparation technique.

Root canal preparation with FlexMaster: asessment of torque and force in relation to canal anatomy

“…Torsional fractures occur when the apical portion of a rotating instrument is forced into narrow root canals. Friction increases at this point, high torque is required to rotate the instrument and the fragile instrument tip is subjected to excessive torque (Blum et al 1999, Peters et al 2003. This e¡ect has been described as`taper lock' because it might occur with similarly tapered instruments of varying tip diameters rather than with variably tapered instruments (Yared et al 2002).…”

“…Other suggestions in that regard include limiting the use of rotary instruments while shaping root canals to between 10 or 20 s and not to remain in a canal once a certain working length has been reached (Ruddle 2002). Another method addressing torsional fractures is to construct cross-sectional geometries without radial lands, thereby increasing cutting e¤ciency and consequently reducing contact areas and torsional loads (Blum et al 1999), for example in ProTaper (Dentsply Maillefer, Ballaigues, Switzerland) or FlexMaster instruments ( Fig. 1).…”

Hand-operated and rotary mity instruments in combination with an endodontic handpiece and endodontic motor preparation: A comparison of shaping ability in simulated curved root canals

“…Higher stress levels are produced by decreasing the radius and moving from the apical to the mid-root position [12]. In and a strong instrument load due to torsional forces [15,16].…”

Cervical shaping in curved root canals: comparison of the efficiency of two endodontic instruments

“…Due to the fact that ste el ins tru ments are more ri gid, nic kel-ti ta ni um (Ni-Ti) ins tru ments have ga ined spa ce in the en do don tic ar se nal due to its great fle xi bi lity and "elas tic me mory". It ful fills the re qui re ments for ins tru men ta ti on of cur ved canals: re sis tan ce to frac tu res and fle xi bi lity 2,11,19 .…”