Analysis Of Torque During Canal Instrumentation Using Rotary Endonontic Instruments Under Dynamic Condition

Aim A new accurate device was developed to measure the torque duringinstrumentation under dynamic conditions. Analyse the characteristics of the torque , which would help to enhance the understand of torsional fracture and reduce the risk of torsional fracture of instrument in the clinical therapy. Furthermore, the new device could be potentially developed to a new canal preparation equipment.Methods A specially designed machine, the Auto Synchronous TorqueMeasure System (ASTMS), was constructed to measure the torque during instrumentation. ASTMS reflected the torque generated during instrumentation by the current flowing the motor which drove the instruments. 222 bovine bone simulated root canals of identical size with different lengths were made and divided into three parts. Part one, including total 120 simulated canals of which lengths were 2, 4, 6,and 8mm respectively, was divided into five groups matching with lengths and source of canals, being tested for five instruments of size 25, 0.04-tapered Profile, 0.06-tapered Profile, 0.02-tapered Nitiflex, 0.02-tapered Smart, and 0.02-taper Mini U-file, penetrating through the canals at a cross-speed of 6mm/min with continuous irrigation respectively. Part two, including 72 simulated canals of which lengths were 2, 4, 6,and 8mm respectively, was divided into three groups matching with lengths and source of canals, being tested for 0.04-tapered Profile, 0.06-tapered Profile, 0.02-tapered Smart penetrating through the canals at a cross-speed of 6mm/min without continuous irrigation respectively. Part three, including 30 simulated root canals of which lengths were 4mm, was divided into five groups matching with source of canals, being tested for 0.04-tapered Profile penetrating through the canals at five different speeds of 3,6,12,24,and 36mm/min with continuous irrigation respectively. All instruments worked in a rotation of 300rpm.Result (1) The current flowing through the endodontic motor had a liner relationship with the torque applied to the instruments .The current could reflect the torque in real time; (2)The torques were different from various instruments duringinstrumentation; (3)The bigger the taper or size was, the bigger the torque; the faster the penetrating-speed or the longer the canal that instruments penetrating through was, the bigger the torque also; (4)The value and the variation of torque was significantly higher without irrigation during mechanical preparation, or when the simulated root canals of which instruments penetrating through were longer than 4mm, or when the speed that instruments penetrating the simulated root canals was faster than 12mm/min(p<0.05); (5) when the tip size was less than 0.59mm and the length of stimulated canals that instruments penetrating through was 2mm, the torque of 0.04T Profile was not more than 10.50?.72gcm. While the length of simulated canals was 4mm, the torque of 0.04T Profile was not more than 33.63?6.33gcm and that of 0.06T Profile was not more than 78.00?.39 gem.Conclusion (1) The use of ASTMS provided a new approach to theanalysis of mechanical preparation. In this way, an efficient clinical potential can be confirmed for engine-driven rotary instruments in canal preparation; (2) The irrigation condition, the design of instruments, the speed and the depth of instruments penetrating into canals all effected on the torque during canal instrumentation and the factors could do a magnifying superpose effect; (3) As anti-torsional-fracture was concerned, enlarging the canals by various taper crown-down technique with continuous irrigation, avoiding not inserting the instruments faster than 6mm/min or deeper than 4mm, might reduce the risk of fracture.