Effects of Pitch Length and Heat Treatment on the Mechanical Properties of the Glide Path Preparation Instruments

• Four types of instruments with different pitch length and heat treatment were fabricated.
• All instruments had same size and shape except the pitch length and alloy treatment.
• Cyclic fatigue resistance, torsional strength, and screw-in force were compared.
• Heat treat makes files more flexible, lower screw-in force and torsional resistance.
• Short pitch makes files more flexible and torsion-resistant, lower screw-in force.

IntroductionThis study aimed to compare the effects of pitch length and heat treatment on the mechanical properties of glide path establishing instruments.MethodsPrototypes of glide path preparation files (#14/.03 taper) were made to evaluate the effects of different pitch lengths and heat treatments. The files were divided into 4 groups according to the pitch length (pG and OneG) and heat treatment (pGH and OneGH). For the torsional resistance test, ultimate strength and fracture angle were measured, and the file tip was fixed at 3 different levels of 2, 4, and 6 mm from the tip (n = 10 for each level). The toughness was calculated by multiplying the ultimate strength and the fracture angle. The cyclic fatigue resistance was compared by measuring the number of cycles to fracture in a curved metal canal (n = 10). The screw-in forces were measured during instrumentation motions with a sequential increase in the pecking distance of 1 mm until the file reached the end of the simulated resin canal (n = 10).ResultsThe heat-treated groups showed lower toughness and higher cyclic fatigue resistance than the non–heat-treated groups. The short pitch groups showed significantly higher torsional strengths than the long pitch groups. The heat-treated groups had significantly lower screw-in forces than the non–heat-treated groups.ConclusionsUnder the limitations of this study, the torsional strength of the experimental file was reduced by heat treatment and increased by the short pitch length. Thus, a non–heat-treated file with a shorter pitch length would be favorable as a rotary glide path instrument.