| Objective:Root canal therapy is the basic treatment of pulp disease and periodontitis, in which good root canal preparation is the foundation of treatment success. The preparation of curved root canal is a difficult point in clinical work. It is not only to prepare the root canal shape that meets the requirements, but also to avoid and reduce the occurrence of fracture of the root canal preparation equipment. The application clinical commonly used stainless steel root canal file and using dental root canal instruments cycle fatigue performance test system to explore different root file cycle fatigue properties and variation of pipe bending degree and different cross-sectional area of the root canal, to guide the clinical practice to avoid root canal preparation instrument brokenMethods:1. Consulting reference and designing independently to develop experiment system of root canal instruments' cycle fatigue.2. 30 instruments of 30# stainless steel K files were randomly divided into 3 groups which included 10 for each one. From group 1 to 3 was inserted were tested cycle fatigue performance in three artificial canal with 45, 60, 90 degree alternatively.Useing 16:1 machine(350rpm,52Nmm) to drive stainless steel K files, record and statistics instrument fatigue time of each group, then observe fatigue surface by scan electronic mirror(SEM).3. 30 instruments of 25# stainless steel K files, the same to30 # and 35#, every kind of files are randomly divided into 3 groups which included 10 for each one, the total groups is 9, mark them 1-9 and 1-3 specific 25#-45°?30#-45°?35#-45°,4-6 specific 25#-60°?30#-60°?35#-60°, 7-9 specific 25#-90°?30#-90°?35#-90 °, the 9 groups were tested in 45, 60, 90 degree root canals alternatively. Using 16:1 machine(350rpm,52Nmm) to drive stainless steel K files, record and statistics the results.4. Continue with 3, collect fractures of 9 groups and measure fatigue crack tip of every group by electronic caliper and statistics results.Results:1. This experiment developed by ourselves maked the experimental environment stability. It maked experiment with high repeatability and normalization.2. The results of 1-3 groups are 3998.83±509.32,552.78±113.28,180.36±58.51,as shown in table 1, comparison of three groups has statistical significance(p<0.05).According to SEM images three groups files' fractures all are ductile crack,around fracture there are many dimples and make up the micro holes.3. The results of 1-9 groups are 7280.63(±1142.12),3998.83(± 509.32),2946.94(±541.45),1055.90(±239.71),552.78(±113.28),497.82(±81.21),240.62(±41.9),180.36(± 58.51),120.28(±18.14), comparison of 9 groups has statistical significance(P<0.05).4. The fracture crack tips of 1-9 groups are 5.60±0.40, 5.88±0.88, 5.50±0.35,5.40±0.48, 5.78±0.47, 5.10±0.21, 5.26±0.45, 5.00±0.22, 4.90±0.27(mm), In the same bending angle of root canal, root of different types of pipe file tip length was not statistically significant(P > 0.05), 25# stainless steel K-file in 45 #and 60 #,90 # bend root canal the length of the segment becomes shorter, the difference is not obvious(P > 0.05). 30#,35# stainless steel K-file in 45 # and 60#, 90 # bend root canal the length of the segment becomes shorter, the difference is statistically significant(P < 0.05).Conclusions:1. This experiment used in the test makes the experimental environment stability. It makes experiment with high repeatability and normalization.2. Through the fatigue test experiment of same type stainless steel K files in three typical angles crooked artificial root canals, analyze and verify that the larger angle of root canal the stainless steel K files will be fractured easier.3. The cross sectional area of stainless steel K files influence the fracture. Larger area lower cycle fatigue performance, and instruments fracture easier. Meanwhile,the result shows same effects on three different angles of canals.4. Measure fracture crack tips and statistics the results show that cross sectional area has unconspicuous impact on fracture position and the larger angle of root canal the shorter fracture crack tips, the stainless steel K files will be fractured easier. |
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