Effects Of Different Root Canal Preparation Instruments On The Formation Of Dentinal Microcracks Of The Older And The Young

Objective:To compare the incidence of dentinal microcracks in roots of extracted teeth after the root canal instrument with the stainless steel hand K-files,ProTaper Universal(PTU),Reciproc,M3 Pro-Gold systems in patients of the older and the young.Methods:According to the unified standard,one hundred fifty fresh mandibular premolar were extracted using an atraumatic procedure because of reasons unrelated to this study were collected and divided based on the patient age(in old patients between 65~80 years,in young patients between 16~30 years).Silicone rubber was used to simulate periodontal ligament,methacrylic acid resin was used to simulate alveolar bone.The samples for each age group were divided into five groups randomly.The control group was left unprepared.Four experimental groups were instrumented with the stainless steel hand K-files,PTU,Reciproc and M3 Pro-Gold.All premolar were accessed coronally with a diamond bur.Afterwards,a size 10~#K-file was placed in the canal until it was visible at the apical foramen,and working length(WL)was established 1.0mm shorter,0.25mm as a working width(WW)of unity.Then the roots were cut horizontally at 3mm,6mm,9mm form the apices using a emery grinding disc,and observed under a surgical microscope pictures and taken with a camera at a magnification of×25 to examine the sections for dentin microcracks.Finally,the Chi-square test was used to respectively analyze and compare the number of microcracked teeth produced by the of root canal instruments and the total number of microcracked teeth produced by all groups in three sections with SPSS 20.0 software of each age group.Results:1.Different degree of dentinal microcracks were observed in all five groups in older group,and there were significant differences in the number of microcracked teeth between five groups(P<0.05).2.No dentinal microcracks were found in the control group without preparation and hand K-files group in younger group,different degree of dentinal microcracks were observed in all three NiTi preparation groups,and there were significant differences in the number of microcracked teeth between five groups(P<0.05).3.In the K-files group?Reciproc group and the M3 Pro-Gold group,there was statistically difference in the number of microcracked teeth between2 age groups(P<0.05).4.From 2 age groups,the total number of microcracked teeth in the horizontal section from the apical 3mm was respectively higher than from the apical 6mm and 9mm of all preparatory groups,and there was statistically difference in the same horizontal section(P<0.05).Conclusion:1.The older groups are more likely than the youth to produce dentinal microcrackes after root canal preparation.2.Compared to the traditional K-files group,PTU group,Reciproc group and M3 Pro-Gold group can significantly increase the incidence of dentinal microcrackes of the root canal wall.3.The dentinal microcrackes produced at root canal wall from the apical 3mm were significantly more than at 6mm and 9mm during the root canal preparation.