The Influence Of Different Techniques On Removal Of Smear Layer With Thermoplasticized Gutta-perch Injection On Coronal Microleakage

Objective:The coronal microleakage is a main factor causing to endodontic failure after root canal therapy,which is more important than apical microleakage. The result of incomplete coronal obturation leads to the microorganisms and their metabolized substances penetrating through the gap between obturation materials and the wall of root canals.The cleanness of root canal influences the sealing of the root filling material and root canal walls. The smear layer is the major factor which affects root canal sealing .Many techniques can remove the smear layer including chemical preparation, ultrasonic irrigation and laser irradiation.But the single technique can not remove the smear layer completely. There are a few reports about the application of the combination of different methods .The purpose of this study is to compare the effect of five different techniques on removal of smear layer under scanning electron microscope. At the same time,the coronal microleakage is checked using Obtura II thermoplasticized gutta-perch injection technique by dye penetration and transparent technique.Methods:Seventy-two human single-rooted teech were extracted and their crowns were cut at the cervical limit.Then they were instrumented using the crown-down technique with the PROTAPER system to 1mm from the anatomical apex to a size 30.06 taper file.The instrumented teeth were then distributed randomly in six experimental groups of 12 teeth each. Group A:smear layer left; Group B: smear layer removed with 5.25%sodium hypochlorite(NaOCl) and ethylenediamine tetraacetic(EDTA) gel; Group C: smear layer removed with ultrasonic irrigation; Group D: smear layer removed with Nd:YAG laser irradiation; Group E: smear layer removed with 5.25%NaOCl +EDTA gel and ultrasonic irrigation; Group F: smear layer removed with 5.25%NaOCl +EDTA gel +ultrasonic irrigation and Nd:YAG laser irradiation. Two specimens of every group were then split longitudinally into equal segments and canal walls at coronal,middle, and apical portion were examined at 500x magnification under an scanning electron microscope.Then ten teeth of every group were filled using Obtura II thermoplasticized gutta-perch injection technique. The teeth were stored in the condition of 37 degrees C and 100% humidity for 2 days. Then they were thermocycled and the extent of coronal leakage were determined for each group after immersion in methylene blue for one week . The teeth were demineralized, dehydrated and immersed in methylsalicylate, which rendered them transparent. Linear measurement of maximum dye penetration was recorded under a steremicroscope and a microphotograph system .The data obtained were statistically analysed by one-way anova and Student Newman-keuls test.Results:1.An SEM study :In group A there were smear layer and debris remained and dentine tubules were covered; The cleanness of root canal walls have an improvement with open dentine tubules in group B and C,but the effection in coronal,middle portion were better than apical portion;In group D the root canal dentine were melted and ablated; In group E the use of ultrasonic with 5.25%NaOCl and EDTA gel improved smear layer removal; In group F the distinct cleanness of root canal walls especially apical portion by the combination of three techniques .2.Coronal microleakage: The results showed that mean depths of coronal microleakage for group A,B,C,D,E and F were 2.15+0.38mm,1.75+0.28mm,2.02+0.37mm,1.73+0.36mm,1.33+0.30mm and 1.20+0.33mm respectively. The analysis showed that the linear in the groups of the smear layer removed were shorter than group A; and group E and group F performed significantly better than group A,B,C and D.There were no significant difference between group B,C and D(p>0.05). There were no significant difference between group E and group F(p>0.05). There were no significant difference between group A and group C(p>0.05). Conclusion:1.Because of the risk of coronal microleakage, the corona of endodontically treated teeth should be restored as quickly as possible.2.It was concluded that the removal of smear layer has an significant influence on the degree of coronal microleakage.3.The combination of three techniques was better than single method on removal of smear layer,especially in the apical third.