Effects Of Dentin Moisture Conditions On The Closure Property Of Four Root Canal Sealers

Defects of tooth caused by dental diseases such as caries may act as pathway for bacteria to break into root canal systems, leading to dental pulp diseases and periapical diseases. The aims of treatment for these diseases are to remove the infected tissues in root canal systems, to restore the defects, and to recover the form and functions of teeth. Root canal therapy(RCT) is so far the most common and effective method to achieve these aims,which is composed of root canal preparation, disinfection and obturation.The obturation quality is an important index to evaluate the quality of the root canal treatment,because “ in the final analysis, it is the sealing of the complex root canal system from the periodontal bone that ensures the health of the attachment apparatus against breakdown of endodontic origin”.Therefore, an ideal post-RCT canal system is a canal system without any microleakage. The microleakage is a kind of small space inside the obturation materials or between the obturation materials and the canal wall.Endodontic sealers are used for the filling of any voids and gaps between the solid-core filling materials, semisolid-core filling materials and dentin. Because of poor flowability and poor compliance, solid-core filling materials or semisolid-core filling materials alone for canal obturation will inevitably result in viods and gaps, which can be compensated by sealers. Therefore microleakage can be decreased.With the development of dental materials, apparatuses and equipments,new clinical techniques have been developed, which greatly improve the diagnosis and treatment efficiency, so that both the operation time and the number of appointments are decreased.However, new techniques are facing intractable clinical scenarios. For example, it is a problem for single-visit RCT to effectively control the liquid infiltration.The residual liquid can make the root canal present different conditions of dentin moisture. To what extent the dentin moisture conditions will affect the closure property of root canal sealers?This is the topic we are paying close attention to, and will be investigated in our research.Experiment One: Detection for the difference of dentin moisture conditions caused by four drying methods.One freshly extracted upper third molar with single root canal was included in this study.After crown removal and root canal preparation, the root canal was filled with distilled water. There were 4 drying methods:(1)D(Dry):distilled water was removed with paper points followed by dehydration with 95% ethanol.(2)L(Less dry):the canal was blot dried with paper points with the last one appearing dry.(3)m(Moist):the canal was blot dried with one single paper point for 30 s.(4) W(Wet):the canal was left totally flooded. Firstly the root canal was handled using method D, then the first spot of 6 spots humidity indicatorcard was used to measure the moisture level(moisture level would be reflected by color change of the indicatorcard).Subsequently the second spot of 6 spots humidity indicatorcard was used to measure the moisture level after method D handling. Moisture levels of the other three drying methods were also measured and the results were determined according to the manufacturer's instructions.The results showed that the humidity level after handled by method D was 10%~20%;20%~30% by method L;50%~60% by method m; more than 60% by method W. Based on the results, it was concluded that different drying methods could make different dentin moisture conditions.Experiment Two: Effects of dentin moisture conditions caused by water on the closure property of four root canal sealers.One hundred and twelve freshly extracted permanent teeth with single root canal were included in this study.After crown removal and root canal preparation,ninty-six were random Ly divided into four groups of twenty-four each:group A(AH-plus), group M(MTA), group I(IRoot) and group E(Endosequence).Each group were further divided into four sub-groups with respect to the moisture conditions: D, L, m and W. The remaing sixteen teeth were used as positive controls and negative controls.After different drying methods, the root canals were filled with corresponding sealers, together with warm gutta-percha using vertical compaction. Microleakage was assessed by ink staining after seven days.The results showed that there were different closure property of four root canal sealers under various dentin moisture conditions(P < 0.05).Under dry and less dry root canal conditions, the closure property of IRoot and Endosequence had no significant difference with that of AH-plus(P>0.05),but were better than that of MTA(P<0.05).Under moist and wet root canal conditions, the closure property of IRoot was better than those of AH-plus and MTA(P<0.05).Experiment Three: Observation of microleakage of four root canal sealers by SEM under different dentin moisture conditions.Sixteen freshly extracted permanent teeth with single root canal were randomLy divided into sixteen groups by the conditions of sixteen sub-groups in Experiment Two. After crown removal and root canal preparation,sixteen teeth were dried and filled according to the group conditions. After seven days, forty-eight specimens were obtained by sectioning at 2mm,4mm,6mm distance from every apex of 16 teeth, by using a low speed diamond disk.These specimens were then processed using acid etching, douching, drying and metal spraying. SEM was then used to observe the interfaces between the sealers and semisolid core filling materials, together with the interfaces between the sealers and dentin.The results showed there were more graps in Ah-plus,IRoot and Endosequence in the moist condition than in the dry conditon(P<0.05). MTA and gutta-percha were missing at the specimen 2mm distance from the apex. The results of Experiment Three partly explained the results of Experiment Two.closure property of four root canal sealers.Experiment Four : Effects of dentin moisture conditions caused by blood on theTwenty-six freshly extracted permanent teeth with single root canal were included in this study. After crown removal and root canal preparation,twenty-four teeth were random Ly divided into four groups of six each : A(AH-plus), M(MTA), I(IRoot)and E(Endosequence). The remaining two teeth were used as positive controls.After crown removal and root canal preparation, the root canals were filled with blood of one laboratory rat. They were dried by m drying method. And then the root canals were filled with corresponding sealers by warm gutta-percha. Microleakage was assessed by ink staining after seven days.The results showed that there were differences between blood and water. The closure property in blood of Endosequence were better than that in water(P < 0.05). And the closure property in blood of IRoot and Endosequence were the same to dry root canal condition in water(P>0.05). The closure property in blood of AH-plus and MTA had no significant difference with moist root canal condition in water(P>0.05).To sum up, there were effects of dentin moisture conditions on the closure property of four root canal sealers. The degree of effect depended on the type and quantity of liquid and the type of sealers. It is suggested that suitable sealers should be choosen according to dentin moisture conditions.