Efficacy Of Different Nickel-titanium Preparation Systems In Removing The Filling From Oval Root Canals: A Comparative Study

Objective:Root canal therapy is usually considered to be the first treatment option for pulpal and periapical disease.However,due to various reasons such as the complexity of the anatomy of the root canal system and the limitations posed by the design of conventional instruments,the success rate is also uneven.Nonsurgical root canal retreatment is usually considered to be the first treatment option for endodontic failure because of the persistence of bacteria within the root canal system.Removing the filling material and gaining access to the apical foramen are the key steps for retreatment.At present,there are a variety of clinical methods for removing root canal fillings.Among them,nickel-titanium instruments for root canal retreatment are widely used in clinics because of their advantages of high rigidity,cutting ability and strong penetration.Pro Taper retreatment system（PTUR）was suggested for this purpose.This system comprises D1,D2,and D3 files that have convex,triangular cross section in a continuous rotation motion.D1 file has an active working tip that first penetrates into the root canal filling material.The XP-endo Shaper（XPS）instrument is made of Max-Wire alloy and can undergo phase transformation at body temperature,assuming a snake-like shape that expands and contracts to adapt itself to the canal morphology.Previous studies have shown that its ability to shape root canals is better than traditional nickel-titanium instruments,but there are few studies on its application in root canal retreatment.Con Cept One Plus（CCOP）is a single file system made of M-wire material,its unique loose spiral design and longitudinal slitting on the cross section make it expand the space in the root canal.In addition,its high-quality nano-ceramic material coating makes it have extremely high hardness,so its cutting ability is strong.However,its application in root canal retreatment is still unclear.However,according to previous research,there is no way to completely remove the fillings in the root canal.Fillings material remnants can shield residual bacteria located on canal walls,or in dentinal tubules,lateral canals and isthmuses and protect them from the antibacterial effects of irrigants and medicaments used during retreatment.Therefore,we aimed to assess the efficacy of 3 different retreatment techniques in mandibular premolars by using micro-CT.Method:Thirty extracted mandibular premolars with a single oval root canal were collected clinically.The specimens were carried out access cavity preparation using a high speed diamond bur under water.A size 10 Stainless steel K-file was used to standardize the working length of all roots to 1mm.Then dredged to size 15 K-file.The specimens were instrumented up to F2 with Pro Taper.Irrigation and drying.The root canal was filled by using continuous wave of condensation technique.Store at 37℃,100%humidity for 1 week.The specimens were randomly divided into 3 groups:Group A:Pro Taper Universal Retreatment（PTUR）;Group B:XP-endo Shaper（XPS）;Group C:Con Cept One Plus（CCOP）.Record the operation time.The same flushing volume is used during the irrigation.Use 2 ml of distilled water for irrigation between files.The total amount of flushing fluid for each sample is 12 ml.The empty tube collection model was used to collect the debris pushed out from the apical foramen during retreatment,accurately weighed(10^-5 g)and analyzed statistically.Before and after re-treatment,the samples were scanned by Micro-CT and 3D reconstruction.The volume of the filling were measured using image processing software,and the data were analyzed.Results:1.Residual amount of filling:none of the three mechanical instruments can completely remove the filler in the root canal,and there is no significant difference in the volume of the residual filler compared with the three groups（P>0.05）.2.Operation time and complications:The root canal preparation time of the CCOP group is the shortest,followed by the PTUR group,and finally the XPS group,and all three groups have statistical differences（P<0.05）.No complications such as device separation and perforation occurred in each group.3.Amount of apically extruded debris:The PTUR group had the largest the amount of apically extruded debris,which was statistically different from the other two groups（P<0.05）,followed by the XPS group,at least the CCOP group,there is no statistical difference between the two（P>0.05）.Conclusion:1.Three nickel-titanium instruments can safely and effectively remove most of the filling in the root canal.Among them,CCOP has the highest rate of removing root fillings.2.In the root canal retreatment,the amount of debris in the apical region of CCOP is the smallest.But this result still needs to be verified by clinical trials.