Micro-Computed Tomographic Evaluation Of The Effect Of Instrumentation And Irrigation In C-shaped Canal

Objectives:To investigate the morphological features of C-shaped canal system in mandibular molar using the two-dimensional(2D)and three-dimensional(3D)morphometry parameters with the high-resolution Micro-CT scanning and image analysis software.To evaluate the effect of instrumentation using Reciproc Blue(RB;VDW,Munich,Germany)and XP-endo Shaper(XP-S;FKG Dentaire,La Chaux-de Fonds,Switzerland)systems on the area of untouched canal wall(AUCW),volume of dentin removal(VDR),accumulated hard tissue debris(AHTD),and the efficacy of three irrigation protocols on percentage reductions(red%)of AHTD within C-shaped canals of mandibular molars.Material and methods:Experiment One:The extracted mandibular molar with C-shaped canal system were selected with the 30μm Micro-CT scanning and data reconstruction.The canals were segmented using the two-dimensional Otsu image segmentation method in the CTAn software(v.1.14.4.1+,Sky Scan;Bruker micro-CT,Kontich,Belgium).The three-dimensional surface-models of C-shaped canal were created and saved as STL format files for further measurement.The distribution of each3D type of C-shaped canal was calculated.The two-dimensional and three-dimensional morphometry parameters included area,perimeter,major diameter,minor diameter,roundness,form factor,aspect ratio,volume and surface area were analyzed in the total canal and the different regions(apical&middle&coronal thirds).The classification in the cross sections of C-shaped canal was recorded in the different 3D types and locations.The numbers and location of accessory canals in C-shaped canal were recorded.Experiment two:Seventy specimens were scanned,anatomically matched,and assigned randomly to 2 shaping groups(n=35):RB and XP-S.Following instrumentation,specimens were scanned again.The scanning data sets before and after instrumentation were co-registered.The area of untouched canal wall(AUCW,in mm~2),volume of dentin removal(VDR,in mm~3)and volume of accumulated hard tissue debris(AHTD,in mm~3)in the total canal and the different regions were calculated.Data(AUCW%,VDR and AHTD%)were analyzed using comparisons for two groups(RB vs XP-S)and for different regions.Experiment three:Following instrumentation,specimens were triple-matched with respect to the amount of remaining debris and assigned to three irrigation subgroups(n=10):syringe-and-needle irrigation(SNI),XP-endo Finisher(XP-F;FKG Dentaire)and passive ultrasonic irrigation(PUI).The percentage of reduction(red%)of AHTD after irrigation were calculated from Micro-CT.Data were analyzed using comparisons for three subgroups in RB or XP-S groups,respectively.Results:Experiment One:The distribution of the three-dimensional classification of mandibular molars with C-shaped canal system was 63.1%in Type I,24.6%in Type II and 12.3%in Type III,respectively.There were significant difference in the proportion among three types(P<0.05).Type I was significantly more than Type II,which,in turn,was significantly more than Type III.The volume of C-shaped canal in various3D Types had no significant difference in the total canal and the different regions(P>0.05).The surface area of C-shaped canal in various 3D Types had significant difference in the total canal and the different regions(P<0.05).The surface area of Type I or II was significantly less than Type III in the total canal and the middle and coronal thirds(P<0.05);only the surface area of Type I was significantly less than Type III in apical third(P<0.05).The prevalence rate of accessory canal of mandibular molar with C-shaped canal was 36.8%(63/171).With a total accessory canals of 77,43(55.8%)were located at the apical third,28(36.4%)at the middle third and 6(7.8%)at the coronal third.About the distribution of accessory canal,the apical third was highest and the coronal third was lowest(P<0.05).The occurrence rate of accessory canal in the Type I,II and III C-shaped canal was 36.1%,35.7%and 42.9%,respectively.The occurrence rate of accessory canal had no significant difference among the different3D types(P>0.05).The Type I C-shaped canals predominantly exhibited C1 and C4configurations and the Type II and III predominantly exhibited C3 configuration in the cross sections at the location 1 mm and 2 mm from the apex.At the 3 mm level from apex,the C1 configuration was the most prevalent in Type I;the C3 configuration was the most prevalent in Type II;and the C1,C2 and C3 configurations could be found in Type III.In the middle region of the root canal,the C1 configuration was the most prevalent in Type I;the C3 configuration was the most prevalent in Type II;and the C2and C3 configurations were more common in Type III.In the coronal region of the root canal,the C1 configuration was the most prevalent in Type I;the C3 configuration was the most prevalent in Type II;and the C1 and C2 were more common in Type III.In the apical region,the C1 and the distal canal of the C2 configurations exhibited the lower roundness value and form factor,wider major diameter,longer perimeter,and higher aspect ratio of the root canals compared with C3 and C4 configurations.Experiment two:The pre-instrumentation surface areas(mm~2)and volumes(mm~3)were 86.7(43.6-172.6)mm~2 and 13.4(4.9-50.9)mm~3 in the RB group and 94.0(51.8-189.6)mm~2 and 17.4(3.9-37.6)mm~3 in the XP-S group,respectively.There was no significant difference in surface areas and volumes between the RB and XP-S groups before instrumentation(P>0.05).After instrumentation,the VDR and AUCW of the entire canal were 5.1(IQR 2.9)mm~3 and 33.0±6.5%in the RB group and 4.1(IQR 4.1)mm~3 and 30.5±9.0%in the XP-S group,respectively.There was no significant difference in the volume of dentin removal(VDR)or the percentage area of untouched canal wall(AUCW%)between the two groups(P>0.05).The apical and middle regions had significantly higher AUCW%when compared with coronal region in the RB group(P<0.05).For the XP-S group,the apical region had significantly higher AUCW%than the middle and coronal regions(P<0.05).Instrumentation with RB left more debris(2.8%)than XP-S(1.1%)(P<0.05).Significant differences between the RB and XP-S groups could only be identified from the apical and middle regions of the canal space.For canals instrumented with the RB or XP-S system,the coronal region of the canal space had significantly less debris than the middle region,which,in turn,had significantly less debris than the apical region(P<0.05).Experiment three:The vol%of AHTD before and after supplementary irrigation in three subgroups had no significant difference(P>0.05).Irrespective of the type of file system employed for canal shaping,the three supplementary irrigation protocols reduced the debris significantly in C-shaped canals(P<0.05).For the RB group,instrumented canals that had been subjected to XP-F or PUI activation had significantly higher mean red%of AHTD than instrumented canals that had been subjected to SNI(P<0.05);there was no significant difference between the XP-F and PUI subgroups(P>0.05).For the XP-S group,there was no significant difference among the three supplementary irrigation protocols in the red%of AHTD after canal shaping(P>0.05).Conclusions:The anatomy of C-shaped root canal system in mandibular molar is extremely complex.The morphology of C-shaped canal varies at different levels from the orifice to the apex considerably.Clinically,when a C-shaped canal orifice is found under the operating microscope,more glide paths should be designed on the basis of the specific anatomic shape to improve the effect of debridement.The occurrence rate of the accessory canal is high in mandibular molar with C-shaped canal.The incidence rate of the accessory canal beyond 3 mm from the anatomic apex was more than 50%.Therefore,it is inadequate to the mandibular molars with C-shaped canal to remove the most of accessory canals by cutting only 3 mm apical root in the endodontic surgery.The Reciproc Blue and XP-endo Shaper systems were associated with high percentages of untouched canal wall after shaping C-shaped canals in mandibular molars.The XP-endo Shaper system produced less hard tissue debris during instrumentation compared with the Reciproc Blue system.More untouched canal areas and a larger proportion of AHTD were observed in the apical region of the C-shaped canals irrespective of the canal instrumentation system used.None of the methods tested was capable of thoroughly removing the AHTD from the C-shaped canals.All three irrigation protocols were capable of significantly decreasing the amount of debris in instrumented C-shaped canals,irrespective of the file system employed for canal shaping.In the Reciproc Blue shaping group,XP-F and PUI were more effective than the SNI technique but did not differ from each other in their ability to clean the debris from the C-shaped canals.In the XP-endo Shaper group,there was no difference in debridement efficacy irrespective of the supplementary irrigation protocol examined.The cleaning of C-shaped canals might be achieved irrespective of irrigation regimen that was subsequently used.