Comparison Study On The Effect Of Three Nickel-Titanium Rotary Instruments In Root Canal Preparation

Objective:Both pulpitis and periapical periodontitis are common oral diseases and harmful to human oral health.They are caused by many reasons and mainly by bacterial infections.When the lesions develop to the dental pulp and root apex,an effective and perfect canal treatment will be used as the preferred method in the treatment of pulpitis and periapical disease.The root canal preparation plays roles of complete removal the inflamed dental pulp and necrotic tissue from the root canal,expansion of shaped root canal and appropriate root canal disinfection,providing a basis for tight root canal obturation.A continuous tapered and funnel-shaped root canal is considered suitable for root canal obturation during complete removal of infected root canal in modern Oral Medicine,which is one of the key factors determining the success or failure in root canal treatment.Any instrument used for root canal preparation will cause the generation of debris and dentinal smear layers on the internal wall of root canal in the process of preparation.These debris and dentinal smear layers are firmly attached to the internal wall of root canal and squeezed to the apical foramen region by the instrument used for root canal preparation and partially or completely blocked the apical foramen region in the process of root canal preparation,resulting in incompletely filled apical 1/3 or completely unfilled apical foramen region.This will lead to the secondary infection in the apical region and affect of root canal filling,thus increasing the probability of root canal infection.These factors affecting the root canal filling materials and adhesion between root canal walls may cause incomplete apical filling and lead to the emergence of apical microleakage,thus affecting the filling effect.Therefore,the comparison of the cleaning degrees of debris and dentinal smear layer on the root canal wall with different rotary nickel-titanium instruments is the key in comparison of the degrees of root canal cleanliness and apical microleakage with different engine-driven nickel-titanium instruments in root canal preparation.This study intends to investigate the effects of three engine-driven nickel-titanium instruments in the process of rootcanal treatment,compare the ability of root canal preparation and apical sealing ability among three instruments,and infer the differences in work efficiencies of three endodontic instruments and their best adapting conditions,thus providing an experimental basis for selection of instruments used for root canal preparation and root canal filling materials.Methods:Sixty maxillary first and second premolar teeth removed for orthodontic reasons were selected in this study.The sample teeth were all intact,with complete apical foramen,without parenchymal lesions or various lesions in the apical region.The root canal curvatures were greater than 25 degrees.They were numbered and randomly divided into three groups,including group P(Protaper),group M(Mtwo)and group K(K3).The root canals were prepared in three groups referring to the recommended methods by the manufacturer.The teeth were divided into two groups by the random sampling method.The tooth samples in each group were divided into two subgroups.A subgroup was used for comparative study of the cleaning ability of root canal in three engine-driven nickel-titanium instruments.The samples were cut off at the tooth neck with a slow-speed handpiece,keeping the whole root of each sample.A longitudinal fissure was then polished with a slow-speed handpiece equipped with an emery grinding head from the development line of the root in the imaginary plane along the curved root,which was not penetrated with the root canal.The whole root was then gently scraped into two parts with the bone hammer and bone chisel in accordance with the direction of the longitudinal fissure,which avoided the generation of tooth debris cut by a slow-speed handpiece and prevented anthropogenic pollution of root canal.The samples were fixed with 2.5%glutaraldehyde in phosphate treatment solution(pH7.3)for 48 hours,followed by gradient dehydration with 75%,85%,95%and 100%ethanol respectively.The samples were placed in a vacuum dryer for critical point drying.The distribution of debris and dentinal smear layer formation on the internal wall of root canal in in vitro teeth after root canal preparation of different nickel-titanium instruments were observed by scanning electron microscope.They were scored by the evaluation criteria.The scoring was completed and then examined by using Kruskal-Wallis test method.When the statistical results showed P<0.05,it was indicated that there were significant difference in root canal shaping and cleaning effect.The other subgroup was used for determination of the sealing ability of root canal.After root canal preparation,the canals were then filled with AH paste and hot gutta-percha.The specimens required in testing apical sealing ability were prepared.The transparent technology was used for microleakage detection.Photoshop 10.0 software was used for analysis of the length of root canal microleakage,which was then recorded.Chi-square test was used for analysis of enumeration data and analysis of variance was used for analysis of measurement data.Results:Dentinal smear layer:After the root canal preparation of engine-driven nickel-titanium instruments,the dentin smear layer was concentrated in apical 1/3.The dentinal tubules were clearly visible in canal and root parts.Meanwhile,scattered cloudy or lumps debris were occasionally visible in group P and group K,without statistically significant differences.Debris on the root canal wall:The debris scores on the internal wall of root canal at root canal coronal 1/3 were compared among three nickel-titanium instruments and were no significantly different(P>0.05).The debris scores were no significantly different at root canal 1/3 between group P and group M,while it was significantly different in group K compared with group P and group M(P<0.05).The results of debris scores at apical 1/3 were the same with those at root 1/3(P<0.05).The amount of dye penetration in group K was the highest among three groups of engine-driven nickel-titanium instruments.It was no significantly different among three groups(P>0.05).Conclusions:1.The distribution of smear layer formation on the internal wall of root canal after root canal preparation by three nickel-titanium instruments was observed by scanning electron microscope(SEM at 1500×magnification)and no significantly different among three groups.The results suggested that the difference in smear layer formation was not significant among ProTaper,Mtwo and K3 root canal preparation.2.The distribution of debris formation on the internal wall of root canal after root canal preparation of three nickel-titanium instruments was observed by scanning electron microscope(SEM at 1500× magnification)and no significantly different among the debris scores on the internal wall of root canal of three nickel-titanium instruments at coronal 1/3(P>0.05);but significantly different at middle 1/3 and apical 1/3(P<0.05).The result suggested that the cleaning effects of ProTaper and Mtwo middle and apical 1/3 were better than that of K3 3.The detection of apical microleakage showed that three kinds of instruments were the same.