A Study On The Root Canal Taper Of Ⅳ Type Maxillary First Premolars And Comparative Of Two Different Rotary Nickel Titanium Systems In The Preparation Of Canals

AIM: Measuring the original diameter and taper of the type IV maxillaryfirst premolars, and provide the basis and device selection for the clinical rootcanal preparation.MATERIALS AND METHODS: Collection a total of40samples maxillaryfirst premolars of age40-60-year-old from Jilin, China.After pretreatment andMicro-CT tomography,get the maxillary premolar image to import MIMICS16.0software system. Measure the diameter of every root canal segment. Accordingto the formula: C＝（D－d）/l，calculate the taper of root canals.RESULTS:①The buccal and palatal lateral root canal diameters of type Ⅳ maxillaryfirst premolar are all bucco-lingual diameter greater than the mesio-distaldiameter and bucco-lingual diameter gradually increases from the apical to thecoronal. There was significant difference (P＜0.05) except between the apicaland foramen; similarly, mesio-distal diameter gradually increases from theapical to the coronal. There was aslo significant difference (P＜0.05) exceptbetween the apical and foramen.②Comparison of the buccal and palatal root: the mesio-distal and thebucco-lingual diameters were buccal’s far bigger than palatal’s.There was significant differences between the every two comparison (P＜0.05).③The buccal and palatal lateral root canal taper of type Ⅳmaxillary firstpremolar in bucco-lingually are coronal1/3greater than the middle1/3andapical1/3. There was significant differences between the every two comparison(P＜0.05), while there without significant difference between the apical1/3andmiddle1/3(P＞0.05); In mesio-distally, the taper of coronal1/3was greaterthan the middle1/3and middle1/3was greater than the apical1/3,however therewas no significant difference (P＞0.05). That is, for the taper, bucco-lingualwas greater than the mesio-distal’s; coronal1/3greater than the middle1/3andapical1/3obviously. There was no significant changes from the apical1/3to themiddle1/3, also from the apical1/3to the coronal1/3in mesio-distal.CONCLUSIONS: For type Ⅳ maxillary first premolar, root canalmorphology of double root is similar to the single’s. Buccal lateral apicaldiameter greater than the palatal’s. It should be use the corresponding numbersof instruments espectively to prepare root canal in clinical. The two root bothhave non-continuous taper, and it ought to prepare segmented.Part II:Comparing study on the effect of two nickel-tianium rotaryinstruments in root canal preparationAIM: Comparison of the before and after preparated root canalcross-section by the two instruments. Analysis the effects of the root canal preparation, thus provide the experimental basis for the choice of clinical rootcanal preparation equipment.MATERIALS AND METHODS: Take the total of40specimens maxillary firstpremolar and random divided into2groups of20samples each: Mtwo (groupM), Revo-S (group R). Group M: canals were prepared by using a standardtechnique, dredgethe root canal with15#C file firstly, measuring the length ofthe root canal, then prepared the buccal and palatal to40#/0.06.Group R: useSC1open the crown2/3of the root canal, dredge the root canal with15#C file,measuring the length of the root canal. Then use SC2、SU、AS30、AS35、AS40with crown-down preparation technique prepared the buccal and palatal toAS40.Repeatedly pulling and make root canal wall smooth, and unobstructed.After each instrument, the root canals were flushed with1ml of a3%H2O2、1mlof a5.25%NaOCl solution and at the end of instrumentation with2mL of saline.Collected cross-section images after prepared, analyze the overlap images beforeand after preparation. Then acquisition images of cross-section after root canalpreparation overlap analysis with the preparation before. Record the differencebetween the cross-section area、root canal center offset and offset direction.RESULTS: There was significant differences in cross-section coronal1/3of group M and group R (P＜0.05), while without significant differences incross-section middle1/3, apical1/3, foramen1/3(P＞0.05). Preparation time forthe group R is shorter than the group M.CONCLUSIONS: Revo-S file and Mtwo file have a good root canal shaping ability, Mtwo has a better ability to maintain the original direction of theroot canal. Revo-S is more suitable for the root canal with variability taper, alsosave the time of root canal preparation meanwhile.