The SEM Observation Of The Ability To Clean The Infected Root Canal By Two Root Canal Prepared Instruments

Pulpitis and periapical periodontitis are the commonly and frequently-occurring diseases in Stomatological Department, while the root canal therapy is the preferred method to the treatment of pulpitis and periapical periodontitis. Clean the root canal pulp inflammation and necrosis of root canal completely , form root canal properly, then disinfect the root canal, fill it tightly to remove the infected root canal contents on periapical tissue of the negative stimulus, to prevent the occurrence of periapical periodontitis or promote the healing of the periapical periodontitis. Root canal preparation is the key to success of root canal therapy, the effect of it is to chean and shape the root canal. The process mainly relies on the equipmentsto complete. Therefore, the equipment used in root canal preparation is very important. With the developement of technology, root canal preparation instruments also has made replacement.Stainless instruments, as the traditional instruments, have greater rigidity, the flexibility decrease with the increasing of the diameter of equipment, also it could lead to deviation of root canal easily and form the bench. In recent years, there is a new type of instruments named nickel-titanium root canal preparation instruments, which is a "shape memory alloys" with high cutting efficiency, good anti-reverse and ultra-flexible features. Nickel-titanium root canal preparation instruments have two kinds which are hand and rotary.ProTaper is a new nickel-titanium instruments of root canal preparation, it is composed by six files, including three shape files (S_x, S₁, S₂) and three complete files (F₁, F₂, F₃). The design of hand and rotary ProTaper nickel-titanium file is exactly the same. Rotary instruments used a dedicated variable speed motor with high-torque,which is at the speed of 150～350r/min generally. Objective: The process of root canal preparation can produce smear layer. Smear layer is due to the deformation of tooth tissue elastic and plastic, because of local-heat and shear force in the process of cutting teeth,resulting in the disintegration of inorganic matter and the solidified of organic matter denaturation. The components of smear layer include collagen caused by the collagen degeneration, coagulation protein, blood, saliva, dentinal tubule fluid, a variety of microorganisms, pollutants, etc.The existence of smear layer can delay or prevent the disinfectants from effecting the bacteria in dentin tubules, also prevent root filling material and root canal wall from penetrating and cohereing.This study compare debris and smear layer of ProTaper hand and rotary root canal preparation instruments in preparation, then explore the differences of cleaning ability between the two instruments to guide clinical practice.Methods: Choose 30 maxillary first molar which are removed because of periapical periodontitis. The are randomly divided into two groups: A and B, and prepare the palatal root canal with the ProTaper hand and the rotary instruments respectively. Then made specimens which are observed debris and smear layer by electron microscopy, to assess the cleanliness of the root canal walls. According to the results, compare the ability of cleaning infected root canal about the two instruments.1 Choice of the ex vivo teeth: Choose 30 maxillary first molar with root canal infection removed for periapical periodontitis. Scrape the dental calculus and soft tissue on surface of the teeth. Place them in 10% formalin solution, 4℃refrigerator for use.2 Grouping and root canal preparation: Divide the teeth into A, B groups randomly, each group has 15 teeth. Then conventional open pulp, remove the coronal pulp, remove the pulp of the palatal root canal . A group: prepare the palatal root canal with crown-down technique, using hand ProTaper nickel-titanium instruments, B group: prepare the palatal root canal with the same way, using rotary ProTaper nickel-titanium instruments. In the process of root canal preparation, the canal is flush with sodium hypochlorite solution and 3% hydrogen peroxide alternately when the instrument is changed. After preparation, slices palatal root with a diamond bur, and prepared two guide groove along the long axis of teeth on each side of the masial and distal . The guide groove pass through the tip hole as much as possible, but avoid penetrating into the root canal. Cut open the root vertically with bone hammer and osteotome. The root canal should be avoid pollution during the process of operation. Then the specimens are placed in 2.5% glutaraldehyde solution, making specimens of scanning electron microscope.3 The preparation of scanning electron microscopy sample: Each group of teeth specimens are immersed in the 2.5% glutaraldehyde, fixed for 48 hours, dehydrated step by step from 50% to absolute alcohol, then dried at the critical point, and coated with vacuum ion coating machine, in the end observed debris and smear layer situation of the root canal wall by SEM.4 Evaluation of debris and smear layer: Observe the debris and smear layer of the root coronal 1/3, the middle 1/3 and the apical 1/3 by the scanning electron microscope. Two visual fields of every observation object are observed randomly, and scored them based on scoring criteria.5 Statistical treatment: List the results of the scored and analyz the results with the statistical software of SPSS16.0, using the Wilcoxon rank sum test to compare the debris and smear layer of root coronal 1/3, the middle 1/3 and the apical 1/3. Statistical tests of significance level is set to 0.05.Results:1 After root canal preparation, the group of rotary ProTaper nickel-titanium instruments compare with the hand ProTaper nickel-titanium instruments group, have smooth surface of the root canal walls and less debris and smear layer, dentinal tubule is much more open.2 There are significantly differences of cleaning results of two root canal preparation instruments on the apical 1/3 and middle 1/3 (P <0.05), but root coronal 1/3 of the cleaning shows no significant difference (P> 0.05).Conclusions: Compared with the hand ProTaper nickel-titanium instruments, rotary ProTaper nickel-titanium instruments have a better effect of cleaning ability of root canal preparation on the apical 1/3 and middle 1/3, the cleaning ability of root coronal 1/3 is no significant differences.