| Root canal therapy (RCT) is a common and very effective treatment of pulp and periapical disease. The treatment will thoroughly clean inflamed pulp and necrotic material in the root canal, expand the sharped root canal, disinfect the root canal properly, and finally fill the root canal tightly to remove negative irritants of infectious contents to periapical tissues, which can prevent the occurrence of periapical disease or promote healing of apical lesions[1]. A successful root canal therapy depends on the good root canal preparation, root canal irrigation, root canal disinfection and three-dimensional filling to root canal systems. The root canal irrigation plays an important role in the healing process. Ultrasonic root canal irrigation is a fast and effective physical cleaning methods developed in recent years. It can increase the movement of flushing fluid, increase flushing and disinfection effect, and work well on eliminating smear layer [2].Sodium hypochlorite (NaCIO) solution is a frequently-used chemical root canal irrigation in clinical practice, which can effectively remove the surface coating of root canal wall, decompose dentin collagen proteins, and leverage antibacterial ability by influencing adhesion of bacteria within the dentinal tubules to collagen [3]. Ultrasonic irrigation can achieve better disinfection effect if it is used in combination with sodium hypochlorite irrigation fluid. In order to investigate the optimum ratio of ultrasonic irrigation power and NaCIO concentration, in experiment, I will establish a model of root canal infected by porphyromonas gingivalis in vitro, group different combinations of ultrasonic power and NaCIO concentration, compare the quantity of porphyromonas gingivalis, change of micro hardness value and cleanup effect of smear layer of each group, perform statistical analysis, and obtain the appropriate ultrasonic irrigation power and NaCIO concentration to provide experimental bases for the application to clinical practice of ultrasonic irrigation.Objective:To obtain different implications of using different ultrasonic power and NaCIO concentration model on porphyromonas gingivalis count within root canal before and after root canal preparation, dental micro hardness value of each group, and cleanup effect of smear layer, a model of root canal infected by porphyromonas gingivalis in vitro is established in experiment, which is aimed to figure out a combination of ultrasonic power and NaCIO concentration, which has a good effect on root canal irrigation and low damage to root canal wall, and it can provide experimental bases for the application to clinical practice of ultrasonic irrigation.Method:Select 260 fresh maxillary and mandibular molars extracted because of orthodontics or periodontal disease (requirements:single root canal, no cracks in root, no near pulp caries, no root canal therapy before, the apical foramen is completely developed) remove dental calculus and periodontium around root, place the molars in saline and store it at 4℃ in refrigerator for later use. First, establish a model of root canal infected by porphyromonas gingivalis in vitro. Cut off dental crown, scale the root canal length to 14mm, prepare it to 25# with stainless steel k file after removing pulp, seal apical with composite resin. Select 10 molars to test the effect of sterilization after the sterilization under high temperature and pressure.Culture porphyromonas gingivalis in medium, choose the bacterial solution, whose McFarland is 2 in biohazard safety equipment, inoculate it with sterile root canals. Then incubate it in incubator under 37℃. Select 10 teeth to be tested after renewing medium for 21 days. Observe the infection stations of dentin, include the root canals into experiment if there is no other bacterial. The models are divided into 8 groups at random with 30 teeth in each group. For each group, take a random sample of 10 teeth to test micro-hardness value。 Then sample infected root canals and count bacterial for the first time before root canal preparation。 Root canal was prepared with nickel-titanium preparation instrument-Protaper. Use different combination of ultrasonic power and NaCIO irrigation to irrigate root canals:Group A:concentration of NaCIO being 0.5%, ultrasonic power being 1 gear;Group B:concentration of NaCIO being 2.0%, ultrasonic power being 1 gear;Group C:concentration of NaCIO being 0.5%, ultrasonic power being 2 gear;Group D:concentration of NaCIO being 2.0%, ultrasonic power being 2 gear;Group E:concentration of NaCIO being 0.5%, ultrasonic power being 3 gear;Group F:concentration of NaCIO being 2.0%, ultrasonic power being 3 gear;Group G:concentration of NaCIO being 0.5%, ultrasonic power being 4 gear;Group H:concentration of NaCIO being 2.0%, ultrasonic power being 4 gear;Control groups (ultrasonic and NaCIO irrigation are replaced with normal saline irrigation, n=20) are included in this experiment. Then sample infected root canals and count bacterial for the second time. Revive bacterial to determine there is no microorganisms contamination. Conduct statistical analysis in the end. Count the finished models, and divide samples of each group into 2 subgroups (n1=10, n2=10). Cross cut the model of the first subgroup in the middle into 7mm-long segment. Embed coronal section in direct restorative acrylic resin, polish it with diamond and rubber wheel under distilled water cooling condition. Then measure 3 points, which are 500 μm and 1000 μm away from pulp cavity, of the specimen section with micro-hardness measuring instrument. Load them with 500g for 10 minutes, record the Vicker’s micro-hardness value. Take the mean of 3 test points for each model; detect the clearance of root canal smear layer in the upper third, middle third and lower third root by scanning electron microscope.Result:1. Successfully established the model of root canal infected by porphyromonas gingivalis in vitro;2. Bactericidal capacity:there is no statistical difference in root canal colony counting of each group before rinsing. Compared with the same group before rinsing, there is a significantly decrease in colony counting and statistical difference (P<0.05) after rinsing. After rinsing, the root canal colony counting in experimental groups (group Al-Hl) is less than those in control groups (P< 0.05). Also with the power increase of root canal ultrasonic therapeutic apparatus, the disinfection ability increases gradually. The disinfection effect of NaCIO with 2.0% concentration is better than the one with 0.5% concentration. However, the difference of disinfection effect becomes smaller as the increase of ultrasonic frequency (P< 0.05). Group A1 has the most colonies after ultrasonic irrigation, and group H1 has the least colonies (P <0.05);3. Micro-hardness value:there is no statistical difference in micro-hardness value of dentin, which is 500 μ m to 1000 μ m away from pulp cavity in root canal, of each group before rinsing. Compared with the same group before rinsing, there is a significantly decrease in micro-hardness value and statistical difference (P<0.05) after rinsing. After rinsing, the dental micro-hardness value in experimental groups (group A1-H1) is less than those in control groups (P< 0.05). Also with the power increase of root canal ultrasonic therapeutic apparatus, the micro-hardness value of root canal decreases gradually. The influence on root canal wall of NaCIO with 2.0% concentration is more than the one with 0.5% concentration. However, the difference of micro-hardness value becomes smaller as the increase of ultrasonic frequency (P< 0.05). Group H1 has the highest micro-hardness value after ultrasonic irrigation, and group A1 has the lowest micro-hardness value (P<0.05);4. The cleanup effect of root canal smear layer:there is no statistical difference in cleanup effect of root canal smear layer of each group before rinsing. Compared with the same group before rinsing, there is a significantly decrease in cleanup score of root canal smear layer (better cleanup effect of smear layer) and statistical difference (P<0.05) after rinsing. After rinsing, the cleanup score of root canal smear layer in experimental groups (group A1-H1) is lower than those in control groups (P< 0.05). the A2-H2 groups have more statistical significance (p< 0.05). Group H2 gets the lowest cleanup score (the best cleanup effect of smear layer) of smear layer, and group A2 gets the lowest score (the worst cleanup effect of smear layer).Compared among the upper third, middle third and lower third root in the same group: the upper third of root get the lowest cleanup score smear layer in all groups, the lower third root get the highest cleanup score. All differences have statistical significance (P<0.05);Conclusion:1. Be capable of establishing the model of root canal infected by porphyromonas gingivalis in vitro successfully;2. The intracanal sterilization effect increases and the cleanup effect of root canal smear layer improves with the increase of influence on physical property of root canal wall, the power of root canal ultrasonic therapeutic apparatus, and the NaCIO concentration. However, difference becomes smaller (P< 0.05) with the increase of the power of root canal ultrasonic therapeutic apparatus, and the NaCIO concentration. The forth gear of ultrasonic power combined with NaCIO of 2.0% concentration has the best effect on removing intracanal porphyromonas gingivalis with the lowest impact on micro-hardness value of dentin and best cleanup effect of root canal smear layer.3. The effect of combination of ultrasonic power and NaCIO irrigation is good, and can meet the requirements of the root canal disinfection. |
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