[Effect of titanium nitride coatings with different thickness on microhardness and cutting efficiency of nickel-titanium instruments].

PURPOSE: To investigate the effect of titanium nitride (TiN) coatings with different thicknesses on microhardness and cutting efficiency of nickel-titanium (NiTi) instruments, and to provide a basis for improving the efficiency of clinical root canal preparation. METHODS: Fifteen KV4 NiTi alloy sheets and sixty KV4 rotary NiTi files were selected and randomly divided into 5 groups: uncoated group, coating 1 h group, coating 2 h group, coating 3 h group and coating 4 h group. A layer of TiN coatings of different thicknesses was prepared on the surface of the coated groups by controlling the deposition time. The film thickness of each group was measured by scanning electron microscopy (SEM). The microhardness of each group of NiTi alloy sheets was measured by a Vickers hardness tester. Sixty transparent resin modules were selected and each resin module was prepared with one NiTi file. The cutting efficiency of each group was measured by the weight loss method. SEM was used to examine the surface of NiTi instruments in 5 groups before and after preparation. One-way variance analysis was used to determine the statistical differences with SPSS 22.0 software package. RESULTS: With the increase of the thickness of titanium nitride coating, the microhardness of NiTi alloy gradually increased(P＜0.05). With the increase of the thickness of titanium nitride coating, the cutting efficiency of NiTi instrument was improved, and the cutting efficiency was the largest when the coating thickness was 860 nm(P＜0.05). The surface morphology of the coated group was better than that of the uncoated group. CONCLUSIONS: The thickness of TiN coating affects microhardness and cutting efficiency of the nickel-titanium instruments, the microhardness and cutting ability enhanced as the thickness increased. If the thickness is too large, the cutting efficiency will be reduced.

[Comparison of wear resistance and flexural strength of three kinds of bulk-fill composite resins].

PURPOSE: To compare the abrasion resistance and flexure strength of three bulk-fill resin composites with an universal nano-hybrid composite resins. METHODS: The specimens were prepared with three kinds of bulk fill composites (SDR , sonicfill, Tetric N-Ceram Bulk Fill) and an universal nano-hybrid composite resins(Herculite Precis). 10 mm in diameter × 2mm in height specimens were prepared for abrasion resistance, while 2 mm in width × 2 mm in depth×25 mm in length specimens were prepared for flexure strength. The specimens were mounted in a bal1-on-disc wear testing machine and abraded with the media artificial saliva(50 N loads, 10000 cycles).Flexural test was performed with an Universal Testing Machine at a cross-head speed of 1mm/min. One-way variance analysis was used to determine the statistical differences of volume loss and flexural strength among groups with SPSS 13.0 software package(P<0.05). RESULTS: The volume loss was as follows: SDR (1.2433±0.11) mm30.05). CONCLUSIONS: With regard to wear resistance and flexural strength, Tetric N-Ceram Bulk Fill is recommended as an alternative for posterior restorations.

[Treatments of second mesiobuccal canals in maxillary permanent molar: a report of 2 cases].

With the increasing maturation of 3D printing technology, as well as its application in various industries, investigation of 3D printing technology into clinic medical education becomes an important task of the current medical education. The teaching content of oromaxillofacial head and neck surgical oncology is complicated and diverse, making lower understanding/memorizing efficiency and insufficient skill training. To overcome the disadvantage of traditional teaching method, it is necessary to introduce 3D printing technique into teaching of oromaxillofacial head and neck surgical oncology, in order to improve the teaching quality and problem solving capabilities, and finally promote cultivation of skilled and innovative talents.

[Expression of Wnt5a in chronic apical periodontitis and its clinical significance].

PURPOSE: To detect the expression of Wnt5a in lesions of chronic apical periodontitis and determine the relationship between expression of Wnt5a and inflammation degree. METHODS: Ten patients with chronic apical periodontitis and 5 healthy controls were enrolled in this study. According to the inflammatory cell infiltration, the specimens were divided into 2 groups: severe inflammation group and mild inflammation group. The expression of Wnt5a was measured by real-time PCR (RT-PCR) and immunohistochemical analysis in the lesions of chronic apical periodontitis. The amount of Wnt5 expression was assayed and compared in different inflammation levels. Statistical analysis was performed using SPSS 13.0 software package. RESULTS: Wnt5a was detected in both groups. Expression of Wnt5a mRNA in patients were significantly higher than the controls (P<0.05). According to inflammation level, the positive expression rate of Wnt5a in severe inflammation group was significantly higher than the controls (P<0.01), and Wnt5a positive expression in mild inflammation group was also significantly higher than the controls (P<0.05). The expression of Wnt5a was significantly different between severe inflammation group and mild inflammation group (P<0.05). CONCLUSIONS: The expression of Wnt5a increases as the severity of tissue inflammation increases, which indicates that Wnt5a plays an important role in the development of chronic apical periodontitis.

[An in vitro evaluation of the effect of carboxymethyl chitosan and its composites against Enterococcus faecalis in the root canal].

PURPOSE: To evaluate the bacteriostasis effect of carboxymethyl chitosan and its composites on intracanal E. faecalis. METHODS: The pattern of E. faecalis infecting root canal was established, and then divided into 4 groups(A, B, C and D).They were filled with 2% chlorhexidine solution, 140 mg/mL mixture of carboxymethyl chitosan and chlorhexidine solution, 5 mg/mL carboxymethyl chitosan solution and calcium hydroxide paste respectively and incubated for 7 days. Samples obtained before and after the intracanal medication were plated onto BHI media to determine the colony-forming units (CFU/mL) after 48 hours. The data were analysed using SPSS 13.0 software package. RESULTS: Before intracanal medication, the variance of bacterial counts were not significantly different (P>0.05). After medication, the four groups showed significant difference in bacterial counts immediately(P<0.05).The antimicrobial effects of A and B group were better than group C and D. CONCLUSIONS: The antibiotic activity of 2% chlorhexidine solution and 140 mg/L mixture of carboxymethyl chitosan and chlorhexidine solution to E.faecalis were better. Supported by Key Science and Technology Project of Liaoning Province(2010225001).

[Effect of root canal filling with warm vertical condensation under dental operating microscope].

PURPOSE: To evaluate the clinical effect of root canal filling with warm vertical condensation with or without dental operating microscope. METHODS: Fifty maxillary anterior teeth with single, straight canals were divided into two groups. Each tooth was instrumented by X-Smart rotary nickel-titanium files to a master file 0.06 taper F3, root canal in the group 1 was obturated with warm vertical condensation using system B for downpack and Obtura II for backfilling without dental operating microscope; root canal in the group 2 was obturated using the same methods under the dental operating microscope. The effect of quality of root canal filling was evaluated by X-ray radiograph post-operatively and after two years of treatment. SPSS10.0 software package was used for Chi-square test. RESULTS: Significant difference was found between the two groups on the quality of root canal filling post-operatively (P < 0.05),with better quality of root canal filling in the group using dental operating microscope, no significant difference was found between the two groups after two years (P > 0.05). CONCLUSIONS: Warm vertical condensation under the dental operating microscope is a good method for root canal filling. It may improve the quality of root canal filling effectively, and therefore, worthy of clinical application.

[Comparative study on the shaping ability of canals with 2 new nickel- titanium rotary instruments].

PURPOSE: To compare the shaping ability of two nickel-titanium rotary systems: Mtwo and K3. METHODS: Thirty-six mesio-buccal root canals of maxillary first molars were divided into two groups: group A(> or =20> or =) and group B(<20 degrees ),according to the angle of the canal. Then, each group was randomly divided into two subsets and prepared by Mtwo,K3, respectively. All root canals were injected with the contrast medium and digital images of all canals were recorded before and after instrumentation. The computer assistant analyze image software was used to form the geometrical central line of pre-instrumented canals. Then the central line was imaged to the post-instrumented canals. The canal transportation and the decrease of curvature were measured. All the data was analyzed with SPSS11.0 software package. RESULTS: Difference between groups was compared using t test.When the curvature of canal > or =20 degrees ,the transportation at the beginning of the curvature and the decrease of curvature of Mtwo were significantly less than those of K3(P<0.05).When the curvature of canal <20 degrees there was no significant difference between Mtwo and K3 in the transportation and decrease of curvature(P>0.05). CONCLUSIONS: Both Mtwo and K3 systems show good preservation of the original geometry of the root canals, the Mtwo system can better preserve original curvature of canals, when the curvature of canal is larger than 20 degrees .

[A study on acquired acid resistance of enamel and dentine irradiated by Er, Cr: YSGG laser in vitro].

OBJECTIVE: To evaluate the acid resistance of enamel and dentin irradiated by Er, Cr: YSGG laser to artificial caries formation in vitro. METHODS: Enamel and dentin samples were irradiated with Er, Cr: YSGG laser at 6 W or 4 W for 6 second, respectively. Every sample was immersed in 3 ml of lactic demineralization solution at pH 4.8 and incubated at 37 degrees C for 24 hours. The parts per million of calcium ion of each solution was measured by atomic absorption spectrophotometry, the quantities of calcium and phosphate on the surface of enamel and dentin sample were examined by SED-X and the ultrastructure was investigated by SEM. RESULTS: In the enamel and dentin samples, the dissolved Ca(2+) concentration in laser group were significantly decreased compared with that of the control group (P < 0.05). The quantities of Ca (weight%) in enamel and dentin were significantly higher in the laser group than in the control group (P < 0.05). The content of P was increased in dentin and enamel samples, but only the increase in enamel sample was significant (P < 0.05). In both samples, no significant changes on Ca/P weight ratio were found between the groups. The irradiated enamel and dentin surface lacked a smear layer and showed various patterns of microirregulation with a scaly appearance, the openings of dentinal tubules were clearly visible, but no melting or carbonization was observed. CONCLUSION: Er, Cr: YSGG laser irradiation is effective for increasing acid resistance of dental hard tissue and does not cause thermal side effect.

[Research on the effect of root canal seal achieved by irradiation of Er, Cr:YSGG laser].

PURPOSE: To evaluate the effect of root canal seal achieved by routine root canal preparation and irradiation of Er, Cr:YSGG laser in root canal therapy. METHODS: One hundred and five freshly single-rooted extracted human teeth were selected for the study, which were randomly divided into seven groups of fifteen each. The anatomic crowns were removed at the cementoenamel junction and the remaining roots were prepared endodontically with conventional methods. Then they were treated with Er, Cr:YSGG laser in different parameters and patterns. The effect of root canal seal achieved by Er, Cr:YSGG laser was evaluated with microleakage measurements. Newman-Keuls test and one-way analysis of variance were used to determine the statistical differences between various groups. A value of P<0.05 was considered to be significant. RESULTS: The amount of dye penetration from an apical stop with irradiation of Er, Cr:YSGG laser was significantly lower (P<0.05) except 3W laser without water flow, and in 1W Er, Cr:YSGG laser without water flow, the amount of apical dye penetration was significantly decreased (P<0.01). CONCLUSIONS: The utilizing of Er, Cr:YSGG laser in small parameters prior to root canal filling could promote the effect of apical seal. Based on our results, it appeared that the seal effect of 1W Er, Cr:YSGG laser without water flow was superior to the effects of others.