Objective:To evaluate the influence of sodium hypochlorite (NaOCl) solution used during root canal therapy on dentin bond strength.Methods:In the study,15 freshly extracted human third molars with complete dental crowns,caries and filling-free were selected.The occlusal enamel was removed perpendicular to the long axis of the tooth to expose middle flat surfaces of sound dentin.The occlusal dentin surfaces were then polished using 600-grit silicon papers for 1 min and rinsed with deionized water for 1 min.The teeth were randomly divided into three groups according to the treatment received:group A (negative control group),the samples were immersed in deionized water for 20 min;group B,the dentin surfaces were immersed in 2.50％ NaOCl solution for 20 min,with the solution being renewed every 5 min;group C,the dentin surfaces were immersed in 5.25％ NaOCl solution for 20 min,with the solution being renewed every 5 min.All the treated dentin surfaces were bonded using a self-etching adhesive system (SE bond) with a 5 mm in height resin composite (AP-X).After storage in deionized water at 37 ℃ for 24 h,the adhesive samples were sectioned longitudinally to produce 1.0 mm ± 1.0 mm stick specimens (n =45) for micro-tensile bond strength testing (MPa).Failure modes (adhesive failure,cohesive failure or mixed failure) at the dentin-resin interface were observed using a stereomicroscope.The micro-tensile bond strength data among the three groups were analyzed by a one-way ANOVA,then the Post-hoc test(LSD) was employed for pairwise comparison.The distribution of failure modes among the groups were analyzed by chi square test.Results:Significant decreased bond strength values were found for the 2.50％ NaOCl-treated group (26.04 ± 5.74) MPa and 5.25％ NaOCl-treated group (24.46 ± 3.77) MPa when compared with the strength of negative control group (48.71 ± 7.77) MPa,P =0.000.Compared with the negative control group,themicro-tensile bond strength of the 2.50％ NaOCl-treated group and 5.25％ NaOCl-treated grouphad dropped by 46.5％ and 50.2％.However,there was no significant difference of bond strength between the 2 NaOCl-treated groups (P =0.214).The distribution of failure modes showed significant difference in all the three groups (2 =56.324,P =0.000).The mixed failure (68.9％) was the most mode of fracture in the negative control group,followed by adhesive failure (24.4％),and the cohesive failure was leas t (6.7％).The proportion of adhesive failure mode was higher in NaOCl-treated groups than in negative control group (P =0.000).There was no significant difference of the distribution of failure modes between the 2.50％ NaOCl-treated group and 5.25％ NaOCl-treated group(P =0.197),and there was no cohesive failure mode detected in the two groups.Conclusion:The micro-tensile bond strength of dentin to composite resin was lower after exposure to NaOCl solution.

Objective Study on the clinic value of the application of two-dimensional and three-dimensional sonography on observing the fetal facial structure. Methods Applying Voluson 730 three-dimensional probe surface imaging mode and two-dimensional probe to make sonography on 16～48 weeks fetus in 1805 cases, emphasized on observing the fetal facial structure, saving the image information, making three-dimensional reconstruction and comparing the result of post partum and the result after induction of labor. Results In 1805 cases, applying two-dimensional and three-dimensional sonography to observe the facial structure of the fetus of 23～35 weeks, the display rate is 93.1% and 95.1% respectively, and there is no obvious difference between the two modes. The three-dimensional is higher than two-dimensional for the fetus less than 23 weeks, with the display rate 69.6% and 84.8% respectively, and the two-dimensional is a bit higher than three-dimensional for the fetus more than 35 weeks, with the display rate 90.4% and 88.7% respectively. One cleft lip case is excluded. Conclusion As long as mastering the optimum examination time and operation skill, there is no obvious difference between the display rate of two-dimensional and three-dimensional sonography on observing the fetal facial structure, the two modes can be complementary in the work to improve the accuracy of the diagnosis and be favorable for the prepotency.

Objective:To evaluate the efficacy and security of two type of rotary nickel titanium system (Twisted File and ProTaper Universal)for root canal preparation based on micro-computed tomography (micro-CT).Methods:Twenty extracted molars (including 62 canals)were divided into two experimen-tal groups and were respectively instrumented using Twisted File rotary nickel titanium system (TF)and ProTaper Universal rotary nickel titanium system (PU)to #25/0.08 following recommended protocol. Time for root canal instrumentation (accumulation of time for every single file)was recorded.The 0-3 mm root surface from apex was observed under an optical stereomicroscope at 25 ×magnification.The presence of crack line was noted.The root canals were scanned with micro-CT before and after root canal preparation.Three-dimensional shape images of canals were reconstructed,calculated and evaluated. The amount of canal central transportation of the two groups was calculated and compared.Results:The shorter preparation time [(0.53 ±0.1 4)min]was observed in TF group,while the preparation time of PU group was (2.06 ±0.39)min (P<0.05).In mid-root level,TF group shaping resulted in less ca-nal center transportation than PU group [(0.070 ±0.056)mm vs.(0.097 ±0.084)mm,P<0.05]. No instrument separation was observed in both the groups.Cracks were not found in both the groups ei-ther based in micro-CT images or observation under an optical stereomicroscope at 25 × magnification. Conclusion:Compared with ProTaper Universal,Twisted File took less time in root canal preparation and exhibited better shaping ability,and less canal transportation.

Objective:To compare the assessments of the presence or absence and the changes of post-treatment periapical lesions using periapical radiographs versus cone-beam computed tomography (CBCT).Methods:Imaging records were selected from a sample of 233 radiographic examinations (in-cluding periapical radiographs and CBCT)of patients with chronic apical periododontitis who received treatment and review in Department of Cariology and Endodontology of Peking University School of Stoma-tology.After testing the inter-observer and intra-observer agreement,two observers determined the pre-sence or absence of a periapical lesion and classified the changes of lesions in 4 categories:absence,re-duction or enlargement of lesion,or uncertain.The differences between CBCT and periapical radiographs in detecting the presence or absence and the changes of periapical lesions were compared using McNemar test and Fisher’s exact test respectively.Results:In the study,233 teeth were assessed with both periapi-cal radiographs and CBCT images.Periapical lesions were detected in 178 teeth on CBCT scans and in 146 teeth on periapical radiographs.CBCT images revealed a significantly larger number of lesions than were revealed by periapical radiographs (P <0.01 ).There was disagreement on the changes of lesions between the two radiological technologies in 25% teeth,and the difference was statistically significant (P <0.01 ). Conclusion:Significant differences were observed between periapical radiographs and CBCT in detection of post-treatment periapical lesions and assessment of the changes of periapical lesions.

Objective: To compare the incidences of root cracks after canal instrumentation with HyFlex CM system and the ProTaper Universal system .Methods:Sixty mandibular incisors were mounted in resin blocks with simulated periodontal ligaments , and the apex was exposed .The control group of 20 teeth was not prepared , and the other 40 teeth were divided into 2 experimental groups ( n=20 ) .The 40 root canals of the experimental groups were instrumented using HyFlex CM and ProTaper Universal to the major apical foramen ( AF).The horizontal sections 1 mm, 2 mm, and 3 mm from the apex were observed under an optical stereomicroscope at 25 ×magnification .The presence of cracks was noted . Results:No cracks were found in the control teeth .Cracks were found in 1 of 20 ( 5%) teeth in HyFlex CM group , and 17 of 20 ( 85%) teeth in ProTaper Universal group .The difference between the two experimental groups was statistically significant (P<0.01).Conclusion: The HyFlex CM files caused fewer root cracks than the ProTaper Universal files during the root canal instrumentation .

Objective To compare clinical curative effects of two types of compression hollow screws in the treatment of femoral neck fractures. Methods A retrospective analysis was carried out on clinical records of 87 cases of femoral neck fracture from February 1996 to September 2004 treated with two types of compression hollow screws,that is,doubleheaded compression hollow screws(46 cases,Group A) and AO titanium compression hollow screws(41 cases,Group B).Results A follow-up was conducted for 3 months~8 years(mean,4.2 years).No statistically significant differences were observed between the two groups.The intraoperative blood loss was significantly less and the time to bone union was significantly shorter in the Group B than in the Group A(t=5.147,P=0.000;t=5.472,P=0.000).The surgical outcomes were classified as "excellent" in 34 cases,"good" in 8,"fair" in 1,and "poor" in 3 in the Group A,while "excellent" in 37 cases,"good" in 2,"fair" in 2,and "poor" in no cases in the Group B,without statistically significant differences between the two groups in the rate of "good" or "excellent" results(89.1% vs 95.1%,?~2=0.398,P=0.528).No femoral head necrosis or non-union was found in the Group B. Conclusions Both of two types of compression hollow screws have showed advantages of simplicity of performance,minimal invasion,short operative time,reliable fixation,and high success rate,being an ideal option for femoral neck fractures.

Objective:To compare the fracture resistance of roots of mandibular premolar with different apical preparation diameters.Methods:Sixty single-rooted single canal permanent mandibular premolar teeth extracted newly for orthodontic reason without immatureness,fracture or cracks were selected,with a curvature less than 10°,and internal length:short diameter of less than 2 at a level 5 mm from the apex.All the teeth were decoronated,leaving roots 13 mm in length.The initial apical file size for the teeth was ≤ 15#.The roots were assigned to 6 groups based on weights with random block design.Group A:blank control group,no instrumentation was performed.Groups B-F:the master apical file (MAF) was 40#,45#,50#,55# and 60#,respectively.In the five experimental groups the roots were instrumented using hand files with step-back technique at 1 mm increments,resulting in a taper of 0.05.The irrigant used was distilled water.After mounted in acrylic resin,all the teeth were subject to vertical loading using an Instron testing machine until fractured.The occurrence of fractures was detected when the applied load suddenly decreased.The fracture load values and fracture modes were recorded.Oneway ANOVA and post-hoc Tukey test were used to determine the difference of fracture load values between the groups (P ＜ 0.05).Chi-square tests were used to compare the modes of root fracture.Results:Five experimental groups exhibited lower fracture load values than that of control group [(1 444 ± 155) N].The mean fracture load values for roots instrumented to an apical diameter of 50# [(1 027 ± 128) N],55# [(994 ± 150) N] and 60# [(983 ± 166) N] were significantly lower than that of control group and 40# group [(1 339 ± 131) N] and 45# [(1 287 ± 144) N] (P ＜0.05).Buccal-lingual fracture,mesio-distal fracture and compound fracture occurred 55％,13％ and 32％,respectively.No difference of fracture mode was detected in the six groups.Conclusion:The fracture resistance reduced significantly when the roots were instrumented to an apical diameter of 50# or larger.

Objective To evaluate and compare the results of air-conduct and bone-conduct auditory brainstem response(ABR)for the purpose of clinical application of the bone-conduct ABR.Methods A group of normal hearing young adults(61 ears)were measured with click stimulation air-conduct ABR and bone-conduct ABR in a soundproof chamber.Results The waveforms of bone-conduct ABR were almost the same as those of air-conduct ones with the threshold of 26.08?7.71 dB(nHL),but with a lower rate of wave derivation.There were no significant differences between male and female for both air-conduct and bone-conduct ABR testing.The threshold for bone-conduct ABR was higher than that of air-conduct one with a very high positive correlation(r=0.7740)and there were significant differences (P0.05) for the wave intervals.Conclusion The limitation of the bone-conduct ABR application and the differences from air-conduct should be considered when it was used clinically.

Objective To investigate the different characters between conventional frequency audiometry (125 Hz～8 kKHz) and high frequency audiometry (9～16 kHz)in the normal youth and provide the references for the clinical application of the HFA.Methods 52 male and 48 female normal-hearing subjects were tested with both conventional-frequency (0.25～8 kHz) and high-frequency (10～18 kHz) audiometry.Results Data showed that no difference between male and female in different frequencies. However, the threshold of HFA went up gradually with the frequency increasing. The average threshold of HFA was significantly higher than that of CFA and speech frequency (SFA) and had a positive correlation with both CFA and SFA. Conclusion The results of this study suggest that HFA might be used as an early indicator for CFA and SFA hearing loss resulting from acoustic trauma, ototoxicity and presbycusis.

AIM: To investigate the effects of early application of thymosin peptide alpha 1 on lymphocyte subsets after operation in patients with hepatocellular carcinoma. METHODS: Forty-six patients with hepatocellular carcinoma were randomly divided into control and treatment groups for this study. Thymosin α1 at dose of 1.6 mg was injected subcutaneously on day 1, 3, and 5 after operation in treatment group. The percentages of CD3+, CD4+ and CD8+ cells, and CD4+/CD8+ ratio in both groups were counted before operation and on day 1, 4, and 7 after hepatectomy. RESULTS: CD4+ cell population and CD4+/CD8+ ratio decreased, but CD8+ increased after operation in control group (P<0 05). In thymosin peptide alpha 1 treatment group, there was no statistical difference in the percentages of CD3+, CD4+, CD8+, and CD4+/CD8+ before and after operation. In addition, thymosin α1 significantly increased CD4+ cell population and CD4+/CD8+ ratio (P<0 05). CONCLUSION: Operation suppresses the immune function in patients with hepatocellular carcinoma. Thymosin α1 increases CD4+ T lymphocyte subsets in patients after operation.