Objective:To study the stress distribution of the mandibular premolar cervix during clenching and mastication. Methods:Models of anisotropic enamel of the mandibular first premolar and the opposite maxillary first premolar crown were establishied. The stress distributions in the cervical region of the mandibular premolar were investigated in different loading conditions: simulating working, nonworking and vertical micromotions. In each case, the stroke was applied to the maxillary first mandibular premolar in a stepping procedure using nonlinear contact analysis. Results:The stress in the cervical region under loading condition simulating vertical micromotion was lower than that under loading conditions simulating working and nonworking micromotions. The stress was mainly concentrated near the buccal or the lingual cervical enamelo-dentinal junction under loading conditions simulating lateral excursion. Conclusion:The stress distribution in the cervical region is closely related to the pattern of occlusal force including location and direction.

In-stent thrombosis after cessation of antiplatelet medications in patients with drug-eluting stents (DES) is a significant problem in medical practice, particularly in the perioperative period. We report a case of an 87-year-old man with a medical history of hypertension, coronary artery disease and chronic atrophic gastritis. Very late thrombosis of a sirolimus-eluting stent occurred 1207 days after implantation, seven months after discontinuation of clopidogrel, and the interruption of aspirin 13 days in preparation of an elective endoscopic gastroin-testinal procedure presented with acute myocardial infarction. The patient was treated with thrombectomy and successfully revascularized with superimposition of two sirolimus-eluting stents. Medications administered in the catheterization laboratory included low molecular weight heparin and nitroglycerin. Flow was defined as grade 2 according to the thrombolysis in myocardial infarction scale. Electrocardio-gram after the procedure revealed persistent, but decreased, ST-segment elevation in the anterolateral leads. The patient recovered and was discharged on aspirin and clopidogrel indefinitely. There was no cardiac event during the two year follow-up period. This case underlines the importance of maintaining the balance of thrombosis and bleeding during perioperation of non-cardiac procedure and the possible need for continuation of aspirin therapy during periendoscopic procedures among patients with low bleeding risks who received DES.

Objective To measure various parameters with tissue Doppler imaging, quantitatively score left ventricular wall motion, assess longitudinal wall motion in total and regional myocardium of myocardial infarction patients. Methods Tissue tracking was adopted for assessing left ventricular regional myocardium of 30 myocardial infarction patients (MI group) and 30 normal subjects (control group). After collecting dynamic images and analyzing information off-line, maximum displacement along long axis asynchronously in annular, basal, mid and apical segments of different walls were acquired, and left ventricular wall motion score indexes(TT score indexes) were calculated. Results Maximum displacement in different segments of left ventricular regional myocardium was lower in MI group than control group, especially in infarcted segments. TT score indexes were lower in MI group than control group( 6.23? 1.93 vs 9.71? 1.08, P

Objective To observe longitudinal motion characteristics of regional myocardium in left bundle branch block(LBBB) patients. Methods Left ventricular regional myocardium of 15 LBBB patients and 15 normal subjects were assessed by tissue Doppler imaging(TDI). Peak velocities(V_S,V_E,V_A) during isovolumic contraction, ejection, isovolumic relaxation, early relaxation, atrial systole phases and maximum time velocity integral(TVI_(max)), displacement(D_(max)) in mitral(tricuspidal) annulets of different walls were measured. Furthermore, the different parameters from the beginning of electrocardiogram QRS wave to the beginning of S wave(Q-Sb),to the tip of S wave(TTP), the acceleration time of IVC wave(IVA), the acceleration time of the E wave(Eac),the durations of different phases(IVC,S,IVR,D)and IVC/S and others were acquired. Results Peak velocities(V_S,V_E)and TVI_(max) in left ventricular septal, inferior, anterior, posterior walls were lower in LBBB group than control group; those parameters in different segments of left and right ventricular lateral myocardium were not significantly lower in LBBB group than control group. What is more, D_(max) of mitral annular sites in LBBB group were lower than control group. Q-Sb, TTP and IVC in left ventricular septal, inferior, anterior, posterior walls were longer in LBBB group than in control group; IVA lengthened, Eac and Edc shortened in left ventricular septal, inferior walls; IVR lengthened, diastole shortened, IVC/S increased in left ventricular septal, inferior, and posterior walls. Conclusions Abnormal left ventricular activation sequence during LBBB caused obvious impairment in total and regional systolic and diastolic function. And delayed contraction with different degrees were resulted from different walls of left ventricle with intraventricular dyssynchrony; but contraction in right ventricle was not significantly delayed, with interventricular dyssynchrony.

Objective To investigate the alteration of left atrial(LA) electromechanical characteristics of patients with hypertensivon and patients with hypertension complicated with paroxysmal atrial fibrillation(PAF). Methods By use of two-dimentional echocardiography and Doppler and tissue Doppler imaging(TDI) techniques,we mensurated and calculated the indexes representing LA structure and systolic and diastolic function and electromechanical characteristics in 30 nornal subjects(group1),25 patients with hypertension lasting less than ten years(group2),24 patients with hypertension lasting more than ten years(group3) and patients with hypertension complicated PAF(group4). Indexes representing LA electromechanical characteristics consisted of the difference in time intervals between the QRS onset and the tricuspid A wave,and the QRS onset and the mitral A wave (DQAT),electromechanical time (P-A),electromechanical time dispersion(P-Ad),the maximum P wave duration,the minimum P wave duration,and P wave dispersion (Pd=Pmax-Pmin) calculated from 12-lead surface electrocardiograms. Results The P-A3 in group 4 was much longer than that in group 1,group 2 and group 3. The P-Ad2 in group 4 was much longer than that in group 1,group 2 and group 3.Conclusion There are prolonged P-A3 and P-Ad2 in patients with hypertension complicated PAF. Some indexes,such as P-A3 and P-Ad2,perhaps can predict the onset of PAF in patients with essential hypertension better.

Objective To investigate the changes of peroxynitrite(ONOO-)in acute myocardial infarction during ischemia-reper fusion.Methods Thirty patients with actute myocardial infarction(single coronary arterial stenosis of left anterior descending in proximal-middle segment) and twenty-four healthy cases were enrolled as the control in our research.Peripheral blood were taken at the time of 24 h and 72 h after primary percutaneous coronary intervention.The patients were further divided into 2 groups according to their serum cTnI level(mild myocardium injury group with cTnI 0.05).Conclusion Plasma peroxynitrite(ONOO-) is related to myocardium injury during ischemia-reperfusion in actue myocardial infarction which suggest that peroxynitrite may aggravate myocardium injury in acute myocardial infarction during ischemia-reperfusion.

Objective Previous studies have reported that the incidence of atrial fibrillation (AF)/atrial fluttler in patients with AMI who were treated with thrombolysis is 7%-10%. However, little is known concerning the incidence of AF/atrial fluttler and its effects on the prognosis of patients with AMI who are treated with PCI. Methods A total of 668 consecutive patients were studied in Beijing Chaoyang Hospital from Nov. 2000 to Jan. 2004. Patients were categorized into 2 groups according to the presence of AF/ atrial flutter. Results The results showed that the incidence of AF/atrial fluttler was 10% and that the patients with AF/atrial fluttler were older, were in higher Killip classes, had higher rates of previous myocardial infarction and previous cerebrovascular diseases, multivessel disease, and had poorer reperfusion of the infarc-related artery than those without AF/atrial fluttler. Patients with AF/atrial fluttler had higher in-hospital (11.9% vs 5.3%, P

Objective To elucidate the clinical implication of early ST segment changes after PCI for IRA for acute ST segments elevation myocardial infarction.Methods From Jan.2001 to Dec.2001,216 patients with AMI after successful angiographical primary PCI Who were admitted to Beijing Chaoyang Hospital were retrospectively analysed.Forty-one patients with index of ST segment elevation≥50%and 50 randomised patients from 175 patients with index of ST segment elevation

Objective To investigate the feasibility,safety and efficacy of sirolimus-eluting stent implanting in diabetic patients with ST-segment elevation myocardial infarction(STEMI)treated by emergency percutaneous coronary intervention(PCI).Methods One hundred and six diabetic patients with STEMI treated by emergency PCI were included into this study.The incidence of major adverse cardiovascular event(MACE),stent thrombosis and restenosis was evaluated.Results Totally 105 patients were successfully treated by emergency PCI and there were no complication during the procedure.Totally 134 sirolimus-eluting stents were successfully implanted on 110 target lesions.There was one subacute stent thrombosis in 106 patients during one month.One-month follow-up result showed that the MACE was 4.72% and the death rate was 3.77%.The MACE was 10.38% and the death rate was 3.77% one year later.One-year angiography follow-up showed that restenosis rate was 11.54%.Conclusion Implanting sirolimus-eluting stent in STEMI patients during emergency PCI is safe and effective.Sirolimus-eluting stent can reduce restenosis rate and MACE in diabetic patients with STEMI treated by emergency PCI.