Deep bite is a common clinical malocclusion that has a great impact on patients’ facial aesthetics and oral function. Bite opening is the key step in the treatment of deep bite, playing a decisive role in the development of mandible and the progress of orthodontic treatment. Torque and tip control during the correction of deep bites is a hot topic in orthodontics. The three-dimensional finite element method can accurately simulate clinical processes and conduct dynamic stress analysis, which provides the basis of the biomechanical mechanism. This paper reviewed the finite element analysis of various orthodontic systems for bite opening to provide a reference for clinical application. The emergence of mini-implants provided a new idea for anchorage control in bite opening. Finite element studies found that high-positioned mini-implants are beneficial for bodily tooth intrusion and proposed the ideal position for force application. For the finite element simulation of the reverse curve archwire, it was found that the intrusion and inclination of the anterior teeth increased with the curve depth of the archwire. The application of clear aligners has also been flourishing, but these forces are still difficult to effectively control. Finite element studies on their attachment design and corresponding tooth movement may be helpful to open the bite quickly and effectively. However, the existing studies still have modeling limitations. The structural simplification, linearization and nonstandard parameter definition of the model reduce model accuracy. Additionally, the existing research mostly focused on initial tooth movement, and studies on long-term tooth movement after bone remodeling are lacking. These studies are needed in the future.

Objective To explore the effect of controlled low central venous pressure(CLCVP)on venous congestion and postoperative acute kidney injury(AKI)in cardiac surgery under cardiopulmonary bypass(CPB).Methods A total of 137 patients scheduled for elective cardiac surgery under general anes-thesia with CPB were selected,including 73 males and 64 females,aged 18 to 70 years,with a BMI of 20 to 28 kg/m2,and ASA physical status Ⅱ or Ⅲ.The patients were randomly assigned into two groups:the controlled low central venous pressure group(group CL,n=68)and the control group(group C,n=69).In group CL,CLCVP was applied by pumping nitroglycerin to reduce CVP to below 10 mmHg after 20 minutes of CPB cessation until the end of surgery.If necessary,norepinephrine was applied to maintain MAP≥65 mmHg.Patients in group C received standardized anesthesia management.Urine samples were collected before anesthesia induction and 12 hours postoperatively to detect the concentration of kidney injury molecule-1(KIM-1).Urine samples were also collected before anesthesia induction and 2 hours postopera-tively to detect the concentration of neutrophil gelatinase-associated lipocalin(NGAL).Cumulative time a-bove 10,12,16,and 20 mmHg and time-weighted average CVP were used to assess venous congestion.The occurrence of postoperative AKI,stage 2 or above AKI,renal replacement therapy(CRRT),postoperative low cardiac output syndrome(LCOS),acute kidney injury following cardiac surgery(AKICS)score when arriving in ICU,in-hospital mortality,ICU stay,and postoperative hospital stay were recorded.Results Compared with group C,the cumulative time of CVP above 10,12,16,and 20 mmHg after CPB in group CL was significantly shorter,and the time-weighted average CVP was significantly lower(P＜0.05).AKI occurred in 9 patients(13.2%)in group CL and 15 patients(21.7%)in group C postoperatively,and there was no significant difference between the two groups.One case(1.5%)of stage 2 or above AKI oc-curred in group CL and 2 patients(2.9%)in group C,with one patient in group C requiring CRRT.Com-pared with group C,the concentrations of KIM-1 at 12 hours postoperatively and NGAL at 2 hours postoper-atively were significantly lower in group CL(P＜0.05).There were no statistically significant differences between the two groups in LCOS,AKICS score,in-hospital mortality,ICU stay,and postoperative hospital stay.Conclusion Controlled low central venous pressure in cardiac surgery under cardiopulmonary bypass can reduce venous congestion and decrease the occurrence of postoperative renal injury,thereby exerting a certain renal protective effect.