Objective The Improved segmental arch technique can effectively intrude incisors and correct deep overbites. To research its biomechanical characteristics, we reconstruct 3D nonlinear finite element model of mandibular teeth with improved segmen-tal arch, study the biomechanical characteristics and the suitable loading force of intrusion arch. Methods Combined with the re-sults of previous research, we complete the reconstruction of 3D nonlinear finite element model of mandibular teeth with improved seg-mental arch.Then, we set loading force of intrusion arch five conditions from 0.2 N~0.6 N, calculate the movement trend and stress distribution of improved segmental arch. Results In the five conditions of improved segmental arch, lateral incisors and canines in-truded and tipped labially, first molars tipped distally and rotated. In addition, the moment the initial loading force of intrusive arch in-creased, the movement of these teeth increased. However, other teeth did not move clearly. When the initial loading force of improved segment arch was 0.5 N, it can achieve appropriate intrusion of anterior teeth. Conclusion Under an appropriate intrusive force, improved segment arch can effectively intrude incisors and control the extrusion of posterior teeth. It can be used to correct the deep overbites, especially with high mandibular planes, gummy smile or adult stage.

OBJECTIVETo reconstruct a three-dimensional nonlinear finite element model of mandibular teeth with three-pieces segment arch, and analyze the mechanical properties of intrusive arch and the biomechanical characteristics of three-pieces segment arch.

METHODSThree-dimensional nonlinear finite element model of mandible with three-pieces segment arch was reconstructed by multi-slice spiral CT scanning, Mimics, CATIA and Anasys software. Then, the mechanical properties of intrusive arch, the movement trend and stress distribution of three-pieces segment arch were calculated by Anasys software.

RESULTSIn the range of 5 degrees-25 degrees, with the degree of intrusive arch increased, the force of intrusive arch also increased rapidly. The maximal force was 0.604 8 N in 30 degrees; the force was about 0.59 N in 30 degrees-65 degrees range. In condition of three-pieces segment arch mechanics, lateral incisor tipped labially and intruded; the first moral tipped distally and rotating; other teeth did not move clearly. The largest stress distribution in the whole arch was in the one-third labial cervical area of the lateral incisor root and the root bifurcations of first moral.

CONCLUSIONUnder an appropriate intrusive force, three-pieces segment arch can intrude incisors and control the extrusion of posterior teeth. It can be used to correct the deep overbite, especially with high mandibular planes, gummy smile or adult patients.

Dental Arch ; Finite Element Analysis ; Humans ; Incisor ; Mandible ; Tooth Root

Objective:To explore the risk factors for death within 1 year after hip fracture surgery in the elderly.Methods:A case control study was made on the clinical data of 551 elderly patients with hip fracture treated in Second Affiliated Hospital of Soochow University from January 2019 to December 2020, including 182 males and 369 females; aged 65-100 years [80(73,86)years]. Joint replacement, cannulated screw fixation or proximal femoral nail fixation were performed. The patients were divided into survival group ( n=494) and death group ( n=57) based on the death within 1 year after surgery recorded at postoperative telephone follow-up. The gender, age, hypertension, diabetes, cardiovascular diseases, chronic respiratory diseases, neurological diseases, chronic renal failure, anemia on admission, fracture types, American anesthesiologist Association (ASA) classification, operative methods, preoperative waiting time, duration of operation and perioperative blood transfusion were recorded in two groups. Univariate Cox regression was used to analyze the correlation between the above indexes and death within 1 year after surgery. All indexes with P<0.2 in the univariate analysis were included in multivariate Cox regression analysis to clarify the independent risk factors for death within 1 year after surgery. Results:Univariate Cox regression analysis showed that death within 1 year after surgery correlated with gender, age chronic respiratory diseases, chronic renal failure and anemia on admission (all P<0.01), but not with hypertension, diabetes, cardiovascular diseases, neurological diseases, fracture types, ASA classification, operative methods, preoperative waiting time, duration of operation or perioperative blood transfusion (all P>0.05). Multivariate Cox regression analysis showed that male ( HR=2.08, 95% CI 1.20, 3.61, P<0.01), age ≥ 80 years ( HR=2.22, 95% CI 1.15, 4.28, P<0.05), chronic respiratory diseases ( HR=2.54, 95% CI 1.19, 5.40, P<0.05), chronic renal failure ( HR=4.57, 95% CI 1.27, 16.44, P<0.05), anemia on admission ( HR=2.82, 95% CI 1.38, 5.76, P<0.01) were significantly associated with death within 1 year after surgery. Conclusion:Male age≥ 80 years, chronic respiratory disease, chronic renal failure and anemia on admission are independent risk factors for death within 1 year after hip fracture surgery in the elderly.