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1.
《Dental materials》2022,38(1):204-213
ObjectiveTo investigate the fatigue behavior of restored teeth, in particular the mechanisms of longitudinal dentinal cracking under cyclic mechanical loading, using finite element analysis (FEA) and the stress-life (S-N) approach.MethodsTen root-filled premolars restored with resin composites were subjected to step-stress cyclic loading to produce longitudinal cracks. Fracture loads and number of cycles completed at each load level were recorded. FEA was used to predict the stress amplitude of each component under the global cyclic load. Both intact and debonded conditions were considered for the dentin-composite interface in the FEA. The predicted stress concentrations were compared with the fracture patterns to help elucidate the failure mechanisms. The S-N approach was further used to predict the lifetimes of the different components in the restored teeth. Cumulative fatigue damage was represented by the sum of the fractions of life spent under the different stress amplitudes.ResultsLongitudinal cracks were seen in ~50% of the samples with a mean fracture load of 770 ± 45 N and a mean number of cycles to failure of 32,297 ± 12,624. The longitudinal dentinal cracks seemed to start near the line angle of the cavity, and propagated longitudinally towards the root. The sum of fractions of life spent for the dentin-composite interface exceeded 1 after ~7000 cycles when that for dentin was much lower than 1, indicating that interfacial debonding would occur prior to dentin fracture. This was supported by micro-CT images showing widened interfacial space in the cracked samples. In the debonded tooth, FEA showed dentinal stress concentrations at the gingival wall of the cavity, which coincided with the longitudinal cracks found in the cyclic loading test. The sum of fractions of life spent for dentin was close to 1 at ~30,000 cycles, similar to the experimental value.SignificanceDebonding of the dentin-composite interface may occur prior to longitudinal cracking of dentin in root-filled teeth under cyclic loading. The approximate time of occurrence for these events could be estimated using fatigue analysis with stresses provided by FEA. This methodology can therefore be used to evaluate the longevity of restoration designs for root-filled teeth. 相似文献
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《Journal of cranio-maxillo-facial surgery》2022,50(2):114-123
The aim of this retrospective study was to evaluate the outcomes of simultaneous LeFort I osteotomy and zygomatic/dental implant placement for oral rehabilitation of patients with extremely atrophic/dysmorphic edentulous maxilla.Simultaneous LeFort I osteotomy and zygomatic/dental implant placement was performed with patient-specific anatomical models and surgical guides produced through three-dimensional virtual planning methods. All patients received their final prosthesis, with immediate loading, on the day after surgery. The primary outcome variables were the implant survival rate, and the incidence of intra/postoperative complications. In total, 15 zygomatic implants and 33 conventional dental implants were inserted in eight patients. The mean follow-up of the patients was 38.5 months. The implant survival rate was 93.3% for zygomatic implants and 100% for dental implants. No intra/postoperative complications were observed.Simultaneous LeFort I osteotomy associated with zygomatic/dental implant surgery can be considered as a valuable treatment option for rehabilitation of patients with extremely atrophic edentulous maxilla and esthetic issues of the face. 相似文献
4.
目的:观察护理服务精准加载法在永久性肠造口病人中的应用效果。方法:选择收治于我院接受低位直肠癌永久性肠造口者88例为研究样本,以随机数字表法分为试验组和对照组各44例,对照组按永久性肠造口常规护理执行,试验组接受护理服务精准加载法干预,对两组干预后的各观察指标进行比较。结果:试验组永久性肠造口者干预后的肠造口自我效能评分和自我护理能力评分显著高于对照组,肠造口相关并发症发生率显著低于对照组(P<0.05)。结论:采用护理服务精准加载法对永久性肠造口病人施加干预,可显著提升该类病人肠造口自我效能与自护水平,降低肠造口相关并发症发生率。 相似文献
5.
Paul Macadam Kim D. Simperingham John B. Cronin 《Journal of Science and Medicine in Sport》2019,22(3):348-352
Objectives
Arm swing is a distinctive characteristic of sprint-running with the arms working in a contralateral manner with the legs to propel the body in a horizontal direction. The purpose of this study was to determine the acute changes in kinematics and kinetics when wearable resistance (WR) of 1 kg (equivalent to ~1% body mass) was attached to each forearm during over ground short distance (20 m) maximal sprint-running.Design
Cross-sectional study.Methods
Twenty-two male amateur rugby athletes (19.4 ± 0.5 years; 97.0 ± 4.8 kg; 180.4 ± 7.2 cm) volunteered to participate in the study. Radar and Optojump were used to examine kinematic and kinetics between WR and unloaded sprint-running conditions.Results
No significant (p < 0.05) differences were found at 2 m or 5 m between conditions, however, the WR condition resulted in a significant increase in 10 m, 20 m and 10–20 m split time (all, ~2%, small effect size) compared to the unloaded condition. Significant decreases were also found in theoretical maximum velocity (V0) (?1.4%, small effect size) and relative peak horizontal power production (Pmax) (?5.5%, small effect size). Step length (2.1%, small effect size) and contact time (6.5%, medium effect size) were significantly increased, while step frequency (?4.1%, small effect size) and flight time (?5.3%, medium effect size) were significantly decreased.Conclusions
WR forearm loading provides a movement specific overload of the arms which significantly alters step kinematics and sprint times ≥10 m. 相似文献6.
目的优化丁香苦苷聚乳酸(Syr)-羟基乙酸共聚物[poly(lactic-co-glycolic acid),PLGA]纳米粒(Syr-NPs)的处方。方法采用纳米沉淀法制备Syr-NPs,以包封率、载药量、平均粒径以及总评"归一值"为评价指标,采用星点设计-效应面法考察PLGA质量浓度(A)、丁香苦苷质量浓度(B)、水相与有机相比例(C)3因素考察对包封率、载药量、平均粒径以及总评归一值的影响,以星点设计-效应面法选取最佳处方条件进行预测分析。结果最优处方工艺为PLGA质量浓度为9.63 mg/mL,Syr质量浓度为12.88 mg/mL,有机相与水相的比例为1∶9.46,制得的Syr-NPs的包封率、载药量、平均粒径分别为(27.86±0.87)%、(7.02±0.15)%、(110.0±1.20)nm。结论该方法稳定可行,可用于优化包载Syr的PLGA纳米粒处方与制备工艺。 相似文献
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8.
《Gait & posture》2021
BackgroundA growing body of quantitative evidence has been provided regarding age-related differences in plantar foot loading, multi-segment foot kinematics and muscle activity. Fundamental insight into the joint mechanics and energetics of the maturing foot has yet to be provided.Research question/HypothesisIt was hypothesized that so-called ‘biomechancial maturation’ joint kinetics would be observed in children underneath the age of eight and that older age-groups would not differ from each other in these parameters.MethodsFourty-three typically developing boys were recruited and allocated to three different age groups: 1) an early childhood group, 2) a middle childhood group, and 3) an early and late adolescence group. Multi-segment joint kinematics and kinetics of the Ankle-, Chopart-, Lisfranc- and Hallux joint were collected during barefoot walking. One-way Analysis of Covariance was conducted to examine differences among the outcome measures with group as a fixed factor and walking cadence as covariate.ResultsThe youngest group differed significantly from the other two age groups with respect to their ankle and chopart joint peak plantarflexion moment (p < 0.05). Ankle and chopart joint peak power generation as well as the lisfranc peak plantarflexion moment was found to be significantly lower in the youngest age group compared to the oldest group (p < 0.05). At the lisfranc joint, the youngest age group demonstrated a significantly higher peak plantarflexion velocity compared to the two older age groups (p < 0.05).SignificanceThis study provides novel insight into the biomechanical maturation of the developing foot which may guide clinical interventions in paediatric cohorts. 相似文献
9.
目的通过载药量对后交联凝胶贴膏流变学及体外经皮渗透特性的影响,考察后交联凝胶贴膏基质的载药量。方法采用流变学技术测定不同载药量时胶料的各项流变学参数,并以祖师麻乙醇提取物为模型药物,以祖师麻甲素的累积透过率及皮肤滞留率为指标,对成品贴膏进行体外经皮渗透试验,确定基质载药量。结果当载药量在4.0%~12.4%时,含药胶料的结构强度、黏弹性、耐温耐剪切性及抗变形能力、稳定性均符合要求,其中以载药量为6.8%时最佳;祖师麻甲素的累积透过率随载药量逐渐增大,皮肤滞留率分别变化不明显。结论通过比较流变学及体外经皮渗透试验结果,确定基质处方的最佳载药量为6.8%。 相似文献
10.
Michal Koínek Radim Halama Frantiek Fojtík Marek Pag
Jií Kr
ek David Krzikalla Radim Kocich Lenka Kun
ick 《Materials》2021,14(1)
The aim of this work was to monitor the mechanical behavior of 316L stainless steel produced by 3D printing in the vertical direction. The material was tested in the “as printed” state. Digital Image Correlation measurements were used for 4 types of notched specimens. The behavior of these specimens under monotonic loading was investigated in two loading paths: tension and torsion. Based on the experimental data, two yield criteria were used in the finite element analyses. Von Mises criterion and Hill criterion were applied, together with the nonlinear isotropic hardening rule of Voce. Subsequently, the load-deformation responses of simulations and experiments were compared. Results of the Hill criterion show better correlation with experimental data. The numerical study shows that taking into account the difference in yield stress in the horizontal direction of printing plays a crucial role for modeling of notched geometries loaded in the vertical direction of printing. Ductility of 3D printed specimens in the “as printed” state is also compared with 3D printed machined specimens and specimens produced by conventional methods. “As printed” specimens have 2/3 lower ductility than specimens produced by a conventional production method. Machining of “as printed” specimens does not affect the yield stress, but a significant reduction of ductility was observed due to microcracks arising from the pores as a microscopic surface study showed. 相似文献