Epoxy-resin injection of the cerebral arterial microvasculature: An evaluation of the limits of spatial resolution in 8 Tesla MRI

The purpose of this study was to quantify the spatial resolution of microscopic arteries on magnetic resonance images acquired at 8 Tesla (T). Techniques similar to those used for standard MRI of the human brain in vivo at 8 T were utilized to generate high-resolution gradient echo (GE) images of a whole postmortem human brain whose common carotid arterial system had been injected with an epoxy-resin. Single slice images, along with summed images of up to 5 contiguous slices, were then compared to color digital photographs detailing the distribution of the arterial system on the surface of the same injected brain. There was excellent MR visualization of the microscopic cerebral arteries down to a spatial resolution of 200 microm. Through the use of an 8 T whole-body MRI scanner and standard GE imaging sequences, microscopic arterial structures can be clearly resolved down to a dimension of 200 microm.     

Finite element analysis of three designs of an implant-supported molar crown

STATEMENT OF PROBLEM: The optimal method of implant support for a single mandibular molar crown is controversial because commonly used, threaded, root-form implants developed by Branemark were not originally designed to support individual crowns. PURPOSE: The purpose of this study was to develop a finite element model of a single mandibular first molar crown supported by (1) a standard 3.75-mm-diameter implant, (2) a 5-mm, wide-diameter implant, and (3) double standard-diameter implants, and to compare the induced displacements as a result of various loading conditions. MATERIAL AND METHODS: Three-dimensional finite element models were made to simulate the 3 single-molar implant designs. Each model was analyzed with 2 force magnitudes (35 N and 70 N) and with 2 force directions (vertical and 15 degrees to the vertical axis). Displacements in 3-dimensional space as a result of the simulated loading conditions were evaluated along 3 primary axes, mesiodistal, faciolingual, and superior-inferior. RESULTS: Mesiodistal and buccolingual displacements for the crown supported by the 5-mm-diameter implant were reduced by approximately 50% compared with the crown supported by the 3.75-mm implant when the crowns were loaded at the distobuccal cusp tip or the distal marginal ridge. The double-implant design recorded the least mesiodistal displacement with off-center loading of the crown. CONCLUSION: When the crown was loaded off-center, the double-implant design produced substantially less displacement when compared with either of the single-implant designs.     

MR imaging visualization of the cerebral microvasculature: a comparison of live and postmortem studies at 8 T

Summary: In this study, we compared 8-T gradient-echo MR images of the microvasculature in the live human brain with images of the unembalmed and embalmed postmortem brain. Small vessels were well visualized in the live brain and even better seen in the unembalmed postmortem brain, but they could not be visualized in the embalmed postmortem brain. These findings are important for direct comparisons of the microvasculature on 8-T MR images and on histologic sections.     

Secondary trauma from occlusion: three-dimensional analysis using the finite element method.

Clinical effects of forces applied by dental occlusion on the periodontium have been evaluated for decades. Historically, trauma from occlusion has been considered as a major etiologic factor of inflammatory periodontal diseases, while some researchers have interpreted it to be of less importance or without any detectable importance in periodontics. In this study, five three-dimensional models of a maxillary central incisor were created using ANSYS 5.40. The only difference in each model was the height of the alveolar bone that showed from normal height (13 mm of alveolar bone height) to 8 mm of alveolar bone loss (5 mm of alveolar bone height). Five-point forces of 0.3 N summing up to 1.5 N were applied in a parallel line, 1 mm apical to the incisal edge on the palatal side in a palatolabial direction. The maximum (S1) and minimum (S3) principal stresses in the nodes of the labial side of the periodontal ligament (apical to the alveolar crest) were assessed. Analysis was done using the finite element method. An increase of S1 (up to 16 times in the cervical and 11.25 times in the apical area) and S3 (up to 17.13 times in the cervical and 9.9 times in the apical area) in comparison to the normal model was shown. The highest stress levels were traced in the subcervical area, except for the last model (8 mm of the alveolar bone loss). According to the results of this study, 2.5 mm of alveolar bone loss can be considered as a limit beyond which stress alterations were accelerated. Based on the FEM analysis, alveolar bone loss increases stress (S1 and S3) produced in the PDL, in spite of applying the same force vector.     

Diagnosis and management of abdominal pregnancy. A case report

BACKGROUND: Abdominal pregnancy is a rare obstetric emergency, occurring in 1 in 10,000 pregnancies. CASE: An 18-year-old woman, gravida 3, para 1, presented for evaluation of an abnormal level of maternal serum alpha-fetoprotein. Transabdominal ultrasound examination revealed absence of amniotic fluid with limited imaging ability. Transabdominal amnioinfusion was done to better visualize the fetus. A small uterus was seen in the pelvis, and an abdominal pregnancy was identified with the placenta attached anteriorly over the right pelvic sidewalls. After delivery of the fetus, the placenta was left in situ. The patient recovered postoperatively and was doing well a year after the procedure. A 12 x 10-cm mass remains over the right pelvic sidewall without detectable Doppler blood flow. CONCLUSION: State-of-the-art imaging and prenatal diagnostic techniques allowed correct diagnosis, adequate preparation and optimal management of this dangerous condition.     

Is meconium passage a risk factor for maternal infection in term pregnancies?

OBJECTIVE:To study the association between meconium and maternal infection. METHODS:This was a retrospective cohort study of 678 pregnant women. All term deliveries during a 31-month period with meconium passage were included. Each meconium delivery was matched with a consecutive delivery without meconium at the same gestational age. RESULTS: The overall infection rate was 16%, with 13% of the infections directly related to the pregnancy, labor, and delivery. The endometritis rate was 5%, with 7.1% and 3% in the meconium and no-meconium group, respectively. The chorioamnionitis rate was 8.3%, with 9.5% in the meconium and 7.1% in the no-meconium group. Factors found to be associated with overall obstetric infections had the following odds ratios (ORs) and 95% confidence intervals (CIs): meconium (OR 1.8, 95% CI 1.1, 2.8), internal monitoring (OR 3.4, 95% CI 1.9, 5.9), amnioinfusion (OR 2.0, 95% CI 1.3, 3.3), number of vaginal exams (OR 4.5, 95% CI 2.8, 7.1), length of labor (OR 2.8, 95% CI 1.8, 4.4), and cesarean (OR 3.1, 95% CI 1.9, 5.1). Logistic regression analyses revealed the following ORs and 95% CIs: 1) for endometritis-cesarean (OR 4.2, 95% CI 1.9, 8.9), internal monitoring (OR 2.5, 95% CI 1.1, 5.9), and meconium (OR 2.5, 95% CI 1.1, 5.5), and 2) for chorioamnionitis-length of labor greater than 10 hours (OR 2.7, 95% CI 1.4, 5.6), number of vaginal exams greater than seven (OR 3.4, 95% CI 1.7, 6.6), and use of internal monitors (OR 2.5, 95% CI 1.2, 5.3). CONCLUSION: Meconium passage increases the risk of postpartum endometritis but not chorioamnionitis. Length of labor, internal monitoring, and number of vaginal exams are risk factors for chorioamnionitis.     

IPS-Empress II inlay-retained fixed partial denture reinforced with zirconia bar: Three-dimensional finite element and in-vitro studies

Abstract Objective. This study evaluated von Mises stress distribution, flexural strength and interface micrographs of IPS-Empress II (IPS) inlay-retained fixed partial dentures (IRFPD) reinforced with Zirconia bars (Zb). Materials and methods: In the Finite element analysis, six three-dimensional models of IRFPD were designed using Solid Works 2006. Five models were reinforced with different Zb and a model without Zb was considered as a control. The bridges were loaded by 200 and 500 N forces at the middle of the pontic on the occlusal surface. Subsequently, von Mises stress and displacement of the models were evaluated along a defined path. In the experimental part, 21 bar shape specimens were fabricated from lithium disilicate and zirconia ceramic in three different designs. The zirconia-IPS interfaces and the fractured surfaces of flexural test were observed using SEM. Results. In the connector area, von Mises stress and displacement of the models with Zb under a load of 500 N were decreased compared to the model without the Zb; however, this difference was not considerable at a load of 200 N. In the mesial connector, Von Mises stress and displacement was decreased from 12.5 Mpa for the control model tested at 500 N to 7.0 Mpa for the model with Zb and from 0.0050-0.0041 mm, respectively. SEM analyses showed that, before fracture, interfacial gaps were not observed along the interfaces, but initiated cracks propagated along the interfaces after flexural loading. Conclusion: IPS IRFPD reinforced by Zb can tolerate higher stresses while still functioning effectively and the interfaces may have desirable adaption.