Stress distribution on dentin-cement-post interface varying root canal and glass fiber post diameters. A three-dimensional finite element analysis based on micro-CT data

Objective

The aim of the present study was to analyze the influence of root canal and glass fiber post diameters on the biomechanical behavior of the dentin/cement/post interface of a root-filled tooth using 3D finite element analysis.

Material and Methods

Six models were built using micro-CT imaging data and SolidWorks 2007 software, varying the root canal (C) and the glass fiber post (P) diameters: C1P1-C=1 mm and P=1 mm; C2P1-C=2 mm and P=1 mm; C2P2-C=2 mm and P=2 mm; C3P1-C=3 mm and P=1 mm; C3P2-C=3 mm and P=2 mm; and C3P3-C=3 mm and P=3 mm. The numerical analysis was conducted with ANSYS Workbench 10.0. An oblique force (180 N at 45º) was applied to the palatal surface of the central incisor. The periodontal ligament surface was constrained on the three axes (x=y=z=0). Maximum principal stress (σ_max) values were evaluated for the root dentin, cement layer, and glass fiber post.

Results:

The most evident stress was observed in the glass fiber post at C3P1 (323 MPa), and the maximum stress in the cement layer occurred at C1P1 (43.2 MPa). The stress on the root dentin was almost constant in all models with a peak in tension at C2P1 (64.5 MPa).

Conclusion

The greatest discrepancy between root canal and post diameters is favorable for stress concentration at the post surface. The dentin remaining after the various root canal preparations did not increase the stress levels on the root.     

Immune Responses during Human Schistosomiasis Mansoni

T lymphocyte immunoregulatory subsets (T4+ and T8+ cells) have been analysed in eight cases of hepatosplenic schistosomiasis mansoni, and compared to parallel analyses of seven intestinal Schistosoma mansoni-infected patients and four uninfected control subjects. The mean T4+:T8+ ratio in hepatosplenic cases was markedly less than observed in other groups (0.94 vs 1.86 vs 2.22, respectively). Proliferative responses stimulated by a soluble adult worm extract correlated directly with the observed T4:T8 ratios. Normal levels of E rosette-positive and surface immunoglobulin-bearing lymphoid cells were observed in intestinal patients, while hepatosplenic patients demonstrated normal B lymphocyte proportions but highly erratic E rosette-positive percentages. Curiously, in hepatosplenic patients the percentage of E rosette-positive cells often did not correlate with the proportion of T3+ cells.     

Lymphocyte Migration into Collagen Gels: Role of Lymph

In the present investigation we found that the presence of lymph within a 3-D collagen gel potentiates the invasion of mature recirculating lymphocytes into the gel. Preferential accumulation of lymphocytes in lymph-containing gels follows the sume rules that apply for both in vitro lymphocyte adhesion to high endotheltal venules of frozen sections of the lymph noues and in vivo lymph node entry of lymphocytes. Furthermore, the results obtained suggest that lymph is chemolacttc for lymphocytes. This chemoaltractant activity of lymph could be assigned mainly to a protein fraction precipitating in the. range of 40–60% concentration of ammonium sulphate. The biological significance of these findings for the selective process of lymphocyte emigration from blood to lymph, across the parenchyma of ihe nodes, is discussed.     

Limiting Dilution Analysis of Interleukin 2-Producing Mature T Cells

Evaluation of lymphokine production by individual activated T cells is necessary to characterize their growth requirements. We have studied interleukin 2 (IL-2) secretion by mature T lymphocytes using a high resolution assay system with the following characteristics: (a) a threshold of IL-2 detection 25 times lower than classic IL-2 titration; (b) the ability to discriminate between IL-2 and IL-4 activities; (c) absence of 'in situ' IL-2 absorption; (d) IL-2 production revealed at the single cell level. By this method an average of 10% of spleen cells, and 75% of L3T4+ cells were detected as producers in a concanavalin A (Con A)-dependent T cell activation system. Our results also suggest the complete restriction of IL-2 secretion to cells with this phenotype. Therefore, factors other than IL-2 must play a major role in Lyt 2+ mitogen-driven, helper-independent T cell proliferation.     

Comparison of Time-Domain Short-Term Heart Interval Variability Analysis Using a Wrist-Worn Heart Rate Monitor and the Conventional Electrocardiogram

Background: Wrist-worn heart rate monitors have not been extensively validated for heart rate variability analysis. The purpose of this study was to compare time-domain variability of heart interval series (R-Ri) recorded by the Polar S810 monitor (Polar Electro Oy, Kempele, Finland) and the conventional electrocardiogram (ECG).
Methods: Agreement was verified between variability indices of 5-minute R-Ri simultaneously recorded by both devices and processed by unique software, from 33 subjects aged 18 to 42 years, normal or with different clinical conditions, in rest supine and active standing. ECG minus Polar differences were quantified by the Bland-Altman analysis, and tested by the one-sample t-test or Wilcoxon test.
Results: In the supine position, the Polar overestimates (P < 0.0001) the absolute and percentage mean or median of the number (−2.00; −0.49%) and mean of R-Ri (–1.85 ms; –0.20%) and pNN50 (−2.20%; −8.68%), and underestimates the standard deviation (SDNN) (0.32 ms; 0.59%) (P = 0.08; P = 0.02) and root mean square successive difference (RMSSD) (0.90 ms; 1.56%) (P = 0.0008; P < 0.0001). The coefficient of variation (CV) showed null difference. On standing, differences were overestimated for the number (−2.61 intervals; −0.64%) and mean of R-Ri (−0.70 ms; −0.09%), and underestimated for rMSSD (1.70 ms; 10.84%) (P < 0.0001 to < 0.02). The SDNN, CV, and pNN50 indices did not show differences (P = 0.12 to 0.73).
Conclusions: The Polar S810 monitor was feasible and reliable for recording short-term R-R interval series, showing excellent agreement with the ECG in providing the time-domain indexes of heart interval variability with differences functionally not relevant. The CV showed the higher agreement in both postures, and the SDNN and pNN50 in the standing posture.