A three dimensional finite element study on stress distribution in maxillary central incisor restored with fiber post / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To study the stress changes of maxillary central incisor restored with or without fiber post using three dimensional finite element method, and analysis the role of fiber post in determining the stress distribution in dentin.</p><p><b>METHODS</b>Three dimensional finite element models of maxillary central incisor with various remaining tooth structure were established by spiral CT, Mimics software and ANSYS software. Test samples were restored with all-ceramic crown and fiber post all-ceramic crown, respectively. The von Mises stress and maximal tensile stress of dentin were recorded.</p><p><b>RESULTS</b>The stress level in dentin of maxillary central incisor restored with fiber post all-ceramic crown was smaller than that restored with all-ceramic crown, the stress distribution of both were similar.</p><p><b>CONCLUSION</b>The apply of fiber post can reduce the stress level in dentin of maxillary central incisor and decrease the risk of tooth breakage, but not change the stress pattern.</p>

Validation of the non-cellular metastasis hypothesis of malignant tumors in mice / 南方医科大学学报

<p><b>OBJECTIVE</b>To test the hypothesis that malignant tumor metastasis is mediated also through a non-cellular, essentially molecular, mechanism in addition to the cellular pathway.</p><p><b>METHODS</b>The sex-determining region on the Y chromosome was detected as the marker of the primary tumors using PCR in Lewis lung carcinoma (LLC) in vitro and in female C57BL/6 mice bearing LLC with spontaneous metastasis. The macroscopic and microscopic metastases in the tumor-bearing mice were examined for SRY expression by PCR and in situ hybridization, using the tissues from male and female mice as the positive or negative controls.</p><p><b>RESULTS AND CONCLUSION</b>Positive SRY gene expression was detected in the metastatic foci in the LLC-bearing female mice, suggesting the origination of these tumor cells from the primary tumor foci. We have failed to verify the non-cellular metastasis hypothesis in this animal experiment, but given the limitations of this experiment, we consider further investigation still necessary for verification of this hypothesis using other methods.</p>

Dynamic finite element analysis of three ferrule designs in post crown under impact loading / 南方医科大学学报

<p><b>OBJECTIVE</b>To investigate the stress distribution in three ferrule designs in a maxillary central incisor restoration using PFM crown with post, and evaluate the biomechanical mechanism of the ferrule effect in the post crown by 3D finite element dynamic analysis.</p><p><b>METHODS</b>The 3D finite element model of a maxillary central incisor restored with post and PFM crown was established. By simulating three types of ferrule effect [crown wrapping dentine (A), core collar wrapping (B), and contrabevel (C)] under dynamic loading, the dentin stress was analyzed.</p><p><b>RESULTS</b>During dynamic loading, the stress distribution tended to increase from the cervical part to root middle and radical part of the tooth, and greater high stress area was found around the apex of the post, where the peak stress was observed value. The stress of the labial dentin of the root inferior segment increased obviously. The high stress areas were invariable at every loading step during dynamic loading. The peak stress was sigma(vonA)<sigma(vonC), sigma(vonB)<sigma(vonC), (P<0.05). The contrabevel had the minimal effect in decreasing the peak stress.</p><p><b>CONCLUSIONS</b>When the ferrule is 2 mm, the ferrule effect maintained by crown wrapping cervical dentine (A) and core collar wrapping (B) is greater than that maintained by contrabevel (C),but there is no significant difference between A and B. The post with higher elastic modules may cause restore failure due to the high stress at the post apex and labial dentin.</p>

Comparison of the failure mode of various types of glass ionomer cements / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the failure mode of various types of glass ionomer cements by Hertzian indentation test.</p><p><b>METHODS</b>Discs of 10 mm diameter and 2 mm thickness were prepared for six glass ionomer cement products (A-D: conventional type setting through an acid-base chemical reaction, A and B without reinforcement, C with silver reinforcement, D with ceramic reinforcement; E and F: resin-modified type), ten for each. These were tested on top of glass-reinforced polyamide-nylon 6, 6 substrates by a universal testing machine, loading centrally with a 20 mm diameter ball. Load at the first crack was recorded. Failure mode was observed under scanning electron microscope.</p><p><b>RESULTS</b>The former four products presented typical brittle fracture, while the latter two usually fractured incompletely. The failure loads at the first crack of the six glass ionomer cements were (258.86 +/- 10.49), (230.88 +/- 21.66), (281.90 +/- 25.39), (282.11 +/- 9.60), (756.67 +/- 83.50) and (1 148.00 +/- 147.78) N, respectively. Significant difference was found between the former four and the latter two products.</p><p><b>CONCLUSIONS</b>The type (setting mode) of glass ionomer cement controls its failure mode. Inclusion of metallic or ceramic filler has little effect on increasing the load bearing capacity of glass ionomer cement.</p>