Three-dimensional finite element analysis of stress distribution in peri-implant bone with relined dentures and different heights of healing caps.

The purpose of this study was to evaluate the influence of height of healing caps and the use of soft liner materials on the stress distribution in peri-implant bone during masticatory function in conventional complete dentures during the healing period by using finite element analysis. Three-dimensional models of a severely resorbed mandible with two recently placed implants in the anterior region were created and divided into the following situations: (i) submerged implants, (ii) healing cap at gingival level and (iii) 1·5-mm supragingival. All these situations were also analysed for a conventional complete denture and a denture relined with a 3-mm-thick layer of soft liner material. The models were exported to mechanical simulation software that presented two simulations, one with load in the inferior right canine (35 N) and the other in the inferior right first molar (50 N). Data were evaluated using Maximum Principal Stress provided by the software. All models showed a stress concentration in the cortical bone corresponding to the cervical part of the implant. The simulations with non-submerged implants showed higher values of stress concentration than those that were submerged. Likewise, soft liner materials presented better results than when the denture base was not relined. The height of the healing caps seems to have a direct influence on the stress distribution in the peri-implant bone during the healing period. Considering the values obtained in this study, the use of soft liners with submerged implants seems to be the most suitable method to use during the period of osseointegration.

Genotoxicity and morphological changes induced by the alkaloid monocrotaline, extracted from Crotalaria retusa, in a model of glial cells.

Plants of Crotalaria genus (Leguminosae) present large amounts of the pyrrolizidine alkaloid monocrotaline (MCT) and cause intoxication to animals and humans. Therefore, we investigated the MCT-induced cytotoxicity, morphological changes, and oxidative and genotoxic damages to glial cells, using the human glioblastoma cell line GL-15 as a model. The comet test showed that 24h exposure to 1-500microM MCT and 500microM dehydromonocrotaline (DHMC) caused significant increases in cell DNA damage index, which reached 42-64% and 53%, respectively. Cells exposed to 100-500microM MCT also featured a contracted cytoplasm presenting thin cellular processes and vimentin destabilisation. Conversely, exposure of GL-15 cells to low concentrations of MCT (1-10microM) clearly induced megalocytosis. Moreover, MCT also induced down regulation of MAPs, especially at the lower concentrations adopted (1-10microM). Apoptosis was also evidenced in cells treated with 100-500microM MCT, and a later cytotoxicity was only observed after 6 days of exposure to 500microM MCT. The data obtained provide support for heterogenic and multipotential effects of MCT on GL-15 cells, either interfering on cell growth and cytoskeletal protein expression, or inducing DNA damage and apoptosis and suggest that the response of glial cells to this alkaloid might be related to the neurological signs observed after Crotalaria intoxication.