Step-wise analysis of the dental implant insertion process using the finite element technique

OBJECTIVES: Using the finite element method (FEM), the insertion process of a dental implant into a section of the human mandible is analysed. The ultimate aim of this article is to advance the use of an innovative engineering approach in dental practices, especially in the process of dental implantation. MATERIAL AND METHODS: The FEM and analysis techniques are used to replicate and evaluate the stress profile created within the mandible during the implantation process. RESULTS: The von Mises stress profiles in both cancellous and cortical bone are examined during implant insertion. The applied torque and the insertion stage are found to strongly influence the resulting stress profile within the surrounding jawbone. CONCLUSIONS: Through the combination of both dental and engineering expertise, a simplified and efficient modelling technique is developed. This improves the understanding of the biomechanical reaction that the jawbone exhibits due to the insertion of implant. The current research is a pilot study using the FEM to model and simulate the dental implantation process. The assumptions made in the modelling and simulation process are: (1) the implantation process is simulated as a step-wise process instead of a continuous process; (2) the implant is parallel threaded and the implant does not rotate during insertion into the jawbone. Although the modelling and simulation techniques had to be simplified, a significant amount of information is gained that helps lay a good foundation for future research. Recommendations for future studies include the variation of the torque applied during the implantation process and upgrading the software capabilities to simulate the full dynamical process of implantation.     

[11C]5-HTP and microPET are not suitable for pharmacodynamic studies in the rodent brain

The PET tracer [¹¹C]5-hydroxytryptophan ([¹¹C]5-HTP), which is converted to [¹¹C]5-hydroxytryptamine ([¹¹C]5-HT) by aromatic amino acid decarboxylase (AADC), is thought to measure 5-HT synthesis rates. But can we measure these synthesis rates by kinetic modeling of [¹¹C]5-HTP in rat? Male rats were scanned with [¹¹C]5-HTP (60 minutes) after different treatments. Scans included arterial blood sampling and metabolite analysis. 5-HT synthesis rates were calculated by a two-tissue compartment model (2TCM) with irreversible tracer trapping or Patlak analysis. Carbidopa (inhibitor peripheral AADC) dose-dependently increased [¹¹C]5-HTP brain uptake, but did not influence 2TCM parameters. Therefore, 10 mg/kg carbidopa was applied in all subsequent study groups. These groups included treatment with NSD 1015 (general AADC inhibitor) or p-chlorophenylalanine (PCPA, inhibitor of tryptophan hydroxylase, TPH). In addition, the effect of a low-tryptophan (Trp) diet was investigated. NSD 1015 or Trp depletion did not affect any model parameters, but PCPA reduced [¹¹C]5-HTP uptake, and the k₃. This was unexpected as NSD 1015 directly inhibits the enzyme converting [¹¹C]5-HTP to [¹¹C]5-HT, suggesting that trapping of radioactivity does not distinguish between parent tracer and its metabolites. As different results have been acquired in monkeys and humans, [¹¹C]5-HTP-PET may be suitable for measuring 5-HT synthesis in primates, but not in rodents.     

The neural basis of unwanted thoughts during resting state

Human beings are constantly engaged in thought. Sometimes thoughts occur repetitively and can become distressing. Up to now the neural bases of these intrusive or unwanted thoughts is largely unexplored. To study the neural correlates of unwanted thoughts, we acquired resting-state fMRI data of 41 female healthy subjects and assessed the self-reported amount of unwanted thoughts during measurement. We analyzed local connectivity by means of regional homogeneity (ReHo) and functional connectivity of a seed region. More unwanted thoughts (state) were associated with lower ReHo in right dorsolateral prefrontal cortex (DLPFC) and higher ReHo in left striatum (putamen). Additional seed-based analysis revealed higher functional connectivity of the left striatum with left inferior frontal gyrus (IFG) in participants reporting more unwanted thoughts. The state-dependent higher connectivty in left striatum was positively correlated with rumination assessed with a dedicated questionnaire focussing on trait aspects. Unwanted thoughts are associated with activity in the fronto-striatal brain circuitry. The reduction of local connectivity in DLPFC could reflect deficiencies in thought suppression processes, whereas the hightened activity in left striatum could imply an imbalance of gating mechanisms housed in basal ganglia. Its functional connectivity to left IFG is discussed as the result of thought-related speech processes.     

Novel Approach to Repeated Arterial Blood Sampling in Small Animal PET: Application in a Test-Retest Study with the Adenosine A1 Receptor Ligand [<Superscript>11</Superscript>C]MPDX

Purpose

Small animal positron emission tomography (PET) can be used to detect small changes in neuroreceptor availability. This often requires rapid arterial blood sampling. However, current catheterization procedures do not allow repeated blood sampling. We have developed a procedure which allows arterial sampling on repeated occasions in the same animal.

Procedures

Eleven male Wistar rats were two times catheterized via a superficial branch of a femoral artery and scanned with [¹¹C]MPDX and blood sampling. PET images were co-registered to a magnetic resonance imaging (MRI) template. Regional tracer distribution volumes (V _T) in the brain were calculated by the Logan analysis. The procedure was repeated after 1 week.

Results

Surgery was successful in 90 % of the cases, and discomfort was minor. The V _T data showed small differences between test and retest, low between subject variability, and a strong agreement between and within subjects.

Conclusion

Repeated quantitative imaging with a high reproducibility is possible with this approach.

     

Stimulation of Toll-like receptor 3 and 4 induces interleukin-1beta maturation by caspase-8

The cytokine interleukin (IL)-1β is a key mediator of the inflammatory response and has been implicated in the pathophysiology of acute and chronic inflammation. IL-1β is synthesized in response to many stimuli as an inactive pro–IL-1β precursor protein that is further processed by caspase-1 into mature IL-1β, which is the secreted biologically active form of the cytokine. Although stimulation of membrane-bound Toll-like receptors (TLRs) up-regulates pro–IL-1β expression, activation of caspase-1 is believed to be mainly initiated by cytosolic Nod-like receptors. In this study, we show that polyinosinic:polycytidylic acid (poly[I:C]) and lipopolysaccharide stimulation of macrophages induces pro–IL-1β processing via a Toll/IL-1R domain–containing adaptor-inducing interferon-β–dependent signaling pathway that is initiated by TLR3 and TLR4, respectively. Ribonucleic acid interference (RNAi)–mediated knockdown of the intracellular receptors NALP3 or MDA5 did not affect poly(I:C)-induced pro–IL-1β processing. Surprisingly, poly(I:C)- and LPS-induced pro–IL-1β processing still occurred in caspase-1–deficient cells. In contrast, pro–IL-1β processing was inhibited by caspase-8 peptide inhibitors, CrmA or vFLIP expression, and caspase-8 knockdown via RNAi, indicating an essential role for caspase-8. Moreover, recombinant caspase-8 was able to cleave pro–IL-1β in vitro at exactly the same site as caspase-1. These results implicate a novel role for caspase-8 in the production of biologically active IL-1β in response to TLR3 and TLR4 stimulation.     

Value of 11C-methionine PET in imaging brain tumours and metastases

¹¹C-methionine (MET) is the most popular amino acid tracer used in PET imaging of brain tumours. Because of its characteristics, MET PET provides a high detection rate of brain tumours and good lesion delineation. This review focuses on the role of MET PET in imaging cerebral gliomas. The Introduction provides a clinical overview of what is important in primary brain tumours, recurrent brain tumours and brain metastases. The indications for radiotherapy and the results and problems arising after chemoradiotherapy in relation to imaging (pseudoprogression or radionecrosis) are discussed. The working mechanism, scan interpretation and quantification possibilities of MET PET are then explained. A literature overview is given of the role of MET PET in primary gliomas (diagnostic accuracy, grading, prognosis, assessment of tumour extent, biopsy and radiotherapy planning), in brain metastases, and in the differentiation between tumour recurrence and radiation necrosis. Finally, MET PET is compared to other nuclear imaging possibilities in brain tumour imaging.