Evaluation of the accuracy of nine electronic apex locators by using Micro-CT.

AIM: To determine the accuracy of locating the apical constriction using apex locators. METHODOLOGY: Extracted teeth were micro-CT scanned preoperatively to localize the apical constriction. Electronic length measurements of 91 root canals were made using nine electronic apex locators (EAL) connected to a mounting model. Distances from the major foramen were recorded at each scale bar of the EALs, and a file was fixed in the canal at a position indicated by each EAL to be the apical constriction. A second micro-CT scan was conducted, and distances from the file tip to constriction and major foramen were calculated for each EAL. The accuracy of EALs was determined with a tolerance of 0.1, 0.25, 0.5 and 1 mm, and the 95% confidence interval was used to compare the EALs. A rank analysis was performed in which measurements beyond the major foramen were considered as inaccurate. RESULTS: Regardless of the type of teeth, there was no significant difference in the accuracy of determining the apical constriction and major foramen between the nine EALs within a tolerance of ±0.5 mm and 1 mm, but there was a significant difference for the tolerances of ±0.1 and 0.25 mm. The highest ranks close to the constriction (98% and 94%) and to the major foramen (86% and 73%) were observed in Dentaport ZX and Elements Diagnostic Unit, respectively. Overestimation of working length beyond the major foramen was observed in all EALs (5% to 71%) when the scale for the major foramen, as recommended by the manufacturers, was used. However, when the scale for the constriction was used, only 3% of the measurements were beyond the major foramen. CONCLUSION: Electronic apex locators were able to determine the apical constriction. Using EALs to determine the major foramen led to overestimation of the working length. Therefore, it may be recommended to use the EAL scale of the constriction.

Validity of longitudinal sections for determining the apical constriction.

AIM: To validate the use of longitudinal sections against cross sections using micro-CT for disclosing the topography and location of the apical constriction. METHODOLOGY: Seventy extracted human teeth with 117 completely developed roots were micro-CT scanned and reconstructed at a voxel size of 27 µm. The 3DSlicer program was used to navigate the longitudinal sections parallel to the long axis of the canal and also to rotate and tilt the views. Each root canal was evaluated in both mesio-distal and bucco-lingual planes. Constriction topographies were identified as described in the literature. In each canal, the number of different topographies detected was recorded. Further, serial cross-sectional analysis of the apical portion of the canal was performed. Reconstructed plots of canal areas were assessed to locate the constriction and determine its form. A descriptive analysis of both longitudinal and cross section methods was conducted. In each canal, the frequency of constriction forms was calculated in the mesio-distal or bucco-lingual aspects and the 99% confidence interval was computed. RESULTS: When both aspects of the longitudinal sections were pooled, all root canals had two or more topographies and consequently different locations of the apical constriction. In contrast, cross-sectional analysis constantly yielded one constriction form per canal. CONCLUSION: Compared to cross-sectional analysis, longitudinal sections of the root canal conveyed inconsistent results regarding the topography and the location of the apical constriction.

Akt2/PKBbeta-sensitive regulation of renal phosphate transport.

AIM: The protein kinase B (PKB)/Akt is known to stimulate the cellular uptake of glucose and amino acids. The kinase is expressed in proximal renal tubules. The present study explored the influence of Akt/PKB on renal tubular phosphate transport. METHODS: The renal phosphate transporter NaPi-IIa was expressed in Xenopus oocytes with or without PKB/Akt and Na(+) phosphate cotransport determined using dual electrode voltage clamp. Renal phosphate excretion was determined in Akt2/PKBbeta knockout mice (akt2(-/-)) and corresponding wild-type mice (akt2(+/+)). Transporter protein abundance was determined using Western blotting and phosphate transport by (32)P uptake into brush border membrane vesicles. RESULTS: The phosphate-induced current in NaPi-IIa-expressing Xenopus oocytes was significantly increased by the coexpression of Akt/PKB. Phosphate excretion [micromol per 24 h per g BW] was higher by 91% in akt2(-/-) than in akt2(+/+) mice. The phosphaturia of akt2(-/-) mice occurred despite normal transport activity and expression of the renal phosphate transporters NaPi-IIa, NaPi-IIc and Pit2 in the brush border membrane, a significantly decreased plasma PTH concentration (by 46%) and a significantly enhanced plasma 1,25-dihydroxyvitamin D(3) concentration (by 46%). Moreover, fractional renal Ca(2+) excretion was significantly enhanced (by 53%) and bone density significantly reduced (by 11%) in akt2(-/-) mice. CONCLUSIONS: Akt2/PKBbeta plays a role in the acute regulation of renal phosphate transport and thus contributes to the maintenance of phosphate balance and adequate mineralization of bone.

Combined PET/MR imaging--technology and applications.

The combination of PET and MR in one imaging device has certain advantages over conventional imaging modalities. These include: no additional radiation dose from the MR, superior soft tissue contrast and a multitude of tracers for PET. Certain technical challenges exist when designing a PET/MR system. On the one hand these stem from the presence of the strong MR magnetic field and the addition of PET components to the MR system. Different approaches are presented to overcome these technical obstacles ranging from long optical fibers to systems that use semiconductor light detectors for photon counting. The applications of combined PET/MR are profound in the field of oncology and allow imaging of the four main processes in cancer formation: apoptosis resistance, angiogenesis, proliferation and metastasis. PET/MR has also many clinical and research applications in neurology and cardiology. Alternative techniques such as image fusion, hyperpolarized imaging, 17O imaging and whole body diffusion are discussed in respect to their relevance regarding PET/MR. Simultaneous multifunctional and anatomical imaging using PET/MR has a great potential to impact biomedical imaging in research and clinic.