In vitro dentine tubule occlusion by a novel toothpaste containing calcium silicate and sodium phosphate.

OBJECTIVES: To investigate the deposition, formation of hydroxyapatite (HAP) and acid resistance of dentine surfaces following brushing with a toothpaste containing calcium silicate and sodium phosphate (CSSP) and fluoride in vitro. METHODS: Human dentine specimens were brushed with a slurry of CSSP toothpaste followed by exposure to simulated oral fluid (SOF) in two in vitro studies, with a silica-based non-occluding toothpaste as control. The surface and tubule deposits were analysed after 14 cycles with scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). In a third study, dentine specimens were additionally exposed to citric acid erosive challenges for 30, 300 or 600 s after 2, 6, 10 and 14 cycles of SOF and either the CSSP toothpaste or a positive control toothpaste containing calcium sodium phosphosilicate and fluoride. The level of tubule occlusion was evaluated using SEM. RESULTS: The SEM analyses indicated complete coverage of the dentine surface following 14 cycles of brushing with CSSP toothpaste with no observable patent tubules, in contrast to the non-occluding control toothpaste. The TEM and SAED analyses confirmed the deposited material on the surface and within tubules was HAP. The deposited material from CSSP toothpaste was more acid resistant than the deposited material from the positive control toothpaste at all time points and acid exposure levels (p < 0.05). CONCLUSIONS: The CSSP toothpaste fully occluded dentine tubules and formed the mineral HAP. The dentine deposition on and within dentine tubules was resilient to acid erosive challenges. CLINICAL SIGNIFICANCE: A novel toothpaste containing CSSP can form HAP on dentine surfaces and within tubules. The potential of this technology is for a novel approach for the protection of dentine surfaces to acid challenges and the reduction of dentine hypersensitivity.

Mode of action studies on the formation of enamel minerals from a novel toothpaste containing calcium silicate and sodium phosphate salts.

OBJECTIVES: To investigate in vitro and in situ the deposition and formation of hydroxyapatite (HAP) on enamel surfaces following brushing with a novel toothpaste containing calcium silicate (CaSi), sodium phosphate salts and fluoride. METHODS: Polished enamel blocks were brushed in vitro with a slurry of the CaSi toothpaste. After one brush and four weeks simulated brushing the enamel surfaces were analysed. In an in situ protocol, enamel blocks were attached to first or second molar teeth of healthy subjects, exposed to 4 weeks twice per day brushing with the CaSi toothpaste and then analysed. The surface deposits were analysed using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). In addition, the CaSi toothpaste was slurried in simulated oral fluid (SOF) over a 3 hour period and the solids were isolated and analysed by Fourier transform infrared spectroscopy (FTIR). RESULTS: The FTIR study demonstrated that calcium phosphate phases had formed and these became increasingly crystalline over 3 hours. CaSi was deposited onto enamel surfaces following one brushing with the toothpaste in vitro.The deposited particles showed evidence of HAP crystalline phases associated with the CaSi. Following 4 weeks brushing in vitro, the deposition increased and analyses showed that the deposited material was HAP. These results were confirmed by the in situ study. CONCLUSIONS: Calcium silicate can be deposited onto enamel surfaces from a novel toothpaste formulation where it can form the enamel mineral HAP. CLINICAL SIGNIFICANCE: A novel toothpaste formulation containing CaSi can form HAP on enamel surfaces. The potential of this technology is for a novel approach to the repair of demineralised enamel and the protection of enamel during acid exposure.

Development of electron energy-loss spectroscopy for nanoscience.

Electron energy-loss spectroscopy (EELS) has been well established in providing the composition and chemical bonding information of materials, particularly for light elements. Its potential for structural determination has long been known but has yet to be fully explored. With the convergence of rapid development in computing power and improvement in the efficiency of the material specific electronic structure simulation, plus the recent breakthrough in the development of C(s)-corrected electron microscopy, the reconstruction of the local three dimensional structure of nanomaterial using EELS in conjunction with advanced structural imaging and diffraction techniques is becoming increasingly feasible. In this paper, we will review from our own examples the progress in EELS instrumentation, methods and simulation to illustrate the progress that has been made. They include the density-function-theory-based ab initio spectroscopic simulation for standard-less fingerprint applications for metastable polymorph identification, magic angle electron energy-loss spectroscopy as well as recent results from the dual-detectors EELS system which allows the energy instability of the spectrometer to be analyzed in real-time and eventually compensated on-line.

Multivariate statistical analysis of electron energy-loss spectroscopy in anisotropic materials.

Recently, an expression has been developed to take into account the complex dependence of the fine structure in core-level electron energy-loss spectroscopy (EELS) in anisotropic materials on specimen orientation and spectral collection conditions [Y. Sun, J. Yuan, Phys. Rev. B 71 (2005) 125109]. One application of this expression is the development of a phenomenological theory of magic-angle electron energy-loss spectroscopy (MAEELS), which can be used to extract the isotropically averaged spectral information for materials with arbitrary anisotropy. Here we use this expression to extract not only the isotropically averaged spectral information, but also the anisotropic spectral components, without the restriction of MAEELS. The application is based on a multivariate statistical analysis of core-level EELS for anisotropic materials. To demonstrate the applicability of this approach, we have conducted a study on a set of carbon K-edge spectra of multi-wall carbon nanotube (MWCNT) acquired with energy-loss spectroscopic profiling (ELSP) technique and successfully extracted both the averaged and dichroic spectral components of the wrapped graphite-like sheets. Our result shows that this can be a practical alternative to MAEELS for the study of electronic structure of anisotropic materials, in particular for those nanostructures made of layered materials.