Nigel Bubb

Diagnostic ultrasound tooth imaging using fractional fourier transform

An ultrasound contact imaging method is proposed to measure the enamel thickness in the human tooth. A delay-line transducer with a working frequency of 15 MHz is chosen to achieve a minimum resolvable distance of 400 μm in human enamel. To confirm the contact between the tooth and the transducer, a verification technique based on the phase shift upon reflection is used. Because of the high attenuation in human teeth, linear frequency-modulated chirp excitation and pulse compression are exploited to increase the penetration depth and improve the SNR. Preliminary measurements show that the enamel-dentin boundary creates numerous internal reflections, which cause the applied chirp signals to interfere arbitrarily. In this work, the fractional Fourier transform (FrFT) is employed for the first time in dental imaging to separate chirp signals overlapping in both time and frequency domains. The overlapped chirps are compressed using the FrFT and matched filter techniques. Micro-computed tomography is used for validation of the ultrasound measurements for both techniques. For a human molar, the thickness of the enamel layer is measured with an average error of 5.5% after compressing with the FrFT and 13.4% after compressing with the matched filter based on the average speed of sound in human teeth.

An investigation into the crystallization of Dicor glass-ceramic.

The aim of this work was to investigate the crystallization of Dicor TM glass-ceramic, with a particular emphasis on the role of fluorine, and silicon tetrafluoride on the crystallization mechanism.

In vivo reproducibility study of ultrasound for monitoring enamel thickness

OBJECTIVE This work assesses ultrasounds reproducibility for monitoring enamel thickness in vivo. STUDY DESIGN This clinical reproducibility study recruited 30 healthy consenting volunteers. The enamel thickness on an intact maxillary central incisor was evaluated at 3 sites on 3 separate visits, 1 week apart. Bland-Altman statistical test and intraclass coefficients (ICC) were used to assess reproducibility. RESULTS Reproducibility results were highest for the cervical site (bias [mm] = -0.01; 95% limits of agreement = -0.05, 0.04), followed by midbuccal (bias = 0.01; 95% limits of agreement = -0.04, 0.06) and incisal site (bias = 0; 95% limits of agreement = -0.25, 0.25). ICC was highest for the cervical site (0.96) followed by midbuccal (0.71). CONCLUSIONS Ultrasound is a sufficiently reproducible and reliable technique for monitoring change in enamel thickness, as in erosive tooth surface loss (TSL). The preferred sites for ultrasonographic measurements are cervical and midbuccal.

In Vitro Enamel Thickness Measurements with Ultrasound

In the work described here, agreement between ultrasound and histologic measurements of enamel thickness in vitro was investigated. Fifteen extracted human premolars were sectioned coronally to produce 30 sections. The enamel thickness of each specimen was measured with a 15-MHz hand-held ultrasound probe and verified with histology. The speed of sound in enamel was established. Bland-Altman analysis, intra-class correlation coefficient and Wilcoxon sign rank test were used to assess agreement. The mean speed of sound in enamel was 6191 ± 199 m s(-1). Bland-Altman limits of agreement were -0.16 to 0.18 mm when the speed of sound for each specimen was used, and -0.17 to 0.21 mm when the mean speed of sound was used. Intra-class correlation coefficient agreement was 0.97, and the Wilcoxon sign rank test yielded a p-value of 0.55. Using the speed of sound for each specimen results in more accurate measurement of enamel thickness. Ultrasound measurements were in good agreement with histology, which highlights its potential for monitoring the progressive loss of enamel thickness in erosive tooth surface loss.

Tooth characterization using ultrasound with fractional Fourier transform

Ultrasound allows the internal tooth structure to be imaged non-destructively and has been demonstrated experimentally using the pulse-echo technique at different frequencies since the 1960s. For low frequencies the resolution is limited but changing to higher frequencies increases attenuation and decreases the penetration depth. The proposed solution in this paper is to use a long-duration, frequency modulated excitation signal in order to improve SNR and increase penetration depth. Although long-duration excitation provides a better penetration, the internal reflections inside the enamel and dentin layers make the received signal uninterpretable. The fractional Fourier transform (FrFT) allows frequency modulated signals overlapping in time and frequency to be separated. In this work, we present the application of the fractional Fourier technique to tooth imaging by analyzing and filtering chirp signals, overlapping in both the time and frequency domains, where the common time or frequency based filtering is not applicable. The intended application of the proposed technique is producing an image of tooth enamel and underlying dentino-enamel junction (DEJ).

Real Time Neutron Diffraction Studies of Apatite Glass Ceramics

Apatite-mullite glass-ceramics have been developed based on SiO2-Al2O3-P2O5-CaOCaF2 glasses. The glasses crystallise to form fluorapatite (FAP) and mullite with an appropriate heat treatment. The crystallisation mechanism has been thought to occur via a prior amorphous phase separation. The aim of this study was to carry out real time neutron diffraction of apatite-mullite glass-ceramics in order to develop an understanding of the crystal growth and crystal dissolution phenomena in the temperature regime between 550 and 1200oC. The results show that during the initial stages of fluorapatite crystallisation pronounced line broadening was observed indicating crystallisation on a nanoscale. Mullite starts to crystallise once there is insufficient charge balancing cations in the glass to maintain aluminium in a four fold coordination state. As a result of this work it is suggested that the mechanism of crystal growth of FAP is thought to involve the dissolution of smaller FAP crystals during the crystal growth temperature followed by re-crystallisation of FAP on the remaining larger crystallites during cooling.

An approach to understanding tribological behaviour of dental composites through volumetric wear loss and wear mechanism determination; beyond material ranking

OBJECTIVE To investigate the fundamental wear mechanisms of six resin-based composite (RBC) formulations during short-term in vitro wear testing. MATERIALS RBC materials were condensed into rectangular bar-shaped specimens and light irradiated using the ISO 4049 specimen manufacture and irradiation protocol. Wear testing (n=10 specimens for each RBC) was performed on a modified pin-on-plate wear test apparatus and wear facets were analysed for wear volume loss using a white light profilometer. The wear tested RBC specimens and their corresponding antagonists were analysed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), respectively to determine the wear mechanism. RESULTS Data generated using the profilometer showed variations in the mean total wear volume (mm3) between the RBCs tested (p<0.05). Abrasive wear was evident in all RBCs investigated with varying degrees of damage. Material transfer/deposition of the filler particles on the corresponding antagonists was evident in two RBC materials (Filtek Supreme and Kalore) indicative of a further adhesive wear mechanism. CONCLUSION It is proposed that the approach employed to use a combination of measurement and analytical techniques to quantify the wear facet volume (profilometry), wear trough (SEM) and material transfer (EDS) provides more useful information on the wear mechanism and the tribology of the system rather than relying on a simple wear ranking for the RBC materials as is routinely the case in dental research studies.

Detection of restoration faults under fillings in human tooth using ultrasound

An ultrasound contact imaging technique for detecting the restoration faults under the fillings in human tooth is proposed. A linear frequency modulated chirp signal is used to improve the signal-to-noise ratio and increase the penetration depth to allow the detection of the echoes from restoration-tooth boundary at 200 kPa acoustic pressure. Although the detection threshold is improved, it is observed that the duration of the excitation signal is longer than the duration of time of flight in the restoration, which causes signal overlapping between consecutive internal reflections. Due to these reverberations, the applied chirp signals interfere arbitrarily with the successive reflections, where the received echoes are not identifiable in the time domain. Separation in the frequency domain is not possible, since all reflections have the same bandwidth and the center frequency. In this work, the fractional Fourier transform (FrFT) is employed to separate chirp signals overlapping in both time and frequency domains. By analyzing the received echoes with FrFT, this work presents the ultrasonic non-destructive evaluation of dental restorations in human teeth.

Novel Fluorapatite-Mullite Coatings for Biomedical Applications

The bioactivity of cast fluorapatite glass-ceramic LG112 was investigated using SBF and a culture of human osteoblasts. The glass-ceramic underwent differe nt heat treatments at 800 and 1000 ̊C in both air and in a vacuum. The bioactivity was determined using SB F and osteoblast cell culture, examined using SEM, using Ti6Al4V and unheated glass as control s. The glass was successfully deposited as a coating by electrophoretic deposition and by magnetron sputt er coating. Introduction Apatite-mullite glasses and glass-ceramics have been developed f rom dental ionomer glasses, by careful heat treatment. These have an advantage over other bioactive glass s as the interlocking needle shaped crystals have high fracture toughness [1]. The mix of t he bioactive fluorapatite and the inert mullite, makes a bioactive glass ceramic with a low dissolution rate. The fluorine, in the fluorapatite, forms denser bone at the interfaces, and, in dental applic ations, can prevent caries. LG112, has an advantage over other apatite-mullite glass-ceramic s ystem as it has the same calcium to phosphorus ratio, 1:1.67, as hydroxyapatite, the mineral phase in bone . It is d signed to have a similar thermal expansion coefficient as titanium, which m akes it a suitable material for coating titanium and titanium alloy implants. Glass-ceramics have brittle properties and therefore are more succ ssfully used as a coating. Many coating systems have been tried using bioactive materials, including dipping, blasting, plasma spray, sol gel, enameling, sputter coating and electrophoretic deposition with varying degrees of success [2,3,4,5,6,7]. There has been some discussion over the bioactivity of similar g lass-ceramics [8,9]. This paper will be examining the bioactive properties of cast LG112 and investigating the possibilities of using this glass as a coating using electrophoret ic deposition (EPD) and magnetron sputter coating. Methods Glass Production. Apatite-mullite glass ceramics are based on the Al 2O3-SiO2P2O5-CaCO3-CaF system. Both the glass and the glass-ceramic were used for te sting the bioactivity and for coating by EPD. The glasses were produced by weighing the constituents and place in a rotary mill for one hour. The resulting mixed powder was subsequently placed in a 250cm 3 mullite crucible and heated in at 1550°C for two hours. The molten glass was then quenched in room temperature w e . The cooled glass frit was then placed in a grinding dish (ring and puck) s et at low amplitude and ground for 17 minutes. Grinding homogenises the glass. This powder was remelt ed at 1550 ̊C for two hours. A cylindrical graphite mould was preheated at 580 ̊C for 20 minutes . Th molten glass was poured into this mould and annealed at 580 ̊C for 2 hours. 580 ̊C is 50 ̊ below the gl ass transition temperature of this glass and it has been found, by trial and error, t o be the best annealing temperature. The final glass rod was cut into 3mm discs using an Accutom 5 cutting mac hine. Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 335-338 doi:10.4028/www.scientific.net/KEM.254-256.335