The aim of this study was to assess the detection of calculus by Laser Induced Breakdown Spectroscopy (LIBS). The study was performed with an Nd:YVO4 laser, emitting pulses with a duration of 8 ps at a wavelength of 1064 nm. A
repetition rate of 500 kHz at an average power of 5 W was used. Employing a focusing lense, intensities of the order of
1011 W/cm2 were reached on the tooth surface. These high intensities led to the generation of a plasma. The light emitted
by the plasma was collimated into a fibre and then analyzed by an echelle spectroscope in the wavelength region from
220 nm - 900 nm. A total number of 15 freshly extracted teeth was used for this study. For each tooth the spectra of
calculus and cementum were assessed separately. Comprising all single measurements median values were calculated for
the whole spectrum, leading to two specific spectra, one for calculus and one for cementum. For further statistical
analysis 28 areas of interest were defined as wavelength regions, in which the signal strength differed regarding the
material. In 7 areas the intensity of the calculus spectrum differed statistically significant from the intensity of the
cementum spectrum (p < 0.05). Thus it can be concluded that Laser Induced Breakdown Spectroscopy is well suited as
method for a reliable diagnostic of calculus. Further studies are necessary to verify that LIBS is a minimally invasive
method allowing a safe application in laser-guided dentistry.
The aim of this study was to assess heat generation in dental restoration materials following
laser ablation using an Ultra Short Pulse Laser (USPL) system.
Specimens of phosphate cement (PC), ceramic (CE) and composite (C) were used. Ablation
was performed with an Nd:YVO4 laser at 1064 nm and a pulse length of 8 ps.
Heat generation during laser ablation depended on the thickness of the restoration material. A
time delay for temperature increase was observed in the PC and C group.
Employing the USPL system for removal of restorative materials, heat generation has to be
considered.
The aim of the study was to assess the impact of laser irradiation during antimicrobial
photodynamic therapy.
Test chambers containing each a salivary pellicle layer and a Stretococcus mutans culture
were analyzed using confocal laser microscopy after adding a photosensitizer. Half of the
chambers were irradiated with a diode laser.
Comparing baseline fluorescence with the values after laser irradiation, a decrease of
fluorescence could be observed. The non-irradiated group showed a slight increase of
fluorescence.
The present study indicates that laser irradiation is an essential part to reduce bacteria by
antimicrobial photodynamic therapy.
The aim of this study was to assess the difference of fluorescence signals of cement and
calculus using a 405 nm excitation wavelength.
A total number of 20 freshly extracted teeth was used. The light source used for this study
was a blue LED with a wavelength of 405nm. For each tooth the spectra of calculus and
cementum were measured separately. Fluorescence light was collimated into an optical fibre
and spectrally analyzed using an echelle spectrometer (aryelle 200, Lasertechnik Berlin,
Germany) with an additionally bandpass (fgb 67, Edmund Industrial Optics, Karlsruhe,
Germany). From these 40 measurements the median values were calculated over the whole
spectrum, leading to two different median spectra, one for calculus and one for cementum.
For further statistical analysis we defined 8 areas of interest (AOI) in wavelength regions,
showing remarkable differences in signal strength.
In 7 AOIs the intensity of the calculus spectrum differed statistically significant from the
intensity of the cementum spectrum (p < 0.05). A spectral difference could be shown between
calculus and cement between 600nm and 700nm.
Thus, we can conclude that fluorescence of calculus shows a significant difference to the
fluorescence of cement. A differentiation over the intensity is possible as well as over the
spectrum. Using a wavelength of 405nm, it is possible to distinguish between calculus and
cement. These results could be used for further devices to develop a method for feedback
controlled calculus removal.
The aim of the study was to assess the impact of laser induced antimicrobial photodynamic
therapy on the viability of Streptococcus mutans cells employing an aritificial biofilm model.
Employing sterile chambered coverglasses, a salivary pellicle layer formation was induced in
19 chambers. Streptococcus mutans cells were inoculated in a sterile culture medium. Using a
live/dead bacterial viability kit, bacteria with intact cell membranes stain fluorescent green.
Test chambers containing each the pellicle layer and 0.5 ml of the bacterial culture were
analyzed using a confocal laser scan microscope within a layer of 10 μm at intervals of 1 μm
from the pellicle layer. A photosensitizer was added to the test chambers and irradiated with a
diode laser (wavelength: 660 nm, output power: 100 mW, Helbo) for 2 min each.
Comparing the baseline fluorescence (median: 13.8 [U], min: 3.7, max: 26.2) with the values
after adding the photosensitizer (median: 3.7, min: 1.1, max: 9), a dilution caused decrease of
fluorescence could be observed (p<0.05). After irradiation of the samples with a diode laser,
an additional 48 percent decrease of fluorescence became evident (median: 2.2, min: 0.4,
max: 3.4) (p<0.05). Comparing the samples with added photosensitizer but without laser
irradiation at different times, no decrease of fluorescence could be measured (p>0.05).
The present study indicates that antimicrobial photodynamic therapy can reduce living
bacteria within a layer of 10 μm in an artificial biofilm model. Further studies have to
evaluate the maximum biofilm thickness that still allows a toxic effect on microorganisms.
The aim of the study was to assess the ability of a fluorescence based optical system to detect
secondary caries.
The optical detecting system (VistaProof) illuminates the tooth surfaces with blue light
emitted by high power GaN-LEDs at 405 nm. Employing this almost monochromatic
excitation, fluorescence is analyzed using a RGB camera chip and encoded in color
graduations (blue - red - orange - yellow) by a software (DBSWIN), indicating the degree of
caries destruction. 31 freshly extracted teeth with existing fillings and secondary caries were
cleaned, excavated and refilled with the same kind of restorative material. 19 of them were
refilled with amalgam, 12 were refilled with a composite resin. Each step was analyzed with
the respective software and analyzed statistically. Differences were considered as statistically
significant at p<0.05.
There was no difference between measurements at baseline and after cleaning (Mann
Whitney, p>0.05). There was a significant difference between baseline measurements of the
teeth primarily filled with composite resins and the refilled situation (p=0.014). There was
also a significant difference between the non-excavated and the excavated group (Composite
p=0.006, Amalgam p=0.018).
The in vitro study showed, that the fluorescence based system allows detecting secondary
caries next to composite resin fillings but not next to amalgam restorations. Cleaning of the
teeth is not necessary, if there is no visible plaque. Further studies have to show, whether the
system shows the same promising results in vivo.
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