Ultra-short pulsed laser (USPL) systems for dental application have overcome many of their initial disadvantages. However, a problem that has not yet been addressed and solved is the beam delivery into the oral cavity. The functional system that is introduced in this study includes an articulated mirror arm, a scanning system as well as a handpiece, allowing for freehand preparations with ultra-short laser pulses. As laser source an Nd:YVO<sub>4</sub> laser is employed, emitting pulses with a duration of t<sub>p</sub> < 10 ps at a repetition rate of up to 500 kHz. The centre wavelength is at 1064 nm and the average output power can be tuned up to 9 W. The delivery system consists of an articulated mirror arm, to which a scanning system and a custom made handpiece are connected, including a 75 mm focussing lens. The whole functional system is compact in size and moveable. General characteristics like optical losses and ablation rate are determined and compared to results employing a fixed setup on an optical table. Furthermore classical treatment procedures like cavity preparation are being demonstrated on mammoth ivory. This study indicates that freehand preparation employing an USPL system is possible but challenging, and accompanied by a variety of side-effects. The ablation rate with fixed handpiece is about 10 mm<sup>3</sup>/min. Factors like defocussing and blinding affect treatment efficiency. Laser sources with higher average output powers might be needed in order to reach sufficient preparation speeds.
During ablation of oral hard tissue with an USPL system a small amount of the incident laser power does not contribute
to the ablation process and is being transmitted. Partial transmission of ultra-short laser pulses could potentially affect the
dental pulp. The aim of this study was to assess the transmission during ablation and to deduce possible risks for the
patient. The study was performed with an Nd:YVO<sub>4</sub> laser, emitting pulses with a duration of 8 ps at a wavelength of
1064 nm. A repetition rate of 500 kHz and an average power of 9 W were chosen to achieve high ablation efficiency. A
scanner system created square cavities with an edge length of 1 mm. Transmission during ablation of mammoth ivory
and dentin slices with a thickness of 2 mm and 5 mm was measured with a power meter, placed directly beyond the
samples. Effects on subjacent blood were observed by ablating specimens placed in contact to pork blood. In a separate
measurement the temperature increase during ablation was monitored using an infrared camera. The influence of
transmission was assessed by tuning down the laser to the corresponding power and then directly irradiating the blood.
Transmission during ablation of 2 mm specimens was about 7.7% (ivory) and 9.6% (dentin) of the incident laser power.
Ablation of specimens directly in contact to blood caused coagulation at longer irradiation times (t≈18s). Direct
irradiation of blood with the transmitted power provoked bubbling and smoke formation. Temperature measurements
identified heat generation as the main reason for the observed coagulation.
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
10<sup>11</sup> W/cm<sup>2</sup> 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 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.