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Objective: It was the objective of this in-vitro study to investigate photon-based techniques for identifying the
composition and fragmentation of salivary stones using a Ho:YAG laser.
Materials and Method: Salivary stones (n=47) extracted from patients with clinical symptoms of sialolithiasis were
examined in-vitro. After extraction, the stones were kept in Ringers solution until size and volume measurements could
be performed. Thereafter, dual-energy CT scans (DECT) were performed to classify the composition of the stones.
Subsequently, fluorescence measurements were performed by taking images under blue light excitation as well as by
fluorescence spectroscopy, measuring excitation-emission-matrixes (EEM). Further investigation to identify the exact
composition of the stone was performed by Raman spectroscopy and FTIR spectroscopy of stone fragments and debris.
Fragmentation was performed in an aquarium set-up equipped with a mesh (hole: 1.5mm) using a Ho:YAG-laser to
deliver laser pulses of 0.5, 1.0 and 1.5J/pulse at a frequency of 3Hz through a 200μm-fibre to the stone surface. The
collected data were analyzed and fragmentation rates were calculated. Finally, correlation between stone composition
and fragmentation was performed.
Results: Blue light fluorescence excitation resulted in either fluorescence in the green spectral region or in a
combination of green and red fluorescence emission. EEM-measurement showed the corresponding spectra. Raman
spectroscopy showed a mixture of carbonate apatite and keratin. DECT results in evidence of calcium containing
components. FTIR-spectroscopy results showed that carbonate apatite is the main component. Fragmentation experiment
showed a dependency on the energy per pulse applied if the evaluation implies the ratio of fragmented weight to pulse,
while the ratio fragmented weight to energy remains about constant for the three laser parameter used.
Conclusion: The composition of salivary stones could be determined using different photonic techniques. Attempts to
correlate salivary stone composition to fragmentation rates resulted in no correlation. Thus it could be concluded that
each salivary stone could be easily destroyed using Ho:YAG-laser light by means of a 200μm bare fibre at lowest energy
per pulse.
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