Laser induced fragmentation of salivary stones: an in vitro comparison of two different clinically approved laser systems
Background: Clinical laser lithotripsy in urology promises a good fragmentation combined with a minimal risk of soft
tissue damage and low medical complications. This in vitro study investigates the fragmentation of salivary stones by
means of two clinically used laser systems.
Materials and Methods: The effects induced by the FREDDY laser (WOM, Germany, λ=532 nm / 1,064 nm,
Epulse=120-160 mJ/pulse) and the Ho:YAG (AURIGA, StarMedTec, Germany, λ=2,100 nm,Epulse=300-800 mJ/
pulse) on clinical salivary calculi (n=15) and on salivary gland tissue were investigated using clinical laser parameter
settings. All experiments were performed in an under water experimental set-up using flexible fibres (core diameter
230μm) positioned in front of each specimen. In order to assess fragmentation efficacy, each stone was placed on a
grating (rhombic mash-diameter 1-3 mm). The fragmentation rate was calculated with respect to the energy applied
(mg/J), to the number of pulses (mg/pulse), and to the time needed (mg/minute). In addition the composition of the
stones were analysed spectrographically. The soft tissue interaction on human salivary duct mucosa was examined
Results: Spectrographic composition of the salivary stones showed a two component ratio of protein/carbonate apatite
varying between 5/95 and 25/75. Stones treated by the Ho:YAG were vaporised in a milling-like process, while using
the FREDDY laser stones are cracked into pieces and fragmentation failed in two cases. The fragmentation rates
achieved by the FREDDY laser were greater than those of the Ho:YAG laser, but fragments mainly bigger. A
dependency on the composition of the stones could not be found. Laser pulse effects on soft tissue were found slightly
beyond the mucosa.
Conclusion: This study clearly demonstrated the different processes of destroying salivary stones using two different
laser systems. While the Ho:YAG vaporises the calculi in a more milling and soft sense, the FREDDY shows a more
cracking and explosive destruction. Although both laser systems showed little direct risk to the surrounding tissue, it has
to be proven whether cracked and accelerated particles could cause harm to soft tissue. With respect to this, further in
vitro studies and clinical treatments in selected cases are needed to proof these results.
This paper was published in SPIE Proceedings Vol. 7161