Effects of Water Mist Flow Rate in Erbium - Yttrium Aluminum Garnet Laser Ablated Bone

<b><i>Objectives:</i></b> The aim of this study is to investigate the impact of water mist flow rate on the energy stability of Erbium - doped Yttrium Aluminum Garnet (Er:YAG) laser and ablation of bone. <b><i>Materials and Methods:</i></b> The pig tibiae surface was ablated with Er:YAG laser (100 mJ, 20 Hz, 100 μs) at the flow rate of water mist of 0, 3, 6, 9, 12 mL/min, respectively, for 1 min each. An energy meter was used to record the energy of each laser pulse under different water mist flow rates. A thermocouple was inserted into the bone marrow cavity to record the temperature changes. Infrared thermography, stereomicroscope, and electronic balance were employed to record the surface temperature, morphology, and mass changes, respectively. <b><i>Results:</i></b> As the water mist flow rate escalates, the laser energy experiences a notable attenuation of 27.4%, and the stability parameter Root Mean Square (RMS) escalates by a factor of 30. Despite the relatively minor temperature change within the bone marrow cavity, obviously different surface morphologies are evident. In cases where water mist is less than 3 mL/min, the surface temperature soars, resulting in carbonization. Conversely, when the water mist is greater than 9 mL/min, the ablating mass deteriorates significantly, to merely 25.2% of the value without water mist cooling. <b><i>Conclusions:</i></b> The water mist can affect the laser energy reaching the bone surface and its stability. When the water mist is insufficient, surface temperatures rise, causing carbonization. Conversely, it significantly reduces the ablating mass. Therefore, it is crucial to adjust the amount of water mist appropriately in erbium laser ablated bone. Given such large fluctuations in laser energy, the accuracy of erbium laser bone ablation is dramatically reduced, and the use of water mist cooling should be carefully considered.