Abstract
.Significance: The highest absorption peaks of the main components of bone are in the mid-infrared region, making Er:YAG and lasers the most efficient lasers for cutting bone. Yet, studies of deep bone ablation in minimally invasive settings are very limited, as finding suitable materials for coupling high-power laser light with low attenuation beyond is not trivial.Aim: The first aim of this study was to compare the performance of different optical fibers in terms of transmitting Er:YAG laser light with a wavelength at high pulse energy close to 1 J. The second aim was to achieve deep bone ablation using the best-performing fiber, as determined by our experiments.Approach: In our study, various optical fibers with low attenuation () were used to couple the Er:YAG laser. The fibers were made of germanium oxide, sapphire, zirconium fluoride, and hollow-core silica, respectively. We compared the fibers in terms of transmission efficiency, resistance to high Er:YAG laser energy, and bending flexibility. The best-performing fiber was used to achieve deep bone ablation in a minimally invasive setting. To do this, we adapted the optimal settings for free-space deep bone ablation with an Er:YAG laser found in a previous study.Results: Three of the fibers endured energy per pulse as high as 820 mJ at a repetition rate of 10 Hz. The best-performing fiber, made of germanium oxide, provided higher transmission efficiency and greater bending flexibility than the other fibers. With an output energy of 370 mJ per pulse at 10 Hz repetition rate, we reached a cutting depth of in sheep bone. Histology image analysis was performed on the bone tissue adjacent to the laser ablation crater; the images did not show any structural damage.Conclusions: The findings suggest that our prototype could be used in future generations of endoscopic devices for minimally invasive laserosteotomy.
Highlights
In the field of osteotomy, the use of lasers has been studied for several years;[1,2,3,4,5,6,7,8] some early clinical studies showed severe collateral damage and a prolonged healing process.[9]
Since beam propagation differs depending on the type of fiber it passes through, the lens was designed for the fiber that we considered most suitable for endoscopic laser surgeries, based on the experimental findings
The transmission efficiency obtained for the sapphire fiber was 64% Æ 2%; other researchers have shown that the sapphire fiber can reach up to 90% transmission efficiency.[18]
Summary
In the field of osteotomy, the use of lasers has been studied for several years;[1,2,3,4,5,6,7,8] some early clinical studies showed severe collateral damage and a prolonged healing process.[9]. Modern Er:YAG laser systems have been used to remove intraoral hard tissue in humans, without showing damage in subsequent histological analyses.[10] More recent studies have shown how the use of new irrigation and temperature feedback detection systems for Er:YAG laserosteotomy can help achieve safe, deep bone ablation.[11] Other results from a robotic free-space laser device, CARLO®, based on an Er:YAG laser, show potential for use in osteotomy applications. After years of investigation in the field, the device was used in July 2019 for an in vivo mid-face osteotomy at the Department of Oral Maxillofacial Surgery, University Hospital Basel, Switzerland.[7,12,13]
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