Abstract
The effect of tissue micro-architecture and water content on ablation rates in bone is examined. Precisely machined and prepared porcine calvarial lamellar and cortical bone were ablated with a Holmium-YAG laser (λ=2.1Μm). Lamellar and cortical bone differ substantially in their tissue micro-architecture. Both are porous hard tissues, which differ predominantly in size and distribution of pores within the bone matrix. These hard tissues were ablated under physiological (wet) and chemically dehydrated conditions. The ablation rates over the range of energy densities examined assumes many linear characteristics. Ablation rate (as a function of fluence) is considerably higher for dehydrated cortical bone (4.7Μm cm2 J−1) compared to fresh cortical bone (1.49Μm cm2 J−1). This trend is also observed in lamellar bone (2.31Μm cm2 J−1 for wet and 0.37Μm cm2 J−1 for dry). Under both physiological and dehydrated conditions, cortical bone was ablated faster. Mechanisms accounting for these observations are discussed.
Highlights
Lasers have gained rapid acceptance in middle ear surgery since the successful performance of a stapedotomy using an Argon laser in 1980 [1]
In laser surgery of the skull base and temporal bone, the bone tissue can vary considerably from the very spongy and trabecular bone of the mastoid cavity to the extremely dense bone encountered in the otic capsule or diseased stapes footplate as in otosclerosis
Studies which have examined the use of lasers for performing stapedotomy operations in animals or cadaveric human tissue have all overlooked the issue of bone density and ar chi t e c t ur e [8, 10,11,12,13,14,15]
Summary
Lasers have gained rapid acceptance in middle ear surgery since the successful performance of a stapedotomy using an Argon laser in 1980 [1]. Since t hen CO2 (k=10.6 /zm), Argon (k=488-514 rim) and KTP-Nd-YAG (~=532 nm) systems have gained wide usage in the treatment of middle ear disorders [2,3,4], for otosclerosis [5,6,7,8]. In laser surgery of the skull base and temporal bone, the bone tissue can vary considerably from the very spongy and trabecular bone of the mastoid cavity to the extremely dense bone encountered in the otic capsule or diseased stapes footplate as in otosclerosis. Continued ablation depends on formation of carbonized organic matter acting as an absorber of visible wavelengths [16] This suggests a strong dependence on pyrolysis as a means of tissue destruction. This is true with respect to near and mid infra-red and ultrawiolet wavelengths
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