Holmium-YAG laser ablation characteristics in calvarial lamellar and cortical bone: The role of water and tissue micro-architecture

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 (lambda=2.1 mu m). 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 (4.7 mu m cm(2) J(-1)) compared to fresh cortical bone (1.49 mu m cm(2) J(-1)). This trend is also observed in lamellar bone (2.31 mu m cm(2) J(-1) for wet and 0.37 mu m cm(2) J(-1) for dry). Under both physiological and dehydrated conditions, cortical bone was ablated faster. Mechanisms accounting for these observations are discussed.