Abstract
Ultrasonic surgical devices are increasingly used in oral, craniofacial and maxillofacial surgery to cut mineralized tissue, offering the surgeon high accuracy with minimal risk to nerve and vessel tissue. Power ultrasonic devices operate in resonance, requiring their length to be a half-wavelength or multiple-half-wavelength. For bone surgery, devices based on a half-wavelength have seen considerable success, but longer multiple-half-wavelength endoscopic devices have recently been proposed to widen the range of surgeries. To provide context for these developments, some examples of surgical procedures and the associated designs of ultrasonic cutting tips are presented. However, multiple-half-wavelength components, typical of endoscopic devices, have greater potential to exhibit nonlinear dynamic behaviours that have a highly detrimental effect on device performance. Through experimental characterization of the dynamic behaviour of endoscopic devices, it is demonstrated how geometrical features influence nonlinear dynamic responses. Period doubling, a known route to chaotic behaviour, is shown to be significantly influenced by the cutting tip shape, whereas the cutting tip has only a limited effect on Duffing-like responses, particularly the shape of the hysteresis curve, which is important for device stability. These findings underpin design, aiming to pave the way for a new generation of ultrasonic endoscopic surgical devices.
Highlights
The term high-power ultrasonics (HPU) has been used historically to differentiate applications of ultrasound above a certain power or intensity threshold from those below the threshold
A typical power ultrasonic surgical device consists of a generator, which transforms mains power to a signal whose frequency corresponds with the resonant frequency of the device, and a transducer which uses a transduction material to convert an electrical signal into micrometric vibration
Power ultrasonic devices capable of cutting mineralized tissue have only been routinely employed in surgical procedures since the start of this century [3], but the introduction of ultrasonic devices for clinical procedures was initiated in the middle of the last century with the development and trials of an industrial ultrasonic impact grinder to cut cavities in extracted teeth [5]
Summary
The term high-power ultrasonics (HPU) has been used historically to differentiate applications of ultrasound above a certain power or intensity threshold from those below the threshold. It was reported that mild heat shock (47◦C for 60 s or less) could enhance bone healing through mineralization of osteoblast-like cells as well as differentiation and mineralization of mesenchymal stem cells, stem cells that are capable of differentiating to a variety of cells such as osteoblasts [24] It is beneficial for post-operative recovery if the maximum temperature and duration of exposure at the surgical site is controlled. The results of these studies are difficult to compare due to differences in the ultrasonic device used, procedure duration, presence of coolant, or in vitro or in vivo conditions They all conclude that ultrasonic cutting of bone, as with cutting with conventional bone saws and burs, causes thermal shock in tissue sufficient to induce necrotic or apoptotic responses. Similar success was reported in another study which exhibited a complete absence of palatal mucosal injury after 140 palatal expansions using an ultrasonic cutting device [19]
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