Abstract
This review summarizes current knowledge and experience with piezosurgery, a promising, meticulous and soft tissue-sparing system for bone cutting, based on ultrasonic microvibrations. The main advantages of piezosurgery include soft tissue protection, optimal visibility in the surgical field, decreased blood loss, less vibration and noise, increased comfort for the patient and protection of tooth structure. To date it has been indicationed for use in oral and maxillofacial surgery, otorhinolaryngology, neurosurgery, ophthalmology, traumatology and orthopaedics. The main indications in oral surgery are sinus lift, bone graft harvesting, osteogenic distraction, ridge expansion, endodontic surgery, periodontal surgery, inferior alveolar nerve decompression, cyst removal, dental extraction and impacted tooth removal. In conclusion, piezosurgery is a promising technical modality for different aspects of bone surgery with a rapidly increasing number of indications throughout the whole field of surgery.
Piezosurgery (piezoelectric bone surgery) is a promising, meticulous and soft tissue-sparing system for bone cutting, based on ultrasonic microvibrations. It was developed by Italian oral surgeon Tomaso Vercellotti in 1988 to overcome the limits of traditional instrumentation in oral bone surgery by modifying and improving conventional ultrasound technology. Not only is this technique clinically effective, but histological and histomorphometric evidence of wound healing and bone formation in experimental animal models has shown that tissue response is more favourable in piezosurgery than it is in conventional bone-cutting techniques such as diamond or carbide rotary instruments . Shock waves in the fluid environment assist in reducing the levels of bacteria, providing a disinfecting action . The number of indications for piezosurgery is increasing in oral and maxillofacial surgery and in other disciplines such as otorhinolaryngology, neurosurgery, ophthalmology, traumatology and orthopaedics.
Literature search
This review is based on an analysis of 343 original papers, case reports and short communications published in the English language from January 1988 to September 2010 in peer-reviewed journals. Keywords used included piezosurgery; piezoelectric surgery; piezoelectric bone surgery; bone surgery; piezosurgical; osteotomy; ultrasound surgery; oral surgery. A publication was included if the experimental or clinical study used piezosurgery in any manner during the treatment of patients. Special interest was placed on prospective and retrospective clinical studies and on meta-analyses. The search for papers was performed using Medline; Web of Science; OVID and Google Scholar. Any discussion related to the use of piezosurgery was taken into account if appropriate for this review.
Inclusion criteria included: published study in peer-reviewed journal; randomized, prospective or retrospective study; assessing the effectivity of piezosurgery by qualitative and/or quantitative methods; absence of any other significant disease in patients. Exclusion criteria included: study not performed on humans; not meeting any of the inclusion criteria.
Piezosurgery overview
Piezosurgery is based on the piezoelectric effect, first described by Jean and Marie Curie in 1880, which states that certain ceramics and crystals deform when an electric current is passed across them, resulting in oscillations of ultrasonic frequency. The vibrations obtained are amplified and transferred to a vibration tip which, when applied with slight pressure on bone tissue, results in a cavitation phenomenon – a mechanical cutting effect that occurs exclusively on mineralised tissue . A piezosurgery unit is approximately three times as powerful as a conventional ultrasonic dental unit, allowing it to cut highly mineralised cortical bone.
The most important part of the device is the piezoelectric handpiece, connected to the main unit, which has holders for the handpiece and irrigation fluids. A foot switch activates the interchangeable handpiece tips. The frequency of vibrations and power of cutting, as well as the amount of irrigation, can be adjusted. The frequency is usually set between 25 and 30 kHz. This frequency causes microvibrations of 60–210 μm amplitude, providing the handpiece with power exceeding 5 W.
Several tool tips (inserts) of different sizes, shapes and material are available, and new ones are being developed. They can be coated with titanium or diamond of different grades. Examples include the scalpel, cone compressor, bone harvester and sharp-tipped saw.
Several forms of application (modes) are available. Low mode is useful for apical root canal treatment in dentistry. High mode is useful for cleaning and smoothing bone borders. Boosted mode is most often used in oral and maxillofacial surgery in osteoplasty and osteotomies. In the boosted mode, digital modulation of the oscillation pattern produces alternating high-frequency vibrations, with pauses at frequencies up to 30 Hz; this prevents the insert from impacting bone and thus avoids overheating, while maintaining optimal cutting capacity.
Piezosurgery requires sufficient irrigation so the flow rate of the cooling solution must be set to avoid overheating the bone. Light handpiece pressure and an integrated saline coolant spray keep the temperature low and the visibility of the surgical site high . To increase cooling effectiveness, the solution should be refrigerated to 4 °C. After prolonged cutting, the handpiece warms up so a short pause may be necessary to allow it to cool . The cooling system is generally less efficient when cutting deep layers of bone because increased pressure on the bone decreases cutting speed, so interrupted cutting is advisable. In the case of a deep osteotomy, the combination of piezosurgery and subsequent use of a chisel is useful.
In use, the handpiece is guided firmly over the bone, but without excessive force. In contrast to conventional microsaws or drills, to which the surgeon must apply a certain degree of pressure, the piezosurgery device needs only minimal pressure, permitting a precise cut. Pressure acts in a clearly counterproductive manner, limiting movement of the instrument tip and generating a significant amount of heat. The sound of the cutting can be used as acoustic feedback for the force to be used. At maximum pressure, when the tip stops moving and only heat is generated, a tone warns that bone damage is imminent so cutting should be stopped immediately. The translation speed, the speed of the tip in contact with bone, has an effect on the cutting power. High-level surgical control is required for piezosurgery, because the strength required to cut bone effectively is far less than that required for a drill or oscillating saw. This different bone cutting principle requires a change of habits from those used in conventional osteotomy and osteoplasty techniques.
Piezosurgery overview
Piezosurgery is based on the piezoelectric effect, first described by Jean and Marie Curie in 1880, which states that certain ceramics and crystals deform when an electric current is passed across them, resulting in oscillations of ultrasonic frequency. The vibrations obtained are amplified and transferred to a vibration tip which, when applied with slight pressure on bone tissue, results in a cavitation phenomenon – a mechanical cutting effect that occurs exclusively on mineralised tissue . A piezosurgery unit is approximately three times as powerful as a conventional ultrasonic dental unit, allowing it to cut highly mineralised cortical bone.
The most important part of the device is the piezoelectric handpiece, connected to the main unit, which has holders for the handpiece and irrigation fluids. A foot switch activates the interchangeable handpiece tips. The frequency of vibrations and power of cutting, as well as the amount of irrigation, can be adjusted. The frequency is usually set between 25 and 30 kHz. This frequency causes microvibrations of 60–210 μm amplitude, providing the handpiece with power exceeding 5 W.
Several tool tips (inserts) of different sizes, shapes and material are available, and new ones are being developed. They can be coated with titanium or diamond of different grades. Examples include the scalpel, cone compressor, bone harvester and sharp-tipped saw.
Several forms of application (modes) are available. Low mode is useful for apical root canal treatment in dentistry. High mode is useful for cleaning and smoothing bone borders. Boosted mode is most often used in oral and maxillofacial surgery in osteoplasty and osteotomies. In the boosted mode, digital modulation of the oscillation pattern produces alternating high-frequency vibrations, with pauses at frequencies up to 30 Hz; this prevents the insert from impacting bone and thus avoids overheating, while maintaining optimal cutting capacity.
Piezosurgery requires sufficient irrigation so the flow rate of the cooling solution must be set to avoid overheating the bone. Light handpiece pressure and an integrated saline coolant spray keep the temperature low and the visibility of the surgical site high . To increase cooling effectiveness, the solution should be refrigerated to 4 °C. After prolonged cutting, the handpiece warms up so a short pause may be necessary to allow it to cool . The cooling system is generally less efficient when cutting deep layers of bone because increased pressure on the bone decreases cutting speed, so interrupted cutting is advisable. In the case of a deep osteotomy, the combination of piezosurgery and subsequent use of a chisel is useful.
In use, the handpiece is guided firmly over the bone, but without excessive force. In contrast to conventional microsaws or drills, to which the surgeon must apply a certain degree of pressure, the piezosurgery device needs only minimal pressure, permitting a precise cut. Pressure acts in a clearly counterproductive manner, limiting movement of the instrument tip and generating a significant amount of heat. The sound of the cutting can be used as acoustic feedback for the force to be used. At maximum pressure, when the tip stops moving and only heat is generated, a tone warns that bone damage is imminent so cutting should be stopped immediately. The translation speed, the speed of the tip in contact with bone, has an effect on the cutting power. High-level surgical control is required for piezosurgery, because the strength required to cut bone effectively is far less than that required for a drill or oscillating saw. This different bone cutting principle requires a change of habits from those used in conventional osteotomy and osteoplasty techniques.
Advantages of piezosurgery
Piezosurgery was invented for safely performing sinus lift operations, but new indications are still appearing. The device is generally useful in cases in which bone needs to be cut close to important soft tissues such as nerves, vessels, Schneiderian membrane and dura mater, where mechanical or thermal injury must be avoided. S chaeren et al. have shown that direct exposure of a nerve to piezosurgery, even in worst-case scenarios, does not dissect the nerve but only induces some structural or functional damage. In most cases the nerve is able to regenerate with the perineural sheath intact, in contrast to using a conventional drill or oscillating saw . They also observed that the extent of damage was significantly higher with the application of increased force on the nerve by the device, but not by activation of ultrasonic vibration . This feature makes piezosurgery a promising tool for performing osteotomy close to the nerve.
In contrast to a conventional microsaw, where blood is moved in and out of the cutting area and visibility is decreased, the operative field in piezosurgery remains almost free of blood during the cutting procedure. The reason lies in the cavitation effect created by the cooling fluid distribution and by the type of vibration the instrument generates, in which the blood is essentially washed away, leading to ideal visibility in the operative field .
Bleeding from the surrounding soft tissues, as well as the total amount of blood loss, is significantly reduced. In osteotomies and bone biopsies, it is possible to place the cut at exactly the desired location on the bony surface. The main source of soft tissue damage during conventional bone drilling or sawing is the greater necessity of rotational and torsional power, inadvertently applied close to soft tissue, needed to remove the dense, mineralised tissue. Microscopic examination of bone fragments obtained during piezosurgery showed no signs of the coagulative necrosis and viable cells typically found when using low-power ultrasonic devices and classical drills. Tooth vitality is also protected. Piezosurgery virtually eliminates the need for the chisel .
Piezosurgery produces less vibration and noise because it uses microvibrations, in contrast to the macrovibrations and extreme noise that occur with a conventional surgical saw or bur. Microvibration and reduced noise minimise a patient’s psychological stress and fear during osteotomy under local anaesthesia .
Piezosurgery enables meticulous preparation of small bone pieces, such as during periodontal surgical procedures, facilitating the removal of small quantities of bone adjacent to exposed root surfaces in order to avoid damaging the tooth surface. It permits inflammatory tissue removal, root surface debridement and root planing . Piezosurgery is targeted mainly at bone removal and soft tissue protection, but the modified setting can be used for excision of soft tissue lesions , a feature useful in children .
Bone graft harvesting and biopsy
Bone graft harvesting includes several procedures for obtaining chips or blocks of bone tissue. Bone chips are used as space makers and guides for bone regeneration through osteoconduction, and for support of growth factors at the recipient site to speed up bone healing. Bone blocks should be used when large defects need to be filled or when the immobilisation of particulate grafting material is not possible. Piezosurgery is important in bone graft harvesting, which also includes bone separation by burs; bone scrapers; back-action, gouge-shaped bone chisels; trephines; ronguers and en bloc harvesting. B erengo et al. have shown that piezosurgery spares a significant amount of surviving osteoblasts and osteocytes. Better results have been obtained only by ronguers and en bloc bone harvesting . C hiriac et al. did not find any significant differences between piezosurgery and conventional rotating drills in collecting cortical bone chips in terms of their detrimental effects on viability and differentiation of cells growing out of autogenous bone chips derived from intraoral cortical sites .
In the study by H appe , bone grafts were harvested from the mandibular ramus by piezosurgery in 40 patients, resulting in 93% uneventfully healed donor sites and 96% uneventfully healed graft sites . All transplanted bone grafts integrated without major complications and provided sufficient bone for implant placement, the complication rate at the donor sites was low, resorption of most grafts was minimal and the graft size obtained was comparable with that seen using conventional techniques. This study highlighted the ability of piezosurgery to provide precise, clean and smooth cutting with excellent visibility . The preparation of bone blocks is generally easier and safer with piezosurgery, but is more time consuming .
Piezosurgery can also be used for obtaining a bioptic sample. The main advantage of the specimen thus obtained is that the structures of the surgical bone margins are less impaired by this technique compared with conventional burs .
Sinus lift
Sinus augmentation surgery is the widely accepted preprosthetic gold standard for creating sufficient bone volume for the placement of endosseous implants in an atrophic posterior maxilla ( Fig. 1 ). The most frequent intraoperative complication of sinus elevation surgery is perforation of the sinus mucosa (Schneiderian membrane) reported to occur in 14–56% of cases . Repairing perforations can be simple, difficult or impossible. For this purpose several techniques have been proposed, including application of a bioabsorbable collagen-barrier membrane. In the authors’ experience, this procedure significantly increases costs and operative time, and increases the risk of patient morbidity in terms of postoperative oedema, sinus congestion or sinus graft infection rate (Pavlíková and Foltán, unpublished observation). Occasionally, there might be bleeding from the anastomosis of the lower branch of the posterior superior alveolar artery or the infraorbital artery, most often from vertical osteotomy cuts. This artery is present in 100% of cases . If the perforation cannot be repaired, subsequent procedures using particulate graft materials will probably have to be abandoned. In oral and maxillofacial surgery, piezosurgery was first used in the sinus lift operation which significantly changed the perspectives of lateral (open) sinus lift operations. Using piezosurgery is usually more time-consuming than using other techniques, but the frequency and number of Schneiderian membrane perforations or lacerations is generally lower. For example, W allace et al. experienced only 7 of 100 cases of Schneiderian membrane perforation in their study when using piezosurgery . Perforations occurred owing to the presence of a septum in 4 cases, and from an extremely thin membrane in 3 cases. None of the perforations occurred because of piezosurgery inserts, all were caused by subsequent elevation of the Schneiderian membrane with hand instruments. They concluded that the perforations were eliminated during antrostomy preparation and the initial membrane release phases of the surgery when piezosurgery was employed . V ercellotti et al. observed perforation of the Schneiderian membrane in only 5% of patients . The authors think that inadvertent perforations of the membrane are unlikely when piezosurgical techniques are appropriately applied.
