Cutting bone with drills, burs, lasers and piezotomes: A comprehensive systematic review and recommendations for the clinician

Background: New tools for bone-cutting were introduced to oral and maxillofacial surgery in the last decade, such as lasers and piezotomes. Purpose: to evaluate most recent evidence, when surgical procedures performed with drills or burs are compared with laserand/or piezotome-surgical procedures in experimental and clinical studies and to assess possible advantages of their use in daily practice. Methods: a systematic search of various medical databases with specifi c keywords was performed, excluding studies published before 2006 for their possible invalidity by technological progress. Systematic reviews were assigned to Group 1, experimental studies ex vivo to Group 2, in vivo to Group 3 and clinical studies to Group 4. All studies in each of the groups 2 – 4 were appraised regarding their evidence, starting with a value of 0 for no evidence of advantages of lasers and/or piezotomes compared to rotary instruments, 1 for moderate evidence with verifi ed clinical impact and 2 for strong evidence and signifi cant clinical impact and statistically processed for their Evidence Value (EV) in each group and their Overall mean Evidence Value (OmEV). Results: 129 studies were fi nally included for evaluation. Two systematic reviews concluded lack of evidence for lasers to be advantageous over burs/drills. Nine reviews for piezotomes reveal strong evidence piezotome-surgery to signifi cantly reduce morbidity and to enhance soft-tissue preservation. Comparative experimental and clinical studies of burs/drills vs lasers revealed a low EV in Group 2 (EV:0,8), Group 3 (EV:0,5) and Group 4 (EV:0,5) with an OmEV of 0,6. Comparative studies burs/drills vs piezotomes resulted in a signifi cant EV in all groups (Group 2: 1,4, Group 3: 1,3, Group 4: 1,59) with an OmEV of 1,4. Conclusions: the results suggest too little evidence to establish lasers as an alternative to rotary instruments. Piezotomes seem to defi ne a possible new gold-standard in bone cutting due to their improved bone-healing, almost bone-lossless and precise osteotomy design, precise depth-control, softtissue protection as well as reduced intrasurgical and post-surgical morbidity. Review Article Cutting bone with drills, burs, lasers and piezotomes: A comprehensive systematic review and recommendations for the clinician Angelo Troedhan1*, Ziad Tarek Mahmoud2, Marcel Wainwright3 and Mohamed Moataz Khamis4 1Institute for Oral & Maxillofacial Surgery and Dentistry, General Hospital “Krankenhaus Hietzing” of the City of Vienna, Vienna 2Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Alexandria University, Egypt 3School of Dentistry, University of Seville, Spain 4Department of Prosthodontics, Faculty of Dentistry, Alexandria University, Egypt Dates: Received: 29 July, 2017; Accepted: 12 August, 2017; Published: 14 August, 2017 *Corresponding author: Angelo Troedhan, Krankenhaus Hietzing, Institute for Oral & Maxillofacial Surgery and Dentistry, Wolkersbergenstraße 1, 1130 Vienna, Austria, Tel: 0043 664 5009246; Fax: 0043 1 544912821; Email:


Introduction
Performing bone-cuts and bone-trepanations is the very basis of the Oral and Maxillofacial surgeon´s daily task and until recently were carried out exclusively with rotary instruments like drills and burs or slow-oscillating saws. Only in the last decade, new technologies evolved as commercially available and certifi ed devices for bone cutting such as lasers and piezotomes. Drills, burs, lasers and piezotomes act fundamentally different in their physical mechanism of cutting bone.

Drills, burs, slow-oscillating saws
Driven by micro-motors or air-pressure-turbines, drills, burs and slow oscillating saws cause a mere mechanical ablation by hacking, crushing and shearing bone with serrated or diamond coated rotational hard-metal bodies of spherical, conical, cylindrical or saw-like shapes. The speed of action depends on the size and coarseness of the serrated surface (from macro-serration to diamond coating), speed of the handpiece and pressure exerted onto the bone, thus causing frictional heat, which might cause bone-necrosis [1]. Heat dissipation by water-beam cooling decreases signifi cantly in surgical practice if the water-beam is not precisely adjusted to target exactly the cutting center of the bur, is blocked by softtissues or other surgical instruments, or is refl ected by the adjacent bone-surfaces of the osteotomy line with increasing depth of the osteotomy or drill-hole [2].
Drills, burs or low-frequency oscillating instruments are diffi cult to handle when used on cortical and trabecular bone due to its procedural high physical torque-moment especially in the initial phase of the osteotomy-design on cortical bone. The more coarse the serration of the bur, the more diffi cult it is to design a perfect osteotomy-line or an anatomical precise drill hole for implant-placement especially for novices.
The major and unavoidable medical drawback of drills, burs and slow-oscillating saws is the enormous procedural bone loss due to the minimum necessary diameter of the instrument of at least 1,5 -2 mm and the imprecision of the cut due to the high torque-moment, which has to be tamed by the hand of the surgeon as the author´s demonstration in vivo shows ( Figure 1). Additional, there is a high risk of soft tissue injury to important anatomical structures such as the inferior alveolar nerve (IAN) [3] or maxillary sinus-membrane and deposition of metal shavings and bacterial contamination [4].

Lasers
Compared to drills, burs and slow-oscillating saws, lasers act completely different on bone when performing bone cuts. Commercial available laser-devices for bone-cutting in dentistry and oral and maxillofacial surgery -commonly called "Erbium-laser", "Neodymium-laser" and "Carbon-Dioxidelaser" -emit a coherent light-beam of a precisely defi ned wavelength in the invisible infrared spectrum of light. The invisible infrared heat beam is transmitted either by optical lenses, hollow tubes or quartz-fi bers to the focus-spot on the bone, which typically has a diameter of 0,4 -1,0 mm depending on the focus-mechanism, the precision of the quartz-fi ber tip and distance of the laser-handpiece to the bone by divergence of the coherent infrared light beam [5].
Once the heat-beam hits the intra-and extracellular water-molecules in dentin (~20% H 2 O), cortical or trabecular bone (~20-30% H 2 O) and molecular composition of carbonated Hydroxyapatite (OH-, CO 3 , PO 4 , intercrystal free H 2 O), the heat is instantly almost fully absorbed ( Figure 2) and leads to micro-explosions of vaporized superheated water vapor ("plasma plume"). The micro-explosions -heat energy transformed into kinetic acoustic energy -are well audible by the patient and surgeon by achieving up to 120 dB in bone [5] and by this enormous kinetic sound-pressure shock wavecalled "photoacoustic effect" -ablates the bone by shattering the Hydroxyapatite crystals and disrupting collagen fi bers. Physically it is a heat-induced cavitation-effect creating cavitation-bubbles ( Figure 3). Once the water in bone-tissue is consumed, the heat energy cannot be transformed into kinetic sound-energy anymore and thus leads to carbonization Figure 1: Comparison of procedural bone-loss when a bone block of 1 cm 2 is cut out by micro-bur, piezotome and Er:YAG-laser. Bone-cut on the most upper right side was performed with an experimental Excimer-UV-laser and is not included in the rating.

Figure 2:
Laser energy absorption gradient in water for common, commercially available laser-systems for bone cutting (Er,Cr:YSGG, Er:YAG, CO2). Depending on the infrared wavelength ("invisible heat radiation"), lasers act different on calcifi ed tissues. Erbium-lasers have a high water-absorption-coeffi cient resulting in very little depth-penetration into tissues per single-pulse but suffi cient energy-density on the focal spot to cause the photoacoustic-and cavitation-effect depicted in Figure 3.

Figure 3:
Depiction of the physical effects -photoacoustic effect and cavitationcaused by a single laser-pulse on bone. If the laser-pulse is well focused the heat energy at the target (bone-surface) is completely absorbed immediately and converted into a superheated plasma plume causing the generation of acoustic shockwaves sent into to bone. The rapid expansion of the plasma-plume leads to the creation of a cavitation-bubble, which fi nally collapses and ejects bone-particles. This is also the cause for the characteristic knocking sound when lasers are used for bone cutting while cutting lasers for soft-tissues have a more humming sound. In case the laser pulse is not precisely focused (dotted red lines) bone is only heated and carbonized. and necrosis of the adjacent bone-layers [6], in case of dentin and enamel to vast cracks and unwanted separation of tissuelayers as the author´s investigations on freshly extracted teeth show ( Figure 4). To reduce the risk of heat-induced bonenecrosis by lasers (especially in deeper osteotomies) and to deliver water to the osteotomy-site, a water-spray-coolant is mandatory although this might lead to unwanted patient´s body-liquid-splatter in the surgery room [5].
The effi cacy of bone cuts with commonly used Erbiumor CO2-lasers depend on the precision and cleanliness of the focal-system (mirrors or quartz-fi bers), the focus-spotdimension and energy-density in the focus-spot and the pulse quality of the intermittent blasting laser-beam (to allow dispersion of the heated "laser-plume" carrying the debris and cooling of the osteotomy-site between the intermittent laser-pulses [6]). Furthermore, focal laser energy cannot and must not be increased above the threshold of the laser-specifi c bone-ablation-property since an increase would only lead to detrimental bone-necrosis and not to faster bone cutting [5,6].
Although osteotomies with lasers allow a precise osteotomy-design (since only the laser-beam should touch the bone) [7] with substantial less procedural bone loss compared to drills and burs ( Figure 1) and disinfection of the surgical site itself [6] (but dispersion of possible infective agents in the oral cavity and OR-room [5]), a major drawback is still the complete lack of osteotomy-depth-control, haptic feedback and soft-tissue preservation [8].

Piezotomes
Although on the macroscopic level piezoelectric surgical tools resemble drills, burs and slow-oscillating saws by their shape, their physical mechanism of action is merely mechanical only to the smallest part. Piezoelectric crystal rings -activated by electric current -initiate a precise unidirectional ultrasonic oscillation -especially in medical literature wrongly described as "vibrations" -at a rate of 28.000 -36.000 modulated harmonic oscillations per second and a distance between 60 and 200 μm ( Figure 5). Any rigid physical body oscillating at ultrasonic speed in liquids creates the physical phenomenon of the pressure-induced cavitation effect, which is very similar to the photoacoustic effect caused by infrared laser beams in liquids, but at signifi cant lower temperatures [9]. Thus, the physical mechanism of cutting bone with Piezotomes is based on precise disruption of mineralized bone-components by harmonic acoustic shockwaves and cavitation -similar to ultrasonic kidney stone crushers -but completely preserves soft tissues from damage due to the ultrasonic frequency of the devices [10,11]. The pressure-induced cavitation effect -as demonstrated by the author´s investigations of various piezotome-surgical tips ( Figure 6) -enhances the clean separation of mineralized tissue formations, enables a signifi cant improved bone healing [10,11], and -at lower power-settings -an improved and non-destructive dissection of soft-tissues [12] with improved postsurgical hemodynamic microcirculation [13].
Possible heat generation caused by the ultrasonic oscillating instrument is suffi ciently counteracted by the applied coolingliquid, which adheres to the working-tip at the surgical site due to acoustic resonance-adhesion as demonstrated by the author´s investigations ( Figure 7). Only improper handling of or faulty constructed piezotomes might lead to increased intrabony heat-peaks (e.g. too high manual pressure by the surgeon, reduction of cooling saline-fl ow beyond required minimum, faulty constructed piezotomes causing irregular vibrations instead of harmonic, modulated oscillations of the working tip).
Piezotomes provide least procedural bone-loss ( Figure 1) due to working tips of a cutting width of only 0,1 -0,2 mm and allow a precise osteotomy-design comparable to lasers but with precise depth-control and least risk to damage softtissues due to the oscillation frequency-range.

Figure 4:
Histology of a freshly extracted tooth at the enamel-dentin-margin treated with 3 pulses of an Er:YAG-laser (Azan-staining) without copious irrigation: coagulation and carbonization-zones are visible as well as cracks between dentin and enamel and within dentin, caused by the plasma-plume and the intital shockwaves.
All references matching the keywords, but were being published before the year 2006, were excluded to avoid inclusion of studies with experimental and technological outdated devices or already analyzed in published systematic reviews and meta-analysis.
The abstracts of the remaining retrieved reports then were thoroughly scanned and a set of criteria applied for their inclusion in the preliminary reference list.

Inclusion criteria
The abstracts were assigned to four thematically different

Exclusion criteria
All abstracts reporting case studies, general reviews, overviews, technical notes, expert opinions, non-comparative experimental and clinical studies or published in non-peerreview journals were excluded.

Critical appraisal
The included systematic reviews and studies were retrieved as full text, critically evaluated separately by each author regarding procedural fl aws, inadequate study-or review-design or too many potential biases. In case a unanimous assessment by the authors could not be achieved, an independent referee evaluated the report or systematic review for in-or exclusion.

Statistical evaluation
All included reports in each of the groups 2 -4 were appraised regarding their evidence, starting with a value of 0 for no evidence of advantages of lasers and/or Piezotomes

Primary outcome evaluation
To assess weak or strong evidence if the use of lasers and/ or piezotomes has advantages regarding precision of bone cuts, improves bone healing and reduces post-surgical patientmorbidity when compared with traditional rotary instruments.

Secondary outcome evaluation
To assess applicability, indications and restrictions of lasers and/or piezotomes in the daily work of oral and maxillofacial surgeons when compared with traditional rotary instruments to give evidence-based recommendations to the clinician.

Results
954 potential references were found in the databases of which 461 were published since 2006. 279 abstracts then had to be excluded in accordance with the exclusion-criteria. From the fi nal 182 full-text publications 53 had to be excluded due to procedural fl aws (e.g. imprecise study design with too many variables and/or wrong settings of the used devices), inadequate study design (e.g. primary outcome evaluation not focused on instrumentation-comparison bur vs laser and/or piezotome) and possible bias (e.g. product-related comparative studies with confl ict of interest-background).
A total of 129 publications, meeting the inclusion-criteria and were agreed by all authors and the referee, were fi nally assigned to group 1-4 and group 2-4 for evidence-staging ( Figure 8).

Group 1 (systematic reviews and meta-analyses)
Only two very recent systematic reviews were found comparing rotary instruments with lasers in general [14,15], pointing out that "additional research is necessary to evaluate different laser types with appropriate laser setting variables to increase ablation rates, with control of depth, change in bone type and damage to adjacent soft tissue " [14] and "because of the lack of clinical studies, it is not possible to make a conclusive result whether there is superiority of laser osteotomy in clinical practice" [15].
Nine very recent systematic reviews comparing rotary instruments with piezotome-instrumentation focused on comparative clinical studies regarding specifi c surgical procedures such as alveolar crest-split technique [16], lateral maxillary sinus-fl oor elevation [17,18], acceleration of orthodontic tooth movement [19] and surgical removal of impacted third molars [20-24] and conclude piezotomeinstrumentation to signifi cantly reduce post-surgical morbidity (pain, swelling, trismus) but to prolong surgerytime and the need for further randomized clinical studies with a precise study-design.
No systematic reviews were found directly comparing rotary instruments with lasers and piezotomes or piezotomes with lasers.

Group 2 (experimental studies ex vivo)
Burs/drills vs lasers: Comparative ex vivo studies burs/ drills vs laser [25-29] suffer from the heterogeneity of used laser-technology (Er:YAG, Er,Cr:YSGG -wavelength) and laser-settings (focus-spot-size/energy-density at focus-spot/ laser-pulse-duration and -frequency). Ex vivo-studies are not comparable among each other, point out partly increased thermal bone necrosis depending on the power-settings, but state sharper and cleaner osteotomy lines with less debris when compared with rotary instruments. The evidence-value (EV) 0,8 (Table 1) indicates minor evidence of lasers to substantially improve bone-cutting procedures in oral & maxillofacial surgery.
Burs/drills vs piezotomes: EX VIVO comparisons between rotary instruments and piezotome-osteotomies [30-47] provide substantial evidence with possible high impact on clinical practice with an evidence value (EV) of 1,4 ( Table 1). Although with piezotome-instrumentation there is still a risk of thermal bone-damage too (when used improperly), all comparative studies proved piezotome-osteotomies to lead to more precise, debris-free and less destructive bone-cuts as well as superior soft-tissue-preservation especially in the hands of novices in oral surgery.

Burs/drills vs lasers vs piezotomes:
Only two studies were found investigating differences of microscopic osteotomymorphology and temperature rise when burs, lasers and piezotomes [48,49] are used to cut bone. One [49] revealed a minor procedural fl aw in the piezotome-settings regarding fl ow-rate of saline-irrigation, which lead to a higher intrabony temperature-rise. Both studies present moderate evidence (EL=1, Table 1) and suggest advantages of Er:YAG-lasers over piezotome-instrumentation and burs, however pointing out comparable precise bone cuts with both lasers and piezotomes

Piezotomes vs Piezotomes
Five comparative studies investigate the cutting performance, osteotomy quality and intrabony temperaturerise of different devices from different piezotomemanufacturers [50-54], but were not rated for their evidencelevel since the small number of published studies, different settings and study-designs do not allow a valid meta-analysis.

Burs/drills vs lasers vs piezotomes:
Only two published studies provide a direct comparison of rotary instruments against Er:YAG-laser and piezotomes of which one [87] describes a signifi cant delay in bone-healing when laser was used and a faster bone healing with piezotome-instrumentation, whereas a comparative study comparing implant drill-sites [88] fi nds no signifi cant differences between the osteotomy methods. Due to the small number of studies the Evidence Value (EV) is insignifi cant (0,3; Table 1)

Lasers vs piezotomes
Four published studies [89][90][91][92] suggest Er:YAG-lasers in non-contact application with a computerized scanninghandpiece to provide faster bone-healing in vivo than piezotome-instrumentation, but was equal when Er:YAG-laser was used in contact-mode. The evidence value of these studies is low with EV: 0,5 (Table 1).

Group 4 (Comparative Clinical Studies)
Burs/drills vs Laser: Only two comparative clinical studies were published until now [93,94], both comparing Er:YAG lasers with rotary instruments in surgical removal of impacted third molars, with only little evidence (EV: 0,5; Table 1 No clinical studies were found comparing burs/drills with lasers and piezotomes as well as lasers with piezotomes.
Contrary, the use of piezotomes -also backed by the high number of experimental and clinical studies -seem to have a signifi cant clinical impact on improved bone-healing, superior soft-tissue-preservation and reduced postsurgical morbidity with an OmEV of 1,4 ( Table 1) when compared with rotary instruments.
( Table 2) gives an overview of evidence-based comparative properties of burs/drills, lasers and piezotomes with burs/drills as "baseline-values" as a descriptive result of this systematic review.

Discussion
As in abdominal surgery traditional surgical procedures with large transabdominal skin-incisions are more and more replaced by minimal invasive endoscopic procedures with reduced intrasurgical complications and post-surgical morbidity, advanced laser-and ultrasonic-technology might replace traditional surgical techniques performed with burs, drills or slow oscillating instruments likewise in oral and maxillofacial surgery and implantology. The plasma-plume, the photoacoustic and cavitation-effect might also splinter the polished surface of the fi ber when it is made of quartz glasses.
Most of these technical problems in the application of laser-beams on bone were not taken into account in most experimental and clinical studies, which might explain the contradictory results even with lasers of a single type (e.g. Er:YAG-lasers). The majority of studies report substantial heatinduced bone-necrosis compared to rotary instruments. The desired heat induced cavitation-effect, with its characteristic loud and intermittent knocking sound and least undesired thermal side effects, is generated only with a precise focus spot (Figure 3, Figure 10B).
For the clinician, the daily routine of bone-cutting close to delicate soft-tissue-structures such as sinus-membrane, trigeminal nerves and major intrabony blood-vessels, is the major challenge. The complete lack of any type of depthcontrol of the laser-beam and its ability to cut through softtissues faster than through bone might make a laser -beside the high acquisition-cost -the least instrument of choice for osteotomies in the daily routine, especially for novices.
The construction-principles of piezotomes are subject to tight technical parameters: the oscillation rate is restricted to 28.000 -36.000 modulated harmonic oscillations per second (28 -36 KHz) and the distance of physical movement between 60 and 200 μm, to achieve the least risk of soft-tissue damage by frequency and working-tip-design. The separation or ablation of bone is also based on the cavitation-effect, but contrary to lasers is not heat-induced but pressure induced at much lower temperatures (Fig. 6). Heat induced bone-necrosis only occurs when no or too little continuous irrigation is supplied to the working tip, too high manual pressure is exerted onto the handpiece by the surgeon or a faulty constructed piezoelectric device for bone cutting generates irregular and uncoordinated vibrations instead of modulated harmonic oscillations.
Beside signifi cant lower acquisition cost (starting with 8.000 US$) compared to lasers, the surgeons investment in time to get acquainted with piezotome-surgical protocols seems to be a matter of a few training hours as studies report.
Novices in oral and maxillofacial surgery achieve better results with piezotomes than with rotary instruments when it comes to delicate procedures such as sinuslifting and IAN-lateralization as this systematic review revealed.
Microscopically the surfaces of bone cuts with piezotomes are as sharp and clean as reported for lasers, but with signifi cant less or no procedural iatrogenic bone-loss due to scalpel-thin working-tips attached to the handpiece and without signs of heat-induced bone-necrosis. Like lasers, piezotomes allow an individual precise straight or curved design of any osteotomy, tuned to the needs of individual surgical procedures. Furthermore, the use of piezotomes for bone cutting seems to improve bone healing although the precise mechanism is not clear until now.
The ability to perform lossless bone cuts with superior soft tissue preservation lead to new bone-preserving surgical protocols for all kinds and subspecialties of oral implantology and oral and maxillofacial surgery, as demonstrated by the author´s case-examples (Figures 11-13).
Both technologies for bone cutting -lasers and piezotomes -are signifi cantly technology-sensitive: since the precision of the desired physical effects cannot be observed by the surgeon (lasers: precise focus-spot without divergence, precise and stable energy-density on the focus-spot, laser-pulsecharacteristic/Q-switch, mechanical resistive and optical clean optical fi bers; piezotomes: harmonic modulated oscillations, verifi ed cavitation-effect at the acting part of each sold tip) enormous care has to be taken when considering a purchase without proof of these effects by the manufacturer.
Since this systematic review includes the most current and multidisciplinary literature and was not restricted to oral and maxillofacial surgery, experimental and clinical studies recommend piezotomes to be introduced as superior bone cutting tool also in ENT-, cosmetic -and neurosurgery for their proven property to reduce intrasurgical blood-loss, superior soft-tissue preservation and signifi cantly reduced post-surgical morbidity. Figure 9: Depiction of appliances for commercial available Er,Cr:YSGG-lasers in surgical periimplantitis-therapy. A-C. resective periimplantitis-surgery both for granulation-tissue and infected bone-regions. The surface of the implant is decontaminated with a highly defocused laser beam utilizing the heat-effects of defocused laser-beams. D. use of lasers for extracorporal shaping of bone-blockgrafts. Figure 10: A. wavenlengths of commercially available infrared heat-lasers for softand hard-tissue-cutting; B: Both power density on the focal spot and pulse duration and -frequency highly influence the performance of lasers on calcifi ed tissues. Defocused laser-beams with insuffi cient power density on the focal spot and too long pulse durations (or too high pulse-frequencies) lead to highly undesired effects on bone, such as coagulation, carbonization, thermal bone-necrosis and photochemical reactions which on the other hand might be useful in decontamination of implantsurfaces (Fig. 9 B). A well constructed laser provides mainly photoablative and photodisruptive effects on bone, provided the surgeon precisely keeps the distance for a perfect focus all the time during bone-cutting. Due to the lack of larger clinical split-mouth studies with precise and standardized surgical protocols for burs, lasers and piezotomes, evidence of improved bone healing in the clinical routine -as proven in experimental studies-is limited and cannot be answered by this review.
From the patient´s point of view, any surgical instrument and procedure, that might signifi cantly reduce intrasurgical iatrogenic or procedural complications as mentioned above, will always be preferred. For the patient, the use of piezotomes implies less risk of iatrogenic lesions of the inferior alveolar nerve, mental nerve, sinus-membrane and major blood vessels and provides a proven signifi cant reduction of post-surgical sequelae (trism, pain, edema), allowing the patient to proceed with regular activities sooner after surgeries.

Conclusions
Lasers in their variety of available wavelengths and application modes still lack evidence to establish them as a viable alternative to rotary instruments. Substantial research and development efforts as well as experimental and clinical studies are needed to defi ne standards regarding power-density, laser-pulse duration and frequency and consistent focusing on bone to achieve better results than with rotary instruments in the clinical routine. If technological developments can overcome the major disadvantages of lasers -the complete lack of depth-control of any osteotomy and unacceptable risk of iatrogenic soft-tissue lesions -seems doubtful.  : surgical removal of an impacted mandibular third molar and coronary cyst with piezotome. A. presurgical panoramic X-ray, B. bone-lossless removal of the buccal compact bone with the bone-scalpel-tip to reveal the cyst and the impacted third molar, C. loosening of the impacted third molar with a piezotome-periodontal ligament-cutter. D. forceless removal of the impacted third molar and removal of the cyst-tissue with a piezotome-tip designed for sinus-lifting. E. surgical site after removal of both impacted third molar and cyst in toto: adhering to the cyst-tissue before, the IAN and accompanying blood-vessels are fully intact after cyst removal including the enveloping connective tissue. Almost no bleeding occurs due to the superior soft-tissue preservation. F. anatomical correct full reconstruction of the mandibular angle after surgery. Due to the precise osteotomy-design and almost lossless bone cut no fi xation of the reposed buccal compact-bone -plate with osteosynthesis plates is necessary. G. healing-result after 6 months. The second molar was preserved vital. H. piezotome-tips used for this surgery (clockwise: bonescalpel, sinus-membrane-detachment tip used for cyst-detachment, angulated sawtip for baseline-osteotomy, periodontal ligament-cutter).