The International Journal of Periodontics & Restorative Dentistry © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
355
Piezoelectric Surgery in Autogenous Bone Block Grafts
Piotr Majewski, DDS, PhD1
This article describes alveolar ridge reconstruction in the esthetic zone using autogenous bone blocks harvested from the chin, taking into account the way the bone block is harvested, stabilized, and contoured in the recipient site. The 38 procedures were divided into two groups: group 1, using piezoelectric surgery, and group 2, using rotary instruments. The piezoelectric surgery technique made it possible to introduce surgical modifications. An observation of bone regeneration and follow-up clinical observations 5 to 7 years after the procedure revealed that the piezoelectric surgery technique provides better and more predictable clinical results for bone regeneration. (Int J Periodontics Restorative Dent 2014;34:355–363. doi: 10.11607/prd.1279)
Head of Implantological Department, Collegium Medicum, Jagiellonian University, Cracow, Poland.
1
Correspondece to: Dr Piotr Majewski, Klinika Implantologiczno-Stomatologiczna, ul. Milkowskiego 3/701 30-349 Cracow, Poland; email: [email protected]. ©2014 by Quintessence Publishing Co Inc.
The anterior part of the maxilla is regarded as one of the most difficult areas for implant treatment. This is due to the fact that ensuring a positive outcome for such treatment depends not only on the function of the integrated implants, but also on the esthetics of the implant-supported restorations. Bone tissue and soft tissue defects complicate treatment because of the need to carry out effective tissue regeneration procedures.1 Depending on the type of augmentation used, ie, vertical, horizontal, or mixed, numerous authors have offered a variety of treatment methods.2–7 Among these, two main groups can be distinguished. The first includes guided bone regeneration (GBR) using biomaterials, autogenous bone particles, and barrier membranes, while the second uses bone block grafts.8 A combination of both techniques has also been applied: biomaterials and membranes with autogenous bone blocks. Growth factors9,10 and bone morphogenetic proteins appear to enhance bone formation. However, there are insufficient long-term data reports to support
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356 these promising clinical and histologic observations. Many factors affect the predictable results of bone formation. Among them, Wang and Boyapati have noted primary wound closure, angiogenesis, space creation, and stability.11 This indicates that one of the most important factors for the procedure is the surgical technique applied. This article describes the use of piezoelectric surgery in the bone regeneration procedure using autogenous bone block grafts together with biomaterials and bioresorbable membranes. With the help of this device, certain operational modifications were made to the standard surgical procedure that, according to clinical observations and an assessment of the results of healing (incorporation) of the bone block in the recipient site, help improve healing results and reduce resorption that may affect the grafted bone tissue in the area around implants. The surgical method of grafting bone block with the use of drills is referred to here as the standard method, as opposed to the modified method, in which piezoelectric surgery is applied. With the modified method, it was possible to more accurately harvest the correct shape of the block for a ridge defect and properly stabilize it in the recipient site. In the second phase of the procedure, Piezoelectric surgery tips were used to delicately prepare and thin a layer of cortical block that could serve as an element supporting the shape of the reconstructed alveolar process.
Piezoelectric surgery tips do not generate vibrations in the bone when it is being prepared and all maneuvers are more precise and gentle compared with those made using drills. These were the basic factors distinguishing the two procedures (ie, standard and modified) from each other. Both surgical elements, the harvesting of the block together with its stabilization, and then the precise and delicate preparation using piezoelectric surgery, helped achieve better clinical results with regard to reconstructing the alveolar ridge.
Method and materials In accordance with this method, a total of 38 regenerative procedures were performed on patients aged from 24 to 47 years. One regeneration procedure was carried out on each patient and implant placement was performed after 6 months. The clinical observation period was 5 to 7 years after implant placement and prosthetic reconstruction (a single porcelain crown cemented onto an abutment). Patients qualifying for the procedure were in good general health and were nonsmokers. Patients with existing pathologic changes of an inflammatory character in the region of the mucous membrane, the periodontium, or hard tissue were excluded from the procedures until the pathology was eliminated. Patients were prepared for prosthetic restoration by setting the correct occlusal conditions with the aim of making a prosthetic crown on the implant placed in the
regeneration site. They exhibited defects (missing single teeth) in the anterior maxilla together with extensive damage to the labial plate of the alveolar ridge, such that it was not possible to achieve immediate implant stability. The extent of the defect was, in the author’s assessment, a contraindication for GBR because it would be difficult to create and maintain the shape of the alveolar ridge during the regeneration process. The procedures were divided into two groups. Group 1 involved grafts of autogenous bone block taken from the chin using piezoelectric surgery (a modified procedure), while group 2 was a standard procedure using bone drills (control method). There were 19 patients in each group. The procedure can be divided into the following stages: the preparation of the recipient site, bone block harvesting, stabilization of the bone block in the recipient site, contour modification of the bone block after its stabilization in situ, and primary wound closure. In both phases, the procedure was carried out according to the same sequence and in the same way. The difference consisted of instrument use: piezoelectric surgery in group 1 and bone drills in group 2 (Table 1). The purpose of this study was to assess how the use of piezoelectric surgery affects the course of the operation and what possible differences appear in the bone tissue regeneration process from the perspective of creating the proper conditions for correct implant placement.
The International Journal of Periodontics & Restorative Dentistry © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
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Table 1
Comparison of groups 1 and 2 Group 1 Group 2 (piezoelectric surgery) (rotary instruments)
Patients (n)
19
19
Fragmentation of bone block during harvesting
0
2
Bone block fixation with microscrews in recipient site
1
16
Destabilization of bone block while shaping in situ
0
9
Fragmentation of bone block while shaping in situ
0
2
Sequestration or destabilization of bone block during implant placement
0
6*
19
13
Soft tissue dehiscence at the labial aspect of the regenerated area after 5–7 y
No. of implants after bone regeneration
0
7
Bone remodeling below first thread of implant on periapical radiograph
0
0
*Need for GBR and delayed implant placement.
The modified autogenous bone block graft procedure uses piezoelectric surgery to harvest bone block from the chin in a shape that best corresponds with that of the bone defect. After the bone has been inserted and stabilized, piezoelectric surgery is used again to prepare the correct shape of the cortical bone in the recipient site. The aim of these modifications was to create a stable, biologic space in the defect enclosure for bone formation and to minimize the negative effects connected with autogenous bone block resorption. The procedure was performed with an antibiotic prophylaxis that patients took 1 hour prior to surgery (Augmentin 375 mg, GlaxoSmithKline). The patients were instructed to rinse the oral cavity with a 0.1% chlorhexidine solution three times a day for 3 days before and 2 weeks after the surgery. The operations were performed under local anesthesia (4 to 6 mL Ubistesin 4%
1:100,000, 3M ESPE). In the first stage, the size and shape of the defect were assessed after the mucoperiosteal flap was elevated and the tooth root was removed together with any inflammatory lesions of a chronic character. The second stage involved harvesting bone block from the area of the chin. The procedure followed the same sequence for both groups. The only difference was that rotary instruments were used in group 2. In group 1 (Figs 1a to 1g), a suitably sized bone block was excised with the help of a Piezosurgery device (Mectron) and by means of a saw-shaped insert (OT6, OT7). The upper incision line in the bone was 5 mm below the lower incisor root apices so as to minimize potential nerve and vessel injury. The shape and size of the defect was reproduced with the use of a template made from sterile aluminium foil. This made it possible to outline the contours and size of the bone block according to
the geometry of the recipient site. The bone cut was deep enough to obtain a corticocancellous block with an approximate thickness of 5 to 6 mm. In the second phase, the released block was compared with the geometry of the defect. Both the bone block itself and the wall defect were prepared with the help of a Piezosurgery device so as to ensure that both elements matched each other very closely in shape. The bone block was then wedged between the sidewalls of the bone defect. In three-wall defects, where inlay-type blocks were used, preparing the contours in this way ensured stable fixation for the bone block in the defect, without the need for additional miniscrews or miniplates. In group 2 (Figs 2a to 2c), block fixation miniscrews were used in 16 cases because the bone block harvesting and initial preparation were not as precise compared with the piezoelectric surgery technique (Fig 3).
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Fig 1a Bone defect at the site of missing maxillary left lateral incisor (patient no. 1).
Fig 1b Shaping of cortical part and adjustment of contours of bone block to the alveolar ridge after its stabilization in the recipient site (patient no. 1).
Fig 1c Bone block in recipient site before modification (patient no. 1).
Fig 1d (left) Bone block in recipient site after modification (patient no. 1).
Fig 1e (right) Autogenous bone block and Bio-Oss covered with Bio-Gide membrane (patient no. 1).
Fig 1f (below left) Status of bone block incorporation into the defect 6 months after postregenerative surgery. The cortical part of the grafted bone block is incorporated into the recipient site. No symptoms of necrosis or sequestration of bone block are visible (patient no. 1).
Fig 1g (right) Ridge morphology at the implant site in the regenerated area prior to implant placement. Stable bone block in situ after drilling (patient no. 1).
The next stage involved the final preparation and adjustment of the bone block to the contours of the alveolar ridge in the recipient site. Suitable Piezosurgery inserts (OP1, OP3) were used for this purpose (see Figs 1b and 2b). An effort was made to prepare the bone block in such a way that its external cortical surface represented a continuity of the walls of the alveolar ridge. During the course of this action, the thickness of the cortical layer of the
bone block was simultaneously reduced (Fig 1d). The purpose of this procedure was to reduce both necrosis in the cortical part of the block and graft resorption by facilitating revascularization of the thinner layer of the cortical bone. The author observed the rule that the thickness of the cortical part should not exceed 2 to 3 mm. In the clinical observation, this thickness was sufficient to maintain the mechanical properties of the grafted block and sustain its stability in
the regenerated defect. The gap that appeared between the block and the base of the defect was first filled with cancellous bone chips harvested from the inferior area of the donor site and then with particulated biomaterial (BioOss, Geistlich). The bone block was covered with an external layer of Bio-Oss as a slow-resorbing material. The regenerated area was secured with a Bio-Gide collagen membrane (Geistlich) to achieve better regeneration effects (see
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359 Fig 1e). The membrane was stabilized with titanium pins, horizontal or cross mattress sutures, and nonabsorbable monofilament (4/0 Seralene, SeragWeissner). In 16 of the 38 cases, the membranes were stabilized with titanium pins onto the buccal plate of the bone surrounding the defect. Crossmattress sutures were used to secure the membrane if it was to be pinned directly over the thin bone plate covering the roots of adjacent teeth and there was a risk of periodontium injury. After periosteal releasing incisions and flap extension were performed, the wound was closed tightly without pressure and primary wound closure was achieved using 5/0 Seralene (SeragWeissner). The bone defect created during bone block harvesting in the donor site was filled with the Bio-Oss particles and secured with a Bio-Gide membrane. Patients were given 800 mg ibuprofen every 8 hours to manage the pain. The sutures were removed after 7 days. Veneers or acrylic/composite crowns were used as provisional restorations. They were attached to adjacent teeth with the aid of glass-fiber splints. The healing process was uneventful. No wound dehiscence was observed. In two cases (group 2), local paresthesia in the chin area was observed. However, these complications resolved 4 to 6 weeks after surgery. No other complications associated with the second surgical site were noted. The implants (Biomet 3i) were placed 6 months after the regeneration procedures.
Fig 2a Stable fixation of bone block in the recipient site. No miniscrew used (patient no. 2).
Fig 2b Bone block in situ and shaping and thinning with piezoelectric surgery (patient no. 2).
Fig 2c State of soft tissue at the regenerated area 6 years after implant placement (patient no. 2).
Fig 2d (right) Periapical radiograph 6 years after implant placement in the regenerated area. Normal pattern of bone remodeling at implant shoulder (patient no. 2).
Results In a comparative analysis of the two groups, both the operation phase and the result of the bone tissue regeneration process were analyzed together with, over a 5 to 7 year observation period, the state of the soft tissue in the region of the crowns placed on the implants and the bone level in radiographs targeted in the region. In two cases (10%) in group 2, involving the use of bone drills,
the bone block fragmented during mobilization from the osseous bed in the donor site. In these situations, instead of a single piece, two smaller fragments of the block were used, which had to be stabilized using microscrews. In group 1, no defragmentation was observed. In group 2, the bone block was accurately adjusted to the contours of the defect in only three patients (15%) such that there was no need to stabilize it with the help of microscrews. The remaining patients
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Fig 3 The bone block harvested with the use of rotary instruments and stabilized with miniscrews.
Fig 4 Thick cortical part of bone block destabilization during implant placement procedure when rotary instruments were used in bone block graft procedure.
required the use of microscrews: in 14 patients, a bone monoblock was fixated, and in 2 patients, two sections of block that fragmented during the harvesting process were stabilized with microscrews. Only 1 patient (5%) in group 1 required additional stabilization for the block in the recipient site with the help of a microscrew. In group 1, no destabilization or defragmentation of the block occurred during the preparation and thinning of the core layer, whereas in group 2, the bone block lost stabilization during these maneuvers in 9 patients (47%), and it was necessary to refrain from bone-block shaping procedures and to stabilize the block once again with miniscrews. In two patients (10%) in this group, the block defragmented into 2 to 3 fragments. This necessitated the use of GBR procedures without the need for a bone block due to the impossibility of stabilizing small fragments of the block.
After 6 months, ie, during the implant placement procedure, both the shape of the regenerated region and the possibility of placing the implant in the proper position were assessed. The state of the soft tissue was deemed satisfactory both with regard to the shape and the amount, ie, the thickness and width, of the attached gingiva zone (5 mm or more). In group 1, after flap elevation, no border or difference was noticeable between the grafted bone block and the surrounding host bone tissue of the recipient site (see Fig 1f). In clinical terms, the bone tissue of the grafted bone block adequately conformed to the contours of the alveolar ridge, which ensured that the implant could be properly placed. The width of the alveolar ridge was 6 mm or more, allowing for 4-mmdiameter implants to be placed. No separation was observed in the visible layer of the compact, corti-
cal region of the graft above the surface of the alveolar ridge, as was noted in the bone block graft procedures performed in group 2. In six patients (32%) in group 2, the cortical part of the grafted bone blocks fragmented or destabilized during implant site preparation or during implant placement (Fig 4). These patients were excluded from implant placement, and further GBR procedures were performed at that time with delayed (another 6 months later) implant placement. In group 1, no breakup, fragmentation, or destabilization of the cortical part of the graft was observed during the implant placement procedure (see Fig 1g). The same provisional crowns or veneers were used during the osseointegration period. The implant was exposed after 4 months. No implant was lost in either group (there were 19 in group 1 and 13 in group 2). After the implant was exposed, new provisional acrylic crowns were
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361 screw-retained on the implant. The purpose of this was to ensure final modeling of the soft tissue and interdental papillae around the future definitive implant-supported ceramic crowns. After another 6 to 8 months, full ceramic crowns were cemented onto the implant abutments. Patients were seen for follow-up examinations once a year after the prosthetic phase. In the 5- to 7-year observation period, the implant-supported prosthetic crowns in group 1 performed their function properly. No pathologies or soft tissue dehiscences were observed in the region of the implants and prosthetic crowns. In group 2, soft tissue dehiscences of up to 2 to 3 mm at the buccal aspect of the grafted area were observed in seven patients (37%) in the 5- to 7-year observation period. Periapical radiographs, taken directly after crown cementation and then every year postsurgery, revealed a normal pattern of remodeling up to the first thread of the implant in both groups (see Fig 2d).
Discussion The surgical procedure described here involved the use of corticocancellous block grafts. Both components in the grafted block have different biologic and mechanical characteristics. An undoubted advantage of using autogenous tissue is the biologic compatibility of the graft material. In grafted corticocancellous blocks, the cortical part was used as an appropriate scaffold for
supporting soft tissue and maintaining the stability of the contours of the regenerated site. One of the most serious problems connected with the use of bone blocks is their resorption in the recipient site. The literature shows variations in the scale of the resorption, from 25% to 60%.12–15 On the one hand, the cortical layer of the bone graft undergoes resorption at a slower rate than the cancellous partof teh bone graft.16 On the other, the cancellous part acts as a carrier for osteogenic cells in the recipient site, which facilitates the revascularization process and graft healing.17 The healing and incorporation of autogenous bone block grafts, ie, the phenomenon known as creeping substitution, is described by Burchardt18 as a biologic reconstruction process involving the gradual replacement of necrotic tissue with new, vital bone tissue. A purely cortical bone block is less likely to undergo revascularization than a corticocancellous block.18 In connection with this fact, the blood supply to this part of the bone block is poorer. Consequently, necrosis of the grafted tissue may occur as the cortical bone blocks heal. The aim of the surgical method described in this paper was to create the best possible conditions for bone block incorporation. A single procedure was carried out using two different tools: a Piezosurgery device in group 1 and rotary instruments in group 2. The bone block must be properly stabilized in the site. Precise
block harvesting and shaping using the piezoelectric surgery device allowed for a perfect match and stabilization of the transplanted bone block in the defect enclosure. Because of bone loss during cutting, bone harvesting with rotary instruments is not as precise, which is why it is difficult to harvest bone blocks that correspond exactly to the geometry of the defect. In most patients in group 2 (16), the bone block had to be stabilized with microscrews. The most important characteristic of the cortical component is its mechanical property of maintaining contours. On the other hand, the thicker this layer is, the worse the conditions for revascularization. The use of Piezosurgery insert tips for precision shaping and thinning of the cortical layer after bone block stabilization in situ was intended specifically to create the best possible conditions for graft incorporation. The thin cortical layer (not exceeding 2 to 3 mm) of transplanted block still maintained the contours of the regenerated site after 6 months. The smooth, gentle contouring of the cortical part of the bone block was made possible by the use of a Piezosurgery device. In group 2, the same maneuver was difficult due to vibrations of the drills during the procedure and because stabilizing of the bone block with microscrews was insufficient to sustain mechanical shaping. In two patients, fragmentation of the bone block occurred during the shaping procedure with drills, and a GBR procedure had to be performed. When rotary
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362 instruments were used, the author observed cracks and sometimes defragmentation or destabilization of cortical bone during the preparation stage. This was due to the vibrations and mechanical pressure of the rotary instruments used to contour the bone block. For the same reason, in nine patients, the bone block started to move during mechanical shaping with rotary instruments and had to be stabilized once again. The author had to desist from bone block contouring, leaving it with a thick cortical portion extending along the alveolar contour. The autogenous bone blocks, functioning as a biologic scaffold, provided a platform for reconstruction of the buccal wall of the defect. The use of bone substitutes to fill the space between the bone blocks and the defect walls and also to act as an external layer to cover the graft material together with resorbable collagen membranes was intended to compensate for the resorption of the autogenous bone.19 Simultaneously, the biomaterial layer acted as an additional support and provided extra volume for the soft tissue after the regeneration process. In group 2, defragmentation or destabilization of the bone block occurred in six patients during the implant placement procedure. The cortical part of the block graft was not stable enough and could not guarantee implant stabilization, which was why the implant could not be placed at the time of the surgery. In group 1, fine and delicate osseous preparation with
piezoelectric surgery facilitated bone block regeneration. No surgical complications occurred during this procedure, and the implants were stabilized with 35 to 40 Ncm force. This provided clinical proof that the bone block had been properly incorporated. The use of piezoelectric surgery facilitates the healing process and reduces inflammatory reaction when the graft is healing, which helps keep the live bone tissue in place after it has been grafted.20–23 The 5- to 7-year follow-up period in group 1 revealed no soft tissue change in the regenerated site, thus clinically indicating that the buccal bone of the transplanted block remained stable without any symptoms of resorption. In 37% of group 2 patients, dehiscence was observed. This indicated that leaving the thick area of cortical bone in the grafted bone block may lead to resorption of the buccal wall in the long term. There was no difference in bone remodeling around implants on the periapical radiographs. These findings indicate that resorption affects the cortical portion of the grafted bone block, whereas the level of interproximal bone is related not only with transplanted bone but also with the bone around adjacent teeth.
Conclusion Bone block grafting performed with piezoelectric surgery is a more precise and gentle technique compared with the same procedure carried out with rotary instruments.
With the use of piezoelectric surgery, it was possible to more accurately harvest the correct shape of block for a ridge defect and to properly stabilize it in the recipient site. This allowed for final shaping and contouring of the cortical part of the graft. In the second phase of the procedure, piezoelectric surgery was used to delicately shape and thin a layer of cortical block that could serve as an element supporting the shape of the reconstructed alveolar process. Piezosurgery tips do not generate pressure and vibrations in the bone when it is being prepared. All of these maneuvers are difficult or impossible to perform with the use of rotary instruments. This is, in the author’s opinion, the most important factor affecting the clinical outcome of bone block incorporation. The piezoelectric surgery technique is more predictable because it helps reduce complications involving bone block fragmentation and destabilization during the surgical procedure. There are also fewer complications affecting the regeneration process and the condition of the peri-implant tissue in longterm observations. The piezoelectric surgery technique allowed for modifications in the autogenous bone block grafting procedure, which helped achieve better clinical results in the rehabilitative treatment of patients with bone defects in the esthetic zone.
Acknowledgments The author reported no conflicts of interest related to this study.
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363 References 1. Ishikawa T, Kitajima H, Salama H. Three-dimensional bone and soft tissue requirements for optimizing esthetic results in compromised cases with multiple implants. Int J Periodontics Restorative Dent 2010;30:503–511. 2. Smukler H, Capri D, Landi L. Harvesting bone in the recipient sites for ridge augmentation. Int J Periodontics Restorative Dent 2008;28:411–419. 3. Fabbri G, Brennan M, Manfredi M, Ban G. Guided bone regeneration technique in the esthetic zone: A novel approach using resorbable PLLA-PGA plates and screw fixation. A case report. Int J Periodontics Restorative Dent 2009;29: 543–547. 4. Buser D, Dula K, Belser U, Hirt HP, Berthold H. Localized ridge augmentation using guided bone regeneration. Surgical procedure in maxilla. Int J Periodontics Restorative Dent 1993;13:29–34. 5. Ohayon L. Ridge enlargement using deproteinized bovine bone and bioresorbable collagen membrane: A tomodensitometric, histologic, and histomorphometic analysis. Int J Periodontics Restorative Dent 2011;31:237–245. 6. Wang HL, Misch C, Neiva RF. Sandwich bone augmentation technique: Rationale and report of pilot cases. Int J Periodontics Restorative Dent 2004;24:232–245. 7. Simion M, Trisi P, Piatelli A. Vertical ridge augmentation using a membrane technique associated with osseointegrated implants. Int J Periodontics Restorative Dent 1994;14:496–511.
8. Pendarvis WT, Sandifer J. Localized ridge augmentation using a block allograft with subsequent implant placement: A case report. Int J Periodontics Restorative Dent 2008;28:509–515. 9. Cardaropoli D. Vertical ridge augmentation with the use of recombinant human platelet-derived growth factor-BB and bovine mineral: A case report. Int J Periodontics Restorative Dent 2009;29: 289–295. 10. Byun HY, Wang HL. Sandwich bone augmentation using recombinant human platelet-derived growth factor and BetaTricalcium Phosphate alloplast: Case report. Int J Periodontics Restorative Dent 2008;28:83–87. 11. Wang HL, Boyapati L. “PASS” principles for predictable bone regeneration. Implant Dent 2006;15:8–17. 12. Sclar A. Strategies for management of single tooth extraction sites in aesthetic implant therapy. J Oral Maxillofac Surg 2004;62(suppl 2):90–105. 13. Hunt DR, Jovanovic SA. Autogenous bone harvesting: A chin graft technique for particulate and monocortical bone blocks. Int J Periodontics Restorative Dent 1999;19:165–173. 14. Simion M, Jovanovic SA, Trisi P, Scarano A, Piatelli A. Vertical ridge augmentation around dental implants using a membrane technique and autogenous bone or allografts in humans. Int J Periodontics Restorative Dent 1998;18:9–23. 15. Widmark G, Andersson B, Ivanoff CJ. Mandibular bone graft in the anterior maxilla for single-tooth implants. Presentation of surgical method. Int J Oral Maxillofac Surg 1997;26:106–109.
16. Gordh M, Alberius P. Some basic factors essential to autogenic nonvascularized onlay bone grafting to the cranial skeleton. Scand J Plast Reconstr Hand Surg 1999;32:129–146. 17. Pallesen L, Schou S, Aaboe M, HjørtingHansen E, Nattestad A, Melsen F. Influence of particle size on the early stage of bone regeneration: A histologic and stereologic study in rabbit calvarium. Int J Oral Maxillofac Implants 2002;17: 498–506. 18. Burchardt H. The biology of bone graft repair. Clin Orthop 1983;174:28–42. 19. Maiorana C, Bereta M, Salina S, Santoro F. Reduction of autogenous bone resorbtion by means of BioOss coverage: A prospective study. Int J Periodontics Restorative Dent 2005;25:19–25. 20. Sohn DS, Ahn MR, Lee WH, Yeo DS, Lim SY. Piezoelectric osteotomy for intraoral harvesting of bone blocks. Int J Periodontics Restorative Dent 2007;27:127–131. 21. Chiriac G, Herten M, Schwarz F, Rothamel D, Becker J. Autogenous bone chips: Influence of a new piezoelectric device on chip morphology, cell viability and differentiation. J Clin Periodontol 2005; 9:994–999. 22. Vercelloti T, Nevins ML, Kim DM, et al. Osseous response following respective therapy with piezoelectric surgery. Int J Periodontics Restorative Dent 2005; 25:543–549. 23. Happe A. Use of piezoelectric surgical device to harvest bone grafts from the mandibular ramus: Report of 40 cases. Int J Periodontics Restorative Dent 2007; 27:241–249.
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355
Piezoelectric Surgery in Autogenous Bone Block Grafts
Piotr Majewski, DDS, PhD1
This article describes alveolar ridge reconstruction in the esthetic zone using autogenous bone blocks harvested from the chin, taking into account the way the bone block is harvested, stabilized, and contoured in the recipient site. The 38 procedures were divided into two groups: group 1, using piezoelectric surgery, and group 2, using rotary instruments. The piezoelectric surgery technique made it possible to introduce surgical modifications. An observation of bone regeneration and follow-up clinical observations 5 to 7 years after the procedure revealed that the piezoelectric surgery technique provides better and more predictable clinical results for bone regeneration. (Int J Periodontics Restorative Dent 2014;34:355–363. doi: 10.11607/prd.1279)
Head of Implantological Department, Collegium Medicum, Jagiellonian University, Cracow, Poland.
1
Correspondece to: Dr Piotr Majewski, Klinika Implantologiczno-Stomatologiczna, ul. Milkowskiego 3/701 30-349 Cracow, Poland; email: [email protected]. ©2014 by Quintessence Publishing Co Inc.
The anterior part of the maxilla is regarded as one of the most difficult areas for implant treatment. This is due to the fact that ensuring a positive outcome for such treatment depends not only on the function of the integrated implants, but also on the esthetics of the implant-supported restorations. Bone tissue and soft tissue defects complicate treatment because of the need to carry out effective tissue regeneration procedures.1 Depending on the type of augmentation used, ie, vertical, horizontal, or mixed, numerous authors have offered a variety of treatment methods.2–7 Among these, two main groups can be distinguished. The first includes guided bone regeneration (GBR) using biomaterials, autogenous bone particles, and barrier membranes, while the second uses bone block grafts.8 A combination of both techniques has also been applied: biomaterials and membranes with autogenous bone blocks. Growth factors9,10 and bone morphogenetic proteins appear to enhance bone formation. However, there are insufficient long-term data reports to support
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356 these promising clinical and histologic observations. Many factors affect the predictable results of bone formation. Among them, Wang and Boyapati have noted primary wound closure, angiogenesis, space creation, and stability.11 This indicates that one of the most important factors for the procedure is the surgical technique applied. This article describes the use of piezoelectric surgery in the bone regeneration procedure using autogenous bone block grafts together with biomaterials and bioresorbable membranes. With the help of this device, certain operational modifications were made to the standard surgical procedure that, according to clinical observations and an assessment of the results of healing (incorporation) of the bone block in the recipient site, help improve healing results and reduce resorption that may affect the grafted bone tissue in the area around implants. The surgical method of grafting bone block with the use of drills is referred to here as the standard method, as opposed to the modified method, in which piezoelectric surgery is applied. With the modified method, it was possible to more accurately harvest the correct shape of the block for a ridge defect and properly stabilize it in the recipient site. In the second phase of the procedure, Piezoelectric surgery tips were used to delicately prepare and thin a layer of cortical block that could serve as an element supporting the shape of the reconstructed alveolar process.
Piezoelectric surgery tips do not generate vibrations in the bone when it is being prepared and all maneuvers are more precise and gentle compared with those made using drills. These were the basic factors distinguishing the two procedures (ie, standard and modified) from each other. Both surgical elements, the harvesting of the block together with its stabilization, and then the precise and delicate preparation using piezoelectric surgery, helped achieve better clinical results with regard to reconstructing the alveolar ridge.
Method and materials In accordance with this method, a total of 38 regenerative procedures were performed on patients aged from 24 to 47 years. One regeneration procedure was carried out on each patient and implant placement was performed after 6 months. The clinical observation period was 5 to 7 years after implant placement and prosthetic reconstruction (a single porcelain crown cemented onto an abutment). Patients qualifying for the procedure were in good general health and were nonsmokers. Patients with existing pathologic changes of an inflammatory character in the region of the mucous membrane, the periodontium, or hard tissue were excluded from the procedures until the pathology was eliminated. Patients were prepared for prosthetic restoration by setting the correct occlusal conditions with the aim of making a prosthetic crown on the implant placed in the
regeneration site. They exhibited defects (missing single teeth) in the anterior maxilla together with extensive damage to the labial plate of the alveolar ridge, such that it was not possible to achieve immediate implant stability. The extent of the defect was, in the author’s assessment, a contraindication for GBR because it would be difficult to create and maintain the shape of the alveolar ridge during the regeneration process. The procedures were divided into two groups. Group 1 involved grafts of autogenous bone block taken from the chin using piezoelectric surgery (a modified procedure), while group 2 was a standard procedure using bone drills (control method). There were 19 patients in each group. The procedure can be divided into the following stages: the preparation of the recipient site, bone block harvesting, stabilization of the bone block in the recipient site, contour modification of the bone block after its stabilization in situ, and primary wound closure. In both phases, the procedure was carried out according to the same sequence and in the same way. The difference consisted of instrument use: piezoelectric surgery in group 1 and bone drills in group 2 (Table 1). The purpose of this study was to assess how the use of piezoelectric surgery affects the course of the operation and what possible differences appear in the bone tissue regeneration process from the perspective of creating the proper conditions for correct implant placement.
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Table 1
Comparison of groups 1 and 2 Group 1 Group 2 (piezoelectric surgery) (rotary instruments)
Patients (n)
19
19
Fragmentation of bone block during harvesting
0
2
Bone block fixation with microscrews in recipient site
1
16
Destabilization of bone block while shaping in situ
0
9
Fragmentation of bone block while shaping in situ
0
2
Sequestration or destabilization of bone block during implant placement
0
6*
19
13
Soft tissue dehiscence at the labial aspect of the regenerated area after 5–7 y
No. of implants after bone regeneration
0
7
Bone remodeling below first thread of implant on periapical radiograph
0
0
*Need for GBR and delayed implant placement.
The modified autogenous bone block graft procedure uses piezoelectric surgery to harvest bone block from the chin in a shape that best corresponds with that of the bone defect. After the bone has been inserted and stabilized, piezoelectric surgery is used again to prepare the correct shape of the cortical bone in the recipient site. The aim of these modifications was to create a stable, biologic space in the defect enclosure for bone formation and to minimize the negative effects connected with autogenous bone block resorption. The procedure was performed with an antibiotic prophylaxis that patients took 1 hour prior to surgery (Augmentin 375 mg, GlaxoSmithKline). The patients were instructed to rinse the oral cavity with a 0.1% chlorhexidine solution three times a day for 3 days before and 2 weeks after the surgery. The operations were performed under local anesthesia (4 to 6 mL Ubistesin 4%
1:100,000, 3M ESPE). In the first stage, the size and shape of the defect were assessed after the mucoperiosteal flap was elevated and the tooth root was removed together with any inflammatory lesions of a chronic character. The second stage involved harvesting bone block from the area of the chin. The procedure followed the same sequence for both groups. The only difference was that rotary instruments were used in group 2. In group 1 (Figs 1a to 1g), a suitably sized bone block was excised with the help of a Piezosurgery device (Mectron) and by means of a saw-shaped insert (OT6, OT7). The upper incision line in the bone was 5 mm below the lower incisor root apices so as to minimize potential nerve and vessel injury. The shape and size of the defect was reproduced with the use of a template made from sterile aluminium foil. This made it possible to outline the contours and size of the bone block according to
the geometry of the recipient site. The bone cut was deep enough to obtain a corticocancellous block with an approximate thickness of 5 to 6 mm. In the second phase, the released block was compared with the geometry of the defect. Both the bone block itself and the wall defect were prepared with the help of a Piezosurgery device so as to ensure that both elements matched each other very closely in shape. The bone block was then wedged between the sidewalls of the bone defect. In three-wall defects, where inlay-type blocks were used, preparing the contours in this way ensured stable fixation for the bone block in the defect, without the need for additional miniscrews or miniplates. In group 2 (Figs 2a to 2c), block fixation miniscrews were used in 16 cases because the bone block harvesting and initial preparation were not as precise compared with the piezoelectric surgery technique (Fig 3).
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Fig 1a Bone defect at the site of missing maxillary left lateral incisor (patient no. 1).
Fig 1b Shaping of cortical part and adjustment of contours of bone block to the alveolar ridge after its stabilization in the recipient site (patient no. 1).
Fig 1c Bone block in recipient site before modification (patient no. 1).
Fig 1d (left) Bone block in recipient site after modification (patient no. 1).
Fig 1e (right) Autogenous bone block and Bio-Oss covered with Bio-Gide membrane (patient no. 1).
Fig 1f (below left) Status of bone block incorporation into the defect 6 months after postregenerative surgery. The cortical part of the grafted bone block is incorporated into the recipient site. No symptoms of necrosis or sequestration of bone block are visible (patient no. 1).
Fig 1g (right) Ridge morphology at the implant site in the regenerated area prior to implant placement. Stable bone block in situ after drilling (patient no. 1).
The next stage involved the final preparation and adjustment of the bone block to the contours of the alveolar ridge in the recipient site. Suitable Piezosurgery inserts (OP1, OP3) were used for this purpose (see Figs 1b and 2b). An effort was made to prepare the bone block in such a way that its external cortical surface represented a continuity of the walls of the alveolar ridge. During the course of this action, the thickness of the cortical layer of the
bone block was simultaneously reduced (Fig 1d). The purpose of this procedure was to reduce both necrosis in the cortical part of the block and graft resorption by facilitating revascularization of the thinner layer of the cortical bone. The author observed the rule that the thickness of the cortical part should not exceed 2 to 3 mm. In the clinical observation, this thickness was sufficient to maintain the mechanical properties of the grafted block and sustain its stability in
the regenerated defect. The gap that appeared between the block and the base of the defect was first filled with cancellous bone chips harvested from the inferior area of the donor site and then with particulated biomaterial (BioOss, Geistlich). The bone block was covered with an external layer of Bio-Oss as a slow-resorbing material. The regenerated area was secured with a Bio-Gide collagen membrane (Geistlich) to achieve better regeneration effects (see
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359 Fig 1e). The membrane was stabilized with titanium pins, horizontal or cross mattress sutures, and nonabsorbable monofilament (4/0 Seralene, SeragWeissner). In 16 of the 38 cases, the membranes were stabilized with titanium pins onto the buccal plate of the bone surrounding the defect. Crossmattress sutures were used to secure the membrane if it was to be pinned directly over the thin bone plate covering the roots of adjacent teeth and there was a risk of periodontium injury. After periosteal releasing incisions and flap extension were performed, the wound was closed tightly without pressure and primary wound closure was achieved using 5/0 Seralene (SeragWeissner). The bone defect created during bone block harvesting in the donor site was filled with the Bio-Oss particles and secured with a Bio-Gide membrane. Patients were given 800 mg ibuprofen every 8 hours to manage the pain. The sutures were removed after 7 days. Veneers or acrylic/composite crowns were used as provisional restorations. They were attached to adjacent teeth with the aid of glass-fiber splints. The healing process was uneventful. No wound dehiscence was observed. In two cases (group 2), local paresthesia in the chin area was observed. However, these complications resolved 4 to 6 weeks after surgery. No other complications associated with the second surgical site were noted. The implants (Biomet 3i) were placed 6 months after the regeneration procedures.
Fig 2a Stable fixation of bone block in the recipient site. No miniscrew used (patient no. 2).
Fig 2b Bone block in situ and shaping and thinning with piezoelectric surgery (patient no. 2).
Fig 2c State of soft tissue at the regenerated area 6 years after implant placement (patient no. 2).
Fig 2d (right) Periapical radiograph 6 years after implant placement in the regenerated area. Normal pattern of bone remodeling at implant shoulder (patient no. 2).
Results In a comparative analysis of the two groups, both the operation phase and the result of the bone tissue regeneration process were analyzed together with, over a 5 to 7 year observation period, the state of the soft tissue in the region of the crowns placed on the implants and the bone level in radiographs targeted in the region. In two cases (10%) in group 2, involving the use of bone drills,
the bone block fragmented during mobilization from the osseous bed in the donor site. In these situations, instead of a single piece, two smaller fragments of the block were used, which had to be stabilized using microscrews. In group 1, no defragmentation was observed. In group 2, the bone block was accurately adjusted to the contours of the defect in only three patients (15%) such that there was no need to stabilize it with the help of microscrews. The remaining patients
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Fig 3 The bone block harvested with the use of rotary instruments and stabilized with miniscrews.
Fig 4 Thick cortical part of bone block destabilization during implant placement procedure when rotary instruments were used in bone block graft procedure.
required the use of microscrews: in 14 patients, a bone monoblock was fixated, and in 2 patients, two sections of block that fragmented during the harvesting process were stabilized with microscrews. Only 1 patient (5%) in group 1 required additional stabilization for the block in the recipient site with the help of a microscrew. In group 1, no destabilization or defragmentation of the block occurred during the preparation and thinning of the core layer, whereas in group 2, the bone block lost stabilization during these maneuvers in 9 patients (47%), and it was necessary to refrain from bone-block shaping procedures and to stabilize the block once again with miniscrews. In two patients (10%) in this group, the block defragmented into 2 to 3 fragments. This necessitated the use of GBR procedures without the need for a bone block due to the impossibility of stabilizing small fragments of the block.
After 6 months, ie, during the implant placement procedure, both the shape of the regenerated region and the possibility of placing the implant in the proper position were assessed. The state of the soft tissue was deemed satisfactory both with regard to the shape and the amount, ie, the thickness and width, of the attached gingiva zone (5 mm or more). In group 1, after flap elevation, no border or difference was noticeable between the grafted bone block and the surrounding host bone tissue of the recipient site (see Fig 1f). In clinical terms, the bone tissue of the grafted bone block adequately conformed to the contours of the alveolar ridge, which ensured that the implant could be properly placed. The width of the alveolar ridge was 6 mm or more, allowing for 4-mmdiameter implants to be placed. No separation was observed in the visible layer of the compact, corti-
cal region of the graft above the surface of the alveolar ridge, as was noted in the bone block graft procedures performed in group 2. In six patients (32%) in group 2, the cortical part of the grafted bone blocks fragmented or destabilized during implant site preparation or during implant placement (Fig 4). These patients were excluded from implant placement, and further GBR procedures were performed at that time with delayed (another 6 months later) implant placement. In group 1, no breakup, fragmentation, or destabilization of the cortical part of the graft was observed during the implant placement procedure (see Fig 1g). The same provisional crowns or veneers were used during the osseointegration period. The implant was exposed after 4 months. No implant was lost in either group (there were 19 in group 1 and 13 in group 2). After the implant was exposed, new provisional acrylic crowns were
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361 screw-retained on the implant. The purpose of this was to ensure final modeling of the soft tissue and interdental papillae around the future definitive implant-supported ceramic crowns. After another 6 to 8 months, full ceramic crowns were cemented onto the implant abutments. Patients were seen for follow-up examinations once a year after the prosthetic phase. In the 5- to 7-year observation period, the implant-supported prosthetic crowns in group 1 performed their function properly. No pathologies or soft tissue dehiscences were observed in the region of the implants and prosthetic crowns. In group 2, soft tissue dehiscences of up to 2 to 3 mm at the buccal aspect of the grafted area were observed in seven patients (37%) in the 5- to 7-year observation period. Periapical radiographs, taken directly after crown cementation and then every year postsurgery, revealed a normal pattern of remodeling up to the first thread of the implant in both groups (see Fig 2d).
Discussion The surgical procedure described here involved the use of corticocancellous block grafts. Both components in the grafted block have different biologic and mechanical characteristics. An undoubted advantage of using autogenous tissue is the biologic compatibility of the graft material. In grafted corticocancellous blocks, the cortical part was used as an appropriate scaffold for
supporting soft tissue and maintaining the stability of the contours of the regenerated site. One of the most serious problems connected with the use of bone blocks is their resorption in the recipient site. The literature shows variations in the scale of the resorption, from 25% to 60%.12–15 On the one hand, the cortical layer of the bone graft undergoes resorption at a slower rate than the cancellous partof teh bone graft.16 On the other, the cancellous part acts as a carrier for osteogenic cells in the recipient site, which facilitates the revascularization process and graft healing.17 The healing and incorporation of autogenous bone block grafts, ie, the phenomenon known as creeping substitution, is described by Burchardt18 as a biologic reconstruction process involving the gradual replacement of necrotic tissue with new, vital bone tissue. A purely cortical bone block is less likely to undergo revascularization than a corticocancellous block.18 In connection with this fact, the blood supply to this part of the bone block is poorer. Consequently, necrosis of the grafted tissue may occur as the cortical bone blocks heal. The aim of the surgical method described in this paper was to create the best possible conditions for bone block incorporation. A single procedure was carried out using two different tools: a Piezosurgery device in group 1 and rotary instruments in group 2. The bone block must be properly stabilized in the site. Precise
block harvesting and shaping using the piezoelectric surgery device allowed for a perfect match and stabilization of the transplanted bone block in the defect enclosure. Because of bone loss during cutting, bone harvesting with rotary instruments is not as precise, which is why it is difficult to harvest bone blocks that correspond exactly to the geometry of the defect. In most patients in group 2 (16), the bone block had to be stabilized with microscrews. The most important characteristic of the cortical component is its mechanical property of maintaining contours. On the other hand, the thicker this layer is, the worse the conditions for revascularization. The use of Piezosurgery insert tips for precision shaping and thinning of the cortical layer after bone block stabilization in situ was intended specifically to create the best possible conditions for graft incorporation. The thin cortical layer (not exceeding 2 to 3 mm) of transplanted block still maintained the contours of the regenerated site after 6 months. The smooth, gentle contouring of the cortical part of the bone block was made possible by the use of a Piezosurgery device. In group 2, the same maneuver was difficult due to vibrations of the drills during the procedure and because stabilizing of the bone block with microscrews was insufficient to sustain mechanical shaping. In two patients, fragmentation of the bone block occurred during the shaping procedure with drills, and a GBR procedure had to be performed. When rotary
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362 instruments were used, the author observed cracks and sometimes defragmentation or destabilization of cortical bone during the preparation stage. This was due to the vibrations and mechanical pressure of the rotary instruments used to contour the bone block. For the same reason, in nine patients, the bone block started to move during mechanical shaping with rotary instruments and had to be stabilized once again. The author had to desist from bone block contouring, leaving it with a thick cortical portion extending along the alveolar contour. The autogenous bone blocks, functioning as a biologic scaffold, provided a platform for reconstruction of the buccal wall of the defect. The use of bone substitutes to fill the space between the bone blocks and the defect walls and also to act as an external layer to cover the graft material together with resorbable collagen membranes was intended to compensate for the resorption of the autogenous bone.19 Simultaneously, the biomaterial layer acted as an additional support and provided extra volume for the soft tissue after the regeneration process. In group 2, defragmentation or destabilization of the bone block occurred in six patients during the implant placement procedure. The cortical part of the block graft was not stable enough and could not guarantee implant stabilization, which was why the implant could not be placed at the time of the surgery. In group 1, fine and delicate osseous preparation with
piezoelectric surgery facilitated bone block regeneration. No surgical complications occurred during this procedure, and the implants were stabilized with 35 to 40 Ncm force. This provided clinical proof that the bone block had been properly incorporated. The use of piezoelectric surgery facilitates the healing process and reduces inflammatory reaction when the graft is healing, which helps keep the live bone tissue in place after it has been grafted.20–23 The 5- to 7-year follow-up period in group 1 revealed no soft tissue change in the regenerated site, thus clinically indicating that the buccal bone of the transplanted block remained stable without any symptoms of resorption. In 37% of group 2 patients, dehiscence was observed. This indicated that leaving the thick area of cortical bone in the grafted bone block may lead to resorption of the buccal wall in the long term. There was no difference in bone remodeling around implants on the periapical radiographs. These findings indicate that resorption affects the cortical portion of the grafted bone block, whereas the level of interproximal bone is related not only with transplanted bone but also with the bone around adjacent teeth.
Conclusion Bone block grafting performed with piezoelectric surgery is a more precise and gentle technique compared with the same procedure carried out with rotary instruments.
With the use of piezoelectric surgery, it was possible to more accurately harvest the correct shape of block for a ridge defect and to properly stabilize it in the recipient site. This allowed for final shaping and contouring of the cortical part of the graft. In the second phase of the procedure, piezoelectric surgery was used to delicately shape and thin a layer of cortical block that could serve as an element supporting the shape of the reconstructed alveolar process. Piezosurgery tips do not generate pressure and vibrations in the bone when it is being prepared. All of these maneuvers are difficult or impossible to perform with the use of rotary instruments. This is, in the author’s opinion, the most important factor affecting the clinical outcome of bone block incorporation. The piezoelectric surgery technique is more predictable because it helps reduce complications involving bone block fragmentation and destabilization during the surgical procedure. There are also fewer complications affecting the regeneration process and the condition of the peri-implant tissue in longterm observations. The piezoelectric surgery technique allowed for modifications in the autogenous bone block grafting procedure, which helped achieve better clinical results in the rehabilitative treatment of patients with bone defects in the esthetic zone.
Acknowledgments The author reported no conflicts of interest related to this study.
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363 References 1. Ishikawa T, Kitajima H, Salama H. Three-dimensional bone and soft tissue requirements for optimizing esthetic results in compromised cases with multiple implants. Int J Periodontics Restorative Dent 2010;30:503–511. 2. Smukler H, Capri D, Landi L. Harvesting bone in the recipient sites for ridge augmentation. Int J Periodontics Restorative Dent 2008;28:411–419. 3. Fabbri G, Brennan M, Manfredi M, Ban G. Guided bone regeneration technique in the esthetic zone: A novel approach using resorbable PLLA-PGA plates and screw fixation. A case report. Int J Periodontics Restorative Dent 2009;29: 543–547. 4. Buser D, Dula K, Belser U, Hirt HP, Berthold H. Localized ridge augmentation using guided bone regeneration. Surgical procedure in maxilla. Int J Periodontics Restorative Dent 1993;13:29–34. 5. Ohayon L. Ridge enlargement using deproteinized bovine bone and bioresorbable collagen membrane: A tomodensitometric, histologic, and histomorphometic analysis. Int J Periodontics Restorative Dent 2011;31:237–245. 6. Wang HL, Misch C, Neiva RF. Sandwich bone augmentation technique: Rationale and report of pilot cases. Int J Periodontics Restorative Dent 2004;24:232–245. 7. Simion M, Trisi P, Piatelli A. Vertical ridge augmentation using a membrane technique associated with osseointegrated implants. Int J Periodontics Restorative Dent 1994;14:496–511.
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16. Gordh M, Alberius P. Some basic factors essential to autogenic nonvascularized onlay bone grafting to the cranial skeleton. Scand J Plast Reconstr Hand Surg 1999;32:129–146. 17. Pallesen L, Schou S, Aaboe M, HjørtingHansen E, Nattestad A, Melsen F. Influence of particle size on the early stage of bone regeneration: A histologic and stereologic study in rabbit calvarium. Int J Oral Maxillofac Implants 2002;17: 498–506. 18. Burchardt H. The biology of bone graft repair. Clin Orthop 1983;174:28–42. 19. Maiorana C, Bereta M, Salina S, Santoro F. Reduction of autogenous bone resorbtion by means of BioOss coverage: A prospective study. Int J Periodontics Restorative Dent 2005;25:19–25. 20. Sohn DS, Ahn MR, Lee WH, Yeo DS, Lim SY. Piezoelectric osteotomy for intraoral harvesting of bone blocks. Int J Periodontics Restorative Dent 2007;27:127–131. 21. Chiriac G, Herten M, Schwarz F, Rothamel D, Becker J. Autogenous bone chips: Influence of a new piezoelectric device on chip morphology, cell viability and differentiation. J Clin Periodontol 2005; 9:994–999. 22. Vercelloti T, Nevins ML, Kim DM, et al. Osseous response following respective therapy with piezoelectric surgery. Int J Periodontics Restorative Dent 2005; 25:543–549. 23. Happe A. Use of piezoelectric surgical device to harvest bone grafts from the mandibular ramus: Report of 40 cases. Int J Periodontics Restorative Dent 2007; 27:241–249.
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