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Guided “Sandwich” Technique: A Novel Surgical Approach for Safe Osteotomies in the Treatment of Vertical Bone Defects in the Posterior Atrophic Mandible: A Case Report Pietro Felice, MD, DDS, PhD,* Carlo Barausse, DDS,* Roberto Pistilli, MD, DDS, PhD,† Sergio Spinato, DDS, PhD,* and Fabio Bernardello, MD, DDS‡
he demand for implant-supported rehabilitation is increasing as more patients desire fixed restorations to replace a missing dentition. Correct implant treatment planning has therefore become an essential part of the prosthetic reconstruction of the lost dentition.1 A fixed implant-supported prosthesis is an established procedure to treat edentulous jaws if adequate bone volume is available.2 Unfortunately, ridge reabsorption is a physiological process after tooth loss frequently resulting in a horizontally and vertically deficient ridge.3,4 Such unavoidable bone remodeling, particularly in the posterior mandible, can make the insertion of dental implants of adequate length impossible or difficult, due to anatomical limitations caused by superficialization of the alveolar nerve.5 The augmentation of these areas is a challenging procedure and often a prerequisite to create sufficient bone volume for ideal
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*Unit of Periodontology and Implantology, Dental School, University of Bologna, Bologna, Italy. †Oral and Maxillofacial Department, A.C.O. San Filippo Neri, Rome, Italy. ‡Private practice, Terranegra di Legnago, Verona, Italy.
Reprint requests and correspondence to: Fabio Bernardello, MD, DDS, Via F. Bonvicini 42, Terranegra di Legnago, Verona 37040, Italy, Phone: 0039-0442-24711, Fax: 0039-0442-24711, E-mail: [email protected] ISSN 1056-6163/14/02306-738 Implant Dentistry Volume 23 Number 6 Copyright © 2014 by Lippincott Williams & Wilkins DOI: 10.1097/ID.0000000000000168
Purpose: A novel technique to perform safe osteotomies during inlay block regenerative procedures in the posterior atrophic mandible is described. Material and Methods: A 52year-old male patient with vertical atrophy of the left posterior mandible was treated adopting an inlay block “sandwich” technique using an allogenic cancelous block and a mixture of mineralized and demineralized human bone allograft in putty form as graft. The horizontal osteotomy for the lifting of the osteotomized bone segment was performed using a template prepared from a virtual anatomical replica of the patient’s mandible obtained from cone beam computed tomography data. In the second surgical phase, 3 months after the augmentation, 2 implants were easily placed.
Results: The horizontal osteotomy was carried out, with no risk, very close to the nerve structures after the precise osteotomy line established preoperatively on the three-dimensional computed tomography (3D-CT) virtual reconstruction. No neurological complications were observed in the first days after the procedure, and no subsequent problems were recorded during the 3-month healing period. Conclusion: Radiographic evaluations and complication-free clinical healing demonstrate the effectiveness of this technique to obtain safe and precise osteotomies. (Implant Dent 2014;23:738–744) Key Words: vertical regeneration, human allograft, inlay bone graft, mandibular atrophy, safe osteotomy, surgical template
implant placement because implants have to be placed in a prosthetically driven position to achieve long-term stability, function, and esthetic results.6–8 Various bone augmentation procedures, such as guided bone regeneration (GBR) generally using nonreabsorbable membranes9,10 or titanium meshes11,12 and alveolar distraction osteogenesis13,14 have
been developed and are widely used for vertical augmentations. However, when treating severely resorbed ridges, the use of block grafts is preferred.15,16 Block grafts can be used in the performance of both “onlay” (appositional)17–20 or “inlay” (interpositional) techniques.21–23 One well-established procedure for the augmentation of extremely
IMPLANT DENTISTRY / VOLUME 23, NUMBER 6 2014 atrophic mandibles is the “sandwich” osteotomic technique, initially proposed by Schettler et al24 in 1976 for the correction of anterior areas, but recently applied to the posterior atrophic mandible with positive outcomes.21,23 The procedure consists of the interposition, that is, inlay of a bone block graft in the space obtained after coronally raising the cranial osteotomized segment of the mandible. The lifted bone segment remains connected to the lingual periosteum, ensuring adequate blood supply for the remodeling of the inlay graft25,26 and is fixed to the basal bone with a rigid fixation using 2.0-mm miniplates.26 Different block grafts can be used in regenerative procedures: autogenic,18 allogenic,16,17,27 or xenogenic.22,28,29 Autogenic blocks have always been considered the gold standard material for their osteogenic, osteoinductive, and osteoconductive properties.18 However, if harvested from intraoral donor sites, as the chin and mandibular ramus, autologous bone is available in limited quantities30 and a significant morbidity (ie, edema, infection, paresthesia, loss of muscle tone, loss of tooth vitality, and gingival recession) is reported.30–32 Autogenic blocks can also be obtained from extraoral sites such as the iliac crest22,29 but high costs33 and significant morbidity, that is, transitory claudication34 of the donor site have to be taken into account. Therefore, to counteract these limitations associated with the use of autogenic blocks, grafts of different nature have been developed and used.5,16,22,27–29,35,36 In a recent study, Felice et al22 compared the use of deproteinized bovine bone mineral (DBBM) blocks versus autologous bone blocks harvested from the iliac crest in the sandwich technique. Clinical and histological results overlapped, however, the use of xenogenic blocks proved to be less invasive and therefore preferable.29 However, the use of bovine bone blocks is challenged by their extreme friability comporting considerable risk of breakage during shaping and positioning. In these cases, an insufficient vertical bone gain has been observed.22,29,37 The use of different equine xenogenic blocks showed contrasting outcomes, with some
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Fig. 1. Preoperative CBCT image of posterior left mandible.
Fig. 2. CBCT cross sections revealing a severe crestal atrophy. A, At section 13, 14 mm (6 mm of available bone) above mental nerve foramen are evident. B, At section 16, 10.3 mm (6 mm of available bone) above nerve canal are evident. C, At section 18, 10.9 mm (6 mm of available bone) above nerve canal are evident.
Fig. 3. Surgical template realization. A, 3D virtual anatomical replica. B, Universal fork worn during the radiographic examination. C, CAD phase with the virtual design of the osteotomic line reveals a distance of 2 mm coronally and parallel to the course of the alveolar canal. D, CAM phase: creation of a PMMA surgical template obtained by milling.
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Fig. 4. A, Paracrestal incision in the buccal aspect. B, A flap was carefully elevated, and the surgical template was positioned. C and D, The horizontal osteotomy was performed using the surgical template.
Fig. 5. A, Vertical osteotomies. B, The osteotomized segment was raised 5 mm coronally. C, The allograft block was positioned in the space obtained, and the lifted segment was then fixed to the basal bone in this position using 1 titanium miniplate and 2 miniscrews. D, An allogenic membrane was applied to protect the surgical site.
encouraging results38 but also with unacceptable failure rate (54.3%).39 Moreover, the use of xenografts has been
associated with the persistence of a high percentage of residual graft due to a slow remodeling process.10,22
Considering these disadvantages and limitations associated with autogenic and xenogenic blocks, new materials, which could ideally integrate with the surrounding bone in a physiological time40 and remodel into highly vital new bone with minimal residual graft have been evaluated. Allogenic grafts seem to be the materials with these optimal characteristics.41 Allografts are bone-derived grafts obtained by processing and sterilization of human bone harvested from donors. These materials are safe easily storable, and their use in the treatment of vertical and horizontal atrophies is widely described.17,27,42,43 The sandwich technique requires the execution of a horizontal osteotomy performed parallel to the inferior alveolar nerve. Given that this technique is often applied in very atrophic posterior mandibles, sometimes with only 5 to 6 mm of residual vertical bone, the distracted segment could result thin because the osteotomy has to be performed coronally and at a safe distance from the alveolar nerve. In these markedly atrophic situations, the risk of fracture of the thin osteotomized segment during fixation with a surgical plate is real and described.22 Therefore, it is always fundamental to guarantee an adequate thickness of the segment to be raised. Consequently, it is advisable to apply the procedure in ridges with bone height $6 mm above the mandibular canal to ensure adequate thickness of the coronally distracted segment and sufficient clearance of the inferior alveolar nerve.21 However, in very atrophic cases to obtain this fundamental prerequisite, the horizontal osteotomy has to be performed very close to the course of the nerve with an obvious increased risk of neurological complications.44 For these reasons, the authors propose the use of a safe-guided osteotomy performed using a template prepared using a virtual anatomical replica obtained from cone beam computed tomography (CBCT) scan data of the surgical site.
CASE REPORT A 52-year-old systemically healthy male was referred to the Unit of
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Fig. 6. Postoperative orthopantomography of posterior left mandible.
Periodontology and Implantology of the University of Bologna (Italy) requiring a fixed prosthetic rehabilitation of the second premolar and molar zone of the posterior left mandible. A preoperatory CBCT scan was evaluated to plan implant positioning and to establish alveolar residual bone anatomy (Fig. 1). The evaluation of the images obtained showed a mandibular vertical atrophy precluding insertion of implant of adequate length in the second premolar and first molar area (Fig. 2). The coronal defect was horizontal but that bone was not usable and was eliminated during surgery; so, we considered this defect as vertical. Preoperative residual bone heights were: 14.0 mm (6 mm of available bone) above the left mental nerve foramen at section 13 (Fig. 2, A); 10.3 mm (6 mm of available bone) distal to the left mental nerve foramen at section 16 (Fig. 2, B); and 10.9 mm (6 mm of available bone) at section 18 (Fig. 2, C). A monolateral sandwich vertical augmentation procedure was chosen to allow subsequent placement of 2 implants. The patient declined autogenous bone harvesting; and therefore, the use of a cancelous allogenic block plus a mixture of mineralized and demineralized human bone allograft in putty form (Ready Graft Crunch Putty; LifeNet, Virginia, VA) was proposed. Written informed consent was obtained. A surgical template was prepared to guide the horizontal osteotomy in full safety. This template was prepared with CAD-CAM technology using a 3D
virtual anatomical replica (Fig. 3, A). Preoperative CBCT data and optical images obtained by scanning the master cast (Open Technologies, San Zeno Naviglio, Brescia, Italy) were combined by using a DS (Digital Surgery; San Martino Buon Albergo, Verona, Italy) universal fork (Fig. 3, B) worn by the patient during the radiographic examination. The CAD phase provided a virtual design of the surgical template with a cleft made 2 mm coronally and parallel to the course of the alveolar canal (Fig. 3, C). The CAM phase allowed the milling of a polymethyl methacrylate surgical template with the ideal osteotomic line. (Fig. 3, D). After local anesthesia, the procedure began with a paracrestal incision in the buccal aspect (Fig. 4, A). A flap was carefully elevated avoiding tension on the ipsilateral mental nerve, and the surgical template was positioned (Fig. 4, B). No mucoperiosteal dissection is performed toward the alveolar crest or on the lingual side to preserve an adequate blood supply to the bone segment to be osteotomized. Three Piezo surgical inserts (OT8R, OT8L, and OT7; Mectron Piezosurgery Device; Mectron, Carasco, Italy) were used to obtain the pre-established horizontal osteotomy approximately 2 mm above the mandibular canal (Fig. 4, C and D), and 2 additional divergent vertical bone incisions were extended to reach the lingual cortex. The mesial cut was made approximately 2 mm distal to the last tooth in the arch, whereas the distal cut was made in accordance with the implant treatment plan (Fig. 5, A).
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To compensate the vertical defect, a chisel was used to raise the osteotomized segment approximately 5 mm cranially (Fig. 5, B) while maintaining the integrity of the lingual periosteum. An appropriately shaped allogenic cancelous block (Oragraft, LifeNet, VA) was then fitted into the space obtained between the basal bone and the osteotomized segment. The lifted segment was then fixed to the basal bone in this position using 1 titanium miniplate and miniscrews (KLS Martin, Tuttlingen, Germany) (Fig. 5, C). The gaps between the block and the native bone were gently filled by injecting a mixture of mineralized and demineralized allograft in putty form (Ready Graft Crunch Putty; LifeNet). An allogenic membrane, obtained from human dermis (Oracell, LifeNet) was applied above the buccal surface to protect the surgical site (Fig. 5, D). Finally, the flaps were carefully sutured with Vicryl 4.0 (Ethicon FS-2; St-StevensWoluwe, Belgium). The patient was prescribed amoxicillin (Ratiopharm GmbH, Ulm, Germany) and non-steroid anti-inflammatory drugs (NSAIDs) (ketoprofen, Orudis; Aventis Pharma, Bridgewater, NJ) before surgery. The patient was instructed to start the course of antibiotics 2 hours before surgery and to continue it for 6 days. The NSAIDs were taken for 4 days starting at the day of surgery. Postsurgical instructions were a softfood diet for 2 weeks and appropriate oral hygiene with twice daily rinsing with a 0.2% chlorhexidine digluconate mouthwash (Corsodyl; GlaxoSmithKline). The sutures were removed 15 days postoperatively. A panoramic radiograph was performed immediately after surgery (Fig. 6). The patient was clinically checked 1 week after surgery, twice in the first month, and once in each of the subsequent 3 months. No neurosensory disturbances or other complications were recorded.
DISCUSSION Vertical regeneration of the posterior mandible is probably one of the most difficult challenges among all the augmentation techniques. To avoid any regenerative procedure, the use of short implants is a promising alternative.5,45
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The scarcity of comparative studies evaluating the above-mentioned procedures demonstrates that there is no evidence that the results of 1 augmentation procedure clearly surpass those of all other procedures. Esposito et al46 in a recent review on this topic confirmed that bone augmentation is an achievable goal, despite the heavy incidence of failures and complications especially for vertical bone augmentations (.20%).47 Furthermore, the review highlights that all these procedures can show good outcomes and that the choice is entirely in relation to surgeon skill.46 The blocks can be used as “onlay” (appositional technique)16–20 or “inlay” (interpositional technique).21,23 Inlay block grafting augmentations allow postoperative vertical bone gains of 4 to 8 mm29,37,48 with an acceptable complication rate29,47 and reported success outcomes $90%.22,47 Interpositional grafts have the best potential for bone incorporation because the graft is interposed between the basal bone and the osteotomized segment.21 For this reason, osteoblasts from both sides easily colonize the inlay block. Furthermore, the integrity of the lingual periosteum allows optimal blood supply to the graft reducing its resorption.21,26,48 Therefore, surgical differences between the inlay block technique and GBR and onlay block procedures necessitating the elevation of a lingual flap are evident. Inlay grafts guarantee good volume stability and subsequently more predictable results when compared with onlay grafts, which usually require an overcorrection of the defect to compensate expectable bone volume shrinkage.49 In a recent study, Felice et al29 obtained a vertical bone gain of approximately 5 to 6 mm with the inlay block technique and a vertical bone loss of only 1 mm after a 4-month healing period. Survival rates and limited periimplant marginal bone loss after loading22 of implant inserted in areas treated with the “sandwich” technique are comparable with those in native alveolar bone,47 probably because the cranially lifted osteotomized segment is composed entirely of native bone and thus maintains its vitality. Moreover, this technique exhibits
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rapid remodeling and integration of the inlay block using different graft typologies.21–23,35,37,49 This is evidenced by a reduced necessary healing time before implant insertion of only 3 to 4 months of waiting instead of the 5 to 6 months for GBR, with consequent decrease of the time necessary to complete patient care and final rehabilitation.22,35,49 The use of augmentation procedures in the treatment of vertical bone defects entails a number of complications with a failure rate of well above 20%, which is too high to recommend widespread use of such techniques.46,47 Significant atrophy, especially in the posterior mandible, can increase the risk of neurological complications after augmentation procedures because of the superficialization of the inferior alveolar nerve. A significant rate of dysesthesia of the inferior alveolar nerve after inferior alveolar nerve transposition50 and onlay augmentation51 is reported. Similar complications are possible, but very rare, also after interpositional block augmentations21,44 especially when extremely atrophic posterior mandibles are treated. In these cases, when only 5 to 6 mm of residual bone height is available, which is the minimal advisable height for the applicability of the procedure,21 the prerequisite to perform the osteotomy at a safe distance from the mandibular nerve provides mobilization of a thin segment with an increased risk of fracture during its fixation with a surgical plate.22 Therefore, to ensure adequate thickness of the distracted segment, the horizontal osteotomy has to be performed very close to the course of the nerve with an obvious increased risk of possible neurological complications.44 For these reasons, the use of the described template seems to be very helpful because it allows an osteotomy to be performed sufficiently close to the mandibular canal to obtain an optimal thickness of the distracted segment but without increased risk of neurological complications. Moreover, a pre-established and safe planning of the osteotomic incisions reduces surgical times and complications because the operator has presurgically established the minimal safe distance from the nerve avoiding a stressful and consequently slow osteotomic phase.
Autografts are widely considered as the gold standard for their osteogenic, osteoinductive, and osteoconductive properties.18 However, the harvesting of autologous blocks entails significant patient discomfort due to a double surgical site, postoperative morbidity, and complications, including possible nerve damage, gingival recession, edema, loss of tooth vitality, and chin drooping.32 To avoid these problems, the use of allografts42,43 and xenografts22,29 has been suggested. However, histomorphometric evaluations evidenced better results in terms of new vital bone and lower residual graft amounts for allografts when compared with xenografts.52 The comparison between DBBM blocks and autologous blocks harvested from the iliac crest in the inlay technique showed similar clinical and histological outcomes. However, the use of xenogenic blocks resulted preferable due to lower invasiveness.22,29 Moreover, the use of bovine bone blocks is disputable because of their evident friability during shaping and positioning; and in these cases, an insufficient vertical bone gain has also been described.22,29,37 Furthermore,the useof xenografts entailsa slower remodeling process with a high long-term percentage of residual graft.22,53,54 The use of equine xenogenic grafts has also been evaluated but with conflicting outcomes: some with positive results,38 whereas others with an unacceptable failure rate (54.3%).39 In this case report, the authors preferred to use a human cancelous bone block between the coronal osteotomized segment and the basal bone to obtain a better and faster revascularization of the graft from the native bone. A mixture of mineralized allograft and demineralized bone matrix (DBM) in putty form was used to fill residual gaps. This mixed graft could offer additional advantages: the mineralized component is osteoconductive with a relatively slow resorption rate, whereas DBM is considered to have osteoconductive activity in intraoral edentulous sites55 and osteoinductive potential, as demonstrated by new bone formation, when implanted submuscularly in animals.56,57 This combined use of grafts could be useful when considering that DBM seems to induce new bone formation and mineralized allograft acts
IMPLANT DENTISTRY / VOLUME 23, NUMBER 6 2014 as a stable scaffold during remodeling and new bone formation, as demonstrated in sinus elevation and socket preservation procedures.58,59
CONCLUSION With the evident limits of a case report, the optimal clinical outcome and the absence of complications evidence the usefulness of the guided sandwich technique in markedly atrophic mandibles allowing safe osteotomies. Moreover, the use of allogenic grafts avoids the disadvantages related to the use of autologous bone harvesting. This case report is a preliminary assessment before an incoming Randomized Clinical Trial that will confirm or refute potential advantages of this guided modification of the sandwich technique when compared with other regenerative procedures for the treatment of significant vertical atrophies in the posterior mandible.
DISCLOSURE The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.
ACKNOWLEDGMENTS The authors thank Laboratorio Odontotecnico Orisline of Giberti Lorenzo and C Snc (Bologna, Italy) for his valuable technical support.
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Res. 2013;doi: 10.1111/cid.12115. [Epub ahead of print]. 40. Figuelredo M, Henriques J, Martins G, et al. Physicochemical characterization of biomaterials commonly used in dentistry as bone substitutesdComparison with human bone. J Biomed Mater Res B Appl Biomater. 2010;92:409–419. 41. Scarano A, Degidi M, Iezzi G, et al. Maxillary sinus augmentation with different biomaterials: A comparative histologic and histomorphometric study in man. Implant Dent. 2006;15:197–207. 42. Morelli T, Neiva R, Wang HL. Human histology of allogeneic block grafts for alveolar ridge augmentation: Case report. Int J Periodontics Restorative Dent. 2009;29:649–656. 43. Menoni A, Bernardello F, Spinato S, et al. Full-arch vertical reconstruction of an extremely atrophic mandible with “Box Technique”. A novel surgical procedure: A clinical and histological case report. Implant Dent. 2013;22:2–7. 44. Felice P, Checchi V, Pistilli R, et al. Bone augmentation versus 5-mm dental implants in posterior atrophic jaws. Fourmonth post-loading results from a randomized controlled clinical trial. Eur J Oral Implantol. 2009;2:267–281. 45. Felice P, Pistilli R, Piattelli M, et al. Posterior atrophic jaws rehabilitated with prostheses supported by 5 x 5 mm implants with a novel nanostructured calcium-incorporated titanium surface or by longer implants in augmented bone. Preliminary results from a randomized controlled trial. Eur J Oral Implantol. 2012;5: 149–161. 46. Esposito M, Grusovin MG, Felice P, et al. The efficacy of horizontal and vertical bone augmentation procedures for dental implantsdA Cochrane systematic review. Eur J Oral Implantol. 2009;2: 167–184. 47. Bianchi A, Felice P, Lizio G, et al. Alveolar distraction osteogenesis versus inlay bone grafting in posterior mandibular atrophy. A prospective study. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2008;105:282–292. 48. Yeung R. Surgical management of the partially edentulous atrophic mandibular ridge using a modified sandwich osteotomy: A case report. Int J Oral Maxillofac Implants. 2005;20:799–803. 49. Felice P, Pistilli R, Lizio G, et al. Inlay versus onlay iliac bone grafting in
atrophic posterior mandible: A prospective controlled clinical trial for the comparison of two techniques. Clin Implant Dent Relat Res. 2009;11(suppl 1):e69–e82. 50. Ferrigno N, Laureti M, Fanali S. Inferior alveolar nerve transposition in conjunction with implant placement. Int J Oral Maxillofac Implants. 2005;20:610–620. 51. McGrath CJR, Schepers SHW, Blijdorp PA, et al. Simultaneous placement of endosteal implants and mandibular onlay grafting for treatment of the atrophic mandible. Int J Oral Maxillofac Surg. 1996;25:184–188. 52. Froum SJ, Wallace SS, Elian N, et al. Comparison of mineralized cancellous bone allograft and anorganic bovine bone matrix for sinus augmentation: Histomorphometry at 26 to 32 weeks after grafting. Int J Periodontics Restorative Dent. 2006;26:543–551. 53. Simion M, Fontana F, Rasperini G, et al. Vertical ridge augmentation by expanded-polytetrafluoroethylene membrane and a combination of intraoral autogenous bone graft and deproteinized anorganic bovine bone (Bio-Oss). Clin Oral Implant Res. 2007;18:620–629. 54. Traini T, Valentini P, Iezzi G, et al. A histologic and histomorphometric evaluation of anorganic bovine bone retrieved 9 years after a sinus augmentation procedure. J Periodontol. 2007;78:955–961. 55. Cammack GV, Nevins M, Clem DS, et al. Histologic evaluation of mineralized and demineralized freezedried bone allograft for ridge and sinus augmentation. Int J Periodontics Restorative Dent. 2005;25:231–237. 56. Urist MR. Bone: Formation by autoinduction. Science. 1965;150:893–899. 57. Zhang M, Powers RM Jr, Wolfinbarger L. A quantitative assessment of osteoinductivity of human demineralized bone matrix. J Periodontol. 1997;68: 1076–1084. 58. Kim DM, Nevins ML, Camelo M, et al. The efficacy of demineralized bone matrix and cancellous bone chips for maxillary sinus augmentation. Int J Periodontics Restorative Dent. 2009;29: 415–423. 59. Spinato S, Galindo-Moreno P, Zaffe D, et al. Is socket healing conditioned by buccal plate thickness? A clinical and histologic study 4 months after mineralized human bone allografting. Clin Oral Implants Res. 2014;25:e120–e126.
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Guided “Sandwich” Technique: A Novel Surgical Approach for Safe Osteotomies in the Treatment of Vertical Bone Defects in the Posterior Atrophic Mandible: A Case Report Pietro Felice, MD, DDS, PhD,* Carlo Barausse, DDS,* Roberto Pistilli, MD, DDS, PhD,† Sergio Spinato, DDS, PhD,* and Fabio Bernardello, MD, DDS‡
he demand for implant-supported rehabilitation is increasing as more patients desire fixed restorations to replace a missing dentition. Correct implant treatment planning has therefore become an essential part of the prosthetic reconstruction of the lost dentition.1 A fixed implant-supported prosthesis is an established procedure to treat edentulous jaws if adequate bone volume is available.2 Unfortunately, ridge reabsorption is a physiological process after tooth loss frequently resulting in a horizontally and vertically deficient ridge.3,4 Such unavoidable bone remodeling, particularly in the posterior mandible, can make the insertion of dental implants of adequate length impossible or difficult, due to anatomical limitations caused by superficialization of the alveolar nerve.5 The augmentation of these areas is a challenging procedure and often a prerequisite to create sufficient bone volume for ideal
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*Unit of Periodontology and Implantology, Dental School, University of Bologna, Bologna, Italy. †Oral and Maxillofacial Department, A.C.O. San Filippo Neri, Rome, Italy. ‡Private practice, Terranegra di Legnago, Verona, Italy.
Reprint requests and correspondence to: Fabio Bernardello, MD, DDS, Via F. Bonvicini 42, Terranegra di Legnago, Verona 37040, Italy, Phone: 0039-0442-24711, Fax: 0039-0442-24711, E-mail: [email protected] ISSN 1056-6163/14/02306-738 Implant Dentistry Volume 23 Number 6 Copyright © 2014 by Lippincott Williams & Wilkins DOI: 10.1097/ID.0000000000000168
Purpose: A novel technique to perform safe osteotomies during inlay block regenerative procedures in the posterior atrophic mandible is described. Material and Methods: A 52year-old male patient with vertical atrophy of the left posterior mandible was treated adopting an inlay block “sandwich” technique using an allogenic cancelous block and a mixture of mineralized and demineralized human bone allograft in putty form as graft. The horizontal osteotomy for the lifting of the osteotomized bone segment was performed using a template prepared from a virtual anatomical replica of the patient’s mandible obtained from cone beam computed tomography data. In the second surgical phase, 3 months after the augmentation, 2 implants were easily placed.
Results: The horizontal osteotomy was carried out, with no risk, very close to the nerve structures after the precise osteotomy line established preoperatively on the three-dimensional computed tomography (3D-CT) virtual reconstruction. No neurological complications were observed in the first days after the procedure, and no subsequent problems were recorded during the 3-month healing period. Conclusion: Radiographic evaluations and complication-free clinical healing demonstrate the effectiveness of this technique to obtain safe and precise osteotomies. (Implant Dent 2014;23:738–744) Key Words: vertical regeneration, human allograft, inlay bone graft, mandibular atrophy, safe osteotomy, surgical template
implant placement because implants have to be placed in a prosthetically driven position to achieve long-term stability, function, and esthetic results.6–8 Various bone augmentation procedures, such as guided bone regeneration (GBR) generally using nonreabsorbable membranes9,10 or titanium meshes11,12 and alveolar distraction osteogenesis13,14 have
been developed and are widely used for vertical augmentations. However, when treating severely resorbed ridges, the use of block grafts is preferred.15,16 Block grafts can be used in the performance of both “onlay” (appositional)17–20 or “inlay” (interpositional) techniques.21–23 One well-established procedure for the augmentation of extremely
IMPLANT DENTISTRY / VOLUME 23, NUMBER 6 2014 atrophic mandibles is the “sandwich” osteotomic technique, initially proposed by Schettler et al24 in 1976 for the correction of anterior areas, but recently applied to the posterior atrophic mandible with positive outcomes.21,23 The procedure consists of the interposition, that is, inlay of a bone block graft in the space obtained after coronally raising the cranial osteotomized segment of the mandible. The lifted bone segment remains connected to the lingual periosteum, ensuring adequate blood supply for the remodeling of the inlay graft25,26 and is fixed to the basal bone with a rigid fixation using 2.0-mm miniplates.26 Different block grafts can be used in regenerative procedures: autogenic,18 allogenic,16,17,27 or xenogenic.22,28,29 Autogenic blocks have always been considered the gold standard material for their osteogenic, osteoinductive, and osteoconductive properties.18 However, if harvested from intraoral donor sites, as the chin and mandibular ramus, autologous bone is available in limited quantities30 and a significant morbidity (ie, edema, infection, paresthesia, loss of muscle tone, loss of tooth vitality, and gingival recession) is reported.30–32 Autogenic blocks can also be obtained from extraoral sites such as the iliac crest22,29 but high costs33 and significant morbidity, that is, transitory claudication34 of the donor site have to be taken into account. Therefore, to counteract these limitations associated with the use of autogenic blocks, grafts of different nature have been developed and used.5,16,22,27–29,35,36 In a recent study, Felice et al22 compared the use of deproteinized bovine bone mineral (DBBM) blocks versus autologous bone blocks harvested from the iliac crest in the sandwich technique. Clinical and histological results overlapped, however, the use of xenogenic blocks proved to be less invasive and therefore preferable.29 However, the use of bovine bone blocks is challenged by their extreme friability comporting considerable risk of breakage during shaping and positioning. In these cases, an insufficient vertical bone gain has been observed.22,29,37 The use of different equine xenogenic blocks showed contrasting outcomes, with some
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Fig. 1. Preoperative CBCT image of posterior left mandible.
Fig. 2. CBCT cross sections revealing a severe crestal atrophy. A, At section 13, 14 mm (6 mm of available bone) above mental nerve foramen are evident. B, At section 16, 10.3 mm (6 mm of available bone) above nerve canal are evident. C, At section 18, 10.9 mm (6 mm of available bone) above nerve canal are evident.
Fig. 3. Surgical template realization. A, 3D virtual anatomical replica. B, Universal fork worn during the radiographic examination. C, CAD phase with the virtual design of the osteotomic line reveals a distance of 2 mm coronally and parallel to the course of the alveolar canal. D, CAM phase: creation of a PMMA surgical template obtained by milling.
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Fig. 4. A, Paracrestal incision in the buccal aspect. B, A flap was carefully elevated, and the surgical template was positioned. C and D, The horizontal osteotomy was performed using the surgical template.
Fig. 5. A, Vertical osteotomies. B, The osteotomized segment was raised 5 mm coronally. C, The allograft block was positioned in the space obtained, and the lifted segment was then fixed to the basal bone in this position using 1 titanium miniplate and 2 miniscrews. D, An allogenic membrane was applied to protect the surgical site.
encouraging results38 but also with unacceptable failure rate (54.3%).39 Moreover, the use of xenografts has been
associated with the persistence of a high percentage of residual graft due to a slow remodeling process.10,22
Considering these disadvantages and limitations associated with autogenic and xenogenic blocks, new materials, which could ideally integrate with the surrounding bone in a physiological time40 and remodel into highly vital new bone with minimal residual graft have been evaluated. Allogenic grafts seem to be the materials with these optimal characteristics.41 Allografts are bone-derived grafts obtained by processing and sterilization of human bone harvested from donors. These materials are safe easily storable, and their use in the treatment of vertical and horizontal atrophies is widely described.17,27,42,43 The sandwich technique requires the execution of a horizontal osteotomy performed parallel to the inferior alveolar nerve. Given that this technique is often applied in very atrophic posterior mandibles, sometimes with only 5 to 6 mm of residual vertical bone, the distracted segment could result thin because the osteotomy has to be performed coronally and at a safe distance from the alveolar nerve. In these markedly atrophic situations, the risk of fracture of the thin osteotomized segment during fixation with a surgical plate is real and described.22 Therefore, it is always fundamental to guarantee an adequate thickness of the segment to be raised. Consequently, it is advisable to apply the procedure in ridges with bone height $6 mm above the mandibular canal to ensure adequate thickness of the coronally distracted segment and sufficient clearance of the inferior alveolar nerve.21 However, in very atrophic cases to obtain this fundamental prerequisite, the horizontal osteotomy has to be performed very close to the course of the nerve with an obvious increased risk of neurological complications.44 For these reasons, the authors propose the use of a safe-guided osteotomy performed using a template prepared using a virtual anatomical replica obtained from cone beam computed tomography (CBCT) scan data of the surgical site.
CASE REPORT A 52-year-old systemically healthy male was referred to the Unit of
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Fig. 6. Postoperative orthopantomography of posterior left mandible.
Periodontology and Implantology of the University of Bologna (Italy) requiring a fixed prosthetic rehabilitation of the second premolar and molar zone of the posterior left mandible. A preoperatory CBCT scan was evaluated to plan implant positioning and to establish alveolar residual bone anatomy (Fig. 1). The evaluation of the images obtained showed a mandibular vertical atrophy precluding insertion of implant of adequate length in the second premolar and first molar area (Fig. 2). The coronal defect was horizontal but that bone was not usable and was eliminated during surgery; so, we considered this defect as vertical. Preoperative residual bone heights were: 14.0 mm (6 mm of available bone) above the left mental nerve foramen at section 13 (Fig. 2, A); 10.3 mm (6 mm of available bone) distal to the left mental nerve foramen at section 16 (Fig. 2, B); and 10.9 mm (6 mm of available bone) at section 18 (Fig. 2, C). A monolateral sandwich vertical augmentation procedure was chosen to allow subsequent placement of 2 implants. The patient declined autogenous bone harvesting; and therefore, the use of a cancelous allogenic block plus a mixture of mineralized and demineralized human bone allograft in putty form (Ready Graft Crunch Putty; LifeNet, Virginia, VA) was proposed. Written informed consent was obtained. A surgical template was prepared to guide the horizontal osteotomy in full safety. This template was prepared with CAD-CAM technology using a 3D
virtual anatomical replica (Fig. 3, A). Preoperative CBCT data and optical images obtained by scanning the master cast (Open Technologies, San Zeno Naviglio, Brescia, Italy) were combined by using a DS (Digital Surgery; San Martino Buon Albergo, Verona, Italy) universal fork (Fig. 3, B) worn by the patient during the radiographic examination. The CAD phase provided a virtual design of the surgical template with a cleft made 2 mm coronally and parallel to the course of the alveolar canal (Fig. 3, C). The CAM phase allowed the milling of a polymethyl methacrylate surgical template with the ideal osteotomic line. (Fig. 3, D). After local anesthesia, the procedure began with a paracrestal incision in the buccal aspect (Fig. 4, A). A flap was carefully elevated avoiding tension on the ipsilateral mental nerve, and the surgical template was positioned (Fig. 4, B). No mucoperiosteal dissection is performed toward the alveolar crest or on the lingual side to preserve an adequate blood supply to the bone segment to be osteotomized. Three Piezo surgical inserts (OT8R, OT8L, and OT7; Mectron Piezosurgery Device; Mectron, Carasco, Italy) were used to obtain the pre-established horizontal osteotomy approximately 2 mm above the mandibular canal (Fig. 4, C and D), and 2 additional divergent vertical bone incisions were extended to reach the lingual cortex. The mesial cut was made approximately 2 mm distal to the last tooth in the arch, whereas the distal cut was made in accordance with the implant treatment plan (Fig. 5, A).
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To compensate the vertical defect, a chisel was used to raise the osteotomized segment approximately 5 mm cranially (Fig. 5, B) while maintaining the integrity of the lingual periosteum. An appropriately shaped allogenic cancelous block (Oragraft, LifeNet, VA) was then fitted into the space obtained between the basal bone and the osteotomized segment. The lifted segment was then fixed to the basal bone in this position using 1 titanium miniplate and miniscrews (KLS Martin, Tuttlingen, Germany) (Fig. 5, C). The gaps between the block and the native bone were gently filled by injecting a mixture of mineralized and demineralized allograft in putty form (Ready Graft Crunch Putty; LifeNet). An allogenic membrane, obtained from human dermis (Oracell, LifeNet) was applied above the buccal surface to protect the surgical site (Fig. 5, D). Finally, the flaps were carefully sutured with Vicryl 4.0 (Ethicon FS-2; St-StevensWoluwe, Belgium). The patient was prescribed amoxicillin (Ratiopharm GmbH, Ulm, Germany) and non-steroid anti-inflammatory drugs (NSAIDs) (ketoprofen, Orudis; Aventis Pharma, Bridgewater, NJ) before surgery. The patient was instructed to start the course of antibiotics 2 hours before surgery and to continue it for 6 days. The NSAIDs were taken for 4 days starting at the day of surgery. Postsurgical instructions were a softfood diet for 2 weeks and appropriate oral hygiene with twice daily rinsing with a 0.2% chlorhexidine digluconate mouthwash (Corsodyl; GlaxoSmithKline). The sutures were removed 15 days postoperatively. A panoramic radiograph was performed immediately after surgery (Fig. 6). The patient was clinically checked 1 week after surgery, twice in the first month, and once in each of the subsequent 3 months. No neurosensory disturbances or other complications were recorded.
DISCUSSION Vertical regeneration of the posterior mandible is probably one of the most difficult challenges among all the augmentation techniques. To avoid any regenerative procedure, the use of short implants is a promising alternative.5,45
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The scarcity of comparative studies evaluating the above-mentioned procedures demonstrates that there is no evidence that the results of 1 augmentation procedure clearly surpass those of all other procedures. Esposito et al46 in a recent review on this topic confirmed that bone augmentation is an achievable goal, despite the heavy incidence of failures and complications especially for vertical bone augmentations (.20%).47 Furthermore, the review highlights that all these procedures can show good outcomes and that the choice is entirely in relation to surgeon skill.46 The blocks can be used as “onlay” (appositional technique)16–20 or “inlay” (interpositional technique).21,23 Inlay block grafting augmentations allow postoperative vertical bone gains of 4 to 8 mm29,37,48 with an acceptable complication rate29,47 and reported success outcomes $90%.22,47 Interpositional grafts have the best potential for bone incorporation because the graft is interposed between the basal bone and the osteotomized segment.21 For this reason, osteoblasts from both sides easily colonize the inlay block. Furthermore, the integrity of the lingual periosteum allows optimal blood supply to the graft reducing its resorption.21,26,48 Therefore, surgical differences between the inlay block technique and GBR and onlay block procedures necessitating the elevation of a lingual flap are evident. Inlay grafts guarantee good volume stability and subsequently more predictable results when compared with onlay grafts, which usually require an overcorrection of the defect to compensate expectable bone volume shrinkage.49 In a recent study, Felice et al29 obtained a vertical bone gain of approximately 5 to 6 mm with the inlay block technique and a vertical bone loss of only 1 mm after a 4-month healing period. Survival rates and limited periimplant marginal bone loss after loading22 of implant inserted in areas treated with the “sandwich” technique are comparable with those in native alveolar bone,47 probably because the cranially lifted osteotomized segment is composed entirely of native bone and thus maintains its vitality. Moreover, this technique exhibits
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rapid remodeling and integration of the inlay block using different graft typologies.21–23,35,37,49 This is evidenced by a reduced necessary healing time before implant insertion of only 3 to 4 months of waiting instead of the 5 to 6 months for GBR, with consequent decrease of the time necessary to complete patient care and final rehabilitation.22,35,49 The use of augmentation procedures in the treatment of vertical bone defects entails a number of complications with a failure rate of well above 20%, which is too high to recommend widespread use of such techniques.46,47 Significant atrophy, especially in the posterior mandible, can increase the risk of neurological complications after augmentation procedures because of the superficialization of the inferior alveolar nerve. A significant rate of dysesthesia of the inferior alveolar nerve after inferior alveolar nerve transposition50 and onlay augmentation51 is reported. Similar complications are possible, but very rare, also after interpositional block augmentations21,44 especially when extremely atrophic posterior mandibles are treated. In these cases, when only 5 to 6 mm of residual bone height is available, which is the minimal advisable height for the applicability of the procedure,21 the prerequisite to perform the osteotomy at a safe distance from the mandibular nerve provides mobilization of a thin segment with an increased risk of fracture during its fixation with a surgical plate.22 Therefore, to ensure adequate thickness of the distracted segment, the horizontal osteotomy has to be performed very close to the course of the nerve with an obvious increased risk of possible neurological complications.44 For these reasons, the use of the described template seems to be very helpful because it allows an osteotomy to be performed sufficiently close to the mandibular canal to obtain an optimal thickness of the distracted segment but without increased risk of neurological complications. Moreover, a pre-established and safe planning of the osteotomic incisions reduces surgical times and complications because the operator has presurgically established the minimal safe distance from the nerve avoiding a stressful and consequently slow osteotomic phase.
Autografts are widely considered as the gold standard for their osteogenic, osteoinductive, and osteoconductive properties.18 However, the harvesting of autologous blocks entails significant patient discomfort due to a double surgical site, postoperative morbidity, and complications, including possible nerve damage, gingival recession, edema, loss of tooth vitality, and chin drooping.32 To avoid these problems, the use of allografts42,43 and xenografts22,29 has been suggested. However, histomorphometric evaluations evidenced better results in terms of new vital bone and lower residual graft amounts for allografts when compared with xenografts.52 The comparison between DBBM blocks and autologous blocks harvested from the iliac crest in the inlay technique showed similar clinical and histological outcomes. However, the use of xenogenic blocks resulted preferable due to lower invasiveness.22,29 Moreover, the use of bovine bone blocks is disputable because of their evident friability during shaping and positioning; and in these cases, an insufficient vertical bone gain has also been described.22,29,37 Furthermore,the useof xenografts entailsa slower remodeling process with a high long-term percentage of residual graft.22,53,54 The use of equine xenogenic grafts has also been evaluated but with conflicting outcomes: some with positive results,38 whereas others with an unacceptable failure rate (54.3%).39 In this case report, the authors preferred to use a human cancelous bone block between the coronal osteotomized segment and the basal bone to obtain a better and faster revascularization of the graft from the native bone. A mixture of mineralized allograft and demineralized bone matrix (DBM) in putty form was used to fill residual gaps. This mixed graft could offer additional advantages: the mineralized component is osteoconductive with a relatively slow resorption rate, whereas DBM is considered to have osteoconductive activity in intraoral edentulous sites55 and osteoinductive potential, as demonstrated by new bone formation, when implanted submuscularly in animals.56,57 This combined use of grafts could be useful when considering that DBM seems to induce new bone formation and mineralized allograft acts
IMPLANT DENTISTRY / VOLUME 23, NUMBER 6 2014 as a stable scaffold during remodeling and new bone formation, as demonstrated in sinus elevation and socket preservation procedures.58,59
CONCLUSION With the evident limits of a case report, the optimal clinical outcome and the absence of complications evidence the usefulness of the guided sandwich technique in markedly atrophic mandibles allowing safe osteotomies. Moreover, the use of allogenic grafts avoids the disadvantages related to the use of autologous bone harvesting. This case report is a preliminary assessment before an incoming Randomized Clinical Trial that will confirm or refute potential advantages of this guided modification of the sandwich technique when compared with other regenerative procedures for the treatment of significant vertical atrophies in the posterior mandible.
DISCLOSURE The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.
ACKNOWLEDGMENTS The authors thank Laboratorio Odontotecnico Orisline of Giberti Lorenzo and C Snc (Bologna, Italy) for his valuable technical support.
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