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Overcorrection in vertical alveolar distraction osteogenesis for dental implants
Int. J. Oral Maxillofac. Surg. 2007; 36: 398–402 doi:10.1016/j.ijom.2006.11.009, available online at http://www.sciencedirect.com
Clinical Paper Pre-Implant Surgery
Overcorrection in vertical alveolar distraction osteogenesis for dental implants
T. Kanno1, M. Mitsugi1, Y. Furuki1, M. Hosoe1, H. Akamatsu2, T. Takenobu3 1 Division of Oral and Maxillofacial Surgery, Kagawa Prefectural Central Hospital, Kagawa, Japan; 2Dental Office Akamatsu, Kagawa, Japan; 3Department of Dentistry and Maxillofacial Surgery, Kobe City General Hospital, Kobe, Hyogo, Japan
T. Kanno, M. Mitsugi, Y. Furuki, M. Hosoe, H. Akamatsu, T. Takenobu: Overcorrection in vertical alveolar distraction osteogenesis for dental implants. Int. J. Oral Maxillofac. Surg. 2007; 36: 398–402. # 2006 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. Abstract. A decrease in bone height following alveolar distraction osteogenesis (DO) before implant placement is common, and can be severe when alveolar DO is performed soon after surgical intervention. The aim of this study was to investigate the decrease in bone height after vertical alveolar DO and determine the need for overcorrection with implant placement. Thirty-five patients (17 males and 18 females, mean age 43.9 years) underwent 38 procedures with successful placement of 141 dental implants. Alveolar ridge height was evaluated using digital orthopantomographic radiographs taken shortly after the end of distraction, at consolidation and before implant placement. The mean distraction was 9.7 mm. The total vertical alveolar bone decrease was 2.1 mm (21%) during the consolidation period and 3.6 mm (37%) at implant placement. Although the 20 sites with a healthy alveolus (surgery >6 months) had bone reductions of 1.5 and 2.5 mm (15 and 25%) the 18 sites at which alveolar DO was performed within 6 months (mean 3.0) of surgical intervention had much greater bone loss of 2.7 and 4.8 mm (28 and 50%), respectively (**P < 0.01). These results indicate that any alveolar DO protocol should include a waiting period after the surgical intervention, as well as consider an overcorrection of more than 25% within the limits of the applied surgical protocol.
One of the most common problems with oral implants is that of insufficient bone height. This is often a contraindication for implant placement and implies that the ratio of crown to implant length is too great, a factor that will probably reduce not only the useful lifespan of the implant from the perspective of biomechanical functional but also the aesthetic outcome 4,13. 0901-5027/050398 + 05 $30.00/0
Recently, a useful tissue-engineering technique that allows the height of the alveolar ridge to be increased effectively has gained increasing acceptance, namely alveolar distraction osteogenesis (DO) 9,12 . The concept, originally described by Ilizarov 7, has been applied with predictable results to the alveolar ridge to improve the treatment of bony and soft-
Keywords: alveolar distraction osteogenesis; stability; overcorrection. Accepted for publication 17 November 2006 Available online 28 February 2007
tissue defects in oral and maxillofacial surgery and implantology without major complications 3,5. Some of the advantages of this technique are its predictability, elimination of a donor site for autogenous grafts, and bone and soft-tissue regeneration 1,16. A number of studies strongly support the success of this clinical procedure 1,3,11,12. The long-term prognosis of
# 2006 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Overcorrection in vertical alveolar distraction osteogenesis for dental implants
399
Fig. 1. A 17-year-old male underwent vertical alveolar DO at the right maxillary canine and first premolar for implant placement 2 months after alveolar trauma. Intraoral photos and orthopanoramic radiographs. (a) Sufficient overcorrection to the maximum of the distractor was obtained by the end of the distraction activation period. (b) A decrease in bone height was observed 3 months after the end of the consolidation period (before distractor removal), and (c) a further bone decrease was observed after 1 month of soft tissue healing at successful implant placement.
the alveolar bone gain for implants seems to be more predictable than with conventional procedures 2. For more than 6 years and in more than 60 cases, alveolar DO using the Tracktype alveolar distractor (KLS Martin, Tuttlingen, Germany) has been performed in the authors’ hospital for implant placement. Although the prognosis seems to be well established, the relapse or bone decrease is sometimes marked. In some cases, there is a surprising amount of bony relapse at the time of implant placement after removing the distractor, despite successful placement of the dental implants (Fig. 1). Only a few clinical reports have mentioned the possibility of bony relapse following DO in the maxillofacial and alveolar regions 1,17,19. It has been suggested that overcorrection might be beneficial. SAULACIC et al.16 presented the results of 14 cases in which 20% overcorrection was included in alveolar DO using an intraosseous distractor (LEAD system, Stryker Leibinger, Kalamazoo, MI, USA) for implant placement 17, but there have been no other reports on the necessity of overcorrection or its indications. When alveolar DO is performed for implants soon after a surgical intervention there may a greater risk of relapse as compared to distraction performed on a stable, healthy alveolar ridge (Fig. 1). The aim of this study was to investigate and
clarify the indications for overcorrection and the predictability of implant placement.
Materials and methods Patients
There were 38 alveolar sites selected in 35 systemically healthy patients (17 males, 18 females; age range 17–65 years, mean 43.9) who were surgically corrected for vertical alveolar ridge defects for implantborne prostheses, along with the appropriate follow-up data. In three patients, distraction was performed in both the maxilla and mandible. They all underwent the same surgical procedure for alveolar
DO using the same type of distractor and following the protocol described below, after giving informed consent (Fig. 2). Of the 35 patients, the alveolar bone subject to DO was considered healthy at 20 sites (10 maxillary and 10 mandibular vertical alveolar DO) in 19 patients (Group A) who had not required any surgical intervention less than 6 months before DO. The other 18 sites (9 maxillary and 9 mandibular vertical alveolar DO) in 16 patients (8 males and 8 females) (Group B) had undergone some surgical intervention, such as tooth extraction, the removal of a failed implant, alveolar bone fracture or tooth avulsion due to alveolar trauma, less than 6 months prior to DO (range 0.8–5.5 months; mean 3.0).
Fig. 2. Treatment protocol for alveolar DO and implant placement.
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Kanno et al.
Surgical technique and protocol
In all patients, we used Track-type distractors (KLS Martin), following the original surgical procedure described by HIDDING & ZOLLER 8,14. With a paramarginal incision under local anaesthesia with intravenous sedation, a vestibular mucoperiosteal flap was raised, leaving the mucoperiosteum adhering to the lingual bone. The Tracktype vertical alveolar distractor was fitted and placed in the transport segment following vertical and horizontal osteotomies using a micro bone saw and chisel. The distractor was activated during surgery, and the mobility of the transport segment was confirmed. After the segments were deactivated to the original positions, the incisions were closed with 4-0 Vicryl. After a latent period of 10 days, distraction was started at an average rate of 0.4 mm (0.3 mm for Track 1.0 distractors and 0.5 mm for Track 1.5 distractors) every 12 h. On the second day, the patients began to activate the distractor following verbal and written instructions. The number of activations performed by the patients depended on the required amount of vertical movement, which was often as much as possible, for each individual case. Once this had been achieved, the distractor was left in place for 3 months to ensure bony consolidation and then it was removed to allow implant insertion. A total of 141 dental implants were placed 1 month after removing the distractor, to allow time for soft-tissue healing, as shown in the protocol in (Fig. 2).
at the midpoint of each inserted implant, and the average distance was calculated as the height obtained by alveolar DO. The amount of distraction was calculated as the distance of the distraction gap at T2. The rate of bone relapse, i.e. the bone decrease, was calculated as the ratio of the vertical bone decrease (T2 to T1 and T3 to T1) to the amount of alveolar DO based on the distraction gap. Statistical analysis
The significance of differences was determined using Student’s t-test. Data are expressed as the mean SEM. Statistical significance was defined as P < 0.05 and P < 0.01.
Results
For the 38 cases appraised, the mean bone augmentation was 9.7 mm (range 5.1– 14.8 mm) (Fig. 3). The length of distraction obtained in Groups A and B was 9.9 mm (range 5.1–14.7 mm) and 9.5 mm (range 6.4–14.8 mm), respectively (Fig. 3). The difference in bone augmentation between the two groups was not statistically significant (P > 0.05). Following a 3-month period of consolidation (T2), the alveolar bone height obtained by distraction decreased to 79% (range 49–99%) of the amount at the end of distraction (T1) for all cases (Fig. 4). The mean amount of bony relapse during the consolidation period at the
Fig. 3. The length of distraction obtained (NS: not statistically significant; P > 0.05).
Bone height evaluation
Computed tomography (CT) (Siemens, Somatom AR SP, Erlangen, Germany) was performed preoperatively, and four digital orthopanoramic radiographs were obtained postoperatively for radiographic evaluation at the end of the activation period (T1), 3 months after the end of the consolidation period (before distractor removal) (T2), 4 weeks after distractor removal (before implant placement) (T3) and after implant placement (T4). The augmented bone was measured on the panoramic radiographs. For this evaluation, the magnification factor of each radiograph was determined and corrected by dividing the real size of the activation rod by the image size of the activation rod, as described previously 12. The evaluation points were first located in the middle of each inserted implant using the T4 radiographs. The bone height was measured as the distance from the osteotomy line in the basal bone to the top of the alveolar crest
Fig. 4. The rate of bone decrease or bony relapse during the 3-month consolidation period before distractor removal and an additional month of soft-tissue healing after distractor removal and prior to implant placement. The rate of bone decrease was calculated as the ratio of the vertical bone decrease to the amount of alveolar DO based on the distraction gap. Total 38 alveolar sites; Group A: healthy alveolus, surgical intervention >6 months before DO (20 alveolar sites); Group B: surgical intervention <6 months prior to DO (18 alveolar sites). ** Statistically significant: P < 0.001.
Overcorrection in vertical alveolar distraction osteogenesis for dental implants central aspect of the implants was 2.1 mm (range 0.2–4.4 mm). The decrease in Groups A and B was 85% (range 55– 99%) or 1.5 mm (range 0.2–3.7 mm) versus 72% (range 48–89%) or 2.7 mm (range 1.0–4.4 mm), respectively (Fig. 4). The difference in relapse during the consolidation period in the two groups was statistically significant (P < 0.01) (Fig. 4). After allowing 1 month for soft-tissue healing before implant placement (T3), the vertical height of the bone decreased further to 63% (range 20–98%), as compared to that at the end of distraction (T1) for all cases (Fig. 4). The mean bony relapse at the time of implant placement at the central aspect of each implant was 3.6 mm (range 0.3–7.0 mm) in relation to the vertical alveolar bone height immediately after the end of bone augmentation. While Group A maintained a height of 75% (range 33–98%) or a 2.4 mm (range 0.3–6.0 mm) decrease compared to the vertically distracted bone height at the end of distraction, there was a greater change in Group B, with a height of 50% (range 20–86%) and a 4.8 mm (range 1.3–7.0 mm) decrease (Fig. 4). The differences in relapse at the time of implant placement between the two groups were statistically significant (P < 0.001) (Fig. 4). Discussion
Alveolar DO is an attractive option for increasing the amount of alveolar bone and surrounding tissues in patients requiring dental implants. DO has the potential for almost unlimited new bone formation between osteomized gaps with no need for bone harvesting, which avoids donor-site morbidity 1,15. As in the case of the alveolar and maxillofacial regions, the protocol for vertical alveolar DO was based on results found in long bones, with insufficient data regarding predictability for implant placement 7,15. The success of bone regeneration has been well documented and was further supported in this study, but there have been a few reports of relapse in bone height following distraction during the consolidation period, and this will inevitably affect functional implant stability 1,16,17,19. In the present study, some degree of bone decrease was observed in all cases, but the relapse was more marked than in previous reports 1,9,17. A major reason for this could have been the time assigned to the two groups (A and B). When alveolar vertical DO was performed within 6 months (mean 3.0) of surgery (Group B), there was significantly more relapse
(28% or 2.7 mm) during the 3-month consolidation period and 50% (4.8 mm) after 1-month soft-tissue healing for implant placement after distractor removal, as compared to Group A (15% (1.5 mm) and 24% (2.4 mm), respectively), as shown in (Fig. 4). Much accumulated data show that the restoration of alveolar and craniofacial bone in adults requires about 6 months with healthy bone metabolism and remodelling 10,18. Groups A and B both followed this basic protocol (Fig. 2), yet the difference between the groups was statistically significant (Fig. 4). Another reason for the degree of relapse may have been that the amount of vertical augmentation (mean 9.7 mm) was nearly 1.5 times more than in previous reports (Fig. 3) 2,9,17 . This was due to overcorrection of the transport segment, not only to regenerate bone and soft tissue but also to prevent lingual inclination of the distraction vector in most cases 8,12. Using this protocol, there has been no experience of fatal wound dehiscence or major complications. In fact, given the amount of overcorrection, and considering the subsequent decrease in bone vertically and horizontally, the implants were successfully placed with no complications, given sufficient bone and soft tissue (Fig. 1). This surgical protocol (Fig. 2), allowing 3 months for consolidation and another month for soft-tissue healing, was similar to reported protocols and made sense in terms of the regeneration of bone and tissue management for implant placement 2,4,12 . It is likely that the amount of vertical bone decrease seen in this study includes resorption of the transport segment, dislocation, incorrect inclination of the distracted segment due to difficulty in vector control and plate deformation resulting from mucoperiosteal tension stress. Since the difference between Groups A and B was statistically significant (Fig. 4), the main reason for the vertical bone decrease at well augmented alveolar sites was likely active resorption of the transport segments during the distraction and consolidation periods. Regarding measures to ameliorate bone decrease after sufficient overcorrection, as reported here, improvement of the distractor itself might be necessary in order to maintain the distracted transport segment at the desired position during the consolidation period and prevent the wrong directional inclination, including the possibility of distraction rod removal to bury it6,16. Although the application of other hardware, such as osteosynthesis plates or screws, to stabilize the distracted seg-
401
ments might be an alternative, this could have a negative effect on bone and softtissue regeneration, in addition to requiring further surgery 11. Modification of the surgical protocol, such as implant placement simultaneous to or immediately after distractor removal, might reduce bone decrease in the pre-implant period, but more unpredictable marginal bone loss around the implants followed by deeper installation could occur due to the larger mucoperiosteum incision and reflection to obtain simultaneous access for distractor removal on the lateral side and implant placement, as previously described 11,17. Further clinical studies are necessary to increase the predictability of the regenerative outcome of alveolar DO using appropriate protocols for implant placement. Some previous studies have shown that overcorrection could be useful and effective for various implants and for preventing bone relapse with alveolar DO 5,11,15,17 . From the present results, if a vertical alveolar DO is planned within 6 months of surgery, such as for tooth extraction or alveolar trauma, there should be sufficient overcorrection to compensate for a bone relapse of up to 50%. Given that even healthy alveolar sites showed nearly 25% relapse at the time of implant placement following vertical alveolar DO, it is recommended that the alveolar bone augmentation be performed more than 6 months after any surgery, with sufficient overcorrection. While some instability was noted in terms of alveolar DO, sufficient overcorrection should solve this problem and eliminate any functional problems regarding dental implant placement. CHIAPASCO et al.1 and others have shown that alveolar DO is a reliable technique that does not incur major complications such as infection, and has better long-term prognosis and stability, especially after implant placement, than the conventional guided bone regeneration and bone transplantation techniques 2,4,5,16,19. References 1. Chiapasco M, Consolo U, Bianchi A, Ronchi P. Alveolar distraction osteogenesis for the correction of vertically deficient edentulous ridges: a multicenter prospective study on humans. Int J Oral Maxillofac Implants 2004: 19: 399–407. 2. Chiapasco M, Romeo E, Casentini P, Rimondini L. Alveolar distraction osteogenesis vs. vertical guided bone regeneration for the correction of vertically deficient edentulous ridges: a 1–3-year prospective study on humans. Clin Oral Implants Res 2004: 15: 82–95.
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3. Chin M. Distraction osteogenesis for dental implants. Atlas Oral Maxillofac Surg Clin North Am 1999: 7: 41–63. 4. Garcia-Garcia A, Somoza-Martin M, Gandara-Vila P, Saulacic N, Gandara-Rey JM. Alveolar distraction before insertion of dental implants in the posterior mandible. Br J Oral Maxillofac Surg 2003: 41: 376–379. 5. Hidding J, Lazar F, Zoller JE. Initial outcome of vertical distraction osteogenesis of the atrophic alveolar ridge. Mund Kiefer Gesichtschir 1999: 3(Suppl. 1):79–83. 6. Iizuka T, Hallermann W, Seto I, Smolka W, Smolka K, Bosshardt DD. Bi-directional distraction osteogenesis of the alveolar bone using an extraosseous device. Clin Oral Implants Res 2005: 16: 700–707. 7. Ilizarov GA. Clinical application of the tension-stress effect for limb lengthening. Clin Orthop Relat Res 1990: 250: 8–26. 8. Jahangiri L, Devlin H, Ting K, Nishimura I. Current perspectives in residual ridge remodeling and its clinical implications: a review. J Prosthet Dent 1998: 80: 224–237. 9. Jensen OT, Cockrell R, Kuhike L, Reed C. Anterior maxillary alveolar distraction osteogenesis: a prospective 5year clinical study. Int J Oral Maxillofac Implants 2002: 17: 52–68.
10. Kanno T, Takahashi T, Ariyoshi W, Tsujisawa T, Haga M, Nishihara T. Tensile mechanical strain up-regulates Runx2 and osteogenic factor expression in human periosteal cells: implications for distraction osteogenesis. J Oral Maxillofac Surg 2005: 63: 499–504. 11. Klesper B, Lazar F, Siessegger M, Hidding J, Zoller JE. Vertical distraction osteogenesis of fibula transplants for mandibular reconstruction–a preliminary study. J Craniomaxillofac Surg 2002: 30: 280–285. 12. Mazzonetto R, Allais de Maurette M. Radiographic evaluation of alveolar distraction osteogenesis: Analysis of 60 cases. J Oral Maxillofac Surg 2005: 63: 1708–1711. 13. Moheng P, Feryn JM. Clinical and biologic factors related to oral implant failure: a 2-year follow-up study. Implant Dent 2005: 14: 281–288. 14. Rachmiel A, Srouji S, Peled M. Alveolar ridge augmentation by distraction osteogenesis. Int J Oral Maxillofac Surg 2001: 30: 510–517. 15. Raghoebar GM, Liem RS, Vissink A. Vertical distraction of the severely resorbed edentulous mandible: a clinical, histological and electron microscopic study of 10 treated cases. Clin Oral Implants Res 2002: 13: 558–565. 16. Saulacic N, Gandara-Vila P, Somoza-Martin M, Garcia-Garcia
A. Distraction osteogenesis of the alveolar ridge: a review of the literature. Med Oral 2004: 9: 321–327. 17. Saulacic N, Somoza-Martin M, Gandara-Vila P, Garcia-Garcia A. Relapse in alveolar distraction osteogenesis: an indication for overcorrection. J Oral Maxillofac Surg 2005: 63: 978–981. 18. Schropp L, Wenzel A, Kostopoulos L, Karring T. Bone healing and soft tissue contour changes following singletooth extraction: a clinical and radiographic 12-month prospective study. Int J Periodontics Restorative Dent 2003: 23: 313–323. 19. van Strijen PJ, Breuning KH, Becking AG, Tuinzing DB. Stability after distraction osteogenesis to lengthen the mandible: results in 50 patients. J Oral Maxillofac Surg 2004: 62: 304–307. Address: Masaharu Mitsugi Division of Oral and Maxillofacial Surgery Kagawa Prefectural Central Hospital 5-4-16 Bancho Takamatsu Kagawa 760-8557 Japan Tel.: +81 87 835 2222 Fax: +81 87 837 6210 E-mail: [email protected]
Clinical Paper Pre-Implant Surgery
Overcorrection in vertical alveolar distraction osteogenesis for dental implants
T. Kanno1, M. Mitsugi1, Y. Furuki1, M. Hosoe1, H. Akamatsu2, T. Takenobu3 1 Division of Oral and Maxillofacial Surgery, Kagawa Prefectural Central Hospital, Kagawa, Japan; 2Dental Office Akamatsu, Kagawa, Japan; 3Department of Dentistry and Maxillofacial Surgery, Kobe City General Hospital, Kobe, Hyogo, Japan
T. Kanno, M. Mitsugi, Y. Furuki, M. Hosoe, H. Akamatsu, T. Takenobu: Overcorrection in vertical alveolar distraction osteogenesis for dental implants. Int. J. Oral Maxillofac. Surg. 2007; 36: 398–402. # 2006 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved. Abstract. A decrease in bone height following alveolar distraction osteogenesis (DO) before implant placement is common, and can be severe when alveolar DO is performed soon after surgical intervention. The aim of this study was to investigate the decrease in bone height after vertical alveolar DO and determine the need for overcorrection with implant placement. Thirty-five patients (17 males and 18 females, mean age 43.9 years) underwent 38 procedures with successful placement of 141 dental implants. Alveolar ridge height was evaluated using digital orthopantomographic radiographs taken shortly after the end of distraction, at consolidation and before implant placement. The mean distraction was 9.7 mm. The total vertical alveolar bone decrease was 2.1 mm (21%) during the consolidation period and 3.6 mm (37%) at implant placement. Although the 20 sites with a healthy alveolus (surgery >6 months) had bone reductions of 1.5 and 2.5 mm (15 and 25%) the 18 sites at which alveolar DO was performed within 6 months (mean 3.0) of surgical intervention had much greater bone loss of 2.7 and 4.8 mm (28 and 50%), respectively (**P < 0.01). These results indicate that any alveolar DO protocol should include a waiting period after the surgical intervention, as well as consider an overcorrection of more than 25% within the limits of the applied surgical protocol.
One of the most common problems with oral implants is that of insufficient bone height. This is often a contraindication for implant placement and implies that the ratio of crown to implant length is too great, a factor that will probably reduce not only the useful lifespan of the implant from the perspective of biomechanical functional but also the aesthetic outcome 4,13. 0901-5027/050398 + 05 $30.00/0
Recently, a useful tissue-engineering technique that allows the height of the alveolar ridge to be increased effectively has gained increasing acceptance, namely alveolar distraction osteogenesis (DO) 9,12 . The concept, originally described by Ilizarov 7, has been applied with predictable results to the alveolar ridge to improve the treatment of bony and soft-
Keywords: alveolar distraction osteogenesis; stability; overcorrection. Accepted for publication 17 November 2006 Available online 28 February 2007
tissue defects in oral and maxillofacial surgery and implantology without major complications 3,5. Some of the advantages of this technique are its predictability, elimination of a donor site for autogenous grafts, and bone and soft-tissue regeneration 1,16. A number of studies strongly support the success of this clinical procedure 1,3,11,12. The long-term prognosis of
# 2006 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Overcorrection in vertical alveolar distraction osteogenesis for dental implants
399
Fig. 1. A 17-year-old male underwent vertical alveolar DO at the right maxillary canine and first premolar for implant placement 2 months after alveolar trauma. Intraoral photos and orthopanoramic radiographs. (a) Sufficient overcorrection to the maximum of the distractor was obtained by the end of the distraction activation period. (b) A decrease in bone height was observed 3 months after the end of the consolidation period (before distractor removal), and (c) a further bone decrease was observed after 1 month of soft tissue healing at successful implant placement.
the alveolar bone gain for implants seems to be more predictable than with conventional procedures 2. For more than 6 years and in more than 60 cases, alveolar DO using the Tracktype alveolar distractor (KLS Martin, Tuttlingen, Germany) has been performed in the authors’ hospital for implant placement. Although the prognosis seems to be well established, the relapse or bone decrease is sometimes marked. In some cases, there is a surprising amount of bony relapse at the time of implant placement after removing the distractor, despite successful placement of the dental implants (Fig. 1). Only a few clinical reports have mentioned the possibility of bony relapse following DO in the maxillofacial and alveolar regions 1,17,19. It has been suggested that overcorrection might be beneficial. SAULACIC et al.16 presented the results of 14 cases in which 20% overcorrection was included in alveolar DO using an intraosseous distractor (LEAD system, Stryker Leibinger, Kalamazoo, MI, USA) for implant placement 17, but there have been no other reports on the necessity of overcorrection or its indications. When alveolar DO is performed for implants soon after a surgical intervention there may a greater risk of relapse as compared to distraction performed on a stable, healthy alveolar ridge (Fig. 1). The aim of this study was to investigate and
clarify the indications for overcorrection and the predictability of implant placement.
Materials and methods Patients
There were 38 alveolar sites selected in 35 systemically healthy patients (17 males, 18 females; age range 17–65 years, mean 43.9) who were surgically corrected for vertical alveolar ridge defects for implantborne prostheses, along with the appropriate follow-up data. In three patients, distraction was performed in both the maxilla and mandible. They all underwent the same surgical procedure for alveolar
DO using the same type of distractor and following the protocol described below, after giving informed consent (Fig. 2). Of the 35 patients, the alveolar bone subject to DO was considered healthy at 20 sites (10 maxillary and 10 mandibular vertical alveolar DO) in 19 patients (Group A) who had not required any surgical intervention less than 6 months before DO. The other 18 sites (9 maxillary and 9 mandibular vertical alveolar DO) in 16 patients (8 males and 8 females) (Group B) had undergone some surgical intervention, such as tooth extraction, the removal of a failed implant, alveolar bone fracture or tooth avulsion due to alveolar trauma, less than 6 months prior to DO (range 0.8–5.5 months; mean 3.0).
Fig. 2. Treatment protocol for alveolar DO and implant placement.
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Kanno et al.
Surgical technique and protocol
In all patients, we used Track-type distractors (KLS Martin), following the original surgical procedure described by HIDDING & ZOLLER 8,14. With a paramarginal incision under local anaesthesia with intravenous sedation, a vestibular mucoperiosteal flap was raised, leaving the mucoperiosteum adhering to the lingual bone. The Tracktype vertical alveolar distractor was fitted and placed in the transport segment following vertical and horizontal osteotomies using a micro bone saw and chisel. The distractor was activated during surgery, and the mobility of the transport segment was confirmed. After the segments were deactivated to the original positions, the incisions were closed with 4-0 Vicryl. After a latent period of 10 days, distraction was started at an average rate of 0.4 mm (0.3 mm for Track 1.0 distractors and 0.5 mm for Track 1.5 distractors) every 12 h. On the second day, the patients began to activate the distractor following verbal and written instructions. The number of activations performed by the patients depended on the required amount of vertical movement, which was often as much as possible, for each individual case. Once this had been achieved, the distractor was left in place for 3 months to ensure bony consolidation and then it was removed to allow implant insertion. A total of 141 dental implants were placed 1 month after removing the distractor, to allow time for soft-tissue healing, as shown in the protocol in (Fig. 2).
at the midpoint of each inserted implant, and the average distance was calculated as the height obtained by alveolar DO. The amount of distraction was calculated as the distance of the distraction gap at T2. The rate of bone relapse, i.e. the bone decrease, was calculated as the ratio of the vertical bone decrease (T2 to T1 and T3 to T1) to the amount of alveolar DO based on the distraction gap. Statistical analysis
The significance of differences was determined using Student’s t-test. Data are expressed as the mean SEM. Statistical significance was defined as P < 0.05 and P < 0.01.
Results
For the 38 cases appraised, the mean bone augmentation was 9.7 mm (range 5.1– 14.8 mm) (Fig. 3). The length of distraction obtained in Groups A and B was 9.9 mm (range 5.1–14.7 mm) and 9.5 mm (range 6.4–14.8 mm), respectively (Fig. 3). The difference in bone augmentation between the two groups was not statistically significant (P > 0.05). Following a 3-month period of consolidation (T2), the alveolar bone height obtained by distraction decreased to 79% (range 49–99%) of the amount at the end of distraction (T1) for all cases (Fig. 4). The mean amount of bony relapse during the consolidation period at the
Fig. 3. The length of distraction obtained (NS: not statistically significant; P > 0.05).
Bone height evaluation
Computed tomography (CT) (Siemens, Somatom AR SP, Erlangen, Germany) was performed preoperatively, and four digital orthopanoramic radiographs were obtained postoperatively for radiographic evaluation at the end of the activation period (T1), 3 months after the end of the consolidation period (before distractor removal) (T2), 4 weeks after distractor removal (before implant placement) (T3) and after implant placement (T4). The augmented bone was measured on the panoramic radiographs. For this evaluation, the magnification factor of each radiograph was determined and corrected by dividing the real size of the activation rod by the image size of the activation rod, as described previously 12. The evaluation points were first located in the middle of each inserted implant using the T4 radiographs. The bone height was measured as the distance from the osteotomy line in the basal bone to the top of the alveolar crest
Fig. 4. The rate of bone decrease or bony relapse during the 3-month consolidation period before distractor removal and an additional month of soft-tissue healing after distractor removal and prior to implant placement. The rate of bone decrease was calculated as the ratio of the vertical bone decrease to the amount of alveolar DO based on the distraction gap. Total 38 alveolar sites; Group A: healthy alveolus, surgical intervention >6 months before DO (20 alveolar sites); Group B: surgical intervention <6 months prior to DO (18 alveolar sites). ** Statistically significant: P < 0.001.
Overcorrection in vertical alveolar distraction osteogenesis for dental implants central aspect of the implants was 2.1 mm (range 0.2–4.4 mm). The decrease in Groups A and B was 85% (range 55– 99%) or 1.5 mm (range 0.2–3.7 mm) versus 72% (range 48–89%) or 2.7 mm (range 1.0–4.4 mm), respectively (Fig. 4). The difference in relapse during the consolidation period in the two groups was statistically significant (P < 0.01) (Fig. 4). After allowing 1 month for soft-tissue healing before implant placement (T3), the vertical height of the bone decreased further to 63% (range 20–98%), as compared to that at the end of distraction (T1) for all cases (Fig. 4). The mean bony relapse at the time of implant placement at the central aspect of each implant was 3.6 mm (range 0.3–7.0 mm) in relation to the vertical alveolar bone height immediately after the end of bone augmentation. While Group A maintained a height of 75% (range 33–98%) or a 2.4 mm (range 0.3–6.0 mm) decrease compared to the vertically distracted bone height at the end of distraction, there was a greater change in Group B, with a height of 50% (range 20–86%) and a 4.8 mm (range 1.3–7.0 mm) decrease (Fig. 4). The differences in relapse at the time of implant placement between the two groups were statistically significant (P < 0.001) (Fig. 4). Discussion
Alveolar DO is an attractive option for increasing the amount of alveolar bone and surrounding tissues in patients requiring dental implants. DO has the potential for almost unlimited new bone formation between osteomized gaps with no need for bone harvesting, which avoids donor-site morbidity 1,15. As in the case of the alveolar and maxillofacial regions, the protocol for vertical alveolar DO was based on results found in long bones, with insufficient data regarding predictability for implant placement 7,15. The success of bone regeneration has been well documented and was further supported in this study, but there have been a few reports of relapse in bone height following distraction during the consolidation period, and this will inevitably affect functional implant stability 1,16,17,19. In the present study, some degree of bone decrease was observed in all cases, but the relapse was more marked than in previous reports 1,9,17. A major reason for this could have been the time assigned to the two groups (A and B). When alveolar vertical DO was performed within 6 months (mean 3.0) of surgery (Group B), there was significantly more relapse
(28% or 2.7 mm) during the 3-month consolidation period and 50% (4.8 mm) after 1-month soft-tissue healing for implant placement after distractor removal, as compared to Group A (15% (1.5 mm) and 24% (2.4 mm), respectively), as shown in (Fig. 4). Much accumulated data show that the restoration of alveolar and craniofacial bone in adults requires about 6 months with healthy bone metabolism and remodelling 10,18. Groups A and B both followed this basic protocol (Fig. 2), yet the difference between the groups was statistically significant (Fig. 4). Another reason for the degree of relapse may have been that the amount of vertical augmentation (mean 9.7 mm) was nearly 1.5 times more than in previous reports (Fig. 3) 2,9,17 . This was due to overcorrection of the transport segment, not only to regenerate bone and soft tissue but also to prevent lingual inclination of the distraction vector in most cases 8,12. Using this protocol, there has been no experience of fatal wound dehiscence or major complications. In fact, given the amount of overcorrection, and considering the subsequent decrease in bone vertically and horizontally, the implants were successfully placed with no complications, given sufficient bone and soft tissue (Fig. 1). This surgical protocol (Fig. 2), allowing 3 months for consolidation and another month for soft-tissue healing, was similar to reported protocols and made sense in terms of the regeneration of bone and tissue management for implant placement 2,4,12 . It is likely that the amount of vertical bone decrease seen in this study includes resorption of the transport segment, dislocation, incorrect inclination of the distracted segment due to difficulty in vector control and plate deformation resulting from mucoperiosteal tension stress. Since the difference between Groups A and B was statistically significant (Fig. 4), the main reason for the vertical bone decrease at well augmented alveolar sites was likely active resorption of the transport segments during the distraction and consolidation periods. Regarding measures to ameliorate bone decrease after sufficient overcorrection, as reported here, improvement of the distractor itself might be necessary in order to maintain the distracted transport segment at the desired position during the consolidation period and prevent the wrong directional inclination, including the possibility of distraction rod removal to bury it6,16. Although the application of other hardware, such as osteosynthesis plates or screws, to stabilize the distracted seg-
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ments might be an alternative, this could have a negative effect on bone and softtissue regeneration, in addition to requiring further surgery 11. Modification of the surgical protocol, such as implant placement simultaneous to or immediately after distractor removal, might reduce bone decrease in the pre-implant period, but more unpredictable marginal bone loss around the implants followed by deeper installation could occur due to the larger mucoperiosteum incision and reflection to obtain simultaneous access for distractor removal on the lateral side and implant placement, as previously described 11,17. Further clinical studies are necessary to increase the predictability of the regenerative outcome of alveolar DO using appropriate protocols for implant placement. Some previous studies have shown that overcorrection could be useful and effective for various implants and for preventing bone relapse with alveolar DO 5,11,15,17 . From the present results, if a vertical alveolar DO is planned within 6 months of surgery, such as for tooth extraction or alveolar trauma, there should be sufficient overcorrection to compensate for a bone relapse of up to 50%. Given that even healthy alveolar sites showed nearly 25% relapse at the time of implant placement following vertical alveolar DO, it is recommended that the alveolar bone augmentation be performed more than 6 months after any surgery, with sufficient overcorrection. While some instability was noted in terms of alveolar DO, sufficient overcorrection should solve this problem and eliminate any functional problems regarding dental implant placement. CHIAPASCO et al.1 and others have shown that alveolar DO is a reliable technique that does not incur major complications such as infection, and has better long-term prognosis and stability, especially after implant placement, than the conventional guided bone regeneration and bone transplantation techniques 2,4,5,16,19. References 1. Chiapasco M, Consolo U, Bianchi A, Ronchi P. Alveolar distraction osteogenesis for the correction of vertically deficient edentulous ridges: a multicenter prospective study on humans. Int J Oral Maxillofac Implants 2004: 19: 399–407. 2. Chiapasco M, Romeo E, Casentini P, Rimondini L. Alveolar distraction osteogenesis vs. vertical guided bone regeneration for the correction of vertically deficient edentulous ridges: a 1–3-year prospective study on humans. Clin Oral Implants Res 2004: 15: 82–95.
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A. Distraction osteogenesis of the alveolar ridge: a review of the literature. Med Oral 2004: 9: 321–327. 17. Saulacic N, Somoza-Martin M, Gandara-Vila P, Garcia-Garcia A. Relapse in alveolar distraction osteogenesis: an indication for overcorrection. J Oral Maxillofac Surg 2005: 63: 978–981. 18. Schropp L, Wenzel A, Kostopoulos L, Karring T. Bone healing and soft tissue contour changes following singletooth extraction: a clinical and radiographic 12-month prospective study. Int J Periodontics Restorative Dent 2003: 23: 313–323. 19. van Strijen PJ, Breuning KH, Becking AG, Tuinzing DB. Stability after distraction osteogenesis to lengthen the mandible: results in 50 patients. J Oral Maxillofac Surg 2004: 62: 304–307. Address: Masaharu Mitsugi Division of Oral and Maxillofacial Surgery Kagawa Prefectural Central Hospital 5-4-16 Bancho Takamatsu Kagawa 760-8557 Japan Tel.: +81 87 835 2222 Fax: +81 87 837 6210 E-mail: [email protected]