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Distraction implants – a new possibility for augmentative treatment of the edentulous atrophic mandible: case report
British Journal of Oral and Maxillofacial Surgery (1999) 37, 481–485 © 1999 The British Association of Oral and Maxillofacial Surgeons
BRITISH JOURNAL OF ORAL
& M A X I L L O FA C I A L S U R G E RY
Distraction implants – a new possibility for augmentative treatment of the edentulous atrophic mandible: case report A. Gaggl,* G. Schultes,† H. Kärcher‡ *Surgeon in Training;† Surgeon;‡ Head, Clinical Department of Oral and Maxillofacial Surgery, University Hospital Graz, Graz, Austria (Head: Professor Dr H. Kärcher) Stucki-McCormick and Shvyrkov et al. (unpublished observations) have proposed the use of osteotransport distractors in so-called ‘bone of seconary quality’ after tumour resection and radiation. The build-up of missing bony mandibular structures was the first step in implementing this technique in elderly patients. Block et al.8 have described successful augmentation of the alveolar ridge with an intraoral distractor as preparation for a dental implant in an experiment in dogs, and Chin and Toth9 were the first to describe this operation to allow closure of the defect in humans with alveolar ridge distraction after traumatic tooth loss. Both distraction methods resulted in an adequate site for dental implants. Callus distraction as augmentation of mandibular defects is also possible in elderly patients despite their reduced ability to form bone. A two-step approach to distraction and implant is required for both methods.8,9 The distractor itself must be removed later. To use a distraction device with the qualities of a dental implant is easy, reduces operating time, and is more comfortable for patients. Such an implant was created in 1997 in the Department of Oral and Maxillofacial Surgery at Graz University, Austria. We describe the implementation of this system in augmentation of a toothless atrophic mandibular alveolar ridge.
INTRODUCTION Callus distraction has become an accepted way of elongating tubular bones since it was first described by Codivilla in 1905.1 It has mainly been used in orthopaedic surgery to elongate tubular bones since the 1960s, and since standardization of the method by Ilizarov.2–4 When bone is broken, the defect is covered by secondary osseous repair and initially immature, barely differentiated and non-calcified bone (callus) is formed. Endosteum and periosteum both from callus and ideally the defect is covered rapidly by combined endosteal and periosteal bone. Callus distraction directs new bone formation by slowly separating fragments of bone in an axial direction. After circular corticotomy or osteotomy, the interfragmental haematoma that results is replaced within a week by granulation tissue. Which contains a high percentage of undifferentiated connective tissue cells and fibroblasts that already produce collagenous fibres. This first period results in interfragmental distractible tissue. Successful distraction should not be attempted before this distractible tissue has formed, so a resting phase of five to seven days is recommended. The tissue can then be distracted by activation of an external or an internal distraction device that enables distraction in a single direction and stabilization in two further directions. Fibroblasts and corresponding collagenous fibres are then polarized, and during this phase more collagenous fibres are produced which lead to transformation of the granulation tissue into well-vascularized collagenous tissue. Vascular tissue arises from the periosteum as well as the endosteum and can be found as early as 10 days after osteotomy.3,4 During this phase, the bone is distracted in steps of 0.5–1 mm/day. After distraction, the fragments must be immobilized to enable formation of the final calcified bone. The bone becomes restructured through resorption and new bone formation and after three months a functionally orientated and differentiated tubular bone has been formed that is able to bear weight. Tubular bones of the extremities are not the only bones capable of new bone formation. In the past few years, callus distraction has also been used to treat osseous growth deficits of the face, as described, for example, by McCarthy et al.5,6 and Karp et al.7 It can also been used in maxillofacial surgery to correct defects after resection of tumours. Mandibular continuity can be re-established by callus distraction.
DESIGN AND SURFACE OF THE IMPLANT The SIS®-Distraction-Implant is made of titanium and contains two mobile endosteal parts. It combines the qualities of a screw implant with those of a callus distraction device and, with a mobile insert, enables heightening of the alveolar ridge (Fig. 1). The implant consists of a conical titanium screw with a maximum diameter of 4.1 mm. At present it is available in lengths of 7,9 and 11 mm. The surface of the screw is roughened by laser to increase the surface area. The depth of roughage is 50 µm with a secondary roughness of 2–6 µm. For functional reasons, the surface of the distraction cylinder is smooth. The coronal endosteal part of the implant measures 4 mm for all implants. It is a selfcutting screw implant. Preoperatively, the endosteal part contains the distraction head (Fig. 2). A freeplaced screw in the head end of the distraction device can be turned from above. By winding this central screw anticlockwise, it can be removed from the endosteal apical implant by which the apical part extends up to 6 mm out of the coronal part (Fig. 3). A spring lock prevents further distraction. 481
482
British Journal of Oral and Maxillofacial Surgery
Fig. 1 – Principle of the operative technique: (A) partial osteotomy with implant in place; (B) rhomboid osteotomy with implant in place but not extended; (C) maximal distraction with the distraction head in place; and (D) maximal distraction after changing the head of the implant. The distraction implant has turned into a screw implant.
Fig. 2 – The distraction implant measuring 9 mm. The distraction insert can be used to extended the implant to 15 mm with an internal distraction screw.
Fig. 3 – The 9-mm distraction implant in distraction.
Distraction implants
483
Fig. 5 – Principle of the operation: Combined segmental osteotomy and insertion of the implant in the interforaminal area in correct position. The insertion axis (A) is parallel to the other implant and at a 90° angle to the horizontal osteotomy. Fig. 4 – The preoperative orthopantomogram showing severe atrophy of the alveolar ridge of the mandible.
Fig. 6 – Preoperative photograph showing extensive atrophy of the alveolar ridge.
CASE REPORT A 62-year-old man with atrophy of the alveolar ridge of the mandible (Fig. 4) was treated with two distraction implants in the interforaminal area (Fig. 5). He asked for help after three lower prostheses had been made and none of them stayed in place when he spoke. The cranial margin of the alveolar limb was under the floor of the mouth (Fig. 6) and the prosthesis was unstable, so osseous augmentation and dental implantation became necessary.
Operative technique The operation was done under general anaesthesia. The site was exposed by a limbal incision and a vestibular pedicled mucoperiostal flap was prepared in the interforaminal area. The small and peaked alveolar limb was then reduced with a milling cutter. The first osteotomy was made horizontally 4 mm from the implantation surface, corresponding to the attachment of the mobile to the fixed part of the implant. The osteotomy was made with a narrow oscillating saw, including the lingual bone cortex (Fig. 7). We took care to avoid the mental nerve. When the implant site was stable, the implants were inserted.
Fig. 7 – After preparation of the mucoperiostal flap and flattening of the crestal part during horizontal osteotomy in a distance of 4 mm from the surface of the alveolar ridge.
Two distraction implants were used, and were inserted in the position of the lower lateral incisors. As with most selfcutting screw implants, they were inserted into the alveolar process after pilot and core drilling. Finally, the lateral osteotomy was made in the mental foramen 5 mm from the upper margin of the alveolar ridge down to the lateral ends of the horizontal osteotomy (Fig. 8). An implant activation trial was made to check the mobility of the segment of bone to be distracted (Fig. 9). When this had been completed successfully, the distraction screw was wound to its initial position and conventional wound closure completed for transgingival healing. The implant was allowed to heal at rest for one week before distraction begun.
Period of distraction The screw implants measured 9 mm and were extended to 15 mm with a distraction telescope cylinder. The apical part of the implant was extended with screws within the neck of the implant, which lifted the bone above the osteotomy and
484
British Journal of Oral and Maxillofacial Surgery
Fig. 8 – Milling model showing the creation of an osseous implantation surface, insertion of two implants, and completion of the lateral osteotomy.
Fig. 9 – After insertion of two distraction implants and complete osteotomy. An attempt of distraction of about 2 mm is done during the operation make sure that the osteotomy has been done completely and that distraction will be possible later.
Fig. 10 – Milling model with fully distracted implants. The alveolar ridge is 6 mm higher. Fig. 11 – Fully distracted implants as in Figure 10 after the change of the insert. The implants are now stable.
broadened the osteotomy site in by callus distraction (Fig. 10). A continual transition of callus to bone took place at the osteotomy site provided that the implant was mobilized correctly at certain intervals (1 × 0.5 mm/day corresponding to a turn of the screw of 360°). The height of the alveolar ridge increased by 6 mm within 12 days.
Post-distraction period When distraction had been completed, the implant inserts (head of distraction device) were replaced by the secondary insert, which was screwed to the apical part of the distraction device and filled the hollow within the implant (Fig. 11). This secondary insert carries the neck part of the secondary implant and can be closed by turning a screwed conical cap. Coverage screws are need temporarily until the implant and alveolar ridge have formed correctly. After six months’ healing the prosthesis was built up further in the manner of conventional SIS® Implants (Fig. 12). A barbased prosthesis was made for the lower jaw, and a total prosthesis for the upper jaw.
Results The implants were stable when examined at 1, 2, 3, 4, 6, 8, 12, 14, 16, 20 and 24 weeks (Fig. 13) after the end of the distraction process and, three and six months after the prosthetic treatment, the gingiva around the implants was normal and the functional and aesthetic results were good.
DISCUSSION There are many techniques for augmentation of atrophy of the alveolar ridge in preprosthetic surgery, most of which are based on techniques of bone transplantation. The augmenting bone is nonally taken from a donor site some distance away.10 Callus distraction to augment the alveolar ridge was first described by Chin and Toth9 and provides a means of improving the osseous implantation site before the actual dental implantation itself by using bone from near the
Distraction implants
485
Fig. 13 The orthopantomogram 6 months postoperatively showing the vertical distracted mandible with the inserted distracted implants. Fig. 12 – After prosthetic treatment with a bar. The alveolar ridge is raised and well-formed.
deficient structures. patients must therefore not be treated in an area other than the region to be augmented. The only handicap of this technique is, that more steps were necessary for bone substitution and implantation. Now augmentation preprosthetic surgery has been aided by the development of a screw implant, which facilitates augmentation of the alveolar ridge with a centrally positioned distraction cylinder telescope. After distraction, it stabilizes the osseous gain through immobilization of the bone fragments, and can also be need as a dental implant for a further prosthesis after the operation site has healed. The implant is designed as a conical self-cutting screw implant, so constant distribution of pressure within the bone is possible. Overheating as a result of the insertion being too short (a cutting distance of onethird of the length) is prevented as well as screw angulation or erroneous cut. An excellent primary fit is required with the short retention distance of 5 mm apically and 4 mm coronally. The implant material, grade 4 titanium, provides the basis for good osseous healing and long-term stability as it is resistant to corrosion. It also has good bone-integrating properties. Brånemark11 insisted on the necessity for a solid surface to the implant, which he achieves by use of titanium screws without surface coating. This is important for osseous integration. A smooth implant surface combined with micropores of 50 µm with secondary roughness of 2–6 µm was achieved in the distraction implant by specific laser treatment which enabled the distraction implant to integrate well. This is the main advantage of using implant as a distraction device. After distraction, the bone fragments should be immobilized as with every implant. This may be done by changing the distraction insert on to the secondary insert, so that the distraction implant is turned into a complete implant like a screw osteosynthesis that acts as a splint for unstable bone fragments. Transgingival healing is also necessary for distraction and leads to improved gingival attachment, which is also important for gingival aesthetics and periimplant hygiene; these are the main preconditions for long-term survival of the implants.
References 1. Codivilla A. On the means of lengthening, in the lower limbs, the muscles and tissue which are shortened through deformity. Am J Orthop Surg 1905; 2: 353–359 2. Ilizarov GA. The tension-stress effect on the genesis and growth of tissues. I. The influence of stability of fixation and soft tissue preservation. Clin Orthop 1989; 238: 249–281. 3. Ilizarov GA. The tension-stress effect on the genesis and growth of tissues. II. The influence of the rate and frequency of distraction. Clin Orthop 1989; 239: 263–285. 4. Ilizarov GA. Clinical application of the tension-stress effect for limb lengthening. Clin Orthop 1990; 250: 8–26. 5. McCarthy JG, Schreiber J, Karp NS. Lengthening of the human mandible by gradual distraction. Plast Reconstr Surg 1992; 89: 1–13. 6. McCarthy JG. The role of distraction osteogenesis in the reconstruction of the mandible in unilateral craniofacial microsomia. Clin Plast Surg 1994; 21: 625–631. 7. Karp NS, Thorne CHM, McCarthy JG, Sisson HA. Bone lengthening in the craniofacial skeleton. Ann Plast Surg 1990; 24: 231–234. 8. Block MS, Chang A, Crawford C. Mandibular alveolar ridge augmentation in the dog using distraction osteogenesis. J Oral Maxillofac Surg 1996; 54: 309–314. 9. Chin M, Toth BA. Distraction osteogenesis in maxillofacial surgery using internal devices: review of five cases. J Oral Maxillofac Surg 1996; 54: 45–53. 10. McGrath CJ, Schepers SH, Blijdrop PA, Hoppenreijs TJ, Erbe M. Simultaneous placement of endosteal implants and mandibular onlay grafting for treatment of the atrophic mandible: a preliminary report. Int J Oral Maxillofac Surg 1996; 25: 184–188. 11. Branemark PI. Gewebeintegrierter Zahnersatz: Osseointegration in der klinischen Zahnheilkunde. Berlin: Quintessenz-Verlag, 1985.
The Authors Alexander Gaggl MD, DDS Surgeon in Training Günter Schultes MD, DDS Surgeon Hans Kärcher MD, PhD Head Clinical Department of Oral and Maxillofacial Surgery University Hospital Graz Graz, Austria Correspondence and requests for offprints to: Dr med. Dr med. dent. Alexander Gaggl, Clinical Department of Oral and Maxillofacial Surgery, Auenbruggerplatz 7, A-8036 Graz, Austria Paper received 21 September 1998 Accepted 13 January 1999
BRITISH JOURNAL OF ORAL
& M A X I L L O FA C I A L S U R G E RY
Distraction implants – a new possibility for augmentative treatment of the edentulous atrophic mandible: case report A. Gaggl,* G. Schultes,† H. Kärcher‡ *Surgeon in Training;† Surgeon;‡ Head, Clinical Department of Oral and Maxillofacial Surgery, University Hospital Graz, Graz, Austria (Head: Professor Dr H. Kärcher) Stucki-McCormick and Shvyrkov et al. (unpublished observations) have proposed the use of osteotransport distractors in so-called ‘bone of seconary quality’ after tumour resection and radiation. The build-up of missing bony mandibular structures was the first step in implementing this technique in elderly patients. Block et al.8 have described successful augmentation of the alveolar ridge with an intraoral distractor as preparation for a dental implant in an experiment in dogs, and Chin and Toth9 were the first to describe this operation to allow closure of the defect in humans with alveolar ridge distraction after traumatic tooth loss. Both distraction methods resulted in an adequate site for dental implants. Callus distraction as augmentation of mandibular defects is also possible in elderly patients despite their reduced ability to form bone. A two-step approach to distraction and implant is required for both methods.8,9 The distractor itself must be removed later. To use a distraction device with the qualities of a dental implant is easy, reduces operating time, and is more comfortable for patients. Such an implant was created in 1997 in the Department of Oral and Maxillofacial Surgery at Graz University, Austria. We describe the implementation of this system in augmentation of a toothless atrophic mandibular alveolar ridge.
INTRODUCTION Callus distraction has become an accepted way of elongating tubular bones since it was first described by Codivilla in 1905.1 It has mainly been used in orthopaedic surgery to elongate tubular bones since the 1960s, and since standardization of the method by Ilizarov.2–4 When bone is broken, the defect is covered by secondary osseous repair and initially immature, barely differentiated and non-calcified bone (callus) is formed. Endosteum and periosteum both from callus and ideally the defect is covered rapidly by combined endosteal and periosteal bone. Callus distraction directs new bone formation by slowly separating fragments of bone in an axial direction. After circular corticotomy or osteotomy, the interfragmental haematoma that results is replaced within a week by granulation tissue. Which contains a high percentage of undifferentiated connective tissue cells and fibroblasts that already produce collagenous fibres. This first period results in interfragmental distractible tissue. Successful distraction should not be attempted before this distractible tissue has formed, so a resting phase of five to seven days is recommended. The tissue can then be distracted by activation of an external or an internal distraction device that enables distraction in a single direction and stabilization in two further directions. Fibroblasts and corresponding collagenous fibres are then polarized, and during this phase more collagenous fibres are produced which lead to transformation of the granulation tissue into well-vascularized collagenous tissue. Vascular tissue arises from the periosteum as well as the endosteum and can be found as early as 10 days after osteotomy.3,4 During this phase, the bone is distracted in steps of 0.5–1 mm/day. After distraction, the fragments must be immobilized to enable formation of the final calcified bone. The bone becomes restructured through resorption and new bone formation and after three months a functionally orientated and differentiated tubular bone has been formed that is able to bear weight. Tubular bones of the extremities are not the only bones capable of new bone formation. In the past few years, callus distraction has also been used to treat osseous growth deficits of the face, as described, for example, by McCarthy et al.5,6 and Karp et al.7 It can also been used in maxillofacial surgery to correct defects after resection of tumours. Mandibular continuity can be re-established by callus distraction.
DESIGN AND SURFACE OF THE IMPLANT The SIS®-Distraction-Implant is made of titanium and contains two mobile endosteal parts. It combines the qualities of a screw implant with those of a callus distraction device and, with a mobile insert, enables heightening of the alveolar ridge (Fig. 1). The implant consists of a conical titanium screw with a maximum diameter of 4.1 mm. At present it is available in lengths of 7,9 and 11 mm. The surface of the screw is roughened by laser to increase the surface area. The depth of roughage is 50 µm with a secondary roughness of 2–6 µm. For functional reasons, the surface of the distraction cylinder is smooth. The coronal endosteal part of the implant measures 4 mm for all implants. It is a selfcutting screw implant. Preoperatively, the endosteal part contains the distraction head (Fig. 2). A freeplaced screw in the head end of the distraction device can be turned from above. By winding this central screw anticlockwise, it can be removed from the endosteal apical implant by which the apical part extends up to 6 mm out of the coronal part (Fig. 3). A spring lock prevents further distraction. 481
482
British Journal of Oral and Maxillofacial Surgery
Fig. 1 – Principle of the operative technique: (A) partial osteotomy with implant in place; (B) rhomboid osteotomy with implant in place but not extended; (C) maximal distraction with the distraction head in place; and (D) maximal distraction after changing the head of the implant. The distraction implant has turned into a screw implant.
Fig. 2 – The distraction implant measuring 9 mm. The distraction insert can be used to extended the implant to 15 mm with an internal distraction screw.
Fig. 3 – The 9-mm distraction implant in distraction.
Distraction implants
483
Fig. 5 – Principle of the operation: Combined segmental osteotomy and insertion of the implant in the interforaminal area in correct position. The insertion axis (A) is parallel to the other implant and at a 90° angle to the horizontal osteotomy. Fig. 4 – The preoperative orthopantomogram showing severe atrophy of the alveolar ridge of the mandible.
Fig. 6 – Preoperative photograph showing extensive atrophy of the alveolar ridge.
CASE REPORT A 62-year-old man with atrophy of the alveolar ridge of the mandible (Fig. 4) was treated with two distraction implants in the interforaminal area (Fig. 5). He asked for help after three lower prostheses had been made and none of them stayed in place when he spoke. The cranial margin of the alveolar limb was under the floor of the mouth (Fig. 6) and the prosthesis was unstable, so osseous augmentation and dental implantation became necessary.
Operative technique The operation was done under general anaesthesia. The site was exposed by a limbal incision and a vestibular pedicled mucoperiostal flap was prepared in the interforaminal area. The small and peaked alveolar limb was then reduced with a milling cutter. The first osteotomy was made horizontally 4 mm from the implantation surface, corresponding to the attachment of the mobile to the fixed part of the implant. The osteotomy was made with a narrow oscillating saw, including the lingual bone cortex (Fig. 7). We took care to avoid the mental nerve. When the implant site was stable, the implants were inserted.
Fig. 7 – After preparation of the mucoperiostal flap and flattening of the crestal part during horizontal osteotomy in a distance of 4 mm from the surface of the alveolar ridge.
Two distraction implants were used, and were inserted in the position of the lower lateral incisors. As with most selfcutting screw implants, they were inserted into the alveolar process after pilot and core drilling. Finally, the lateral osteotomy was made in the mental foramen 5 mm from the upper margin of the alveolar ridge down to the lateral ends of the horizontal osteotomy (Fig. 8). An implant activation trial was made to check the mobility of the segment of bone to be distracted (Fig. 9). When this had been completed successfully, the distraction screw was wound to its initial position and conventional wound closure completed for transgingival healing. The implant was allowed to heal at rest for one week before distraction begun.
Period of distraction The screw implants measured 9 mm and were extended to 15 mm with a distraction telescope cylinder. The apical part of the implant was extended with screws within the neck of the implant, which lifted the bone above the osteotomy and
484
British Journal of Oral and Maxillofacial Surgery
Fig. 8 – Milling model showing the creation of an osseous implantation surface, insertion of two implants, and completion of the lateral osteotomy.
Fig. 9 – After insertion of two distraction implants and complete osteotomy. An attempt of distraction of about 2 mm is done during the operation make sure that the osteotomy has been done completely and that distraction will be possible later.
Fig. 10 – Milling model with fully distracted implants. The alveolar ridge is 6 mm higher. Fig. 11 – Fully distracted implants as in Figure 10 after the change of the insert. The implants are now stable.
broadened the osteotomy site in by callus distraction (Fig. 10). A continual transition of callus to bone took place at the osteotomy site provided that the implant was mobilized correctly at certain intervals (1 × 0.5 mm/day corresponding to a turn of the screw of 360°). The height of the alveolar ridge increased by 6 mm within 12 days.
Post-distraction period When distraction had been completed, the implant inserts (head of distraction device) were replaced by the secondary insert, which was screwed to the apical part of the distraction device and filled the hollow within the implant (Fig. 11). This secondary insert carries the neck part of the secondary implant and can be closed by turning a screwed conical cap. Coverage screws are need temporarily until the implant and alveolar ridge have formed correctly. After six months’ healing the prosthesis was built up further in the manner of conventional SIS® Implants (Fig. 12). A barbased prosthesis was made for the lower jaw, and a total prosthesis for the upper jaw.
Results The implants were stable when examined at 1, 2, 3, 4, 6, 8, 12, 14, 16, 20 and 24 weeks (Fig. 13) after the end of the distraction process and, three and six months after the prosthetic treatment, the gingiva around the implants was normal and the functional and aesthetic results were good.
DISCUSSION There are many techniques for augmentation of atrophy of the alveolar ridge in preprosthetic surgery, most of which are based on techniques of bone transplantation. The augmenting bone is nonally taken from a donor site some distance away.10 Callus distraction to augment the alveolar ridge was first described by Chin and Toth9 and provides a means of improving the osseous implantation site before the actual dental implantation itself by using bone from near the
Distraction implants
485
Fig. 13 The orthopantomogram 6 months postoperatively showing the vertical distracted mandible with the inserted distracted implants. Fig. 12 – After prosthetic treatment with a bar. The alveolar ridge is raised and well-formed.
deficient structures. patients must therefore not be treated in an area other than the region to be augmented. The only handicap of this technique is, that more steps were necessary for bone substitution and implantation. Now augmentation preprosthetic surgery has been aided by the development of a screw implant, which facilitates augmentation of the alveolar ridge with a centrally positioned distraction cylinder telescope. After distraction, it stabilizes the osseous gain through immobilization of the bone fragments, and can also be need as a dental implant for a further prosthesis after the operation site has healed. The implant is designed as a conical self-cutting screw implant, so constant distribution of pressure within the bone is possible. Overheating as a result of the insertion being too short (a cutting distance of onethird of the length) is prevented as well as screw angulation or erroneous cut. An excellent primary fit is required with the short retention distance of 5 mm apically and 4 mm coronally. The implant material, grade 4 titanium, provides the basis for good osseous healing and long-term stability as it is resistant to corrosion. It also has good bone-integrating properties. Brånemark11 insisted on the necessity for a solid surface to the implant, which he achieves by use of titanium screws without surface coating. This is important for osseous integration. A smooth implant surface combined with micropores of 50 µm with secondary roughness of 2–6 µm was achieved in the distraction implant by specific laser treatment which enabled the distraction implant to integrate well. This is the main advantage of using implant as a distraction device. After distraction, the bone fragments should be immobilized as with every implant. This may be done by changing the distraction insert on to the secondary insert, so that the distraction implant is turned into a complete implant like a screw osteosynthesis that acts as a splint for unstable bone fragments. Transgingival healing is also necessary for distraction and leads to improved gingival attachment, which is also important for gingival aesthetics and periimplant hygiene; these are the main preconditions for long-term survival of the implants.
References 1. Codivilla A. On the means of lengthening, in the lower limbs, the muscles and tissue which are shortened through deformity. Am J Orthop Surg 1905; 2: 353–359 2. Ilizarov GA. The tension-stress effect on the genesis and growth of tissues. I. The influence of stability of fixation and soft tissue preservation. Clin Orthop 1989; 238: 249–281. 3. Ilizarov GA. The tension-stress effect on the genesis and growth of tissues. II. The influence of the rate and frequency of distraction. Clin Orthop 1989; 239: 263–285. 4. Ilizarov GA. Clinical application of the tension-stress effect for limb lengthening. Clin Orthop 1990; 250: 8–26. 5. McCarthy JG, Schreiber J, Karp NS. Lengthening of the human mandible by gradual distraction. Plast Reconstr Surg 1992; 89: 1–13. 6. McCarthy JG. The role of distraction osteogenesis in the reconstruction of the mandible in unilateral craniofacial microsomia. Clin Plast Surg 1994; 21: 625–631. 7. Karp NS, Thorne CHM, McCarthy JG, Sisson HA. Bone lengthening in the craniofacial skeleton. Ann Plast Surg 1990; 24: 231–234. 8. Block MS, Chang A, Crawford C. Mandibular alveolar ridge augmentation in the dog using distraction osteogenesis. J Oral Maxillofac Surg 1996; 54: 309–314. 9. Chin M, Toth BA. Distraction osteogenesis in maxillofacial surgery using internal devices: review of five cases. J Oral Maxillofac Surg 1996; 54: 45–53. 10. McGrath CJ, Schepers SH, Blijdrop PA, Hoppenreijs TJ, Erbe M. Simultaneous placement of endosteal implants and mandibular onlay grafting for treatment of the atrophic mandible: a preliminary report. Int J Oral Maxillofac Surg 1996; 25: 184–188. 11. Branemark PI. Gewebeintegrierter Zahnersatz: Osseointegration in der klinischen Zahnheilkunde. Berlin: Quintessenz-Verlag, 1985.
The Authors Alexander Gaggl MD, DDS Surgeon in Training Günter Schultes MD, DDS Surgeon Hans Kärcher MD, PhD Head Clinical Department of Oral and Maxillofacial Surgery University Hospital Graz Graz, Austria Correspondence and requests for offprints to: Dr med. Dr med. dent. Alexander Gaggl, Clinical Department of Oral and Maxillofacial Surgery, Auenbruggerplatz 7, A-8036 Graz, Austria Paper received 21 September 1998 Accepted 13 January 1999