- Email: [email protected]
Fixation of mandibular fractures with biodegradable plates and screws
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Vol. 94 No. 3 September 2002
ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY ORAL AND MAXILLOFACIAL SURGERY
Editor: Larry J. Peterson✝
Fixation of mandibular fractures with biodegradable plates and screws Kaan C. Yerit, MD,a Georg Enislidis, MD, DMD,b Christian Schopper, MD,c Dritan Turhani, MD,d Felix Wanschitz, MD,e Arne Wagner, MD, DMD,f Franz Watzinger, MD, DMD, PhD,g and Rolf Ewers, MD, DMD, PhD,h Vienna, Austria UNIVERSITY OF VIENNA
Objective. Little data exist regarding the use of biodegradable plates and screws for the internal fixation of human mandibular fractures. The purpose of this study was to evaluate the stability of biodegradable, self-reinforced poly-Llactide plates and screws for the internal fixation of fractures of the human mandible. Study design. Twenty-two individuals (14 male, 8 female; average age, 26.3 years) with a variety of fracture patterns of the mandible underwent management with a biodegradable fixation system. After surgery, maxillomandibular fixation was applied in 3 cases. Images (panoramic radiograph, computed tomographic scan) were taken immediately after surgery and at the 4-week, 8-week, 12-week, and 24-week intervals. The follow-up period averaged 49.1 weeks (range, 22 to 78 weeks). Results. Mucosal dehiscences over the resorbable devices were present in 2 patients. In 1 of these 2 cases, the material had to be replaced with titanium plates. Mucosal healing and consolidation of the fracture were normal in all other patients. Conclusion. Self-reinforced biodegradable osteosynthesis materials provide a reliable and sufficient alternative to conventional titanium plate systems. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;94:294-300)
The body of literature on biodegradable materials goes back more than 30 years. Many reports have been published by different authors.1-6 Rokkanen et al7 reported the first clinical application of biodegradable devices in orthopedic surgery. In oral and maxillofacial surgery, resorbable materials were first tested in animal studies8-11 and later used clinically in humans for fixation in trauma12-16 and orthognathic surgery.17-19 No publication rea-e
University Assistant, University Hospital of Cranio-Maxillofacial and Oral Surgery, Medical School, University of Vienna. f Resident, University Hospital of Cranio-Maxillofacial and Oral Surgery, Medical School, University of Vienna. g Assistant Professor, University Hospital of Cranio-Maxillofacial and Oral Surgery, Medical School, University of Vienna. h Professor and Head, University Hospital of Cranio-Maxillofacial and Oral Surgery, Medical School, University of Vienna. Received for publication Jun 12, 2001; returned for revision Aug 23, 2001; accepted for publication Jan 7, 2002. © 2002, Mosby, Inc. 1079-2104/2002/$35.00 ⫹ 0 7/12/122833 doi:10.1067/moe.2002.122833 ✝Deceased.
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ports the internal fixation of human mandibular fractures with biodegradable self-reinforced poly-L-lactide (SRPLLA) plates and screws. Few publications report the fixation of fractures with biodegradable materials. Bos et al8 published in 1989 a study on 6 dogs; high-molecular PLLA screws and plates served for the fixation of artificial mandibular corpus fractures. The osteosynthesis was done in the zeroline with a 4-hole plate and 4 monocortical screws of 2.7-mm thickness and 6-mm length; no maxillomandibular fixation (MMF) was applied. The healing took place without callus formation. The 2 mm-thick plates resisted the biomechanical load, although they were weaker than the Champy 4-hole miniplates (Martin Medizintechnik, Tuttlingen, Germany) with comparable dimensions. However, in vitro, the elastic modulus of 5 GPa equalled that of steel plates with 5 to 7 GPa. The study was limited to 12 weeks of clinical observation. The complete resorption of the material was not examined, and a statement about late complications with this highmolecular fixation material was not made. In 1993, a
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publication by Bergsma et al20 reported that the material at that time caused late complications after clinical use in patients and was therefore not applicable for the fixation of mandibular fractures. The study of Bessho, Iizuka, and Murakami21 described the use of PLLA screws and PLLA plates on 50 patients. In that study, the indications were fractures, osteotomies, and bone graft fixations on facial bones. In 34 patients, fractures of the mandible were treated with 2 or 3 plates (4-hole, 6-hole,or 8-hole plates with or without bar) of 1.6-mm thickness and with 8 mm-long screws of 2 mm in diameter. Neither the accurate amount of implanted material nor the location of the fracture sites was mentioned in the publication. MMF up to 7 days was applied to all patients. The average clinical observation period was 3 years and 8 months, but no information was given about failure ratio during the observation period. Two infections that occurred after 3 and 7 months were treated with antibiotic therapy and implant removal. Bone dislocation was stated radiologically in 14% of the cases; the exact locations and clinical consequences were not described in detail. In 1999, Kallela et al22 published a study about the fixation of 11 patients with anterior mandibular fractures that had been treated with biodegradable lag screws manufactured from SR-PLLA. Six of these were fixed maxillomandibular from 1 to 5 weeks. One patient showed an osteolysis around the fracture line already 6 weeks after the fixation, and regeneration was seen after 6 months with new bone formation. The 3 most commonly used materials for resorbable plating systems are polyglycolic acid, poly-L-lactic acid, copolymers of these 2, and poly-dioxanone-sulphate. These materials were initially used as suture materials,23 but use has since spread to many fields of surgery because of their advantages compared with metal plates and screws. Besides palpability or sometimes visibility, metal fixation systems are hampered by temperature sensitivity and interference with radiographic imaging. Also, excessive stress shielding may be found from rigid plate fixation, leading to the wellknown effect of atrophy of cortical bone and the need for a subsequent operation for removal. Bioabsorbable implants gradually transfer load to the healing bone as they resorb. Stress shielding and osteopenia seen with metal implants24,25 are rarely seen with biodegradable implants. The main reason for restriction of use of biodegradable devices was their mechanical weakness. The physical demands on absorbable fixation devices are suitable rigidity, adequate stability, and complete degradation without any complications. The unreinforced degradable implants lack sufficient mechanical strength and stiffness to provide secure internal fixation
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of mandibular fractures. Unreinforced PLLA plates and screws have been used in the fixation of low-load bearing fractures, such as zygomatic fractures.13,15,16 To¨ rma¨ la¨ et al26 developed a special technique in reinforcing the implant with highly orientated fibers of the same polyester drawn in a longitudinal axis, termed self reinforcement. This method produces a more durable composition of matrix and fibers and shows significantly higher tensile and flexural modulus of elasticity.26 Because of the reinforcement, the mechanical demands needed for initial fracture stability within the first 6 to 8 weeks are provided. The appropriate strength needed during this postoperative time to meet the initial biomechanical demands and the gradual biodegradation of the reinforced material with gradual load transfer to the healing bone make the reinforced material sufficient for fixation of mandibular fractures. The main mode of degradation of PLLA biomaterials is hydrolysis.27 The tissue reaction is thought to be the result of the inability to absorb the degradation products that are associated with rapid hydrolysis. In contrast to PLLA, polyglycolic acid undergoes a more rapid hydrolysis and therefore incites higher inflammatory reactions. For that reason, PLLA devices retain strength longer. The degradation time of PLLA is up to 6 years, with a loss of mechanical strength of SR-PLLA devices after approximately 36 weeks.28 The biocompatibility of PLLA has been the subject of numerous studies. In 1966, Kulkarni et al1 first reported the potential of polylactides as resorbable biomaterials for use in surgery. The excellent biocompatibility of PLLA is generally accepted. Nevertheless, inflammatory tissue reactions around PLLA implants and late adverse reactions were reported in animal and clinical studies by different authors.28,29 The tissue reaction changes as biodegradation progresses. In 1993 and 1995, Bergsma et al20,28 reported late tissue response to PLLA used for fracture fixation of the zygomatic bone. Four of 10 patients showed intermittent painless swelling in the operative site more than 3 years after fracture fixation. In 4 patients, surgical removal of the implants was necessary. The reduction of the volume of the implanted material with the self-reinforcing technique to the definitely necessary minimum could help to enhance the biocompatibility during the degradation phase. PATIENTS AND METHODS Twenty-two patients with mandibular fractures underwent operation over a period of 18.5 months. All patients volunteered after receiving study information. The indications for open reduction and internal fixation were displaced fractures of the mandible not older than 3 days (Figs 1 and 2). Patients with infections, systemic
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after the operation. MMF was applied in patients with concomitant fractures of the condyles (nos. 9, 15, and 17). All patients were placed on an initial soft diet for 10 to 14 days, with progression gradually to a regular nutrition afterwards.
Fig 1. Panoramic radiograph of fracture before operation.
Examination methods In addition to clinical examinations, panoramic radiographs were taken immediately after surgery and at 1, 2, 3, and 6 months after the open reduction. A computed tomographic (CT) scan also was used for examinations and evaluations 3 and 6 months after the operation. Radiographs and CT scans were analyzed by the same person for displacement, diastasis, visibility of the fracture line and the drill channels, callus formation, and ossification of the mandibular fracture.
diseases, and edentulous or atrophic jaws were excluded. Fracture sites were located as specified in the Table. Fractures of the mandibular angle were present in 6 patients (nos. 7, 11, 18, 19, 20, and 21). Another 3 patients with body and concomitant ramus (no. 8) or condylar (nos. 15 and 17) fractures were treated with fixation of both fracture sites with biodegradable devices. Patients no. 15 and 17 had their conditions stabilized with MMF for 3 weeks. One patient (no. 9) had a body fracture and concomitant, nondisplaced condylar fractures on both sides; after open reduction of the corpus with biodegradable osteosynthesis, MMF was applied for 2 weeks. Detailed information about the 22 patients is given in the Table. A resorbable nonmetallic fixation system (BiosorbFX 2.0 system, Bionx Implants, Inc, Tampere, Finland) constructed of self-reinforced polylactic acid copolymer (SR-P[L/DL]LA [70/30]) was used for the fixation of all mandibular fractures. The instrumentation consisted of an appropriately sized bone drill, a bone tap, a screwdriver, and bending forceps. A transbuccal system from the same company was used for the reduction of angular and condylar fractures. The polylactide plates of the BiosorbFX 2.0 system are available in sizes from 4-hole to 16-hole plates (5.5-mm wide and 1.2-mm thick). The screws of the same system (2 mm in diameter) range from 4 to 40 mm in length.
RESULTS The patient population consisted of 8 female and 14 male patients with an average age of 26.3 years (range, 11.5 to 69 years). The mean follow-up period was 49.1 weeks (range 22 to 78 weeks).
Operative technique The open fracture reduction with general anesthesia was performed with standard operative techniques, with the only exception being that biodegradable plates and screws were used to fix each fracture. Two 6-hole plates and screws of 6, 8, or 10 mm in length of the BiosorbFX 2.0 fixation system were used at each fracture site (Figs 3 and 4). A nonresorbable suture material was used for wound closure and was removed 10 days
Imaging No signs of bone healing disturbances of the other patients were noticed via panoramic or CT scan imaging during the entire follow-up period. Bone formation and fading of the fracture line was seen between 2 and 3 months after surgery in the panoramic films. However, the fracture line continued to be detectable in all CT scans. Drill channels were also visible in all samples of the CT scans during the entire study period. The
Clinical follow-up Primary healing was uneventful in 20 patients. No infections were diagnosed. A slight submucosal swelling was seen in 1 patient (no. 1) but disappeared within 1 week. No extrusion of the implants occurred. Postoperative occlusion was correct in all patients. Hypesthesia or anesthesia of the lower lip was observed in all patients but was always transient. Two patients had mucosal wound dehiscences over the plates after 5 days. In 1 patient (no. 6), secondary sutures were applied and wound healing was uneventful afterwards. Patient no. 2 was totally incompliant and did not refrain from nicotine and alcohol abuse. Secondary sutures were ineffective, and wound healing was seriously compromised. Because of local infection, the biodegradable plates and screws had to be removed and conventional metal plates and screws were applied. Two months later, the patient underwent reoperation because of nonunion at the fracture site. The mandible was stabilized with a metal reconstruction plate, and further wound healing was uneventful.
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Fig 2. Endoral view before fixation plates were applied.
Table. Details about patients Patient no.
Sex
Age (y)
1 2
M M
21 57
3 4 5 6
M F M F
7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Region of fracture fixed with biodegradable devices
Maxillomandibular fixation (wk)
Follow-up (wk)
Mandibular body Mandibular body
No No
78 2, reoperated
17.5 19 46 36
Mandibular Mandibular Mandibular Mandibular
No No No No
70 65 64 64
F F M
24.5 13.5 11.5 13.5 21 25 19.5 21 26 69 22.5 20 22.5 18.5 29.5 27.5
No No Yes, 2 condyles not operated No No No No No Yes, 3 No Yes, 3 No No No No No
61 59 57
M M F F M M M M M F F M M
Mandibular body ⫹ right angle Mandibular body ⫹ left ramus Mandibular body, left ⫹ right condyle Mandibular body Left angle Mandibular body Mandibular body Mandibular body Mandibular body ⫹ left condyle Mandibular body Mandibular body ⫹ left condyle Mandibular body ⫹ left angle Mandibular body ⫹ right angle Mandibular body ⫹ left angle Right angle Mandibular body
Submucosal swelling Dehiscence, infection, removal of material Uneventful Uneventful Uneventful Dehiscence, closure with sutures Uneventful Uneventful Uneventful
56 56 54 52 52 48 46 45 45 31 27 27 22
Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful
body body body body
Healing complications
M, male; F, female.
fractures were considered to be consolidated on the basis of the radiologic examination after 3 months. The fracture ends were united by new bone after 3 months, and cortical bone was apparent after 6 months in all cases examined after this period.
The images of the follow-up of patient no. 3 show the steps of bone healing; the initial situation with a fracture of the mandibular body is seen in the panoramic radiograph (Fig 1) and endoral view (Fig 2). The postoperative clinical situation is seen in Fig 3.
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Fig 3. View of fracture after fixation with 2 biodegradable 6-hole plates and screws of 8 and 10 mm in length. Appropriate reduction and stabilization is achieved.
Fig 4. Panoramic radiograph immediately after open reduction and internal fixation, showing reduced fracture and radiolucent areas of drill channels.
Immediately after surgery, the fracture line and drill holes were well visible (Fig 4). Six months after internal fixation, fracture ends were united and the fracture line was not visible, but the drill channels were still detectable as radiolucent areas (Fig 5). DISCUSSION The adaptation of the biodegradable plates to the bone surface was as uncomplicated as with titanium miniplates. A slight grade of overbending was necessary because of the elasticity of the material. In contrast to other biodegradable fixation systems, no heating device was necessary. The plates were easily bendable with forceps at room temperature, and none of the plates broke during bending. At the bending areas, white lines occurred in the transparent plates, but this
ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY September 2002
Fig 5. Panoramic radiograph 24 weeks after operation without fracture line. Reduction and maintenance of inferior border continuity is seen. Drill channels are still detectable.
did not influence the physical quality of the devices. This phenomenon is described as microdelamination in the instructions of the manufacturer. The screws were threaded and fit well into the bone. Screw failure was low; only 2 screws broke during the insertion (1 material failure, 1 incorrect handling). In such cases, a new hole was easily drilled through the broken screw and a new screw was inserted without problems, fitting perfectly into the mandibular bone. Nine screws could not be used because of production failures; their cruciform heads did not fit on the screwdriver. As far as we know, this is the first clinical report on the appliance of biodegradable self-reinforced polylactide plates and screws for the open reduction of human mandibular fractures. The investigators attempted to refrain from MMF whenever possible. MMF was only applied in 3 patients with concomitant condylar fractures. Patient no. 9 did not have condyle fixation, and therefore, MMF was used. In 2 cases (nos. 15 and 17), MMF was applied for 3 weeks after fixation of the condyles with biodegradable material for further stability. No MMF was used after the reduction of all other fractures. Only 3 complications were seen during the entire follow-up period. In patient no. 2, the biodegradable implant material had to be removed because of healing disturbances and infection. The mandibular fracture then was stabilized with conventional metal implants. Further bone healing was uncomplicated. Although different factors, like total noncompliance, may have caused this special condition, it cannot be excluded that the implant material itself was a cause. In patient no. 1, the implant material might have caused a mild mucosal swelling that was self-limiting. The implant positioning
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also possibly caused the wound dehiscence in patient no. 6 that was treated with closure with sutures. However, 2 of 3 complications were managed easily. No complications occurred in the remaining 19 patients, and postoperative healing did not differ from patients with metal implants. Occlusion was normal, and no dislocation, diastasis, or nonunion was seen. All patients showed perfect occlusion after the operation and also during the period of follow-up. Unlike conventional metal plates, the less rigid biodegradable implants seemed to allow a minimal but smooth degree of settling of the occlusion while at the same time providing a stable reduction of the fracture. Ossification of the fracture was seen after 3 months in the radiologic analysis. In 1 patient, the drill channels seemed uncommonly large during the whole follow-up period. However, this patient had no clinical symptoms, and the reason for this enlargement is unknown. At the end of the follow-up period, screw holes could still be detected radiologically in all patients as radiolucent areas. No early adverse reactions were seen to date. Except for the complications in patients no. 1, 2, and 6, mentioned previously, no further evidence was seen of implant-related tissue reactions, like local swelling, infection, sinus formation, discharge, fistula formation, discoloration, or osteolysis, during the follow-up period. The possibility of late reactions to biodegradable implants as reported in the literature26-28 will be monitored. What makes biodegradable fracture fixation devices more attractive than metal ones is that no removal operation is needed after bone healing. In our clinic, it is common practice to remove metal plates and screws after bone healing. If not removed, the metal implants may be painful and irritating. Also, imaging techniques, such as CT scans and magnetic resonance imaging, show interference with the metal devices remaining in situ, above all with ferrous metals. Stress shielding with local osteoporosis and possible refracture after removal are additional disadvantages of metal implants. They may incite allergic reactions and long-term metal ion release, creating another cause for concern. This is particularly relevant because there are reports of possible release of free metals from osteosynthesis materials,30-32 and removal is recommended for all young patients. This means a second operation and, in most cases, also general anesthesia and hospitalization. Considering the previously mentioned arguments, the authors believe that self-reinforced biodegradable osteosynthesis material is a good alternative to metal implants. Furthermore, it is also more economic because minor differences in the expenses for the acquisition of bioabsorbable implants are clearly offset by
the avoidance of a second procedure for implant removal. However, because the clinically applied biodegradable fixation systems have no long-term results in the open reduction of mandibular fractures, all patients of this study were closely observed. Patients were also advised to apply to the clinic if any clinical symptoms like swelling or inflammation occurred. This fixation device does not appear to interfere with the normal healing pattern of the fractured bone. Also, no systemic or severe local disorders have been reported during the entire time of follow-up. CONCLUSION The mechanical properties of the SR-PLLA plates and screws applied for mandibular fracture fixation are comparable with those of metal fixation systems. The treatment goals of immobilization, fixation, and stabilization were found to be fulfilled. The skeletal stability was comparable with actual standards and sufficient for the time needed for mandibular bone healing. On the basis of the results of this study, it can be concluded that biodegradable SR-PLLA implants have the potential for successful use in the fixation of human mandibular fractures. REFERENCES 1. Kulkarni RK, Pani KC, Neumann C, Leonard F. Polylactic acid for surgical implants. Arch Surg 1966;93:839-43. 2. Cutright DE, Hunsuck EE, Beasley JD. Fracture reduction using a biodegradable material, poly lactic acid. J Oral Surg 1971;9: 393-7. 3. Getter L, Cutright DE, Bhaskar SN, Augsburg JK. A biodegradable intraosseous appliance in the treatment of mandibular fractures. J Oral Surg 1972;30:344-8. 4. Ewers R, Forster H. Resorbable materials for osteosynthesis. An experimental animal study. Dtsch Z Mund Kiefer Gesichtschir 1985;196-201. 5. Ewers R, Ha¨ rle F. Experimental and clinical results of new advances in the treatment of facial trauma. Plast Reconstr Surg 1985;75:25-31. 6. Gerlach L, Krause HR, Eitenmu¨ ller J. Absorbable osteosynthesis materials for immobilization of mandibular fractures. Animal experimental study. Dtsch Z Mund Kiefer Gesichtschir 1988;12: 418-22. 7. Rokkanen P, Bo¨ stman O, Vainionpa¨ a¨ S, et al. Biodegradable implants in fracture fixation: early results of treatment of fractures of the ankle. Lancet 1985;1:1422-4. 8. Bos RRM, Rozema FR, Boering G, Nijenhuis AJ, Pennings AJ, Verwey AB. Bio-absorbable plates and screws for internal fixation of mandibular fractures. A study in six dogs. Int J Oral Maxillofac Surg 1989;18:365-9. 9. Suuronen R. Comparison of absorbable self-reinforced poly-llactide screws and metallic screws in the fixation of mandibular condyle osteotomies. Experimental study in sheep. J Oral Maxillofac Surg 1991;49:989-95. 10. Suuronen R, Pohjonen T, Wessmann L, To¨ rma¨ la¨ P, Vainionpa¨ a¨ S. New generation biodegradable plate for fracture fixation. Comparison of bending strengths of mandibular osteotomies fixed with absorbable self-reinforced multi-layer poly-l-lactide plates and metallic plates. An experimental study in sheep. Clin Mater 1992;9:77-84. 11. Suuronen R, To¨ rma¨ la¨ P, Vasenius J, Wessmann L, Mero M,
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Partio E, et al. Comparison of shear strength of osteotomies fixed with absorbable self-reinforced poly-l-lactide and metallic screws. J Mater Sci-Mater Med 1992;3:288-92. Cutright DE, Hunsuck EE. The repair of fractures of the orbital floor using biodegradable poly-lactic acid. Oral Surg 1972;33: 28-34. Bos RR, Boering G, Rozema FR, Leenslag JW. Resorbable poly(L-lactide) plates and screws for the fixation of zygomatic fractures. J Oral Maxillofac Surg 1987;45:751-3. Cordewener FW, Bos RR, Rozema FR, Houtman WA. Poly(Llactide) implants for repair of human orbital floor defects: clinical and magnetic resonance imaging evaluation of long-term results. J Oral Maxillofac Surg 1996;54:9-14. Enislidis G, Pichorner S, Kainberger F, Ewers R. Lactosorb panel and screws for repair of large orbital floor defects. J Craniomaxillofac Surg 1997;25:316-21. Enislidis G, Pichorner S, Lambert F, Wagner A, Kainberger F, Kautzky M, et al. Fixation of zygomatic fractures with a new biodegradable copolymer osteosynthesis system. Preliminary results. Int J Oral Maxillofac Surg 1998;27:352-5. Suuronen R, Laine P, Lindquist C. Sagittal ramus osteotomies fixed with biodegradable screws: a preliminary report. J Oral Maxillofac Surg 1994;52:715-20. Haers PE, Sailer HF. Biodegradable self-reinforced poly-L/DLlactide plates and screws in bimaxillary orthognathic surgery: short-term skeletal stability and material related failures. J Craniomaxillofac Surg 1998;26:363-72. Kallela I, Laine P, Suuronen R, Iizuka T, Pirinen S, Lindqvist C. Skeletal stability following mandibular advancement and rigid fixation with polylactide biodegradable screws. Int J Oral Maxillofac Surg 1998;27:3-8. Bergsma E, Rozema F, Bos R, De Bruijn W. Foreign body reactions to resorbable poly(L-lactide) bone plates and screws used for the fixation of unstable zygomatic fractures. J Oral Maxillofac Surg 1993;51:666-70. Bessho K, Iizuka T, Murakami K. A bioabsorbable poly-l-lactide miniplate and screw system for osteosynthesis in oral and maxillofacial surgery. J Oral Maxillofac Surg 1997;55:941-5. Kallela I, Iizuka T, Salo A, Lindquist C. Lag-screw fixation of anterior mandibular fractures using biodegradable polylactide screws: a preliminary report. J Oral Maxillofac Surg 1999;57: 113-8. Herrmann JB, Kelly RJ, Higgins GA. Polyglycolic acid sutures. Laboratory and clinical evaluation of a new absorbable suture material. Arch Surg 1970;100:486-90.
ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY September 2002 24. Uhthoff H, Boisvert D, Finnegan M. Cortical porosis under plates. Reaction to unloading or to necrosis? J Bone Joint Surg Am 1994;76:1507-12. 25. Viljanen J, Kinnunen J, Bandestam S, Majola A, Rokkanen P, Torma¨ la¨ P. Bone changes after experimental osteotomies fixed with absorbable self-reinforced poly-L-lactide screws or metallic screws studied by plain radiographs, quantitive computed tomography, and magnetic resonance imaging. Biomaterials 1995;16: 1353-8. 26. To¨ rma¨ la¨ P, Pellinen M, Pohjonen T, et al. Totally biodegradable self-reinforced rods and screws for internal fixation of bone fractures. Acta Othop Scand 1990;227:17. 27. Williams DF. Some observations on the role of cellular in the in vivo degradation of polymers. In: Syrett BC, Acharya A, editors. STM special technical publications, corrosion and degradation of implant materials. Philadelphia: American Society for Testing and Materials; 1979. p. 61-75. 28. Bergsma JE, de Bruijn, Rozema FR, Bos RR, Boering G. Late degradation tissue response to poly(L-lactide) bone plates and screws. Biomaterials 1995;16:25-31. 29. Bos RR, Rozema FR, Boering G, Nijenhuis AJ, Pennings AJ, Verwey AB, et al. Degradation of and tissue reaction to biodegradable poly(L-lactide) for use as internal fixation of fractures: a study in rats. Biomaterials 1991;12:32-6. 30. Rosenberg A, Gratz KW, Sailer HF. Should titanium miniplates be removed after bone healing is complete? Int J Oral Maxillofac Surg 1993;22:185-8. 31. Schliephake H, Lehmann H, Kunz U, Schmelzeisen R. Ultrastructural findings in soft tissues adjacent to titanium plates used in jaw fracture treatment. Int J Oral Maxillofac Surg 1993;22: 20-5. 32. Jorgenson DS, Mayer MH, Ellenbogen RG, Centeno JA, Johnson FB, Mullick FG, et al. Detection of titanium in human tissues after craniofacial surgery. Plast Reconstr Surg 1997;99:976-9. Reprint requests: Kaan C. Yerit, MD University Hospital of Cranio-Maxillofacial and Oral Surgery Medical School, University of Vienna Wa¨ hringer Gu¨ rtel 18-20 A-1090 Wien Austria [email protected]
Vol. 94 No. 3 September 2002
ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY ORAL AND MAXILLOFACIAL SURGERY
Editor: Larry J. Peterson✝
Fixation of mandibular fractures with biodegradable plates and screws Kaan C. Yerit, MD,a Georg Enislidis, MD, DMD,b Christian Schopper, MD,c Dritan Turhani, MD,d Felix Wanschitz, MD,e Arne Wagner, MD, DMD,f Franz Watzinger, MD, DMD, PhD,g and Rolf Ewers, MD, DMD, PhD,h Vienna, Austria UNIVERSITY OF VIENNA
Objective. Little data exist regarding the use of biodegradable plates and screws for the internal fixation of human mandibular fractures. The purpose of this study was to evaluate the stability of biodegradable, self-reinforced poly-Llactide plates and screws for the internal fixation of fractures of the human mandible. Study design. Twenty-two individuals (14 male, 8 female; average age, 26.3 years) with a variety of fracture patterns of the mandible underwent management with a biodegradable fixation system. After surgery, maxillomandibular fixation was applied in 3 cases. Images (panoramic radiograph, computed tomographic scan) were taken immediately after surgery and at the 4-week, 8-week, 12-week, and 24-week intervals. The follow-up period averaged 49.1 weeks (range, 22 to 78 weeks). Results. Mucosal dehiscences over the resorbable devices were present in 2 patients. In 1 of these 2 cases, the material had to be replaced with titanium plates. Mucosal healing and consolidation of the fracture were normal in all other patients. Conclusion. Self-reinforced biodegradable osteosynthesis materials provide a reliable and sufficient alternative to conventional titanium plate systems. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;94:294-300)
The body of literature on biodegradable materials goes back more than 30 years. Many reports have been published by different authors.1-6 Rokkanen et al7 reported the first clinical application of biodegradable devices in orthopedic surgery. In oral and maxillofacial surgery, resorbable materials were first tested in animal studies8-11 and later used clinically in humans for fixation in trauma12-16 and orthognathic surgery.17-19 No publication rea-e
University Assistant, University Hospital of Cranio-Maxillofacial and Oral Surgery, Medical School, University of Vienna. f Resident, University Hospital of Cranio-Maxillofacial and Oral Surgery, Medical School, University of Vienna. g Assistant Professor, University Hospital of Cranio-Maxillofacial and Oral Surgery, Medical School, University of Vienna. h Professor and Head, University Hospital of Cranio-Maxillofacial and Oral Surgery, Medical School, University of Vienna. Received for publication Jun 12, 2001; returned for revision Aug 23, 2001; accepted for publication Jan 7, 2002. © 2002, Mosby, Inc. 1079-2104/2002/$35.00 ⫹ 0 7/12/122833 doi:10.1067/moe.2002.122833 ✝Deceased.
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ports the internal fixation of human mandibular fractures with biodegradable self-reinforced poly-L-lactide (SRPLLA) plates and screws. Few publications report the fixation of fractures with biodegradable materials. Bos et al8 published in 1989 a study on 6 dogs; high-molecular PLLA screws and plates served for the fixation of artificial mandibular corpus fractures. The osteosynthesis was done in the zeroline with a 4-hole plate and 4 monocortical screws of 2.7-mm thickness and 6-mm length; no maxillomandibular fixation (MMF) was applied. The healing took place without callus formation. The 2 mm-thick plates resisted the biomechanical load, although they were weaker than the Champy 4-hole miniplates (Martin Medizintechnik, Tuttlingen, Germany) with comparable dimensions. However, in vitro, the elastic modulus of 5 GPa equalled that of steel plates with 5 to 7 GPa. The study was limited to 12 weeks of clinical observation. The complete resorption of the material was not examined, and a statement about late complications with this highmolecular fixation material was not made. In 1993, a
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publication by Bergsma et al20 reported that the material at that time caused late complications after clinical use in patients and was therefore not applicable for the fixation of mandibular fractures. The study of Bessho, Iizuka, and Murakami21 described the use of PLLA screws and PLLA plates on 50 patients. In that study, the indications were fractures, osteotomies, and bone graft fixations on facial bones. In 34 patients, fractures of the mandible were treated with 2 or 3 plates (4-hole, 6-hole,or 8-hole plates with or without bar) of 1.6-mm thickness and with 8 mm-long screws of 2 mm in diameter. Neither the accurate amount of implanted material nor the location of the fracture sites was mentioned in the publication. MMF up to 7 days was applied to all patients. The average clinical observation period was 3 years and 8 months, but no information was given about failure ratio during the observation period. Two infections that occurred after 3 and 7 months were treated with antibiotic therapy and implant removal. Bone dislocation was stated radiologically in 14% of the cases; the exact locations and clinical consequences were not described in detail. In 1999, Kallela et al22 published a study about the fixation of 11 patients with anterior mandibular fractures that had been treated with biodegradable lag screws manufactured from SR-PLLA. Six of these were fixed maxillomandibular from 1 to 5 weeks. One patient showed an osteolysis around the fracture line already 6 weeks after the fixation, and regeneration was seen after 6 months with new bone formation. The 3 most commonly used materials for resorbable plating systems are polyglycolic acid, poly-L-lactic acid, copolymers of these 2, and poly-dioxanone-sulphate. These materials were initially used as suture materials,23 but use has since spread to many fields of surgery because of their advantages compared with metal plates and screws. Besides palpability or sometimes visibility, metal fixation systems are hampered by temperature sensitivity and interference with radiographic imaging. Also, excessive stress shielding may be found from rigid plate fixation, leading to the wellknown effect of atrophy of cortical bone and the need for a subsequent operation for removal. Bioabsorbable implants gradually transfer load to the healing bone as they resorb. Stress shielding and osteopenia seen with metal implants24,25 are rarely seen with biodegradable implants. The main reason for restriction of use of biodegradable devices was their mechanical weakness. The physical demands on absorbable fixation devices are suitable rigidity, adequate stability, and complete degradation without any complications. The unreinforced degradable implants lack sufficient mechanical strength and stiffness to provide secure internal fixation
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of mandibular fractures. Unreinforced PLLA plates and screws have been used in the fixation of low-load bearing fractures, such as zygomatic fractures.13,15,16 To¨ rma¨ la¨ et al26 developed a special technique in reinforcing the implant with highly orientated fibers of the same polyester drawn in a longitudinal axis, termed self reinforcement. This method produces a more durable composition of matrix and fibers and shows significantly higher tensile and flexural modulus of elasticity.26 Because of the reinforcement, the mechanical demands needed for initial fracture stability within the first 6 to 8 weeks are provided. The appropriate strength needed during this postoperative time to meet the initial biomechanical demands and the gradual biodegradation of the reinforced material with gradual load transfer to the healing bone make the reinforced material sufficient for fixation of mandibular fractures. The main mode of degradation of PLLA biomaterials is hydrolysis.27 The tissue reaction is thought to be the result of the inability to absorb the degradation products that are associated with rapid hydrolysis. In contrast to PLLA, polyglycolic acid undergoes a more rapid hydrolysis and therefore incites higher inflammatory reactions. For that reason, PLLA devices retain strength longer. The degradation time of PLLA is up to 6 years, with a loss of mechanical strength of SR-PLLA devices after approximately 36 weeks.28 The biocompatibility of PLLA has been the subject of numerous studies. In 1966, Kulkarni et al1 first reported the potential of polylactides as resorbable biomaterials for use in surgery. The excellent biocompatibility of PLLA is generally accepted. Nevertheless, inflammatory tissue reactions around PLLA implants and late adverse reactions were reported in animal and clinical studies by different authors.28,29 The tissue reaction changes as biodegradation progresses. In 1993 and 1995, Bergsma et al20,28 reported late tissue response to PLLA used for fracture fixation of the zygomatic bone. Four of 10 patients showed intermittent painless swelling in the operative site more than 3 years after fracture fixation. In 4 patients, surgical removal of the implants was necessary. The reduction of the volume of the implanted material with the self-reinforcing technique to the definitely necessary minimum could help to enhance the biocompatibility during the degradation phase. PATIENTS AND METHODS Twenty-two patients with mandibular fractures underwent operation over a period of 18.5 months. All patients volunteered after receiving study information. The indications for open reduction and internal fixation were displaced fractures of the mandible not older than 3 days (Figs 1 and 2). Patients with infections, systemic
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after the operation. MMF was applied in patients with concomitant fractures of the condyles (nos. 9, 15, and 17). All patients were placed on an initial soft diet for 10 to 14 days, with progression gradually to a regular nutrition afterwards.
Fig 1. Panoramic radiograph of fracture before operation.
Examination methods In addition to clinical examinations, panoramic radiographs were taken immediately after surgery and at 1, 2, 3, and 6 months after the open reduction. A computed tomographic (CT) scan also was used for examinations and evaluations 3 and 6 months after the operation. Radiographs and CT scans were analyzed by the same person for displacement, diastasis, visibility of the fracture line and the drill channels, callus formation, and ossification of the mandibular fracture.
diseases, and edentulous or atrophic jaws were excluded. Fracture sites were located as specified in the Table. Fractures of the mandibular angle were present in 6 patients (nos. 7, 11, 18, 19, 20, and 21). Another 3 patients with body and concomitant ramus (no. 8) or condylar (nos. 15 and 17) fractures were treated with fixation of both fracture sites with biodegradable devices. Patients no. 15 and 17 had their conditions stabilized with MMF for 3 weeks. One patient (no. 9) had a body fracture and concomitant, nondisplaced condylar fractures on both sides; after open reduction of the corpus with biodegradable osteosynthesis, MMF was applied for 2 weeks. Detailed information about the 22 patients is given in the Table. A resorbable nonmetallic fixation system (BiosorbFX 2.0 system, Bionx Implants, Inc, Tampere, Finland) constructed of self-reinforced polylactic acid copolymer (SR-P[L/DL]LA [70/30]) was used for the fixation of all mandibular fractures. The instrumentation consisted of an appropriately sized bone drill, a bone tap, a screwdriver, and bending forceps. A transbuccal system from the same company was used for the reduction of angular and condylar fractures. The polylactide plates of the BiosorbFX 2.0 system are available in sizes from 4-hole to 16-hole plates (5.5-mm wide and 1.2-mm thick). The screws of the same system (2 mm in diameter) range from 4 to 40 mm in length.
RESULTS The patient population consisted of 8 female and 14 male patients with an average age of 26.3 years (range, 11.5 to 69 years). The mean follow-up period was 49.1 weeks (range 22 to 78 weeks).
Operative technique The open fracture reduction with general anesthesia was performed with standard operative techniques, with the only exception being that biodegradable plates and screws were used to fix each fracture. Two 6-hole plates and screws of 6, 8, or 10 mm in length of the BiosorbFX 2.0 fixation system were used at each fracture site (Figs 3 and 4). A nonresorbable suture material was used for wound closure and was removed 10 days
Imaging No signs of bone healing disturbances of the other patients were noticed via panoramic or CT scan imaging during the entire follow-up period. Bone formation and fading of the fracture line was seen between 2 and 3 months after surgery in the panoramic films. However, the fracture line continued to be detectable in all CT scans. Drill channels were also visible in all samples of the CT scans during the entire study period. The
Clinical follow-up Primary healing was uneventful in 20 patients. No infections were diagnosed. A slight submucosal swelling was seen in 1 patient (no. 1) but disappeared within 1 week. No extrusion of the implants occurred. Postoperative occlusion was correct in all patients. Hypesthesia or anesthesia of the lower lip was observed in all patients but was always transient. Two patients had mucosal wound dehiscences over the plates after 5 days. In 1 patient (no. 6), secondary sutures were applied and wound healing was uneventful afterwards. Patient no. 2 was totally incompliant and did not refrain from nicotine and alcohol abuse. Secondary sutures were ineffective, and wound healing was seriously compromised. Because of local infection, the biodegradable plates and screws had to be removed and conventional metal plates and screws were applied. Two months later, the patient underwent reoperation because of nonunion at the fracture site. The mandible was stabilized with a metal reconstruction plate, and further wound healing was uneventful.
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Fig 2. Endoral view before fixation plates were applied.
Table. Details about patients Patient no.
Sex
Age (y)
1 2
M M
21 57
3 4 5 6
M F M F
7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Region of fracture fixed with biodegradable devices
Maxillomandibular fixation (wk)
Follow-up (wk)
Mandibular body Mandibular body
No No
78 2, reoperated
17.5 19 46 36
Mandibular Mandibular Mandibular Mandibular
No No No No
70 65 64 64
F F M
24.5 13.5 11.5 13.5 21 25 19.5 21 26 69 22.5 20 22.5 18.5 29.5 27.5
No No Yes, 2 condyles not operated No No No No No Yes, 3 No Yes, 3 No No No No No
61 59 57
M M F F M M M M M F F M M
Mandibular body ⫹ right angle Mandibular body ⫹ left ramus Mandibular body, left ⫹ right condyle Mandibular body Left angle Mandibular body Mandibular body Mandibular body Mandibular body ⫹ left condyle Mandibular body Mandibular body ⫹ left condyle Mandibular body ⫹ left angle Mandibular body ⫹ right angle Mandibular body ⫹ left angle Right angle Mandibular body
Submucosal swelling Dehiscence, infection, removal of material Uneventful Uneventful Uneventful Dehiscence, closure with sutures Uneventful Uneventful Uneventful
56 56 54 52 52 48 46 45 45 31 27 27 22
Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful Uneventful
body body body body
Healing complications
M, male; F, female.
fractures were considered to be consolidated on the basis of the radiologic examination after 3 months. The fracture ends were united by new bone after 3 months, and cortical bone was apparent after 6 months in all cases examined after this period.
The images of the follow-up of patient no. 3 show the steps of bone healing; the initial situation with a fracture of the mandibular body is seen in the panoramic radiograph (Fig 1) and endoral view (Fig 2). The postoperative clinical situation is seen in Fig 3.
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Fig 3. View of fracture after fixation with 2 biodegradable 6-hole plates and screws of 8 and 10 mm in length. Appropriate reduction and stabilization is achieved.
Fig 4. Panoramic radiograph immediately after open reduction and internal fixation, showing reduced fracture and radiolucent areas of drill channels.
Immediately after surgery, the fracture line and drill holes were well visible (Fig 4). Six months after internal fixation, fracture ends were united and the fracture line was not visible, but the drill channels were still detectable as radiolucent areas (Fig 5). DISCUSSION The adaptation of the biodegradable plates to the bone surface was as uncomplicated as with titanium miniplates. A slight grade of overbending was necessary because of the elasticity of the material. In contrast to other biodegradable fixation systems, no heating device was necessary. The plates were easily bendable with forceps at room temperature, and none of the plates broke during bending. At the bending areas, white lines occurred in the transparent plates, but this
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Fig 5. Panoramic radiograph 24 weeks after operation without fracture line. Reduction and maintenance of inferior border continuity is seen. Drill channels are still detectable.
did not influence the physical quality of the devices. This phenomenon is described as microdelamination in the instructions of the manufacturer. The screws were threaded and fit well into the bone. Screw failure was low; only 2 screws broke during the insertion (1 material failure, 1 incorrect handling). In such cases, a new hole was easily drilled through the broken screw and a new screw was inserted without problems, fitting perfectly into the mandibular bone. Nine screws could not be used because of production failures; their cruciform heads did not fit on the screwdriver. As far as we know, this is the first clinical report on the appliance of biodegradable self-reinforced polylactide plates and screws for the open reduction of human mandibular fractures. The investigators attempted to refrain from MMF whenever possible. MMF was only applied in 3 patients with concomitant condylar fractures. Patient no. 9 did not have condyle fixation, and therefore, MMF was used. In 2 cases (nos. 15 and 17), MMF was applied for 3 weeks after fixation of the condyles with biodegradable material for further stability. No MMF was used after the reduction of all other fractures. Only 3 complications were seen during the entire follow-up period. In patient no. 2, the biodegradable implant material had to be removed because of healing disturbances and infection. The mandibular fracture then was stabilized with conventional metal implants. Further bone healing was uncomplicated. Although different factors, like total noncompliance, may have caused this special condition, it cannot be excluded that the implant material itself was a cause. In patient no. 1, the implant material might have caused a mild mucosal swelling that was self-limiting. The implant positioning
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also possibly caused the wound dehiscence in patient no. 6 that was treated with closure with sutures. However, 2 of 3 complications were managed easily. No complications occurred in the remaining 19 patients, and postoperative healing did not differ from patients with metal implants. Occlusion was normal, and no dislocation, diastasis, or nonunion was seen. All patients showed perfect occlusion after the operation and also during the period of follow-up. Unlike conventional metal plates, the less rigid biodegradable implants seemed to allow a minimal but smooth degree of settling of the occlusion while at the same time providing a stable reduction of the fracture. Ossification of the fracture was seen after 3 months in the radiologic analysis. In 1 patient, the drill channels seemed uncommonly large during the whole follow-up period. However, this patient had no clinical symptoms, and the reason for this enlargement is unknown. At the end of the follow-up period, screw holes could still be detected radiologically in all patients as radiolucent areas. No early adverse reactions were seen to date. Except for the complications in patients no. 1, 2, and 6, mentioned previously, no further evidence was seen of implant-related tissue reactions, like local swelling, infection, sinus formation, discharge, fistula formation, discoloration, or osteolysis, during the follow-up period. The possibility of late reactions to biodegradable implants as reported in the literature26-28 will be monitored. What makes biodegradable fracture fixation devices more attractive than metal ones is that no removal operation is needed after bone healing. In our clinic, it is common practice to remove metal plates and screws after bone healing. If not removed, the metal implants may be painful and irritating. Also, imaging techniques, such as CT scans and magnetic resonance imaging, show interference with the metal devices remaining in situ, above all with ferrous metals. Stress shielding with local osteoporosis and possible refracture after removal are additional disadvantages of metal implants. They may incite allergic reactions and long-term metal ion release, creating another cause for concern. This is particularly relevant because there are reports of possible release of free metals from osteosynthesis materials,30-32 and removal is recommended for all young patients. This means a second operation and, in most cases, also general anesthesia and hospitalization. Considering the previously mentioned arguments, the authors believe that self-reinforced biodegradable osteosynthesis material is a good alternative to metal implants. Furthermore, it is also more economic because minor differences in the expenses for the acquisition of bioabsorbable implants are clearly offset by
the avoidance of a second procedure for implant removal. However, because the clinically applied biodegradable fixation systems have no long-term results in the open reduction of mandibular fractures, all patients of this study were closely observed. Patients were also advised to apply to the clinic if any clinical symptoms like swelling or inflammation occurred. This fixation device does not appear to interfere with the normal healing pattern of the fractured bone. Also, no systemic or severe local disorders have been reported during the entire time of follow-up. CONCLUSION The mechanical properties of the SR-PLLA plates and screws applied for mandibular fracture fixation are comparable with those of metal fixation systems. The treatment goals of immobilization, fixation, and stabilization were found to be fulfilled. The skeletal stability was comparable with actual standards and sufficient for the time needed for mandibular bone healing. On the basis of the results of this study, it can be concluded that biodegradable SR-PLLA implants have the potential for successful use in the fixation of human mandibular fractures. REFERENCES 1. Kulkarni RK, Pani KC, Neumann C, Leonard F. Polylactic acid for surgical implants. Arch Surg 1966;93:839-43. 2. Cutright DE, Hunsuck EE, Beasley JD. Fracture reduction using a biodegradable material, poly lactic acid. J Oral Surg 1971;9: 393-7. 3. Getter L, Cutright DE, Bhaskar SN, Augsburg JK. A biodegradable intraosseous appliance in the treatment of mandibular fractures. J Oral Surg 1972;30:344-8. 4. Ewers R, Forster H. Resorbable materials for osteosynthesis. An experimental animal study. Dtsch Z Mund Kiefer Gesichtschir 1985;196-201. 5. Ewers R, Ha¨ rle F. Experimental and clinical results of new advances in the treatment of facial trauma. Plast Reconstr Surg 1985;75:25-31. 6. Gerlach L, Krause HR, Eitenmu¨ ller J. Absorbable osteosynthesis materials for immobilization of mandibular fractures. Animal experimental study. Dtsch Z Mund Kiefer Gesichtschir 1988;12: 418-22. 7. Rokkanen P, Bo¨ stman O, Vainionpa¨ a¨ S, et al. Biodegradable implants in fracture fixation: early results of treatment of fractures of the ankle. Lancet 1985;1:1422-4. 8. Bos RRM, Rozema FR, Boering G, Nijenhuis AJ, Pennings AJ, Verwey AB. Bio-absorbable plates and screws for internal fixation of mandibular fractures. A study in six dogs. Int J Oral Maxillofac Surg 1989;18:365-9. 9. Suuronen R. Comparison of absorbable self-reinforced poly-llactide screws and metallic screws in the fixation of mandibular condyle osteotomies. Experimental study in sheep. J Oral Maxillofac Surg 1991;49:989-95. 10. Suuronen R, Pohjonen T, Wessmann L, To¨ rma¨ la¨ P, Vainionpa¨ a¨ S. New generation biodegradable plate for fracture fixation. Comparison of bending strengths of mandibular osteotomies fixed with absorbable self-reinforced multi-layer poly-l-lactide plates and metallic plates. An experimental study in sheep. Clin Mater 1992;9:77-84. 11. Suuronen R, To¨ rma¨ la¨ P, Vasenius J, Wessmann L, Mero M,
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ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY September 2002 24. Uhthoff H, Boisvert D, Finnegan M. Cortical porosis under plates. Reaction to unloading or to necrosis? J Bone Joint Surg Am 1994;76:1507-12. 25. Viljanen J, Kinnunen J, Bandestam S, Majola A, Rokkanen P, Torma¨ la¨ P. Bone changes after experimental osteotomies fixed with absorbable self-reinforced poly-L-lactide screws or metallic screws studied by plain radiographs, quantitive computed tomography, and magnetic resonance imaging. Biomaterials 1995;16: 1353-8. 26. To¨ rma¨ la¨ P, Pellinen M, Pohjonen T, et al. Totally biodegradable self-reinforced rods and screws for internal fixation of bone fractures. Acta Othop Scand 1990;227:17. 27. Williams DF. Some observations on the role of cellular in the in vivo degradation of polymers. In: Syrett BC, Acharya A, editors. STM special technical publications, corrosion and degradation of implant materials. Philadelphia: American Society for Testing and Materials; 1979. p. 61-75. 28. Bergsma JE, de Bruijn, Rozema FR, Bos RR, Boering G. Late degradation tissue response to poly(L-lactide) bone plates and screws. Biomaterials 1995;16:25-31. 29. Bos RR, Rozema FR, Boering G, Nijenhuis AJ, Pennings AJ, Verwey AB, et al. Degradation of and tissue reaction to biodegradable poly(L-lactide) for use as internal fixation of fractures: a study in rats. Biomaterials 1991;12:32-6. 30. Rosenberg A, Gratz KW, Sailer HF. Should titanium miniplates be removed after bone healing is complete? Int J Oral Maxillofac Surg 1993;22:185-8. 31. Schliephake H, Lehmann H, Kunz U, Schmelzeisen R. Ultrastructural findings in soft tissues adjacent to titanium plates used in jaw fracture treatment. Int J Oral Maxillofac Surg 1993;22: 20-5. 32. Jorgenson DS, Mayer MH, Ellenbogen RG, Centeno JA, Johnson FB, Mullick FG, et al. Detection of titanium in human tissues after craniofacial surgery. Plast Reconstr Surg 1997;99:976-9. Reprint requests: Kaan C. Yerit, MD University Hospital of Cranio-Maxillofacial and Oral Surgery Medical School, University of Vienna Wa¨ hringer Gu¨ rtel 18-20 A-1090 Wien Austria [email protected]