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Metallic fragments on the surface of miniplates and screws before insertion
British Journal of Oral and Maxillofacial Surgery (1998) 37, 14–18 © 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
Metallic fragments on the surface of miniplates and screws before insertion M. S. Ray, I. R. Matthew, J. W. Frame University of Birmingham, School of Dentistry, Oral Surgery Unit, Birmingham, UK SUMMARY. Particulate metal fragments have been identified histologically within the tissues adjacent to miniplates and screws after they have been removed. These were thought to have been caused by corrosion and degradation of the metal. However, the particles may have originated from rough edges or from protuberances left on the metal surface after cutting and machining during manufacture, and subsequently become detached. This study was undertaken to analyse the incidence and distribution of metal fragments on the surface of miniplates and screws before use. Fifteen miniplates and 60 screws were examined by stereomicroscopy and scanning electron microscopy. Rough metal edges or protuberances were identified on over half the samples, mostly in the countersink area of screw holes on the mini-plates. Fragments were detected within some of the cruciform screw heads and on some screw threads. We conclude that metal protuberances are present on the surface of mini-plate components when they are received from the manufacturer. There is a risk that the fragments might be detached and deposited into the tissues during insertion.
Germany) were bought from the UK distributor (Albert Waeschle, Surgical, Laboratory and Dental Supplies, Bournemouth). The surfaces of 15 miniplates (5 stainless steel, code no. 25–250–04; 10 titanium, code no. 25–350–04) and 60 screws (all 7 mm long; 20 each of stainless steel, code no. 25–090–07; titanium, code no. 25–092–07 (cruciate head design); and titanium alloy, code no. 25–095–07 (Centre-drive® head design) were examined by visual inspection, stereomicroscopy (Wild MC3, Type-S, Heerbrugg, Switzerland, 6.4 ×, 16 ×, and 40 × magnification) and scanning electron microscopy (EM) (JEOL 5300LV apparatus, Jeol Technics Ltd, Tokyo, Japan, 50–350 × magnification). Energy dispersive analysis (PGT system 4+ apparatus, Princeton Gamma-Tech Inc, Princeton, NJ, USA) was used to confirm the elemental composition of metal fragments. A systematic examination of the miniplates covered the inferior, superior, and lateral surfaces of the miniplate, and the screw holes (countersinks). The screw heads were examined before the screw threads. Statistical analysis was undertaken on an IBM compatible PC with Minitab version 11 (Minitab Inc, State College, PA, USA).
INTRODUCTION Rigid internal fixation methods using miniplates and screws have an important role in maxillofacial trauma, and orthognathic and reconstructive surgery.1 Loose metal particles are created during handling of plates and screws, some of which may be released into the surrounding tissues, and macroscopic evidence of tissue pigmentation from stainless steel and titanium miniplate components has been reported.2–5 Light microscopy examination of the pigmented tissues has shown metal deposits within the tissues which were thought to have arisen from corrosion or degradation of the metal.3,4,6 Atomic absorption spectrophotometry studies have shown raised levels of metal ions in the tissues adjacent to miniplate components.7 Titanium particles have been identified in the submandibular lymph nodes after removal of miniplates and screws from patients.8 However, the metal particles may get into the tissues by a different mechanism. Rough metallic edges and protuberances might be formed during manufacture of the plates and screws by the milling machinery that makes the screw threads and miniplate screw holes. The loose metallic fragments may subsequently be released into the tissues through friction or abrasion of the miniplate or screw surface during contact with instruments or burs.9 The aim of this study was to examine the surface of miniplates and screws before use to find out the incidence and distribution of the metal fragments produced during their manufacture.
RESULTS Few obvious finishing defects were detected on visual inspection of the plates and screws. On stereomicroscopic examination of the flat surfaces of the miniplates there were a few gouge marks with raised but adherent metal fragments. However, rough metallic edges and protuberances (burrs) were present around the circumference of several screw holes, particularly at the upper and lower rim of the countersink (Figs 1, 2, and 3). There were more burrs on the titanium plates than on the stainless steel ones. Scanning EM
MATERIALS AND METHODS Miniplate components (Martin-Medizin-Technik, Gebrüder Martin GmbH & Co. KG, Tuttlingen, 14
Metallic fragments on the surface of miniplates and screws before insertion
15
Fig. 1 – Scanning EM view of a metallic burr at the upper rim of a screw hole countersink on a titanium miniplate.
Fig. 2 – Scanning EM view of multiple metal fragments along the upper rim of a screw hole countersink of a stainless steel miniplate.
Fig. 3 – Scanning EM view of a lip of metal that has been formed at the lower rim of the screw hole countersink, adjacent to the fitting surface of the miniplate.
Fig. 4 – Scanning EM view of a metal fragment adherent to the lateral surface of a titanium miniplate.
examination and energy dispersive analysis confirmed that the metal irregularities were of similar composition to the adjacent metal surface. A few splinters were present on the lateral surfaces of miniplates (Fig. 4). There were also metal fragments around the machined screw threads and within the cruciformshaped slots on the stainless steel and titanium screw heads (Figs 5 and 6). Fewer burrs were present within the Centre-drive® screw head recesses compared with the stainless steel and titanium screw cruciform heads. Splinters of metal were attached to the machined
screw thread on over half the screws examined (Fig. 7). The incidence and distribution of metal burrs are summarized in Tables 1 and 2. There was no significant difference between the length of metallic burrs on titanium and stainless steel plates (Mann-Whitney U test; P = 0.30), but there was a significant difference between the length of metallic burrs on titanium, stainless steel, and titanium alloy (Centre-drive®) screws (Kruskal-Wallis test; H = 20.46, DF = 2, P = 0.00). The overall median lengths of metallic burrs on titanium, stainless steel, and titanium alloy
16
British Journal of Oral and Maxillofacial Surgery
Fig. 5 – Scanning EM view of the cruciform-shaped head of a titanium screw, illustrating adherent fragments of metal within the slot.
Fig. 7 – Scanning EM view of multiple metal fragments, at the periphery of a screw thread close to the tip of a titanium screw.
(Centre-drive®) screws were 80, 50, and 40 µm, respectively. Most metallic burrs were identified on pure titanium screws (41), whereas Centre-Drive® screws had the least (17).
DISCUSSION This study has shown that there are finishing defects on titanium and stainless steel miniplates, and screws of the cruciate and Centre-drive® design, when they
Fig. 6 – A higher power scanning EM view of the metal fragments shown in Fig. 5.
are received from the manufacturer. These may subsequently become detached during manipulation, and metal debris may be deposited within the tissues at the site of implantation. Fragments may become detached from the miniplate through contact between the rotating drill and the miniplate countersink during preparation of the screw hole. Other fragments may be released through friction between the screw head and screwdriver tip, or between the self-tapping thread of the screw and the bone. Fretting corrosion at the plate screw interface is another potential source of metal particles, yielding small aggregates of metal as the degradation product.6 It is necessary to bend most miniplates before insertion for perfect adaptation of the plate to the bone surface. This may create microfractures and loosening of metal particles.4 What is the importance of metal debris within the tissues? Particulate titanium debris within the tissues may have a mild inflammatory potential.10 Particles measuring 1–10 µm in diameter are a potent stimulator of macrophages in vitro.11 Torgersen et al.3 identified metal particles of various size (up to 100–200 µm in diameter), occupying over half the total area of some of the histological sections examined. Although some of the particles were engulfed by macrophages and fibroblasts, most were surrounded by fibrous connective tissue with no associated inflammatory reaction. Metal particles have been shown in vitro to stimulate fibroblasts, which results in increased collagen synthesis.11 Schliephake et al.5 suggested that lysosomal degradation of the phagocytosed particles may occur in conjunction with gradual isolation of the phagocytic cells by collagen fibres during healing. Active transport of some of the particles from the tissues by the phagocytes is therefore prevented. Once the phagocytic cells die, groups of partially degraded particles remain within the connective tissues.
Metallic fragments on the surface of miniplates and screws before insertion
17
Table 1 – The incidence, distribution, and median length of metallic protuberances found on the miniplates Total number of particles found on:
Titanium plates (n = 10) screw holes = 40
Miniplate countersinks (upper rim) Median length in µm (range) Miniplate countersinks (lower rim) Median length in µm (range) Miniplate flat surfaces Median length in µm (range) Miniplate lateral surfaces Median length in µm (range)
19 90 (570) 11 900 (1850) 2 45 (10) 2 135 (30)
Stainless steel plates (n = 5) screw holes = 20 7 75 (690) 9 550 (1030) 0 – 1 50 (0)
Table 2 – The incidence, distribution, and median length of metallic protuberances found on the screws Total number of particles found on: Screw thread Median length in µm (range) Screw head Median length in µm (range)
Titanium screws (n = 20)
Stainless steel screws (n = 20)
41 80 (160) 17 70 (180)
Torgersen et al.3 noted in retrieval studies that lymphocytes and macrophages were common within the tissues adjacent to loose screws. Bone-resorbing mediators such as prostaglandin E2 and interleukin 1 may be released from macrophages in association with titanium wear debris.12 Interleukin 1 is a potent bone resorbing agent,13 and may be responsible for the aseptic loosening of miniplate screws that is observed occasionally on removal, in the absence of previous wound infection or soft tissue dehiscence. Thermal damage may occur even during careful preparation of the screw hole, giving rise to loosening of the screw by aseptic necrosis.1 The biological effects of exposure to metal particles occur not only at the site of implantation, but also at distant sites as a result of phagocytosis and active transport.5 Lymphatic transport of metal particles is recognized, both from animal studies14 and from clinical case reports.8 The use of metal plates and screws as permanent implants is likely to prolong exposure to metal particles and metal ions. The formation of metal particles will increase the surface area available for oxidation and ion release.6 The long term clinical and toxicological effects of dispersed metal ions are uncertain. The design and method of use of implants that do not release particulate debris are becoming of major importance in orthopaedics, more so than the development of biomaterials of improved biocompatibility.15,16 This is true also of maxillofacial implants. Levy et al.17 recommended copious irrigation after fixation of a miniplate to remove bony or metal debris from the fracture site. This may, however, disperse metal particles throughout the tissues. Metal fragments will remain within the tissues even after removal of the miniplate, although the formation of particles by fretting corrosion would cease. Release of metal particles into the tissues from miniplates and screws is undesirable, and may be minimized by
29 70 (80) 14 60 (110)
Titanium alloy screws (n = 20) 17 40 (70) 3 40 (20)
careful surgical technique. In addition, metal plates and screws should be free of all rough edges or protuberances on the surface to minimize the risk of detachment and deposition into the adjacent tissues.
References 1. Millar BG, Frame JW, Browne RM. A histological study of stainless steel and titanium screws in bone. Br J Oral Maxillofac Surg 1990; 28: 92–95. 2. Matthew IR, Frame JW, Browne RM, Millar BG. In vivo analysis of titanium and stainless steel miniplates and screws. Int J Oral Maxillofac Surg 1996; 25: 463–468. 3. Torgersen S, Gjerdet NR, Erichsen ES, Bang G. Metal particles and tissue changes adjacent to miniplates. A retrieval study. Acta Odontol Scand 1995; 53: 65–71. 4. Rosenberg A, Grätz KW, Sailer HF. Should titanium miniplates be removed after bone healing is complete? Int J Oral Maxillofac Surg 1993; 22: 185–188. 5. 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: 20–25. 6. French HG, Cook SD, Haddad RJ, Jnr. Correlation of tissue reaction to corrosion in osteosynthetic devices. J Biomater Res 1984; 18: 817–828. 7. Moberg L-E, Nordenram Å, Kjellman O. Metal release from plates used in jaw fracture treatment. A pilot study. Int J Oral Maxillofac Surg 1989; 18: 311–314. 8. Onodera K, Ooya KO, Kawamura H. Titanium lymph node pigmentation in the reconstruction plate system of a mandibular defect. Oral Surg Oral Med Oral Pathol 1993; 75: 495–497. 9. Torgersen S, Gjerdet S. Retrieval study of stainless steel and titanium miniplates and screws used in maxillofacial surgery. J Mater Sci: Mater Med 1994; 5: 256–262. 10. Rae T. The biological response to titanium and titaniumaluminium-vanadium alloy particles. I. Tissue culture studies. Biomaterials 1986; 7: 30–40. 11. Goldring SR, Bennett NE, Jasty MJ, Wang, J-T. In vitro activation of monocyte macrophages and fibroblasts by metal particles. In: St. John KR, Ed. Particulate debris from medical implants: mechanisms of formation and biological consequences. ASTM STP 1144. Philadelphia: American Society for Testing and Materials, 1992: 136–142.
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British Journal of Oral and Maxillofacial Surgery
12. Shanbhag AS, Jacobs JJ, Black J, Galante JO, Glant TT. Macrophage/particle interactions: Effect of size, composition, and surface area. J Biomed Mater Res 1994; 28: 81–90. 13. Meikle MC. Control mechanisms in bone resorption: 240 years after John Hunter. Ann R Coll Surg Engl 1997, 79: 20–27 14. Meachim G, Brooke G. The synovial response to intraarticular Co-Cr-Mo particles in Guinea pigs. Biomaterials 1983; 4: 153–159. 15. Evans EJ. Cell damage in vitro following direct contact with fine particles of titanium, titanium alloy and cobalt-chromemolybdenum alloy. Biomaterials 1994; 15: 713–717. 16. Lalor PA, Revell PA. T-lymphocytes and titanium aluminium vanadium (TiAIV) alloy: evidence for immunological events associated with debris deposition. Clin Mater 1993; 12: 57–62. 17. Levy FE, Smith RW, Odland RM, Marentette LJ. Monocortical miniplate fixation of mandibular angle fractures. Arch Otolaryngol Head Neck Surg 1991, 117: 149–154.
The Authors M. S. Ray BSc (Hons) Research student I. R. Matthew MDentSc, BDS, FDSRCS Lecturer in Oral Surgery J. W. Frame PhD, MSc, BDS, FDSRCS Professor of Oral Surgery The University of Birmingham, School of Dentistry, Oral Surgery Unit, St. Chad’s Queensway Birmingham B4 6NN, UK Correspondence and requests for offprints to Mr I. R. Matthew Paper received 10 March 1997 Accepted 26 June 1997
BRITISH JOURNAL OF ORAL
& M A X I L L O FA C I A L S U R G E RY
Metallic fragments on the surface of miniplates and screws before insertion M. S. Ray, I. R. Matthew, J. W. Frame University of Birmingham, School of Dentistry, Oral Surgery Unit, Birmingham, UK SUMMARY. Particulate metal fragments have been identified histologically within the tissues adjacent to miniplates and screws after they have been removed. These were thought to have been caused by corrosion and degradation of the metal. However, the particles may have originated from rough edges or from protuberances left on the metal surface after cutting and machining during manufacture, and subsequently become detached. This study was undertaken to analyse the incidence and distribution of metal fragments on the surface of miniplates and screws before use. Fifteen miniplates and 60 screws were examined by stereomicroscopy and scanning electron microscopy. Rough metal edges or protuberances were identified on over half the samples, mostly in the countersink area of screw holes on the mini-plates. Fragments were detected within some of the cruciform screw heads and on some screw threads. We conclude that metal protuberances are present on the surface of mini-plate components when they are received from the manufacturer. There is a risk that the fragments might be detached and deposited into the tissues during insertion.
Germany) were bought from the UK distributor (Albert Waeschle, Surgical, Laboratory and Dental Supplies, Bournemouth). The surfaces of 15 miniplates (5 stainless steel, code no. 25–250–04; 10 titanium, code no. 25–350–04) and 60 screws (all 7 mm long; 20 each of stainless steel, code no. 25–090–07; titanium, code no. 25–092–07 (cruciate head design); and titanium alloy, code no. 25–095–07 (Centre-drive® head design) were examined by visual inspection, stereomicroscopy (Wild MC3, Type-S, Heerbrugg, Switzerland, 6.4 ×, 16 ×, and 40 × magnification) and scanning electron microscopy (EM) (JEOL 5300LV apparatus, Jeol Technics Ltd, Tokyo, Japan, 50–350 × magnification). Energy dispersive analysis (PGT system 4+ apparatus, Princeton Gamma-Tech Inc, Princeton, NJ, USA) was used to confirm the elemental composition of metal fragments. A systematic examination of the miniplates covered the inferior, superior, and lateral surfaces of the miniplate, and the screw holes (countersinks). The screw heads were examined before the screw threads. Statistical analysis was undertaken on an IBM compatible PC with Minitab version 11 (Minitab Inc, State College, PA, USA).
INTRODUCTION Rigid internal fixation methods using miniplates and screws have an important role in maxillofacial trauma, and orthognathic and reconstructive surgery.1 Loose metal particles are created during handling of plates and screws, some of which may be released into the surrounding tissues, and macroscopic evidence of tissue pigmentation from stainless steel and titanium miniplate components has been reported.2–5 Light microscopy examination of the pigmented tissues has shown metal deposits within the tissues which were thought to have arisen from corrosion or degradation of the metal.3,4,6 Atomic absorption spectrophotometry studies have shown raised levels of metal ions in the tissues adjacent to miniplate components.7 Titanium particles have been identified in the submandibular lymph nodes after removal of miniplates and screws from patients.8 However, the metal particles may get into the tissues by a different mechanism. Rough metallic edges and protuberances might be formed during manufacture of the plates and screws by the milling machinery that makes the screw threads and miniplate screw holes. The loose metallic fragments may subsequently be released into the tissues through friction or abrasion of the miniplate or screw surface during contact with instruments or burs.9 The aim of this study was to examine the surface of miniplates and screws before use to find out the incidence and distribution of the metal fragments produced during their manufacture.
RESULTS Few obvious finishing defects were detected on visual inspection of the plates and screws. On stereomicroscopic examination of the flat surfaces of the miniplates there were a few gouge marks with raised but adherent metal fragments. However, rough metallic edges and protuberances (burrs) were present around the circumference of several screw holes, particularly at the upper and lower rim of the countersink (Figs 1, 2, and 3). There were more burrs on the titanium plates than on the stainless steel ones. Scanning EM
MATERIALS AND METHODS Miniplate components (Martin-Medizin-Technik, Gebrüder Martin GmbH & Co. KG, Tuttlingen, 14
Metallic fragments on the surface of miniplates and screws before insertion
15
Fig. 1 – Scanning EM view of a metallic burr at the upper rim of a screw hole countersink on a titanium miniplate.
Fig. 2 – Scanning EM view of multiple metal fragments along the upper rim of a screw hole countersink of a stainless steel miniplate.
Fig. 3 – Scanning EM view of a lip of metal that has been formed at the lower rim of the screw hole countersink, adjacent to the fitting surface of the miniplate.
Fig. 4 – Scanning EM view of a metal fragment adherent to the lateral surface of a titanium miniplate.
examination and energy dispersive analysis confirmed that the metal irregularities were of similar composition to the adjacent metal surface. A few splinters were present on the lateral surfaces of miniplates (Fig. 4). There were also metal fragments around the machined screw threads and within the cruciformshaped slots on the stainless steel and titanium screw heads (Figs 5 and 6). Fewer burrs were present within the Centre-drive® screw head recesses compared with the stainless steel and titanium screw cruciform heads. Splinters of metal were attached to the machined
screw thread on over half the screws examined (Fig. 7). The incidence and distribution of metal burrs are summarized in Tables 1 and 2. There was no significant difference between the length of metallic burrs on titanium and stainless steel plates (Mann-Whitney U test; P = 0.30), but there was a significant difference between the length of metallic burrs on titanium, stainless steel, and titanium alloy (Centre-drive®) screws (Kruskal-Wallis test; H = 20.46, DF = 2, P = 0.00). The overall median lengths of metallic burrs on titanium, stainless steel, and titanium alloy
16
British Journal of Oral and Maxillofacial Surgery
Fig. 5 – Scanning EM view of the cruciform-shaped head of a titanium screw, illustrating adherent fragments of metal within the slot.
Fig. 7 – Scanning EM view of multiple metal fragments, at the periphery of a screw thread close to the tip of a titanium screw.
(Centre-drive®) screws were 80, 50, and 40 µm, respectively. Most metallic burrs were identified on pure titanium screws (41), whereas Centre-Drive® screws had the least (17).
DISCUSSION This study has shown that there are finishing defects on titanium and stainless steel miniplates, and screws of the cruciate and Centre-drive® design, when they
Fig. 6 – A higher power scanning EM view of the metal fragments shown in Fig. 5.
are received from the manufacturer. These may subsequently become detached during manipulation, and metal debris may be deposited within the tissues at the site of implantation. Fragments may become detached from the miniplate through contact between the rotating drill and the miniplate countersink during preparation of the screw hole. Other fragments may be released through friction between the screw head and screwdriver tip, or between the self-tapping thread of the screw and the bone. Fretting corrosion at the plate screw interface is another potential source of metal particles, yielding small aggregates of metal as the degradation product.6 It is necessary to bend most miniplates before insertion for perfect adaptation of the plate to the bone surface. This may create microfractures and loosening of metal particles.4 What is the importance of metal debris within the tissues? Particulate titanium debris within the tissues may have a mild inflammatory potential.10 Particles measuring 1–10 µm in diameter are a potent stimulator of macrophages in vitro.11 Torgersen et al.3 identified metal particles of various size (up to 100–200 µm in diameter), occupying over half the total area of some of the histological sections examined. Although some of the particles were engulfed by macrophages and fibroblasts, most were surrounded by fibrous connective tissue with no associated inflammatory reaction. Metal particles have been shown in vitro to stimulate fibroblasts, which results in increased collagen synthesis.11 Schliephake et al.5 suggested that lysosomal degradation of the phagocytosed particles may occur in conjunction with gradual isolation of the phagocytic cells by collagen fibres during healing. Active transport of some of the particles from the tissues by the phagocytes is therefore prevented. Once the phagocytic cells die, groups of partially degraded particles remain within the connective tissues.
Metallic fragments on the surface of miniplates and screws before insertion
17
Table 1 – The incidence, distribution, and median length of metallic protuberances found on the miniplates Total number of particles found on:
Titanium plates (n = 10) screw holes = 40
Miniplate countersinks (upper rim) Median length in µm (range) Miniplate countersinks (lower rim) Median length in µm (range) Miniplate flat surfaces Median length in µm (range) Miniplate lateral surfaces Median length in µm (range)
19 90 (570) 11 900 (1850) 2 45 (10) 2 135 (30)
Stainless steel plates (n = 5) screw holes = 20 7 75 (690) 9 550 (1030) 0 – 1 50 (0)
Table 2 – The incidence, distribution, and median length of metallic protuberances found on the screws Total number of particles found on: Screw thread Median length in µm (range) Screw head Median length in µm (range)
Titanium screws (n = 20)
Stainless steel screws (n = 20)
41 80 (160) 17 70 (180)
Torgersen et al.3 noted in retrieval studies that lymphocytes and macrophages were common within the tissues adjacent to loose screws. Bone-resorbing mediators such as prostaglandin E2 and interleukin 1 may be released from macrophages in association with titanium wear debris.12 Interleukin 1 is a potent bone resorbing agent,13 and may be responsible for the aseptic loosening of miniplate screws that is observed occasionally on removal, in the absence of previous wound infection or soft tissue dehiscence. Thermal damage may occur even during careful preparation of the screw hole, giving rise to loosening of the screw by aseptic necrosis.1 The biological effects of exposure to metal particles occur not only at the site of implantation, but also at distant sites as a result of phagocytosis and active transport.5 Lymphatic transport of metal particles is recognized, both from animal studies14 and from clinical case reports.8 The use of metal plates and screws as permanent implants is likely to prolong exposure to metal particles and metal ions. The formation of metal particles will increase the surface area available for oxidation and ion release.6 The long term clinical and toxicological effects of dispersed metal ions are uncertain. The design and method of use of implants that do not release particulate debris are becoming of major importance in orthopaedics, more so than the development of biomaterials of improved biocompatibility.15,16 This is true also of maxillofacial implants. Levy et al.17 recommended copious irrigation after fixation of a miniplate to remove bony or metal debris from the fracture site. This may, however, disperse metal particles throughout the tissues. Metal fragments will remain within the tissues even after removal of the miniplate, although the formation of particles by fretting corrosion would cease. Release of metal particles into the tissues from miniplates and screws is undesirable, and may be minimized by
29 70 (80) 14 60 (110)
Titanium alloy screws (n = 20) 17 40 (70) 3 40 (20)
careful surgical technique. In addition, metal plates and screws should be free of all rough edges or protuberances on the surface to minimize the risk of detachment and deposition into the adjacent tissues.
References 1. Millar BG, Frame JW, Browne RM. A histological study of stainless steel and titanium screws in bone. Br J Oral Maxillofac Surg 1990; 28: 92–95. 2. Matthew IR, Frame JW, Browne RM, Millar BG. In vivo analysis of titanium and stainless steel miniplates and screws. Int J Oral Maxillofac Surg 1996; 25: 463–468. 3. Torgersen S, Gjerdet NR, Erichsen ES, Bang G. Metal particles and tissue changes adjacent to miniplates. A retrieval study. Acta Odontol Scand 1995; 53: 65–71. 4. Rosenberg A, Grätz KW, Sailer HF. Should titanium miniplates be removed after bone healing is complete? Int J Oral Maxillofac Surg 1993; 22: 185–188. 5. 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: 20–25. 6. French HG, Cook SD, Haddad RJ, Jnr. Correlation of tissue reaction to corrosion in osteosynthetic devices. J Biomater Res 1984; 18: 817–828. 7. Moberg L-E, Nordenram Å, Kjellman O. Metal release from plates used in jaw fracture treatment. A pilot study. Int J Oral Maxillofac Surg 1989; 18: 311–314. 8. Onodera K, Ooya KO, Kawamura H. Titanium lymph node pigmentation in the reconstruction plate system of a mandibular defect. Oral Surg Oral Med Oral Pathol 1993; 75: 495–497. 9. Torgersen S, Gjerdet S. Retrieval study of stainless steel and titanium miniplates and screws used in maxillofacial surgery. J Mater Sci: Mater Med 1994; 5: 256–262. 10. Rae T. The biological response to titanium and titaniumaluminium-vanadium alloy particles. I. Tissue culture studies. Biomaterials 1986; 7: 30–40. 11. Goldring SR, Bennett NE, Jasty MJ, Wang, J-T. In vitro activation of monocyte macrophages and fibroblasts by metal particles. In: St. John KR, Ed. Particulate debris from medical implants: mechanisms of formation and biological consequences. ASTM STP 1144. Philadelphia: American Society for Testing and Materials, 1992: 136–142.
18
British Journal of Oral and Maxillofacial Surgery
12. Shanbhag AS, Jacobs JJ, Black J, Galante JO, Glant TT. Macrophage/particle interactions: Effect of size, composition, and surface area. J Biomed Mater Res 1994; 28: 81–90. 13. Meikle MC. Control mechanisms in bone resorption: 240 years after John Hunter. Ann R Coll Surg Engl 1997, 79: 20–27 14. Meachim G, Brooke G. The synovial response to intraarticular Co-Cr-Mo particles in Guinea pigs. Biomaterials 1983; 4: 153–159. 15. Evans EJ. Cell damage in vitro following direct contact with fine particles of titanium, titanium alloy and cobalt-chromemolybdenum alloy. Biomaterials 1994; 15: 713–717. 16. Lalor PA, Revell PA. T-lymphocytes and titanium aluminium vanadium (TiAIV) alloy: evidence for immunological events associated with debris deposition. Clin Mater 1993; 12: 57–62. 17. Levy FE, Smith RW, Odland RM, Marentette LJ. Monocortical miniplate fixation of mandibular angle fractures. Arch Otolaryngol Head Neck Surg 1991, 117: 149–154.
The Authors M. S. Ray BSc (Hons) Research student I. R. Matthew MDentSc, BDS, FDSRCS Lecturer in Oral Surgery J. W. Frame PhD, MSc, BDS, FDSRCS Professor of Oral Surgery The University of Birmingham, School of Dentistry, Oral Surgery Unit, St. Chad’s Queensway Birmingham B4 6NN, UK Correspondence and requests for offprints to Mr I. R. Matthew Paper received 10 March 1997 Accepted 26 June 1997