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Current experiments in polymeric mandibular implants for bone induction
British Journal of Oral Surgery (I973), Io, 326-333
. CURRENT
EXPERIMENTS IMPLANTS
IN P O L Y M E R I C
MANDIBULAR
FOR BONE INDUCTION
M. RAPPOPORT, D.Sc., and D. L. LEAKE, D.M.D., M.D. 1 Department of Surgery, Division of Oral Surgery, Harbor General Hospital, Torrance, and the University of California at Los Angeles, Schools of Dentistry and Medicine, Los Angeles, California OSSEOUScontour defects have long been a challenge to the reconstructive surgeon (Ivy, I95I; Brown et al., 1963; Bascom, 1964; Braley, 1968; Cipcic, 1968; Zarem, 1968; Rhodes, I969; Boyne, 197o, 197o, 1971; Laub et al., 197o). The task is more difficult when the bone is stress-bearing as is the case with the mandible (Small et al., 1964; Cohen, 1967; Phillips, I967; Schecter & Pories, 1967; Cook, 1968; Gaskins, et al., 1969; Leake et al., 1971). Autologous bone grafts were first reported in the late nineteenth century and were popularised as a result of the First World War (Ivy, I95I). Iliac crest bone, solid grafts from the tibia, the metatarsals and ribs have been used. Shortcomings include adapting the bone to facial contour and the problems of unpredictable resorption and remodelling which may lead to failure of the graft due to fracture. Particulate bone grafting has been successful in the fusion of joints and in filling surgical defects (Urist, 1965; Urist et al., I967; Urist & McLean, 1968). By using a rigid metal tray to bridge defects and hold bone particles, mandibles have been effectively reconstructed. The technique requires great skill in fabricating and
FIG. I Bone and urethane/dacron trays to hold the particulate bone graft material.
installing the metal tray and has received limited acceptance. By devising a polymeric tray which could be easily made in quantity, at low cost, and in a variety of sizes and shapes and which possessed the qualities desirable for implantation, the 1 Reprint requests to Doctor Leake, Harbor General Hospital, Torrance, California, 9o5o 9. 326
CURRENT EXPERIMENTS IN POLYMERIC MANDIBULAR IMPLANTS
327
bone induction system could be invoked to restore bony defects including those of the mandible. Obviously too, because of ease in its use, the technique might find greater acceptance than previously described procedures. The application of alloplastic materials for repair and reconstruction of mandibular and maxillo-facial anomalies presents a unique challenge to the biomaterials scientist. Problems of histocompatibility, local and systemic cytotoxicity and chemical inertness, in addition to the demands of high physical strength, optimal rigidity and simple fabricating technology were assessed in a study of oral surgical prostheses by Bloch & Hastings in x967. The purpose of the present study was the development and evaluation of materials, methods, and techniques which would facilitate surgical repair and reconstruction of malformations, of both hard and soft tissues of the face and jaws due to genetic, traumatic or carcinogenic causes. The modus operandi included fabrication and testing of newly designed composite structures, moulded into hollow mesh prostheses which reproduce normal contours and thus facilitate regeneration of bone by the bone induction principle (Fig. I). The application of this technique facilitates the reconstruction of large bony defects by providing an environment conductive to osteogenesis wherein repair is effected by the growth of new bone.
MATERIALS AND METHODS The materials currently employed to provide the prototype implant prostheses are polyether urethane elastomers (Athley, I965). These are medium viscosity casting liquids processed and cured at elevated temperatures. Properties of the liquid polymers are listed in Table I. When catalysed with 4"4'-methylene-bis (2 chloroaniline) at proper stoichiometric levels and cured by heat and extended ambient exposure, the prototype prostheses possess the physical properties outlined in Table II. TABLE I
Liquid Chemical Composition Physical Form Available Isocyanate Brookfiled Viscosity Catalyst
:
urethane polymer Fully saturated polyether urethane Viscous amber liquid 9-0 per cent 86°F-2o,ooo CPS I58°F-I,OOO CPS 4'4'-Methylene-bis (2 chloroaniline) 27"2 per cent/unit weight
The implants being fabricated include trays for the restoration of bony contour defects. The trays are prepared by saturating Dacron mesh in the catalysed urethane and removing excess polymer by calendering between sheets of polyethylene. The impregnated mesh is then draped on to a solid model of the section to be reconstructed and contoured tightly around the model by means of small spring damps. This structure is oven-cured for six hours at 2oo°F and subsequently trimmed to finabisize and shape. It is sterilised by autoclaving.
328
BRITISH JOURNAL OF ORAL SURGERY TABLE I I
Properties of cured unsupported urethane elastomer Hardness~ Shore Durometer ' D ' 72 IOO per cent Modulus~ P S I 5ooo Tensile Strength, P S I 9ooo Elongations per cent 3oo Flexural Modulus ( A S T M D-79o-6IB) 90,0oo Heat Distortion Temperature (66 PSI) °F 275 I2oD Impact ( A S T M D-256) N o break Compression Set ' A ' (135o PSI/22 hrs/I58°F) per cent IO N B S Abrasion Index 45o Solenoid Brittle Point Less than - 9 4 ° F Cure: 6 hours at 212°F Post Cure: 3 days ambient
Surgical Technique. Maxillary and mandibular teeth were extracted unilaterally in eight mongrel dogs and the alveolar ridges allowed to heal for approximately three weeks. Mandibular discontinuity defects ranging from 4 cm to hemi-mandibles were created in the edentulous mandible through an extra-oral surgical approach. Segments were resected with a water-cooled bur. Each defect was bridged with a prefabricated hollow mesh tray or tube implant made of Dacron or nylon mesh impregnated with polyether urethane moulded to the contour of the excised section and sutured securely in place with 28 gauge stainless steel wire (Figs. 2, 3). The implants were filled with autologous cancellous and particulate bone chips, measuring 3 to 5 ram3 (Bloch & Hastings, 1967) taken from the iliac crest. Following this procedure, the animals were returned to recovery cages and placed on soft diets. Antibiotics were given post-operatively for five days (BiciUin 1,2oo,ooo units IMqd). Periodic X-ray examination was used to monitor bone regeneration. Biopsies were taken at five weeks, two, three and five months. Biopsy specimens were fixed in IO per cent formalin, decalcified and stained with haematoxylin and eosin. Intravital staining using oxytetracyclinewas studied in three dogs at intervals of two, three and six months after insertion of the implant and bone graft. Each dog received 2oo mg of oxytetracycline one week prior to biopsy. RESULTS
Radiography. Initially, the ostectomy site can be seen filled with discrete chips of particulate bone graft material. Gradually these particulate chips become less individually distinctive and the radiograph appears more homogeneous. In the lateral jaw radiograph taken at five months (Fig. 4), the area of the defect can be seen where new bone bridges the gap. Radiographs taken later show that lamellar bone appears on the outer surface and progressively thickens with time to form cortex. New bone fills the tray conforming to the contours. Histology. Biopsy specimens were taken at intervals of five weeks, two, three and five months. At two months it can be seen that there are osteogenic loci which eventually coalesce to form a continuum of new cancellous bone and fibrous tissue.
CURRENT EXPERIMENTS IN POLYMERIC MANDIBULAR IMPLANTS
FIG. 2 A discontinuity defect is seen between the ends of bone clamps. T h e composite tray can be trimmed with scissors to improve the fit. A submandibular approach is used.
FIG. 3 T h e tray has been secured in position with 28 gauge stainless steel wires and has been filled with particulate bone graft material.
329
BB0
BRITISH JOURNAL OF ORAL SURGERY
FIG. 4 A radiograph taken at three months shows the defect bracketed. New bone has formed bridging the gap and presents a homogenous appearance. T h e arrow shows the site of biopsy.
FIG. 5 Histology of the biopsy site seen in Figure 4. There is slight surface remodelling of the particulate bone graft, and a finger-like projection of new bone can be seen extending into the interstitial areas.
CURRENT EXPERIMENTS I N POLYMERIC MANDIBULAR I M P L A N T S
331
Spindle-shaped cells with areas of mitoses and osteoid are evident in the interstitial areas. Some areas on the surface of bone graft particles are resorbed, and others are covered with new bone (Fig. 5). Only a small fraction of the particulate bone graft surfaces appear to be resorbed and new bone is laid down as evidenced by the cement line. A finger-like projection of new bone can be seen projecting into the interstitial area of the section shown. New bone continues to be laid down and lamellar bone appears on the outer surfaces at approximately three months and will progressively thicken to form cortex. Additional evidence for new bone formation is provided by labelling with intra-vital stains. Tetracyline will react with newly deposited mineral, and when examined under ultraviolet light will fluoresce a light yellow colour. Three dogs
FIG. 6 P r o t o t y p e t r a y for i m p l a n t a t i o n i n m a n .
were studied at intervals of two, and three months after the insertion of the implant. Initially, there are numerous small areas of osteogenesis, and later areas of coalescence in these calcification fronts are apparent until a continuum of new bone unites the host and graft bone. Additionally, periosteal new bone formation is prominent in specimens taken after three months. Evaluation of the plastic tray taken from sacrificed animals revealed no appreciable change in tensile strength, weight or rigidity. Control samples of urethane/dacron structure immersed in physiologicial saline solution for 6o days at 25°C confirmed the hydrolytic stability of this implant after initial water absorption equilibrium has been achieved. Implications. This tissue-compatible, preformed plastic tray implant provides the maxillo-facial surgeon with a light-weight rigid prosthesis which can
332
BRITISH JOURNAL OF ORAL SURGERY
be trimmed easily at the operating table to meet patient requirements. In mandibular reconstruction the structure will also support the floor of the mouth and tongue thus improving function. After a period of approximately six months, when new bone formation has been satisfactorily formed, it would support a denture, so further increasing function. Other facial bony contour defects could be restored using a similar method. The urethane/dacron composite is easily and accurately made at very nominal expense. The ability to effect final trimming at the operating table (using only scissors) is a significant advantage permitting 'customising' of prostheses from prefabricated mass-produced units. It may be that this current success with urethane polymers is attributable in part to precise stoichiometry, resin temperature, mixing, curing and other physical factors which can readily influence physical behaviour of the cured elastomer. Deviations in any of these considerations generally resulted in inferior polymers with markedly reduced physical ability to survive the biologically active environment as inert implants. A prototype tray for human mandibular reconstruction is shown in Figure 6. SUMMARY A technique for fabricating a urethane composite tray to hold particulate bone graft material for utilisation of the bone induction principle in mandibular reconstruction has been described. Eight mongrel dogs had discontinuity defects created in unilaterally edentulous mandibles. The defect was bridged by the composite tray and filled with particulate bone chips prepared from an iliac crest bone graft. New bone formation was progressive and the form assumed was that imposed by the limits of the implant tray, which suggests a use in the reconstruction of other bony contour defects where aesthetic considerations are of paramount importance. REFERENCES ATHLEY, R. J. (1965). Water resistance of liquid urethane vulcanizates. Rubber Age, 96, 705. BASCOM,P. (1964). The use of silicones in maxillofacial abnormalities. Plastic and Reconstructive Surgery, 34, 419. BLOCH,B. & HASTINGS,G. (1967). Plastics in Surgery. Illinois: Thomas. BOYNE,P. J. (197o). Restoration of osseous defects in maxillofacial casualties. Journal of the American Dental Association, 78, 767. BOYNE, P. J. (197o). Autogenous cancellous bone and marrow transplants. Clinical Orthopaedics, 73, 199. BOYNE, P. J. (1971). Transplantation, implantation and grafts. Dental Clinics of North America, 15, 433. BRALEY,S. (1968). The silicones as subdermal engineering materials. Annals of the New York Academy of Science, 146, 148. BRALEY,S. (1968). The silicones in maxillofacial surgery. Laryngoscope, 78, 549. BROWN,J. B., FRYAR,N. P. & COLIAS,P. (1963). Silicone and Teflon Prostheses including full jaw substitution. Annals of Surgery, I57, 932. CIPClC, J. (1968). Silicone implant correction of facial deformities. Laryngoscope, 78, 565. COHEN,J. (1967). Bio-materials in orthopedic surgery. American Journal of Surgery, II4, 3I COOK, H. P. (1968). Immediate reconstruction of the mandible by metallic implant following resection for neoplasm. Annals of the Royal College of Surgeons, England, 42, 233. , :
CURRENT EXPERIMENTS IN POLYMERIC MANDIBULAR IMPLANTS
333
FITZPATRICK, B. (1968). A comparative study of some implant materials. Australian Dental Journal, I3, 360; I3, 422. GASKINS, J. A., JR., ERTUGRI_rL,G. & RUSH, B. F., JR. (I969). Tolerance to stainless steel prostheses in patients after post radiation hemi-mandibulectomy. American Journal of Surgery, IX7, 375. HARRIS,H. (I964). The use of silicones in maxillofacial abnormalities. Plastic and Reconstructive Surgery, 34, 419. IvY, R. H. (I95I). Bone grafting for restoration of defects of the mandible. Plastic and Reconstructive Surgery, 7, 333. LAUB, D. R., SPOHN,W., LASH,H., WEBER,J. & CHASE,R. A. (197o). Accurate reconstruction of traumatic bony contour defects of periorbital area with prefabricated Silastic. Journal of Trauma, IO, 472. LEAKE, D., MURRAY,J. E., HABAL,M. B. • SWANSON,L. (1971). Custom fabrication of mandibular reconstruction. Oral Surgery, Oral Medicine and Oral Pathology, (in press). PHILLIPS, C. M. (1967). Primary and secondary reconstruction of the mandible after ablative surgery. Report of 24 cases using stainless steel prostheses. American Journal of Surgery, II7, 375. RHODES,III, R. (I969). Restoration of facial defects with individually prefabricated silicone prostheses. Plastic and Reconstructive Surgery. 43, 2Ol. RICHTER, H. E., SUGG, W. E. & BOYNE, P. J. (1968). Stimulation of osteogenesis in the dog mandible by autogenous bone matrow transplants. Oral Surgery, Oral Medicine and Oral Pathology, 26, 396. ROBINSON,M., (1959). Silver implant in situ 51 years after resection of mandible. Journal of the American Medical Association, I7I, 890. SCHECTER,L. & PORIES,W., (1967). Partial mandibular replacement with a silicone strut. American Journal of Surgery, II3, 846. SMALL, I. A., BROWN, S. & KOEERNICK,S. D. (I964). Teflon and Silastic for mandibular replacement; experimental studies and reports of cases. JournalofOralSurgery,22,377. URIST, M. R. (1965). Bone formation by autoinduction. Science, I5O, 893. URIST, M. R., SILVERMAN,B. F., BURING,K., BUBUC,F. L. & ROSENBURG,J. D. (1967). The bone induction principle. Clinical Orthopedics, 53, 254. URIST, M. R. & McLEAN, F. C. (1968). Bone, fundamentals of the physiology of skeletal tissue. Illinois: University of Chicago Press. WESOLOWSKI,S. A. & McMAHoN, J. D. The surgical uses of plastics. SPE Journal, 24, 43YEAGER,J. E. & BOYNE,P. J. (1969). The use of bone homografts and autogenous marrow in restoration of alveolar ridges. Journal of Oral Surgery, 27, 185. ZAREM,H. (1968). Silastic implants in plastic surgery. Surgical Clinics of North America, 48 , 129.
. CURRENT
EXPERIMENTS IMPLANTS
IN P O L Y M E R I C
MANDIBULAR
FOR BONE INDUCTION
M. RAPPOPORT, D.Sc., and D. L. LEAKE, D.M.D., M.D. 1 Department of Surgery, Division of Oral Surgery, Harbor General Hospital, Torrance, and the University of California at Los Angeles, Schools of Dentistry and Medicine, Los Angeles, California OSSEOUScontour defects have long been a challenge to the reconstructive surgeon (Ivy, I95I; Brown et al., 1963; Bascom, 1964; Braley, 1968; Cipcic, 1968; Zarem, 1968; Rhodes, I969; Boyne, 197o, 197o, 1971; Laub et al., 197o). The task is more difficult when the bone is stress-bearing as is the case with the mandible (Small et al., 1964; Cohen, 1967; Phillips, I967; Schecter & Pories, 1967; Cook, 1968; Gaskins, et al., 1969; Leake et al., 1971). Autologous bone grafts were first reported in the late nineteenth century and were popularised as a result of the First World War (Ivy, I95I). Iliac crest bone, solid grafts from the tibia, the metatarsals and ribs have been used. Shortcomings include adapting the bone to facial contour and the problems of unpredictable resorption and remodelling which may lead to failure of the graft due to fracture. Particulate bone grafting has been successful in the fusion of joints and in filling surgical defects (Urist, 1965; Urist et al., I967; Urist & McLean, 1968). By using a rigid metal tray to bridge defects and hold bone particles, mandibles have been effectively reconstructed. The technique requires great skill in fabricating and
FIG. I Bone and urethane/dacron trays to hold the particulate bone graft material.
installing the metal tray and has received limited acceptance. By devising a polymeric tray which could be easily made in quantity, at low cost, and in a variety of sizes and shapes and which possessed the qualities desirable for implantation, the 1 Reprint requests to Doctor Leake, Harbor General Hospital, Torrance, California, 9o5o 9. 326
CURRENT EXPERIMENTS IN POLYMERIC MANDIBULAR IMPLANTS
327
bone induction system could be invoked to restore bony defects including those of the mandible. Obviously too, because of ease in its use, the technique might find greater acceptance than previously described procedures. The application of alloplastic materials for repair and reconstruction of mandibular and maxillo-facial anomalies presents a unique challenge to the biomaterials scientist. Problems of histocompatibility, local and systemic cytotoxicity and chemical inertness, in addition to the demands of high physical strength, optimal rigidity and simple fabricating technology were assessed in a study of oral surgical prostheses by Bloch & Hastings in x967. The purpose of the present study was the development and evaluation of materials, methods, and techniques which would facilitate surgical repair and reconstruction of malformations, of both hard and soft tissues of the face and jaws due to genetic, traumatic or carcinogenic causes. The modus operandi included fabrication and testing of newly designed composite structures, moulded into hollow mesh prostheses which reproduce normal contours and thus facilitate regeneration of bone by the bone induction principle (Fig. I). The application of this technique facilitates the reconstruction of large bony defects by providing an environment conductive to osteogenesis wherein repair is effected by the growth of new bone.
MATERIALS AND METHODS The materials currently employed to provide the prototype implant prostheses are polyether urethane elastomers (Athley, I965). These are medium viscosity casting liquids processed and cured at elevated temperatures. Properties of the liquid polymers are listed in Table I. When catalysed with 4"4'-methylene-bis (2 chloroaniline) at proper stoichiometric levels and cured by heat and extended ambient exposure, the prototype prostheses possess the physical properties outlined in Table II. TABLE I
Liquid Chemical Composition Physical Form Available Isocyanate Brookfiled Viscosity Catalyst
:
urethane polymer Fully saturated polyether urethane Viscous amber liquid 9-0 per cent 86°F-2o,ooo CPS I58°F-I,OOO CPS 4'4'-Methylene-bis (2 chloroaniline) 27"2 per cent/unit weight
The implants being fabricated include trays for the restoration of bony contour defects. The trays are prepared by saturating Dacron mesh in the catalysed urethane and removing excess polymer by calendering between sheets of polyethylene. The impregnated mesh is then draped on to a solid model of the section to be reconstructed and contoured tightly around the model by means of small spring damps. This structure is oven-cured for six hours at 2oo°F and subsequently trimmed to finabisize and shape. It is sterilised by autoclaving.
328
BRITISH JOURNAL OF ORAL SURGERY TABLE I I
Properties of cured unsupported urethane elastomer Hardness~ Shore Durometer ' D ' 72 IOO per cent Modulus~ P S I 5ooo Tensile Strength, P S I 9ooo Elongations per cent 3oo Flexural Modulus ( A S T M D-79o-6IB) 90,0oo Heat Distortion Temperature (66 PSI) °F 275 I2oD Impact ( A S T M D-256) N o break Compression Set ' A ' (135o PSI/22 hrs/I58°F) per cent IO N B S Abrasion Index 45o Solenoid Brittle Point Less than - 9 4 ° F Cure: 6 hours at 212°F Post Cure: 3 days ambient
Surgical Technique. Maxillary and mandibular teeth were extracted unilaterally in eight mongrel dogs and the alveolar ridges allowed to heal for approximately three weeks. Mandibular discontinuity defects ranging from 4 cm to hemi-mandibles were created in the edentulous mandible through an extra-oral surgical approach. Segments were resected with a water-cooled bur. Each defect was bridged with a prefabricated hollow mesh tray or tube implant made of Dacron or nylon mesh impregnated with polyether urethane moulded to the contour of the excised section and sutured securely in place with 28 gauge stainless steel wire (Figs. 2, 3). The implants were filled with autologous cancellous and particulate bone chips, measuring 3 to 5 ram3 (Bloch & Hastings, 1967) taken from the iliac crest. Following this procedure, the animals were returned to recovery cages and placed on soft diets. Antibiotics were given post-operatively for five days (BiciUin 1,2oo,ooo units IMqd). Periodic X-ray examination was used to monitor bone regeneration. Biopsies were taken at five weeks, two, three and five months. Biopsy specimens were fixed in IO per cent formalin, decalcified and stained with haematoxylin and eosin. Intravital staining using oxytetracyclinewas studied in three dogs at intervals of two, three and six months after insertion of the implant and bone graft. Each dog received 2oo mg of oxytetracycline one week prior to biopsy. RESULTS
Radiography. Initially, the ostectomy site can be seen filled with discrete chips of particulate bone graft material. Gradually these particulate chips become less individually distinctive and the radiograph appears more homogeneous. In the lateral jaw radiograph taken at five months (Fig. 4), the area of the defect can be seen where new bone bridges the gap. Radiographs taken later show that lamellar bone appears on the outer surface and progressively thickens with time to form cortex. New bone fills the tray conforming to the contours. Histology. Biopsy specimens were taken at intervals of five weeks, two, three and five months. At two months it can be seen that there are osteogenic loci which eventually coalesce to form a continuum of new cancellous bone and fibrous tissue.
CURRENT EXPERIMENTS IN POLYMERIC MANDIBULAR IMPLANTS
FIG. 2 A discontinuity defect is seen between the ends of bone clamps. T h e composite tray can be trimmed with scissors to improve the fit. A submandibular approach is used.
FIG. 3 T h e tray has been secured in position with 28 gauge stainless steel wires and has been filled with particulate bone graft material.
329
BB0
BRITISH JOURNAL OF ORAL SURGERY
FIG. 4 A radiograph taken at three months shows the defect bracketed. New bone has formed bridging the gap and presents a homogenous appearance. T h e arrow shows the site of biopsy.
FIG. 5 Histology of the biopsy site seen in Figure 4. There is slight surface remodelling of the particulate bone graft, and a finger-like projection of new bone can be seen extending into the interstitial areas.
CURRENT EXPERIMENTS I N POLYMERIC MANDIBULAR I M P L A N T S
331
Spindle-shaped cells with areas of mitoses and osteoid are evident in the interstitial areas. Some areas on the surface of bone graft particles are resorbed, and others are covered with new bone (Fig. 5). Only a small fraction of the particulate bone graft surfaces appear to be resorbed and new bone is laid down as evidenced by the cement line. A finger-like projection of new bone can be seen projecting into the interstitial area of the section shown. New bone continues to be laid down and lamellar bone appears on the outer surfaces at approximately three months and will progressively thicken to form cortex. Additional evidence for new bone formation is provided by labelling with intra-vital stains. Tetracyline will react with newly deposited mineral, and when examined under ultraviolet light will fluoresce a light yellow colour. Three dogs
FIG. 6 P r o t o t y p e t r a y for i m p l a n t a t i o n i n m a n .
were studied at intervals of two, and three months after the insertion of the implant. Initially, there are numerous small areas of osteogenesis, and later areas of coalescence in these calcification fronts are apparent until a continuum of new bone unites the host and graft bone. Additionally, periosteal new bone formation is prominent in specimens taken after three months. Evaluation of the plastic tray taken from sacrificed animals revealed no appreciable change in tensile strength, weight or rigidity. Control samples of urethane/dacron structure immersed in physiologicial saline solution for 6o days at 25°C confirmed the hydrolytic stability of this implant after initial water absorption equilibrium has been achieved. Implications. This tissue-compatible, preformed plastic tray implant provides the maxillo-facial surgeon with a light-weight rigid prosthesis which can
332
BRITISH JOURNAL OF ORAL SURGERY
be trimmed easily at the operating table to meet patient requirements. In mandibular reconstruction the structure will also support the floor of the mouth and tongue thus improving function. After a period of approximately six months, when new bone formation has been satisfactorily formed, it would support a denture, so further increasing function. Other facial bony contour defects could be restored using a similar method. The urethane/dacron composite is easily and accurately made at very nominal expense. The ability to effect final trimming at the operating table (using only scissors) is a significant advantage permitting 'customising' of prostheses from prefabricated mass-produced units. It may be that this current success with urethane polymers is attributable in part to precise stoichiometry, resin temperature, mixing, curing and other physical factors which can readily influence physical behaviour of the cured elastomer. Deviations in any of these considerations generally resulted in inferior polymers with markedly reduced physical ability to survive the biologically active environment as inert implants. A prototype tray for human mandibular reconstruction is shown in Figure 6. SUMMARY A technique for fabricating a urethane composite tray to hold particulate bone graft material for utilisation of the bone induction principle in mandibular reconstruction has been described. Eight mongrel dogs had discontinuity defects created in unilaterally edentulous mandibles. The defect was bridged by the composite tray and filled with particulate bone chips prepared from an iliac crest bone graft. New bone formation was progressive and the form assumed was that imposed by the limits of the implant tray, which suggests a use in the reconstruction of other bony contour defects where aesthetic considerations are of paramount importance. REFERENCES ATHLEY, R. J. (1965). Water resistance of liquid urethane vulcanizates. Rubber Age, 96, 705. BASCOM,P. (1964). The use of silicones in maxillofacial abnormalities. Plastic and Reconstructive Surgery, 34, 419. BLOCH,B. & HASTINGS,G. (1967). Plastics in Surgery. Illinois: Thomas. BOYNE,P. J. (197o). Restoration of osseous defects in maxillofacial casualties. Journal of the American Dental Association, 78, 767. BOYNE, P. J. (197o). Autogenous cancellous bone and marrow transplants. Clinical Orthopaedics, 73, 199. BOYNE, P. J. (1971). Transplantation, implantation and grafts. Dental Clinics of North America, 15, 433. BRALEY,S. (1968). The silicones as subdermal engineering materials. Annals of the New York Academy of Science, 146, 148. BRALEY,S. (1968). The silicones in maxillofacial surgery. Laryngoscope, 78, 549. BROWN,J. B., FRYAR,N. P. & COLIAS,P. (1963). Silicone and Teflon Prostheses including full jaw substitution. Annals of Surgery, I57, 932. CIPClC, J. (1968). Silicone implant correction of facial deformities. Laryngoscope, 78, 565. COHEN,J. (1967). Bio-materials in orthopedic surgery. American Journal of Surgery, II4, 3I COOK, H. P. (1968). Immediate reconstruction of the mandible by metallic implant following resection for neoplasm. Annals of the Royal College of Surgeons, England, 42, 233. , :
CURRENT EXPERIMENTS IN POLYMERIC MANDIBULAR IMPLANTS
333
FITZPATRICK, B. (1968). A comparative study of some implant materials. Australian Dental Journal, I3, 360; I3, 422. GASKINS, J. A., JR., ERTUGRI_rL,G. & RUSH, B. F., JR. (I969). Tolerance to stainless steel prostheses in patients after post radiation hemi-mandibulectomy. American Journal of Surgery, IX7, 375. HARRIS,H. (I964). The use of silicones in maxillofacial abnormalities. Plastic and Reconstructive Surgery, 34, 419. IvY, R. H. (I95I). Bone grafting for restoration of defects of the mandible. Plastic and Reconstructive Surgery, 7, 333. LAUB, D. R., SPOHN,W., LASH,H., WEBER,J. & CHASE,R. A. (197o). Accurate reconstruction of traumatic bony contour defects of periorbital area with prefabricated Silastic. Journal of Trauma, IO, 472. LEAKE, D., MURRAY,J. E., HABAL,M. B. • SWANSON,L. (1971). Custom fabrication of mandibular reconstruction. Oral Surgery, Oral Medicine and Oral Pathology, (in press). PHILLIPS, C. M. (1967). Primary and secondary reconstruction of the mandible after ablative surgery. Report of 24 cases using stainless steel prostheses. American Journal of Surgery, II7, 375. RHODES,III, R. (I969). Restoration of facial defects with individually prefabricated silicone prostheses. Plastic and Reconstructive Surgery. 43, 2Ol. RICHTER, H. E., SUGG, W. E. & BOYNE, P. J. (1968). Stimulation of osteogenesis in the dog mandible by autogenous bone matrow transplants. Oral Surgery, Oral Medicine and Oral Pathology, 26, 396. ROBINSON,M., (1959). Silver implant in situ 51 years after resection of mandible. Journal of the American Medical Association, I7I, 890. SCHECTER,L. & PORIES,W., (1967). Partial mandibular replacement with a silicone strut. American Journal of Surgery, II3, 846. SMALL, I. A., BROWN, S. & KOEERNICK,S. D. (I964). Teflon and Silastic for mandibular replacement; experimental studies and reports of cases. JournalofOralSurgery,22,377. URIST, M. R. (1965). Bone formation by autoinduction. Science, I5O, 893. URIST, M. R., SILVERMAN,B. F., BURING,K., BUBUC,F. L. & ROSENBURG,J. D. (1967). The bone induction principle. Clinical Orthopedics, 53, 254. URIST, M. R. & McLEAN, F. C. (1968). Bone, fundamentals of the physiology of skeletal tissue. Illinois: University of Chicago Press. WESOLOWSKI,S. A. & McMAHoN, J. D. The surgical uses of plastics. SPE Journal, 24, 43YEAGER,J. E. & BOYNE,P. J. (1969). The use of bone homografts and autogenous marrow in restoration of alveolar ridges. Journal of Oral Surgery, 27, 185. ZAREM,H. (1968). Silastic implants in plastic surgery. Surgical Clinics of North America, 48 , 129.