DIAG IM3 - Page 67

Tel +44 0845114 130258 9596 8530info@vetinst.com info@vetinst.com Dental Equipment & Instrumentation Internal Fixation15 3 Compression Plates and Cortical Screws (AO/ ASIF type) By carefully positioning screws within the special holes of compression plates, compression can be exerted at the reduced fracture site as the screw is tightened. As the spherical head of the screw strikes the rear edge of the hole in the plate, the screw, (and the attached bone) are forced away from the edge of the hole and towards the fracture site. The object of compression is to provide for primary bone union. A special guide must be used to position accurately the screw hole within the plate. The oval shaped holes in DCP’s allow a greater range of screw angulations than round hole plates. Cortical screws are available in both tapped and self tapping formats. AO type screws and plates have, for many years, been the human and veterinary standard implants. They were originally designed in the 1950s by the AO study group [Arbeitsgemeinschaft für Osteosynthesefragen (English: Association for the Study of Internal Fixation, AO/ASIF) ] which continues to this day to lead the world in implant design. The design of the spherical screw head and the compression hole are particularly important as, unless made to very exacting specifications, they will not work properly together. The composition and design of AO type implants are laid down in very detailed international standards. The specification for plates and screws are detailed below. Provided implants are made to these exacting standards it is safe to mix and match sources. Be very wary about using implants which may not comply. Materials BS 7252-1:1997 ISO 5832-1:1997 Metallic materials for surgical implants. Specification for wrought stainless steel. BS 7252-3:1997 ISO 5832-3:1996 Metallic materials for surgical implants. Specification for wrought titanium 6al4v. BS 7252-9:1993 ISO 5832-9:1992 Metallic materials for surgical implants. Specification for high nitrogen stainless steel BS ISO 5832-2:1999 Implants for surgery. Metallic materials. Unalloyed titanium. Bone Screws BS 3531-5.3:1991, ISO 5835:1991 Implants for osteosynthesis. Bone screws and auxiliary equipment. Specification for the dimensions of screws having hexagonal drive connection, spherical under-surfaces and asymmetrical thread. BS 3531-5.6:1991, ISO 6475:1989 Implants for osteosynthesis. Bone screws and auxiliary equipment. Specification for the mechanical requirements and test methods for screws having asymmetrical thread and spherical undersurface. BS 3531-5.4:1993, ISO 9268:1988 Implants for osteosynthesis. Bone screws and auxiliary equipment. Specification for screws having symmetrical and asymmetrical thread and conical undersurfaces. Bone Plates BS 3531- 23.1:1991 ISO 9585:1990 Implants for osteosynthesis. Bone plates. Method for determination of bending strength and stiffness. BS 3531- 23.2:1993 ISO 9269:1988 Implants for osteosynthesis. Bone plates. Specification for holes and slots for use with screws of 4.5mm 4.2mm 4.0mm 3.9mm 3.5mm and 2.9mm nominal sizes. BS 3531- 23.3:1991 ISO 5836:1988 Implants for osteosynthesis. Bone plates. Specification for holes corresponding to screws with asymmetrical thread and spherical under surfaces. Quality Control & Product Development Team Veterinary Instrumentation is pleased to have its own ‘in-house’ Quality Control and Product Development Team. David is a practising surgeon with interests in all aspects of surgery. He also has extensive CAD and engineering skills to facilitate the development of new instruments and implants. Chris joined Veterinary Instrumentation just over 5 years ago and has over 40 year’s experience working in manufacturing. His role comprises of quality checks of instrumentation and implants involving the tolerances and specification checks following manufacturing of the instruments and implants. Chris Pignon Quality Engineer Colin & Gillian joined the Veterinary Instrumentation Team, assisting both Chris & David as our Product Development Engineers. Their role comprises of the technical drawing of new products, along with setting tolerances and checking specifications of instruments and implants. David Strong BVM&S., MRCVS. Technical Director 51 Colin Jolly Gillian Butterwick Product Development Engineer Product Development Engineer