Feature article: PIM International, Vol.1 No. 1 March 2007, pages 12-19, 3370 words

Author: Bernard Williams, Consultant, Shrewsbury, UK

Introduction

Powder injection moulding has made significant advances in developing appropriate materials and production know-how for a wide range of applications in the medical and dental sectors. In the following review Bernard Williams highlights some interesting and novel success stories and case studies.

Orthodontics/dental applications

One of the earliest success stories for powder injection moulding (PIM) in the medical/dental field were the orthodontic brackets used for realigning teeth by progressive stressing. Such brackets were originally made by investment casting but as the requirement from dentists increased for ever smaller brackets with thin walls and blind pockets, so manufacturers turned to PIM or for the most part metal injection moulding (MIM). Global sales of orthodontic MIM brackets is estimated to be in the region of $130 million with a high proportion being produced in-house at companies such as American Orthodontics, Rocky Mountain Orthodontics, Ortho Organisers, Unitek 3M, SDC Ormco, Dentaurum, Bernhard Förster GmbH. Other orthodontic companies buy in MIM brackets from producers such as Injectamax, Flomet, and World Class Technologies to name just a few. The selling price of MIM brackets through distributors ranges from $1 to $2 per piece, which is about double the manufacturing cost, but these can be sold on to dentists at prices from $3 to $10 per piece [1].

PIM orthodontic brackets (Fig.1a and Fig.1b) have an average weight of around 0.1gr and come in a variety of designs and sizes for selection by the dentist. The brackets are produced from stainless steels – 17-4PH or 316L medical grades for biocompatibility – using multi-cavity injection moulding tooling, followed by debinding and sintering. PIM orthodontic brackets are also made from nickel-free stainless steels (Fig.1b) and titanium where there is any risk of an allergic reaction. A limited number of orthodontic brackets are made by ceramic injection moulding (CIM) using pure alumina or zirconia to make them translucent. Some crown preforms are also made by CIM.

The key to MIM’s success in this application is the production of stronger, smoother, and more precise brackets, without secondary machining or deburring, which helps to reduce friction and improves sliding mechanics. The low-profile rounded edge, one-piece designs made possible by MIM increases patient comfort, is easier to ligate, and eliminates bracket/pad separation..........

Further sections of this article include:

- Medical instrument devices
- Medical implants
- Porous PIM implant components
- PIM magnets in medical applications
- CIM medical devices

Figures and Tables:

Fig. 1(a) Example of metal injection moulded stainless steel bracket in orthodontic applications. (b) shows bracket made from nickel-free stainless steel and (c) example of MIM orthodontic brackets in situ. (Courtesy: Dentaurum AG, Germany).

Fig. 2 Laser-structured MIM brackets with identification code. (Courtesy: Dentaurum, Germany)

Fig. 3 MIM carriere distalisers comprising interior rod and ball with bracket. (Courtesy:MPIF, USA)

Fig. 4 Application of carriere distalisers in orthodontics. (Courtesy: MPIF, USA)

Fig. 5 MIM orthodontic buccal tube system parts. (Courtesy: MPIF, USA)

Fig. 6 MIM dental manifold used in hand-held fibre-optic swivel system. (Courtesy: MPIF, USA)

Fig. 7 MIM parts used in sleep apnea device applied by dentists or orthodontist. (Courtesy: BASF, Germany)

Fig. 8 MIM 17-4PH and 316L parts used in disposable female sterilisation equipment. (Courtesy: Metal Injection Moulding Ltd, UK)

Fig. 9 MIM parts used in laparoscopic jaws for vessel fusion. (Courtesy: MPIF, USA)

Fig. 10 MIM parts used in suturing jaws. (Courtesy: MPIF, USA)

Fig. 11 Needle driver and distal clevis containing MIM parts. (Courtesy: MPIF, USA)

Fig. 12 Complex surgical procedures are performed with the high precision robotic system. (Courtesy: MPIF, USA)

Fig. 13 MIM 11-piece automatic biopsy instrument. (Courtesy: MPIF, USA)

Fig. 14 WFeNi MIM electrode and pure alumina CIM insulator used in the electrode tip of ablation systems. (Courtesy: Advanced Materials Technology, Singapore)

Fig. 15 MIM Titanium alloy miniscrews for teeth crown implants. (Courtesy: Tijet Medizintechnik, Germany)

Fig. 16 MIM compression Ti alloy screw incorporating longitudinal continuous bore with a hexagonal cross section. (Courtesy: Tijet Medizintechnik, Germany)

Fig. 17 Patented ‘Force Distributing Dental Implant’ system combining MIM Ti and plastic molding. (Courtesy: Mathson Corp.USA)

Fig. 18 Production sequence for the Space Holder process to produce porous MIM parts. (Ref.22)

Fig. 19 Examples of various types of porous MIM structures achievable by the Space Holder process. (Ref.22)

Fig. 20 Biofoam titanium dental implant produced by PIM. (Courtesy: National Research Council, Canada)

Fig. 21 Combination of injection moulded plastic composite and foam Ti-Ni material used in anchoring for hip implant. (Courtesy: National Research Council, Canada)

Fig. 22 Ceramic injection moulded dental implant screws. (Courtesy SPT Roth AG, Switzerland)

Fig. 23 Ceramic injection moulded parts used in endoscopic or laparoscopic surgery. Photos courtesy: Ceradyne Quest Technology.

Table 1 Typical mechanical properties of commonly available stainless steels for metal injection molding (MIM) in comparison with wrought materials (Ref.10) 3from product literature: Advanced Materials Technologies (Singapore); 4 ASM Specialty Handbook: Stainless Steels (ASM International 1994) 5Product literature: BASF (Germany)

Table 2 Mechanical properties of MIM Ti and Ti alloys for medical applications. (Published in: ‘MIM von Titan’, Tijet Medizintechnik, Germany)