The initially used external snap coupling principle as shown in Figure 9 (top left) was abandoned because it protruded too much from the outer surface of the head. Instead the idea was to use the interior of the abutment for the retention or coupling components. It was found that the bayonet coupling, with first prototype shown in Figure 9 (bottom) and then the final design shown in Figure 10 (left) fulfilled most of the demands. The bayonet coupling develops sufficient coupling force by compressing the O-ring between the plastic insert and the abutment and exerts minimum stress to the implant as well as the transducer in the coupling procedure. This coupling was used with minor modifications from the first generation until the new snap coupling was released 2001-2002.

The most severe drawback with the bayonet coupling was that it was tricky for the patient to reinstall the plastic insert and the O-ring after it had been released due to accidental overload or when worn out (should be replaced every 6 month in the maintenance plan). Another drawback, that became even more serious when we started to develop the more powerful body worn devices in the beginning of the 1990’ies (Megabass HC-380, later called Cordelle), was that the coupling force between the implant and the bayonet was too low to provide a distortion free transmission. The first prototype of the snap coupling having a flexing male unit (typically snap couplings have flexible female units as shown in Figure 4 and 9) is shown in Figure 10 (middle). In this case we simply snapped it into the existing abutment for the bayonet coupling (it snapped into the inner grove where O-ring engaged). This coupling functioned so well that it was patented and that design also included a disconnect mechanism to protect the implant for unnecessary forces. Also, a new abutment for this internal snap principle was developed that is used today.

Figure 10: Bay onet coupling used 1982-2002 ( 1 ) and snap couplings first used 1992: Mega Bass ( 2 ) and present design ( 3 ).

This article is copyright. Bo Hakansson. July 2006.

If you wish to reproduce any of this article, please contact the author.

See Issue 18, Winter, for the rest of this article, beginning with :

The first generation of the BAHA HC-100: 1981-1986.
 
I would like to thank Bo for writing this fascinating article for us.

Page 1      Page 2      Page 3      Page 4      Page 5

Page 6      Page 7      Page 8      Page 9      Page 10

Page 11    Page 12    Page 13    Page 14    Page 15