Theoretical basics

Attachment technique: It’s matching! How does it work?

A matchbox is used as a descriptive example to explain the basic functioning of an attachment in dental prosthetics. The drawer is held as well horizontally as vertically. Why doesn‘t the inner part fall to the ground in an upright position?

Both parts have parallel contact surfaces. They move against each other with a certain resistance (friction), which holds both parts together. Now imagine that the inner part is a primary telescopic crown (fixed) and the outer part, a secondary telescopic crown (removeable). In this example, it’s easy to show, how a telescopic or attachment denture is inserted inside a client’s oral cavity and cannot be removed without external forces.

Attachment technique using a matchbox as an example

How does it work? It doesn’t make any difference whether the matchbox is held horizontally…

…or vertically – there is always frictional resistance which keeps the parts together.

Sir Isaac Newton was the “spiritual father"…

 …of the friction laws.

How does it fit?

We differentiate three kinds of fit:

1. Wider fit (loose fit):

R1 < R2 There will be less friction to fix the denture in a client’s oral cavity. The hold of the prosthesis must be secured by a locking element.

2. Tighter fit (pressed fit):

R1 > R2 The denture can’t be removed without strong forces. The periodontium of the support teeth will be damaged. Exception: tapering or conical crowns.

3. Transitional fit:

R1 = R2 That’s an ideal fit, if the layer of saliva is taken into consideration; consequently a transitional fit with tendency to a loose fit.