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Home page  |  Techniques  |  Technical info about dental attachments  |  What is an attachment?  |  In fact not everyone knows that…

In fact not everyone knows that…

No rigid attachment can resist alone! Why?

Because they must necessary have small dimensions to be functional and aesthetic!
Here you are the mathematical demonstration.

Everyone knows that:

  1. 1 kg 9,81 N and so it can be assumed for convenience that 1 kg 10 N
  2. the average mastication force for posterior teeth is equal to 400-600 N
  3. the mastication forces are not uniformly distributed between pillar tooth and mucosa because the resilience of the first one is highly inferior in comparison with that of the second one. For this reason, using rigid attachments, begin some rotating movements loading on the pillar tooth that can be defined as bending moment.

How long can a rigid attachment resist to the stress caused by the mastication forces before to wear out, to break down or before to cause damages to the pillar teeth? The resistance to bending ( σ),that is the resistance of rigid attachments to this solicitation, is determined:

  1. by their geometric shape (resistant section), that determines the modulus of resistance to bending

    SQUARE ATTACHMENTS with side (h) 2 mm

    RECTANGULAR ATTACHMENTS with base (b) 1 mm and height (h) 4 mm
     
  2. by the safe load of the used material that, for instance, for stainless steel is equal to
    In fact the resistance to bending is defined by the formula

The attachments with the above mentioned dimensions that, even if are only examples, can be considered similar to the ones currently on the market, have a resistance to bending of respectively:

SQUARE ATTACHMENTS

RECTANGULAR ATTACHMENTS


But which is the stress to which they are submitted?

Supposing a mastication force (F) equal to 600 N and a lever arm (l ) of 20 mm, the average solicitation (Fxl) will be 12.000 Nmm which is to say 1.200 Ncm.
Here is the mathematical demonstration of why RIGID ATTACHMENTS, excluded those with huge dimensions not compatible with their using in the oral cavity (for instance 7x7 mm or 4,5x9 mm), ARE ABSOLUTELY NOT ABLE TO RESIST TO MASTICATION FORCES!!! THEY HAVE A RESISTANCE TO BENDING OF 26 OR 54 Ncm, THAT IS ABOUT 30 TIMES LESS THEN THE SUBMITTED SOLICITATION (1.200 Ncm).
AFTER THIS CONCRETE PROOF, BEWARE OF THOSE WHO SAY THE OPPOSITE.

Nevertheless, in case rigid attachments should be assembled without the milling, it would be necessary to remind what would occur: wear, retention loss, deformation and breaking due to stress.
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