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:
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:
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:
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.