Which is the optimum retentive force of an attachment?
The fundamental reference parameter of pro-regress of the retentive force establishes that this should reach its maximum (about 7N) unconditionally and exclusively when the prosthesis is completely inserted.
The retention force of the attachments with parallel sliding walls, gradually increases during the insertion and decreases, ever gradually, during the removing.
The retention is maximum (about 7N) in the final insertion position of the matrix with the patrix. This is a movement dynamics favourable for the patient, as now scientifically validated.
Retention peaks higher than the retentive value have to be avoided during the removal, because in this case the natural or implant pillar would suffer a too high extraction stress.
For this reasons the systems with elastic underequatorial retention present a higher stress on the prosthetic supporting structures (natural teeth or implants).
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