The casting-on
The casting-on is an alternative technique to the soldering used for the fixing of prefabricated traditional attachments.
The use of this technique, whose employment is primarily known in dentistry, allows to insert a component of the attachment (generally the female) directly in the position desired in the wax or resin cap. With the casting-on of the metal we will get therefore not only the construction of the crown but also the union of the components of the attachment. This is obtained thanks to a “metallic connection” originated from a phenomenon of “superficial adhesion for diffusion” between the alloy of the crown and that of the attachment.
In order to obtain a good casting-on result the following conditions and indications must be respected:
- The attachment alloy must not oxidize;
- The solidus temperature of the attachment alloy must be at least 100 °C higher than the casting temperature of the casting alloy;
- Sprues should be far and should not be placed near to the attachment;
- The preheating temperature should be higher than usual;
- The stay time of the cylinder at the preheating temperature should be longer than usual;
- The cooling time of the cylinder should be longer than usual;
- Attachments with thickness higher than 0,5 mm have to be preferred to attachments with thickness lower than 0,5 mm because after the casting-on these latter can shows deformations or penetrations hardly removable with a mechanical touch-up;
- If not already conceived in the construction of the attachment, realise a mechanical retention on the contact side;
- If possible, create a cap that includes all the attachment.
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