A prosthesis has to be prepared in such a way that the patient can insert it without difficulty. Additionally, it must provide the feeling of fitting snugly and firmly. The denture should also be removable without difficulty whilst not loosening at the wrong moment or due to sticky foods. The criteria must remain valid over a longer period of wear.
Note: The force required for removal of the prosthesis: 250–300 P is regarded as acceptable to patients. The maximal force required for removal should not exceed 650 P, as with higher levels the patient can often not remove the prosthesis.
Achieving the correct friction of the individual telescope components is only possible with considerable experience and skill as well as a close collaboration with the dentist.
In the dental surgery -Planning and preparation of telescopes
When producing a telescope prosthesis, a few fundamental considerations have to be made with regard to the arrangement of the anchor teeth. There is a large difference in the production of multi-unit bridges, which require a common direction of insertion from the start. With crowns, one is less concerned with the original alignment of the supporting teeth as the primary crowns are applied individually and these are milled to provide the parallel sides for a common axis of insertion for the secondary crown. As telescopic crowns have multifaceted elements, care must be taken during preparation so that there is sufficient room in the interdental area for effectively four crown wall strengths (2 x inner crown plus 2 x external crown = circa 0. 7–1 mm interdentally and also taking into consideration the attachment direction). A similar situation exists for the occlusally required space (primary component + external crown).
The secondary crowns attached to the prosthesis require a common alignment axis. The most important considerations are therefore: How the preparation must be positioned in order to obtain an abutment preparation in which all the primary components have two opposing parallel surfaces with circa 3. 5 to 4 mm axial length, which in turn must all be parallel to each other.
Manufacturing primary crowns
After taking impressions using custom trays, the optimal attachment alignment/direction is established on the cast, for milling using a parallelometer.