For the purposes of this article, we will discuss only the telescope technique and show the lab work to introduce the different solutions. Conus systems like the Atlantis Conus are not telescopes, do not duplicate the telescope function, and are an entirely different category.

The double-crown technique is considered to be the “king’s class” of dental restorations in Germany. In essence, the double-crown technique describes two different systems of a crown or superstructure sitting atop a primary coping or abutment—telescope crowns and CONUS crowns. The fundamental difference: Telescopes glide easily on top of each other while maintaining friction fit and are easily removed by the patient. Conus crowns do not glide; they lock in a final, definite position and require a substantial force of removal, which gets greater the longer the patient wears it. Implants and milled bars can also fall into these classifications.

The primary telescope is precision-milled using specialized burs, then the external surface is highly polished. In the traditional analog method we would then make a coping of pattern resin and cast this or, more recently, use the Galvano method to fabricate the coping. My current method is fabricating the secondary telescope in PEEK.

The key step in all these procedures is fitting the secondary coping with a friction fit. This involves painstakingly dialing in and polishing the intaglio of the secondary telescope until the desired level of friction fit is achieved. In a nutshell, for single telescopes, one would select a higher level of friction fit than, say, for six telescopes. The friction fit is additive, so too much friction fit will make the telescope jam and prevent the smooth gliding action that makes it a telescope. By comparison, the CONUS system does not have this function; it just locks in the end position.

The method is pretty much the same regardless of which material or system is utilized. This turns the telescope into a 360-degree attachment, providing a very stable base for any framework or superstructure. They do not have the snap-in of, say, locators and therefore do not require a great removal force, but glide easily.

We all know the principle of two slabs of glass gliding on top of each other—or, more practically, think of the function of your car’s shock absorbers. The two tubes glide frictionlessly on top of each other. The CONUS crown, by comparison, would be your wheel mount, securely locked in place and definitely not moving.

When telescopes first were created, it was a fully analog procedure, using cast gold primary copings that had been milled parallel in wax, cast, remilled after try-in and pickup, then highly polished. Only then was the secondary crown/coping waxed and cast.

The actual process of dialing in the level of friction fit required superior skill and lots of patience, bearing in mind that this was cast coping on cast coping, and back then dental investments left a lot to be desired. There were several generational changes in materials, each of which changed the process substantially:

· First came to the invention of high-precision phosphate-based investments, which created a far finer grain structure and allowed for smoother fit.

· The next leap was the invention and adaptation of Galvano processes to generate the secondary coping.

· This, in turn, created the necessity of bonding these copings into ever-more complex superstructures but also turned out to be the ideal combination to treat implant cases with telescopes.

· Now we are in the digital age, and both primary and secondary structures can be CAD/CAM-milled.

We believe the best combination for longevity in the friction fit is the fabrication of the primary copings in CAD/CAM-milled medical-grade nonprecious and the secondary in PEEK. However, the traditional analog cast and coping technique (Figs. 2–4) still comes in very handy on many occasions.