In this first of two articles we will discuss the technical side of the telescopic den-

tures before presenting the clini-

cal side in the second part.

Telescope prosthesis or dou-ble crowns are a proven option

for the prosthetic treatment of dramatically reduced dentition (fewer teeth might serve in some cases as an alternative to im-

plants). However, the production of such a prosthesis demands high technical skills on the side of the dentist and the dental tech-

nician. Of equal importance is a good communication between dentist and technician. These are the main keys to a success-ful case.

The telescopic attachment consists of two parts: 1. The primary (inner) crown, or coping, which is permanently fixed to the anchor teeth, and is preferably made out of a pre-cious metal, a high gold alloy.2. The secondary (outer) crown implemented in to the prosthe-sis, made out of the same alloy.

The usual type of double crown system next to the conus type is the parallel telescopic crown. They are named due to the fact that all surfaces from the primary (inner) and the sec-ondary (outer) telescopic are not only parallel to each other but also parallel to the axis of each incorporated tooth. However in the case of a conus telescopic system a 4 degree angle of both telescopes to the axis of the tooth is aimed for, provided by the ex-act preparation of the dentist.

IndicationsDouble crowns can be used in the following situations: where there is a strongly depleted den-tition uncertain prognosis of in-dividual teeth in a periodontally damaged jaw (existing bone de-pletion, increased loosening of the anchor teeth) with a subop-timal distribution of the remain-ing teeth for the retention of re-movable bridges

The almost universal appli-cability is characteristic for this anchoring system. Telescopic crowns can be applied as clasp-free connecting elements with purely periodontally and peri-odontally-gingivally supported partial prostheses.

The pros and cons of double crownsAdvantages of the telescopic sys-tem: • a predominantly axial loading of the pillars leading to a favour-able distribution of force pro-tection of the anchor teeth from decay • the option of primary splinting for the securing and fixing of loose teeth• integrated tilt-avoidance • a straightforward ability to ex-tend the prosthesis even up to a full denture the aesthetic advan-tage as no clasps are used the beneficial and straightforward treatment and control of the par-odontium and the internal coping •can be used as a cost effective alternative to implantsDisadvantages of the telescopic system: • requires a high technical effort• correspondingly higher costs• over sizing of the secondary crowns if the pile has not been efficiently reduced

Telescope or double crownsPart 1 of precision dental prosthetics with highly engineered con-nections. By Ulrich Heker, Master Dental Technician & Verena Tunn- Salihoglu, dentist, Aberdeen, Scotland

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How double crowns workPhysical principlesThe patient expects the pros-thesis to be easily inserted and removed. At the same time, the prosthesis has to be sufficiently attached so that it cannot be leveraged off by motion dur-ing speech and eating. In order for these conditions to be met, you need certain physical pre-conditions. These are explained below.

In order to achieve a hold be-tween the primary and second-ary telescopic, these have to fit in a particular manner. There are three different types of fit:1. a clearance fit, in which there is still a small bit of give/play 2. the medium fit, in which there is a large tolerance or over-sizing before the joining of the components (which gives totally useless telescopic crowns)3. the pressure fit, where the components are tight and inter-act such that friction is created during fitting

On the principle that both crown pieces have to join ex-actly and without obstruction, parallel telescopic crowns are always pressure fittings; this is why telescopic crowns are pref-erably made from precious al-loys, because of their high elas-ticity.

The importance of frictionThe inner and outer telescopes are joined together by friction. Stated simply, the friction is due to the interaction between the surface layers of the inner and outer telescope. The binding forces of the telescopic crowns are therefore a consequence of this friction.

Friction in telescopic crowns is a value that is difficult to meas-ure. It is principally dependent on the technical construction of the crown, which is influenced by the following factors:• the number of the planned tel-escopic crowns• the length of the friction sur-faces of the individual tooth and also the sum of all available tel-escopes• the placement of the friction surfaces relative to one another. Only oppositely facing paral-lel surfaces can provide the re-quired friction with the elastici-ty of the materials, which is why gold alloys are generally used • the quality of the work

A prosthesis has to be pre-pared in such a way that the patient can insert it without dif-ficulty. Additionally, it must pro-vide the feeling of fitting firmly.

The denture should also

be removable without difficul-ty 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 ac-ceptable to patients. The maxi-mal force required for removal should not exceed 650 P, as with

higher levels the patient can of-ten not remove the prosthesis.

Achieving the correct fric-tion of the individual telescopic components is only possible with considerable experience and skill by both parties techni-cally involved; the dentist and the dental technician, and their interdisciplinary communica-tion. The success also depends on the precision of each step

page 24DTà Telescope during insertion

23ClinicalOctober 25-31, 2010United Kingdom Edition

and each detail.

Conclusion to Part 1We have given you an overview of the technical aspects of tel-escopic prostheses or double crowns and their almost uni-versal applicability. The basic priciples of how they work and the importance of achieving the right level of friction are de-scribed. Success is dependent

on good communication and technical skill on both the den-tists and the technical labora-tory’s part.

In the next article of “Part 2 of precision dental prosthetics with highly engineered con-nections” we will illustrate the clinical side to the telescopes or double crowns, i.e. the planning and preparation required. DT

page 23DTß

About the authorUlrich Heker is the ow n e r - m a n a g e r of Ulrich Heker Dental Laboratory founded in 1996 with the strap line TEETH ‘R’ US. As a qualified master craftsman (Ger-man Master Dental Technician) since 1991, he has over

26 years’ experience both at the bench and in running a successful business. Ulrich lives in Mülheim on the river Ruhr and is an accomplished ‘western-style’ rider in his spare time. Ulrich is fluent in English and can easily be contacted at: http://www.german-smile.info, or you can email Ulrich@Teethrus.de

Verena Tunn- Salihoglu,was born close to Stuttgart, Germany. During her training at the Albert-Ludwigs-University in Freiburg, Germany, she developed a keen interest in prostho-dontics,, especially in partial dentures and telescopes. Now her main interest is the integration of holistic dentistry on a high precision dental quality level. Verena is fluent in English and can eas-ily be contacted at: oldmachardental@gmx.com

References

1. Becker, H: Einflüsse des umgebenden Mediums auf das Haftverhalten telesko-pierender Kronen. Zahnärztl Welt 91, 54, (1982). 2. Becker, H: Wirkungsmechanis-mus der Haftung teleskopierender Kronen. Zahnärztl. Prax 34, 281 (1983). 3. Böttger, H: Das Teleskopsystem in der zahnärztli-chen Prothetik. JA Barth, Leipzig 1961. 4. Diedrichs, G: Ist das Teleskopsystem noch zeitgemäß? Zahnärztl. Welt 99, 78 (1990). 5. Goslee, H: Principles and Practice of Crown and Bridge Work Dental Items of Interest Publishing Co., New York 1923. 6. Hedegard, B: Die Mitarbeit des Patienten – ein Planungsfaktor. Zahnärztl. Welt, Ref.88, 680 (1979). 7. Jacoby, W, Gasser, F: Nachträgliche Haltverbesserung von Teleskopkronen. Quintessenz 24, 59 (1973). 8. Jüde, HD, Kühl, W, Roßbach, A: Einführung in die zahnärztliche Prothetik. 5.Aufl. Deutscher Ärzte- Verlag, Köln 1996. 9. Kammertöns, H: Haftreibungsprüfung an Teleskop- und Konuskronenarbeiten. Quintessenz Zahntech 14, 11 (1988). 10. Krämer, A, Weber, H: Präzisionselemente in der Teilprothetik Teleskopierende Sys-teme. Zahnärztl Mitt 80, 2328 (1990). 11. Mack, H: Die teleskopierende Verankerung in der Teilprothetik. Quintessenz Zahntech 9, 17 (1983). 12. Peeso, FA: Crown and Bridgework. Henry Kimpton, London 1924. 13. Schreiber, S: Die Verankerung von Teilprothesen mit Teleskopkronen. Dtsch Zahnärztl Z 14, 983-988 (1959). 14. Schwanewede von, H, Anderseck, E: Prote-za Teleskopowa – Die Teleskopprothese im stark reduzierten Lückengebiß. Prot Stom 35, 166 (1985). 15. Stüttgen, U, Hupfauf, L: Kombiniert festsitzend – abnehmbarer Zahnersatz. In: Horch, H-H, Hupfauf, L, Ketterl, W, Schmuth,G, (Hrsg): Praxis der Zahnheilkunde 6 (Teilprothesen), 2. Aufl. Urban & Schwarzenberg, München Wien – Baltimore 1988, S.163. 16. Wup-per, H: Zur Biomechanik verschiedener Verankerungssysteme – Grundsätze zur Indikation von Geschieben, Stegen und Teleskopen. Zahnärztl Welt 95, 36 (1986).

Single Telescope with retention, showing primary and secondary telescope

Copies upper jaw polishes for modelling the outer crowns

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October 25-31, 201024 United Kingdom EditionClinical