Dental Tribune UK Edition, October 25-3, 2010, No.26 Vol.4

VOCO GmbH · P.O. Box 767 · 27457 Cuxhaven · Germany · Tel. +49 (0) 4721 719-0 · Fax +49 (0) 4721 719-140 · www.voco.com SO “I need a composite that behaves like a tooth!” Dr. Arne Kersting NEW SO TOOTH-likE in the sum of its physical properties, Grandio® SO is the filling material that on a world-wide scale is most similar to natural teeth.* The advantages you will gain are: durable, reliable restorations, and above all satisfied patients. • Meeting highest demands, universally usable in the anterior and posterior areas • Natural opacity for tooth-like results using only one shade • Intelligent colour system with new shades that make good sense: VC A3.25 and VC A5 • Smooth consistency, high light stability, simple high-gloss polishing Please visit us at BDTA Dental Showcase 2010 · london 14.-16.10.2010 · Stand: l04 * Please feel free to request our scientific product information. VOCO_DTI-UK_2610_GrandioSO_210x297.indd 1 22.09.2010 9:44:51 Uhr • in comparison to a PMF crown higher tooth substance loss in preparation can only be coated/ veneered with composites How double crowns work Physical principles The 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 friction The 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