Telescopic crown
A telescopic crown is the not entirely applicable collective term in dentistry for every type of double crown. It is correct to differentiate double crowns into parallel- walled telescopic crowns , conical crowns and resilient telescopic crowns .
Double crowns are incorporated when the aim is to attach removable combined dentures as well as possible, while at the same time optimally protecting the remaining dentition and the teeth used for attachment and avoiding unphysiological (tilting) loads.
All double crowns consist of an inner or primary crown and an outer or secondary crown. The primary crown is used during the integration z. B. cemented firmly on the ground tooth stump with phosphate cement, while the secondary crown is incorporated into the denture (soldered, glued or embedded with retentions in the denture plastic). The principle is that when the prosthesis is inserted, the primary and secondary parts slide into one another telescopically and thus provide the desired support. It is essential to ensure that the insertion direction is parallel.
Double crowns are usually made of gold alloys or with the help of electroplating, but non-precious metal alloys or titanium are now also used. The outer telescopes can be veneered, but not as a ceramic veneer, because this cannot withstand the stresses caused by tilting during insertion and removal.
Parallel-walled telescopic crown
With this type of double crown, the inner telescope is milled completely parallel to the surface with a special milling machine. Accordingly, the secondary telescope has parallel walls from the inside. The crowns are held together by friction . Because it is not always easy to set or readjust (activate) the friction appropriately in individual cases, the outer crowns can also be provided with additional retaining elements: friction pins, bolts or the like.
Conical crown
With a conical crown, the primary crown is not milled parallel, but all around at a defined angle (usually 6–8 °). The secondary crown has the same angle from the inside. In connection with a 0.1 mm wide occlusal gap between the primary and secondary crowns , this should lead to wedging (in contrast to the friction of the parallel-walled double crowns), which should ensure a defined pull-off force of 8 to 10 N.
Resilience telescope crown
A resilience telescope crown differs from the parallel-walled double crown in that the side surfaces are milled parallel, but a gap of 0.3 to 0.5 mm remains occlusally between the inner and outer telescope, so that the crowns sink to a defined extent under load ( springs) and the resilience of the oral mucosa comes into play. The indication for such double crowns can be given with very little residual dentition and the integration of a cover denture prosthesis .
Telescopic crown with clearance fit
In this design of the double crowns, the walls of the primary crown are parallel, but without any friction or clamping to the secondary crown. The retention of the secondary crown on the primary crown is achieved by separate retaining elements such as spring bolts or bolts.
Telescoping bridge
A telescopic bridge is understood to be a bridge whose bridge piers are telescopic crowns (double crowns). Their wearing comfort corresponds to that of fixed dentures, as this construction is carried by the abutment teeth and the oral mucosa has no supporting function.
Advantages of a telescopic bridge:
- The telescope crowns and the bridge body can be cleaned better.
- Any necessary repairs (e.g. on veneers) are possible without having to completely renew the dentures.
- Dentures made from telescopic crowns and bridge bodies can be expanded, which means that if there is further tooth loss, they can be reworked and reused in whole or in part. The existing telescopic crowns can also take on the holding function of a combined dental prosthesis. Reusing the telescopic crowns reduces the effort and costs compared to a new production.
Disadvantage:
- Telescopic crowns cannot be provided with ceramic veneers, as the risk of the ceramic breaking when removing and reinserting the bridge is too high. Telescopic crowns are therefore veneered with plastics, e.g. B. made of UV light-curing composite .
- As a rule, a greater loss of substance from the abutment teeth to be ground must be accepted so that the telescopic crowns do not become too thick, which would impair the aesthetics. This can lead to pulpit discomfort or increased sensitivity to temperature.
- The production requires an increased expenditure of time and thus also causes higher costs.
Rating
The doctrinal opinions about which type of double crown is the best differ greatly. Depending on the university and the “inventor” of individual systems, preference is given to one or the other double crown. All of them certainly have their advantages, but also their disadvantages. Depending on the individual case, the respective finding should be the yardstick for the indication.
See also
- Telescopic prosthesis
- bridge
- Assessment standard for dental services, BEMA no. 91d
- Position and direction designations on the teeth
Web links
Sources / literature
- ↑ J. Wirz, A. Hoffmann: Galvanoprothetik in der Zahnmedizin. Quintessenz-Verlag, Berlin 1999.
- ↑ Klaus M. Lehmann, Elmar Hellwig: Zahnärztliche Propädeutik . 10th edition. Urban & Fischer at Elsevier, 2005, ISBN 3-437-05391-4 , p. 267 .