Telescopic crowns - from conventional to digital production
In conventional technique, telescopic crowns - also known as double crowns - were usually made of gold alloys or with the help of electroplating technology. With the advent of digital technology, new possibilities have opened up in the field of telescopic crown manufacture, such as zirconium, non-precious metal alloys, titanium or PEEK plastics.
Telescopic crown
The telescopic crown consists of an inner crown (also known as a primary or inner telescopic) and an outer crown (also known as a secondary or outer telescopic). It is used to attach removable dentures. The remaining teeth are used for anchoring.
Cemented onto the prepared tooth stump, there is a primary telescopic - designed to a minimum thickness according to the material properties. As its name suggests, the secondary telescopic is pushed over the primary telescopic like a telescope and is firmly connected to the removable part of the denture. The two crowns fit together exactly. For this reason, it is essential to ensure that they are inserted in a parallel direction. The wafer-thin saliva film has a positive effect with this technique, as the crowns slide smoothly into one another and an adhesive bond is created between the crowns.
The term telescopic crown is generally used as a collective term for double crowns. These are divided into three specific classes:
Parallel-walled telescopic crowns
With this technique, the inner telescopic is milled absolutely parallel all around the surface with a parallelometer. The outer telescopic is correspondingly parallel-walled from the inside. They are held together by friction.
Conical crown
In contrast to the parallel-walled telescopic crown, the surface of the conical crown is milled all around at a defined angle. This is usually between 6 and 8 degrees. The inner surfaces of the secondary telescope are correspondingly conical, but here a 0.1 mm wide gap is integrated in the top of the inner surface. This ensures that the double crowns wedge together when they are put together.
Resilience telescopic crowns
The resilience telescopic crown differs from the parallel-walled telescopic crown only in terms of the inner surface of the secondary telescopic. Here - as with the conical crown - a gap of 0.3-0.5mm is incorporated above the top. When pressed, the secondary telescopic can be to a certain extent elastic and the resilience of the oral mucosa comes into play.
Galvano electroplated crown
The galvano crown is a special form of the telescopic crown. The secondary telescopic crown is made of pure gold by electroplating. The gleaming through of the gold results in a high similarity to the natural tooth color when the external telescopic is veneered with tooth-colored material. CAD/CAM manufactured telescopic zirconia crowns serve as inner crowns.
The different double crown techniques are used to anchor removable dentures such as telescopic prostheses. The above-mentioned types of telescopic crowns can form the basis of a single restoration, but usually form the basis for larger work such as telescopic prostheses and telescopic bridges, which are described in more detail below.
Telescopic prosthesis
A prerequisite for the telescopic prosthesis is that one or more teeth are still available for anchoring. The partial denture is a comfortable and removable solution to restore and close lost functions and tooth gaps.
For this type of denture, the remaining teeth must be prepared (ground) by the dentist. In the dental laboratory, the dental technician then creates the thin primary crowns with which the ground teeth are covered. In the next step, the counterpart is created on this, which comes close to the old dentition in terms of function and aesthetics. The prosthesis is attached to the secondary crowns using resin and artificial teeth. The patient can easily remove and reinsert the prosthesis if necessary. This technique is very popular with patients because no metal parts are optically visible. The transmission of the chewing forces is absorbed by the anchoring teeth and the oral mucosa. Thus it belongs to the group of combined dentures, whereas a clasp prosthesis is anchored to retaining teeth by means of bent and cast clasps, so the partial denture is anchored on the teeth and the oral mucosa.
Telescopic bridge
If there are still at least five natural teeth - which do not have to be in very good condition - a telescopic bridge is the best option. The telescopic bridge is significantly more flexible than fixed bridges. If a tooth has to be removed, this part of the dentition can easily be incorporated into the telescopic prosthesis. In healthy teeth, telescopic dentures help stabilize these teeth. Muscles and teeth are strengthened by removing and inserting the partial denture. If the molars are missing and therefore the possibility of attachment to the abutment teeth, the telescopic bridge can be also used. A fixed bridge would not be possible in this case.
Tertiary structure
Here primary crowns are made from ceramic and galvanized (electroplated) copings serve as the secondary framework. The set-up worked out in advance provided the necessary information for the tertiary structure. The upper and lower framework is designed according to the silicone key and converted into CoCr. The galvanized secondary parts should be connected to the tertiary structure via intraoral bonding. This is followed by the finishing process so that the framework disappears behind tooth-colored and pink resins.
Advantages of telescopic works
The telescopic prosthesis / bridge can be extended to a full prosthesis if additional teeth are lost. Older people in particular, who generally find it difficult to adapt to the dental prosthesis, can get used to the foreign body in their mouth more easily. Removing the prosthesis also makes cleaning easier. In contrast to other dental restorations, the prosthesis can be used for a long time.
In the upper jaw, the telescopic prosthesis can in some cases avoid a palate plate, which many patients find more pleasant.
Since this type of restoration is completely coated with resin, it comes aesthetically very close to the natural dentition and is therefore very popular.
Disadvantages of telescopic works
The biggest disadvantage are probably the relatively high costs, since two crowns have to be made for each tooth during production. In addition, it can only be technically implemented if the work is done very precisely.
Requirements for the preparation for telescopic crowns
A lot of space has to be created for telescopics. As a guide, it is recommended to plan two metal thicknesses of 0.3-0.4mm each and the corresponding veneer of 0.8mm.
The transition from artificial to natural tooth crowns must be harmonious and correspond to the anatomy of the tooth. When preparing two or more teeth, a uniform insertion direction must be ensured.
As a result, a more delicate, aesthetically high-quality work can be created and it enables the patient to incorporate the dentures more easily.
Manufacture of telescopic crowns
The digital age has also created many new opportunities in dental technology. Telescopic crowns - manufactured digitally - set this technique to new quality standards. In the meantime, internal telescopic are designed in the CAD software. With just a few clicks, the telescopic can be quickly implemented and circularly in a constant thin wall thickness. Laborious measuring and thinning of the crown are a thing of the past. Steps or cone angles can also be quickly and easily integrated into the construction. A wide variety of manufacturing processes and materials are available for the CAM process.
The customer can choose between telescopics that are manufactured using LaserMelting or subtractive processes. A wide variety of materials is available, from classic cobalt-chrome, titanium and gold to zirconium and PEEK.
In conventional production, the work depended on the precision of the dental technician and his modeling. Problems with the conventional manufacture of telescopic crowns included faulty casting processes, distortions and poor friction. Precise work can also be carried out by the dental technician in digital production. But even if digitization has simplified a lot and some difficulties in the manufacture of telescopic crowns are a thing of the past, there are new challenges that dental technicians have to face.
Telescopics manufactured by LaserMelting have, for example, a different, unfamiliar optical surface that you have to get used to. The workflow has been rethought from analog to digital and, depending on the parameters found, brings with it many new possibilities.
If you have any questions about CAD/CAM manufactured telescopic work, please do not hesitate to contact our experts. We will be glad to advice you on an equal footing!