Depending on the choice of the framework material – zirconium or metal, the assessment of a ceramic-veneered restoration in the mouth of the patient is decisive for the aesthetics. Both materials have specific properties which present a challenge to the dental technician. Particularly with the more demanding metal-ceramic cases, the intra-oral try-in and individual adjustments made on the patient are essential for a successful aesthetic solution. In this article, the author describes three patient cases as examples of everyday, yet critical challenges. All of the cases described were solved with a metal-ceramic solution, which without an assessment of the in-situ situation, would not have led to a convincing result.
Renato Carretti describes three challenging cases that were solved with a metal-ceramic solution.
Reprinted from the November, 2012 issue of Private Laboratory magazine.
Trend towards the use of zirconium
At present, zirconium is a very popular restorative choice. CAD/CAM is the talk of the whole dental community, and in many laboratories and practices the effort is being made to expand machined fabrication as far as possible. However, the well-proven, traditional laboratory method of framework manufacture with modelling, investing, casting, deflasking and the making of final adjustments continues to retain its validity. Experienced dental technicians value the versatility of metal ceramics, which cannot yet be provided by zirconium. As a solution to particular problems, metal-ceramics is aesthetically superior to zirconium. There are also considerable country-specific variations. Whereas zirconium finds very frequent use in Germany and Switzerland, metal-ceramic restorations continue to be the standard in other European countries. This article is devoted to the question of how excellent and aesthetically convincing results can be obtained using the conventional manual laboratory techniques and metal ceramic.
Two worlds: prosthetic restorations on the model and in situ
With even greater consequences than the choice of the framework material is an aspect which mostly remains in the background, but which has a key influence on the aesthetic result, especially with ceramic-veneered restorations: dental technicians often have no opportunity to see their veneered crowns or bridges ‘live’ in the mouth of the patient. Their reality is the model situation. For a relevant assessment, this is insufficient, since restorations look completely different on the model than they do in situ. The play of light and shadow in the mouth, the different light refraction and reflection in the ceramic and the effects of the neighbouring teeth on the shade are factors which do not apply to the plaster model situation. The intra-oral try-in is, therefore, a decisive factor for the success of a high-quality, aesthetic result.
A special case – implant restorations
In the case of screw implants, the try-in represents a significant hurdle on account of the amount of work involved since the provisional restoration, mostly likewise screw- retained, has to be removed first. In order to save time, a try-in in situ is often omitted. In these cases, the only alternative is to aim for the restoration to resemble the adjacent teeth as closely as possible. With this technique, however, it is, at best, possible only to obtain an approximate match. A definitive assessment of shape and shade can be made only in the context of the immediate surroundings of the oral environment.
High-class metal-ceramics: three patient cases
The following article describes three patient cases in which the focus was on a particular aspect of the restoration, and which could not have been solved satisfactorily without the assessment of the dental technician on site. For one or more of the following reasons, there was no question of restorations with zirconium:
- The dentist wanted to ‘be on the safe side’ and chose metal-ceramic crowns on account of their high strength.
- It makes little sense to seat an all-ceramic crown on a metal abutment.
- A severely discoloured tooth stump shows through the veneer of a crown with a zirconium substructure as a grey shimmer.
- With metal ceramics, the abutments can be set to an angle of up to 15 degrees, with zirconium, however, depending on the system, this was not (yet) possible. (In the author’s laboratory, all abutments are screwed directly onto the implants, and in many cases feature an angled design).