Dental ceramics build up
After the metal (or zirconia) framework is fitted on the abutment teeth, the dentist sends it back to the laboratory for ceramics build up.
Porcelain can be placed on all sides of the tooth including the occlusal side. However, there are situations when ceramics is placed only on the visible areas of teeth in the form of partial veneers. The first of the two variations has superior aesthetics.
When porcelain is placed on all sides of the tooth, in most situations, a small area of the dental crown remains uncovered (bare metal). This is the area where the technician grips the dental crown (using special pliers) while applying the ceramic layers.
griping the crown with pliers while applying the ceramic layers
the area where the ceramic crown remains uncovered by porcelain
Many patients wrongly assume that this might be a defect in the construction of the dental crown. The area may have various shapes : metal collar, small metal point etc. It is usually placed in a less visible part of the dental crown in the top and back side. Large dental bridges may have multiple such sections.
When aesthetic demands are very high, it is possible to cover these areas with porcelain (but a second procedure is required).
Porcelain build up technique
Dental ceramics is applied with specific brushes (of various shapes and sizes), in multiple layers. Each layer has to be separately fired in special furnaces at high temperatures (up to 1000 degrees Celsius or 1830 Fahrenheit). During the combustion process, porcelain and metal alloys develop extremely strong chemical bonds between them.
specific brushes used for porcelain build up
Dental porcelain shrinks during firing ; therefore, the dental technician must build artificial teeth about 25% bigger to compensate the shrinking process.
First, the powder corresponding to the desired shade is mixed with water. When porcelain is applied, it may have different colors (white, purple, pink) depending on the manufacturer. The final shade is obtained only after firing.
restoration after porcelain build up and before firing
Dental ceramics is applied in several layers (normally 4 but it can be more). During build up, the technician takes into account all the information received from the dental office (shade, other details).
Layer 1 - Primary or opaque layer
It is a thin layer positioned directly on the metal framework. It consists of specific ceramics that block the passage of light. The main objective is to mask the black color of the metal. After build up, the layer is fired at specific temperatures.
Layer 2 - Base Layer
It is the thickest layer, which gives the basic shape of the crown and defines its shade. Normally, the gum areas have a darker shade while the top areas a lighter one.
dental ceramics build up
Porcelain is applied on all desired sides of teeth, the proximal contacts are adjusted (these are the contacts with the adjacent teeth) and the occlusal side is defined (with cusps and grooves).
When the build-up is completed, the restoration is placed in the ceramic furnace for firing.
Layer 3 - Characterization layer
In this layer, specific features may be added to further improve the aesthetics and give the artificial teeth a close to natural look. Special colors may be added to mimic various anatomical or physiological conditions. For example :
If teeth abrasion is present, a darker coloration can be given to the peak area to mimic the process.
Colorations may be added to mimic various stains : nicotine staining, color changes caused by tartar, erosions etc.
Sometimes, because of excessive bone loss or gingival recession, artificial teeth would appear "too long" or "over-stretched".
In this case, a pink or red colored porcelain may be applied to the top areas to mimic the gums. This way, artificial teeth will not look "over-stretched".
red colored porcelain applied to the top areas.
if tooth-shade porcelain had been applied, artificial teeth would have appeared "over-stretched" and unsightly
slight brown colorations
on the occlusal side of a porcelain crown
Proximal contacts, occlusal contacts (both static and dynamic), gingival tissue contacts, the surface texture and the overall contour of the restoration are adjusted.
After the firing process, the restoration can be sent to the dental office for the final fitting appointment.
Layer 4 - Finishing or glaze layer
The glaze layer is the last layer and it is extremely thin. The glaze layer gives the restoration a smooth surface and the translucency that mimics the enamel or dentin. In this layer, minor shade adjustments can still be made (if required).
after glaze layer build up
after glaze layer build up
It is possible to process dental porcelain using the CAD/CAM systems. As described in the previous chapter, there are some differences between the two techniques, each having certain advantages and drawbacks.
Last review and update: November 2020