Many people don't understand what a dental technician does. Obviously, they know we're involved in the fabrication of dental restorations, but to what degree and how? To better understand this, think of the dental technician as someone acting in concert with the dentist. Many people equate the technician to a pharmacist, in that the technician completes the prescription supplied by the doctor. Although this is true, the technician does so very much more, too. By using impressions taken by the dentist, the technician builds a precise working model of the patient's mouth. From this model, a wide variety of restorations and appliances can be designed and fabricated. Science, skill, and art are all intertwined to make something that if done correctly, won't be noticed by anyone other than the dentist and patient.
Someone once said all roads lead to Rome, it's just a matter of choosing the one that works for you. This is so true for dental labs, for it seems that every lab has it's own way of making restorations. We all use the same science, the same basic components, and basic techniques. It's just that every lab seems to have variations on these. And by choosing the techniques that work for them, they're able to make beautiful restorations. The essentials are still the same, though, no matter which lab is going to make the restoration.
For a typical full gold crown restoration, here is a common approach to it's fabrication once it's left the doctor's office.
Everything starts at the lab with an impression, taken by the doctor, of the patient's teeth (we won't even get into all of the styles and different materials used to make impressions ).
From the impression, a model is made. The most common model is made out of a gypsum product, but synthetic gypsum, epoxy, and resins are gaining in use. Which ever material is used, will produce an accurate working model of the patient's teeth.
The model is constructed so that it's mounted and hinged is a way to represent the working jaw. It's also sectioned to allow the removal of the teeth that will be restored.
Today, the vast majority of fixed restorations incorporate using the lost wax technique at some point during the fabrication process. Full gold crowns and inlays utilize this technique completely, and most porcelain to metal crowns and bridges will use the technique to make the underlying substructure for the porcelain to be built upon. With the advent of computers and other high tech furnaces and casting machines, the quality and consistency has been improved.
The lost wax technique basically is the build-up of the unit in wax to an exact replication of the desired crown or substructure.
The finished wax-up of the crown is removed from the model and placed for investing.
This is then invested in a material which solidifies; is heated to burn out the wax; and then the metal is melted down and cast into the void created by the "lost wax".
The cast metal solidifies in this void and can be finished down to fit on the working model. Today, standards are as such, that microscopes are a common tool in determining the difference between success and failure. They're a great tool in helping insure that the cast gold crown fits properly to the working model.
Porcelain to metal crown fabrication is a bit more involved than that of a full gold crown. Now the technician not only is striving to make a restoration that fits and functions properly, but is also striving to blend this restoration in with the other natural teeth. He/she must take into consideration shades, contours, and texture, as well as the preparation design, working space, and type of materials to be used. And if it's all done properly...no one ever notices the final restoration.
Again as with the gold crown, everything starts with a good working model from which a metal coping is designed (typically using the lost wax technique) to build porcelain upon.
To hide the metal, a thin layer of opaque porcelain is applied and then baked on in a furnace. From very defined firing parameters the opaque will bond to the metal, not only masking out the metal, but also allowing a bonding junction with the porcelain to be added next.
Porcelain is built up in varying layers and shades to the desired shape prior to firing in the porcelain furnace.
The crown is then fired in the furnace to somewhere around 1700 degrees Fahrenheit (depending on the type of material). This 1st baked crown can now be fit to the model and adjusted if need be.
At this point a second correction build-up and bake are done to the crown afterwhich it's again fitted to the models; and then once again fired in the furnace to achieve a nice finished glaze..