Fleming Behrend, CDT, MDTUsing the Pure Press technique I developed, I’m able to create crowns with the strength of a PFM and the esthetics of an all-porcelain restoration. By pressing porcelain to electroformed copings, the ceramic has a bright yellow core instead of a dark oxidized conventional cast metal core.
These restorations are also biocompatible, reduce the cost of materials by plating only to the shoulder of the preparation, reduce labor time and simplify cementation since the dentist can use traditional zinc phosphate cement. Pure Press restorations can also be used on implant components or custom made-abutments.
In all cases, the proper relationship between the unsupported mass of porcelain and the framework should be critically observed. Furthermore, the thermal expansion of your press porcelain must match the thermal coefficiency of gold.
Following is a step-by-step look at how I used the Pure Press technique for a female patient who needed to have teeth #7 and #9 replaced (see top photo at right). In order to create an overall pleasing appearance, she opted for restoring all four anterior teeth. The color matched her existing teeth and she is very pleased with the improvement and her beautiful smile.
The margins were perfect and the incisal translucent effect was acceptable even without a cutback. For optimal cement bonding, I sandblasted the inside of the crowns before insertion.
Before
After
Step 1: I waxed up the ideal shape of the four anteriors on a duplicate model of the patient’s existing teeth.
Step 2: I fabricated models and blocked out the dies. I also made an index from the anatomical waxup on the pre-op model to help later with the full contour waxup.
Step 3: I duplicated the dies for electroforming and then placed them in a plating head and processed overnight; the thickness of the final copings is 0.2 -0.3 mm.
Step 4: For a matrix, I applied a bonding agent between the porcelain and metal and fired the restoration.
Step 5: I then fired opaque onto the surface of the pure gold copings.
Step 6: The number of press pellets used for each restoration is relevant to the weight of the full contour waxup minus the weight of the opaqued copings. After each measurement was accurately noted, I knew exactly how many pellets to use for the four anterior crowns. (Most manufacturers will inform you of the correct relationship between wax weight and number of press pellets.)
Step 7: After burnout at 900°C for 40 minutes, I pressed the crowns at 940°C and allowed them to cool down to room temperature. I opened the mold by first drawing a line at the height of the plunger, marked a horizontal line at the correct height and used a diamond separating disc to cut along the line. Then I used a knife along the vertical edges to separate the mold.
Step 8: To further devest, I blasted with 50-micron glass beads, first at 6 bar pressure and then at 1.5 bar pressure on the copings.
Step 9: I cut the pressed crowns with an all-diamond disc and seated them on the model for final contouring.
Step 10: To obtain a natural glaze, I polished the surface with fine conical diamonds, then used a non-contaminating white silicone rubber point and finished with a leather wheel saturated with white tin oxide. After the surface appeared nice and smooth, I ran the crowns through a glaze bake with a minimum amount of stain liquid applied.