For the last three years, I've been involved in titanium research and development with Precision Milling Center in West Valley City, UT, and read with interest Luke Kahng's recent article on titanium (How to Fabricate an Esthetic Porcelain to Titanium Restoration, LMT November/December 2011, Click here to Read). The piece is well written and supported with excellent photography. However, I'd like to add some technique recommendations that are critical to the success of processing porcelain-fused-to-titanium restorations:
- When designing the framework, follow your manufacturer's instructions regarding minimal thickness, usually .4mm for anteriors and .6mm for posteriors.
- Metal preparations should always be done with SHP burs designed just for titanium. As Khang says, always cut in one direction and also use a maximum speed of 15,000rpm.
- Never use more than 2-2.5 bars or 30-35 psi of pressure when sandblasting titanium. Also, sandblast at a 45o angle and never use a particle size less than 120-150 microns of pure aluminum oxide abrasive. The article instructs you to blast the inside of the frame but first blast the outer surface prior to porcelain application; the inner surface of the abutments will be sandblasted after firing cycles to remove the oxide that forms internally. To clean the inside of the abutments, use a 50-micron-grit abrasive and blast at 2 bars or less of pressure; a larger grit size can damage the margins.
- After sandblasting, bench set the titanium frame for 5-10 minutes (not to exceed 30 minutes) to undergo the passivation process. This step is critical to the success of bonding to titanium; during this time, titanium naturally develops a very fine oxide layer that prevents corrosion and is the contributing factor for biocompatibility of the material. Failure to implement this step will lead to failure of the restoration.
- Avoid ultrasonic cleaning after sandblasting; steam cleaning is recommended by most manufacturers.
- GC recommends that its GC Initial Porcelain Ti™ Bonder be applied in a thin enough layer that the coping shines through. When applying the bonder, brush out pooling and thick streaks of the bonder for a thin, uniform coating. Properly fired bonder surfaceis dark and has a slightly shiny appearance; gray patches of fired bonder indicate the use of too much bonder.
GC also recommends that the first layer of opaque is applied as a very thin wash on the Ti Bonder treated surface; apply additional layers as needed along with appropriate modifiers. Complete the porcelain buildup, finish contours, set occlusion and glaze.
When polishing and cleaning titanium after the glaze, use polish wheels and high-shine compounds specifically designed for titanium. Polish the exposed titanium finish lines, wait 10 minutes for the passivation process to occur, then steam clean the restoration. This passivation process seals the surface of the titanium and prevents corrosion that would discolor the metal later.