Section One:

• I. Model Preparation
• II. Coping Wax Up
• III. Bridge Wax Up
• IV. Press-To-Metal Alloy Selection
• V. Metal Framework Preparation
• VI. Opaque Application and Firing Schedule

I.    Model Preparation

 

• Pour, pin and base model using low expansion die and base stone.
• Articulate models, then section and trim dies in the usual manner

.

II.   Coping Wax-up

1. Dip dies in wax pot to .3mm wax thickness.
   
   Note: Do not build up incisal edges, cusp-tips or interproximals in wax. It is imperative that the mass of the alloy be minimized to maintain an even heating and cooling between the metal framework and the pressable material.
2. Carve back the shoulder area in wax to the junction of the shoulder and the axial wall in preparation for the 360 pressed ceramic shoulder.
3. To enhance light transmission into the root and papilla area, cut the wax coping up the axial wall 1-3mm.
   
   Note: This technique is contraindicated when the preparation is darkened, discolored or ametal post & core is present.
   
   
4. If the tooth was not prepared with a 360 shoulder, create a thin, defined, metal band to support pressable material. When creating this band, keep in mind that final contour/emergence profile of the pressable material is being determined.
5. Metal linguals, occlusals and bite islands (centric stops) are acceptable, preferred alternatives for framework design.
6. Sprue wax copings using conventional crown & bridge techniques, and invest using a precision casting investment (MICROSTAR HS Investment).

III.   Bridge Wax-up

1. Wax abutment copings using aforementioned wax coping technique.
   
   Do not build-up incisal edges, cusp tips or interproximals.
   
   
2. Utilize a hollow pontic system for posterior bridge pontics.
   
   

   Remember: The metal framework is a secondary,or skeleton framework- minimizing the mass of the alloy to obtain an even heating & cooling between the pressable ceramic and the alloy is imperative.
   
   Note:If you dont have a hollow pontic system, you may modify a conventional pontic system as follows:
   
   a) Posterior and anterior pontics should be reduced to 2/3s their normal pontic size.
   
   b) Using an electric wax spatula, heat the center of the pre-formed pontic and hollow it out all the way through to the underside.
   

3. Observing the beam theory, design connectors tall, inciso-gingivally, and narrow, labio-lingually or bucco-lingually. This type of framework design facilitates deeper, more natural looking embrasures, as well as insuring a sufficiently strong bridge restoration.
   
   Try to envision the embrasure space in its final tooth form when designing the connectors. Be certain to allow enough embrasure space between each individual abutment and adjacent pontic for a minimum of .8mm of pressable to cover each respective unit. This constitutes a minimum of 1.8 to 2.0 mm combined embrasure space between any two adjacent units.
   
4. Design connectors so that they are a minimum of 1mm off of the papillae and pontic tissue areas. This will provide adequate clearance to allow for sufficient thickness (1mm min.) of pressable material.
   
5. Using 16-18 gauge wax wire, create a lingual "T" handle, approximately 5-7mm long with a 4-5mm "T" on the end. Place this handle on the lingual of each pontic in the cingulum area on anteriors.
   
   Note:This "T" handle is critical to the success of the PTM bridge; Later, it will serve as an anchor to stabilize and fix the bridge framework in the investment during the pressing process.
   
6. Sprue using conventional crown & bridge casting techniques and invest using a precision casting investment such as Microstar HS investment.

IV.   Press-To-Metal Alloy Selection

Two critical criteria must be satisfied for an alloy to qualify for use:

1. Alloy CTE (Coefficient of Thermal Expansion) @ 600 C range of 15.8 to 16.7, with 16.0-16.4 being the ideal, "sweet spot."
   
2. The minimum solidus temperature is 980 C. The solidus temperature is the temperature at which the alloy becomes dimensionally unstable, softened and pliable.

V.   Metal Framework Preparation

1. Many Alloys which work with the PTM technique contain a higher content of gold, and consequently are predisposed to abrasive contamination if not processed correctly. Use extra care when divesting and finishing frameworks so as not to contaminate them with aluminum oxide, glass beads or any foreign particles from finishing instruments.
   
2. When aluminum oxide is used for fine divesting, be certain to decrease the air pressure to 20-25 psi once metal copings become visible.
   
3. Use cross-cut carbide burs for finishing. Work in one direction at a slower speed to avoid smearing or folding the metal over itself.
   
   Note: Failing to observe this directive may result in gassing or bubbling of the opaque during subsequent porcelain firings.
   
   VIP: Do not sandblast high gold alloys prior to or after degassing.

PTM Alloys

• Authentic HE - Cr-Co (Nickel-free and Beryllium-free)
  
  Note: If you select Authentic HE base alloy, after metal finishing, sand blast coping aggressively using 110 micron aluminum oxide at 80 psi and ultrasonic/steam clean prior to degassing.

VI. Opaque Application

• Mix Press Paste Opaque thoroughly to a latex paint consistency.
  
  Use opaque liquid sparingly and only when necessary: never use water.
• Apply two even coats, avoiding puddling and excessive thickness, especially on the first coat.
• Opaque all areas which will receive pressable material, including the inside and all areas of the hollow pontic, as well as the lingual "T" bar handle. Estimate the final thickness/contour at the "T" bar and opaque slightly beyond that point. Do not fill hollow pontic with opaque!
• Verify opaque firing temperature, and maturation by the sheen or gloss which is achieved. A medium-high gloss is correct.
• When using water to clean opaque from the brush, be certain to dry all moisture from the brush, and then rehydrate sparingly with opaque liquid. This will prevent bubbling of paste opaque.

Opaque Firing Schedule

C/F	Closing Time	Start Temperature	Start Vacuum	Rate of Climb	Hold Time without Vac	First Firing	Second Firing	Cool Time
C	6-8 min	400 C	400C	45 C	1.5 min	935 C	925 C	0
F	6-8 min	752 F	752 F	113 F	1.5 min	1715F	1697F	0

After 2nd opaque firing weigh framework!
This weight will be subtracted from the total weight after waxing up for pressable procedure.

After 2nd Firing, Labial

After 2nd Firing, Lingual

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