Authentic Press-To-Metal Manual

section two:

• VII. Wax Up for Pressable Coverage

• VIII. Spruing Predictably for Optimal Pressing

• IX. Ingot Selection

• X. Divesting Rings

• XI. Sprue Removal

vii.    Wax Up for Pressable Coverage

• Hand wax margins, slightly over-extending, to secure coping/bridge frame to the die.

• Next, hand wax or dip copings in wax dip pot to a minimum of 0.8mm wax thickness. If we fabricated the coping as recommended (0.3mm metal thickness, plus approximately 0.1mm of opaque = 0.4mm,) the total thickness after dipping should measure no less than 1.2mm.

Note: It is absolutely imperative that we maintain a minimum .8mm wax thickness over the top of the copings to insure unrestricted flow of the pressable material to all areas of the restoration(s). Decide which technique will be utilized later for ceramic application (either staining or layering), and wax-up according to the following criteria:

Staining Technique:
Wax to full contour, making certain to observe the minimum 0.8mm wax thickness everywhere. This is particularly important on the occlusal table, in the central groove area and interproximally.

Layering Technique:
Wax up 70-90 % of full anatomical contour, again remembering to maintain at least .8 mm wax thickness, regardless of contour. If you fail to observe this thickness, you may invite cracking.

Note: Inconsistencies in pressable thickness create differences in cooling and heating. In the Press-To-Metal® technique, it is imperative that we achieve an even rate of heating and cooling between the pressable and the metal framework.

• Be certain to inspect the inside of the abutment copings for wax which may have inadvertently flowed between the coping and the die. If this has occurred, simply use a wax carving instrument to trim away excess wax.

• Visually check to confirm a complete, dense interface between the shoulder area and the coping. Any voids should be corrected at this point by reseating the coping/bridge on the die and flowing wax into the voided area(s).



Note: Utilizing this technique eliminates any need to retro-fit the restoration to the master die after pressing. We also avoid the risk of accidental fracture due to unnecessary grinding which may potentially generate excessive heat and vibration.

• Carefully create interproximal embrasures in wax so that very little or no adjustment will be required once we’ve completed the pressing procedure.

VIII. Spruing Predictably for Optimal Pressings

1. Attach one sprue to each individual pontic and abutment.




2. When the first leucite reinforced, pressable ceramic was introduced a little over a decade ago, it was thought that the "hot spot" or thermal zone of the investment cylinder was located in the center of the ring, approximately 15-18 mm above the top of the pedestal. Newer scientific research, however, indicates that the true thermal zone or "hot spot" is located towards the periphery (outside) of the investment cylinder.




3. For this reason, MICROSTAR has created the Authentic® Flex Ring System™ with preformed Wax Sprue Gates™. This system was developed to provide a predictable technique which would insure a correct 30° angle spruing of each pattern, consequently placing each pattern into the true "thermal zone".




4. By spruing into the "thermal zone" several benefits are realized:

5. Less temperature is typically required to attain a complete pressing,
   Usually 5° to 10° C lower than the recommended pressing
   temperature of 940° C.





6. Note: Pressing to Failure," an extremely invaluable technique which entails the incremental lowering of the pressing temperature, usually 5° to 10° C, until a mispress (failure) is attained. At this point, the last temperature at which everything pressed completely is considered the optimal pressing temperature.





7. To make this experiment scientific and valid, we must work with only one variable at a time; in this case, pressing temperature. We must also observe several constants, including: entry temperature, rate of climb, hold time and pressing time.




8. By lowering the pressing temperature, we control the growth of the leucite crystals. Eight percent leucite is considered the ideal volume for maximum strength, ideal color and optimum opacity.




9. Additionally, we produce sharper, more precise margins which lack brittleness.

RESOURCES:
Authentic® Pressing Parameters Guide
Authentic® Firing Parameters Guide

"Tell-Tale Signs of Pressing Too Hot!"

• Inconsistent shades Greater translucency in pressings than expected for the selected ingot and its’ respective opacity. For example, using a (+) ingot, such as SLA1+, the expected opacity of the pressing at a thickness of 0.8mm = 45% opacity.

• Lower value in pressings, grayish appearance.

• Porous (porosity-pitted) pressings.

• Brittle margins.

• Shiny surface gloss.

• Cracking and checking of restorations.

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ix.   ingot selection

1. Authentic® offers a tremendous shade-taking advantage over most pressable systems on the market in that shade tabs of actual ingot material have been pressed to precisely match the enamel shade. They are highly recommended for the staining technique in particular, and are available in all four opacity levels.

2. Using the Authentic® Ingot Selection Guide contained in the Authentic® pressable ceramic manual or on the web, select the appropriate ingot based upon the following criteria:




• Restoration type: all-ceramic crown, veneer, inlay/onlay & ptm

• Ceramic technique: either staining or layering

• Stump discoloration/color

• Opacity level desired

shade

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X.   divesting rings

1. Prior to divesting, we must transfer the location marks for each pattern from the pedestal base to each corresponding sector See instructions in the Authentic® pressable ceramic manual on divesting.
   

2. Extreme caution should be used when divesting rings so as not to strike the aluminum-oxide plunger and/or the button of ingot material. However, with Microstar Disposable Plungers one need not be concerned with striking the plunger as it will be harmlessly absorbed. Many technical advantages are afforded as well.
   

3. When ceramic patterns become visible, be certain to turn down the pressure regulator on the sand blasting unit to 20 psi. This will help prevent accidental removal of margins and/or fracturing of pressings.
   

4. Fine divesting of delicate patterns on occlusal surfaces should be done very carefully with Aluminum Oxide. Hold blasting pencil parallel to the surface you’re removing investment from.
   
   

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xi. Sprue Removal

1. Carefully score the sprue all the way around, approximately 2mm above the junction between the restoration and the sprue. This will control the breaking point if the sprue should decide to fracture off; moreover, if a fracture line should develop, this would control the path of fracture, inhibiting the crack from migrating vertically down the sprue, into the restoration.

2. Avoid generating any unnecessary heat or vibration, as this will cause fracturing.

3. To remove button of sprue, use a ceramic stone or a diamond impregnated silicon/rubber wheel which generates little heat and vibration.
   
   Note:Avoid aggressive, rapid reduction of pressable material.
   This will most certainly cause crazing/fracturing-sometimes even delayed fracturing!
   
   

On to section three

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