PREPARATION OF METAL SUBSTRUCTURE FOR PORCELAIN AND APPLYING/FINISHING PORCELAIN

1st Step remove investment

Remove investment with handpiece using small curbide bur

Then sandblast using 50 microns aluminum oxide

2nd step evaluate

Once the casting is devested (removed from investment) evaluate the casting/framework with a microscope or magnification for any defects

3rd step cut casting/framework off sprue

\-Cutting off- As close as possible to the casting without damage to casting/framework always wear personal protective equipment (PPE).

* Do not use, meant for use during pindexing \\n -Use separating disc Even speed Keep movement straight and even

Equipment (items needed to fit framework after devesting)

Microscope or magnification loupes

• Handpiece •Small round curbide burs

• Small tapered carbide burs

• Small stone points

• Check spray (indicator spray)

• PPE

• Proper vacuum (recovery device)

4th step fit to die

I. Remove any internal roughness (nodules/bubbles)
2\. Gently place on die to determine if casting/framework is to tight or loose
3\. Framework fits correctly when it seats :
• Without using pressure
• Without gaps at margin
• Margins should look just like they did in wax
• Framework should have a passive fit without being too loose.
• Should not twist or wobble on die

5th step sprue removal

\-Before starting look at framework and die, think about the shape of the wax pattern before you sprued it.

• This clarifies how much to remove from sprue area. Make sure to use your metal thickness calipers/ gauges often so to avoid creating a hole in the framework.

• Using a heatless stone slowly remove bulk of sprue.

6th step finishing porcelain baring surfaces

Always continue to check thickness of each coping on the framework.

* Minimum .3 mm. Use carbide burs or ceramic bonded mounted stones (non contaminating)

\
* Do not rubber wheel surface areas porcelain will be applied. • The grooves made from grinding create tiny undercuts which helps gain a tiny bit of mechanical retention.
* Most retention comes from chemical retention.

7TH STEP FINISHING NON-PORCELAIN SURFACES

2 Different approaches


1. Do minimal work check occlusion, shape, and contacts. Wait until after porcelain is applied then complete.
2. Preliminary finishing and rubber wheeling completed before porcelain is applied.

8TH STEP PREPARING FOR OXIDATION

* sand blast Air with 50-microns pure aluminous oxide.
* Keep moving don't focus on one area too long• Could damage casting
* Next steam clean entire framework

9TH STEP OXIDIZING

• Place framework in porcelain oven

• Ceramco 3, Program 10

• If the oxidation step is forgotten or the framework is under-oxidized the chemical bond will not be properly established.

• Porcelain will chip off

• If the framework is over- oxidized the porcelain could come off the framework leaving oxidation on the framework and the porcelain that has fallen off.

Why is it important for your framework to oxidize properly?

So porcelain won't chip off

If the oxidation step is forgotten or the framework is under-oxidized the chemical bond will not be properly established.

Porcelain will chip off

If the framework is over- oxidized

the porcelain could come off the framework leaving oxidation on the framework and the porcelain that has fallen off.

3 reasons why you may need to pre-solder a ceramic framework

1. fit of the framework
2. large frameworks are cast in two pieces then soldered together to become one.
3. Bridge rocks on master cast (it is important for bridges to be stable and not rock).

two types of soldering technique in ceramic

1st pre-soldering

2nd Post Soderling

Pre-soldering

* This is the procedure of uniting components of the bridge before porcelain is applied.
* The solder used has a similar composition to the framework to be soldered.
* High temperature phosphate bonded soldering investment must be used.
* Nowadays laser welding is a better option.

Post-soldering

* Used if different alloys are to be joined.


* Used if porcelain portion of crown has been completed. \\n • Low fusing gold solder is used.
* Low temperature gypsum bonded solder investment is used to avoid damage to glazed porcelain.
* Completed in the porcelain oven.
* Nowadays Laser welding may be a better option.

Both during pre-solder and post-solder the are to be soldered should be lightly finished

.2mm - .3mm wide (the width of a business card).

• If too large way too much solder will be needed, and the solder joint will be weak.

Use solder recommended for the ceramic alloy to be soldered

• Melt several hundred degrees below parent alloy (framework to be soldered). \n • Melt several hundred degrees above porcelain fusion temperature.

Metal ceramic alloys require phosphate bonded soldering \n investment:

Resists slumping when mixed properly \\n • Handles high hea

T/F. Solder investment has no expansion

True

3 methods to determine amount of solder needed for the area to be soldered.

* Freehand soldering
* Cut and fit length of solder
* tadpole solder strip

Hand free soldering

* you hold a strip of solder with solder tweezers and place on joint being soldered while holding torch tip on the solder and joint to heat/melt solder.

Strips of solder

* This method is quick and easy but can be messy


* Can end up with a lot of solder to grind off the newly soldered joint

Cut and fit soldering

more predictable because you limit the amount of solder to be melted.

* Cut piece of solder to the length of the gap to be soldered.

Tadpole soldering

Create a "tadpole" solder strip

* Place one end of piece of solder in a torch flame until it round are balls up.
* Cut this end of the strip of solder off and place in gap to be soldered.

Six steps of pre-soldering

I. Create solder gap
2\. Establish proper position
3\. Luting (sticking it together)
4\. Investing
5\. Soldering
6\. Retrieving/finishing

1st step of pre-solder

Create solder gap .2 to .3 mm (width of business card)

2nd step of pre-solder

Place framework on master cast to establish proper position of the framework for soldering.

3rd step fr pre-solder

Luting (Holding Together) restoration- creating the proper solder relationship.

After placing framework on solid model or master cast:

Place sticky wax or light cured resin in solder gap (while gently holding pieces onto model so not to displace).

Place a toothpick or old bur across occlusal and sticky wax or light cure acrylic to help strengthen framework.

4th step fr pre-solder

* Invest- mix solder investment to manufacturer specifications.
* Gently place investment into retainers making sure they are filled with investment.
* This allows for support during heating/ prevents framework from melting and collapsing.
* Protects margins
* After placing investment in retainers create a patty of investment on a glass slab, gently place bridge on the patty (margins down).

5th step fr pre-solder

* Utilize single orifid torch tip (one hole) , Solder flows toward heat so when freehand soldering hold the solder on the opposite side from the flame. Heat area to be soldered with reducing flame this will cause solder to pull into the gap as it melts.

6th step fr pre-solder

* Once cool remove framework form investment


* Once all investment is removed check fit on solid model
* If fits metal prepare solder joint using normal finishing stones and burs.
* Then blast and oxidize like normal.