Lecture 4: Metal Ceramics (Pfm)

Front 1

For a gold crown CVC prep, the shoulder should measure _____ mm prior to beveling?

Back 1

0.65 - 1.0 mm

Front 2

How can you verify occlusal reduction?

Back 2

You can verify with a 13 hatchet. The 13 hatchet should fit snugly when inserted at a cuspal angle.

Front 3

Which type # of casting gold alloys is used to make gold crowns?

Back 3

Type III is used to make onlays & gold crowns.

More gold = less strength.

From weakest to strongest.

Type I: Has more gold. Small inlays.

Type II: Inlays.

Type III: 70-75% Au; onlays & gold crowns.

Type IV: Has less gold. cast post in endodontic treated tooth & gold RPD framework.

Front 4

What are the characteristics of porcelain?

Back 4

Porcelain is

- strong in compressive strength.

- weak in tensile & shear strength. Therefore, it needs to be supported.

Front 5

What are ceramics?

Back 5

Ceramics are inorganic compounds with both metallic + non-metallic elements... however, they have non-metallic properties.

Front 6

What is a metal coping?

Back 6

A metal coping is a metal cap which is applied over a prepared tooth. It can be used to support porcelain.

The metal collar is part of the coping and prevents it from flexing (provides rigidity).

Front 7

PFMs can be sintered. What is sintering?

Back 7

Sintering is a process that involves heating closely packed particles to a specified T below the MP of the main component, to densify and strengthen a structure as a result of bonding, diffusion, and flow phenomena.

Front 8

What can the metal coping be made of?

Back 8

A. Noble alloys (excludes silver, Ag):

- high-gold alloys: resembles dentin when viewed through porcelain

- low-gold alloys

- palladium-silver

- high palladium

(opaque porcelain is used to mask the dark oxide in low-gold and palladium alloys)

B. Base Metal alloys: >75% base metal or <25% noble metal

- nickel-chromium alloys

- chromium-cobalt alloys

- titanium alloys

Front 9

What can trace elements be used for in a PFM?

Back 9

Trace elements: indium (In), Zinc (Zn), Tin (Sn) are used to create an oxide layer on metal to bond with porcelain.

Front 10

Holding the bur parallel to the POI during theprep will create a _____ convergence anglebetween the walls.

Back 10

6º

Front 11

Occlusal reduction should be _____ mm ideally.

Back 11

1.5 mm (range: 1.0 - 1.75 mm)

Front 12

What are the primary purposes of the metal coping and porcelain within a PFM?

Back 12

Metal coping grants strength.

Porcelain grants esthetics.

Front 13

Name some methods to strengthen porcelain.

Back 13

Use internal coping for support:

- metal (PFM)

- high strength ceramics (all ceramic crowns)

Improve strength of outer porcelain surface

- glazing

Front 14

What are we referring to when we talk about the thermal compatibility of metal ceramics?

Which has a higher thermal CoE? Metal or porcelain?

Back 14

We are talking about the ability of a metal and its veneering porcelain to contract at similar rates during cooling from the ceramic sintering T.

Metal > porcelain (slightly).

Front 15

How thick should the metal coping be? The porcelain?

Back 15

Metal coping = 0.3 mm

Porcelain = 1.0 mm

- opaque porcelain: 0.2 mm

- body porcelain

- enamel porcelain

Front 16

Which one is stronger and supports porcelain better: circumferential (360) metal collar vs porcelain buccal/lingual metal collar?

Back 16

Circumferential (360) metal collar, because its metal collar extends all the way around.

Front 17

What are the advantages of using base metal alloys? Disadvantages?

Back 17

Base metal alloys

Advantages

- high strength

- low weight & cost

Disadvantages

- shrinks easily (causes problems with fit)

- thick oxide layer (makes it more difficult to bond to porcelain, solder)

- nickel allergy (22% for women, 10% for men)

- beryllium toxicity

Front 18

The higher the gold content, the _____ the metal coping must be.

Back 18

Thicker; to compensate for weakness.

Minimum thickness for metal ceramic copings:

- Hi-Au: 0.5 mm

- Low-Au: 0.3 mm

- Ag-Pd: 0.3 mm

- Base metal: 0.1 mm

Front 19

A metal collar requires a _____ prep, while a porcelain labial/buccal margin requires a ____ prep.

Back 19

Metal collar: shoulder-bevel prep

Porcelain labial/buccal margin: shoulder prep

Front 20

A shoulder bevel prep should follow _____.

A shoulder butt joint prep should be _____.

Back 20

POI; 90 degrees to the root surface.

Front 21

A cutback is made to create room for porcelain. What are the purposes of a cutback?

Back 21

Purposes of cutback:

- Provides proper support for porcelain

- Provides for a uniform thickness of porcelain

- Predictable esthetics

- Allows porcelain to "wrap around" the metal framework and increases compressive bonding of porcelain.

Front 22

What does degassing the metal framework do?

Back 22

Degassing creates an oxide layer which helps establish a chemical bond between metal and porcelain.

Front 23

Explain the purpose of adding the 2 layers of opaque porcelain to the metal coping.

Back 23

1. A thin wash layer is applied in order to completely wet the metal to create the bondbetween porcelain and the oxide layer of the metal. The coping is dried and fired under vacuum.

2. A second application is then applied to mask the dark metal oxide color. This layer shouldbe as thin as possible, just thin enough to mask the metal. The opaque layershould be approx 0.1 mm thick.

Front 24

List the steps required to make a PFM.

Back 24

- Wax up (full contour) restoration

- Cut back (to create room forporcelain)

- Cast metal coping/framework

- Oxidizing / Degas

- Opaque porcelain addition/firing

- Body & Incisal porcelainaddition/firing (2-3 firing)

- Glazing/firing

Front 25

What are the 3 types of bonds that exist between porcelain and metal?

Back 25

Mechanical Bonding

- Micro irregularities inmetal: grinding & airabrasion

Chemical Bonding

- Oxide layer: degasing

Compression Bonding

- Framework design

- Thermal CoE

Front 26

Unlike a gold crown CVC prep, a PFM prep requires _____ mm of axial reduction, and _____ mm of occlusal reduction.

Back 26

ideal: 1.3 mm (range 1.0-1.5 mm); ideal: 2.0 mm (range: 1.5-2.5 mm)

Front 27

What instruments can you use to finish a porcelain labial margin?

Back 27

End cutting bur; 13 bin angle chisel.

Front 28

If the lingual metal collar is >1.5 mm tall, the axial reduction should be _____ mm.

If the lingual metal collar is <1.5 mm tall, the axial reduction should be _____ mm.

Back 28

0.65 mm; 0.8 mm

The shorter the metal collar is, the more axial reduction you need to support the porcelain on top.