METAL-CERAMIC RESTORATIONS

Question 1

Porcelain-Metal Bonding Mechanisms:

Answer 1

1-Mechanical
2-Compressive
3-Chemical

Question 2

Note METAL-CERAMIC RESTORATIONS
Are the most popular restorations used in fixed prosthodontics

Question 3

Requirements of alloys used for metal-ceramic restorations:

Answer 3

1-The coefficient of thermal expansion of porcelain and metal should be compatible,

2-The melting range temperature of the metal should be higher than fusing
temperature of porcelain by at least 170 to 280c.

• Porcelain used for metal ceramic have a fusing temperature of 980c for noble alloys
  And melts at 1260c, for base metal ally melts at 1300c.

Question 4

Basic requirements for dental porcelain used as veneering material ?

Answer 4

-Low fusing temperature than the melting range of cast metal substrate.

-Porcelain should resist devitrification

-Coefficient of thermal expansion should be slightly lower than metal by 1x10c

Question 5

Method of construction

Answer 5

-platinum foil matrix of thickness(0.25mm-0.001mm) is adapted on the die Precisely, the ends of the foil folded together to form joint called Tanners Joint this joint placed either lingually or proximally.

Question 6

The first layer applied on the die called……… which mask the
Color of the alloy and it responsible for the metal-ceramic bond .

Answer 6

1- opaque porcelain

Other layers:
2-Body (Dentin) porcelain , main bulk
3-Enamel (Incisal) porcelain , translucency to the final
Restoration

Question 7

There are three methods of porcelain condensation….

Answer 7

1-Vibration:

2-Spatulation:

3-Brush or capillary attraction

Question 8

This slight difference in
coefficients of thermal expansion will cause…

Answer 8

the porcelain to “draw” toward the
metal coping when the restoration cools after firing

Question 9

Chemical bonding plays the major role in metal-ceramic bonding mechanisms, Which is indicated by the formation of ….

Answer 9

an oxide layer on the metal

Question 10

Oxide-forming trace elements such as tin, indium, are added to gold alloys, these would migrate to the interface where they oxidize and form….

Answer 10

covalent or ionic bond
To similar oxides in the opaque porcelain layer across the interface.

Question 11

principles of metal substrate design:

Answer 11

1-No sharp or acute angles:
-Sharp angles on the veneering surface should be avoided,

2-Adequate support to porcelain veneer

3-No occlusal contacts on porcelain/metal interface

Question 12

creating rounded convex metal surface is important as it:

Answer 12

1-Eliminate areas of stress concentration
2-Distribute the occlusal force more evenly
3-Facilitates wetting of the metal substructure by the porcelain

Question 13

Contact at porcelain/metal junction should be…… as it leads to porcelain……

Answer 13

avoided , Fracture

Question 14

The junction should be placed away from all centric occlusal contacts by at…

Answer 14

1-1.5mm, to avoid metal flow and subsequent porcelain fracture.

N.B: Occlusal contacts against natural opposing teeth should be whenever possible in metal.

Question 15

The minimum thickness of porcelain is…. the optimum thickness 0.1mm, the Maximum is …..

Answer 15

0.7 mm, 1.5mm

Question 16

The minimal metal thickness should be for:

Answer 16

Noble metal alloys -Base metal alloys
*0.3-0.5mm. *0.2-0.3mm

Question 17

Proximal contacts
-for anterior teeth it should be on

Answer 17

porcelain for better esthetics and translucency