L5: Foundation restorations in fixed prosthodontics

Question 1

Which are the three primary factors influencing the potential for dislodgment?

Answer 1

• Design of the tooth preparation.
• Fit of the casting
• The nature of the cement

Question 2

What does retention prevent?

Answer 2

prevents removal of the restoration along the path of insertion** or the **long axis of the tooth preparation.

Question 3

What does resistance prevent?

Answer 3

Resistance prevents dislodgment of the restoration by forces directed in an apical direction and prevents any movement of the restoration under occlusal forces.

Question 4

How does surface area affect retention?

Answer 4

the greater the surface are of the preparation, the greater the retention.

Question 5

How does length affect retention?

Answer 5

longer preparations have more surface area and therefore more retentive

Question 6

How do grooves contribute to resistance?

Answer 6

resistance to displacement for a short-walled preparation on a large tooth, can be improved by placing grooves in the axial walls

Question 7

What should the minimum height of a tooth preparation (occlusocervical/incisocervical) be for premolar, molar and anterior teeth?

Answer 7

Premolar and anterior: 3 mm

Molar: 4 mm

Question 8

What is foundation restoration used for?

Answer 8

To replace a coronal tooth structure that was lost as a result of dental caries, previous restorations or tooth fracture and may be fabricated from various restorative materials (ex. amalgam, glass ionomer, composite).

Question 9

Which are the two types of foundation restoration?

Answer 9

• Base:a foundation restoration that does not contribute to the overall retention and resistance form of the tooth preparation (fill undercuts).
• Core: a foundation restoration that augments the retention and resistance provided by the remaining the tooth structure.

Question 10

Which are the desirable features of core material?

Answer 10

• Adequate compressive strength to resist intraoral forces.
• Sufficient flexural strength to prevent flexure of the core during normal intraoral
• functions.
• Biocompatibility.
• Resistance to leakage of oral fluids at the core/tooth interface.
• Ease of manipulation.
• Ability to bond to remaining tooth structure.
• Thermal coefficient of expansion and contraction similar to tooth structure.
• Dimensional stability.
• Minimal potential for water absorption.
• Inhibition of dental caries.

Question 11

Which are the three basic direct core materials?

Answer 11

• silver amalgam
• composite
• glass ionomer

Question 12

What is an amalgam?

Answer 12

• An amalgam is an alloy of mercury and one or more other metals.
• Dental amalgam is produced by mixing liquid mercury with solid particles of an alloy containing predominantly silver, tin, and
  copper.
• Silver amalgam has been reported to perform best as a core material under simulated clinical conditions because of its high compressive strength and rigidity.

Question 13

Why can’t amalgam be used by its own and
needs bonding agents?

Answer 13

It does not bond to tooth structure and therefore does not restore the original strength of the clinical crown.

• Bonding agents have been used but the shear bond strength of amalgam to dentin cannot be compared to the one of composites.
• The clinical relevance of the effect of the bonding procedure after prolonged intraoral function is unknown.

Question 14

What must be supplied to amalgam for large restorations?

Answer 14

Pins, slots, holes, and grooves must be supplied to provide retention for large restorations, but they do not reinforce the amalgam or increase its strength.

Question 15

What is amalgam mostly used as?

Answer 15

Amalgam is mostly used as a core material for posterior endodontically treated teeth (with deep pulpal chambers) along with prefabricated posts.

Question 16

What is glass ionomer?

Answer 16

Glass ionomers are water-based, self-adhesive restorative materials

• the filler is a reactive glass called fluoroaluminosilicate glass
• the matrix is polymer or copolymer of carboxylic acids.

Question 17

Which is the great advantage of glass ionomer?

Answer 17

They have good clinical adhesion to tooth structure.

• Etching of the enamel or dentin surface by phosphoric acid is not needed.

Question 18

What have studies indicated about performance of materials derived from glass ionomer cement?

Answer 18

A number of studies have indicated that materials derived from glass ionomer cement perform poorly as a load-bearing core material.

Question 19

What are glass ionomer cement materials used as?

Answer 19

They are often used as core build-up for pediatric restorations.

Question 20

What is composite composed of?

Answer 20

• an organic polymer matrix
• inorganic filler particles
• coupling agent
• the initiator-accelerator system.

Question 21

Which is the strength of composite compared to the other restoration materials?

Answer 21

It has a strength intermediate between silver amalgam and glass ionomer core material

• It is more flexible than silver amalgam.

Question 22

Which are the advantages of composite core?

Answer 22

• they can be bonded to dentin
• can be finished immediately
• are easy to contour
• can have a more natural color under ceramic restorations

Question 23

How can composite core be bonded to enamel and dentin?

Answer 23

They can be bonded to enamel and dentin with bonding agents.

Question 24

What shouldn’t the final restoration rely on and why?

Answer 24

Retention of the final restoration should not rely on the composite structure

• because adhesion of the composite core to remaining dentin alone is insufficient to resist rotation and dislodgement of the crown.