troublebshooting

Question 1

Name 3 errors that can cause rocking/instability of a PFM bridge.

Answer 1

1) Inaccurate tooth preparation (lack of parallelism-prevents proper path of insertion, over/under-tapering- inadequate frictional retention)
2) Inaccurate fit of metal substructure (casting distortion during wax-up, investing, or casting of metal framework).
3) impression errors (bubbles/voids) and distortion of working models.

Question 2

Which type of bur is used for adjusting occlusion of a PFM crown?

Answer 2

A: Fine-grit diamond bur (red band).

Question 3

Which type of bur is used for adjusting occlusion of a full metal crown?

Answer 3

A: Tungsten carbide bur (multi-fluted).

Question 4

Why use a fine-grit diamond bur for porcelain (PFM) adjustment?

Answer 4

A: Prevents micro-cracks /chipping in the brittle porcelain.

Question 5

Why use a tungsten carbide bur for metal crown adjustment?

Answer 5

A: Efficient cutting of metal without overheating.

Question 6

Buccal reduction needed for a PFM crown?

Answer 6

A: 1.2 – 1.5 mm.

Question 7

Occlusal reduction needed for a PFM crown?

Answer 7

A: 1.5 – 2.0 mm(with occlusal porcelain).

Question 8

Margin design for a PFM crown?

Answer 8

A: Shoulder with bevel or radial shoulder (buccal); chamfer (lingual).

Question 9

Lingual reduction needed for a PFM crown?

Answer 9

A: 0.5 – 1.0 mm.

Question 10

Function of #0 retraction cord?

Answer 10

A: Retracts moderately tight gingiva; provides good sulcus widening.

Question 11

Key benefit of retraction cords during impression taking?

Answer 11

A: Widens sulcus for accurate margin capture.

Question 12

Function of #00 retraction cord?

Answer 12

A: Used for very tight or delicate tissues; placed first in double-cord technique.