Contraindication for an all ceramic crown

# Each of the following patient situations is

considered a contraindication for an all-

ceramic crown EXCEPT one. Which one is

the EXCEPTION?

A. Extensive wear of tooth structure or restorations

B. Previous history of ceramic crown fractures

C. Amalgam restorations with marginal breakdown

D. Severe bruxism

The correct answer is C. Amalgam restorations with marginal breakdown. 

A history of ceramic crown fractures and extensive wear of opposing tooth structure

or restorations suggests to the clinician

that a heavy occlusal load is present during

occlusion.

People who chew hard foods and brux

severely will place the all-ceramic crown

under strong occlusal forces that may

cause it to fracture or overly wear the

opposing teeth.

Extensive and faulty amalgam restorations

that are displayed or are not placed

esthetically can be better replaced with an

all-ceramic crown.

Amalgam restorations with marginal

leakage and/ or breakdown can be

replaced in the core build-up for the PFM crown.

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Loss of apical seat due to overinstrumentation

# Which method is the best to manage loss of apical seat due to over-instrumentation?
A. Increasing the file size and decreasing the file length
B. Prescribing analgesics and antibiotics
C. Filling with a gutta-percha cone that is larger
D. Using a chelating agent and packing with calcium hydroxide
E. Filling with a warm gutta-percha technique

The correct answer is A. Increasing the file size and decreasing the file length. 

When the apical seat is accidentally

removed, the ability to create a hermetic

seal at the apex is compromised.

In order to avoid this procedural error, a

shorter length of file should be used to

establish a correct working length.

The correction of working length will

eventually help re-establish apical seat, then adequate flaring of the apical portion of the canal can be done with the use of larger sized hand files.

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Highest failure risk in endodontic perforation

# Which of the following locations would a
perforation present the HIGHEST failure risk?
A. Furcation
B. Apical 1/3 of the root
C. Crown
D. Middle 1/3 of the root
E. Apex

The correct answer is A. Furcation.

The HIGHEST risk for endodontic failure is
the perforation through the furcation because it is most difficult to seal.
Perforations of the crown may be sealed
with the final restoration.
Perforations near the root apex can be
sealed during obturation.
Teeth with endodontic perforations may still be successful. Perforations are NOT a
guarantee of endodontic failure.

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Dentin bonding agent

# A dentin bonding agent has both hydrophilic and a hydrophobic end. The hydrophilic end bonds to:
A. Collagen of dentin
B. Calcium of enamel
C. Hydroxyapatite of hard tissues
D. Resinous restorative material

The correct answer is A. Collagen of Dentin.

- Bonding of composite restoration to dentin depends on difunctional bonding agent. 

- The dentin is hydrophilic and composites are hydrophobic. So, the primer used for bonding composites to dentin should have both the properties. 

- Generally, 90% of dentin bonding agents are used for mechanical interlocking.

- Key ingredients in primers of dentin bonding systems is hydroxyl ethyl methacrylate. (HEMA)

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