Fixed Prosthodontics

Question 1

What is fixed prosthodontics?

Answer 1

Area of prosthodontics that focuses on permanently attached dental prosthesis.
Same thing as indirect restorations.

Question 2

Give examples of indirect restorations?

Answer 2

Veneers
Bridgework
Crowns
Inlays
Onlays
Post and cores

Question 3

What part of the history taking process is important for fixed prosthodontics?

Answer 3

Any history of trauma?
Any habits- grinding, nail biting?
Smoker?
Drinker?
Any failed restorations in the past?

Question 4

What part of the EO examination is important for fixed prosthodontics?

Answer 4

Smile line- do they have a high smile line?
If so, this means the restorations will be on show entirely.

Question 5

What part of the IO examination is important for fixed prosthodontics?

Answer 5

Look for signs of bruxism- linea alba, tongue fissuring on the lateral aspects, pathological toothwear.

Look at occlusion- incisor relationship, excursive movements of the mandible, canine guidance or group function?

Look at the inter-arch space, inter-tooth space.

Question 6

What special investigations might you wish to carry out before commencing fixed prosthodontics work?

Answer 6

Sensibility testing- ethyl chloride, electric pulp test, hot GP.
Radiographs- to assess for caries, tooth fractures, PA pathology, bone levels, status of existing restorations, assessment of potential abutment teeth.
Study models- mounted on a semi-adjustable articulator.
Facebow- if planning on using the re-organised approach.
Diagnostic wax up- check occlusion, check aesthetics, can show the patient before you actually do the restorations.
Diet diary
MPBS
per charting
Clinical photographs

Question 7

What is a facebow used for?

Answer 7

Allows the technician to mount the maxillary cast on the same axis of the hinge of the articulator, which is the same hinge axis as the condyles in the patient.

More accurate representation of how the patient occludes, to allow further planning.

Question 8

What aspect of the treatment plan does fixed prosthodontics come under?

Answer 8

Reconstructive phase.

Immediate
Initial
Re-evaluation
Reconstructive
Maintenance

Question 9

Before embarking on fixed prosthodontics, what questions do you need to ask yourself?

Answer 9

Is this tooth restorable?
If it is, then what type of restoration am I going to place here?
What tooth preparation is required?

Question 10

What factors would you consider when deciding if a tooth is restorable or not?

Answer 10

Is there any evidence of fractures within the tooth?
Once all the carious tissue is removed, will there be enough coronal dentine for a ferrule?
Are the margins of the tooth sub gingival?
How much tooth tissue will be left after caries removal?
What degree of bone loss is present?
Has it been previously root treated before? Any evidence of fractured instruments? Perforations?

Question 11

What guidelines would you refer to with regards to deciding if a tooth is restorable or not?

Answer 11

Dental practicality index.

Question 12

Why place veneers?

Answer 12

Improve aesthetics
Change teeth shape and/or contour
Trauma causing fracture of the tooth
Toothwear
Correct peg-shaped laterals
Reduce or close proximal spaces or diastema
Align labial surfaces of instanding teeth

Question 13

What type of material can be used for veneers?

Answer 13

Direct- composite
Indirect- ceramic (feldspathic porcelain made in the lab).

Question 14

What are the stages of providing a porcelain veneer?

Answer 14

Take a shade prior to dam placement
Take an impression of the tooth prior to preparation- putty matrix.
Prepare the tooth for veneer
Take an impression of the preparation- send to lab with the shade
Provide a temporary veneer
Then arrange another appointment to remove the temporary and place the definitive veneer.

Question 15

Describe the process of veneer prep.

Answer 15

Labial enamel- 0.5mm reduction
Reduction is extended inter proximally to produce a chamfer label to the contact areas.
Incisal edge- 0.75mm-1.5mm to produce the incisal bevel.
Chamfer finish line is prepared cervically at or just above the gingival margin- 0.3mm.

Question 16

How would you provide a temporary veneer for your patient?

Answer 16

Take a putty index before restoring the tooth.
If the incise edge is missing, then provisionally restore the tooth with RMGI and take a putty index of that before removing the RMGI.

Alternatively, you can take an impression, pour up casts, repair the incisal edge with wax and then take an impression of this.

This is the same for using a direct composite veneer.

Question 17

Under what circumstances would you not want to use a veneer?

Answer 17

Poor OH
High caries rate
Interproximal caries and/or unsound restorations
Gingival recession
Root exposure
High smile lines
Labially positioned, severely rotated and overlapping teeth
Extensive tooth surface loos/insufficient bonding area
Heavy occlusal contacts
Severe discolouration

Question 18

Why might you want to restore teeth with inlays/onlays?

Answer 18

Toothwear cases- increase the OVD
Fractured cusps
Restorations of an endodontically treated tooth- provide cusp coverage
Replace failed direct restorations

Question 19

Why might you not want to restore a tooth with an inlay/onlay?

Answer 19

Cost
Time consuming
Active caries and periodontal diseases

Question 20

Why might you want to restore a tooth with a crown?

Answer 20

To protect weakened tooth structure
To improve or restore aesthetics
For use as a retainer for fixed bridgework
When indicated by the design of a RPD- rest seats, claps, guide planes.
To restore tooth function- restore in OVD.

Question 21

Why might you not want to restore a tooth with a crown?

Answer 21

Active caries and periodontal disease
More conservation options available
Lack of tooth tissue for preparation- is there a ferrule?
Unable to provide post and core
Unfavourable occlusion

Question 22

What are the principles or crown preparation?

Answer 22

1. Preservation of tooth structure
2. Retention and resistance
3. Structural durability
4. Marginal integrity
5. Preservation of the periodontium
6. Aesthetic considerations

Question 23

Why is it important to preserve tooth structure?

Answer 23

If you over-prepare the tooth, you are taking away sound tooth tissue necessarily. Pulp and tooth strength will be compromised.

If you under-prepare the tooth, then there will be poor aesthetics, restoration will not be a sufficient thickness, crown will be overbuilt.

Question 24

What is retention and resistance?

Answer 24

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

Resistance- Prevents dislodgement of the restoration by forces directed in an apical or oblique direction and prevents any movement of the restoration under occlusal forces.

Question 25

What aspects of the preparation increase retention and resistance?

Answer 25

Taper of the preparation- 5-7 degrees
Longer walls
Path of insertion- limit the number of paths of insertion
Grooves and slots-

Question 26

What is the path of insertion?

Answer 26

Imaginary line along which the restoration will be placed onto or removed from the preparation.

This is set before the preparation has begun and all the features of the preparation must coincide with that line.

Question 27

How do you maintain structural durability?

Answer 27

Restoration must contain a bulk of material that is adequate to withstand occlusal forces.

2-2.5mm occlusal reduction in posterior teeth for a MCC.
Functional cusp bevel- allows the restoration to be made thicker in this part, takes more of the occlusal load.
Axial reduction- respect the natural curvature of the tooth.

Question 28

To maintain marginal integrity, describe the margins present on an MCC and all porcelain crown?

Answer 28

MCC- 2-2.5mm occlusal reduction, 1.5-2mm shoulder margin buccally and 1-1.5mm chamfer margin palatally/lingually.

All ceramic- 2-2.5mm occlusal reduction, 1.5-2mm buccal shoulder margin palatal shoulder margin.

For both, non aesthetic margins should be placed supragingivally. In aesthetic margins, the preparation should be 1mm into the gingival sulcus.

Taper is 5-7 degrees.

Question 29

How would you ensure the periodontium is preserved during placement of a crown?

Answer 29

Margins should be smooth and fully exposed to a cleansing action.
Ensure margins of the crown are get supragingivally or at the gingival margin.
- in some cases, this is not possible, i.e. if the patient has a high smile line, then you may have to put the crown subgingivally but ensure you do not encroach on the biological width.

Question 30

What is the biological width?

Answer 30

Height between the depth of the sulcular epithelium and the most coronal part of the alveolar bone.