L10: Fixed Partial Dentures Elements and construction principles

Question 1

What is a Fixed Partial Denture (FPD)?

Answer 1

Any dental prosthesis that is luted, screwed, or mechanically attached or otherwise securely retained to natural teeth, tooth roots, and/or dental implants/abutments that furnish the primary support for the dental prosthesis and restoring teeth in a partially edentulous arch. (GPT9)

• It cannot be removed by the patient.

Question 2

What are FPDs indicated for?

Answer 2

• Short spam edentulous arches (posterior: 2 or shorter, anterior 4 or shorter).
• Abutment teeth healthy (enough structure for support, good periodontal tissues).
• Whenever implants are not preferred (in atrophic or resorb edentulous ridges, health, age, cost/time of treatment).
• When removable prosthesis is not indicated.
• Patient’s preference.

Question 3

Which are the contra-indications of FPDs?

Answer 3

• Young patients, teeth with large pulp chambers.
• Not recommended to prepare sound teeth as abutments.
• Presence of periodontally compromised abutments.
• Long span edentulous spaces.
• Medically compromised patients/very old patients (who need short appointments).

Question 4

Which are the parts of a FPD?

Answer 4

• Abutment teeth.
• Abutment preparation.
• Retainer.
• Pontic.
• Connector.

Question 5

Abutment teeth:

Answer 5

• Should be able to withstand the forces normally directed to the missing teeth in addition to those usually applied to them.
• They should lack of pulp or apical tissue infection. If not, then be properly treated.
• Previously endodontically treated teeth, should be radiographically revaluated.
• When tooth structure is inadequate, plan for foundation restorations or posts were needed.
• The supporting tissues surrounding the abutment teeth must be healthy and free from inflammation before any prothesis can be planned.
• Normally, abutment teeth should not exhibit mobility, since they will be carrying extra load.

Question 6

Which are the evaluating factors for abutment teeth?

Answer 6

• Crown-root ratio.
• Root configuration.
• Periodontal ligament area.

Question 7

Crown-root ratio:

What is crown-root ratio?

Answer 7

The ratio of the length of the tooth occlusal to the alveolar crest of the bone compared with the length of the root embedded in the bone.

Question 8

Crown-root ratio:

Which is the:

1. ideal crown-root ratio?
2. minimum crown-root ratio?
3. acceptable crown-root ratio?

Answer 8

• Ideal** crown-root ration is **1:2
• Minimum** crown-root ratio is **1:1
• Acceptable** crown-root ratio is **1:1.5

Question 9

Root configuration:

Which is the most preferable root configuration?

Answer 9

• Roots that are broader labiolingual than they are mesial-distally are preferable to roots that are around in cross section.
• Multirooted posterior teeth with widely separated roots will offer better periodontal support than roots that converge, fuse or present a conical configuration.

Question 10

Periodontal ligament area:
Which is the advantage of larger teeth?

Answer 10

Larger teeth have a greater surface area and are better able to bear added stress.

Question 11

Periodontal ligament area:

What is the length of the pontic span that can be successfully restored limited by?

Answer 11

The length of the pontic span that can be successfully restored is limited by the abutment teeth and their ability to accept the additional load.

Question 12

Ante’slaw:

Answer 12

The root surface area of the abutment teeth had to equal or surpass that of the teeth being replaced with pontics.

Question 13

Ante’slaw:

Which are the Biomechanical considerations?

Answer 13

• x = bending (flexibility)
• p = length of the pontic
• t = occlusogingival thickness of the pontic

For a certain “t”, a two-tooth (2p) pontic span will bend 8x more than a single tooth (p).

A three-tooth (3p) pontic span will bend 27x more.

Question 14

Abutment preparation:

Answer 14

Question 15

Path of insertion:

What is the path of insertion?

Answer 15

An imaginary line along which the restoration will be placed onto or removed from the preparations.

• It is of special importance for abutment teeth of fixed partial dentures.

Question 16

What should the path of insertion be?

Answer 16

• Path of insertion should be aligned with the central axis of the preparations (black line).
• Not necessarily to be parallel with the central axis of tooth (red line).

Question 17

What should the angulation of the central axis between abutment teeth not be more than?

Answer 17

Angulation of central axis between abutment teeth should not be more than 25°-30°.

Question 18

Tilted molar abutment:

How is tilted molar abutment managed?

Answer 18

• Orthodontically upright the molar.
• Implant placement.
• Proxima half-crown preparation on molar (if tooth in not intact).
• Unless there is no other option, endodontically treat the tooth for better parallelism of the central axis of the preparations.

Question 19

Tilted molar abutment:

How should the path of insertion design be done?

Answer 19

• Take radiographs and preliminary impressions prior procedure.
• Decide path of insertion on the study cast models.

Question 20

Pontic:

What is a pontic?

Answer 20

Is an artificial tooth on a fixed partial denture that replaces a missing natural tooth, restores its function, and usually restores the space previously occupied by the clinical crown (GPT9).

Question 21

Pontic:

Which are the properties that a pontic should have?

Answer 21

They should be able to:

• Restore function.
• Provide esthetics and comfort.
• Be biologically acceptable.
• Permit effective oral hygiene.
• Preserve underlying residual mucosa.

Question 22

What happens to alveolar bone after tooth extraction?

Answer 22

After tooth extraction, alveolar bone resorbs.

Question 23

Pontic:

What should a pontic ensure?

Answer 23

A pontic cannot duplicate exactly the contours of the lost tooth but should ensure good esthetics, hygiene and lack of tissue injury.

Question 24

Pontic:

What is preferred regarding the contacts of the pontic to the underlying tissue?

Answer 24

• Small contact of the pontic to the underlining tissue is preferred.
• Provide enough embrasure space for proper hygiene (floss, interproximal brushes, water flosser systems).

Question 25

Pontic designs:

Answer 25

Question 26

Hygienic – Sanitary:

Answer 26

• No contact with edentulous ridge. Convex shape.
• Allows easier hygiene
• Connectors need to be thick.
• Not esthetic.

Question 27

Saddle (Ridge lap):

Answer 27

• One of the most natural looking designs.
• Wide contact with the underling tissue.
• Difficult for good hygiene.
• Not recommended.

Question 28

Conical:

Answer 28

• Round design with a small tip at the end.
• Easy to clean.
• Recommended for thin ridges at the posterior mandibular arch.
• Not very esthetic.

Question 29

Modified ridge lap:

Answer 29

• Design that gives illusion of the tooth on the facial side.
• Deflective contour on the lingual side.
• Easy to clean.
• Most commonly used design.

Question 30

Ovate:

Answer 30

• Round-end designed.
• Moderate easy to clean.
• Used in highly esthetic areas.
• Requires surgical preparation procedure.

Question 31

Connector:

What is a connector?

Answer 31

The portion of a fixed partial denture that unites the retainer(s) and pontic(s)

Question 32

Connector:

Which are the requirements for a connector?

Answer 32

• They should be large enough to withstand forces during function.
• Adequate access must be available for oral hygiene aids, cervical to the connector.

Question 33

Connector design:

Answer 33

• Most connectors are elliptical (in a cross section).
• For ease of plaque control, the connectors should occupy the normal anatomic interproximal contact areas.
• Anterior connectors are normally placed toward the lingual embrasure.

Question 34

Which is the optimal connector size for metal, zirconia and all ceramic preparations?

Answer 34