Fixed Partial Dentures and Pontic Design Flashcards
Which component of the Fixed Partial Denture will fit onto the abutments?
the retainers
Which component of the Fixed Partial Denture will fit over the edentulous area?
the pontic
How does the pontic attach to the retainers?
through the “connectors”
What are two major contraindications to an FPD?
- Excessive edentulous span
2. Weak abutment teeth
Ante’s Law states that the peri-cemental area of the abutment teeth must be _______ the peri-cemental area of the pontic.
greater than or equal to
What is the effect of length (edentulous area) on deflection of the FPD?
Deflection = length cubed
2x length = 8x deflection
3x length = 27x deflection
What is the effect of “connector thickness/height” on deflection of the FPD?
Increased connector thickness/height results in decreased deflection. D= (1/H)^3
example: 1/2 thickness = 8x deflection
What is the danger of having three pontics between two abutments?
with heavy occlusal loads the metal will flex and the porcelain will chip
What are three considerations for abutment selection?
- Clinical crown-to-root ratio
- Root form
- Tooth angulation
What is the MINIMUM amount of bone (crown-to-root ratio) that is acceptable as an abutment?
1:1
What is the IDEAL crown-to-root ratio (amount of bone) that is acceptable as an abutment?
2:3
True or False: If the clinical crown-to-root ratio is greater than one, the FPD will fail.
True, minimum required bone is a ratio of 1:1
When selecting abutments, what is the importance of “root surface area?”
Root surface area = periodontal support
*Certain teeth have a better cross-sectional configuration for support of the partial
Which teeth have a root surface area (cross-sectional configuration) that is NOT well suited for use as abutments?
Lateral incisors (uniform and ovoid shape)
The root design for abutment teeth will influence stability of the partial. Which is stronger: curved or straight roots?
Curved
The root design for abutment teeth will influence stability of the partial. Which is stronger: convergent or divergent roots?
Divergent
Why are “curved” and “divergent” roots preferred over “straight” and “convergent” roots for abutment teeth?
Curved/Divergent provides greater root surface area
Root Surface Area = Periodontal Support
What happens if the connector size is sacrificed for esthetics?
The connector will break
What are the boundaries within which esthetics may be considered more than strength?
Anterior…or where ever the client thinks it is important
Why must you check the tooth preparations from all different angles?
Because there may be an undercut within one prep, between the two preps, or both
What are three options for preparing abutment teeth that have different long axes?
- Reposition teeth prior to FPD: orthodontics
- Use intracoronal attachments
- Conservative removal of offending proximal contacts
What are precision attachments? Common type?
-Fixed attachments that provide retention and/or support in the case that abutments are not parallel; therefore, there is a contraindication for FPD
Key-Way attachments: “female and male parts” that connect together
If removal of proximal contact is necessary when preparing abutment teeth (due to different long axes), what must be considered for the proximal teeth?
PULP HORNS: careful, patient’s age?
What are the three general considerations when evaluating the edentulous area for a pontic?
- Mesio-distal width
- Occlusocervical distance
- Bucco-lingual diameter of remaining alveolar ridge
_____ _____ _____ has most likely occurred in the edentulous area if a tooth were extracted several years prior.
Buccal Plate Resorption
Why would buccal plate resorption cause an issue for the FPD?
The ridge thickness B-L would most likely be uneven and would cause the pontic to lean toward the recessed area.
If vast amounts of resorption occurred, an edentulous ridge can be prepared for the FPD by use of a ______.
Graft
If cervical lines are uneven (ex. one tooth appears pushed in), how can the arch be restored to a more even contour?
Orthodontics (erupt that tooth)
Why would you use orthodontics prior to extracting a tooth?
Ortho can be utilized in order to erupt teeth and pull BONE down prior to extractions. This will prevent serious resorption of the edentulous area.
What are the six common pontic forms?
- Ridge Lap (saddle)
- Modified Ridge Lap
- Hygienic (sanitary)
- Modified hygienic
- Bullet
- Ovate
What is a “ridge lap” pontic used for? Why is it not recommended?
- Eshthetics*
- emulates the contours and emergence profile of the missing tooth
- Difficult to clean*
- mucosal surface follows the contours of the gingiva
- formation of ulcers
What is a hygienic pontic used for? What is its disadvantage? Advantage?
Use: Mandibular posterior teeth
Disadvantage: No indication for maxillary teeth (shelf)
Advantage: Easy plaque control
The distance between the pontic mucosal surface and gingiva should be _____ mm.
1-2 (definitely not less than 1 mm, 1.5 mm is ideal)
What would happen if the hygienic pontic was not 1-2 mm from the gingiva?
It would be too difficult to clean under, the mucosa would become severely inflamed.
What is the difference between a “modified hygienic” and “hygienic” pontic?
Modified = wider connectors = stronger, less esthetic
What is a “modified ridge lap” pontic design?
MOST COMMON design
- Hygienic from the lingual
- Saddle from the buccal
What are the benefits of the modified ridge lap design?
Esthetic
Cleansible
True or False: The modified ridge-lap design should have a tight T-shaped tissue contact on the lingual.
FALSE. the T-shaped contact should be on the buccal (the side with the saddle, not the hygienic) and contact should be very minimal.
Where is a “bullet” pontic design used?
Mandibular molars with knife-edge alveolar ridges
-if the ridge is wide…use a hygienic or food will get impacted
Of the two mandibular molar pontic designs, which one is in contact with the mucosa?
“Bullet” Pontics (knife edge ridges)
An ______ pontic will most likely be used if it is placed at the time of extraction. It provides good emergence profile but is hard to clean underneath.
Ovate
When using an ovate pontic, what must be done extremely well?
the pontic MUST be highly POLISHED…risk for tissue damage or ulceration due to extension into the open socket
The ovate pontic eliminates the potential for _______ ______ in the cervical portion of an anterior pontic.
Unsupported Porcelain
Which two pontic designs have no contact or slight mucosal contact?
Hygienic (none) Modified Hygienic (slight)
If using a cantilever pontic (one connector), where should the pontic be in regards to the abutment?
MESIAL
distal cantilever causes unfavorable load on abutment
What is the best indication for a cantilever pontic? Why?
Missing lateral incisors
-the canine can be used as an abutment, leaving the central incisor un-prepared
(Biological Consideration)
______-_______ contact between the pontic and underlying tissues is indicated to prevent ulceration and inflammation of soft tissue.
Pressure-free
In the _____ region, a pontic should contact the gingival tissue.
anterior (appearance of emergence from soft tissue)
(Biological Consideration)
To enhance hygiene, what must the patient be instructed to do?
Perform efficient plaque control and prevention
What is a “pier abutment”?
Two edentulous ridges are separated by a tooth that can be prepped and made into an abutment (pier). Therefore, there are three abutment teeth and two ridges.
1110____0____0111
What is the alternative to having a pier abutment? Why would this be chosen instead?
- Non-rigid connector (connects two separate pieces)
-if common POW is too difficult to create - Cantilever one of the pontics
-prevents preparation of three teeth
11111___0___0111
The pontic design should be of ______ form for #20 and of _________ form for #4.
Hygienic #20 (mandibular)
Modified Ridge Lap #4 (maxillary)
