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Module 6 - Removable Prosthodontics > Retention and Stability of Complete Dentures > Flashcards

Retention and Stability of Complete Dentures Flashcards

1
Q

Define retention

A

Resistance of a denture to VERTICAL movement AWAY from the ridge (at rest).

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2
Q

Define stability

A

Resistance of a denture to DISPLACEMENT BY FUNCTIONAL FORCES.

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3
Q

4 displacive forces

A
  1. Gravity
  2. Muscle activity
  3. Sticky foods
  4. Function
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4
Q

Is the U or L and CoCr or acrylic most affected by gravity?

A
  • The upper denture.
  • CoCr affected more as it is heavier than acrylic.
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5
Q

What is the Interfacial surface tension?

A

Tension created when a thin layer of fluid is present between two parallel planes of rigid material (ex. between two glass slides with water).

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6
Q

What does the amount of interfacial surface tension created depend on?

A

The ability of fluid to wet the rigid material.

  • better with serous saliva, worse with mucinic saliva.
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7
Q

Define Interfacial viscous tension

A

The force holding two parallel planes together that is due to the viscosity of the interposed liquid (ex. saliva).

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8
Q

What does the interfacial viscous tension mean regarding saliva?

A

Although highly viscous saliva is less able to flow and wet a denture (less interfacial surface tension) a degree of viscosity to saliva is required to create interfacial viscous tension

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9
Q

What causes interfacial viscous tension to fall? How can this be prevented?

A
  • Viscous force falls rapidly as the thickness of the liquid increases.
  • Optimum adaptation between denture and mucosa with thin salivary film.
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10
Q

Define adhesion

A

The physical attraction of unlike molecules for each other

(ex. saliva to mucous membrane, saliva to denture base).

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11
Q

How can denture adhesion be maximized?

A

By extending over potential load bearing area as possible

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12
Q

Does adhesion play a bigger role in U or L dentures? Why?

A

Upper because we can cover more area.

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13
Q

Define cohesion?

A

The physical attraction between similar molecules (ex. salivary film).

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14
Q

What is the importance of atmospheric pressure/ border seal in dentures (explain the analogy).

A
  • Suction cup and glass analogy – after pressing denture (glass) into mucosa (suction cup) the mucosa wants to return to its original shape. Hence a NEGATIVE PRESSURE is generated underneath the denture.
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15
Q

In which denture is border seal mostly achieved? Why?

A
  • The MAXILLARY denture.
  • Because the pressure increases the greater the area that is covered.
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16
Q

Which two forces increase when more area is covered?

A
  • Adhesion
  • Border seal
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17
Q

Another term for fitting surface

A

Basal surface

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18
Q

Another term for polished surfaces

A

Flanges

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19
Q

3 things to consider to achieve optimum retention and stability in complete dentures

A
  1. Fitting surface.
  2. Polished surface
  3. Occlusal surface
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20
Q

What must be considered in terms of the fitting surface?

A
  • Base shape - must we WELL ADAPTED TO THE MUCOSA
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21
Q

Does greater alveolor bone height happen more in the maxilla or mandible?

A

The mandible.

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22
Q

What is the importance of the basal bone? Is it greater in the U or L.

A
  • Helps with SUPPORTING the denture.
  • Always more in the MAXILLA.
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23
Q

Where does the support for maxillary dentures come from?

A
  • Primary: Basal bone.
  • Secondary supporting structures: Soft tissue, rugae, the tuberosities.
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24
Q

2 requirements for the fitting surface.

A
  1. Should sit as close to the mucosa as possible.
  2. Should create a negative pressure under it (maintain the tension formed between saliva, mucosa and denture).
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25
Q

What is the post dam? What does it do? What thickness must it be?

A
  • Ridge of acrylic
  • 0.5mm deep
  • Post dam gives the seal required at the posterior border - extra pressure at the posterior edge.
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26
Q

Two reasons why we want the border seal/ post dam to sit before the soft palate?

A
  1. The mucosa covering the hard palate does not compress as much as the soft palate
  2. Soft palate has muscles which move.
27
Q

Where do we want the posterior border of the denture to sit?

A

Behind the posterior border of the hard palate but anterior to the vibrating line.

28
Q

Where are palatine fovea located? Where do the palatine fovea sit relative to the vibrating line?

A
  • Soft palate.
  • Just anterior to the vibrating line.
29
Q

Where do we want the post dam depression to sit relative the palatine fovea?

A

Just anterior to the palatine fovea.

30
Q

What is an area that can be utilized to increase the bracing + greater area to extend the denture over in a lower edentulous patient?

A

Retromylohyoid fossa/ lingual pouch?

31
Q

Where is the retromylohyoid fossa/ lingual pouch located?

A

Above and anterior to where the muscles move (lingual aspect of the lower jaw).

32
Q

How can you clinically investigate the retromylohyoid fossa/ lingual pouch?

A
  • Place a mirror along the lateral border of the tongue and ask the patient to move their tongue.
  • Can then see how DEEP the lingual pouch is.
33
Q

What should the shape of the distolingual border of the lower denture be?

A

Extended flare.

34
Q

What does a well adapted fitting surface depend on?

A

Master impressions with good surface detail.

35
Q

What does border moulding do?/ what does it show? What advantage does this result in/what does it prevent?

A
  • Replicates the functional movements the patient will make - shows the space the surrounding muscles need to move in.
  • Prevents an over-extended flange which would dislodge the denture during function.
36
Q

What do undercuts increase? What does this mean about the path of insertion?

A
  • Undercuts increase retention.
  • The path of insertion will have to be tilted slightly (not straight).
37
Q

3 types of undercuts in the lower edentulous patient?

A
  • Labial undercut.
  • Bilateral soft tissue undercuts.
  • Bilateral boney undercuts.
38
Q

2 downsides of a resorbed ridge:

A
  • Less surface area to cover to gain retention.
  • Less scope to engage useful undercuts.
39
Q

Factors that can make retention and stability difficult?

A
  1. Atrophic ridge.
  2. Damaged alveolar ridge (trauma or surgery ex. skin graft, flabby ridge).
  3. Tori
  4. Gagging
  5. Insufficient/ quality (mucinic vs serous) saliva.
40
Q

What is the disadvantage of a flabby ridge?

A

When denture is loaded, the underlying tissues will compress/ move and make the denture feel unstable and possibly break the retentive forces keeping the denture in place.

41
Q

What are tori?

A
  • Benign bony growths that occur in the midline of the palate or the lingual aspect of the premolar region in the lower.
42
Q

Where do tori cause more of a problem and why?

A
  • More problematic in the lower.
  • Cannot bend acrylic to engage them, hence the base would have to be shortened in the area to sit on top of the tori –> may reduce the potential stability of the denture as the lingual extension will be reduced.
43
Q

What is a flabby ridge and where is it most common?

A
  • Soft, mobile, fibrous band of tissue overlying where the alveolar ridge once sat.
  • Most common in the anterior part of the maxilla.
44
Q

What is the effect of gagging on retention?

A

Would have to reduce the palatal coverage, hence compromising border seal and reduce the other retentive forces.

45
Q

What can be used if the patient gags from a full upper acrylic denture?

A
  • Use a double post dam.
  • One in the ideal area, one 1mm inside of that.
  • Provides space to shorten the palatal extension (improve tolerance of denture) yet still provide some compression and border seal (although not at the ideal location).
46
Q

What can be used to treat a patient with insufficient saliva?

A
  • Saliva orthana (SPRAY).
  • Dry mouth saliva replacement GEL (ex. oral balance).
47
Q

3 considerations regarding occlusal surfaces when designing complete dentures

A
  1. Arch form.
  2. Occlusal plane level.
  3. Tooth position.
48
Q

Ideal tooth position for the artificial teeth in U and L complete dentures?

A
  • Lower: over the center of the ridge:
  • Upper: Just to the buccal aspect of the ridge.
49
Q

Where must all teeth (in complete dentures) be positioned?

A

In the NEUTRAL ZONE

50
Q

What is the neutral zone?

A

An area where the outward forces from the tongue are balanced with the inward forces from the cheeks (buccinator and orbicularis oris)

51
Q

3 advantages of placing the teeth in the neutral zone?

A

Increased:
- Stability.
- Retention.
- Comfort

52
Q

What is lateral tongue spread and when does it occur?

A
  • Tongue spreads laterally/ relaxes into this space.
  • Occurs when a patient has not had natural teeth or worn a prosthesis for some time.
53
Q

2 disadvantages of lateral tongue spread?

A
  1. Difficulty in finding sufficient space to position teeth.
  2. Difficult for patient to wear any prosthesis made.
54
Q

What is the effect of a lingual overhang?

A
  • Makes denture unstable as it encroaches into the tongue space.
55
Q

How to check the retention of an upper denture?

A
  • Gentle downwards pressure on the incisor teeth of an upper denture.
56
Q

What does the term polished surfaces refer to?

A
  • The contouring of the buccal, lingual and palatal surfaces.
57
Q

What must the polished surfaces do?

A

Must work in harmony with the muscle function.

58
Q

What is seabond?

A

Film inserted along the entire fit surface of the denture - helps with denture retention and stability.

59
Q

Name two examples of denture adhesives. What is a caution with them and how should they be applied? Where do they work best?

A
  • Fixodent, poligrip
  • Can be toxic if used in high quantity.
  • Ideally use 3 small dots in a triangular pattern on the fit surface of the denture.
  • Works much better in the upper compared to the lower.
60
Q

Two other methods (private) of achieving a good base fit?

A
  1. Valves
  2. Implants
61
Q

What is the advantage of implant retained dentures?

A
  • Help improve retention, especially in mandible.
62
Q

How many implants are required?

A
  • Minimum 2 implants are required to prevent denture rotation.
63
Q

2 requirements for implants?

A
  • Adequate bone levels.
  • Excellent OH.

Module 6 - Removable Prosthodontics (7 decks)

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