Principles of Complete Denture Flashcards
Where do complete denture lie within|?
active muscles
At rest what should a complete denture be?
stable and in function
retentive forces > displacing forces + adequate support = stability
When is the denture stable at rest?
if the retentive forces acting on the denture exceed the displacing forces
What does a stable denture move little in comparison to?
supporting tissues whilst in function
What determines the support for complete dentures?
form and consistency of the denture baring tissues and the accuracy and fit of the denture
retention?
resistance to vertical displacement of the denture away form the mucosa
3 surfaces of a denture proving retention?
occlusal surfaces
polished surfaces
impression surfaces
occlusal surfaces for retention?
makes contact with the opposing denture
polished surfaces for retention?
area that extends from the occlusal surface to the border of the denture
including palate
impression surface for retention
portion of the surface of the denture which is shaped by the impression
describe each colour:
pink
green
red
blue
blue: saliva which will surround the denture
Can the setting of the teeth in complete denture have an effect stability?
yes, need good design
could interfere
2 main forces for retention?
muscular
physical
what exerts muscular forces on denture? - retention
lips, cheek, tongue
on the polished surfaces of the denture
an muscles of mastication indirectly through occlusal surfaces
muscles of mastication?
temporalis, masseter, medial pterygoid and lateral pterygoid muscles
What does successful muscular control of the denture depend upon?
ability of pt to acquire necessary skills
denture design
what usually resists the breaking of the posterior seal?
dorsum of tongue against denture
What do physical forces rely on? - retention
intact film of saliva between saliva and mucosa
Where are physical forces usually/
on the polished surface of the denture and underlying mucosa
retention is dependent upon this seal and the border region of the denture
What happens if the physical forces for retention are poor?
resulting looseness of the denture may lead to rejection by the pt
The types of physical forces?
adhesion
cohesion
surface tension
capillary action
atmospheric pressure and peripheral seal
physical forces: adhesion?
force of attraction between dissimilar molecules
e.g. saliva/acrylic/mucosa
What is retention from adhesion directly proportional to?
surface area of denture base
physical forces: cohesion?
force of attraction between like molecules
maintains the integrity of the film of saliva
physical forces: surface tension?
it is the result of the cohesive forces acting on the surface fluid
resistance of separation of 2 parallel surface with a fluid medium in between
enhance further the retentive forces
closer the fit of the denture is to the tissue, the stronger the retentive forces are attributed to surface tension
What is retention by surface tension dependent upon?
ability of the fluid to wet the rigid surrounding materials
by promoting both contact of saliva and mucosa to the denture base
interfacial surface tensions more apparent in the maxillary or mandibular denture area?
maxillary
mandibular has sufficient saliva - keep external borders of the mandibular denture a wash in saliva
therefore eliminating the effects of interfacial surface tension
With regards to saliva what does cohesive forces form? - surface tension
concave meniscus at the surface of saliva and border region of denture
What happens when a fluid film is bounded by a concave meniscus?
pressure in fluid is less than that of the surrounding medium
- pressure differential will occur between saliva and surrounding air
Why does surface tension occur, the closer the fit of the denture is to the tissue?
As the denture is pulled away from the tissues
saliva is thrown in to the space being created beneath the denture
retentive force is being generated by a resistance to the flow in saliva - resulting form viscous properties of the saliva and the dimensions of the channel which it flows
narrower channel and greater the viscosity of saliva does what with regards to surface tension?
increase
B = proper thickness of denture - narrow flanges
Capillary action? - retention
the quality or state because of surface tension cause elevation or depression of the surface of a liquid that is in contact with a solid
close adaptation of the denture base to the mucosa cause the saliva in between to improve the contact between them
retentive mechanisms an viscosity of saliva?
increased viscosity of the saliva is associated with decreased retention because the excessive viscosity results in a thick and discontinuous film between the denture and mucosa
effect of capillary action on maxillary vs mandibular denture?
mandibular less effect
- saliva accumulates along the periphery and reduces capillary effect
maxillary more effect
- capillary tube not fully submerged in saliva
Are muscular forces important in mandibular denture?
yes, due to reduced denture bearing area
difficulty in maintain a border seal will reduce influence of physical forces
How to maintain good retention?
good border seal
areas of impression surface
accuracy fit
bony undercuts, or any retention aids to offer pt e.g. implants or fixatives?
How to achieve good border seal?
denture border should be shaped so that the channel between the denture and the sulcus tissues is as small as possible
How to overcome the problems of achieving a constant border seal? maxillary
extending flanges of denture laterally so that they contact
slightly displace the buccal and labial mucosa to achieve facio-facial seal
How to overcome the problems of achieving a constant border seal? mandibular
posterior lingual flange extended further than the anterior flange
mylohyoid ridge and mandibular denture design?
adapt lingual flange to accommodate muscle movements
physical retention proportionate to what?
area of impression surface
How to obtain maximum physical retention?
maximum extensions of denture
so that optimum retention for a particular pt is obtained
border moulder required
what areas n the mandibular denture should be captured in the impression to achieve good retention?
pear-shaped pads
- keratinised scar tissue form last standing molar
and part of the retromolar pad
= utilised to combat the action of the mentalis muscle pushing te denture posteriorly
= denture extended in to the retro-mylohyoid area prevent lateral movement
How could you overcome displacement due to bone resorption?
muscular control
physical limitations of F/F?
Displacement forces acting through occlusal surface
- occlusal imbalance
- forces of mastication
- displacement of teeth in relation to adjacent oral structures
- gravity
- reduction in support promotes instability
- alveolar bone resorption - flabby ridges also contribute to displacement - special imps needed
what movement can bone resorption cause?
tipping of denture during mastication
- denture pivoting about midline of palate
resistance to lateral displacement forces will be very poor
flabby ridges also contribute to displacement
