denture processing Flashcards
Which casts require relining?
- new dentures (lose adaptation
- old dentures (bone resorption)
What is rebasing?
replacement of entire denture base with a new material
relining and rebasing should be done without changing which relationship?
occlusal
When is relining indicated?
when denture loses its adaptation to tissues due to bone resorption while other points (occlusion, aesthetics, occlusal vertical dimension and denture base material) are all satisfactory
What is the procedure of relining of complete denture?
- remove the denture out of the patient’s mouth for 48 hours to give time for the mucosa to rest
- reduce the denture borders 2mm (to allow the flow of impression material to reach
the depth of vestibule) - remove undercuts from the fitting surface of the denture.
- take impression while the patient is closing in centric occlusion under closed mouth technique (to preserve occlusion)
- make boxing and pour the cast
- make flasking
- throw away the impression material to make space for new acrylic resin
- pack heat cured acrylic resin in the place of impression material
- curing (45° for 20 minutes) (long curing cycle)
- deflasking then laboratory remounting
- finishing and polishing
If both upper and lower dentures need to be relined, which one is relined first and why?
lower denture as upper denture is supported by the palate but lower denture is not supported
What to do if vertical dimensions are not correct?
remake
What are the steps of rebasing?
- remove the denture out of the patient’s mouth for 48 hours to give time for the mucosa to rest
- reduce the denture borders 2mm and drilling 3 holes through the palate to allow the flow of impression material to reach the
depth of vestibule - remove undercuts from the fitting surface of the denture
- take impression while the patient is closing in centric occlusion under closed mouth technique to preserve occlusion (to preserve VDO)
- make boxing and pour the cast
- mount the cast and the denture on Hooper articulator or simple hinge articulator (to preserve occlusion and VDO)
- grind the denture base and throw it
- make new denture base from wax
- flasking → wax elimination → packing of acrylic resin → curing → deflasking →
laboratory remounting → finishing and polishing
When is rebasing done?
when denture contains cracks but occlusion must be right
What does polishing of denture consist of?
making denture smooth and glossy without changing its contour
When is finishing and polishing done?
after laboratory remounting (processing)
What is the procedure of wax elimination?
placing flask in hot water
What happens before wax elimination?
flasking
What happens after wax elimination?
acrylic resin packing
What happens after flasking is done?
wax is flushed out with hot water
How is the cast remounted?
cast has indices or v-notches
When is laboratory remounting done?
after processing and before finishing and polishing
Who does the laboratory remounting?
lab technician
Why do we remount the cast?
refining of occlusion
What needs to be done if cusps are high in centric relation only?
deepen opposing fossa
What needs to be done if cusps are high in centric and eccentric relations?
grinding working and non-working cusps
What are the working sides of teeth of casts?
- BULL
- buccal upper
- lingual lower
What is grinded in both sides?
non-functional cusps
What should acrylic resin be glued to?
teeth
What is the procedure of acrylic resin packing?
- put cellophane on cast before adding acrylic resin
a- dd acrylic resin then close the flask and bench press - remove cellophane and excess
- add cellophane again and close the flask, then open to remove excess, put cellophane then close the flask and bench press
- repeat until no excess is left
- cure in oven
- cooling
- deflasking
In which stage is acrylic resin packing done?
dough stage
Why is long cycle better than short cycle?
short cycle causes crazing
Which cycle is better for curing: long or short?
long
What are the ways of packing acrylic resin?
- injection method
- open flask method (easier)
What are the types of flasks?
- flask for upper cast
- flask for lower cast
What are the components of a flask?
- base (in the form of a cup)
- middle part
- top part (lid)
What are the steps of flasking?
- place cast in lower part of flask and fill it up with stone until level of cast and then ass separating medium
- place second part of flask and add stone but don’t cover occlusal surface of teeth with stone then add separating medium again
- add last layer of stone then close flask and it should touch occlusal surface of teeth
- put flask in hot water and wax should melt
- throw away trial denture base and add acrylic resin
Why is the lower flask higher than upper?
presence of retromolar pad
Do we add separating medium on occlusal surface of teeth?
no
What is cap layer?
- last layer that covers occlusal surface
- this makes sure teeth don’t dislodge
What happens before deflasking?
acrylic resin packing
What happens after deflasking?
laboratory remounting
What happens during deflasking?
flask cools to room temperature
What is the objective of deflasking?
remove denture from investment material without breaking the denture or dislodging denture from cast for laboratory remounting
What should the contour of the labial and buccal flange be and why?
- concave
- help stabilisation of denture
- adaptation of oral muscles
- muscles are stronger than the denture
What should the contour of the lingual flange be and why?
- convex then concave
- convexity directly beneath the teeth
- tongue may lie in this undercut and dislodge the lower denture
- concavity away from teeth in the middle of the flange (not at any undercuts)
Why should the palate be kept thin?
- pronunciation of “s” sound
- it is the space between tongue and rugae area
- tongue never touches the rugae area
What is lisping?
- “th” sound replaces “s” sound
- the the tongue is crowded against palate particularly on posterior region
What are the causes of lisping?
- increase in thickness of acrylic at rugae area
- backward arrangement of upper anterior teeth which leads to no space to pronounce “s”
What is whistling?
”s” sound is pronounced too sharply
What causes whistling?
- forward arrangement of upper anterior teeth
- decrease thickness of acrylic in rugae area (insufficient waxing up)
- low V.D.O. (short teeth and excessive freeway space)
Why do we stipple gingiva?
to show rough appearance
What should be contoured properly when contouring the root?
canine eminence
