lec 9 - Impression Procedures and Materials for Removable Partial Dentures Flashcards
- Negative likeness or an imprint made placing some soft, semifluid material in the mouth and allowing that material to set.
IMPRESSION
usually used for cast restoration and are elastic when removed from the mouth.
Impression material
IDEAL IMPRESSION MATERIAL (7)
- Complete plasticity before cure (set)
- Sufficient fluidity to record define detail
- The ability to wet the oral tissues
- Dimensional accuracy
- Dimensional stability
- Complete elasticity after cure
- Optional utilities
IMPRESSION MATERIAL CLASSIFICATION
(1) Rigid Impression Materials
(2) Thermoplastic Impression Materials
(3) Elastic Impression Materials
- Set to rigid consistency
- Cannot be removed from the mouth without fracture and reassembly.
RIGID IMPRESSION MATERIALS
RIGID IMPRESSION MATERIALS (2)
Plaster of Paris
Metallic Oxide Paste
- One type of impression material is which has been used in dentistry for over 200 years.
plaster of Paris
was once the only material available for removable partial denture impressions, but now elastic materials have completely replaced the impression plasters in this phase of prosthetic dentistry.
plaster of Paris
usually some form of a zinc oxide–eugenol combination.
METALLIC OXIDE PASTE
they are not used as primary impression materials and should never be used for impressions that include remaining natural teeth.
METALLIC OXIDE PASTE
THERMOPLASTIC MATERIALS (2)
Modelling plastic
Impression waxes and natural resins
- Modelling Compound
Modelling plastic
- Oldest impression material used in prosthetic dentistry
MODELLING PLASTIC
- Most often used for border correction (border molding) of custom impression trays for distal free end classifications. It is manufactured in several different colors, each color being an indication of the temperature range at which the material is plastic and workable.
MODELLING PLASTIC
most commonly used modeling plastic for corrected impressions for extension base areas. (softens around 132°F/55.55°C)
- Red-brown
obtainable in stick form used in border molding
Red, Gray, and Green
- Used to record non-undercut edentulous portions of the oral cavity and are generally used in combination with other impression materials like polysulfide, ZOE impression paste or impression compound.
IMPRESSION WAXES AND NATURAL RESINS
- May be used to correct the borders of impressions made of more rigid materials thereby establishing optimum contact at the border of the denture.
IMPRESSION WAXES AND NATURAL RESINS
- All mouth temperature ____________ have the ability to record border detail accurately and include the correct width of the denture border.
wax impressions
IMPRESSION WAXES AND NATURAL RESINS IS USED FOR (2)
Corrective impression
Bite Registration
developed for used in recording the functional or supporting form of an edentulous ridge. May be used as a secondary impression materials
- Iowa Wax
- Are those that remain in an elastic or flexible state after they have set and have been removed from the mouth
ELASTIC IMPRESSION MATERIALS
- Only ones that can be withdrawn from tooth and tissue undercuts without permanent deformation and therefore are used generally for making impressions for removable partial dentures, immediate dentures, crowns, and fixed partial dentures when tooth and tissue undercuts and surface detail must be recorded with accuracy
ELASTIC IMPRESSION MATERIALS
Elastic Materials (5)
Reversible Hydrocolloids
Irreversible Hydrocolloids
Mercaptan Rubber-base Impression Materials
Polyether Impression Materials
Silicone Impression Materials
- Agar-agar
REVERSIBLE HYDROCOLLOIDS
- Which are fluid at higher temperatures and gel on reduction in temperature
REVERSIBLE HYDROCOLLOIDS
- Are used primarily as impression materials for fixed restorations
REVERSIBLE HYDROCOLLOIDS
- Demonstrate acceptable accuracy when properly used
REVERSIBLE HYDROCOLLOIDS
can also be used for removable partial denture impressions and especially for secondary corrected or altered cast impressions
- Mercaptan rubber base/polysulfide polymer (thiokol) impression materials
- Many of these materials have an unpleasant odor and can stain clothes.
RUBBER BASE IMPRESSION MATERIAL
- Have high tear strength
RUBBER BASE IMPRESSION MATERIAL
- Can be disinfected in liquid, cold-sterilizing solutions
RUBBER BASE IMPRESSION MATERIAL
- Long working and setting times (8 to 10 minutes)
RUBBER BASE IMPRESSION MATERIAL
- These materials are moderately inexpensive
RUBBER BASE IMPRESSION MATERIAL
- Is an elastic-type material, as are the polysulfide and silicone materials.
POLYETHER IMPRESSION MATERIAL
- These materials have demonstrated good accuracy in clinical evaluations and are thixotropic, which provides good surface detail and makes them useful as a border molding material.
POLYETHER IMPRESSION MATERIAL
hydrophilic, which produces good wettability for easy cast forming.
POLYETHER IMPRESSION MATERIAL
low to moderate tear strength and much shorter working and setting times, which can limit the usefulness of the material
POLYETHER IMPRESSION MATERIAL
more accurate and easier to use than the other elastic impression materials.
SILICONE IMPRESSION MATERIALS
- They have a pleasant odor, moderately high tear strength, and excellent recovery from deformation.
SILICONE IMPRESSION MATERIALS
hydrophobic, which can make cast formation a problem.
SILICONE IMPRESSION MATERIALS
can be disinfected in any of the disinfecting solutions with no alteration in accuracy. Ideally, these materials should be poured within 1 hour
SILICONE IMPRESSION MATERIALS
Possible CAUSES of an INACCURATE and/or a Weak Cast of a Dental Arch (7)
- Distortion of the hydrocolloid impression
- A ratio of water to powder that is too high that will result in a weak cast.
- Improper mixing. This also results in a weak cast or one with a chalky surface.
- Trapping of air, either in the mix or in pouring, because of insufficient vibration.
- Soft or chalky cast surface that results from the retarding action of the hydrocolloid or the absorption of necessary water for crystallization by the dehydrating hydrocolloid.
- Premature separation of the cast from the impression.
- Failure to separate the cast from the impression for an extended period.
- Distortion of the hydrocolloid impression
a) By use of an impression tray that is ________
b) By _________ from the tray
c) By ___________ caused by dehydration
d) By __________ caused by imbibition (this will be toward the teeth and will result in an undersized rather than oversized cast
e) By ____________ the cast with stone that has already begun to set.
not rigid
partial dislodgment
shrinkage
expansion
attempting to pour
A STOCK TRAY SHOULD:
- Be _________ to avoid distortion during the impression and cast forming procedures
- Should fit the mouth about _________clearance
- should be made of material that permits ___________ to fit the mouth
sufficiently rigid
4 to 5 mm
trimming and shaping
