5. Impressions Flashcards
Define impression
- A negative likeness or copy in reverse of the surface of an object
- an imprint of the teeth and
adjacent structures for use in dentistry
Aim of every impression?
to obtain a cast (positive) by pouring plaster into the impression (negative) that mimics the oral tissues
Can you get a good cast from a bad impression?
no
Impressions: tissues must be in good condition, both underlying bone and gingiva because…? (2)
- For stability reasons.
- For easiness of impression taking
How long does bone take to heal completely after extraction?
6-9 months
What happens to bone after extraction? (2)
- new bone created into extraction socket
- alveolar ridge has to be remodeled so it is stable over time
A prosthesis wont fit if the treatment for a complete denture occurs before…
6-9 months and bone remodeling
What are the options if a complete denture has to be done before 9 months? (4)
- Carry out an immediate complete denture
- Carry out an interim complete denture
- Use a previous removable partial denture
- Carry out a final complete denture right after soft tissue healing
Before 9 months of healing, what occurs for an immediate complete denture? disadvantages? (4)
- Impressions taken before extraction, and remaining teeth are removed from cast.
- This denture is worn for 9 months.
- Afterwards, a final prosthesis is done.
- Disadvantage: cost of two dentures.
Before 9 months of healing, what occurs for an interim complete denture? disadvantages (4)
- Impressions taken right after soft tissues have healed (2-4 weeks).
- This denture is worn for 9 months.
- Afterwards, a final prosthesis is done.
- Disadvantage: cost of two dentures.
Before 9 months of healing, what occurs for using a previous removable partial denture? (3)
• Convert it into an interim complete denture after
teeth extraction.
• Wear it for 9 months.
• Do a final complete denture after that.
Before 9 months of healing, what occurs for carrying out a final complete denture right after soft tissue healing?
-reline it 9 months afterwards
In case the patient hasn’t got teeth and he/she lost
them more than 9 months ago: (2)
- The complete denture can be carried out right away.
* Condition of the supporting mucosa has to be previously assessed.
What can you find when assessing the mucosa for dentures?
- Prosthetic candidiasis
- Epulis fissuratum (connective tissue hyperplasia)
- Traumatic ulcers.
How do we treat prosthetic candidiasis?
500.000 IU (5 ml) of Mycostatin 2-4 times a day for 2 weeks
How do we treat epulis fissuartum?
Surgical treatment and wait one month until complete healing
How do we treat traumatic ulcers? (2)
- Due to former denture.
- Remove denture for a week, and then take impressions
What are the different types of impressions? (2)
• Anatomical impressions. • Functional impressions.
Whats another name for anatomic impressions? (2)
- mucostatic
- non-pressure
What material is an anatomical impressions preformed with?
alginate
What do anatomical impressions reproduce?
- the mucosa at rest, not under functional load
Describe what happens during anatomic impressions regarding load and muscles (3)
- No functional load over supporting tissues during impression (mastication, deglutition…)
- No perioral muscle activity
- Minimal deformation due to the pressure done by
the impression material
What allows a denture to stay put when the mouth is open? (2)
- Base fit (adhesion and cohesion)
- Adequate extension of denture base
Should there be contact between dentures when the mouth is open?
no
What allows a denture to stay put when the mouth is closed?
balanced articulation
Why is alginate a good material for anatomic impressions? (2)
- Alginate doesn’t exert pressure upon the tissues. - Flows well up to surrounding tissues.
What impression trays do we use for anatomical impressions?
Standard dentate
Anatomic impressions: Why do we get overextended impressions? (2)
- Alginate flows further away than in functional conditions.
- Bottom of the vestibule is reached, as opposed to functional impressions
What are the indications for anatomical impressions? (2)
Good prognosis dentures:
• Wide alveolar ridges (Crespi class I & II) » retention.
• Homogenous and firm attached gingiva.
Where is the denture bases extended to in the cast?
mucogingival junction
corrected in mouth of patient
Whats another name for functional impressions?
Mucodynamic impression
Define functional impression:
seek the reproduction of the tissues at function, not at rest
Functional impression denture base?
must not extend to the area where muscles move the mucosa
What does a functional impression capture? (2)
- Functional area of orofacial muscles by performing movements while taking the impression.
- Orofacial muscles mark off the limits of the denture base.
Types of functional impressions? (3)
- without pressure
- with pressure
- with selective pressure
What is a functional impression without pressure? (3)
- The best type of functional impressions.
* Only minimal deformation of tissues due to the pressure done by the impression material
What material do we use for a functional impression without pressure? (2)
zinquenolic paste or light body silicone
What is a functional impressions with pressure? (2)
• The final impression is taken with a record base
with artificial teeth mounted on it.
• It records the mucosa under occlusal load.
Why is a functional impression with pressure a bad idea? (2)
- Mucosa may suffer a bedsore (decubitus ulcer).
- Denture may lose retention, because tight mucosa will try to throw it out at rest.
What is a functional impressions with selective pressure (2)
- Exert more pressure at the areas that can bear it better while biting.
- It is achieved by the Boucher’s technique, preparing custom trays specially.
Why is a functional impression with selective pressure a bad idea? (2)
- Mucosa may suffer a bedsore (decubitus ulcer).
- Denture may lose retention, because tight mucosa will try to throw it out at rest.
Objective of a function impression? (2)
- To exactly determine the limits of the denture
2. Achieve a good border seal of the denture.
How is the limit of the denture in a function impression achieved? advantages? (3)
- Achieved by modeling the functional edge of the denture and moving the mobile tissues during the impression.
- Usually possible to obtain bases extended 1-2 mm more than with mucostatic impressions.
- It enhances support, retention and stability
How do you achieve a good border seal with a functional impression? (3)
- The edge of the denture will extend up to the bottom of the vestibule of the functionally modeled impression (and therefore, of the cast).
- The edge will fit the mobile mucosa, thus improving border seal.
- This will also enhance retention and stability.
How are functional impressions made? (4)
- With custom trays with its borders functionally modeled (generally with godiva).
- Godiva is a thermoplastic rigid impression material.
- Impression material with good creeping capability, like zinquenolic paste or addition silicone.
- When taking the impression, we make the patient move his/her orofacial muscles, so border structures move.
Where should the denture be extended to in a functional impression? (4)
- Achieve maximum extension of the denture.
- Extension should be within the limits marked off by function of orofacial muscles.
- Extension up to mobile mucosa.
- Health of supporting tissues and surrounding structures must be preserved
Indications for functional impressions? (4)
• In bad prognosis dentures:
- Size and shape of residual ridges (Crespi class III and IV), specially at the mandible.
- Soft and mobile attached gingiva.
• Higher base extension partially compensates this problems
What materials are used for impressions? (4)
- Alginate.
- Low melting point godiva.
- Zinquenolic paste.
- Light-body addition silicone
Alginate properties? (5)
- Irreversible hydrocolloid.
- Good elesticity.
- Bad dimensional stability.
- Impression must be cast before 10 minutes.
- most widely used for complete dentures
Low melting point godiva properties? (4)
- Melts at 45-50C.
- Used in bars.
- Applied at the border of custom trays to functionalize impressions and improve border seal.
- Heated with an alcohol or gas lamp, then immersed in 50C water before carried into the mouth.
Zinquenolic paste properties? (5)
- Paste-to-paste zinc oxide eugenol (ZOE).
- Very accurate impression material.
- Good creeping capability.
- Rigid, so it can get fractured if there are undercuts.
- It is used with custom trays without separator and without adhesive
Light body addition silicone properties? (3)
- Very elastic, so it performs well if there are undercuts.
- Good dimensional stability.
- It is used with custom trays with separator (2mm) and adhesive.
Common impression instruments? (4)
- Mouth mirror.
- Gauzes (to dry the palate). - Suction.
- Air syringe.
Impression trays for impressions? (2)
- Standard trays: stainless steel. Rim-lock retention system.
- Acrylic custom trays
Custom trays previously a _________ must be taken (4 words)
standard tray alginate impression
Custom trays for functional impressions use… (2)?
zinquenolic paste or addition silicone
Separators for Custom trays for functional impressions? (2)
- No separator: for zinquenolic paste.
- 2 mm separator: for silicones.
Minimum thickness for custom tray?
2mm (tough and rigid)
Do custom trays have to be heat resistant? why?
yes to withstand heat from godiva
Custom trays and handles must not…
interfere with lip movements
Customs trays must be made with..? Specifically? (3)
biocompatible material:
- Acrylic resin (best option b/c tougher)
- Truwax®
Where should the patients mouth be for impressions?
At the height of the elbow of the dentist
Should we smooth the surface of alginate with a wet finger?
no
How thick should the impression material be?
5-6mm
How do we take impressions of nausea-easy patients?
topical anaesthetic over the palate
Silicone impressions need adhesive. true or false?
true
Can you put some alginate with your finger when taking an impression? why?
Yes if there are areas difficult to access
How do you insert a tray for impressions? (3)
◦ Vertically.
◦ Upper tray: from back to front.
◦ Lower: from front to back.
Where should the tray be in relation to the teeth when taking an impression?
5mm ahead of the teeth
Should alginate be seen behind the tray when taking impressions?
yes
Should the patient raise their tongue when taking impressions?
yes
How do we detach the tray when taking impressions? (4)
- Firmly.
- Vertically.
- No lateral movements.
- With a singe movement
Why do we reject impressions? (5)
- Perforated (tray is seen through) - Bubbles. - Drags. - Undefined areas. - Not enough extension.
Impression management? (4)
- Plaster wash (not for zinquenolic paste and
silicone impressions). - Gentle drying.
When should impression casting? (5)
- Alginate: before 10 min after being taken.
- Zinquenolic paste and silicones don’t require immediate casting.
- Trimming of unsupported areas of the impression or areas that would touch the resting surface.
- from deeper areas to shallower areas
- moisture chamber for 45-60 mins
FUNCTIONAL IMPRESSION PROCEDURE custom tray preparation? (3)
- Acrylic resin.
- Without separator for zinquenolic paste.
- With 2 mm separator for silicone
FUNCTIONAL IMPRESSION PROCEDURE tray fitting? (2)
- Trimming of tray edges: up to functional line.
* Check that under orofacial muscle activity tray is not detached
FUNCTIONAL IMPRESSION PROCEDURE What must be done during the upper tray try in? (4)
- Pull lips and cheek.
- Perform lateral mandibular movements to check
space for coronoid process. - Open mouth to check space for hamular
notches. - Say letters A, K, G for vibrating line
FUNCTIONAL IMPRESSION PROCEDURE What must be done during the lower tray try in? (3)
- Pull lips and cheek.
- Move tongue up, forth and laterally.
- Open the mouth to check space for
pterygomandibular ligament.
FUNCTIONAL IMPRESSION PROCEDURE Modelling of tray borders? (3)
- With low melting point godiva.
- Same manouvers as when checking the tray.
- Sector by sector.
FUNCTIONAL IMPRESSION PROCEDURE what do we use for the final impression? (2)
• Zinquenolic paste or light body silicone
FUNCTIONAL IMPRESSION PROCEDURE final impression and pressure? movements?
- Press until no more impression material pours out of the holes (mild to no pressure)
- Make functional movements again
FUNCTIONAL IMPRESSION PROCEDURE how long does it take to set completely?
5-6min
Functional impression objective: (2)
- To record the tissues without pressure.
- Find the borders of the mobile mucosa
Functional impression deepest point?
deepest point of the vestibule is where mucosa starts moving while in function.
Functional impression ideal extension?
Base plates will extent up to bottom of vestibule of the cast
When do we get the final extension of the record base for anatomical impressions? (2)
- limit of record base is drawn in the cast
- final extension is at the occlusion tim try in appointment
Do functional impressions have border seals?
Have a good border seal
