3. Complete Denture Impressions Flashcards
Requirements of complete denture
impressions
• The denture base should cover the maximum
possible denture-supporting area
• The impression surface should achieve the closest
possible contact (fit) with the underlying mucosa
compatible with its tolerance
• The border form of the prosthesis should establish a
peripheral seal and, further, help support the lips and
cheeks in a functionally and aesthetically correct
manner
Exam Q Describe the anatomy of the complete denture bearing area (upper)
Incisive papilla
Posterior limit of denture extension (non-moving
junction of hard and soft palates, just anterior
to the ‘vibrating line’)
Tuberosity
Hamular notch
Vestige of palatal
gingival margin
Describe the anatomy of the complete denture bearing area (lower)
retromolar pad
buccal fraenum
external oblique ridge (buccal shelf)
Submandibular salivary gland ducts
lingual fraenum
Lingual sulcus
What factors govern the extension of a complete upper denture?
• Correctly muscled moulded functional impression extending over the maximum denture bearing area. Extension distally should cover tuberosities into hamular notch, and record the full functional depth and width of buccal and labial sulci, posteriorly to non-moving junction of hard and soft palate.
• Muscles and anatomical features influencing border: buccinator, masseter, levator anguli oris, incisivus labii superioris, orbicularis oris.
• Requires a correct preliminary impression in composition. Followed by an individual tray border moulded for sulcular width and depth using an impression material which will not distort the tissues.
What factors govern the extension of a complete
lower denture?
• This is governed by a correctly muscled moulded functional impression extending over the maximum denture bearing area. Extension distally should cover at least 2/3 of the retromolar pad, and record the full functional depth and width of buccal, labial and lingual sulci.
• Muscles and anatomical features influencing border: Mylohyoid, genioglossus, palatoglossus, masseter, buccinator, modiolus, orbicularis oris, sub-lingual salivary gland, genial tubercles.
• Requires a correct preliminary impression in composition. Followed by an individual tray border moulded for sulcular width and depth using an impression material which will not distort the tissues.
How to get the extension right ?
Maximum coverage of upper and lower denture
bearing areas to full functional depth and width of sulci
Principles of first impressions?
Prelim impressions are taken in impression compound in a stock tray
Use plaster cast for special tray
Choose master impression material - ZnO Eugenio is 1st choice or use PVS if undercuts
How to do prelim impressions using stock tray
pick the tray appropriate for the patient, (likely poor fit bc limited no tray sizes, can trim to make better fit)
Impression compound (red compound) in water batch at 55-57 degrees
Take the impression (upper and lower) and inspect to see if it has recorded the desired anatomy
Bc the trays are such a poor fit the impression comound bc of viscosity and plasticity can extend beyond the confines of the tray and can be shaped in the patient’s mouth to record the denture bearing area (a runny alginate wouldn’t allow this bc of its properties therefore use impression compound instead)
Quicker to use impression compound but could get an adaquete impression (not as good) by modifying the tray with some wax in the extension areas)
Principles of stock trays ?
There are a limited range of shapes and sizes of stock trays so the fit is usually poor
Either metal or plastic
What are the properties of impression compound ?
• Mucocompressive
• Rigid
• Poor surface detail
• High coefficient of thermal expansion
• Shrinkage 1.5%
• Has the viscosity to support itself beyond
the tray confines to record the maximum
denture area
What are some other preliminary impression materials ?
• Silicone putty
• Alginate – if tray correctly extended or
rendered so with silicone putty / acrylic resin / modelling wax
Prescribe special tray- (lab card, request)
Special (individual / custom ) impression trays are made in
light or chemically cured acrylic
Exam Q - Assess special trays
Special (individual / custom ) impression trays (made in light or chemically cured acrylic) properties
- Clean and smooth
- Rigid and dimensionally stable
- Allow correct uniform thickness for material to be used
- Handle (intraoral/extraoral) must not interfere with lip
- Finger rests for lowers – to avoid displacing cheeks
- Extended to 2mm short of maximum denture bearing area as delineated from preliminary cast
What is the importance of the tray being 2mm short of the maximum denture bearing area?
To allow enough impression material to flow into the space between the tray and the cheek and be properly border moulded
if the space was too big the material wouldn’t be carried properly to the soft tissue for moulding
if the tray is overextended it would displace the cheek
Problem with grossly resorbed maxilla (upper denture bearing area)
The impression would look grossly overextended but it is not
so the cast poured from the impression would look extremely wide but the tray should still be made to 2mm of the maximum extension of the impression
But often the dentist takes an impression of just the ridge and the technician makes a tray just over this ridge and not out to the full extension
so will not get full functional depth and width of the sulcus and not get retention or stability
result is a grossly underextended tray and one that does not extend to width of the sulcus
Exam Q Prescribe special tray? (lab card request)
How to correct the extension for a stock tray?
Wax spacer to correct extension, technician puts spacer down over denture bearing areas-
0.5mm space needed for Zn/Eugenol, 1.5mm needed for PVS medium viscosity and 3mm needed for alginate
The trays have to be polished and finished
Exam Q- assess special tray
What happens when you receive the trays back into the clinic
Check them ie. quality control check
Try in mouth
Modify if required
If overextended, ie. there is less than 2mm space between the tray and the lips and the cheek then reduce it
Use green stick compound to obtain the correct functionally border moulded impression
(green compound is similar in properties to red compound but it is runnier less vicscous so less likely to distort overextend the cheek and the cheek during border moulding
Upper tray- always put some greenstick compound along the post dam areas of the tray, temper in the water bath and insert and push firmly along the hard palate to seal off the back of the tray
Posterior buccal sulcus tray needs to be customized with greenstick to get full functional depth and width (sometimes anterior addition too)
Lower- addition to posterior part of tray- full functional width and depth of sulcus- if tray covers 2/3 retromolar pad already the no more needed there
Exam Q assess special tray
The correct tray periphery will have?
- Greenstick to post dam and
hamular notches, lingual pouches
of lower - Greenstick to posterior buccal sulci
– esp. width! - Greenstick to correct any area of
underextension - Reduce areas of tray overextension
with bur - ideal when 1 mm short
of reflection of sulci
What is a master impression?
a functionally border
moulded impression of the maximum denture-bearing area with the best fit
to full functional width and depth of the sulci
?Exam Question- describe how to record impressions for complete dentures
Special tray- adapt with greenstick and border mould
low viscosity ZnO paste syringe into stock tray upper and lower and insert into mouth, remove and assess denture- inspection of master impressions card.
If defect then … if upper anterior flabby ridge- …
Exam Q describe how to record impressions for complete dentures
Inspection- master impression criteria?
The fit surface- the hamular notch, all the detail around the ridge to the hamular notch, farily straight line between the two hamular notches (ie clearly delineated post dam area
All the details of the palate, no airblows no defetcts
Buccal and labial periphery are rounded and rolled and to full functional width and depth of the sulci
Lower is covered minimum of after 2/3 of the retromolar pad and no defects
Full functional width and depth of the lingual, buccal and labial sulci
Zinc Oxide Eugenol properties
- Gradual set –amenable to border moulding
- Readily adapts to soft tissues
- Good surface detail
- Rigid
- Dimensionally stable
- Burning sensation
- Adherent to skin!
(if there are small defects can dry the impression and add some impression compound, reseat the impression)
Technique for grossly resorbed lower when
preliminary imp is poor
- ( in the master tray) Take impression with red compound / green compound
mixture (50:50 ratio) in special tray - Carefully border mould and (add/) remove overextension
- Take a ‘wash’ impression using paste or PVS
Other impression material examples
PVS
Plaster of Paris
ZincO is first choice for edentualous ridges that do not have undercuts- why?
unlike alginate or PVS
Because of gradual set- allows a couple of minutes of border moulding to patient’s soft tissues
Requirements of greenstick after having extended the tray with it?
Smooth, rounded and rolled
Mat in colour
Reflecting the correct extension
Shine through the compound (when you’ve used greenstick we don’t seem to have space between the impression compound and the tissues so the impression material will be applied very thinly)
What to do if there is a defect in the impression? ZnO/Eugenol allows this only
Drill a relief hole through the defect and add a bit of material to this -hole allow XS material to escape
(can also correct any under extensions by adding some ZnO)
upper anterior flabby ridge problem
support is poor
difficult to take an impression without displacing that flabby tissue
upper anterior flabby ridge solution
take preliminary impression in mucostatic impression plaster or sloppy alginate (ie non distorting to flabby tissue)
(on the cast make a tray which has (cut a window from the flabby area but has normal tray in the other areas, and border mould (with greenstick in this area and the labial and buccal sulcus and post dam)
in this tray first take an impression in paste (ZnO) in the non flabby area and then take flabby area impression with fluid material (syringe in low viscosity material ie PVS in this area) idea being that this will not displace the normal impression material
Cast is produced of the denture bearing tissues undisplaced at rest and therefore best possible retention
Result of modified impression technique for upper anterior flabby ridge
Cast is produced of the denture bearing tissues undisplaced at rest and therefore best possible retention
What does poor fit of a denture cause
Looseness and pain (if too overextended)
How to communicate to a patient that their denture doesn’t work because it is too loose or too overextended?
Use impressions as a communication tool (show them the lower denture sitting against the lower cast and outline the maximum extension- explain that we have to cover more denture bearing area to functional denture)
so they understand why the denture must be so much bigger
What is gagging
normal protective mechanism to
maintain airway patency
Causes of gagging
normal protective mechanism to
maintain airway patency
- Gag reflex mediated by autonomic nervous
system - Somatic (direct touch: tongue, oro-pharynx) or
psychogenic (non-tactile) stimuli to vomiting
centre in brain - Trigger trigeminal, facial, vagus and
hypoglossal nerves to tongue, pharynx and G-I
tract
Gagging - somatogenic causes
- Local: Tactile irritation mostly –this is physiologically normal but individual response variable
- Systemic exacerbating factors:
? emetic drugs
? alcoholism
? toxic conditions
Gagging Psychogenic
- Apprehension
- Anxiety
- Fear
- Neurosis / psychosis
(may require referral to GMP)
management of gagging
- Relaxation techniques (talk to them, deep nasal breathing, tell them to lift their feet)
- Distraction (talk to them, deep nasal breathing, tell them to lift their feet)
- Hypnosis
- Sedation
- Local anaesthesia
- Desensitisation –give trays home with
patient, provision of palatal training plates
Gagging –management for impression
taking?
- Calm confident approach
- Good communication –reassurance,
encourage, explain what you are doing, - Minimise presence of physical stimulus –tray
size correct, correct amount impression
material, good technique, short setting viscous
materials - Divert patient’s attention –talk, instruct to
breathe through nose, lift feet etc
Causes of gagging that are not to do with the patient?
- Underextension at post dam –common!
A loose upper drops to touch posterior tongue and
induces gag reflex - Overextension at post dam –rare! but many pt’s don’t agree
- Excess occlusal vertical dimension
- Muscle balance –tongue space encroachment / lower occlusal plane high
- Thickness of bases
