IMPRESSIONS OF EDENTULOUS DBAs:Impression: An imprint produced by 'the pressure of one

thing upon or into the surface of another (Impression made not taken).

An active and not a passive procedure.Impression making for complete dentures categorised as:

Primary impressions:Conventional techniquesTemplate techniques

Definitive impressions:Conventional techniquesSelective pressure techniquesFunctional techniquesReline & Rebase techniques (secondary

template imp).

IMPRESSIONS OF EDENTULOUS DENTURE BEARING AREAS (DBAs):Essential Considerations:Survey DBA & select properly extended stock tray. Decide the form of definitive impression based on:

- the nature of the supporting tissues.- patient's functional requirements.

Practice tray insertion in patients’ mouth so that the:- patient become familiar of what to do.- clinician becomes confident of his technique.

Technician knows special tray design requirements:- spacing, handles, lack of perforations.

Use impression material that works best in your hands.In recorded imp, no tissue surface of tray showing: - support problem will be introduced to CDs.Outline areas to be relieved on final impression.

IMPRESSIONS OF EDENTULOUS DBAs:Faulty /flawed impressions major cause of CD problems.1

Most lower impressions 'short' of the retromolar pads.Improperly recorded functional forms of the:

- floor of mouth & and retro-mylohyoid fossae.Impression deficiencies tend to result in:

- an unstable denture.Not to underestimate the importance of recording:

- the form of the floor of the mouth in relation to the mylohyoid muscle and the retro-mylohyoid fossae.

Many think ‘Primary imp” as “First imp” & Unimportant.Poor P. Imps give “Poor casts” not providing good basis for

custom trays.With poor imps clinicians will not earn the respect of the

dental technician.

PRIMARY / PRELIMINARY IMPRESSIONS:BSSPD Guidelines / Requirements:Should accurately record clinical relevant landmarks of the edentulous

mouth without excessive tissue distortion (Displacement).2 Tissue distortion results over-extended impression.Use rigid stock trays.Modify tray to 'fit the form of the DBAs. Record features of all required anatomical areas.Functions of primary impressions for CDs:

Basic function: to outline support for CDs. Secondary function: to obtain a study cast on which: - to make a “custom” or “special” tray.

Outline the DBAs, in indelible pencil on impressions:Assist the technician in making custom trays.

Disinfect impressions by conforming to local health and safety guidelines pouring them.

PRIMARY / PRELIMINARY IMPRESSIONS:Trays selected from a supply of 'stock' trays: - covering a broad range of arch forms & sizes. Examine the edentulous mouth and assess the:

- length & width of the arch to be restored. Assess the stock trays for size by placing the distal part of:

- upper tray just distal to post. landmarks of tuberosities. - lower tray onto the retro-molar pads. Required tray width visualized for recording the functional:

- width of sulcus (covering 5mm beyond external surface RR.Keep the posterior aspect of tray in place.Rotate the anterior portion of the tray towards the labial

sulcus & determine if tray has appropriate length.

PRIMARY / PRELIMINARY IMPRESSIONS:Avoid using over-sized trays to reduce patient discomfort &

incorporation of tissue folds.Use of under-sized trays will result in:

- problems for technician making custom trays on under-sized primary casts. - under-sized primary imps produce:

- inadequate final imps.- support and /or stability problems in CDs.

Select appropriate impression material:A variety of materials are used to record CD impressions. Imp. materials differ in their ability to displace soft tissues.Acceptable maxillary impressions may be recorded by

experienced clinician with a well selected tray in any imp. Material.

Well-formed impression of (lower) lingual sulcus area

Rigid Properly extended stock trays especially in the retro-mylohyoid area.

Cast made of an impression with under-extended posterior lingual pouch (arrowed)

PRIMARY / PRELIMINARY IMPRESSIONS:Practice insertion of the chosen tray.Sit or stand to one side or behind the patient. Educate the patient on how to control his breathing during the

recording of the impression.Upper: Load the upper tray with the impression material.Evert the upper lip hold the tray inferior and anterior to the

incisive papilla & move it upwards and backwards.Initially fill the labial sulcus, then the left and right sulci.Finally press the palatal area into position.Change the operating hand to ensure the impression material

records the right and left sulci.Lower: Sit or stand to one side in front of patient.Hold loaded tray over ridge & press it in the labial sulci in turn.Permit imp. material to fill the functional width of the sulci.

Well-made Impressions Using Twin-phase Hydrocolloid (Alginate) Material

PRIMARY / PRELIMINARY IMPRESSIONS:Recording Definitive Impressions:Should record the entire functional DBA.

- to ensure maximum support, retention & stability for CD during use.

Primary purpose: to record accurately the DB tissues in addition to recording the functional width and depth of the sulci.

Imp. technique for a patient is influenced by the:- condition of the DB tissues & the peri-denture tissues.

Recorded in Special / custom Trays .CDs & Templates / Replicas CDs also used as trays.

Special Trays For Definitive Impressions:Primary casts always slightly overextended. Consider amount & position of u/c deciding spacing b/w

the tray and cast:- 3 mm spacing for alginate if large U/C are present.

Non-perforated tray essential for a peripheral seal. Tray perforated chair-side to enhance retention of

alginate &/or to prevent air-trap in palatal vault.Upper & lower labial flanges not overextended.Incorporate stub handles not distorting the lips;

3 for lower and 1 for upper tray.Place pieces of tracing compo to sp. trays in canine areas

&d gently place tray in mouth. Serve as a spacer and prevent the incorporation of support problems by avoiding hydrostatic pressure.

Conventional Definitive Impression Technique:Disinfect Spl. Trays & rinse in water.Check tray is adequately extended antero-posteriorly &

bucco-lingually. Trays not interfering function of peri-denture soft tissues.Correct overextension (using pressure-relief paste).Correct under-extension (adding green-stick / other

material).Apply tracing compound to the posterior aspect of the upper

tray to produce a posterior seal. The tracing compound should extend uninterrupted from one

border of the tray to the other to create a post dam.In the lower tray, the compound should be added to displace

the retro-molar pad sufficient to give a posterior seal.

Load the tray with the material.Technique is same for the primary impression.Upon setting, remove from mouth.Check for accuracy and form.Disinfect procedure (hypochlorite 1,000 ppm).Indicate the extent of the peripheral roll to be

preserved on the master cast. Creation of the peripheral seal is desirable and this

depends upon the accuracy master cast .

Definitive impression with well-defined area for the placement of carding wax prior to boxing the impression, thereby preserving the functional width and depth of the sulci.

Selective Pressure Impression Techniques:A support problems is overcome by relieving master cast.But in specific cases, modified impression procedures used

B/C of perceived support problems in case of: - displaceable upper anterior (flabby) ridge.- fibrous (unemployed) posterior mandibular ridge.- flat lower ridge covered with atrophic mucosa.

Several variations of these impression techniques exist.General Steps:Fabricate special trays.Adjust special / custom trays.After peripheral moulding, do specific modifications to the

trays / impression techniques.

Impression Technique for Displaceable (Flabby) Anterior Maxillary Ridge:

Achieve seal with peripheral moulding.Record impression of maxilla in ZOE or a medium-bodied

PVS) impression material.ZOE not recommended in a patient with a dry mouth.• On setting, the impression is removed from the mouth.Draw the extent of the displaceable tissue on the

impression surface. This area, and the equivalent area of the tray, are then

removed, using a scalpel and acrylic bur.This modification renders tray no longer retentive.

Fibrous (Unemployed) Posterior Mandibular Ridge:Recognized by the presence of a thin, mobile thread-like

ridge which is essentially fibrous in nature.A Staged sequence impression technique is used for this

situation.Custom tray checked for peripheral extension.Tray loaded with tracing compound (greenstick).Impression of the denture-bearing area recorded.Using the heated spoon-end of a Le Cron carver remove

the greenstick relating to the crestal tissues.Perforate tray in this region. Downward finger pressure of the modified impression, in

the mouth, should elicit no discomfort.Definitive impression using light-bodied PVS.Treat impression as for a conventionally made impression.

Flat Mandibular Ridge Covered With Atrophic Mucosa:Equate to Atwood's Ridge Orders V & VI.Folds of atrophic &/or non-keratinized tissue on the ridge. The impression philosophy is that a viscous admix of cake

imp. Compo & stick compo removes any soft tissue folds & smoothes them over the mandibular bone.

Discomfort arising from the 'atrophic sandwich', i.e creased mucosa B/W CD base & mandibular bone is reduced.

Prepare the impression medium as admix of 3 parts by wt. of (red) imp. compo & 7 parts by wt. of stick compo.

Admix made in hot water by kneading using vaselined gloved fingers.

Make lower impression (Working time of admix is 1–2 minutes) by moulding the peri-tray tissues to give good peripheral border recording.

On removal, impression is chilled in water & then re-inserted.

The operator presses on the stub handles of the tray on the premolar region &reciprocates with his or her thumbs on the inferior body of the mandible: - ideally, discomfort will be felt by the patient in the area pressed by the operator's thumbs!

Any discomfort in the DBA may be treated by adjusting the offending area of the impression with a heated wax knife and re-inserting as required until no further discomfort is felt.

Alternatively, painful area is relieved on the master cast.Admix technique gives a reliable guide to the load-bearing

potential of patient's DBA when making definitive imp.

Definitive impression made with Admix Method (MC Cord & Tyson)

Template (Replica Denture Tray) Impression Technique:

Used when replacing existing CDs by copy method.Replication of the form of polished surfaces of CDs

help the patient's adaptation to new dentures. Fabricate mould of CD to obtain its acrylic replica.Final imp. Recorded in Acrylic replica (template).

Functional impression Techniquesused where problems of stability exist (poor muscle adaptation and/or

imbalance or because of problems of available denture space). Also be useful in patients having recently suffered from a stroke.Two variations are commonly used for functional impressions.

- Local areas of modificationCDs exhibiting looseness, not primarily from retention problems but because of localized areas of poor functional adaptation. In these cases, use a thin mix of a resilient lining material (e.g Visco-Gel, Dentsply, Surrey UK) may be used. The mixed material is added to the fitting surface of the denture.Patient instructed to wear the denture for one hour. After one hour of functional moulding CD removed from the mouth.Conventional relining process completed.

Problems associated with denture space/neutral zoneThis technique is well documented and has been referred

to as the neutral zone technique or anthropoidal pouch technique.

We prefer to use the term denture form impression technique. It is designed for patients with poor track records of (lower) denture stability, a large tongue or other anatomical anomaly.

The clinical stages are standard up to and including the registration visit. After this, the upper denture is set up conventionally to the prescribed occlusal vertical dimension (OVD). Opposing the upper set-up is a resin base with three vertical stops joined by a wire bent in a sinusoidal manner. The stops must contact the upper teeth at the selected OVD.

Reline and rebase techniques (including secondary template impressions)

Conventional reline impression is taken or a:- secondary impression for the template technique.

They are both definitive impressions.Must consider the same degree of attention as

standard impression techniques.The denture, or its replica, to be relined is modified:

Establish peripheries /peripheral seal.Undercuts are removed from fit surface of CD:

to ensure that master cast is not damaged on removal of the denture

ZOE or Elastomer (PS / PVS / PE) imp used.Before recording the definitive impression, there is merit in

placing tracing compound as spacing on the denture in the region corresponding to the ridges of the canine areas (But no OVD Raising).

Perforate maxillary spl. Tray in in the midline of the rugae to prevent any possibility of imperfections in the impression, e.g air bubbles.

Also important is good communications with the laboratory (Good rapport b/w Lab).

Conventional techniques, however, do little to inform the technician on the customizing of upper record rims.