MAXILLARY IMPRESSION PROCEDURES

INTRODUCTION

• The impression procedures are wide and varied

• Complete denture impression can be made by considering certain factors

1. Examination and conditioning of the patient and the mouth

2. Selection of the impression material3. Selection of the impression tray4. Seating of the patient5. Selection of the impression procedure6. Making the preliminary impression7. Constructing the primary cast8. Fabricating the custom tray9. Border molding10.Making the final impression

1.EXAMINATION AND CONDITIONING OF THE PATIENT AND THE MOUTH

• Case history• Clinical examination• Surgical/non-surgical denture foundation

improvement methods• Patient education [Steps to reduce gagging,

salivation-drug prescription]• Assess the anatomical and biological status of

denture foundation area

2.SELECTION OF THE IMPRESSION MATERIAL

• Preliminary impression materials: Impression compound Alginate

• Final impression material: Zinc oxide eugenol Alginate Rubber base Tissue conditioners Impression plaster Impression waxes

3.SELECTION OF THE IMPRESSION TRAY

• Stock trays / Custom trays

• Perforated / Non-perforated

• Dentulous / Edentulous

4.SEATING OF THE PATIENT

FOR MAXILLARY IMPRESSION:• The patient is seated in an upright position• Gravity affects the position of the oral tissues• Reclining the chair can cause the material to

flow down the palate- gagging/discomfort- disruption of impression

• Saliva pooling avoided in upright position

OPERATOR POSITION:• Stands behind and to the right side of the

patient• Left hand is brought around from the back of

the head to the left side of the patient• Left hand for retraction of the lips• Right hand to position the tray in the patient’s

mouth

5.SELECTION OF THE IMPRESSION PROCEDURE

• Majority of the impression techniques employ variations of the selective pressure theory

• Factors affecting the choice of techniques are:1. Clinical findings2. Experience of the dentist3. Availability of the material4. Patient related factors

6.MAKING THE PRELIMINARY IMPRESSION

• Common techniques:

1. Border molded custom tray technique – usually practiced

2. Border molded compound tray technique3. Functional impression technique

Border molded custom tray technique

• First appnt: preliminary impression in stock tray – alginate / impression compound

• Lab phase: study cast and custom tray• Second appnt: border molding and final

impression

Why primary and secondary impression?

• Difficult to place selective pressure with single unmodified primary impression

• Border molding and PPS recording will be more accurate

• Custom tray can provide a relatively uniform space for the thin impression material

Tray Selection

• Select a tray that covers the entire denture bearing area and extends upto the reflection of the mucosa

• 6mm space between tray and ridge

• Posterior extension upto the PPSA

Inserting and centralizing the upper tray

• The operator stands on the right side of the patient• From behind the patient, the left hand is used to retract

the left upper lip and cheek• The tray is inserted with the right hand. The right

posterior corner is inserted first. The tray is then rotated into position

• The upper lip is lifted to visualize the tray in relation to the labial frenum

• It is centered over the ridge so that there is an equal space on all sides of the tray.

• The labial frenum is used as a guide to align the midline of the tray

Preliminary Compound Impression• Impression compound – softened - hot water bath at

14O°F or about 60 to 65°C . After kneading - loaded on to the tray - shaped roughly to the shape of the ridge with the fingers. The surface is then warmed and tempered in the water bath

• The upper lip is retracted - tray centered using the frenum as guide - pressed into position in an upward and backward motion

• The cheeks and lips are gently finger molded. The tray is stabilized with the finger until the modeling compound hardens sufficiently. After removal it is cooled in chilled water. The impression is inspected for completion

7.CONSTRUCTING THE PRIMARY CAST

• Pour the impressions immediately to discard any dimensional instability and to improve accuracy

• Beading and boxing of the compound impression is preferred to preserve details and periphery of the cast

• Pour the cast using plaster• After set, recover the cast by immersing the

whole mass into hot water

• Trim the cast in a wet stone trimmer to attain uniform land area

• Use a knife to provide uniform sulcus depth of 2-3mm

8.FABRICATING THE CUSTOM TRAY

• Marking the cast: the tray extension is marked on the cast with an indelible pencil about 2-3 mm short of the sulcus. Extend tray posteriorly slightly beyond the posterior vibrating line

• Mark location for wax spacer and relief is provided to the incisive papilla, mid-palatine raphae, undercuts, bony prominence and torus

• Wax spacer is designed 2mm short of the tray extension

• Acrylic custom trays: apply separating medium and allow to dry

• Tray fabrication by direct technique, sprinkle on method for acrylic trays, using tray forming molds, vacuum formed trays, light cured trays, shellac trays

• Trimming the trays: The maxillary tray is trimmed 2-3 mm short of the reflection all around and should extend upto and include the posterior vibrating line. Smoothen and polish the borders

• Handle for the tray is fabricated with a dimension of 8x8x4mm with a 45-60 degree angulation in a position that does not interfere with border molding

9.BORDER MOLDING

• Check the tray extension: done segment by segment. Pull lips and cheeks towards the tray and displacement means overextension. Also visually one can check and mark the overextension

• After checking the tray extensions border molding is initiated with a suitable border molding material

• Definition: The shaping of the border areas of an impression tray by functional or manual manipulation of the tissue adjacent to the borders to duplicate the contour and size of the vestibule

• The muscles which are active when we speak, chew, smile or swallow can have a destabilizing effect on the denture

• Border molding shapes the impression and allows the muscles to function in harmony

• Materials available: modeling compound sticks, autopolymerizing acrylic resin, elastomers, impression waxes

• Border molding can be done segmentally or in a single step

• It can be done by digital manipulation or by functional movements

Maxillary Border Molding• Labial frenum and labial flange : The upper lip is lifted up,

then outward, downward and inward. This simulates the movement of the labial frenum

• Buccal frenum and buccal flange : In the region of the buccal frenum the cheek is pulled upward, then outward, downward, inward and finally forward and backward. This simulates the movement of the buccal frenum

• Coronoid notch: The activity of the coronoid process is recorded on the distobuccal region by asking the patient to open the mouth wide. The patient is instructed to move the jaw from side to side

• Posterior palatal seal area: has two partsPosterior palatal seal [PPS] and Pterygomaxillary seal [PMS]• PMS – Behind maxillary tuberosity, in the

hamular notch. Located using T- burnisher – feel for soft depression beyond the tuberosity

• PPS – Anterior vibrating line [AVL] and Posterior vibrating line [PVL]

AVL – cupid’s bow shape – due to projection of posterior nasal spine• Junction of hard and soft palate• Located by : Valsalva maneuver: hold nostrils

firmly and gently blow through nose to position soft palate downwards at its junction with hard palate

• Or say vigorous “ah” in short bursts

PVL – Junction of the aponeurosis of the tensor veli palatini and the muscular portion of the soft palate

Located by asking patient to say “ah” in a normal, unexaggerated fashion

• Multiple techniques can be employed to record the PPSA:

CONVENTIONAL TECHNIQUEFLUID WAX TECHNIQUEARBITRARY SCRAPING OF THE CAST

• CONVENTIONAL TECHNIQUE:Done after making final impressionMaster cast is fabricatedShellac trial base fabricatedLocate PMS and PVL using indelible pencilTrim upto PVLLocate AVL using indelible pencilTransfer markings to master cast

Scrape area between AVL and PVL to a depth of 1-1.5mm on either side of mid palatine raphae and 0.5 mm depth at the mid palatine raphae and scraping tapers to feather edge as it approaches AVLCheck seal in the mouth with mirror after reheating and adapting shellac trial base on the cast

• FLUID WAX TECHNIQUERecorded after making final impressionLocate AVL and PVL in the mouth and transfer to impression surfaceMolten wax [ Korrecta, Iowa] is painted between two linesCool and gently press into place for 4-6 minsFlex head - 30 degree downwards

Remove from mouthGood tissue contact – glossy appearance and poor contact – dull appearanceAdd wax in deficient area and scrape off from excessive areasTerminate in feather edge near AVL

• ARBITRARY SCRAPING OF THE CASTAfter fabrication of master cast, scrape off 0.5-1mm of stone in the PPSA before fabricating the record base.

10. MAKING THE FINAL IMPRESSION

1. Check for retention2. Prepare and instruct the patient3. Prepare the tray for final impression:Remove wax spacerEscape holes or vents are provided to reduce hydrostatic pressure build up. Multiple holes at a distance of 5mm is placed in the midline4. Protect the mouth – use petrolactum5. Dry the mouth

Final impression: equal lengths of base and catalyst paste of ZnOE is mixed to form a smooth uniform mixLoad the tray and spread out the material evenly to all parts of the trayMaterial must be free flowing and not viscousSeat the tray and repeat the border molding movements and allow to set

Remove the impression by breaking the seal by introducing air beneath the denturesInspect the impressionCorrect it or remake if needed.Fabricate the master cast using dental stone

FACTORS THAT COMPLICATE IMPRESSION MAKING

• Uncooperative patients• Gagging• Excessive salivation

CONCLUSION

• A preliminary impression is made for construction of a custom tray to make the final impression

• The objective of making an impression should be to record all areas covered by the impression surface of the denture and the adjacent landmarks with an impression material that is accurate and incorporates the minimum of tissue displacement

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