impression making for complete dentures

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IMPRESSION MAKING FOR

COMPLETE DENTURES

Khaled Q Al Hamad

4 th year, Dent 441-442, 2006



References

Lecture notes.

A Clinical Guide to Complete DentureProsthodontics. J F McCord and A AGrant.



Part I Review of the relevant anatomy for the maxillary

and mandibular dentures.

Part II: impression techniques

Introduction Primary impression

• Choice of tray & material

Definitive impression• Conventional technique

• Selective pressure technique

Flabby ridge

Fibrous ridge

Flat –atrophic- ridge

• Functional impression

Lecture Outline



Mucous membrane Mucosa: stratified squamus epithelium & connective tissue

(lamina propria)

Submucosa: connective tissues made of dens to loose areolartissues• If firmly attached: withstand pressure• If loose, thin, traumatized, mobile, flappy: it wont be suitable to

withstand pressure-not resilient.

Masticatory mucosa (keratinized): hard palate, residual

ridges, residual attachment gingiva.



Hard palate Keratinized.

Mid palatine suture: Submucosa is extremely thin-requires relief

Horizontal portion of the Hard palate: 1 support forareas

Rugae areas: set at an angle with the residual ridge-2 support areas.



The Palatal Gingival Vestige (remnants of thelingual gingival margin)

It is the remains of the palatal gingiva. Aftertooth extraction the position of the vestige

remains relatively constant, the same as theincisive papilla. This can be a very helpfulpointer for posterior tooth positioning duringdenture construction



Residual Ridges Mucous membrane:

• keratinized• firmly attached.

• Submucosa: devoid of glandular tissues. Densecollagenous fibers. Relatively thin, but sufficient toprovide support for the denture base.

Crest of the ridge:• Prone to resorption.

• 2 support area.

Inclined facial surfaces• Loses it’s firm attachment

• Offers little support

• Cannot withstand pressure



Two orifices one each side of the midline. Coalescenceof several mucous glands - always located in the softpalate. They act as collecting ducts for a group of minorpalatine salivary glands



Imaginary line.

Usually 2mm in front of the fovea palatine

Not the junction of the hard and soft palate-always onthe soft palate.

Submucosa Glandular tissues-because it is not supported by bone, it could

be compressed and relocated with the impression to completethe palatal seal.



Crest of the residual ridge Ridge is similar to that of the upper in healthy

mouth. Attachment varies considerably. In some

people, the submucosa is loosely attached tothe bone.

When securely attached to the bone, themucous membrane is capable of providingsupport for the denture. However, becauseunderlying bone is cancelous, the crest of the

residual ridge may be not favorable as aprimary stress bearing area for the lowerdenture.



Buccal shelf area The mucous membrane is more loosely attached and less

keratinized than that covering the residual ridge. Although themucous membrane may not be as suitable histological to providesupport for the denture, the bone of the buccal shelf area iscovered by a layer of cortical bone. This plus the fact that theshelf lies at right angle to the vertical occlusal forces, makes itthe most suitable primary stress bearing area.



The external oblique ridge does not govern the extension of thebuccal flange because the resistance or lack of it varies widely. Thebuccal flange may extend to the external oblique ridge, up onto it or

even over it depending on the location of the muco buccal fold. The bearing of the denture on muscle fiber of the buccinator would

not be possible except for the fact that the fibers run parallel to thebase, and ,hence , its action is parallel to the border and not at rightangle.



The disto buccal border must converge rapidly to avoid the action ofthe masseter which is pushing inward the buccinator.

Distal extension is limited by

Ramus Buccinator

Pterygo mandibular raph.

Superior constrictor

The sharpness of the boundaries of the retromolar fossa. (the

denture should extend slightly to the lingual into the pearlshaped retro molar pad.



The retro molar pad is a triangular soft pad of tissue. Itsmucosa is composed of thin non keratinized epithelium.It submucosa contains

Glandular tissues

Fibers of the buccinator and superior constrictor

Pterygo mandibular raph Fibers of the temporalis

Because of theses structures, the denture base shouldonly extend to one half to two third the retro molar pad.



The retro molar pad: It is split into two sections. The anterior section is usually firm and

fibrous. It is important for denture support and preventing distaldenture displacement

The mylohyoid ridge: Following the extraction of natural teeth and subsequent resorption,

the mylohyoid ridge becomes more prominent. This can result inmucosal soreness beneath the denture bearing area over themylohyoid ridge.



Mylohyoid muscle It is a thin sheet of fibers and in a relaxed state will

not resist the impression material.

Carrying the border under the mylohyoid cannot betolerated. The contraction of this muscle will displacethe denture.

Fortunately, the denture in the posterior area of the

mylohyoid can beyond its attachment because themucobuccal fold is not in this area.

In the retro mylohyoid fossa the border of the denturecan go move back toward the body of the mandibleproducing the S curve of the lingual flange.

In the anterior region, a depression, the premylohyoid fossa can be palpated and acorresponding prominence, the pre mylohyoideminence seen on the impression



Part I Review of the relevant anatomy for the maxillary and

mandibular dentures.

Part II: impression techniques

Introduction Primary impression

• Choice of tray & material


• Selective pressure technique Flabby ridge

Fibrous ridge



Lecture Outline



Impressions are made with a variety ofmaterials and techniques. Some materialsare more fluid than others before they set orharden.

The softer materials displace the tissues toa lesser extent and require less force in theirmolding than do viscous materials.

Impressions that record the tissues withminimal displacement are described as“mucostatic”. Whereas those that displacethe tissues are classified as

“mucocompressive”

Introduction



Regardless of the technique or material used, thetray is the most important part of the impressionmaking procedure.

Tray-too large:

• It will distort the tissues around the borders of the impressionand will pull the soft tissues under the impression away from thebone distorting the dimension of the sulcus.

Tray-too small:• The borders tissues will collapse inward onto the residual ridge

distorting the accurate recording of the border extensions of thedenture.

A properly formed tray enables the dentist to carrythe impression material to the mouth and control itwithout distorting the soft tissues that surround it.



Special trays: have borders that can be adjusted so they do

not distort the soft tissues around them

Provide space –if needed- inside the tray sothat the shape of the tissues may be recordedwith minimal or selective displacement.

These requirements are not met by socktrays so most impression procedures involvemaking a primary impression with a stocktray. This is poured and the resulting

primary cast is used to fabricate the specialtray. The final impression is then made withthe special tray.





Part II: impression techniques Introduction

Primary impression• Choice of tray & material



Fibrous ridge



Lecture Outline



Primary Impression

Primary impression should record clinicalrelevant landmarks of the edentulous mouthwithout excessive tissue distortion- overextended impression.

Stock trays are used for this purpose. The tray ismodified as necessary to fit the denture bearingarea.

The basic function is to outline support. Asecondary function is to provide the basis for aprimary cast on which a customized or specialtray is made.



Choice of Material Silicone Putty

High viscosity,• it will flow beyond the tray to compensate for

underxtensions and support itself.

• Poor details

Elastic: it will record undercut with reasonableaccuracy.

Cannot be corrected or added to once it sets

Irreversible Hydrocolloids Records details accurately

Loses moisture-unstable

Less viscous



Impression Compound Thermoplastic

High viscosity• it will flow beyond the tray to compensate forunderxtensions and support itself.

• Poor details

Can be corrected by addition. Non- elastic- Not suitable for undercuts

Tray selection selected from a supply of ‘stock’ trays which

are deigned to cover road range of arch formsand sizes.

Some trays are metallic, others are plastic



When assessing the stock trays for size, the clinician isadvised to place the distal portion of the tray just distal tothe posterior landmarks of the tuberosities in the upperarch, and onto the retro molar pads of the lower. This

enables the clinician to visualise the width of trayrequired to record the functional width of the sulcus i.e.the tray should extend 5 mm beyond the external surfaceof the residual ridge.

By keeping the posterior aspect of the tray in place and

rotating the anterior portion of the tray towards the labialsulcus, the clinician can determine if the tray is of anappropriate length.



When the stock tray of appropriate size has been selected,there is merit in practising insertion of the tray; ideally theclinician should be positioned to one side and behind thepatient. In addition to confirming that the tray is suitable for

size, it allows the clinician to educate the patient on how tocontrol his breathing during the recording of the impression.

When the upper tray has been loaded with the impressionmaterial, and the upper lip everted, the tray is held inferiorand anterior to the incisive papilla. The tray is inserted

upwards and backwards to fill, first of all, the labial sulcus,then the left and right sulci before the palatal area ispressed into position. The clinician may have to change theoperating hand to ensure the impression material recordsthe right and left sulci.

With lower impressions, the clinician stands to one side infront of the patient, the tray is held over the lower ridge andthe loaded tray depressed, the labial, right and left sulci inturn being everted to permit the impression material to fillthe functional width of the sulci









Fibrous ridge



Lecture Outline



Definitive Impression

'should record the entire functionaldenture-bearing area to ensure maximumsupport, retention and stability for the

denture during use'.

Techniques:

Conventional

Selective pressure

Functional



Trays for definitive impressions

Primary casts are generally poured in dentalstone and should, by virtue of the primaryfunction of primary impressions, be slightly

overextended. Depending on the presence,amount and position of undercuts the clinicianshould outline how much spacing is requiredbetween the tray and the primary cast, e.g. 3

mm spacing is recommended for irreversiblehydrocolloids where large undercuts are present



After disinfection of the trays, andsubsequent rinsing in water, check thateach tray is adequately extended antero-

posteriorly and bucco-lingually Apply tracing compound to the borders of

the tray to fully customize the tray. Thetracing compound should extenduninterrupted from one border of the trayto the other.



When molding the maxillary buccal vestibule, themandible should be moved to the right and left to free

the coronoid process and masseter should be activatedby asking the patient to exert a closing force while thedentist exert a downward pressure on the tray

For the lower, the mandible should open wide to activatethe Pterygo mandibular raph. Also the masseter and

medial Pterygoid should be activated by asking thepatient to exert a closing force while the dentist exert adownward pressure on the tray..

The lingual sulcus is molded by asking the patient toprotrude his tongue forward and then to push the tongueagainst the anterior palate



Depending on the nature of the ridges andthe preference of the clinician, a variety ofmaterials may be selected. It is our

contention that the critical components ofthis technique are that a stable andretentive peripheral seal will be

established and that appropriate spacingis incorporated; the choice of material,within reason, is of secondary importance



should be subjectedto an appropriatedisinfection

procedure, the clinician should

carefully indicate theextent of the

peripheral roll to bepreserved on themaster cast.









Fibrous ridge



Lecture Outline



Selective Pressure ImpressionTechniques

In these techniques, there is a need to modifythe impression procedures because of perceivedsupport problems.

While other support problems may be overcomeby appropriate relief of the master cast, otherconditions are best overcome by modifiedimpression techniques. examples are: Displaceable (flabby) anterior maxillary ridge

Fibrous (unemployed) posterior mandibular ridge

Flat (atrophic) mandibular ridge covered with atrophicmucosa.









Fibrous ridge



Lecture Outline



Displaceable (flabby) anteriormaxillary ridge

ensure that the peripheral moulding orcustomising has resulted in a peripheral seal,

an impression of the whole maxilla is takenusing either zinc-oxide-eugenol (ZOE) or a

medium-bodied polyvinyl siloxane (PVS)impression material. the extent of the displaceable tissue is drawn on

the impression surface. This area, and theequivalent area of the tray, are then removed,using a scalpel and acrylic bur. Insertion of thismodified impression and tray will demonstratethat the tray is no longer retentive.



Holding the modified trayand impression in situ ,use a low-viscositymaterial (Plaster of Parisif ZOE was used, light-

bodied PVS if a medium-bodied one was used)and paint or syringe theseonto the displaceabletissue to record them in aminimally-displacedposition. On setting, itshould be apparent that aperipheral seal has beenre-established








• Selective pressure technique Flappy ridge

Fibrous ridge



Lecture Outline

Fib ( l d) i



Fibrous (unemployed) posteriormandibular ridge

This condition may be recognised by the presence of athin, mobile thread-like ridge which is essentially fibrousin nature



When the customised tray has been adequatelychecked for peripheral extension, it is loaded

with tracing compound (greenstick) and animpression of the denture-bearing arearecorded.



Using the heated spoon-end of a Le Cron carver or a similarinstrument, remove the greenstick relating to the crestal tissues andperforate the tray in this region. Downward finger pressure of themodified impression, in the mouth, should elicit no discomfort.

Inject some light-bodied PVS onto the buccal and lingual shelves ofthe greenstick and gently insert the impression. Excess material willbe extruded through the perforations, and the fibrous ridge willassume a resting central position, having been subjected to evenbuccal and lingual pressures.

The impression is now treated as for a conventionally madeimpression.









Fibrous ridge



Lecture Outline

Fl t ( t hi ) dib l id



Flat (atrophic) mandibular ridgecovered with atrophic mucosa



These ridges equate to Atwood's ridge orders vand vi and may be complicated by folds ofatrophic and/or non-keratinised tissue lying onthe ridge. McCord and Tyson described thistechnique which is specific for this clinicalsituation.The philosophy is that a viscous admix

of impression compound and tracing compoundremoves any soft tissue folds and smoothesthem over the mandibular bone; this reduces thepotential for discomfort arising from the 'atrophic

sandwich', i.e. the creased mucosa lyingbetween the denture base and the mandibularbone.

d i f 3 t b i ht



an admix of 3 parts by weightof (red) impression compoundto 7 parts by weight ofgreenstick; the admix iscreated by placing the

constituents into hot water andkneading with vaselined,gloved fingers.

the lower impression isrecorded. The working time ofthis admix is 1-2 minutes and

this enables the clinician tomould the peri-tray tissues togive good peripheral moulding(Fig. 14).

Any discomfort in the denture-bearing area may be treated

by adjusting the offending areaof the impression with a heatedwax knife and re-inserting asrequired until no furtherdiscomfort is felt. Alternatively,the clinician could indicatewhere relief is required on the

master cast.

L O li

http://www.nature.com/bdj/journal/v188/n9/full/4800516a.html

http://www.nature.com/bdj/journal/v188/n9/full/4800516a.html








• Selective pressure technique Flappy ridge

Fibrous ridge



Lecture Outline

F nctional Impressions



Functional Impressions neutral zone technique

It is designed for patients with poor track recordsof (lower) denture stability, a large tongue orother anatomical anomaly.

The clinical stages are standard up to andincluding the registration visit. After this, theupper denture is set up conventionally to theprescribed occlusal vertical dimension (OVD).Opposing the upper set-up is a resin base with

three vertical stops joined by a wire bent in asinusoidal manner. The stops must contact theupper teeth at the selected OVD.



Polyvinylsiloxane putty is added to the conventionalfitting surface and also to the buccal and lingual aspectsof the lower base which has been coated with therequisite adhesive, and placed in the patient's mouth.Following this, the upper try-in is inserted and the patient

asked to close to the OVD, swallow and carry out closedmouth exercises. These exercises provide an indicationof where inward-directed forces from the buccinatormuscles are equalled or 'neutralised' by outwardly-directed lingual forces i.e. the zone of minimal conflict



The disinfected functional impression and upper try-inare sent to the laboratory and plaster or laboratory-puttykeys made of the functional impression. Into these keys

wax is poured to give a functional form to the polishedsurfaces and occlusal form of the lower denture. Thetechnician is then required to fabricate the lower try-inand, subsequently the lower denture, to match thefunctional template - this will necessitate appropriatecustomising of the occlusal table width and possibly its

impression making for complete dentures

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