techniques of dental impression making/ dental education in india

Concepts and techniques of

impression makingINDIAN DENTAL ACADEMY

Leader in continuing dental education www.indiandentalacademy.com

Contents: Introduction Selection of impression material: Examination Selection of impression technique Selection of impression material

selection of impression tray Prelimnary impression Custom tray Border molding

Secondary impression impression for hypermobile ridges composite compression impression Impression for unemployed

mandibilar ridge denture space determination functional impressions review of literature conclusion references

www.indiandentalacademy.com

The journey towards successful denture fabrication begins with making accurate impressions. Therefore a good impression will help to insure that complete denture is stable, retentive and comfortable. So, the knowledge of different impression techniques are very important for us to achieve a good impression.


• Examination and conditioning of the patient and the mouth.

• Complete case history• Clinical examination• Identifying and correcting adverse conditions• Factors that complicate impression making• Old denture wearer.


• Selection of impression technique:1. Clinical findings.2. Experience of the dentist.3. Availability of materials.4. Patient related factors.

TimeUndercutsOld denture wearer


Selection of impression material:

• Prelimnary impression materials: impression compound alginate.• Final impression materials: Alginate Elastomers Zincoxide eugenol impression paste. Impression plaster Tissue conditioners waxes


• Modelling compound:• Easily correctable.• Can be border molded.• Not influenced by saliva• Can be used as impression tray.• Can be scraped easily to provide relief.• Viscous.• Cannot record fine details.• Compound sticks used for border molding.• Inelastic


• Alginate:• Elastic• Primary and final impression• Records good details• Not correctable but easily remade• Not dimensionally stable.• Donot adhere to tray.


• Elastomeric impression materials:• Elastic• Fine details• Hydrophobic• Adhesive required.• Available in different viscosities• Dimensionally stable.• Cannot be adjusted after set.• Prolonged setting time.


• Zinc oxide eugenol impression paste:• Rigid and inelastic.• Adheres to tray• Flows readily and records fine details.• Burning sensation and tissue irritation.• Dimensionally stable.• bulk of the impression is minimal.• Flaking or breaking during trimming.


• Tissue conditioners:• Functional impression.


• Impression plaster:• Minimal pressure technique.• Flows readily and records fine details.• Rigid• Wash impression• Absorbs saliva.• Dimensionally accurate with anti

expansion solution.


• Waxes:• Flow at mouth temperature.• Exert pressure• Fine details not recorded.• Corrections made.


Selection of impression trays:

• A device that is used to carry ,confine and control impression material while making an impression.

Stock trays.Custom trays

Perforated Non perforated.

Dentulousedentulous


Stock trays

• Caulk’s edentulous rimlock trays.• Mc Gowen’s winkler trays-useful

for flat lower ridge• STOKtrays-designed by Arthur Krol available in Square,round,tapering shapes


• Usually stock trays though supplied in different sizes ,donot fit the edentulous mouth with desired accuracy.

• To produce satisfactory impression and avoid variations in transmitted pressure, there must be a reasonably even thickness of impression material over the entire fitting surface and flanges of the tray almost reach the functional position of the sulci and frena and yet not displace them.

traywww.indiandentalacademy.co

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• Custom trays:• Close fitting or spaced trays

• Shellac• Acylic resin• Thermoformed polymer sheet


• Seating of the patient:maxillary mandibular


• Prelimnary impression: a negative likeliness made

for the purpose of diagnosis or the fabrication of the impression tray.


using alginateusing impression compound.For Primary impression high

viscosity material is preffered as it allows to compensate better for the shortcomings in the fit and extension of the stock tray.


• Selection of stock tray:• Tray extensions checked• Defficiencies corrected.• Lingual border of mandibular tray• maxillary tray for Deep palate


Primary Impression in alginate.

Tray should be adjusted by bending .

Selection of stock tray. . Position borders at hamular notches.

Lift the tray anteriorly, 3-5 mm space for impression material. www.indiandentalacademy.co

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Border of ray should be short of tissue reflection.

Adequate clearance in frenal areas.

Tray should be smoothened.


Deficient borders corrected by adding utility wax.

Tray extension in buccal space and tissue side of posterior border.


Location of hamular notches. Mark the vibrating line.

Some alginate to be placed in vestibule.

Alginate to be placed in deepest part of palate.www.indiandentalacademy.co

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Tray to be rotated into the mouth and seated first at the back of the mouth.

Upper lip elevated.

Tray is held in the mouth. Labial and buccal borders to be molded. www.indiandentalacademy.co

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Completed maxillary Primary Impression with rounded and molded peripheries.


Mandibular alginate impression.

Tray should cover retromolar pad.

metal edentulous tray. Retromolar pad should be identified


Bending and cutting the tray for adjustment.

Adding utility was to extend lingual border.


Patient told to do tongue movements.

Patient told to raise the tongue and tray is rotated in the mouth.

Gently mold the labial and buccal areas.www.indiandentalacademy.com

• Completed Mandibular Primary Impression.


Prelimnary impression with impression compound.

Compound placed in the tray.

Modelling compund. Softenend in water bath and kneaded.


Should cover mylohyoid ridge and external oblique ridge. Molded with fingers to ridge

form.

Gently warmed over a flame. Before insertion, tempering in warm water bath.www.indiandentalacademy.co

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Patient instructed for Tongue movements.

Tray should be gently seated and border moulding done.

Any short areas can be remolded.

Impression should cover all denture bearing area.


Common faults

Mandibular • Insufficient depth in

posterior lingual pouch:

• Insufficient depth in lingual,labial and

buccal sulci.Edge of the tray

showing through the impression.

An asymmetrical impression.

Maxillary:• Defficiency in the

midline of palatal vault.

• Excess material extending beyond posterior palatal border of the tray.

• Insufficient depth in one or more region of sulci

• Tray flange exposure.


Alginate wash impression technique:

• Resorbed mandibular ridges.

• Using impression compound has the benefit of pushing aside the floor of the mouth and cheeks which tend to become trapped by the edge of the tray.


Preperation for Secondary Impression

• Denture outline marked on the primary impression.

Completed preliminary casts.


Denture outline accentuated. Posterior border of tray marked.distal to denture border.

Wax added for relief. Special tray.

custom tray1mm from mucobuccal fold

2mm past the estimated border.

25mm from vestibule to the top of the handle,3-4mm thick


Checking for tray extensions:

• Visual examination• The diagnostic impression• Correction of overextension• Correction of underextension.

Impression materialtray


Borders should be beveled. Vibrating line marked.

Tray inserted in mouth. Overextensions trimmed.www.indiandentalacademy.co

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Tray should be short of 2 mm from base of sulcus Borders should be adjusted.

Extra clearence in frenal areas


External oblique ridge marked.

Tray outline marked 2-3 mm short of denture outline.

Custom tray fabricated.

Posterior border of tray should cover anterior half of the pad.


Pencil mark transferred to fitting surface.

Anterior border of the tray adjusted .

Tray border should be resting against the ridge.

Lingual border adjusted.www.indiandentalacademy.co

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Tissue stops

• Prevent seating of the tray too superiorly or posteriorly.

• Stabilize the tray• Uniform thickness of the material.• Molar or cuspid areas.• Palatal aspect of the ridge till mucobuccal fold.-

maxillary• Mucobuccal fold to the lingual floor –mandibular.• Ways to produce-inlab during construction of

special tray.• Chair side in mouth• Chair side on cast.


Finger rests:

• Keep fingers which stabilise the tray and support the impression.

• Absence of these result in inaccuracies resulting from fingers restricting border molding movements of soft tissue.


• Border molding: The shaping of the border

ares of an impression material by functional or manual manipulation of the size of the vestibule.


Materials:• Modelling compound sticks• Autopolymerizing acrylic resin• Metallic pastes• Elastomeric materials• Impression waxes


• Modelling compound sticks:• Advantages:• Soften easily but are quite hard

at mouth or room temperature so other areas of periphery can be molded with least possible distortion to the previously completed section.

• Corrections easily accomplished.www.indiandentalacademy.co

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• Isofunctional impression plastic sticks.

• Soften easily and have much longer working time .

• Softer at room temperature compared to compound sticks.


• Autopolymerizing acrylic resins:• Rimseal• Flexacryl.• Disadvantages:• Irritating• Strong odor• Heat produced polymerization.


• Premixed self curing soft resins:• Added to the periphery of an existing denture.• Material gradually polymerizes to a semisolid state in

few hours-functional border molding.• Advantages:• Less irritating• Easy to use.• Disadvantage:• Consistency changes each time the container is opened.• If denture border is grossly defficient the material will

slump as it cannot flow into the vestibule that is 6mm away from the border.


• Elastomeric materials:• Heavy body-border molding.• Advantage-wide range of working and

setting time.• Elastic recovery good.• Disadvantage:• Borders difficult to trim • Addition requires time consuming mix of

new materials.www.indiandentalacademy.co

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• Impregum-Smith etal.polyether based material.

• Simultaneous border molding.

Advantages:1.Can be trimmed with knife or burr2.Corrected with modelling compound or wax.

Disadvantages;1.Skill and great care required.Good prelimnary impressions are important as underextensions cannot be detected.


Impression waxes-adaptol Advantages • Simultaneous border

molding.• Donot irritate• Additions easy• Cannot injure oral

tissues if correct temperature is applied

Disadvantages • Distorts easily and

must be handled carefully

• Insertion not to be delayed

• Chilled wax subjected to flaking and breaking while trimming

• Not strong enough to correct underextensions.


• Segment by segment• One step:


• Simultaneous molding of all borders:

• Advantages:• Time saving.• Less discomfort to the patient.• Less effort for the dentist.


• Requirements:• Have sufficient body• Allow some preshaping of the borders• Setting time3-5minutes• Retain adequate flow when seating in the

mouth.• Allow finger placement of the material in to

defficient parts after seating of tray.• Not cause excessive displacement of tissues• Readily trimmed and carved so that excess

material can be carved and borders shaped before the final impression is made


The tray rotated in mouth and cheek gently massaged.

Compound molded with fingers.

Softened again with alcohol torch.

Tempered in warm water bath. www.indiandentalacademy.co

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Appropriate molding will have mat surface.

Compound added in buccal frenum area.


Recording the frenum. Molded buccal and labial borders.

Excess compound on tissue side trimmed.

Compound placed on posterior border.


Junction of tray and compound smoothened. Tray seated in mouth with firm

pressure.

Border molded maxillary custom tray.


Compound placed on posterior border

Compound added on buccal border

The tray gently seated in place.

The border should be smooth,round and convex.


Border molding continued in labial borders.

Border molding the lingual areas.www.indiandentalacademy.co

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Genial tubercles should be covered.

Border molded mandibular tray


TEST FOR RETENTION

mandibular • Protrude the tongue• Move tongue in

lateral direction• Roll tongue back to

touch palate.• Open the mouth.• Exerting vertical pull

on handle• Forward pressure on

distal aspect of the handle.

maxillary• Upward and outward

pressure in the incisor region.

• Upward and outward pressure in the premolar region.

• Pulling the upper lip downward.


Preparing and instructing patient• Preparing tray for impression: removing the relief waxRemoving spacer waxEscape holesReducing the bordersApplying adhesiveProtecting the mouthDrying the mouth.


The final impression:

• Mixing• Loading• Seating• Removing the impression• Inspecting• Correcting• remaking


Master impression with impression plaster.

• Custom tray with2.5mm spacer.• Tissue stops• Pheripheral tracing.• Impression.


The border molded compound tray technique:

• Advantage:• Same appointment.• Impression should be accurate

with proper border molding.• Even thickness of compound in the

tray must be maintained.


• Seperating the compound• Trimming the compound tray• Attaching handles• Border molding• Scraping the compound.• Making the final impression.


• Closed mouth technique:


• Using old dentures as an impression tray.


Patients wearing upper complete denture opposed by lower natural teeth.

Chronic complete denture wearers

Maxillary anterior ridge replaced by fibrous tissue; reduced support for dentures.

Patient complains of loose dentures

Impression techniques to avoid undue tissue displacement.

Impression technique for hypermobile ridges


• Mucocompression without displacement.

• Primary impression with alginate and special tray with relief in that region.

• Hobrik technique• mucostatic ,openwindow technique-

Zafrulla khan technique.www.indiandentalacademy.co

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• Mucocompression without displacement:• Two stage technique designed to compress the

flabby tissue so that the compression through out the whole of the maxillary denture bearing area is as uniform as possible.


mucostatic ,openwindow technique-Zafrulla khan

technique.

– Special tray with a window cut in the region of the displaceable tissue.


– Wash impression with ZOE paste.

Border molding with

low fusing compound.


– Tray re-inserted, impression plaster syringed over displaceable tissue.


Completed impression.www.indiandentalacademy.co

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• Composition compression technique:

• It is designed to take an impression of the tissues underpressure so that ,under the stresses of mastication ,the pressure transmitted through the entire mucosa to the underlying bone is approximately equal over its whole surface.


• Impression technique for unemployed mandibular ridge:

• Impression recorded mucostatic over the crest of the ridge and mucocompressive on the peripheral parts and prevents any load being placed on unemployed part of the ridge.

• Increased bulk and surface area of denture.


• Indicated Indicated – Unemployed lower alveolar ridge

unable to provide acceptable support against vertical loads and positive stability against lateral forces.www.indiandentalacademy.co

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• Method Method – Primary impression made with

alginate or putty elastomer.– Impression relieved over ridge crest

area and wash impression obtained with low viscosity material.www.indiandentalacademy.co

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• Customized special tray with 2mm spacer constructed.

• Spacer removed ; tray perforated in crestal region .www.indiandentalacademy.co

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• Low fusing compound used to obtain impression of primary cast with special tray.www.indiandentalacademy.co

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• Impression reduced in the region of buccal & lingual sulci ; border molding refined in patient’s mouth.

• Painful areas relieved.• Tray re-insertion should not

result in pain.• Impression completed with

light – bodied elastomer.www.indiandentalacademy.com

Denture spaceDenture space

The portion of the oral cavity that is or may be occupied by the maxillary and / or mandibular

denture (s). www.indiandentalacademy.com

Neutral ZoneNeutral Zone• That area in the mouth, where, during That area in the mouth, where, during

functions the functions the forcesforces of the tongue of the tongue

pressing pressing outwardoutward are are neutralizedneutralized by by the the forcesforces of the cheeks and lips of the cheeks and lips pressing pressing inwardinward..

• Hence a possible zone of equilibrium


• IndicationsIndications– Past denture looseness due

to powerful lower lip activity.

– Non-replacement of missing teeth leading to tongue / cheeks / lips partially occupying the usual denture space.

– Enlarged tongue, E.g. Down’s Syndrome.

– Abnormal anatomy, E.g. Hemimandiblectomy.

– Inability to wear a lower denture


• Generally done for lower• Materials used-Waxes,ZnOE,rubber base putty, self-cure acrylic,

impression compound,tissue conditioners.


• On accurate master casts, stabilized denture bases are constructed.

• Wire loops embedded over ridge crest for retention.

Denture space Denture space determination determination


• Low fusing compound rims attached to bases.

• Patient trained to perform a range of functional movements such as smiling, swallowing, speaking, etc.

• Compound rims softened and denture bases inserted ; functional movements carried out.


Recommended movementsRecommended movements

Smile Swallow ‘ooh’ ‘ah’


• Wash impression obtained with light – bodied elastomer brushed on compound rims.

• Functional movements repeated.www.indiandentalacademy.com

• Plaster matrices constructed around records.• Matrices guide in arranging & waxing teeth

& polished surfaces in optimum denture space.


• PrecautionsPrecautions– Stable record bases not interfering with muscle

activity.– Patient to be trained in molding procedure prior to

insertion of loaded tray.– Excessive volume of molded material to be avoided –

causes distortion of potential denture space.– External impression may be totally unlike the shape

of a “normal” denture, hence laboratory staff must be instructed about reproduction of the recorded contours.


Functional impressionsFunctional impressions

• IndicationsIndications– Reduced retentive forces ( Atrophic ridges )– High displacing forces ( Uncontrolled

muscle activity)• Peripheral form molded by peri–denture

musculature. • Existing denture utilized for the

procedure.www.indiandentalacademy.co

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• MethodMethod– Tissue conditioning materials usually

employed for the procedures.www.indiandentalacademy.co

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• Impression surface & periphery of existing denture reduced by 1.5-2mm to create space.

• Fitting surface of denture cleaned & dried. • Material mixed & spread over fitting surface.


• Denture seated in patients mouth; patient instructed to close in centric occlusion.

• Patient encourage to perform functional movements such as talking, swallowing, smiling, to obtain a functionally generated impression.


• Denture removed after 5 – 6 minutes ; Denture removed after 5 – 6 minutes ; inspected and surplus material trimmed.inspected and surplus material trimmed.


• Patient returns after few hours; Patient returns after few hours; impression inspected & cast poured.impression inspected & cast poured.


• Factors complicating impression making:

• Uncooperative patients• Excessive salivation.• Hyperactive gag reflex.


• Hyperactive gag reflex:• Causes:• Iatrogenic-physical and visual

stimuli.• Systemic problems• Psychological factors• Problems in existing prosthesis.


• Management:• Reduction of amount and duration

of stimuli.• Distraction maneuvers• Prosgressive desensitization:• Pharmacologic management.


• John Osborne1964:Two impression methods for mobile fibrous ridges.


• Tryde et al 1965 “Dynamic impression methods :”

• This is an impression procedure for patients with advanced mandibular residual ridge resorption.

• The advantages of dynamic impressions are • Avoidance of the dislocating effect of the

muscles on improperly formed denture borders. • Complete utilization of the possibilities of active

and passive tissue fixation of the denture www.indiandentalacademy.co

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• John D Walter 1973 “Composite impression procedures” :

• These procedures allow the use of more than one impression material according to local indications. Such techniques may also be employed for large impressions which are difficult or impossible to obtain with a single tray. Techniques:

• The edentulous fibrous ridge : • Impression technique for restricted access

to the oral cavity: www.indiandentalacademy.co

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Shanath Shetty,P.Venkat 2007:the selective pressure maxillary

impression :a review of techniques and presentation of alternate custom

tray design


• Conclusion: Though there are many techniques

and procedures available for a dentist to make an ideal impression, the procedures that follows should be based on sound biological principles, depending on patients oral and systemic conditions, by understanding the concept of function of oral tissues.


References:• Prosthetic treatment of the edentulous patient

–Basker and Davenport.4th edition.• Boucher’s prosthodontic treatment for

edentulous patient -9th edition.• Impression for complete dentures-Bernard

Levin • Fenn Clinical dental prosthetics-3rd edition.• Complete denture prosthodontics-3rd edition John .J.Sharry.• Syllabus of complete dentures-fourth edition –

Charles M Heartwell.• Essentials of complete denture prosthodontics-

second edition-Sheldon Winkler.


• John Osborne-Two impression methods for mobile fibrous ridges :British dental journal,november 3,1964,pg392-394

• Tryde et al “Dynamic impression methods :”journal of prosthetic dentistry,1965,volume15,issue 6,pg1023.

• John D Walter “Composite impression procedures” journal of prosthetic dentistry,1973,volume30,issue 4,pg385.

• Shanath Shetty,P.Venkat :the selective pressure maxillary impression :a review of techniques and presentation of alternate custom tray design.journal of indian prosthodontic society,march 2007,volume 7,issue 1.page8-12.

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