techniques of dental impression making/ dental education in india
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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
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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.
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• 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.
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• Selection of impression technique:1. Clinical findings.2. Experience of the dentist.3. Availability of materials.4. Patient related factors.
TimeUndercutsOld denture wearer
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Selection of impression material:
• Prelimnary impression materials: impression compound alginate.• Final impression materials: Alginate Elastomers Zincoxide eugenol impression paste. Impression plaster Tissue conditioners waxes
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• 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
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• Alginate:• Elastic• Primary and final impression• Records good details• Not correctable but easily remade• Not dimensionally stable.• Donot adhere to tray.
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• Elastomeric impression materials:• Elastic• Fine details• Hydrophobic• Adhesive required.• Available in different viscosities• Dimensionally stable.• Cannot be adjusted after set.• Prolonged setting time.
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• 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.
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• Tissue conditioners:• Functional impression.
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• Impression plaster:• Minimal pressure technique.• Flows readily and records fine details.• Rigid• Wash impression• Absorbs saliva.• Dimensionally accurate with anti
expansion solution.
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• Waxes:• Flow at mouth temperature.• Exert pressure• Fine details not recorded.• Corrections made.
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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
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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
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• 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
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• Seating of the patient:maxillary mandibular
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• Prelimnary impression: a negative likeliness made
for the purpose of diagnosis or the fabrication of the impression tray.
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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.
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• Selection of stock tray:• Tray extensions checked• Defficiencies corrected.• Lingual border of mandibular tray• maxillary tray for Deep palate
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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.
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Deficient borders corrected by adding utility wax.
Tray extension in buccal space and tissue side of posterior border.
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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.
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Mandibular alginate impression.
Tray should cover retromolar pad.
metal edentulous tray. Retromolar pad should be identified
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Bending and cutting the tray for adjustment.
Adding utility was to extend lingual border.
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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.
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Prelimnary impression with impression compound.
Compound placed in the tray.
Modelling compund. Softenend in water bath and kneaded.
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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.
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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.
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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.
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Preperation for Secondary Impression
• Denture outline marked on the primary impression.
Completed preliminary casts.
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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
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Checking for tray extensions:
• Visual examination• The diagnostic impression• Correction of overextension• Correction of underextension.
Impression materialtray
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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
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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.
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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.
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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.
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• Border molding: The shaping of the border
ares of an impression material by functional or manual manipulation of the size of the vestibule.
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Materials:• Modelling compound sticks• Autopolymerizing acrylic resin• Metallic pastes• Elastomeric materials• Impression waxes
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• 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.
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• Autopolymerizing acrylic resins:• Rimseal• Flexacryl.• Disadvantages:• Irritating• Strong odor• Heat produced polymerization.
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• 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.
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• 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.
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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.
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• Segment by segment• One step:
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• Simultaneous molding of all borders:
• Advantages:• Time saving.• Less discomfort to the patient.• Less effort for the dentist.
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• 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
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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.
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Recording the frenum. Molded buccal and labial borders.
Excess compound on tissue side trimmed.
Compound placed on posterior border.
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Junction of tray and compound smoothened. Tray seated in mouth with firm
pressure.
Border molded maxillary custom tray.
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Compound placed on posterior border
Compound added on buccal border
The tray gently seated in place.
The border should be smooth,round and convex.
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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
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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.
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Preparing and instructing patient• Preparing tray for impression: removing the relief waxRemoving spacer waxEscape holesReducing the bordersApplying adhesiveProtecting the mouthDrying the mouth.
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The final impression:
• Mixing• Loading• Seating• Removing the impression• Inspecting• Correcting• remaking
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Master impression with impression plaster.
• Custom tray with2.5mm spacer.• Tissue stops• Pheripheral tracing.• Impression.
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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.
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• Seperating the compound• Trimming the compound tray• Attaching handles• Border molding• Scraping the compound.• Making the final impression.
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• Closed mouth technique:
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• Using old dentures as an impression tray.
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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
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• 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.
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mucostatic ,openwindow technique-Zafrulla khan
technique.
– Special tray with a window cut in the region of the displaceable tissue.
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– Wash impression with ZOE paste.
Border molding with
low fusing compound.
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– Tray re-inserted, impression plaster syringed over displaceable tissue.
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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.
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• 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.
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• 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
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• 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
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• Generally done for lower• Materials used-Waxes,ZnOE,rubber base putty, self-cure acrylic,
impression compound,tissue conditioners.
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• On accurate master casts, stabilized denture bases are constructed.
• Wire loops embedded over ridge crest for retention.
Denture space Denture space determination determination
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• 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.
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Recommended movementsRecommended movements
Smile Swallow ‘ooh’ ‘ah’
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• 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.
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• 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.
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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.
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• 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.
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• Denture removed after 5 – 6 minutes ; Denture removed after 5 – 6 minutes ; inspected and surplus material trimmed.inspected and surplus material trimmed.
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• Patient returns after few hours; Patient returns after few hours; impression inspected & cast poured.impression inspected & cast poured.
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• Factors complicating impression making:
• Uncooperative patients• Excessive salivation.• Hyperactive gag reflex.
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• Hyperactive gag reflex:• Causes:• Iatrogenic-physical and visual
stimuli.• Systemic problems• Psychological factors• Problems in existing prosthesis.
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• Management:• Reduction of amount and duration
of stimuli.• Distraction maneuvers• Prosgressive desensitization:• Pharmacologic management.
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• John Osborne1964:Two impression methods for mobile fibrous ridges.
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• 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
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• 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.
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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.
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• 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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