IMPRESSION MATERIALSIMPRESSIONDefinition. : a dental impression is a negative replica of the tissues of the oral cavity.CLASSIFICATION OF IMPRESSION MATERIALS.I) Based on mode of setting & elasticity a) Rigid i) Reversible (thermoplastic) E.g. impression compound ii) Irreversible (thermosest) E.g. Zoe impression paste Impression plaster. b) elastic i) Hydrocolloid a) reversible E.g. Agar b) Irreversible E.g. Alginate ii) Elastomeric impression materials E.g. Polysulfides Polyether Addition silicones Condensation silicones II) Based on type of impression & area of use A) Dentulous i) Primary E.g. alginate ii) Secondary E.g. Elastomers Agar B) Edentulous i) Primary E.g. Impression compound Impression plaster Alginate
ii) Secondary e.g. ZOE impression paste Elastomers for CDIII) based on their use in dentistryA) edentulous For complete denture prosthesis e.g. Impression compound zoe impression paste alginate ElastomersB) dentulousi) FPDii) RPD E.g. Agar Alginate ElastomersIV) based on the amount of pressure applied i) Mucocompressive e.g. Impression compound ii) mucostatic e.g. Impression plasterV) based on the manipulation A) hand mixing i) kneading e.g. Impression compound – wet kneading putty consistency Elastomers ii) circular motion (with glass slab & spatula) eg.zoe impression paste polysulfide iii) vigorous mixing e.g. Alginate (figure of 8 motions) B) mechanical mixingVI) based on the tray used for impression A) stock tray i) types of tray a) rim locked perforated e.g. Alginate Elastomers b) water cooled e.g. Agar
c) plastic e.g. Orthodontic tray ii) based on type of perforation a) perforated e.g. Alginate Elastomers • putty wash impression b) non perforated e.g. Impression compoundB) special tray i) base plate wax e.g. Zoe impression paste medium body ii) resin.
IDEAL REQIUREMENTS OF IMPRESSION MATERIAL 1. have a pleasant taste & odor 2. not contain toxic or irritant constituents. 3. adequate shelf life for requirements of storage & distribution. 4. economically commensurate with the results obtained. 5. easy to use with the minimum of equipment. 6. setting characteristics that meet clinical requirements. 7. satisfactory consistency texture. 8. readily wets oral tissues 9. elastic properties with freedom from permanent deformation after strain. 10. adequate strength so it will not break or tear on removal from the mouth. 11. dimensional stability over temp. & humidity ranges normally found in clinical & lab. Procedures for a period long enough to permit the production of a cast or die. 12. compatibility with cast & die materials. 13. accuracy in clinical use. 14. readily disinfected without loss of accuracy. 15. no release of gas or other by products during the setting of the impression or cast & die materials.
IMPRESSION COMPOUNDIt is a rigid, reversible impression material which sets by physical change.Classification: Acc to ADA sp. No.3: Type I: low fusing compound – green stick compound. medium fusing compound – impression compound. Type II: high fusing compound – tray compound.Supplied as: 1. as sticks, cakes, & cones. 2. colors – green, brown, red.Applications: Type I: For making primary impressions. For individual tooth impression For peripheral tracing or border moulding. To check undercuts in inlay preparation. Type II: To make a special tray.Requirements of an ideal impression compound: 1. harden at or little above mouth temp. 2. be plastic at a temp. not injurious or harmful to oral tissues. 3. not containing irritating or toxic ingredients. 4. harden uniformly when cooled without distortion. 5. have a consistency when softened which will allow it to reproduce fine details. 6. be cohesive but not adhesive. 7. not undergo permanent deformation or fracture while withdrawing the impression from the mouth. 8. be dimensionally stable after removal from mouth & during storage. 9. exhibit a smooth glossy surface after flaming. 10. withstand trimming with sharp knife without flaking or chipping after hardening.Composition Rosin 30 Copal resin 30 Carbuna wax 10 Stearic acid 5 Talc 25 Coloring agent app.
Properties: Thermal propertiesi) thermal conductivity: has low thermal conductivity. Significance: • during softening of the material , the outside will soften first & inside last. So to ensure uniform softening the material should be kept immersed for a long time in water bath. • the layer adjacent to the mouth tissue swill remain soft. Therefore Its imp to cool the compound thoroughly before removing the impression.ii) Coefficient of linear expansion. (CTE) high CTE , 0.3% acceptable.iii) Flow high fusing compounds – < 2% at 37 .C & < 70-85 % at 45.C low fusing compounds - < 3% at 37 C & < 80-85% at 45 C impression compound to be manipulated at least 8 .C for adequate flow.iv) Glass transition temp • it is the temp. at which the material loses its hardness or brittleness on heating or forms a rigid mass. • App. 39.C • Material removed from the mouth after glass transition temp. is reached.v) Fusion Temp. • it’s the temp. at which the impression compound becomes plastic. • Its 43.5.Cvi) Dimensional stability. • Poor dimensional stability. • To prevent distortion pour the cast within 1 hr.vii) surface detail reproduction less because of high viscosity & low flow.Manipulation Sticks Small amt. softened over flame Cakes Softened in a thermostatically controlled water bath.
Precautions: o prolonged immersion in a water bath is not indicated o overheating In water makes the compound sticky & difficult to handle. o avoid incorporating water while kneading.Advantages: 1. cheap 2. reusable 3. does not produce irritation to the patient 4. impression can be remodified & resoftned again till an accurate impression is obtained. 5.Disadvantages: 1. difficult to record details accurately. 2. Soft tissues are compressed due to pressure applied while taking the impression. 3. Distortion. 4. Difficult to remove undercuts. 5. Does not have an pleasant taste. 6. Can be uncomfortable in patients because of the rigidity.
ZINC OXIDE EUGENOL PASTEIntroduction Produce a rigid impression. High degree of accuracy & good surface reproduction of details. Is irreversible, sets by chemical change.Classification: ADA specification No. 16 Type I or hard Type II or softAvailable as In paste form in 2 tubes Base paste (white) Accelerator/ reactor/catalyst paste (red)Composition: Base Paste: Zinc oxide 87 % Olive oil /linseed oil 13% Accelerator paste: Oil of cloves 12% Gum or polymerized rosin 50% Filler (silica type) : 20% Lanolin 3% Resinous balsam 10% Accelerator solution 5%Setting Reaction : ZnO + H2O Zn (OH)2 Zn (OH)2 + 2HE ZnE2+ 2 H2OManipulation: • Dispense equal length of the 2 pastes. Variation in length alters setting time. • Paper pad is used as a mixing slab & a stiff stainless steel spatula with an 8-10 cm blade should be used. • Mixing is done for 30-40 sec. until no color streaks in the mix & a uniform consistency is obtained.
Setting time: Initial setting time final setting time Type I 3-6 min. 10 min. Type II 3-6 min 15 min.Factors controlling setting time: Decreasing setting time: • Small amt. of zinc acetate • Accelerators • Small drop of water mixed in the paste containing eugenol • Increasing the mixing time. • Increasing accelerator paste while mixing. Increasing setting time: • Cooling the spatula & mixing slab • Addition of inert oils & waxes during mixing to reduce hardness like: olive oil. • Increasing base paste while mixing.Properties: i) consistency & flow thick consistency compress the tissues. ii) dimensional stability quite satisfactory, less than 0.1 % shrinkage occurs during hardening. iii) reproduction of details • good. Biologic considerations: Some patients experience burning sensation in the mouth due to eugenol & can also cause tissue irritation. This maybe overcome by using a non eugenol paste.
Uses: 1. cementing & insulating medium 2. temporary filling 3. root canal filling material 4. surgical pack in periodontal surgical procedures. 5. bite registration pastes 6. temporary relining material for dentures. 7. impression material for edentulous patients.Advantages: 1. Good dimensional stability 2. good detail reproduction 3. impression surface can be modified by adding in deficient areas 4. easy to manipulate 5. long working time, so border moulding can be done while relining dentures. Disadvantages 1. burning sensation due to eugenol. 2. messy to work with 3. sticks to skin & instruments , difficult to clean. 4. rigid so tends to break off in areas of undercuts.
ALGINATEIntroduction: • Comes from the term ‘algin’ coined by Scottish chemist. • It is an elastic irreversible hydrocolloid because its sets by chemical reaction.Types: Type I fast setting : 1-2 min. Type II normal setting : 2-4.5 min.Available as : 1. bulk powder 2. preweighed packages 3. color changes alginates: violet during mixing, pink when ready to be seated white when setComposition: Ester salts of alginic acid(sodium or potassium or triethanolamine alginate) 15% Calcium sulphate (reactor) 16% Zinc oxide 4% Potassium titanium fluoride 3% Diatomaceous earth 60% Sodium phosphate 2% Coloring & flavoring agents traces Setting reaction: 2 Na3PO4 + 3 CaSO4 Ca3(PO4)2 + 3Na2SO4 Setting Time: Type I (fast set) : 1-2min Type II (normal) : 2-4.5 min. Control Of gelation time: • Under control by manufacturers: o By the amt of retarder added during manufacturing. • Under Control of clinicians o by altering the W:P ratio
o by changing the mixing time. o by altering the temp. of water o increase in temp. decreases gelation time & vice versa. o Premature gelation causes distortion in the impression & it is rendered useless. o Prolonged gelation time is tedious for both pt. & the dentist.Manipulation : aerate the powder by inverting the can several times. This ensures uniformdistribution of the filler before mixing. The top of the can should be taken offcarefully to prevent the silica particles from being inhaled. The proper W/P ratioas pacified by the manufacturer should be used measured quantity of water andpowder are added in the rubber bowl & mixing is started, with a stirring motion towet the powder with water. Once its moistened rapid spatulation by swiping orstropping against the side of the bowl is done. A vigorous figure eight motion isused. Mixing time: Working time For fast set alginate 45 sec. 1 ¼ min. For normal set alginate 60 sec. 2 minProperties: i) taste & odor • pleasant ii) flexibility • lower w/p ratio results in lower flexibility. iii) elasticity & elastic recovery highly elastic, permanent deformation less if the impression is removed from the mouth quickly. iv) reproduction of the surface detail • lower than agar. v) strength • compressive strength : 5000-8000 gm/cm2 • tear strength : 350-700 gm/cm2 vi) dimensional stability. Poor
Biologic properties: • Silica present in the dust which rises from the can after fluffing alginate powder is a health hazard. • Dustless alginate is also present in the market which contain glycol.Uses: 1. for making primary impression of edentulous patients with undercut ridges. 2. for preliminary impressions for complete dentures. 3. for making impressions for dentulous pts. For construction of study models & temporary removable prosthesis. 4. for making impression for orthodontic study models. 5. used for making impressions for the preparation of mouth protectors for athletes. 6. used as duplicating material.Advantages: 1. ease of mixing & manipulation. 2. no elaborate equipment required. 3. material is elastic & comes out easily from undercuts. 4. economical 5. impression can be removed easily & has pleasant taste & odor, so comfortable for the patient. 6.Disadvantages: 1. can’t be electroplated. 2. poor tear strength especially in thin sections. 3. dimensional stability is poor. 4. distortion may occur if tray is shifted during setting. 5. cant be refined.Types of failures: 1. defects: a. improper mixing b. prolonged mixing c. undue gelation d. w/p ratio is too low. 2. tearing: a. inadequate bulk b. moisture contamination c. premature removal from mouth d. prolonged mixing
3. external bubbles: a. undue gelation preventing flow b. air incorporated during mixing4. irregularly shaped voids: a. moisture5. rough or chalky stone model: a. inadequate cleaning of the impression b. excess water left in impression c. premature removal of model.6. distortion: a. impression not poured immediately
ELASTOMERIC IMPRESSION MATERIALS • basically synthetic rubbers. • Initially they were called rubber impression materials. • Currently known as non aqueous elastomeric dental impression materials. Classification: ( Based on chemical composition) 1. polyether 2. polysulfide 3. silicones. Addition Condensation .POLYSULFIDE ELASTOMERIC IMPRESSION MATERIAL • First elastomeric impression material to be introduced. • also known as mercaptan / thymolSupplied as Base paste (white) Accelerator (brown/grey)Available in 3 viscosities: Light bodied Medium bodied Heavy bodiedComposition: Base paste: Liquid polysulfide polymer 80-85% Inert fillers (titanium oxide, zinc sulfate, silica) 16-18% Reactor Paste: Lead dioxide 60-69% Dibutyl phthalate 30-35% Sulfur 3% Other substances (like magnesium stearate) 2% and deodorants Setting reaction: HS - R - SH ----------PbO2 + S----> HS - R- S – S – R - SH + H2O Properties:
1) setting time – 5-8 min. • colder climate increases setting time. • Drop of water accelerates the reaction. 2) excellent detail reproduction. 3) dimensional stability • curing shrinkage – 0.45% due to continued reaction. • Shrinkage due to loss of byproduct. 4) permanent deformation – 3-5% • highest amongst elastomers. 5) high tear strength – 7000gm/cm2 6) good flexibility of 7%, allows elastic recovery of the material. 7) hydrophobic- tissue should be thoroughly dried before making the impression. 8) can be electroplated with copper. Advantages: 1. long working time. 2. proven accuracy 3. high tear resistance. 4. inexpensive to use 5. less hydrophobic 6. longer shelf life. Disadvantages: 1. must be poured with dental stone immediately. 2. potential for significant distortion. 3. odor is offensive. 4. messy & stains clothes. 5. second pour is less accurate.CONDENSATION SILICONES • It was the first type of silicone impression material. • Also known as conventional silicones. • Setting occurs in room temp , so called as RTV silicones. Composition: Base paste 1. Polydimethyl siloxane (hydroxy terminated) 2.Colloidal silica or micro sized metal oxide filler putty viscosity – 60-70% medium viscosity – 35-75 % low viscosity – 5-15% 3. color pigments accelerator paste 1. alkyl silicate (ortho ethyl silicate)
2. stannous octate 3. inert filler.Setting reaction: Dimethyl orthoethyl silicone ethyl + ----STANNOUS OCTATE----- > + Siloxane silicate rubber alcohol Properties: 1. Setting time – 8-9 min. Mixing time – 45 sec. 2. excellent detail reproduction 3. dimensional stability – high curing shrinkage. 4. permanent deformation – 1-3 % 5. tear strength – 3000gm/cm 6. stffer & harder than polysulfide material. 7. hydrophobic 8. can be electroplated with silver & copper. 9. shelf life - 2 yrs.Advantages: 1. adequate working & setting timer. 2. pleasant odor & no staining. 3. adequate tear strength 4. better elastic properties on removal. 5. less distortion on removal.Disadvantages: 1. adequate accuracy if poured immediately. 2. poor dimensional stability. 3. potential for significant distortion. 4. putty-wash method is technique sensitive. 5. slightly more expensive.ADITION SILICONES • Introduced after condensation silicones • Have better properties than condensation silicones. • Also known as poly vinyl siloxane.
Composition: Base paste 1) poly(methyl hydrogen siloxane) 2) other siloxane prepolymers 3) fillers • putty viscosity – 60-70 % • medium viscosity – 35-75 % • low viscosity – 5-15% accelerator paste 1. divnyl polysiloxane 2. inert oils & fillers 3. platinum salt 4. palladium 5. retarders 6. fillers.Setting reaction: Poly vinyl siloxane + silane siloxane -----Pt ,Salt -----> silicone rubberProperties: 1. setting time: - 5.9 min. mixing time - 45 sec 2. excellent surface detail reproduction. 3. highest dimensional stability amongst elastomers 4. lowest curing shrinkage – 0.17 % 5. good tear strength – 3000gm/cm 6. extremely hydrophobic 7. low flexibility 8. electroplated with copper & silver. 9. shelf life - 1-2 yrs.Advantages: 1. short setting time 2. adequate tear strength 3. extremely high accuracy 4. minimal distortion on removal 5. dimensionally stable even after 1 week 6. if hydrophilic, good compatibility with gypsum.Disadvantages: 1. hydrogen gas may cause dimensional change.
2. hydrophobic & hence requires a very dry field. 3. expensive.POLYETHER IMPRESION MATERIAL • Introduced in Germany in late 1960’s • 1st Elastomers to be developed as impression material.Composition: Base Paste: 1. imine terminated polymer(polyether) 2. colloidal silica 3. glycol ether or phthalate Accelerator Paste: 1. alkyl aromatic sulfonate 2. colloidal silica 3. plasticizers ( glycoether )Setting Reaction: polyether + sulfonic ester ---- cross linked rubber.Properties: 1. setting time: 8.3 min. mixing time – 30 sec. 2. dimensional stability is good. 3. decreased flexibility – 3% 4. hydrophilic 5. activator paste can produce allergy if handled frequently. 6. tear strength – 3000gm/cm 7. shelf life > 2 yrs.Advantages: 1. short working & setting time 2. proven accuracy 3. adequate tear strength 4. hydrophilic 5. long shelf life 6. less distortion on removal 7. good dimensional stability.Disadvantages: 1. stiffness requires blocking of undercuts 2. slightly more expensive
3. multiple casts can’t be poured due to stiffness of the material.Manipulation of Elastomers: Manipulation of two paste systems • equal length of base & activator paste are taken. • Paper pad with graduations is provided by manufacturer. • Pastes are mixed till no streaks are present. • Tray coated with tray adhesive. Uniform two-layer coat is applied & allowed to dry. • The mixed material can either be taken in a syringe or loaded directly in the tray.Manipulation of Putty Material: • Putty dispenser is supplied with scoops for dispensing. • Activator may be a liquid or paste. • Putty material is taken in a scoop & the activator is added. Usually the activator is of different color. • It is kneaded till no streaks are present. • Putty material is used with stock trays.
IMPRESSION TECHNIQUESImpression can be classified as :1. depending on the theories of impression making: a. mucostatic/passive impression. b. Mucocompressive/functional impression c. Selective pressure impression.2. depending on the technique: a. open mouth technique b. closed- mouth technique3. hand manipulation for functional movements: a. border moulding4. depending of the type of tray: a. stock tray impression b. custom tray impression5. depending on the purpose of the impression : a. diagnostic impression b. primary impression c. secondary impression6. depending on the material used: a. reversible hydrocolloid impression b. irreversible hydrocolloid impression c. modeling plastic impression d. plaster impression e. wax impression f. silicone impression g. Thiokol rubber impression.
MUCOSTATIC / PASSIVE IMPRESSION • Proposed by Richardson • Impression is made with the oral mucous membrane & the jaws in a normal relaxed condition. • Border moulding not done. • Impression material – impression plaster • Retention due to interfacial surface tension. • Taken with an oversized tray. • Denture closely adapted to the denture bearing area but has poor peripheral seal. Therefore these dentures have good stability but poor retention.MUCOCOMPRESSIVE/ IMPRESSION • Given by Carole Jones • Records oral tissues in a functional & displaced form. • Imp. Material – imp. Compound , waxes , soft liners. • Dentures don’t get displaced due to tissue rebound at rest. • During function, the constant pressure exerted onto soft tissues limit the blood circulation leading to residual ridge resorption.SELECTIVE PRESSURE TECHNIQUE • Given by Boucher. • Impression made to extend over as much denture bearing area as possible without interfering with the limiting str. At function at rest. • Forces acting on the denture are confined to the stress bearing areas. • Relief is given by using wax in the special tray, which is removed before impression making.FOR ELASTOMERS: PUTTY WASH/RELINE TECHNIQUE • Combination of putty & light body impression are used. • Putty material forms the bulk & supports light bodied material • Light bodied material records fine details. o Single mix technique o Multiple mix technique o Triple tray/ double arch technique
Single mix technique Equal lengths of base paste & accelerator paste are taken. Both putty & light bodied material are simultaneously mixed. The syringe material is then injected into prepared area of impression, tray seated over it, material allowed to set. Multiple Mix Technique Material loaded on the stock tray & primary impression taken with putty material. Relief with cellophane spacer given. Light bodied material mixed & filled in the space provided in the impression, syringe material is injected into the impression area. Putty impression is then seated over it & held till it sets. Triple tray technique Uses a special tray having a plastic frame with a thin mesh work. Material loaded into either side of the tray. Patient asked to occlude into the tray between the arches. Impression records the teeth in both impression arches.
IMPRESSION PROCEDURES.RECORDING THE PRIMARY IMPRESSION. TRAY SELECTION o Known as stock trays. o Can be metal / plastic, perforated or non perforated. o Available in standard sizes. o There should be 2-3 mm clearance between the stock tray & the ridge & should have 5-6 mm clearance for impression compound. o Tray should be extend over the tuberosity & the hamular notch. o If try too large – it will distort the tissue in the borders of the impression & push the tissues away from the bone. o If tray is too small – then modeling wax should be added along the posterior border of the tray. o The tray material should not react with the impression material & should not distort. PRIMARY IMPRESSION MAKING IN MAXILLARY ARCH. o Objective – to obtain a preliminary impression that is slightly overextended along the borders. o Imp material with high viscosity preferred o Imp. Compound softened in water bath at 140.F, then kneaded. o Kneaded material rolled into a tray & rolled into a ball & placed on the tray. Using thumb the operator should spread & adapt the material allover the tray so that it app. To the ridge contour. o If alginate used then small amt. of material is placed in the post. Part of the palate & tuberosities before making the imp. o Pt. asked to sit upright & open the mouth halfway. Operator should position himself towards the side & rear of the patient. o Tray centered over the upper residual ridge by using labial frenum as a centering guide. o After proper positioning the tray is seated over the ridge by applying pressure in the first molar region, until it touches the posterior palatal seal. o Tray stabilized with a finger placed in its center
o Borders are refined by asking the pt. to suck down into the tray, move the mandible side to side & then open wide. This record the labial & buccal vestibules & influence of coronoid process on the shape of the buccal vestibules. o Once the material has set, the cheeks & upper lip are lifted away from the borders to allow for air entry. Tray is then removed from the mouth in one motion & inspected for any deficiency. o Borders of the custom tray can be marked by Marking the peripheral outline on the impression. Outlining the cast o Cast is observed & then poured with dental plaster. PRIMARY IMPRESSION MAKING IN MANDIBULAR ARCH o Choice of material – impression compound / high viscosity alginate. o Astringent mouthwash given to reduce the viscosity of the saliva. o Impression material manipulated & loaded into the tray, if alginate used then small quantity placed on the retromolar pads. o Tray should be rotated within the patients mouth in a horizontal plane until it is in the center of the residual ridge. The pt. should be asked to raise the tongue to fit into the tongue space of the impression tray. o Tray is seated gently using alternate pressure on the molar regions of either side,. o Then passive movements of peripheral musculature is done. o Once the imp. Material sets, the lips & cheek are retracted & the imp. Is removed in a single snap from the patients mouth. o Imp. Should be Checked for any errors like voids etc.
RECORDING THE SECONDARY IMPRESSION SECONDARY IMPRESSION MAKING IN MAXILLARY ARCH It includes: • Border Moulding • Tray preparation after border moulding • Making the wash impression • Recording the posterior palatal seal • Checking for errors in the posterior palatal seal. Border Moulding Two techniques for border moulding: 1. single step or simultaneous border moulding. 2. incremental or sectional border moulding. Single step border moulding Polyether is the material of choice. Done in single step. Incremental border moulding Greenstick compound is the material of choice. Spacer is removed just before impression making. Clinical procedure: o greenstick compound is softened over flame & added along portion of the tray, material should be tempered with warm water before placing intraorally. o Order: Labial vestibule -> buccal vestibule -> posterior palatal seal. o Passive Movements are made. o After border moulding , the moulded section is immersed in cold water. o Then the procedure is repeated for another section.
Tray preparation after border moulding. o The wax spacer is removed to provide space for the impression material. o 0.5-1 mm of the tracing material is removed from the outer, inner & top surfaces of the border. o The material over the posterior palatal seal is not removed. o Green stick compound removed using a scalpel. o The thickness of the flanges & the border should be 2.5-3 mm. o Holes are drilled into the impression tray to allow escapement of the impression material.Making the Master / wash impression. o Material of choice – zinc oxide eugenol impression paste. o Impression material is manipulated & loaded onto the tray. The patient made to sit in an upright position. Operator stands towards the rear or the side of the patient. o Tray is placed in the patients mouth using the labial notch as a guide. o Tray is seated into position by applying alternating pressures on the right & left molar regions using index fingers. o Tray is maintained in this position by placing a finger in the palatal region of the tray, immediately anterior to the posterior palatal seal. o Passive movements are made. o After material has set, the tray is removed in a single jerk. o Impression inspected for deficiencies & voids & is repeated if necessary.Recording the posterior palatal seal. Methods used to record it are: 1. conventional approach 2. fluid wax technique. 3. arbitrary scraping of the master cast. 4. extended palatal technique. Conventional approach : o done after the wash impression is made & master cast is poured.
o Trial base is fabricated using shellac base plate. o The patient is asked to sit in an upright position & asked to rinse his mouth. o T burnisher is used to locate the hamular notch. the full extent of the hamular notch is marked with an inedible pencil. o Posterior vibrating line is marked using a inedible pencil by asking the patient to say “ah” in a non vigorous manner. o Line marked in the hamular notch is connected with the posterior vibrating line using an inedible pencil. o Trial base inserted into the patient’s mouth so that the inedible markings are transferred to the trial base. o Trial base is seated on the master cast to transfer the markings marked in the patient’s mouth to the cast. o Trial base is trimmed till the posterior border. o Anterior vibrating line marked in the patient’s mouth with an inedible pencil & while recording it the patient should perform the valsalva maneuver. o The area between the anterior & posterior vibrating line is scraped in the master cast to a depth of 1-1.5 mm on either side of the mid palatine raphe. o The posterior border of the posterior seal should be tapered so that it blends with the palatal tissues. SECONDARY IMPRESSION MAKING IN MANDIBULAR ARCH It includes: Border moulding Tray preparation after border moulding Making the wash / master impression. Border moulding o Done by two techniques: Single step border moulding Incremental border moulding o Same procedure is carried out in both techniques. o Anterior portion is moulded before the posterior portion. o Labial & buccal flange is moulded first followed by the lingual flange.
Recording the Labial & buccal flange • Labial portion moulded by moving the lip outward, upward & inward. • Buccal frenum is recorded by moving the cheek outward , upward , backward & forward, • Distobuccal sulcus is recorded by retracting the cheek & moving it upward & inward. Recording the lingual flange. • Anterior lingual flange is recorded by asking the patient to protrude his tongue out & touch the anterior part of the palate. Recording the retromolar pad • To record the distal end of the tray the patient is asked to open his mouth wide • After recording the distal end the impression is verified, if a notch is produced in the posteromedial end of the tray it indicates that the tray is overextended up to the pterygomandibular raphe.Tray preparation after border moulding o Procedure similar to maxillary impression. o Escape holes placed 10 mm apart in the alveolar ridge & retromolar pad.Making the final / master / wash impression. o Tray placement should be practiced before making the final impression. o Dry gauze should be placed in the floor of the mouth to remove the saliva & removed before making the impression. o The impression material is manipulated & loaded onto th tray. o The tray is rotated in a horizontal plane & inserted into the mouth using the anterior handle. o Tray is seated completely by applying alternating pressure over the posterior handles. o After the material is set the impression is removed & examined for any defects.
REFERENCES: Basic dental materials by John J. Manappallil Textbook of dental materials by Sharmila Hussain Boucher’s Prosthodontics Treatment for Edentulous Treatment, 9th ed. Textbook of Prosthodontics of Deepak Nallaswamy.