IMPRESSION PROCEDURES BY - PowerPoint Presentation

1. IMPRESSION PROCEDURES BY:SYED MUKHTAR-UN-NISAR ANDRABIASSISTANT PROFESSOR CONSERVATIVE DENTISTRY & ENDODONTICS

2. Introduction

3. An impression is an imprint or negative likeness. A good impression is invaluable in the fabrication of a functionally and esthetically pleasing prosthesis The indirect technique for fabricating inlays, crowns, fixed partial denture has been a boon to the practice of dentistry

4. The materials currently available easily fulfill all the requirements that the practitioner may place on his impression material. However, the fact that these requirements are met collectively and not by any single impression material is the rub and is the reason why the dentist must be knowledgeable about the properties of impression materials and impression techniques.

5. DefinitionAn impression is an “imprint” or negative likeness of the teeth and/or edentulous areas, made in plastic material which becomes hardened or set while in contact with the tissue -Heartwell 1992

6. An impression is the perpetual preservation of what already exists and not the meticulous replacement of what is missing - M.M.Devan 1995

7. HISTORY

8. Philip Pfaff-1756First described taking impression with softened waxChristophe Francois Delabarre-1820Introduced the metal impression trayChapin Haris-1853First used Plaster of Paris for making impressions.Charles Stent-1857Introduced the first impression compound

9. Sears-1937First used agar hydrocolloids for recording crown impressions.United States-1945Introduced alginate during World War II.SL Pearson-1955Developed synthetic rubber base impression materials

10. Polysulfide- Late 1950’S First developed as an industrial sealant.Condensation Silicone- Early 1960’sAddition Silicone-1970’sPolyether- Late 1970’s Polyether Urethane Dimethacrylate - Late 1980’s

11. IDEAL REQUIREMENTS TO OBTAIN AN ACCURATE IMPRESSION

12. Fluid enough to adapt to the oral tissuesViscous enough to be contained in the traySetting time - less than 7 minutesAdequate tear resistanceDimensionally stableBiocompatible Cost effective

13. Classification

14. I. Based on the degree of tissue compression Mucostatic Ex: Impression plaster ZOE impression paste Mucocompressive Ex: Elastomers

15. II. By setting mechanismA. Chemical reaction (irreversible)By elasticity and use Inelastic or rigid Elastic Materials Use Material Use 1.Plaster of Paris 2.Zinc-oxide eugenol Edentulous ridge Interocclusal records 1. Alginate 2. Non-aqueous elastomers Polysulfide Polyether Condensation silicone - Addition silicone Teeth and soft tissue B. Physical reaction (reversible)3.ImpressionCompoundPreliminary impression 3.Agar hydrocolloid Teeth and soft tissue

16. III. Based on the chemical composition

17. MATERIALADVANTAGESDISADVANTAGESALGINATERapid set, HydrophilicLow cost, No custom tray requiredPoor accuracy & surface details, Low tear résistanceLow stability.AGAR-AGARLong working timeHydrophilicLow tear résistanceLow stabilityEquipment requiredPOLYSULFIDEHigh tear resistanceLong setting timeUnpleasant odor, StickyADDITION SILICONEDimensional stability, excellent accuracy, Auto mix availableHydrophobic, release of hydrogen gas, Most expensiveCONDENSATION SILICONEFair accuracy, short setting timeRelease of Alcohol byproduct, Hydrophobic.POLYETHERDimensionally stable, accurate, Auto mix availableRigid, imbibitionshort working time,

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19. IMPRESSION TECHNIQUES

20. Shavell coined the phrase ‘biological impressions’ to signify impressions that capture, with fidelity, healthy tissues in their natural habitat.Most indirect dental restorations are made with only an impression as the unifying element linking the three protagonists, ceramist, patient and dentist (or CPD). Biological Impressions

21. Biological ImpressionsWhether an impression is for a laminate, inlay, crown, bridge, denture or implant, the objective is to reproduce accurately a facsimile of anatomical structures as a morphological platform for fabricating the proposed restoration. This implies that the tissues are neither escharotic nor necrotic.Two types of biological impressions are required: dental and gingival.dental biological impression replicates abutment teeth following preparation.gingival biological impression records the periodontium in a non-deflected state.

22. ClassificationBased on the position of the mouthOpen mouth techniqueClosed mouth technique (functional impression )Based on the pressure applied Positive pressureNegative pressureSelective pressure technique

23. Based on the mixing techniqueDouble mixHeavy-light body techniquePutty wash techniqueOne stage – simultaneousTwo stage – relief channel - 2mm spacer techniqueSingle mix or monophase technique According to the tray used Custom tray impressions Stock tray impressions

24. Double mix technique (Multiple mix technique) The light body material is injected from the filled syringe within and around the tooth preparationThe tray filled with heavy body material is inserted in the mouth and seated over the syringe material. The two materials bond together on settingMost commonly used with custom tray

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26. Advantages Over comes the polymerization shrinkage of the light body materialMargins duplicated in light body Disadvantages Use of custom tray An assistant required for mixing the material - tray/syringe simultaneously Margins duplicated in heavy body in case of excess pressure

27. Single mix technique (Single viscosity technique, monophase technique) Medium viscosity of polyether and addition silicones used in a stock tray Only one mix is made, part of the material placed in the tray and another portion placed in the syringe for injection in the cavity preparation or on prepared teethSuccess of this technique depends on the pseudoplastic behavior of these two materials

28. Advantages Reduced wastage of the materialLess time consumptionAvoids the time involved in fabrication of custom trayDisadvantages Relatively high viscosity and reduced flow of the monophase materials, makes their injection onto the preparation more difficult to control -increased incidence of surface voids - Stephen M. Dunne et al 1998

29. PUTTY – WASH TECHNIQUE

30. Putty wash simultaneously technique (One stage)Light body material syringed on to the preparation while the putty material loaded in a stock tray is simultaneously inserted into the mouth

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32. Advantages Reduced chair side time Disadvantages Absolute lack of control in the bulk of wash materialBy mixing putty, syringe material simultaneously, setting distortion of putty included in over all distortion of impression - Chee and Donovan 1992Possibility of margins duplicated in putty mediumTendency of bubbles to be formed and occluded in the set impression

33. Putty wash relief channel technique Pre-operative putty impression is made intra orallyIn the area where the teeth are to be prepared impression material is removed or channels prepared using putty cutter instrument The impression is then relined with low viscosity material

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35. Advantages Impression can be captured with the wash materialsDisadvantages To confine the wash material to area of relieved impressionIf entire area is washed - creates hydraulic displacement of putty impression resulting in smaller dies - Donovan TE 2004

36. Putty wash 2mm spacer technique2 mm thickness wax spacer is prepared on a diagnostic cast, occlusal stops are provided on non-functional cuspsA putty impression is made with a stock tray resulting in a putty custom tray with 2mm space for the wash materialPutty custom tray is then washed with light body material

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38. Advantages Wash stage carried out after the putty has set and contractedControlled wash bulk compensates for this contraction with minimal dimensional changeDisadvantages Extra chair side time Extra material

39. Copper band technique This technique was used to salvage an impression of multiple preparations when there were only vague margins on one or two preparations that were not adequately replicated in the impressionCopper tube is prepared that extends 1 mm beyond the finish line

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41. Top one - third of copper tube filled with impression compound and sealed on the preparation2 mm of compound was removed from the impressed occlusal surface for the rubber baseDisadvantages Can cause damage to the attachment apparatus Time consuming

42. DUAL ARCH IMPRESSION TECHNIQUE (TRIPLE TRAY TECHNIQUE ,CLOSED MOUTH TECHNIQUE)This technique captures the prepared teeth, the opposing arch and the occlusal articulation in maximum intercuspation (MIP) simultaneously

43. Indications Used with a maximum of two prepared teethUnprepared stops anterior and posterior to the prepared teeth should be presentUsed only with patients that have existing anterior guidance Must be able to close completely in maximum intercuspation position with the impression tray in place

44. Contraindications Presence of third molars Rapidly ascending ramus Excess soft tissue distal to the molars

45. Advantages Accurate recording of the MIPEliminates any mandibular flexure that might be associated with openingDisadvantages Complicated laboratory procedure

46. Segmental impression technique Impressions of multiple prepared teeth due to inherent limits in working time and difficulties maintaining moisture controlArch is broken down into segments of two prepared teethCustom tray prepared for each segment with 1mm of wax relief, trays should extend 3 mm past the gingival margin

47. Low viscosity material is loaded into the syringe as well as the segmental tray, and then an impression madeProcedure repeated with each segmentFinally an over impression is made using a stock trayUses When moisture control is difficult in specific patientsWhen making simultaneously impressions of implants and prepared teeth

48. Indirect dowel, coresIndicated when multiple dowel cores are required or when radicular attachments are to be usedA 25 gauge local anaesthetic needles - vent to allow air to escape as the impression material is injected into the canal spaceNeedle is gradually removed while the low viscosity materials is injected into the canalPlastic impression dowel coated with adhesive is inserted into the canalProcedure is repeated with multiple dowels and finally an over impression is made

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50. Pin-retained restorations Elastomers are strong enough to reproduce a pinhole without tearing However to ovoid bubblesCement tube : the tube filled with impression material is squeezed into each pinhole, making sure no air is trapped by inserting and removing an explorer into the materialLentulospirals : rotated slowly along the sides of the pin-holeReversible hydrocolloid - special nylon bristles are used to register the pin hole

51. Electroplating It is the electro deposition of metals (silver, copper) on the surface of the impression to improve the abrasion resistance of gypsumAdvantages Increased hardness of the dieExcellent abrasion resistance Die is so strong that wax patterns & gold castings can be burnished with little distortion or damage to the die DisadvantagesToxicity of cyanide baths Time required to prepare the die Expense of labor and materials Limited control of die accuracy

52. Gingival displacement

53. Indirect restorations frequently have cervical margins that are intentionally placed in the gingival sulcus for esthetic or functional reasonsProcedure used to facilitate effective impression making with intra crevicular margins – “gingival displacement ”

54. Goal - reversibly displace the gingival tissue in a lateral direction, so that a bulk of low-viscosity impression material can be introduced into the widened sulcus and capture the marginal detailA critical sulcular width of 0.2 mm is required for maximum accuracy of the impression, and to improve the tear strength of the material

55. One of the prime requisites to successful tissue management is to begin the restorative procedure only after the gingival tissues are deemed healthy This is not always possible in the clinical setting, but nonetheless it should be a constant goal

56. According to Bensen Bomberg (1986) gingival tissue can be displaced laterally or vertically Lateral retraction: It displaces the tissues so that an adequate bulk of impression material can be interfaced with the prepared tooth (gingival displacement) Vertical retraction : Exposes the uncut portion of the tooth apical to the finish line

57. Mechanical Chemical Surgical Combination of the three Techniques for gingival displacement

58. Majority clinicians use a combination of mechanical - chemical displacement , using retraction cords along with specific hemostatic medicaments3 main variations of mechanical chemical method Single cord technique Double cord technique Infusion method of gingival displacement

59. Retraction cords designs twisted cord knitted cord braided cordThe key to effective displacement - largest cord that can be atraumatically placed in the sulcus

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61. Aluminium potassium sulfate Aluminium sulfate Aluminium chloride Epinephrine Use of epinephrine as a gingival displacement medicament has the potential to cause systemic side effects, if used inappropriatelyHaemostatic medicaments

62. Indicated - impressions of one or three prepared teeth with healthy gingival tissues The largest diameter braided or knitted cord that fits in the sulcus is selectedSoaked in the medicament of choice Excess is blotted from the soaked cord with sterile cotton sponge Single cord technique

63. The cord is packed in a counter clockwise direction - starting from the inter proximal area Instrument should be angulated towards the cord already packed, to avoid it being displacedThe cord needs 8-10 minutes to effect adequate lateral displacementThe cords should then be soaked in water to allow it to be easily removed from the sulcus

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65. Indicated - impressions of multiple prepared teeth - tissue health is compromised and it is impossible to delay the procedure. A small diameter cord with no medicament is first placed in the depth of the sulcusA larger diameter cord with the medicament is placed above the small diameter cordAfter waiting for 8-10 minutes, the larger diameter cord is soaked in water and removed The small diameter cord is left in the sulcus while taking impressionDouble cord technique

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68. Hemorrhage is controlled using a specifically designed dentoinfusor with a ferric sulfate medicament (15-20%) Used with a burnishing motion in the sulcus and is carried circumferentially 360o around the sulcus A knitted cord is soaked in the ferric sulfate solution and packed into the sulcus - left in place for 1-3 min and then removedThe infusion technique

69. Placing retraction cord simultaneously around all prepared teeth (especially anterior) may result in strangulation of gingival papillae and eventual loss of papillae - resulting in unaesthetic black triangles in the gingival embrassuresEvery other tooth technique

70. Single or double cord technique can be used, retraction cord placed around the alternate prepared tooth - impression made Then gingival retraction accomplished on remaining teeth and second impression made Finally a pick up impression allows fabrication of a master cast with die for all the prepared teeth

71. Merocel : Synthetic material that is chemically extracted from a bio-compatible polymer (hydroxylate polyvinyl acetate) that creates a net like strip - capable of atraumatic gingival retractionUsed in strips of 2mm thickness that expand with absorption of selected oral fluidsNEWER MATERIALS

72. Paste supplied in a syringe, that is designed to be injected into the unretracted sulcus which then becomes rigid and creates space between the tooth and the tissueTakes about 2 min 30 seconds to achieve sulcular exposure. It contains haemostatic astringent - kaolin, aluminium chlorideSafe, exerts moderate and calculated pressure on gingival margin, 0.1 N/mm2, attachment safe guardedExpa- syl

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74. Gingival retraction putty is a condensation silicone formula with potassium aluminium sulfateRetrac

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76. Selective single cord technique

77. PVS retractionmaterial

78. Surgical methods Rotary curettage Electro surgery

79. Is a “troughing” technique - limited removal of epithelial tissue in the sulcus while a chamfer finish line is being created in tooth structure - Amsterdam 1954Also called “gingettage” used with the sub gingival placement of restoration marginsShould always be done on healthy, inflammation free tissue to avoid the tissue shrinkage that occurs when diseased tissue heals Rotary curettage

80. Gingettage

81. Indications For the removal of irritated tissue that has proliferated over preparation finish linesFor enlargement of the gingival sulcus Control of hemorrhage to facilitates impression making Current flows from a small cutting electrode that produces a high current density and a rapid temperature rise at its point of contact with the tissue The cells directly adjacent to the electrode are destroyed by this temperature increase Electro surgery (D’Arsonval 1891)

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83. Coagulating Diamond loop - crown lengthening Round loop - gingivectomy Small, straight - gingival sulcus enlargement Small loop Commonly used electrodes

84. Cardiac pacemakers Not to be used in presence of flammable agents Not in the presence of nitrous-oxide-oxygen analgesia Contraindications

85. Defined as the dimension of the soft tissue, which is attached to the portion of the tooth coronal to crest of the alveolar bone (Gargiulo et al 1961)Biologic width=Junctional epithelium + Connective tissue 2.04 mm 0.97 mm 1.07 mmBiologic width

86. Gingival sulcusMarginal gingivaJunctional epitheliumConnective tissueAlveolar crest}Biologicwidth

87. Violation of biologic width Biologic width forms a “Biologic seal” around the neck of the tooth. Prevents micro organisms and their by products from migrating to the underlying tissue Violation of biologic width Leads to migration of micro organisms and toxinsInflammatory reactionLoss of attachment Apical migration of marginal attachment Periodontal pocket - Bone loss

88. Location of prepared cervical margin – 0.5 mm from the healthy free gingival margin or 2-3mm from the crest of the alveolar bone and must follow the natural scalloped form of the attachment and alveolar housing

89. Factors affecting impression precisionMaking precise impressions depends on two variables, the primary and secondary determinants.Primary determinant – only one i.e tissue or gingival health.Secondary determinants- many factors Stock vs. custom traysInter- vs. intra-archClosed vs. open trayOne vs. two stagesPassive vs. non-passiveWarm vs. cold environmentManual vs. automated mixingManual vs. automated mixingImpression material used

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91. To ensure predictable and consistently accurate impressions, the following sequence isnecessary:(1) Establish presence of primary determinant,i.e. gingival health(2) Choose appropriate secondary determinates:Stock tray for up to three units, custom tray for more than three units Full intra-arch impressions Avoid excessively large holes in trays, minimising intra-oral excess material spillage (or use closed-tray technique) One-stage technique Passive setting of impression material Avoid chilling impression material Use automixing unitsUse either retraction cord as a physical barrier in sulcus or chemical retraction Use either polyether or addition silicone materials

92. DISINFECTION OF IMPRESSIONS

93. The dental impression is one of the ways by which pathogens can leave the operatory and spread their risk abroad The impression must be rendered harmless before being passed on to another person who will work with it or with the gypsum cast made from it, outside the dental operatory

94. Chemical disinfectants used for this purposeChlorine compoundsSynthetic phenolic compounds Glutaraldehydes Iodophors Phenolic/ alcoholic combinations

95. Material Method Disinfectant AlginateAgar-agarDisinfectant with short-term exposure time (<10min )Chlorine compounds or iodophorsPolysulfideSilicone Immersion time should not exceed the recommended pouring timeGlutaraldehydes, Chlorine compounds, iodophors, phenolicsPolyether Disinfectant with short-term exposure time (<10min )Chlorine compounds or iodophors

96. An alternative method for the hydrophilic materials:Disinfectant can be sprayed on the impression - wrapped in a disinfectant soaked paper towel and placed in sealed plastic bag for 10 minLong immersion time may cause the surfactant in hydrophilic PVS to leach out and render the impression less hydrophilic

97. Ultraviolet treatment - effective against Candida organisms, and there was no adverse effect on either dimensional change or surface roughness of impression materialsDisadvantages - cannot kill micro organisms that are shadowed from the emissionUV light unit should be designed in such a way, that the impression rotates on the table and unit surrounded by mirror - Hiroshi Ishida 1991

98. Argon radiofrequency glow dischargeSimultaneously :disinfects the impression : improves surface wettabilityPlasma treatment produces high energy surface on the materialCreates surface microashing that removes hydrocarbon contaminants – ultracleaned surfaceDisadvantage : prolonged exposure results in surface degeneration - Haganman et al 1997

99. Current protocol - recommended by Center for Disease Control - household bleach (1:10 dilution) - iodophors - synthetic phenolsSprayed on exposed surface - wrapped in disinfectant soaked paper towel - sealed plastic bag for 10 min orImmersion - not exceeding 10 mins Disinfection

100. Concepts for transporting impressions to the LaboratorySent well cleaned (rinsed) and undisinfected in a biohazard-labeled, heat sealed plastic bag ORDebride, clean (rinse) and adequately disinfect it, place it in a sealed transport bag labeled with the precautions taken

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102. THANK YOU