Techniques of impression making in complete dentures/ orthodontics courses online


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Techniques of impression making in complete dentures/ orthodontics courses online

  1. 1. Impression techniquesImpression techniques in complete denturesin complete dentures.. INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. Table of contentsTable of contents IntroductionIntroduction DefinitionsDefinitions historyhistory Review of literatureReview of literature Principles of impression makingPrinciples of impression making Theories of impression makingTheories of impression making
  3. 3. Impression techniques.Impression techniques. -muco compressive technique .-muco compressive technique . -muco static technique.-muco static technique. -Selective pressure technique.-Selective pressure technique. Preliminary impressions.Preliminary impressions. Fabrication of custom tray.Fabrication of custom tray. Border molding.Border molding. Secondary impressions.Secondary impressions.
  4. 4.
  5. 5.  Specialized impressionSpecialized impression techniques.techniques.  SummarySummary  ConclusionsConclusions  ReferencesReferences
  6. 6. Introduction.Introduction. The impression appointment is theThe impression appointment is the most important to the dentist and themost important to the dentist and the patient for several reasons. It ispatient for several reasons. It is usually the first prolongedusually the first prolonged appointment following theappointment following the examination and consultation withexamination and consultation with the patient. Good impressions arethe patient. Good impressions are basic to the needs of the contendedbasic to the needs of the contended denture wearer.denture wearer.
  7. 7. The impression problem would notThe impression problem would not be a problem if we take thebe a problem if we take the impressions of the casts. Theimpressions of the casts. The problem is due to the fact that theproblem is due to the fact that the mouth is lined by the displaceablemouth is lined by the displaceable tissue which varies in degree oftissue which varies in degree of displacibility.displacibility.
  8. 8. In view of these facts , it isIn view of these facts , it is reasonable to say that the idealreasonable to say that the ideal impression must be in the mind ofimpression must be in the mind of the dentist before it is in his hand.the dentist before it is in his hand. He must literally make impressionHe must literally make impression rather than take it. The kind ofrather than take it. The kind of impression he will make dependsimpression he will make depends on the factors which we shallon the factors which we shall presently consider.presently consider.
  9. 9. Definitions:-Definitions:- Impression:-A negative likeness orImpression:-A negative likeness or copy in reverse of an object ; ancopy in reverse of an object ; an imprint of the teeth and the adjacentimprint of the teeth and the adjacent structures for use in dentistry.-GPT7.structures for use in dentistry.-GPT7. A complete denture impression isA complete denture impression is negetive registration of the entirenegetive registration of the entire denture bearing, stabilizing anddenture bearing, stabilizing and border seal areas present inborder seal areas present in edentulous mouth (Heartwell)edentulous mouth (Heartwell)
  10. 10. Impression Area:-The surfaceImpression Area:-The surface recorded in an impression.-GPT7recorded in an impression.-GPT7
  11. 11. Impression Surface:-The portion ofImpression Surface:-The portion of the denture surface that has itsthe denture surface that has its contour determined by thecontour determined by the impression.-GPT7impression.-GPT7 Impression tray:- GPT7Impression tray:- GPT7 1.A receptacle into which suitable1.A receptacle into which suitable impression material is placed toimpression material is placed to make the negative likeness.make the negative likeness.
  12. 12. 2.a device used to carry , confine2.a device used to carry , confine &control impression material&control impression material while making an impression.while making an impression. Preliminary impressions:-aPreliminary impressions:-a negative likeness made for thenegative likeness made for the purpose of diagnosis, treatmentpurpose of diagnosis, treatment planning, or fabrication of the trayplanning, or fabrication of the tray .GPT7.GPT7
  13. 13. Preliminary impression is anPreliminary impression is an impression made for the purposeimpression made for the purpose of diagnosis or for theof diagnosis or for the construction of the of the tray. (Heartwell).(Heartwell).
  14. 14. 1.the shaping of the border areas1.the shaping of the border areas of the impression tray by functionalof the impression tray by functional or manual manipulation of theor manual manipulation of the tissue adjacent to the borders totissue adjacent to the borders to duplicate the contour and size ofduplicate the contour and size of the vestibule.the vestibule. Border molding:-GPT7Border molding:-GPT7
  15. 15. 2.determining the extension of the2.determining the extension of the prosthesis by using tissueprosthesis by using tissue function or manual manipulationfunction or manual manipulation of the tissues to shape the borderof the tissues to shape the border areas of the impression material.areas of the impression material.
  16. 16. Final impressions: a impressionFinal impressions: a impression that represents the completion ofthat represents the completion of the registration of the surface orthe registration of the surface or the object.GPT7the object.GPT7 A final impression is a impressionA final impression is a impression for making master casts.for making master casts. (heartwell).(heartwell).
  17. 17. History of impressions.History of impressions. 1600- Prior to 1600 no complete1600- Prior to 1600 no complete dentures were made due to lackdentures were made due to lack of understanding of retention.of understanding of retention. Replacements were made onlyReplacements were made only when the posterior abutmentswhen the posterior abutments were present.were present. 1711- Mathew Gottfried Purman1711- Mathew Gottfried Purman recorded impression using wax.recorded impression using
  18. 18. 1728: Pierre Fauchard made dentures1728: Pierre Fauchard made dentures mesuring with compass and cutting bonemesuring with compass and cutting bone into an appropriate shape to be filled.into an appropriate shape to be filled. 1845-18991845-1899 1848: Westcott, Dwinelle, Dunning1848: Westcott, Dwinelle, Dunning introduced guttapercha. It was used as aintroduced guttapercha. It was used as a impression material.impression material. 1884: Plaster of paris was first used as1884: Plaster of paris was first used as impression material.impression material. Charles Stent introduced ImpressionCharles Stent introduced Impression compoundcompound
  19. 19. many changes became evident in thismany changes became evident in this era. Till then only one impressionsera. Till then only one impressions deemed sufficient.deemed sufficient. It advanced to a method usingIt advanced to a method using preliminary impressions.preliminary impressions. This was followed by secondory washThis was followed by secondory wash impression made of plaster withinimpression made of plaster within preliminary impression.preliminary impression.
  20. 20. 1900: Closed mouth impression1900: Closed mouth impression procedure was introduced.procedure was introduced. 1900-1929: Several basic1900-1929: Several basic principles of making impressionsprinciples of making impressions were introduced. Advances inwere introduced. Advances in accuracy of impression techniqueaccuracy of impression technique and increase in the method ofand increase in the method of border molding and obtainingborder molding and obtaining peripheral seal were among theperipheral seal were among the major advancesmajor advances
  21. 21. Green brothers introduced moco-Green brothers introduced moco- compressive impressioncompressive impression technique.technique. Tyrde et al.,advocated the use ofTyrde et al.,advocated the use of closed mouth technique.closed mouth technique. 1930-1950: several impression1930-1950: several impression materials were introduced suchmaterials were introduced such as reversible hydrocolloid ,zincas reversible hydrocolloid ,zinc oxide and oil of cloves.oxide and oil of cloves.
  22. 22. 1944: Addison described1944: Addison described “mucostatic impression and“mucostatic impression and attributed to Page.attributed to Page. 1950-1964: During this era there1950-1964: During this era there was increased emphasis onwas increased emphasis on biological factors of completebiological factors of complete dentures.dentures. Boucher proposed selectiveBoucher proposed selective pressure technique in1951.pressure technique in1951.
  23. 23. 1965-1980: newer techniques1965-1980: newer techniques have been developed to managehave been developed to manage poor mandibular ridges.poor mandibular ridges. Tyrde and Robert introducedTyrde and Robert introduced sublingual flange technique .sublingual flange technique . Lott and Levin introduced flangeLott and Levin introduced flange technique.technique.
  24. 24. Review of literature:Review of literature: 1.1. Charles H. Moses (1953):Charles H. Moses (1953): physical considerations in impressionphysical considerations in impression making. JPD 1953:3(4);449-62)making. JPD 1953:3(4);449-62) He states that :He states that : there must be no displacement ofthere must be no displacement of tissues in so far as possible totissues in so far as possible to avoid it.avoid it.
  25. 25. physical considerations in impressionphysical considerations in impression making. JPD 1953:3(4);449-62)making. JPD 1953:3(4);449-62) complete denture impressionscomplete denture impressions .JPD1965:15;603-14..JPD1965:15;603-14.  Posterior border seal – its rationale andPosterior border seal – its rationale and importance.JPD1958:8;386-97importance.JPD1958:8;386-97  complete denture impressionscomplete denture impressions .JPD1965:15;603-14.JPD1965:15;603-14
  26. 26. if displacement is necessary atif displacement is necessary at the peripheral borders to takethe peripheral borders to take advantage of atmosphericadvantage of atmospheric pressure, the degree ofpressure, the degree of displacement must be minimizeddisplacement must be minimized so the elastic force is not greaterso the elastic force is not greater than the retentive forcethan the retentive force
  27. 27.  there must be intimate contactthere must be intimate contact between the denture base and thebetween the denture base and the undisplaced tissues. this producesundisplaced tissues. this produces thin film of saliva.thin film of saliva.  physiologic seal areas arephysiologic seal areas are advantageous because atmosphericadvantageous because atmospheric pressure is an important adjunct topressure is an important adjunct to denture retention.denture retention.  ridge form is important retentiveridge form is important retentive factor in denture retention.factor in denture retention.
  28. 28.  the area covered by the denturethe area covered by the denture is a factor of retention. Theis a factor of retention. The greator the area covered thegreator the area covered the greater will be the retention.greater will be the retention.  the viscosity of saliva is the factorthe viscosity of saliva is the factor of retention.of retention.  friction could be a factor, but it isfriction could be a factor, but it is not recommended because of thenot recommended because of the pathogenic conditions it induces.pathogenic conditions it induces.
  29. 29. Glen E. Tilton (1956):Glen E. Tilton (1956): AA minimum pressure completeminimum pressure complete denture impression techniquedenture impression technique JPD1956:6(1);6-23JPD1956:6(1);6-23 States that: The pressure appliedStates that: The pressure applied in impression making must bein impression making must be equally balanced throught theequally balanced throught the entire area of impression.entire area of impression.
  30. 30. The tissues of the mouth , or indeedThe tissues of the mouth , or indeed any tissues of the body ,will notany tissues of the body ,will not tolerate constant pressure withouttolerate constant pressure without change; therefore, pressure on thechange; therefore, pressure on the tissue in function beneath a denturetissue in function beneath a denture must be momentry.must be momentry. In his opinion , all denture-bearingIn his opinion , all denture-bearing tissue will be at rest when thetissue will be at rest when the mandible is in rest position.mandible is in rest position.
  31. 31. Irving R. Hardy (1958)Irving R. Hardy (1958) Posterior border sealPosterior border seal – its rationale and importance.JPD1958:8;386-97.– its rationale and importance.JPD1958:8;386-97. Said that the establishment of theSaid that the establishment of the distal length of the basal seat anddistal length of the basal seat and the development of the PPS is mostthe development of the PPS is most important step in construction of theimportant step in construction of the complete dentures. In addition tocomplete dentures. In addition to providing retention recording PPSproviding retention recording PPS has following advantages:-has following advantages:-
  32. 32.  it provides close contact of theit provides close contact of the denture base with the mucousdenture base with the mucous membrane which prevents foodmembrane which prevents food getting under the tissue.getting under the tissue.  it provides firm contact of theit provides firm contact of the denture base with the tissue,denture base with the tissue, and this diminishes or eliminatesand this diminishes or eliminates gagginggagging
  33. 33.  it supplies sunken distalit supplies sunken distal borders which is lessborders which is less conspicuous to the tongue.conspicuous to the tongue.  it provides a thick borders toit provides a thick borders to counteract denture warpage.counteract denture warpage.
  34. 34.  Henry A. Collett (1965);Henry A. Collett (1965); complete denture impressionscomplete denture impressions .JPD1965:15;603-14..JPD1965:15;603-14. Told that the theories attemptingTold that the theories attempting to explain the retention of theto explain the retention of the denture seem to agree that closedenture seem to agree that close adaptation of the denture basesadaptation of the denture bases to the tissues is desirable , andto the tissues is desirable , and the retention is proportianate tothe retention is proportianate to the area coveredthe area covered
  35. 35. Displaced tissues have aDisplaced tissues have a tendency to return to a positiontendency to return to a position and form of equilibrium. Becauseand form of equilibrium. Because of this , it seems to be desirableof this , it seems to be desirable to have the patient either removeto have the patient either remove his old dentures for a day or twohis old dentures for a day or two or to have the tissue conditionedor to have the tissue conditioned in other manner beforein other manner before impressions.impressions.
  36. 36. Tissues that we displace whileTissues that we displace while making impressions havemaking impressions have tendency to return to theirtendency to return to their original form due to resilienceoriginal form due to resilience and they have tendency toand they have tendency to displace the dentures. A borderdisplace the dentures. A border seal should be created byseal should be created by positive pressure. This will resultpositive pressure. This will result in retention.
  37. 37. The selection of theThe selection of the impression material orimpression material or combination of materialcombination of material should be determined by theshould be determined by the objectives of the dentist andobjectives of the dentist and the skill with which hethe skill with which he manipulates the materialmanipulates the material
  38. 38.  Gred Tryde et al (1965);Gred Tryde et al (1965); dynamicdynamic impression techniques .JPD1965:15;1023-32.impression techniques .JPD1965:15;1023-32. Described that dynamic impressionDescribed that dynamic impression methods are the means ofmethods are the means of overcoming treatment difficulties ofovercoming treatment difficulties of patients with advanced mandibularpatients with advanced mandibular ridge resorption.ridge resorption. The advantages of dynamicThe advantages of dynamic impression methods areimpression methods are
  39. 39.  avoidence of the dislocatingavoidence of the dislocating effect of the muscles oneffect of the muscles on improperly formed dentureimproperly formed denture borders.borders.  complete utilization of thecomplete utilization of the possibilities of the passive andpossibilities of the passive and active tissue fixation of theactive tissue fixation of the dentures.dentures.
  40. 40. These advantages are the directThese advantages are the direct result of the impression materialresult of the impression material being shaped by the functionalbeing shaped by the functional movements of the musclesmovements of the muscles muscle attachments that bordermuscle attachments that border the denture base.the denture base.
  41. 41. V . Kubalek (1966)V . Kubalek (1966) :: impressions byimpressions by the use of subatmospheric pressurethe use of subatmospheric pressure .JPD1966:16;213-23..JPD1966:16;213-23. Described that the denture canDescribed that the denture can no better be than theno better be than the impressions by which it is made.impressions by which it is made. A new concept was developed toA new concept was developed to eliminate the functional limitationseliminate the functional limitations of the impressions.of the impressions.
  42. 42. The term “vacustatics” has beenThe term “vacustatics” has been coined to describe accurately thecoined to describe accurately the concepts and the techniques.theconcepts and the techniques.the term describes subatmosphericterm describes subatmospheric pressure as a significant factor inpressure as a significant factor in this technique. It then denotes thethis technique. It then denotes the equilibrium of forces which resultsequilibrium of forces which results when the controlled vacuum iswhen the controlled vacuum is appliedapplied
  43. 43.  Richard A. Smith (1973)Richard A. Smith (1973) Impression border molding with a coldImpression border molding with a cold cure resin.JPD1973:30;914-17.cure resin.JPD1973:30;914-17. He described a technique for moldingHe described a technique for molding the borders of the impression tray withthe borders of the impression tray with a cold cure resin .a cold cure resin . Advantage :eliminating the use ofAdvantage :eliminating the use of stick modeling compound and itsstick modeling compound and its tempering water bath.tempering water bath.
  44. 44. Impression border molding with aImpression border molding with a cold cure resin.JPD1973:30;914-17cold cure resin.JPD1973:30;914-17  principles involved in completeprinciples involved in complete denturesdentures.JPD1973:29;594-9.JPD1973:29;594-9  border molding of complete dentureborder molding of complete denture impressions using a polyether impressionimpressions using a polyether impression material.JPD1979:41;347-51material.JPD1979:41;347-51 77
  45. 45. It is most applicable with theIt is most applicable with the elastic impression materialselastic impression materials because of the possibility of thebecause of the possibility of the cast fracture in undercut areas ifcast fracture in undercut areas if rigid tray materials are usedrigid tray materials are used throught.throught.
  46. 46.  Theorde E. Logan(1973Theorde E. Logan(1973):): principles involved in completeprinciples involved in complete denturesdentures.JPD1973:29;594-97..JPD1973:29;594-97.  He said that: Inadequate mouthHe said that: Inadequate mouth preparations and improperpreparations and improper tissue control make adequatetissue control make adequate impressions and denture basesimpressions and denture bases impossible.impossible.  over extention of impressionsover extention of impressions and subsequently of the dentureand subsequently of the denture bases may be the result ofbases may be the result of choice of impression materialschoice of impression materials
  47. 47.  Under extention of the the dentureUnder extention of the the denture bases may be due to under extendedbases may be due to under extended impressions.impressions.  Placement of a posterior palatal sealPlacement of a posterior palatal seal and perfection of the thickness andand perfection of the thickness and extension of the denture bordersextension of the denture borders should be determined by the dentist.should be determined by the dentist.  Denture-base extension is dependentDenture-base extension is dependent on the border extension and fullnesson the border extension and fullness in the the impression.
  48. 48.  The use of tissue conditioner beforeThe use of tissue conditioner before the impressions is indicated forthe impressions is indicated for most patients who are wearing themost patients who are wearing the dentures.dentures.  Impressions should be varied toImpressions should be varied to control tissues where surgery iscontrol tissues where surgery is contraindicated.contraindicated.  Dentures require less maintenanceDentures require less maintenance when impressions are properlywhen impressions are properly mademade
  49. 49.  The final impressions determineThe final impressions determine the shape of the basal surface ofthe shape of the basal surface of the denture and extentions of itsthe denture and extentions of its borders.borders.  The impressions made afterThe impressions made after mouth preparation is basic to allmouth preparation is basic to all the steps in denture constructionthe steps in denture construction which follow.which follow.
  50. 50.  Dale E. Smith (1979):Dale E. Smith (1979): one stepone step border molding of complete dentureborder molding of complete denture impressions using a polyetherimpressions using a polyether impression material.JPD1979:41;347-impression material.JPD1979:41;347- 51.51.  A technique was describedA technique was described which uses the polyetherwhich uses the polyether impression material for borderimpression material for border molding the impression.molding the impression.
  51. 51. This technique has the followingThis technique has the following advantages:advantages: There is simultaneous molding ofThere is simultaneous molding of all borders of either maxillary orall borders of either maxillary or mandibular impressions.mandibular impressions. Border molding can beBorder molding can be accomplished with one insertionaccomplished with one insertion of the tray.of the tray.
  52. 52. Functional movements performedFunctional movements performed by the patients are used in borderby the patients are used in border molding.molding. The technique is easily masteredThe technique is easily mastered
  53. 53.  Awni Rihani (1981):Awni Rihani (1981): pressurespressures involved in complete dentureinvolved in complete denture impressionsimpressions.JPD1981:46;610-14..JPD1981:46;610-14.  In his study he showed thatIn his study he showed that thethe pressure in the impression waspressure in the impression was not equally distributednot equally distributed
  54. 54.  the greatest pressure duringthe greatest pressure during impression making was recorded byimpression making was recorded by the manometer located in the centrethe manometer located in the centre of the palate.of the palate.  pressures were not able to registerpressures were not able to register at the the borders.  the shape of the palate did notthe shape of the palate did not effect the distribution of theeffect the distribution of the pressurespressures
  55. 55.  H.Hotkin et al (1987)H.Hotkin et al (1987) ::tonguetongue positions in relation to mandibularpositions in relation to mandibular impressionsimpressions . JPD1987:57;458-62.. JPD1987:57;458-62. Made a study to describe anMade a study to describe an impression technique that providesimpression technique that provides a mandibular denture base with thea mandibular denture base with the contours that encourage anteriorcontours that encourage anterior positioning of the tongue forpositioning of the tongue for effective harnessing of theeffective harnessing of the stabilizing and retentive forcesstabilizing and retentive forces exerted in the forward positionexerted in the forward position
  56. 56. He concluded that this techniqueHe concluded that this technique is indicated where advancedis indicated where advanced residual ridge resorption isresidual ridge resorption is present. An adjustable easilypresent. An adjustable easily located impression tray handlelocated impression tray handle was used as a device to controlwas used as a device to control tongue position and musculartongue position and muscular forces for mandibular completeforces for mandibular complete denture impression –making.denture impression –making.
  57. 57. Mohammed Khaled Ahmed AzzamMohammed Khaled Ahmed Azzam et alet al (1992):(1992): the sublingual crescentthe sublingual crescent extensions and its relation to the stabilityextensions and its relation to the stability and retention of mandibular completeand retention of mandibular complete dentures.JPD1992:67;205-10.dentures.JPD1992:67;205-10. He stated that the extension of theHe stated that the extension of the flange in the sublingual crescentflange in the sublingual crescent region is an important factor forregion is an important factor for mandibular denture stability andmandibular denture stability and retention.retention.
  58. 58. the sublingual crescent extensionsthe sublingual crescent extensions and its relation to the stability andand its relation to the stability and retention of mandibular completeretention of mandibular complete dentures.JPD1992:67;205-10dentures.JPD1992:67;205-10 Functional metallic handles for finalFunctional metallic handles for final impressions of completeimpressions of complete denturesdentures.JPD1998:79;607-8.JPD1998:79;607-8
  59. 59. Making the impression with theMaking the impression with the minimum pressure on the floor ofminimum pressure on the floor of the mouth while the tongue is atthe mouth while the tongue is at rest allows greater mobility of therest allows greater mobility of the underlying tissue without dentureunderlying tissue without denture dislodgement and withoutdislodgement and without occlusion of the sublingual glandocclusion of the sublingual gland ducts.ducts.
  60. 60. The anatomy of the sublingualThe anatomy of the sublingual crescent region and the clinicalcrescent region and the clinical procedure for recording theprocedure for recording the anterior lingual seal region wasanterior lingual seal region was described. Upon completion ofdescribed. Upon completion of the impression, resistance to thethe impression, resistance to the dislodgement is usuallydislodgement is usually achievedachieved ..
  61. 61.  A.R. Odgen (1994A.R. Odgen (1994):): disposable trays fordisposable trays for complete denture construction :acomplete denture construction :a dimensional study of a type frequently useddimensional study of a type frequently used in UK and its suitability for the edentulousin UK and its suitability for the edentulous patientspatients.BDJ1994;23:303-9..BDJ1994;23:303-9.  This study compares the sizes ofThis study compares the sizes of patients edentulous arches with thepatients edentulous arches with the shapes of disposable stock trays fromshapes of disposable stock trays from one manufacturer .in manyone manufacturer .in many dimensions there is considerabledimensions there is considerable discrepancy between the twodiscrepancy between the two
  62. 62. It is concluded that , even withIt is concluded that , even with the tray modification it is almostthe tray modification it is almost impossible to obtain an accurateimpossible to obtain an accurate impressions of the shape of theimpressions of the shape of the all-important sulcus regions. Suchall-important sulcus regions. Such a conclusion emphesises thea conclusion emphesises the importance of obtaining furtherimportance of obtaining further impressions in special traysimpressions in special trays which are modified appropriately.which are modified appropriately.
  63. 63.  Izharul Haque Ansari (1997):Izharul Haque Ansari (1997): establishing the posterior palatal sealestablishing the posterior palatal seal during the final impressionduring the final impression stage.JPD1997:78;324-25.stage.JPD1997:78;324-25.
  64. 64. A procedure for adding theA procedure for adding the posterior palatal seal at the finalposterior palatal seal at the final impression stage with green stickimpression stage with green stick modeling compound is described.modeling compound is described. This procedure was suggested toThis procedure was suggested to be more accurate than thebe more accurate than the arbitary scraping of the masterarbitary scraping of the master castcast
  65. 65. The advantages of this methodThe advantages of this method was :the procedure places thewas :the procedure places the entire responsibility of locatingentire responsibility of locating and incorporating the PPS intoand incorporating the PPS into the hands of the clinician.the hands of the clinician. the practitioner will then be ablethe practitioner will then be able to assess the retentive qualitiesto assess the retentive qualities of the finished dentures.of the finished dentures.
  66. 66. PPS is incorporated into the trialPPS is incorporated into the trial dentures for added retention ,dentures for added retention , thus increasing the diagnosticthus increasing the diagnostic information and accuracy ofinformation and accuracy of record taking procedures.record taking procedures. overcompression of impressionsovercompression of impressions is avoidedis avoided
  67. 67. The fluid wax technique is theThe fluid wax technique is the method of choice but it hasmethod of choice but it has following disadvantages.following disadvantages. more time is required duringmore time is required during impression appointmentsimpression appointments a heating unit is used to conditiona heating unit is used to condition the wax.the wax.
  68. 68. difficulty may be experienced indifficulty may be experienced in handling the material.handling the material. added care during the boxingadded care during the boxing procedure for cast formation isprocedure for cast formation is necessary to prevent distortion ofnecessary to prevent distortion of the carefully added PPS wax.the carefully added PPS wax.
  69. 69.  ALEXANDRE Malachias (1998ALEXANDRE Malachias (1998);:);: Functional metallic handles for finalFunctional metallic handles for final impressions of completeimpressions of complete denturesdentures.JPD1998:79;607-8..JPD1998:79;607-8.  He stated that one of theHe stated that one of the fundamental requirement for thefundamental requirement for the final impressions is the correctfinal impressions is the correct muscular record that can bemuscular record that can be achived with the patient or theachived with the patient or the dentistdentist
  70. 70. His work presented a technicalHis work presented a technical modification in the completemodification in the complete denture final impression by usingdenture final impression by using a removable functional handlea removable functional handle that can be reusable and can bethat can be reusable and can be easily attached to acrylic resineasily attached to acrylic resin individual trays that allowindividual trays that allow muscular records to be obtainedmuscular records to be obtained from the patients movementsfrom the patients movements..
  71. 71.  T. Paul Hyde (1999T. Paul Hyde (1999):): survey ofsurvey of prosthodontic impression proceduresprosthodontic impression procedures for complete dentures in generalfor complete dentures in general practice in United Kingdom.practice in United Kingdom. JPD1999:81;295-9.JPD1999:81;295-9.  This study identifies the materialsThis study identifies the materials and methods used by generaland methods used by general practitioners for recordingpractitioners for recording impressions for the provision ofimpressions for the provision of replacement of complete dentures.replacement of complete dentures.
  72. 72. Within the limits of this study ,theWithin the limits of this study ,the following conclusions were drawnfollowing conclusions were drawn :Irreversible hydrocolloid:Irreversible hydrocolloid dominated the market fordominated the market for impressions materials forimpressions materials for complete dentures.complete dentures. the use of special trays is normalthe use of special trays is normal practice for complete dentures.practice for complete dentures.
  73. 73. Cenk Cura,(2003) Fabrication of aCenk Cura,(2003) Fabrication of a sectional impression tray and sectionalsectional impression tray and sectional complete denture for a patient withcomplete denture for a patient with microstomia and trismus.microstomia and trismus. (J Prosthet Dent 2003;89:540-3.) This article describes techniques usedThis article describes techniques used to fabricate mandibular and maxillaryto fabricate mandibular and maxillary sectional trays and a folding maxillarysectional trays and a folding maxillary complete denture for a patient withcomplete denture for a patient with limited oral opening caused bylimited oral opening caused by scleroderma.scleroderma.
  74. 74. For the foldable denture, theFor the foldable denture, the anterior teeth had to be arrangedanterior teeth had to be arranged on a second base and the hingeon a second base and the hinge fitted at a location higher than thefitted at a location higher than the denture base. These 2 factorsdenture base. These 2 factors increased the thickness of theincreased the thickness of the denture and limited the volume ofdenture and limited the volume of the tongue. Nevertheless, a single-the tongue. Nevertheless, a single- piece denture base provided thepiece denture base provided the patient with ease in placement andpatient with ease in placement and removal of the denture.removal of the denture.
  75. 75. Carl J. Drago(2003)Carl J. Drago(2003) A RetrospectiveA Retrospective Comparison of Two Definitive ImpressionComparison of Two Definitive Impression Techniques and Their AssociatedTechniques and Their Associated Postinsertion Adjustments in CompletePostinsertion Adjustments in Complete Denture ProsthodonticsDenture Prosthodontics.. J Prosthodont 2003;12:192-197.
  76. 76. Compared the number of postinsertionCompared the number of postinsertion adjustment visits required byadjustment visits required by edentulous patients whose denturesedentulous patients whose dentures were made from border-moldedwere made from border-molded definitive impressions using modelingdefinitive impressions using modeling plastic impression compoundplastic impression compound (traditional technique) with patients(traditional technique) with patients whose dentures were made fromwhose dentures were made from border-molded definitive impressionsborder-molded definitive impressions using heavy-body vinyl polysiloxaneusing heavy-body vinyl polysiloxane impression material.impression material.
  77. 77. They concluded Within theThey concluded Within the limitations of this clinical study,limitations of this clinical study, border-molding custom dentureborder-molding custom denture impression trays with vinylimpression trays with vinyl polysiloxane impression materialpolysiloxane impression material provided similar results in terms ofprovided similar results in terms of postinsertion visits for one year aspostinsertion visits for one year as compared to dentures made fromcompared to dentures made from impressions border molded withimpressions border molded with modeling plastic impressionmodeling plastic impression compound.compound.
  78. 78. Vicki C. Petropoulos (2004)Vicki C. Petropoulos (2004) Current Concepts and TechniquesCurrent Concepts and Techniques in Complete Denture Finalin Complete Denture Final Impression ProceduresImpression Procedures J Prosthodont 2003;12:280-287.
  79. 79. In 2001, a survey of U.S. dentalIn 2001, a survey of U.S. dental schools was conducted toschools was conducted to determine which concepts,determine which concepts, techniques and materials aretechniques and materials are currently prevalent in thecurrently prevalent in the teaching of final impressionteaching of final impression procedures for completeprocedures for complete dentures in the predoctoraldentures in the predoctoral clinical curriculumclinical curriculum..
  80. 80. Conclusions:Conclusions: Predoctoral clinicalPredoctoral clinical complete denture educationalcomplete denture educational programs agree on many aspectsprograms agree on many aspects of final impression making,of final impression making, however, there is variability inhowever, there is variability in their teachings regarding thetheir teachings regarding the impression philosophy and theimpression philosophy and the materials used.materials used.
  81. 81. M. M. De Van (2005) basic principlesM. M. De Van (2005) basic principles in impression impression making. JPD2005:93;503-8JPD2005:93;503-8 The objective of his article was toThe objective of his article was to bring to your attention the basicbring to your attention the basic and fundamentals in impressionand fundamentals in impression making- the impressions of mouthmaking- the impressions of mouth tissues for the purpose oftissues for the purpose of constructing mucosa attachedconstructing mucosa attached complete dentures.complete
  82. 82. In conclusion he said that theIn conclusion he said that the importance of impression phase isimportance of impression phase is over emphasized. Steps inover emphasized. Steps in retention have played up while theretention have played up while the forces that lead to stability haveforces that lead to stability have not received the emphasis thatnot received the emphasis that they merit.they merit.
  83. 83. Principles and objectives ofPrinciples and objectives of impression making.impression making. The principles involved in impressionThe principles involved in impression making are:making are: Preservation of the residual alveolarPreservation of the residual alveolar tissue.tissue. Retention.Retention. Stability.Stability. Support.Support. Esthetics.Esthetics.
  84. 84.
  85. 85. Preservation of the residualPreservation of the residual alveolar tissues:alveolar tissues: M.M De Van’s dictum”It is moreM.M De Van’s dictum”It is more important to preserve whatimportant to preserve what already exists than replace thealready exists than replace the missing.missing. It is physiologically accepted thatIt is physiologically accepted that with loss of stimulation of thewith loss of stimulation of the natural teeth the alveolar ridgesnatural teeth the alveolar ridges will atropy and resorb.will atropy and
  86. 86. During making impressions itDuring making impressions it should be kept in mind that theshould be kept in mind that the impression technique andimpression technique and materials may have effect on thematerials may have effect on the health of the hard and softhealth of the hard and soft tissues.tissues.
  87. 87. Pressure in the impressionPressure in the impression technique is reflected as pressure intechnique is reflected as pressure in the denture base and results in softthe denture base and results in soft tissue damage and bone resorption.tissue damage and bone resorption. In making impressions this rule isIn making impressions this rule is followed by not using heavy pressurefollowed by not using heavy pressure and covering as much as supportingand covering as much as supporting areas as possible to minimize theareas as possible to minimize the possibility of soft tissue abuse andpossibility of soft tissue abuse and bone resorption.bone
  88. 88. Retention.Retention. Retention for a denture is itsRetention for a denture is its resistance to removal in a directionresistance to removal in a direction opposite to that of its insertionopposite to that of its insertion (Boucher).(Boucher). Retention is that quality of theRetention is that quality of the prosthesis acting to resist the forcesprosthesis acting to resist the forces of dislodgement along the path ofof dislodgement along the path of placement (GPT7).placement (GPT7)
  89. 89. Denture retention is the resistanceDenture retention is the resistance of the movement of the dentureof the movement of the denture from its basal seat, especially in afrom its basal seat, especially in a vertical direction. (Winkler).vertical direction. (Winkler).
  90. 90. It is the quality inherent inIt is the quality inherent in dentures to resists the force ofdentures to resists the force of gravity , adhesiveness of foods,gravity , adhesiveness of foods, and the forces associated with theand the forces associated with the opening of the jaws.opening of the jaws.
  91. 91. When the soft tissues over theWhen the soft tissues over the bones are displaced underbones are displaced under pressure , the denture bases maypressure , the denture bases may loose their retention because ofloose their retention because of change of adaptation of thechange of adaptation of the denture to the basal seat.denture to the basal seat.
  92. 92. Factors governing the retentionFactors governing the retention 1.Physical factors:1.Physical factors: adhesion.adhesion. cohesion.cohesion. interfacial surface tension.interfacial surface tension. Capillary attraction.Capillary attraction. atmospheric pressure.atmospheric pressure. 2.Physiological factors:2.Physiological factors: physical condition.physical
  93. 93. degree of tissue of tissue tone. condition of mucosa and submucosa.condition of mucosa and submucosa. neuromuscular control.neuromuscular control. ridge characteristics.ridge characteristics. ridge relationship.ridge relationship. 3.Physcological factors:3.Physcological factors: intelligence.intelligence. expectation.expectation. apprehension or fear of embarrassment.apprehension or fear of embarrassment. gagging.gagging.
  94. 94. 4.Mechanical factors.4.Mechanical factors. mechanical locking into themechanical locking into the undercuts.undercuts. Contour of denture bases.Contour of denture bases. magnetsmagnets Suction chambers.Suction chambers. 5.Surgical.5.Surgical. Implant dentures.Implant dentures. ridge extension.ridge
  95. 95. Physical factors.Physical factors. Adhesion:Adhesion: Adhesion is a physical attraction ofAdhesion is a physical attraction of unlike molecules to each other.unlike molecules to each other. It acts when saliva wets and sticks toIt acts when saliva wets and sticks to the basal surface of the dentures andthe basal surface of the dentures and at the same time , to the mucousat the same time , to the mucous membrane of the basal seat.membrane of the basal seat.
  96. 96. The effectiveness of adhesionThe effectiveness of adhesion depends on the closedepends on the close adaptation of the dentures toadaptation of the dentures to the supporting tissues andthe supporting tissues and fluidity of the saliva.fluidity of the saliva.
  97. 97.
  98. 98. Saliva that is thick and ropy adheresSaliva that is thick and ropy adheres well to both the denture base and thewell to both the denture base and the mucosa; but since much of it ismucosa; but since much of it is produced by the palatal glands underproduced by the palatal glands under the maxillary basal seat , it builds upthe maxillary basal seat , it builds up and literally pushes the denture out ofand literally pushes the denture out of position.position.  The forces of adhesion still acts onThe forces of adhesion still acts on both surfaces , but the hydraulicboth surfaces , but the hydraulic pressure produced may overpowerpressure produced may overpower them.them.
  99. 99. In xerostomia adhesion is notIn xerostomia adhesion is not effective for retaining dentures.effective for retaining dentures. Adhesion is best effective in patientsAdhesion is best effective in patients having mixed type of saliva.having mixed type of saliva.
  100. 100. Patients with small jaws (basalPatients with small jaws (basal seats) cannot expect retention byseats) cannot expect retention by adhesion to be as effective asadhesion to be as effective as patients with large jaws can.patients with large jaws can. Thus dentures (and hence theThus dentures (and hence the impressions ) must extend to theimpressions ) must extend to the limits of the oral tissues if they arelimits of the oral tissues if they are to have maximum retention byto have maximum retention by adhesion.adhesion.
  101. 101. Cohesion:Cohesion: Cohesion is attraction of the likeCohesion is attraction of the like molecules to each other.molecules to each other. It is retentive because it occurs in theIt is retentive because it occurs in the layer of saliva between the denture baselayer of saliva between the denture base and the mucosa. Since saliva is a liquid,and the mucosa. Since saliva is a liquid, the layer of saliva should be thin to aid inthe layer of saliva should be thin to aid in retention.retention. Therefore the adaptation of the dentureTherefore the adaptation of the denture base to the mucosa should be as close asbase to the mucosa should be as close as possible.possible.
  102. 102. Cohesive failure means the seperationCohesive failure means the seperation of molecules within the body againstof molecules within the body against inter-or intramolecular forces.inter-or intramolecular forces. The bubbles caused in the saliva filmThe bubbles caused in the saliva film would certainly cause loss ofwould certainly cause loss of retention.retention.
  103. 103.
  104. 104. Interfacial surface tensionInterfacial surface tension Interfacial surface tension isInterfacial surface tension is the resistance to thethe resistance to the separation possessed by theseparation possessed by the thin film of liquid between twothin film of liquid between two well adapted surfaces.well adapted surfaces.
  105. 105. Page refers interfacial surfacePage refers interfacial surface tension as a phenomenon whichtension as a phenomenon which refer to the forces involved inrefer to the forces involved in maintaining the attraction of twomaintaining the attraction of two opposed ground solid plates withopposed ground solid plates with an intervening fluid film thatan intervening fluid film that resists displacing forces appliedresists displacing forces applied at right angles to the fluid filmat right angles to the fluid film surface.surface.
  106. 106.
  107. 107. On assuumption that the denture baseOn assuumption that the denture base is wetted by the saliva, an attempt tois wetted by the saliva, an attempt to withdraw denture generates along itswithdraw denture generates along its periphery a narrow highly negetivelyperiphery a narrow highly negetively curved saliva surface.curved saliva surface. There is therefore a lowered pressureThere is therefore a lowered pressure in the liquid filled space and ain the liquid filled space and a retentive force is experienced.retentive force is experienced.
  108. 108. It is effective in direct proportionIt is effective in direct proportion to the size of the basal surface ofto the size of the basal surface of the dentures.the dentures. One of its requirements isOne of its requirements is minimal distortion or displacementminimal distortion or displacement of the soft tissues by theof the soft tissues by the impressions and of course theimpressions and of course the denture.denture. A perfect fit is essential.A perfect fit is
  109. 109. Capillary attraction:Capillary attraction: Capillary action or capillarity is aCapillary action or capillarity is a force that causes surface of theforce that causes surface of the fluid to elevate or depressedfluid to elevate or depressed when it is in contact with a solid.when it is in contact with a solid.
  110. 110. When the adaptation of theWhen the adaptation of the denture base to the mucosa ondenture base to the mucosa on which it rests is sufficiently close,which it rests is sufficiently close, the space filled with a thin film ofthe space filled with a thin film of saliva acts like a capillary tubesaliva acts like a capillary tube and helps to retain the denture.and helps to retain the denture. This force is directly proportionateThis force is directly proportionate to the area of the basal seatto the area of the basal seat covered by the denture base.covered by the denture base.
  111. 111. Atmospheric pressure:Atmospheric pressure: Atmospheric pressure can act toAtmospheric pressure can act to resist dislodging forces applied toresist dislodging forces applied to the dentures.the dentures. It has been called as ”suction”It has been called as ”suction” because it is a resistance to thebecause it is a resistance to the removal of the forces from theirremoval of the forces from their basal seatbasal seat
  112. 112. For atmospheric force to beFor atmospheric force to be effective the denture should haveeffective the denture should have a perfect seal around the entirea perfect seal around the entire border.border. Sydner et al., in 1945Sydner et al., in 1945 demonstrated the effect ofdemonstrated the effect of reduced atmospheric pressure onreduced atmospheric pressure on the retention of maxillarythe retention of maxillary complete dentures.complete dentures.
  113. 113. Measurements made in aMeasurements made in a pressure chamber at4.7psipressure chamber at4.7psi simulating a 30,000-footsimulating a 30,000-foot ascent from the earthascent from the earth demonstrated a decrease indemonstrated a decrease in retention.retention. With a 70% decrease in atmWith a 70% decrease in atm pressure , 50% decrease ofpressure , 50% decrease of retention was noted.retention was
  114. 114. For atmospheric pressure to beFor atmospheric pressure to be effective the seal around theeffective the seal around the denture is crucial.denture is crucial. It acts by the way of pressureIt acts by the way of pressure difference. Beneath the denturedifference. Beneath the denture there must be a lower pressurethere must be a lower pressure and the full effect will be felt onlyand the full effect will be felt only if there is vacumm .if there is vacumm .
  115. 115.
  116. 116.
  117. 117. Oral and facial musculature:Oral and facial musculature: The oral and facial musculatureThe oral and facial musculature can provide retentive forcescan provide retentive forces provided 1. the teeth areprovided 1. the teeth are positioned in the neutral zonepositioned in the neutral zone between the cheeks and thebetween the cheeks and the tongue. 2. the polished surfacestongue. 2. the polished surfaces of the tongue are perfectlyof the tongue are perfectly shaped.shaped.
  118. 118. The buccal and the lingual flangesThe buccal and the lingual flanges must be shaped so that it makes itmust be shaped so that it makes it possible for the musculature to fitpossible for the musculature to fit automatically against the denture andautomatically against the denture and reinforce the border seal.reinforce the border seal. The buccal flanges of the maxillaryThe buccal flanges of the maxillary denture slope up and out from thedenture slope up and out from the occlusal surfaces of the teeth and theocclusal surfaces of the teeth and the buccal flanges of the mandibularbuccal flanges of the mandibular dentures slope down and out.dentures slope down and
  119. 119. The lingual surfaces of theThe lingual surfaces of the lingual flanges slope towardslingual flanges slope towards the center of the mouth so thethe center of the mouth so the tongue can best fit againsttongue can best fit against them and perfect the borderthem and perfect the border seal on the lingual side of theseal on the lingual side of the denture.denture.
  120. 120.
  121. 121. Physiological factors:Physiological factors:
  122. 122. Ridgecharecteristics:Ridgecharecteristics: ridge formsridge forms influence theinfluence the retention ofretention of dentures;dentures;  Classified byClassified by Charles H MosesCharles H Moses in mandiblein mandible  class1A -invertedclass1A -inverted ‘u’ shaped ridge-‘u’ shaped ridge- very retentivevery retentive  class1B-flatclass1B-flat inverted ‘u’shape.inverted ‘u’shape.
  123. 123. Class1 C ‘u’Class1 C ‘u’ shaped: presentsshaped: presents little retention inlittle retention in comparision tocomparision to class1’A’ butclass1’A’ but resistsresists displacement indisplacement in upper direction.upper direction. Class2 ’v’shapedClass2 ’v’shaped ridge: is the leastridge: is the least retentive of all.retentive of all.
  124. 124. Class 3A parallelClass 3A parallel walled thin ridge:walled thin ridge: there is no muchthere is no much retention as theretention as the area at the crest ofarea at the crest of ridge is very small.ridge is very small. Class 3B parallelClass 3B parallel walled ,broadwalled ,broad crested ridge: it iscrested ridge: it is the most retentivethe most retentive of all.of all.
  125. 125. Degree of tissue tone:the swellingDegree of tissue tone:the swelling which is the charecteristic ofwhich is the charecteristic of inflammation changes the gross forminflammation changes the gross form of the tissues to be recorded in theof the tissues to be recorded in the impression.impression. Inflammation should be reduced byInflammation should be reduced by keeping the old dentures out of thekeeping the old dentures out of the mouth until the tissues are healthy. Ifmouth until the tissues are healthy. If the patient does not agree tissuethe patient does not agree tissue conditioning materials should beconditioning materials should be used.used.
  126. 126. How ever the old dentures should beHow ever the old dentures should be kept out of the mouth atleast 24hrskept out of the mouth atleast 24hrs before the impressions are made.before the impressions are made. If excessive amounts of theIf excessive amounts of the hyperplastic tissue is present a fingerhyperplastic tissue is present a finger massage is done on daily basis ormassage is done on daily basis or surgical removal of the hyperplasticsurgical removal of the hyperplastic tissue.tissue.
  127. 127.
  128. 128. Neuromuscular control: GoodNeuromuscular control: Good neuromuscular is essential for theneuromuscular is essential for the effective use of complete dentures.effective use of complete dentures. When tongue movements are usedWhen tongue movements are used for border molding the lingual flangesfor border molding the lingual flanges of the mandibular impression,theof the mandibular impression,the timing ,the direction and amount oftiming ,the direction and amount of are critical to the success of molding.are critical to the success of molding.
  129. 129. Mechanical factors:Mechanical factors: Undercuts, Rotational insertion pathsUndercuts, Rotational insertion paths and Parallel walls:and Parallel walls: The resiliency of the mucosa and theThe resiliency of the mucosa and the submucosa overlying the basal bonesubmucosa overlying the basal bone allows existance of the modestallows existance of the modest undercuts that can enhance retention.undercuts that can enhance retention.
  130. 130. Less severe undercuts of lateralLess severe undercuts of lateral tuberosities , maxillary premolartuberosities , maxillary premolar area distolingual areas and lingualarea distolingual areas and lingual mandibular mid bone area aremandibular mid bone area are extreamly helpful in retention.extreamly helpful in retention. Some under cuts are onlySome under cuts are only undercuts in relationship to aundercuts in relationship to a linear path of insertion.linear path of insertion.
  131. 131. If the undercut is seated first in aIf the undercut is seated first in a direction that deviates from thedirection that deviates from the vertical and the remainder of thevertical and the remainder of the denture base can be brought intodenture base can be brought into proximity on rotation of theproximity on rotation of the prosthesis around the undercutprosthesis around the undercut that is already seated. Thisthat is already seated. This rotational path provide resistancerotational path provide resistance to the vertical the vertical displacement.
  132. 132. For example : this is found in theFor example : this is found in the area inferior to the retromolar padarea inferior to the retromolar pad into which the distolingualinto which the distolingual extension of the mandibularextension of the mandibular denture is introduced from thedenture is introduced from the posterior and the superior beforeposterior and the superior before rotating the anterior segment ofrotating the anterior segment of the denture down over thethe denture down over the alveolar process.alveolar process.
  133. 133.
  134. 134. Prominent alveolar ridges withProminent alveolar ridges with parallel buccal and lingualparallel buccal and lingual walls provide significantwalls provide significant retention.retention. Very flat ridges resistsVery flat ridges resists displacement perpendicular todisplacement perpendicular to basal seat ,but does not resistbasal seat ,but does not resist movement parallel to basalmovement parallel to basal
  135. 135.
  136. 136. Contour of denture basesContour of denture bases:: Craddock described toCraddock described to maximise the role ofmaximise the role of denture bases indenture bases in retention ,properretention ,proper contour and design ofcontour and design of the polished surfacesthe polished surfaces should harmonise theshould harmonise the function of the lipsfunction of the lips ,cheeks and tongue to,cheeks and tongue to effect seating of theeffect seating of the dentures.dentures.
  137. 137. Magnets: Magnetic retentionMagnets: Magnetic retention offers many advantages as itoffers many advantages as it serves to dissipate lateralserves to dissipate lateral functional forces .functional forces . Small magnets are embeddedSmall magnets are embedded beneath the molar and thebeneath the molar and the premolar teeth and arranged topremolar teeth and arranged to similar poles to each other. Insimilar poles to each other. In theory repulsion keeps both thetheory repulsion keeps both the dentures in place.dentures in
  138. 138. In practice it will be found that ,In practice it will be found that , owing to magnetic force beingowing to magnetic force being inversely proportional to theinversely proportional to the square of the distance and alsosquare of the distance and also small size of the magnets which issmall size of the magnets which is possible to fit, the repulsive effectpossible to fit, the repulsive effect is undetectable when theis undetectable when the dentures are seperated by moredentures are seperated by more then 1-2mm.then 1-2mm.
  139. 139.
  140. 140. Suction chambers:Suction chambers: They resemble relief areas in shape butThey resemble relief areas in shape but differ by having a clearly defineddiffer by having a clearly defined outline instead of merging into theoutline instead of merging into the surrounding surfaces.surrounding surfaces. When the denture is inserted in theWhen the denture is inserted in the mouth the patient creates partialmouth the patient creates partial vaccum in this chamber by sucking,vaccum in this chamber by sucking, this small area of reduced pressurethis small area of reduced pressure keeps the denture in place.keeps the denture in
  141. 141.
  142. 142. Rubber suction discs: theyRubber suction discs: they consists of rubber disc whichconsists of rubber disc which is fixed to a stud on the fittingis fixed to a stud on the fitting surface of the denture.surface of the denture. Partial vaccum is createdPartial vaccum is created within the disc which holds thewithin the disc which holds the upper denture suspended fromupper denture suspended from hard palate.hard palate.
  143. 143.
  144. 144. Surgical factors:Surgical factors: The retention of the dentures canThe retention of the dentures can be increased by the use ofbe increased by the use of implants.implants. Ridge corrections:Ridge corrections: The sharp and spiny residual ridgesThe sharp and spiny residual ridges ,bony tuberosity interferences is,bony tuberosity interferences is surgically corrected to enhancesurgically corrected to enhance retention.retention.
  145. 145. The size of the ridges by surgicalThe size of the ridges by surgical procedures such as boneprocedures such as bone grafts,inserts of biomechanicalgrafts,inserts of biomechanical materials and vestibuloplasties .materials and vestibuloplasties .
  146. 146. Stability:Stability: Stability is quality of prosthesis to beStability is quality of prosthesis to be firm, steady, or constant to resistfirm, steady, or constant to resist displacement by functional horizontaldisplacement by functional horizontal or rotational stresses(GPT7).or rotational stresses(GPT7). It refers resistance against horizontalIt refers resistance against horizontal movement and forces that tend tomovement and forces that tend to alter the relationship between thealter the relationship between the denture base and its supportingdenture base and its supporting foundation in horizontal or rotatoryfoundation in horizontal or rotatory direction.
  147. 147. The factors that contribute to stability ofThe factors that contribute to stability of dentures are:dentures are: 1.Ridge anatomy.1.Ridge anatomy. 2.Base adaptation.2.Base adaptation. 3.Residual ridge relationships.3.Residual ridge relationships. 4.Occlusal harmony.4.Occlusal harmony. 5.Neuromuscular control.5.Neuromuscular control.
  148. 148. Ridge anatomy: Large,square, broadRidge anatomy: Large,square, broad ridges offer greater resistance toridges offer greater resistance to lateral forces than do small, narrow,lateral forces than do small, narrow, tapered ridges.tapered ridges. Small rounded irregularities of theSmall rounded irregularities of the residual ridges also contributeresidual ridges also contribute favorable to stability.favorable to stability.
  149. 149.
  150. 150. Another factor to be considered inAnother factor to be considered in stability is the arch form.stability is the arch form. Square and tapered arches tend toSquare and tapered arches tend to resists rotation of the prosthesisresists rotation of the prosthesis better than oviod arches.better than oviod arches.
  151. 151. The shape of the palatal vaultThe shape of the palatal vault also contributes to stability.also contributes to stability. A steep palatal vault mayA steep palatal vault may enhance stability by providingenhance stability by providing greater surface area of contactgreater surface area of contact and long inclines approaching aand long inclines approaching a right angle to the direction ofright angle to the direction of force.force.
  152. 152.
  153. 153. Impression techniques inImpression techniques in complete dentures.complete dentures.
  154. 154. 2.Relationship of the denture base to2.Relationship of the denture base to tissues:tissues: Friedman describes contacting theFriedman describes contacting the buccal and lingual flanges with thebuccal and lingual flanges with the buccal and lingual slopes of the ridgebuccal and lingual slopes of the ridge is the contributing factor for stability .is the contributing factor for stability .
  155. 155. Adequate extention of the dentureAdequate extention of the denture base as limited by the movablebase as limited by the movable tissues not only allows thetissues not only allows the establishment of the border sealestablishment of the border seal and coverage of maximumand coverage of maximum supporting area but also providessupporting area but also provides maximum contact of the denturemaximum contact of the denture base with the facial and lingualbase with the facial and lingual slope ridges.slope ridges.
  156. 156. Optimal denture stability requiresOptimal denture stability requires that those tissues that providethat those tissues that provide resistance to the horizontal forcesresistance to the horizontal forces be properly recorded and relatedbe properly recorded and related to denture denture base.
  157. 157. Boucher notes that stability isBoucher notes that stability is obtained by incorporating theobtained by incorporating the surfaces of the maxillary andsurfaces of the maxillary and mandibular ridges which are atmandibular ridges which are at right angle to the occlusal plane.right angle to the occlusal plane. He further states that stabilityHe further states that stability requires “maximum use of allrequires “maximum use of all bony foundations where thebony foundations where the tissues are firmly attached totissues are firmly attached to bone”bone”
  158. 158. Residual ridge relationships:Residual ridge relationships: A problem of stability is seen inA problem of stability is seen in prognathic and retrognathicprognathic and retrognathic patients.patients. Normal dental relationships of theNormal dental relationships of the artificial teeth set on ridges thatartificial teeth set on ridges that are in severe posterior crossbiteare in severe posterior crossbite can adversely affect stability.can adversely affect stability.
  159. 159. In complete dentures the normalIn complete dentures the normal tooth –tooth position may betooth –tooth position may be altered to enhance retention andaltered to enhance retention and stability.stability. Weinberg recognizes the need toWeinberg recognizes the need to set the artificial teeth in cross biteset the artificial teeth in cross bite when the ridges are in severewhen the ridges are in severe crossbite.crossbite.
  160. 160. In class III patients they frequentlyIn class III patients they frequently display a lower arch anterior to indisplay a lower arch anterior to in centric relation.centric relation. This causes the maxillary dentureThis causes the maxillary denture to tip anteriosuperiorly ,to tip anteriosuperiorly , traumatizing the maxillarytraumatizing the maxillary anterior ridge and loosening theanterior ridge and loosening the maxillary denture.maxillary denture.
  161. 161. Occlusal harmony:Occlusal harmony: to minimizeto minimize the dislodging forces thethe dislodging forces the occlusion should be balancedocclusion should be balanced throughout the functionalthroughout the functional range of movement of therange of movement of the patient.patient.
  162. 162. Tooth position and occlusal plane:Tooth position and occlusal plane: A mandibular occlusal plane that is tooA mandibular occlusal plane that is too high can reduce the denture stabilityhigh can reduce the denture stability because:because: 1.Lateral tilting forces directed against1.Lateral tilting forces directed against the teeth are magnified as the plane isthe teeth are magnified as the plane is raised.raised. 2.An elevated plane prevents the2.An elevated plane prevents the tongue from reaching the over thetongue from reaching the over the food table in the buccal table in the buccal vestibule.
  163. 163. This compromises stability andThis compromises stability and makes control of the food bolusmakes control of the food bolus and denture more difficult.and denture more difficult.
  164. 164. Occlusal plane: the best stability isOcclusal plane: the best stability is obtained when the occlusal plane isobtained when the occlusal plane is parallel to and anatomically orientedparallel to and anatomically oriented to the the ridges. If the occlusal plane is tipped there isIf the occlusal plane is tipped there is shunting effect and a loss of stability.shunting effect and a loss of stability.
  165. 165.
  166. 166. Relationship of the external surfaceRelationship of the external surface and periphery to surroundingand periphery to surrounding orofacial musculature:orofacial musculature: Actions of the muscles on theActions of the muscles on the denture base generally result indenture base generally result in the lateral and the verticalthe lateral and the vertical dislodging forces.dislodging forces.
  167. 167. The relationship of external surfaceThe relationship of external surface with the denture basewith the denture base
  168. 168. The denture borders should beThe denture borders should be extended to contact the movableextended to contact the movable tissues. This enhances stability.tissues. This enhances stability. The actions of the canninus, incisivus,The actions of the canninus, incisivus, triangularis, mylohyoid, mentalis andtriangularis, mylohyoid, mentalis and genioglossus muscles can lead togenioglossus muscles can lead to dislodging forces if the denture basesdislodging forces if the denture bases does not provide freedom for thesedoes not provide freedom for these muscles to action.muscles to action.
  169. 169. The basic geometric design of theThe basic geometric design of the denture bases should bedenture bases should be triangular.triangular. In frontal cross section , both theIn frontal cross section , both the dentures should appear as twodentures should appear as two triangles whose apex correspondtriangles whose apex correspond to the occlusal the occlusal surface.
  170. 170.
  171. 171. The buccal and labial flanges of theThe buccal and labial flanges of the maxillary and the mandibular denturesmaxillary and the mandibular dentures should be concave to permit positiveshould be concave to permit positive seating of the lips and cheeks. theseating of the lips and cheeks. the proper contour of the flanges permitsproper contour of the flanges permits the horizontally directed forces thatthe horizontally directed forces that occurs during the contraction ofoccurs during the contraction of buccinator and orbicularis orisbuccinator and orbicularis oris muscles to be transmitted as verticalmuscles to be transmitted as vertical forces tending to seat the prosthesis.forces tending to seat the prosthesis.
  172. 172. Support:Support: Support is the resistance of aSupport is the resistance of a denture to the vertical components ofdenture to the vertical components of mastication and to occlusal forces ormastication and to occlusal forces or other forces applied in directionother forces applied in direction towards the basal seat. (boucher)towards the basal seat. (boucher) Support is the resistance to verticalSupport is the resistance to vertical movement of the denture basemovement of the denture base towards the ridge. (Jacobson andtowards the ridge. (Jacobson and Krol)Krol)
  173. 173. Support can be considered from twoSupport can be considered from two points of view:points of view: 1.Maxillary and mandibular dentures1.Maxillary and mandibular dentures should conform to the underlyingshould conform to the underlying tissues so that the occlusal surfacestissues so that the occlusal surfaces can correctly oppose one another atcan correctly oppose one another at the time of insertion.the time of insertion. 2.The denture bases should maintain2.The denture bases should maintain this relationship for a period of time.this relationship for a period of time.
  174. 174. Initial denture support is achievedInitial denture support is achieved by using impression proceduresby using impression procedures that provide optimal extensionthat provide optimal extension and functional loading ofand functional loading of supporting tissues, which vary insupporting tissues, which vary in their resiliency.their resiliency.
  175. 175. Long-term support is obtained byLong-term support is obtained by directing the forces of occlusaldirecting the forces of occlusal loading toward the tissues mostloading toward the tissues most resistant to remodelling andresistant to remodelling and resorptive changes.resorptive changes.
  176. 176. Effective support is realized whenEffective support is realized when The denture is extended to cover aThe denture is extended to cover a maximal surface area withoutmaximal surface area without impinging on movable tissues .impinging on movable tissues . The tissues most capable of resistingThe tissues most capable of resisting resorption are loaded during function.resorption are loaded during function. The tissues most capable of resistingThe tissues most capable of resisting vertical displacement are allowed tovertical displacement are allowed to make firm contact with the denturemake firm contact with the denture base during functionbase during
  177. 177. Compensation is made for theCompensation is made for the varying tissue resiliency tovarying tissue resiliency to provide for uniform denture baseprovide for uniform denture base movement under function andmovement under function and maintain a harmonious occlusalmaintain a harmonious occlusal relationship.relationship.
  178. 178. Nature of supporting tissues:Nature of supporting tissues: Ideally ,the soft tissues should beIdeally ,the soft tissues should be -firmly bound to underlying cortical-firmly bound to underlying cortical bonebone -contain resilient layer of-contain resilient layer of submucosa , and be covered bysubmucosa , and be covered by keratinised mucosa.keratinised mucosa.
  179. 179. The underlying bone should be :The underlying bone should be : -resistant to pressure induced-resistant to pressure induced remodeling.remodeling. -cortical bone is more resistant to-cortical bone is more resistant to resorption than cancellous bone.resorption than cancellous bone.
  180. 180. The areas of support :The areas of support : Primary areas of support: Areas of thePrimary areas of support: Areas of the edentulous ridge that are at rightedentulous ridge that are at right angles to the occlusal forces andangles to the occlusal forces and donot resorb easily.donot resorb easily. Maxillary- residual ridge, horizontalMaxillary- residual ridge, horizontal portion of hard palate.portion of hard palate. Mandible-buccal shelf area .Mandible-buccal shelf area .
  181. 181.
  182. 182.
  183. 183. Secendory:Secendory: Maxilla:rugea areasMaxilla:rugea areas Mandible: slopes of the residualMandible: slopes of the residual ridge.ridge.
  184. 184. Importance of covering the buccalImportance of covering the buccal shelf:shelf: It is the area of support because:It is the area of support because: It has a cortical bone.It has a cortical bone. It is at right angle to the occlusal plane.It is at right angle to the occlusal plane. When the ridge is flat the buccinator isWhen the ridge is flat the buccinator is almost attached to the centre of thealmost attached to the centre of the ridge. The denture can cover this arearidge. The denture can cover this area as this muscle is flaccid and inactiveas this muscle is flaccid and inactive as its fibers function in horizontalas its fibers function in horizontal direction.direction.
  185. 185.
  186. 186. In the maxilla horizontal portion ofIn the maxilla horizontal portion of the hard palate lateral to midthe hard palate lateral to mid palatine raphe should providepalatine raphe should provide primary support to completeprimary support to complete dentures because the submucosadentures because the submucosa contains fatty tissue anterolaterallycontains fatty tissue anterolaterally and glandular tissueand glandular tissue posteriolaterally. This resilientposteriolaterally. This resilient layer acts as a cushion to thelayer acts as a cushion to the functional stresses.functional stresses.
  187. 187. It is enhanced by selectiveIt is enhanced by selective placement of the pressures thatplacement of the pressures that are in harmony with theare in harmony with the resiliency of the tissues thatresiliency of the tissues that make up the basal seat.make up the basal seat.
  188. 188. Esthetics:Esthetics: The role of esthetics in impressionThe role of esthetics in impression making refers to the development ofmaking refers to the development of the labial and buccal borders so thatthe labial and buccal borders so that they are not only retentive but alsothey are not only retentive but also support the lips and the the lips and the cheeks. These structures should not be overThese structures should not be over supported with borders that are toosupported with borders that are too thick.thick.
  189. 189. Hence it is ideal to completeHence it is ideal to complete the impressions with thethe impressions with the peripheral width that will beperipheral width that will be utilized in the polishedutilized in the polished dentures.dentures.
  190. 190.
  191. 191. Theories of impression making:Theories of impression making: Mucostatic theory/minimalMucostatic theory/minimal pressure impressions.pressure impressions. MucocompressiveMucocompressive theory/definitive pressuretheory/definitive pressure impressions.impressions. Selective pressure.Selective pressure.
  192. 192. Mucocompressive theory:Mucocompressive theory: Because denture retention is tested mostBecause denture retention is tested most severly during mastication, manyseverly during mastication, many dentists formerly considered it isdentists formerly considered it is essential for the tissue to remain inessential for the tissue to remain in contact with the denture during with the denture during chewing. It appeared logical to them to makeIt appeared logical to them to make impressions that would press the tissuesimpressions that would press the tissues in the same manner as the chewingin the same manner as the chewing forces.forces.
  193. 193. However the dentures did notHowever the dentures did not fit well at rest , becausefit well at rest , because tissues distorted tend totissues distorted tend to rebound.rebound. There was a question weatherThere was a question weather tissues so abused will longtissues so abused will long maintain the shape that theymaintain the shape that they assumed during the day ofassumed during the day of
  194. 194. Advocates of this techniqueAdvocates of this technique closed-mouth procedures (Trydeclosed-mouth procedures (Tryde et al.,) this technique presumeset al.,) this technique presumes that the occlusal loading duringthat the occlusal loading during the impression will be same asthe impression will be same as the occlusal loading duringthe occlusal loading during function.function.
  195. 195. Critics of this procedure point outCritics of this procedure point out that the dentures are in actualthat the dentures are in actual occlusal contact only for a shortocclusal contact only for a short period of time and the constantperiod of time and the constant pressure will over-stress thepressure will over-stress the tissuestissues
  196. 196. This theory of impression makingThis theory of impression making was not always able to obtain thewas not always able to obtain the desired pressure but tended todesired pressure but tended to create excessive pressure.create excessive pressure. This often resulted in good initialThis often resulted in good initial retention but eventual boneretention but eventual bone resorption and loose dentures.resorption and loose dentures.
  197. 197. Mucostatic impression theory:Mucostatic impression theory: Addison in 1944 described theAddison in 1944 described the mucostatic impressions andmucostatic impressions and attributed them to Page.attributed them to Page. The main point of the mucostaticThe main point of the mucostatic principle concerned Pascal’s lawprinciple concerned Pascal’s law which states that “the pressure onwhich states that “the pressure on the confined liquid will bethe confined liquid will be transmitted throught the liquid intransmitted throught the liquid in all directions”.all directions”
  198. 198. According to this concept. mucosaAccording to this concept. mucosa being more than 80% of water willbeing more than 80% of water will react like liquid in a closed vesselreact like liquid in a closed vessel and thus cannot be compressed.and thus cannot be compressed. This is not true, insofar the fluidsThis is not true, insofar the fluids escape from the border of theescape from the border of the denture.denture. The mucosa is not a closed vessel.The mucosa is not a closed vessel.
  199. 199. According to this principle theAccording to this principle the impression material should record,impression material should record, without distortion, every detail ofwithout distortion, every detail of the mucosa so that the completedthe mucosa so that the completed denture will fit in the elevations anddenture will fit in the elevations and depressions . For this reasondepressions . For this reason separating medium was not usedseparating medium was not used at any point of the any point of the procedure.
  200. 200. But the draw back was theBut the draw back was the impression materials and the castsimpression materials and the casts exhibited sufficient dimensionalexhibited sufficient dimensional change to render worthless thechange to render worthless the care taken to record all the minutecare taken to record all the minute details.details. Mucostatics further demand the useMucostatics further demand the use of metal base than theof metal base than the dimensionally unstable acrylics.dimensionally unstable acrylics.
  201. 201. But Stephen in 1946 told that theBut Stephen in 1946 told that the mucosal topography is not static overmucosal topography is not static over 24hr period. There is difference24hr period. There is difference between the mucosal contour justbetween the mucosal contour just after rising in the morning , and thatafter rising in the morning , and that which exists after 12hrs in uprightwhich exists after 12hrs in upright position.position. So it would appear that the achievedSo it would appear that the achieved impression would be altered by theimpression would be altered by the time the denture is finished.time the denture is
  202. 202. This principle considered interfacialThis principle considered interfacial surface tension as the only importantsurface tension as the only important retentive mechanism in the completeretentive mechanism in the complete dentures.dentures.  Therefore they did not useTherefore they did not use conventional flanges because theyconventional flanges because they could not resists the verticalcould not resists the vertical displacement ,with was only thedisplacement ,with was only the movement interrupting the surfacemovement interrupting the surface tension.tension.
  203. 203. Dykins in 1947 recommended shortDykins in 1947 recommended short lingual flange that resists laterallingual flange that resists lateral movements.movements. The mucostatic principle ignores theThe mucostatic principle ignores the value of dissipating the masticatoryvalue of dissipating the masticatory forces over largest possible basalforces over largest possible basal seat area. The mucostatic denture minimizedThe mucostatic denture minimized the retentive role of muscles, asthe retentive role of muscles, as described by Fish in1948.described by Fish in1948.
  204. 204. Selective pressure theory:Selective pressure theory: This theory combines pressure overThis theory combines pressure over certain areas and little pressure overcertain areas and little pressure over others.others. The principle behind this theory is basedThe principle behind this theory is based on the belief that the mucosa over theon the belief that the mucosa over the ridge is best able to withstand pressure,ridge is best able to withstand pressure, whereas that covering the midline is thinwhereas that covering the midline is thin and contains very little submucosaland contains very little submucosal tissue (Boucher, 1951).tissue (Boucher, 1951).
  205. 205. How ever this technique demandsHow ever this technique demands firm, healthy mucosal coveringfirm, healthy mucosal covering over the ridge.over the ridge. If flabby ridges exists, it isIf flabby ridges exists, it is preferable to use a minimalpreferable to use a minimal pressure impression.pressure impression.
  206. 206. Impression techniques.Impression techniques. Classification:Classification: 1.1. Amount of pressure usedAmount of pressure used -minimal pressure technique.-minimal pressure technique. -mucocompressive technique.-mucocompressive technique. -selective pressure technique.-selective pressure technique. 2.Open or closed mouth technique.2.Open or closed mouth technique. 3.Hand manipulations or functional3.Hand manipulations or functional movements.movements. 4.Type of tray.4.Type of tray.