Essentials ofProsthodonticsEssentials ofProsthodonticsJAYPEE BROTHERSMEDICAL PUBLISHERS (P) LTDNewDelhiSH SoraturBDS(Bombay),FICD(USA)Reader(Retd),RajivGandhiCollegeofDentalSciences,BangaloreFormerly,HouseSurgeonatUniversity College Hospital, London andGlasgowRoyalInfirmary,ScotlandDentalPractitionerinLondonAuthorof:(1)EssentialsofDentalMaterials(2)VivainDentalMaterials,(3)VivainProsthodonticsPublishedbyJitendar P VijJaypeeBrothersMedicalPublishers(P)LtdEMCA House, 23/23B Ansari Road, DaryaganjNew Delhi 110 002, IndiaPhones:+91-11-23272143,+91-11-23272703,+91-11-23282021,+91-11-23245672Fax:+91-11-23276490,+91-11-23245683e-mail:jaypee@jaypeebrothers.comVisitourwebsite:www.jaypeebrothers.comBranches 2/B, Akruti Society, Jodhpur Gam Road SatelliteAhmedabad 380015,Phone:+91-079-30988717 202 Batavia Chambers, 8 Kumara Krupa Road, Kumara Park EastBangalore560 001, Phones: +91-80-22285971, +91-80-22382956, +91-80-30614073Tele Fax: +91-80-22281761 e-mail: jaypeemedpubbgl@eth.net 282 IIIrd Floor, Khaleel Shirazi Estate, Fountain PlazaPantheonRoad,Chennai600008,Phones:+91-44-28262665,+91-44-28269897Fax:+91-44-28262331 e-mail:jpchen@eth.net 4-2-1067/1-3, Ist Floor, Balaji Building, RamkoteCrossRoad,Hyderabad500095,Phones:+91-40-55610020,+91-40-24758498Fax: +91-40-24758499 e-mail: jpmedpub@rediffmail.com 1AIndian Mirror Street, Wellington SquareKolkata700013,Phones:+91-33-22456075,+91-33-22451926Fax: +91-33-22456075 e-mail: jpbcal@cal.vsnl.net.in 106 Amit Industrial Estate, 61 Dr SS Rao Road, Near MGM HospitalParel,Mumbai400012,Phones:+91-22-24124863,+91-22-24104532,+91-22-30926896 Fax:+91-22-24160828 e-mail:jpmedpub@bom7.vsnl.net.in KAMALPUSHPA 38, Reshimbag Opp Mohota Science College,Umred Road, Nagpur 440 009 (MS),Phone: +91-712-3945220, +91-712-2704275e-mail: jpmednagpur@rediffmail.comEssentials of Prosthodontics 2006, SH SoraturAllrightsreserved.Nopartofthispublicationshouldbereproduced,storedinaretrievalsystem, or transmitted in any form or by any means: electronic, mechanical, photocopying,recording, or otherwise, without the prior written permission of the author and the publisher.This book has been published in good faith that the material provided by author is original.Every effort is made to ensure accuracy of material, but the publisher, printer and authorwill not be held responsible for any inadvertent error(s). In case of any dispute, all legalmatters are to be settled under Delhi jurisdiction only.FirstEdition:2006ISBN 81-8061-697-5Typeset at JPBMP typesetting unitPrinted at Gopsons Papers Ltd, A-14, Sector 60, Noida 201 301, IndiaDedicated toAll of my teachersfromPrimary School (Shiragambi)toPostgraduate Level (London)ForewordI am happy to write a foreword to Essentials of Prosthodontics by Dr SH Soratur, whom I know since many years.This book has filled a vacuum felt for long in the field of prosthodontics, and the text is based on the long experiencetheauthorhashadinteachingandclinicalpracticebothinIndiaandabroad.The style of discussing a subject is simply wonderful because it goes to the root of the matter and by giving examplesofeverydaylife,themind-bogglingaspectsofthetopicsaremadeeasilyunderstoodandinteresting. Avastsubjectsuch as prosthodontics cannot be dealt in detail in a book of this size, but its essentials are well-narrated and illustratedtouchingallbranchesofthesubject.I am sure that the students and general dental practitioners will find this book valuable and useful to enhance onesknowledge.DrPrafullaThumatiPrincipalBangaloreInstituteofDentalSciencesandHospitalBangalore560029PrefaceThisbookisaproductofmy40yearsofprivatedentalpracticeinIndiaandabroadincluding24yearsofteachingexperienceindifferentdentalcolleges.Itdealswithbasicsandessentialsofcompleteandpartialdenturesnecessaryforundergraduatestudentsandgeneraldentalpractitioners. Atthesametimeitfulfillstheuniversitysyllabusfromexaminationpointofview.Simplestep-by-stepproceduresexplainedinsimplelanguagewillremoveallconfusionsaboutthetrickyworkofmakingdentures.Thebookisinfiveparts,partonedealswithbasicsfromtheprosthodonticpointofview,parttwodealswithlaboratoryprocedures(Pre-clinical)involvedinmakingcompletedentures,partthreedealswithclinicalproceduresofcompletedentureconstruction,partfourwithpartialdenturesandfinallypartfivewithcrowns,bridges,implantdentures,obturators,andmaxillofacial-prosthesisvery-verybriefly.Since Good Dentures are a Thing of Beauty and Joy Forever, I am of the opinion that sincerity and due attentionto all stages is essential for the success of prosthodontic work. However, use of common sense and belief in Practicemakesperfectequallyholdsgood.Thebookissuitably-illustratedwithplentyofdrawingsandphotographs,whichmake it all the more interesting to read. I hope and wish that students and practitioners of dentistry will be immenselybenefitedbyreadingthisbook.SHSoraturIamthankfulto: My son Dr Puneet Soratur for his painstaking correction of the script, proofreading and valuable suggestions. My another son Rajeev Soratur (Artist) and his wife Vidya for their attractively drawn diagrams and sketches. Dr Prafulla T, MDS (Prosthodontics), Principal, Bangalore Institute of Dental Sciences, Bangalore, for writingaforewordtothisbook. M/sJaypeeBrothersforpublishingthisattractivebook.AcknowledgementsPART 1INTRODUCTION1. Applied Anatomy and Physiology ......................................................................................... 32. Prosthodontics .................................................................................................................... 193. RetentionandStability ...................................................................................................... 244. PreprostheticSurgery ......................................................................................................... 27PART 2LABORATORYPROCEDURESFORCOMPLETEDENTURES5. MakingofCastandModel ................................................................................................. 336. MakingSpecialTrays ......................................................................................................... 387. MakingJawRegistrationBlocks ........................................................................................ 438. Articulators and Mounting .................................................................................................. 479. Setting-upofTeeth ............................................................................................................. 5210. Acrylisation ........................................................................................................................ 6511. Repair,Relining,Rebasing,Etc. ......................................................................................... 75PART 3CLINICALPROCEDURESFORCOMPLETEDENTURES12. Examination of Patient ....................................................................................................... 8313. MakingImpressionsofEdentulousJaws ............................................................................ 9014. JawRelations ................................................................................................................... 10415. SelectionofArtificialTeethandTry-in ........................................................................... 11516. FittingtheDenturesandTeethingTroubles ..................................................................... 119ContentsPART 4PARTIALDENTURES17. Classification ................................................................................................................... 12718. DesignofCastPartialDentures ....................................................................................... 13019. Components of Cast Partial Denture ................................................................................ 13820. ClinicalandLaboratoryProcedures ................................................................................ 152PART 5CROWNS,BRIDGES,ANDMISCELLANEOUS21. Crowns ............................................................................................................................. 17322. Bridges ............................................................................................................................. 18323. Implant Denture ............................................................................................................... 18824. Obturators ........................................................................................................................ 19125. MaxillofacialProsthesis ................................................................................................... 194Index ................................................................................................................................................................... 199xii Essentials of ProsthodonticsPart 1Applied Anatomy and Physiology 31AppliedAnatomy and PhysiologyTheSkullThisisdividedinto;a. Cranialpart Whichcontainsandprotectsbrain.b. Facial part Whichcontainseyes,noseandmouth.Number of bones joined by sutures makeup the skull.BonesofCraniuma. Frontalboneisinthefrontabovetheeyes.b. Parietal and temporal bones form the sidewalls oftheskullabovetheears.c. Occipital bone forms the back of the skull.d. Occipitalbone,temporalbones,andsphenoidbones together form the under surface of the skull.Therearenumerousopenings(foramina)inthebase of the skull through which blood vessels andnervespass(Fig.1.1).FacialBonesThisconsistof:a. Maxilla,upperjaw:Thisismade-upoftwomaxillarybonesjoinedinthemiddle.Thisbonecontributes to mouth cavity, nose cavity, and flooroftheorbitalcavities.Eachmaxillahaslargeairsinuses(maxillarysinusorantrum),whichisconnected,tothenosecavity.Antrumisabovetherootsofuppersecondpremolarandmolars.Hardpalateofmaxillaformstheroofofthemouth;itisformedbytwopalatalprocessesofmaxillarybonejoininginthemiddle.Ifthetwopalatal processes fail to join during development,the result is cleft palate. Surgically untreated cleftpalatesaretreatedbyprosthesisknownasobturator.The maxilla is firmly attached to the skull andso immovable. The maxilla carries maxillary teeth.b. The palatine bonesThese form the posterior partsofthehardpalateandalsosidewallsofnasalcavity.c. Zygomatic (Malar) bonesalso known as Cheekbones form the upper part of the cheeks- this andtheprocessoftemporalbonetogetherformtheZygomaticarchatthesideoftheskull(Fig.1.2).d. MandibleLowerjawThisisasingleboneofhorse shoe shape attached to the base of the skullnot by sutures but by two joints known as tempero-mandibular joints, situated just in front of the ears.Partsofmandible:i. Alveolarprocess:Lowerteetharesocketedinthispartandmucousmembrane(gum)isattachedtoit.ii. Bodyofmandible:Thissupportsthealveolarprocess. Body has lower border forming the chinin the front and angle of the jaw at the back. Ontheoutersurfaceofthebodythereisexternalobliqueridgetowhichbuccinatormuscleisattached.Ontheinnersurfacethereismylohyoidridge(internalobliqueridge)towhichmylohyoidmuscleisattached.Alsoontheoutersurfaceofthebodyofthemandible Fig. 1.1: Human skullPart 14 Essentials of Prosthodonticsbelowthepremolarteeththereisthementalforemenfromwhichnervesandbloodvesselspasstothelowerlipandgumsintheincisorand canine region. Within the body of mandiblethere is the inferior dental canal through whichinferiordentalnerveandbloodvesselstravel.BodyofthemandibleisdevelopedfromMeckelscartilage.Ontheinnersurfaceofthemandibleinthemidlinetherearegenialtubercles(Fig.1.3).iii. Mandibular ramus: This is the vertical plate onthebackofthebodyofthemandible.Theramushastwoprocesses;namely(a)Anteriorcoronoidprocessand(b)Posteriorcondyloidprocess.Betweentheseprocessesisthesigmoidnotch.Ontheinnersideoftheramusthereistheposterioropeningoftheinferiordental(mandibular)canalthroughwhichnerveandbloodvesselsenterthebodyofthemandible.Thetipofthecoronidprocessgetsattachmentoftemporalmuscle.Theuppermostpartofcondyloidprocessisknownasheadofthecondyleandfitsintoahollowspace(glenoidfossa)oftheskullinfrontoftheear.e. TheotherfacialbonesareNasalbone,LacrimalandEthmoidbones.ORALCAVITY(MOUTH)BoundariesAnteriorly LipsPosteriorly PharynxLaterally CheeksAbove Roofofthemouth.Below Floorofthemouth(Fig.1.4)Fig. 1.2: Side of the skull1.Maxilla,2.Mandible,3.Ramusofmandible,4.Zygomaticbone,5. Zygomatic arch, 6. Sphenoid process, 7. Frontal bone, 8. Parietalbone, 9. Temporal bone, 10. Mastoid process, 11. Occipital boneFig.1.3: Outer surface of mandible1. Coronoid process, 2. Alveolar process, 3. Mental foramen, 4. Body,5. Angle, 6. Ramus, 7. Condyler processFig 1.4: Oral cavity1. Maxillary labial frenum, 2. Incisive papilla, 3. Maxillary buccal frenum,4.Alveolarsocket,5.Cheek,6.Tuberosity,7.Hamularnotch,8. Retromolar pad, 9. Cheek, 10. Sulcus, 11. Mandibular alveolar ridge,12. Mandibular buccal frenum, 13. Tongue, 14. Uvula, 15. Palatal fovea,16. Palatal torus, 17. Hard palate, 18. Rugae, 19. Sulcus, 20. Maxillaryalveolar ridgePart 1Applied Anatomy and Physiology 5Theoralcavityislinedwithmucousmembrane,which is attached to the necks of teeth, to the alveolarboneandtothehardpalate.Inotherareas,themucousmembranecoversthemusclesofthelips,cheeks,softpalateandtongue.Histologicallythemucousmembranehassurfaceepithelialcells,andunderlying connective tissue layer consisting of fibres,fibroblasts, small blood vessels; lymph vessels; nerveendings and nerves related to the sensation of pain,touch,hot,coldandtaste.The mucous membrane where it is firmly attachedto the underlying bone is immovable and is used asadenturefoundation.Whereitiscoveringthemusclesitismovableandismoresensitive.Thereflexion of the mucous membrane from the alveolarbonetothelipsandcheeksformsthevestibuleofthemouth.ContentsoftheOralCavitya. Teethindentulousstate.b. Gum(ridge)inedentulousstate.c. Tongued. Salivaryglands.e. Frenalattachments.f. Saliva(Fig.1.5).Permanent TeethTheseare32innumbertogetherintheupperandlower jaw- with 16 in each jaw and 8 on each side ofthe jaw, starting from the midline of the oral cavity.Theseteetharerepresentedasfollows:Patients Right Patients Left87654321 12345678 upper87654321 12345678 lowerDescriptionofToothRoot Toothpartbelowthegumandcoveredbycementum.Crown Toothpartabovethegumandcoveredbyenamel.Mesial Tooth part nearest to the median line.Distal Toothpartawayfromthemedianline.Labial Toothpartofanteriortoothfacingthelips.Buccal Tooth part of posterior tooth touchingthecheek.Incisal Cuttingsurfaceofanteriortooth.Occlusal Chewingsurfaceofposteriortooth.Cervical Toothpartatwhichrootandcrownmeet.Gingival Tooth part which touches the gum orgingiva.Lingual Tooth part which is nearest to tongue.Palatal Toothpartthatisnearesttothepalate.Proximal Toothpartwhichisinclosecontactwithanothertooth(Fig.1.6)Cingulum Itisthelingualbulgeatthebaseofthecrownofanteriortooth.Anterior Thesearethe12teeth(front)teeth (6 in the upper jaw and 6 in the lower)near the upper and lower lips.Fig. 1.5: Dental arches1. Deciduous teeth, 2. Permanent teeth, 3. Maxillary, 4. MandibularFig 1.6: Dental arch1. Labial, 2. Buccal, 3. Lingual or palatal,4. Occlusal, 5. Mesial, 6. DistalPart 16 Essentials of ProsthodonticsFunctionbiting,tearingandshearingPosterior Theseare20teeth(Back)teeth (10intheupperjawand10inthelowersituatedbehindtheanteriors.FunctionChoppingandgrinding.)HistologyofToothToothismadeupofenamel,dentine,pulpandcementum.Rootofthetoothisheldinthealveolarboneofthemainjawbonebymeansofperiodontalmembrane(Fig.1.7).1st Permanent Molar Key of OcclusionTheseteetheruptimmediatelybehindtheseconddeciduousmolarsusuallyattheageofsixyears,whichisaboutoneyearbeforethefirstofthedeciduousteeth,areshed.Proper occlusion of these teeth, upper with lowerandonbothsidesofthearchisoneimportantstepforthereasonsof;a. Propermastication.b. Growth and development of the lower half of face.c. Facialexpression.d. Oralhealthandgeneralhealth.Because these four 1st molars in proper occlusion.1. Holdthejawsinproperrelationduringthechangingoverperiodofdeciduousteethtopermanentteeth.2. Properinter-digitationsofupperandlower1stmolarspreventthefutureirregularitiesofocclusion. So this is called Key of occlusion.3. Thesefourteethsupportthejaws.Then the eruption sequence of permanent teeth isasfollows;CentralIncisorat 7yearsofageLateralIncisorat 8yearsofage1stpremolarat 10yearsofage2nd pre molar at 11yearsofage2nd molars and canines at 12yearsofage3rdmolarat 18-20yearsofage.Whenallthepermanentteethareeruptedtofullocclusion.a. MesiodistalrelationLowerteethcuspsarelittleanteriortothecorrespondingcuspsoftheupperteeth.b. Upperteethoverlapthelowerteethallaroundthearch.c. Buccal cusps of uppers and lingual cusps of lowersshowprominencewhichpreventscheekandtonguebiting,bypushingthecheekandtongueasideduringchewing(Fig.1.8).EDENTULOUS STATEDentureFoundationDenture-bearingAreasTosupportthedenture,theareacoveredbythemucousmembranemusthaveunderlyingbonysupport,calledhardtissueareaandthiswillfirmlysupportthedenture.Theareaswhichtake-upthemainloadofcompression(ofmastication)arethemaxillary and mandibular alveolar ridges which areFig 1.7: Structure of tooth1. Enamel, 2. Dentin, 3. Pulp, 4. Gum (Gingiva), 5. Cementum,6. Periodontal membrane, 7. Alveolar bone, 8. Apical foramenFig 1.8: Occlusion of permanent teethA. Maxilla, B. Body of mandible, C. Ramus of mandible,D. Mental foramenPart 1Applied Anatomy and Physiology 7solidandunyielding,areknownasMainstressbearingareas.ThepalateisconsideredasSecondarystressbearingareabecausetheboneunderneathisthinand slightly flexible but it doesnt undergo resorptionlikealveolarridges.Bonyprominencesliketoruspalatinusandtuberositiesshouldbesuitablyrelievedtopreventpressure and pain.The palatal rugea help in mixing the food into thetastebudsofthetongue.Palatalrugaeshouldbesincerelycopiedonthefittingsurfaceoftheupperdenture.The tissue beyond the main and secondary stressbearingareasarethesofttissueareas,whicharemobile and sensitive, are not the satisfactory denturefoundationareas.Denture coverage: Maxillary complete denture shouldcoverthewholeofthepalate,labialandbuccalaspectsofalveolarridge.Theposteriorbordershould be through the palatal fovea and completelycoverthetuberosities.Mandibularcompletedentureshouldcoverthewholealveolarridgerightuptoitsfulldepthofsulcus.Theposteriorbordershouldgoovertheflabbyretromolarpads(Fig.1.9).Postdam:Thisisaraisedlipontheposteriorborderof the fitting surface of the upper denture as a meansofachievingperfectperipheralseal.TheTongueThe tongue occupies the whole of the oral cavity whenatrestwithteethoccluded.Ithasawonderfulcapacity to change its shape in so many ways duringitsmanyfunctionalactivities.Itcanbeprotruded,retracted,twistedandtheseareduetothecombinationofactionsofintrinsicmusclesofthetongue. Contraction of the intrinsic muscles shortensthetongue.Thesemusclesaresuppliedbythehypoglossal(12thcranial)nerve.Parts of TongueTongueisDividedintoa. Tip.b. Dorsum(uppersurface).c. Rightandleftmargin.d. Undersurface.Anterior2/3rdofthetongueonlyisvisiblebydirectvision,butnottheposterior1/3rd.Theuppersurface(Dorsum)andsidesofthetongue has a mucous membrane with numerous smallpapillae(projections).Theseare:a. Filiform papillaeb. Fungiform papillaeAtthejunctionofanterior2/3rdandposterior1/3rd in the center of the dorsum, there are circum-vallate papillae.These papillae give the tongue a rough surface toprovidefrictionforthemasticationoffood.Mosttastebudsarepresentintheepitheliumofthe tongue and some in the epithelium of soft palate,pharynxandepiglottis.Theundersurfaceofthetongueiscoveredbysmooth,thin,looselyattachedmucousmembraneandthemucousmembraneisconnectedtothefloorofthemouthbythemidlinefrenum (lingual frenum).Theposteriorpartorrootofthetongueismuchmore uneven and nodular due to rounded elevationswith Central crypts. These are also called as lingualtonsils(Fig.1.10).Functions of Tonguea. Formasticationb. Forspeechc. Fortasted. ToexpressemotionsSignificance of Tongue1. Tongues movements, size and position should betakenintoconsiderationwhiledesigningadenture.Fig 1.9: Maxillary denture foundation1.Mainstress-bearingarea,2.Subsidiarystress-bearingarea,3. Postdam area, 4. Soft tissue areaPart 18 Essentials of Prosthodontics2. Ill-fittingdentureorsharp,neglectedtoothcancauseirritation,ulcerorevencanceroftongue.3. Helpduringregistrationofhorizontalrelationofmandibletomaxilla(i.e.centricRelation)byaskingthepatienttoputthetipofthetonguetothe back of palate, the mandible is pulled back bytongue.TheLipsandCheeksThesetogetherformtheanteriorandlateralboundariesoftheoralcavity.Theiroutersurfaceiscoveredbyskinandinnersurfacesbymucousmembrane. They consist mainly of muscle tissue andcollectivelytheyarecalledMusclesofFacialExpression(Fig.1.11).MusclesoftheLipsA. Closing musclesOrbicularisorisThisformsthecircularlooppassingfromoneliptotheotheraroundthecorners of the mouth. When this muscle contractsthe lips are drawn together and mouth is closed.B. Opening musclesZygomaticusTriangularisQudratuslabiinferiorisandsuperiorisIncisivus labi superioris and inferiorisMentalisCaninusAll these muscles enter the lips in a radial manner,and when they contract open the lips.Allthesemusclestogetherformthemusclesoffacialexpressionbytheirvariousreactionsintheemotionalstatesofjoy,anger,sorrowandmanyothers. These muscles are supplied by the facial nerve(7thcranial).Sensoryimpulsespassthroughbuccinatorandmentalnerves.All these muscles meet distal to the corners of themouthtoforma,Modiolus(meetingplace).Inthemidline, upper lip and lower lip are connected to thegum by labial frenums. Upper labial frenum is betterdevelopedthanlowerlabialfrenumandbothhavetoberelievedappropriatelybythedentureperiphery.BuccinatormuscleisthemainMuscleofCheekandittakesitsoriginfromtheoutersurfaceofthemaxillaandisinsertedinthemandible.Attheposterior end it is attached to the pterygomandibularraphe. Its fibers run horizontally forward to continueinto the orbicularis oris muscle, upper as well as lowerFig 1.10: The human tongueA.Uppersurface,B.Sideview(cut)Fig. 1.11: Facial muscles1. Orbicularis oris, 2. Triangularis, 3. Caninus,4.Zygomaticus,5.BuccinatorPart 1Applied Anatomy and Physiology 9part. The buccinator is supplied by the branch of thefacialnerve(7thcranial).Theparotidductpiercesthe buccinators to reach the buccal sulcus in the regionof maxillary 2nd permanent molar tooth on each sideof the face. The mucous membrane lining the cheeksis reflected on the alveolar bone of upper and lowerjawstoformgums.Thespacebetweencheeksandlips on one side and gums and teeth on another side,isknowasVestibuleofthemouth(Fig.1.12).FunctionsWithtongueononesideandlipsandcheeksonanother side keep the food on the occlusal surface oftheteethduringmastication.SignificanceTheareabetweentongueononeside,cheekandlipsonothersideisknownasNeutralZoneasdescribedbySirWilliamKelseyFry.Andartificialteethshouldbeset-upinthisneutralzoneforthedenturestability.Roof of the mouth: Hard and soft palateHard and soft palates separate the oral cavity fromthe nasal cavity and nasopharynx. The bony part ofthehardpalateismadeupbythepalatalprocessesof the two maxilla and the horizontal process of thetwopalatalbones.Anteriorlythereisincisiveforamenandpost-eriorlypalatineforamenatotransmitnervesandbloodvessels.SoftPalateThisiscontinuouswiththehardpalateandendsposteriorly in a free margin. In the center of the freemarginthereisuvula.Thesidesofthesoftpalatehas two folds (pillars)- namely, anterior pillar of thefaucesformedbypalato-glossalfold,andposteriorpillar of the fauces formed by palato pharyngeal fold.Between the two pillars lies the lymphoid tissue calledTonsil.TheMusclesofSoftPalateLevatorvelipalatiniTensorvelipalatini.UvulaPalato glossusPalatopharyngeus.FunctionsofSoftPalate1. It is lifted up during swallowing and thus preventsfoodgoingintothenose.2. Atrestitformsamuscularsealbylyingagainstthebackofthetongue.FlooroftheMouthThisistheareabetweenthetwohorizontalramiofmandibleandisoccupiedbytongue.Themucousmembranecoveringthefloorofthemouthextendsover the inner aspects of mandible to form labial andlingualgingivaeandcoverstheundersurfaceandlateral surface of tongue. Sublingual salivary glandsare situated between the mylohyoid muscle and themucosaofthefloorofthemouthonbothsides.The right and left mylohyoid muscles are connectedin the midline by a raphe. The muscles are attachedanteriorlyatthemylohyoidridgeofthemandible.Abovethemylohyoidtherearetwogeniohyoidmuscles attached anteriorly to the genial tubercle andposteriorlytothehyoidbone.Alsothereisgenio-glossus muscle going into the tongue.Thesubmandibularsalivaryglandissituatedinthefloorofthemouthbetweenthemandibleandthe tongue and under the mucous membrane towardsthebackoftheoralcavity.Theductofeachsub-mandibular gland runs forward to open just behindthelowerincisorteeth(Fig.1.13).Salivary glands: These are mainly 3 pairs1. Parotidgland.2. Submandibular gland3. Sublingual gland.Fig.1.12: Musclesofmasticationandfacialexpression1. Masseter, 2. Triangularis, 3. Mentalis, 4. Quadratus labi inferioris,5.Zygomaticus,6.QuadratuslabisuperiorisPart 110 Essentials of ProsthodonticsParotidgland:Thisissituatedbelowtheearandatthebackofthemandible.Itsduct(Stensensduct)opens in the buccal vestibule in the region of maxillarysecondpermanentmolartoothoneachside.Parotidglandispurelyserousgland.Submandibularglandisamixed,serousandmucous gland.Sublingual gland is almost entirely mucous gland.Minor mucous glands are found in the palate, lipsandcheeksandtongue.FunctionsofSalivaryGlandsTo produce saliva and mucous.TemperomandibularJointTMJThisisahighlyspecializedjointanddistinguishedfrommostotherjointsbythefactthearticulatingsurfaces are not covered by hyaline cartilage but byan avascular fibrous tissue. This is the joint on eachside of the skull between the condyle of the mandibleandtheglenoidfossaandarticulareminenceofthetemporal bone. This is a Ginglymo arthrodial joint.That means it has both hinge and sliding action.Ginglimus = HingeArthrotia = JointThemandiblecarriesteeth,whoseshapeandpositionhaveadecidinginfluenceuponthemove-mentatthejoints.Thisisabilateralarticulationwiththecraniumandexertsarestrictinginfluenceonthemovementofthemandible(Fig.1.14).TheLigaments,whichassistthemuscleinattachingthelowerjawtotheskull,are;1. Temperomandibularligament.2. SphenomandibularSpine to lingula3. StylomandibularStyloidprocesstoposteriorborderofmandible(Fig.1.15)4. Pterygomandibular-Hamulustoposteriorendofmylohyoidridge(Fig.1.16).Thus, the bony elements of the joint are united bya capsule and ligaments. Inside the capsule there is ajointcavityatwhichthemovementsbetweenthebonestakeplace.EachjointcavityisdividedintoupperandlowercompartmentsbyahorizontalarticulardiscorMeniscus.Thediscismadeupofinterwovenbundleofconnectivetissue.Fig. 1.13: Muscles of the floor of the mouthA. Mylohyoid, B. Geniohyoid, C. Hyoid bone, D. Mandibular foramenFig. 1.14: Temperomandibular joint (Sagittal section)1. Zygoma, 2. Articular eminence, 3. Articular Disc, 4. Capsular ligament,5. Suprameatal spine, 6. Condylar process, 7. Lateral pterygoid muscleFig. 1.15: Temperomandibular joint (outer view)1. Temperomandibular ligament, 2. Styloid process,3. Stylomandibular ligamentPart 1Applied Anatomy and Physiology 11Posteriorly it forms a thick pad. Its central part ismuch thinner than the periphery.Thediscisattachedmediallyandlaterallytothecondyle. This attachment is achieved by strong, shortligaments like the collateral ligaments of hinge joint.The condyle is covered with dense fibrous tissue,so also the articulating surface of the temporal bone.Inthefossathecoveringisthin,becomingthickontheposteriorslopeandthearticulareminence.Synovialmembraneassuchdoesnotcoverthearticularsurfacebutthereisacellularlayerattheperipheralboundariesofthejointwhichisrichincells and blood vessels and it is from these cells thesynovialfluidissecretedandthroughthisthebloodlesstissuesofthejointgettheirnutrition.ThetemperomandibularligamentisadensecollagenousthickeningofthecapsularligamentonthelateralsideofthejointpassingdownwardsandbackwardsfromtherootoftheZygomaabove,totheneckofthecondylebelowandbehind.Thisisnormallytautinallpositionsofthejointandthuskeepcondyle,discandthetemporalbonefirmlyopposed and prevent the backward displacement ofcondyle.Inthepositionofrestandnormalocclusion,theheadofthecondyleisheldbalancedbythelateralpterygoid against the posterior slope of the eminentiaand is not permitted to move back up into the depthoftheglenoidfossa.MusclesofMasticationOneofthemainfunctionsofmastication(chewing)iscarriedoutbytheteethandjaws.Themusclesdirectlyinvolvedinthisprocessarecalledmusclesofmastication.1. Masseter. It has two partsa. Superficial part.OriginAnteroir2/3rdofZygomaticarchInsertionLateralsurfaceofthelowerpartoftheramus.b. DeeperpartOriginWholelengthoftheinnersurfaceoftheZygomaticarch.InsertionLateralsurfaceofthecoronoidprocess and upper part of the ramus.Nervesupply5thcranialnervesmandibulardivision.2. Internal (Medial) PterygoidOriginMedialsurfaceofthelateralpterygoidplate and pyramidal process of the palatine bone.InsertionBetweenthemylohyoidgrooveandangle of the jaw on the inner surface of the ramusNervesupply5thcranialnerve(Fig.1.17).3. External (lateral) pterygoidOriginInfratemporalsurfaceofthegreatwingof the sphenoid and the lateral surface of the lateralpterygoidlamina.InsertionAnterioraspectsoftheneckofthecondyle, the meniscus and capsule.Nervesupply-5thcranialnerve(Fig.1.18).Fig. 1.16: Temperomandibular joint (Inner view)1. Condyle, 2. Sphenomandibular ligament, 3. Styloid process,4. Stylomandibular ligamentFig.1.17: Musclesofmastication(Outerview)1. External (lateral) pterygoid, 2. Internal (Medial) pterygoidPart 112 Essentials of Prosthodontics4. TemporalisOrigintemporalfossaonthesideoftheskullInsertionApex and deep surface of the coronoidprocessandtheanteriorsurfaceoftheramusasfarforwardasthelastmolar.Anteriorfibersarevertical.Posteriorfibersarehorizontal.Nervesupply5thcranialnerve(mandibularnerve)(Fig.1.19).5. Digastric.Thishastwobellies.OriginPosteriorbellyfromthemastoidnotchofthetemporalbone.Anteriorbellyfromthedigastricfossainmedianlineofthebaseofthemandible.InsertionBoth the bellies join by an intermediatetendon which attached to the hyoid bone Fig. 1.20.AccessoryMusclesofMasticationi. Buccinator and lip muscles.ii. Mylohyoidiii. Geniohyoidiv. Stylohyoidv. Infrahyoidvi. Tonguemuscles(Fig.1.21).6. MylohyoidOriginWholelengthofthemylohyoidridge,which extends from the symphysis to the 3rd molar(Fig.1.22).InsertionAnterioraspectsofthebodyofthehyoidboneandintothemedianraphe.Fig.1.18: Muscleofmastication(Innerview)1. Lateral pterygoid, 2. Medial pterygoidFig. 1.19: Muscle of mastication1. TemporalisFig. 1.20: Musclesofmastication1. Digastric, 2. Geniohyoid, 3. Mylohyoid,4. Hyoglossus, 5. Hyoid boneFig.1.21: Muscles1. Temporalis, 2. Lateral pterygoid (upper head), 2. Lateral pterygoid(lowerhead),3.Medialpterygoid(deephead),3.Medialpterygoid(superficialhead),4.BuccinatorPart 1Applied Anatomy and Physiology 137. GeniohyoidOriginInferiorgenialtubercleInsertionBodyofthehyoidbone(Fig1.23).MovementsoftheMandibleThepositionofthemandibleismaintainedbythemandibularjointandthesurroundingligaments.The joint itself is peculiar because it is a double joint,like the knee joint, with a disc or meniscus betweentheheadofthecondyleandtheglenoidfossa.Themovementsaregroupedasfollows:1. Openingmovement(Depression)2. Closingmovement(Elevation)3. Protrusivemovement(Forward)4. Retrusivemovement(Backward)5. Rotationmovement(Sidetoside)Movement Contracting muscle Relaxing muscleOpening Lateral ptreygoid Masseters, tempora-Both bellies of digastric lis, medial pterygoid.mylohyoid. Platysma.Closing Masseters, temporalis. Lateral pterygoidsProtrusion Lateral pterygoid Posterior horizontal(with mouth fibers of temporalis.not opened)Retrusion (with Posterior fibres of Lateral pterygoids.mouth not temporalisopened)The masseters, medial pterygoid and anterior fibers of temporalisdo not relax but keep the teeth in contact during protrusion andretrusion.LateralMovement(SidetoSide)RotatoryContractionOn the side towards which Posterior fibers of temporalis andjaw is moving all other muscles of that side.On the opposite side Lateral pterygoids.ForExampleIf the jaw is moved to the right side, the right condyleremainsstationaryintheglenoidfossabuttheleftcondylealonemovesforwardandinwardontheeminentiaarticularis,duetothecontractionofleftsidelateralpterygoidmuscle.Then,ifthejawismovedtotheleftside,leftcondyle first moves backward into the glenoid fossaand the right condyle then moves forward on to theeminentiaarticularis.Working side Isthesidetowardswhichthejawismoved.Balancing side Istheoppositeside.BennetMovementOn the working side, although the condyle remainsstationary,itrotatesaroundaverticalaxis,causingaslightbackwardandlateralmovementduetothecontractionofmasseterandtemporalisofthatside.TheresultofthisislittlelateralshiftofthewholemandibleandthisisBennetmovement(Fig.1.24).ChristiansenPhenomenaDuetothedownwardandforwardmovementofcondyleduringprotrusiveandlateralmovements,posteriorteethofartificialdenturesortheposteriorendsoftheocclusalrimsmaynotmeetcorrectly;insteadtherewillbeaspacebetweenthetwo.ThisisduetochangesthathavetakenplaceintheFig.1.22: Innersurfaceofmandible(Crosssection)1.Insertionoftemporalis,2.Originofgenioglossus,3.Originofgeniohyoid, 4. Insertion of ant belly of digastric, 5. Origin of mylohyoid,6. Insertion of medial pterygoid, 7. Insertion of buccinator, 8. InsertionoflateralpterygoidFig. 1.23: Musclesofmastication1. Geniohyoglossus, 2. Geniohyoid, 3. Hyoid bonePart 114 Essentials of Prosthodonticsedentulousalveolarridge.ThisisknownasChristiansen phenomena, which has to be correctedifthedenturestohaveuniformcontactofteeththroughout.OpeningMovementMechanismFactor Action SiteContracting muscles Rotation of condylar Lower compartmenta. Anterior belly of heads against of joint cavitydigastric. stationary disc (Hinge type)gravity.b. Lateral and Condyles and discs Upper compartmentmedial ptery- are drawn forward of joint cavitygoids out of the glenoid (sliding)fossa on to the emi-nentia articularis.c. Postbelly of Chin is pulled downdigastric and and back, acting frommylohyoids. hyoid bone, which isRelaxing muscles, held stationary byMasseters other muscles.temporalisThetemperomandibularjoints,mandibleandthemusclesofmasticationtogetheractasdoubleleverofclassIII.ForExampleFulcrum(CondyleLoad force(Food) (Muscles)MusclesofMasticationClassification1. Posteriorgroupattachedtotheramusofmandible.ExamplesMassetersTemporalisPterygoidslateralandmedial2. AnteriorgroupAttachmentaboveBodyofmandible.AttachmentbelowHyoidbone.Examples MylohyoidGeniohyoidAnteriorbellyofdigastric.MusclesarealsoClassifiedbytheirAction1. Elevators,e.g.MasseterTemporalisMedialpterygoid2. Depressors.e.g.PlatysmaDigastricMylohyoidGeniohyoid3. Protrusors,e.g.Lateralpterygoid(Rotators)Medialpterygoid4. RetrusorsTemporal(Fig.1.25)Superiorconstrictorofpharynx(Fig1.26)BasicMovementsoftheMandiblea. Rotaryorhingemovementinthelowercompartmentb. Translatoryorslidingmovementintheuppercompartment(Fig1.27)Fig. 1.24: Axis during mandibular movement (Lateral excursion)A.Verticalaxis,B.BennetshiftFig. 1.25: Direction of the pull of muscles of mastication1. Temporalis (Elevation), 2. Masseter (Elevation), 3. Geniohyoid andant belly digastric (Depression), 4. Lateral pterygoid (Rotation) Part 1Applied Anatomy and Physiology 15FunctionalMovementsofMandiblea. Opening and closingb. Symmetricalprotrusionandretrusion.c. AsymmetricallateralshiftorrotationOpeningandClosingOpeningbeginswithalmostpurerotatoryorhingemovement and the mandible is depressed to slightlybeyondrestposition-means2/3rdofopeninghastaken place. Then, for the remaining 1/3rd opening,bothslidingandroratorycomponentscombinetoproduceasmooth,movementofopeningfully.Inthereverseprocessofclosing,thefirst2/3rdistranslatorymovementandremaining1/3rdiscombinationofbothtranslatoryandrotatorymovement until fully closed.MovementsofMandiblecanalsobeClassifiedasa. Free movementswhich starts from rest position,andendinrestpositionofthemandible.b. Masticatorymovements(justdescribed) Cuttingmovements. Grindingmovements.PositionsofMandible1. Restposition:Thisisconstantineachindividualdue to individually fixed and only slightly variabletonusofthemasticatorymuscles,whichintheirrelaxationallowsthemandibletodropslightly.Thereforerestpositionisnotdependentonthepresence of teeth or their shape or position but onthe musculature and on the muscular balance only.2. Occlusal position: it is that position of mandible inwhichteethareincontactYetAnotherClassificationofMandibularMovement1. Masticatorymovements.2. Swallowingmovements.3. Emptymovement-forexamples,During Bruxisum,i.e.GrindingofteethinsleepAxisDuringJawMovements1. HorizontalaxisDuringopeningandclosing.2. Vertical axisDuring lateral movements (Fig 1.28).AspointedoutbyBennet,themandiblemovesbodily laterally and partially rotates during lateralexcursions-andthisisknownasBennetMovement.Fig. 1.26: Direction of the pull of muscles of mastication1.Temporalis,2.Masseter,3.Lateralpterygoid,4.Medialpterygoid, 5. Geniohyoid, 6. Geniohyoid and ant belly digastric,7. Mylohyoid, 8. Lateral pterygoidFig. 1.27: Rotatory and translatory movements of mandible1. Lateral pterygoid muscle, 2. Both the bellies of digastric muscleFig. 1.28: Axis during mandibular movementA. Horizontal axis during opening and closingPart 116 Essentials of ProsthodonticsSalivaItisaclear,colorlessfluidsecretedintothemouthbysalivaryglands.CompositionWater99percentSolid 1 percent Coagulableproteins.Mucin.Inorganic ions of Na, K, andCaChlorideBicarbonateThiocynateUrea.Bacterias and its product: Food particles, epithelial cells,leucocytes. Enzymes- ptyalin. Water helps to dissolvefood.Mucin coats the food and acts as lubricant to makeswallowingeasy.Ptyalinstartsdigestionofstarch.FunctionsofSaliva1. Keeps the mouth moist.2. Necessaryforspeech.3. Helpsinretentionofcompletedentures.4. Maintainsoralhygiene.5. Digestionofstarch.6. Necessaryfortaste,chewingandswallowing.Mastication(Chewing)This is a complicated physiological process involvingmanystructuresliketeeth,tongue,palate,musclesofmastication,nerves,saliva,TMJetc;Teethactastool to cut, tear, and grind the food while it is gettingmixedwithsalivaandmadepalatablebeforebeingswallowed.Powerfulmusclesofmasticationapplyforceontheteeth,sothatallkindsoffoodareproperlycutandgrinded.Incisorscut,caninestearandmolarsgrindthefood.Chewingbeginswithopeningthejaw,andoncethefoodisinsidethemouth it is cut and torn into small pieces and takenbackontothemolarstogrind.Allthewhilethemandible is making continuous opening and closingmovementsandlateralmovementseverynowandthen. Main and accessory muscles of mastication andtongue help in this process.Propriocepticafferentnervesfromteeth,mucousmembrane, periodontal membrane, tongue, TMJ andmusclesetc;sendthemessagetomotornucleiandaccordingly the amount and direction of masticatoryforceiscontrolledbythemuscleswhilechewing.Tastebudstooreactindecidingtheacceptanceorrejection of food and also the amount and nature ofsalivarysecretion.Significance:Patientswearingdentureshastolearntheprocessofeatingduetolossofperiodontalmembranereceptors.The normal mechanism which induces chewing ispurelyreflex.Salivation,chewingandswallowingallareinterrelatedandsothereflexmechanismcontrollingonewillalsocontrolothertwoaswell.Types of Reflexesa. Isotonic reflex: This is initiated by the introductionof any object (food) in the mouth, which stimulatesthereceptorsinthemouth.b. Isometricreflex:Thisisinitiatedbythemovementof teeth in the sockets, which stimulates pressurereceptorsintheperiodontalmembrane.Thus,innervationsofperiodontalmembraneactasaprotective structure in determining the existenceofanydisturbanceineithermasticationorocclusion.Thissensitivityandreflexmechanismtogether control the masticatory pattern (Fig 1.29).RoleofTongueDuringMasticationa. Directcrushingeffectonfoodagainstthehardpalate.Fig.1.29: ReflexesofmasticatoryprocessBCBaraincentre, TBTastebuds,PDMPeriodontalmembrane,PCProprioceptive impulses, AAfferent, EEfferant, SSensory,MMuscles of mastication, MMMucous membrane, 1Control ofsaliva,2Controlofamountanddirectionofforce,3ControlofmusclesofmasticationPart 1Applied Anatomy and Physiology 17b. Pushes the food on the occluding surfaces of teeth.c. Help to mix the food in the saliva.d. Separateschewedfoodfromyettobechewedfood.e. Cleaningeffect.f. Providestaste.Extrinsicmusclesmovethetongueasawhole.Intrinsic muscles change the shape of the tongue.Role of Hard PalateThis is sensitive to touch. Thus, harsh food is rejectedbythepalate.Significance:Denturewearersloosethissensitivity.RoleofCheeksandLipsThese are sensitive to touch and temperature and socontrolthetemperatureoffood.Preventfoodandliquidgoingoutofthemouth.FactorsInfluencingtheStrengthofBitea. Strengthofmusclesofmastication.b. PracticeandExercise.c. Typeoffood.d. Oralhygiene.e. Distancebetweenjaws.f. Sensitivityofperiodontalmembrane.g. Racial inheritance of powerful jaws.EffectsofVigorousMasticationon Oral Tissuesi. Bonegrowth.ii. CleaningeffectPreventionofcaries.iii. Massaging action on gums.iv. PeriodontaleffectsExtrabonedepositiontocompensatefortheloss.v. SoothingeffectPsychologicallyFor example Chewing a gum a modern fashion.SwallowingThis is a co-ordinated activity of various muscles andnerves.It occurs in 3 stages.1st Stage: Oral PhaseThisisvoluntary.Themasticatedfoodiscollectedandmadeasbolusandkeptonthedorsumofthetongue.Lipsareclosed.Teetharebroughttogetherinocclusion.Amylohyoidmusclecontracts,whichpushes the tongue up against the palate and pushesthe food backwards towards the pharynx. Soft palateis raised and thus allows the food to go into pharynxand at the same time prevents food going into nose.2ndStage:PharyngealPhaseThis is involuntary. Food passes through the pharynxtothebeginningofoesophagus.Atthistimebreathingstopstemporarilyandclosureofnasopharynxoccursandlarynxwillbeelevated. Thus laryngeal orifice is shut. At the sametimeoesophagealopeningisraiseduptoahigherleveltoreceivethedescendingbolusoffood.3rdStage:OesophagealPhaseThisisalsoinvoluntary.Theconstrictormusclesofthepharynxcontractfromabovedownwardsandpush the bolus of food through the oesophagus intothestomach.TheMusclestakingPartinSwallowing1. Muscles of mastication.2. Mylohyoid.3. Tongue muscle.4. Lip muscles.5. Hyoidmuscles.6. Elevatingmusclesoflarynx.7. Elevatingmusclesofsoftpalate.8. Muscles closing the laryngeal inlet.9. Pharyngeal muscles.The mucous membrane of the mouth, pharynx, andesophagus through which food passes in swallowingis supplied by sensory fibers of the 5th, 9th and 10thcranialnerves.Thenswallowingistheresultofcoordinatedactivityofnumberofreflexarcsinvolving 5th, 7th, 9th, 10th and 12th cranial nervesandupperspinalnervesandmidbraincenters.Themidbraincentersregulateandcoordinatethereflexmechanism, so that once swallowing begins it cannotbe stopped by any voluntary actions. Therefore oneisnotawareofentryoffoodintostomach.CONCLUSIONMainFunctionsofTeethNaturalorArtificial1. Eating:Whichinvolvesopeningthemouth,intowhichfoodisinsertedandkeptonthechewingPart 118 Essentials of Prosthodonticssurfaceofteethduringchewingandthenswallowed.2. Speaking: Also involves opening of the mouth andmovement of soft palate, tongue and lips. Properspeechdemandscorrectverticaldimension;dentureperiphery,tonguespace.Artificialteethmustbecorrectlypositionedonthedenture.Occlusal plane is suitably fixed, and the polishedsurfacesofdentureareappropriatelyshaped,sothat tongue, which plays a important role in speechfeelsnaturalenvironmentinthemouthforitsfunctions.3. Facialexpression:Involvescontractionofmusclesoffacialexpressionandtongue.4. Appearance: Depends on the scientific constructionofdentures,especiallywithrespecttoverticaldimension, arrangement of teeth, and selection ofteeth.Artificialdenturetooshouldprovidethesefundamentalfunctionsofteeth.Part 1Prosthodontics 192ProsthodonticsDEFINITIONSProsthesis: This is an artificial appliance, constructedin the laboratory to replace a lost or missing naturalpartofthebody.For example: Artificial leg (Jaipur leg)Prosthodontics:Thisisabranchofdentistrywherescientificallyandartisticallydesignedartificialsetsofteetharemade.WordOriginandMeaningProsfromGreekmeaningToThesefromGreekmeaningplacingtoOdontosfromGreekmeaningToothDensorDentisfromLatinmeaningToothDentureThisisaartificialsetofteethEdentulousWithoutteethDentulousWithteethAbutmentAbut from French Abuter = to touch at the end =to end at = to end or lean uponAbutment = An endwise meeting or junction.= A limb of an arch which ends orrestsagainst.(Indentistry) = Atoothwhichabutsaneden-tulous space and which is used tosupport,retainorstabilizepros-thesis.Bridge:Acompact,commonlyfixedprosthesisreplacingoneortwoteethandissupportedandretainedmainlybyinlaysandcrowns.Clasp = FromMiddleEnglish-claspe.= Fastenings, to embrace: to grasp.= Toencloseandholdinthehandorarms.(Dental) = Awroughtorcastmetallicarmattachedtoapartialdenturewhich embraces natural tooth forretention.Itwillalsoprovidebracingandsupport.Crown- from French-CoroneGreek-Koronos=Curved= AroundheadornamentWornby Kings and Queens.Dental1. Thatpartofnaturaltoothabovethegingivaandcoveredbyenamel.2. Anartificialrestorationplacedonthepreparedtoothabovethegingiva.Die-fromoldFrenchde=givenorcast= A tool for shaping a thing.Dental = Apositivereproductionoftoothin a dental stone or die stone, forthe purpose of making a inlay orcrown.Inlay = Toinsert.= Apatternsetintothesurface.Dental = Ametallicornonmetallicrestor-tionconstructedoutsidethemouth and later cemented in thetooth.Pinlay - It is a inlay with pins for retention.Onlay - This is a cast restoration placed on the toothandheldtherewithpinsgoingintothedentin.Dowel- From German- Dobel = A plug.= Apinforfixingthingstogetherbyfittingintoaholeinboth.Dental = Apin,pegorpost.Usedduringcrownmaking.EmbrazureTheopenspacebetweentheproximalsurfaces of neighboring two teeth where they divergebuccally,labiallyorlinguallyfromthepointofcontact.Fossa = Apitordepression.Part 120 Essentials of ProsthodonticsJacket CrownJacket = A short coat especially of leather,Aloosepapercover.= Outercasingofaboiler.Dental = Aveneer(athinlayer)ofporcelain or acrylic resin fitted tothe crown preparation of naturaltooth.KeywayAlockingdevice-grooveorrecess.MandrelAbarofironfittedtoaturninglatheonwhicharticlestobeturnedarefixed.PonticFromLatinPons,Pontis=Bridgeorconnectingpart.PonsofbrainWheremassoffibersjointhetwohemispheresofbrain.Dental = Itisthatpartofdentalbridgewhichstandsbetweentheabutmentsandfunctionsasanartificialtooth.Reservoir = A small bulge on the sprue whichprovides reserves of liquid metalfrom which the casting may drawasitsolidifiesandcools.Sprue = Deadend-Apassagebywhichliquidmetalrunsintoamouldandsolidifiesthere.Pickle = Pick- A small quantity.= Acidusedforcleaningametalcasting.CrucibleAcontainerinwhichmetalsaremelted.CastFromoldNorwegian-Kasta=Tothrow.= A shape of a thing cast.As an adjective mould.CastingA thing cast in a metalFor example - Wheel, Axel etc.= An act of moulding.DentalAmodelmadefromanimpression.PierFromMiddleEnglishPer= Themassofstoneworkbetweentheopeningsinthewallofabuilding.= Thesupportofabridgeorarch.DentalItisthemiddleabutmentinabridgeofthreeabutments.CantileverbridgeAfixedbridgewithonlyoneabutmentatoneend.ThimbleFrom old English- thymel= Thumb.= Acoverforthefingerusedinsewing.ChamferFrom French Chamfrein = to break theedgeorside.= A bevel or slope made by paringofftheedgeofanythingorigi-nallyrightangled.= Agroove,channelorfurrow.BranchesofProsthodonties1. Complete Dentures - C Da. Conventional.b. Immediate.c. Overdenture.d. Implant(Fig.2.1).2. Partial denture: commonly reffered as RemovablePartialDenture(RPD)Basedonthesupport.a. TissueborneAcrylic.b. ToothborneCastmetal(Fig.2.2).c. Disjunct dentureCombination of tooth borneandtissueborne(Fig.2.3).Basedonthepurpose.a. Interimdenture.b. Transitionaldenture.c. Treatmentdenture.Othersa. Clasp-lessdenture.b. Spoondenture.c. Sectionaldenture.d. Everydenture.3. BridgesAlso called Fixed Partial Denture, (FPD)a. Fixedfixed.Fig. 2.1: Complete dentures (All acrylic)A. Maxillary, B. MandibularPart 1Prosthodontics 21b. Fixed movablec. Plain cantileverd. Springcantilever(Fig.2.4).4. Maxillofacialprosthesis.5. Othersa. Obturatorb. Gunning splint6. SupportersandRetainerstoprosthesis.a. Inlaysb. Crowns Full crownsCrownsi. Conventionalii. Pin-lay typeiii. Pin-ledgetypeCompleteDenturesNumberofteethreplacedAllnaturalteeth.FunctionsRestores1. Masticatoryfunction.2. Esthetics.3. Speech.MaterialsusedtoMakea. NonmetalAcrylicresinb. Metallicchrome-cobalt.c. Combinationofmetalandnonmetal(Fig.2.5).Requirements(Fig.2.6)a. Maximumcoverageofdenturefoundationtoget;i. Maximum adhesion.ii. Tospreadmasticatoryload.iii. Toreducealveolarboneresorption.b. Muscleattachmentsmustbesuitablyrelieved.Fig. 2.2: Partial dentures (All acrylic)A.WroughtwireclaspFig.2.3: AssorteddesignsofcastRPDsFig. 2.4: Fixed-Fixed bridge1. Full crowns (Retainers), 2. Pontic (Artificial tooth), 3. Soldered jointFig.2.5:Maxillarycompletedenture(Viewoffittingsurface)A. Chrome-Cobalt base, B. Arcylic flangePart 122 Essentials of Prosthodonticsc. Occlusion should be balanced.d. Flangesshapedtohelpretention.PartialDenturesNumberofteethreplacedoneorfewFunctionsTo Restore1. Masticatoryefficiency.2. Esthetics.3. Speech.4. Toprotectthehealthoftheremainingteeth.5. Topostponeedentulousstate.Requirementsa. Priortreatmentplananddesignb. Propermouthpreparationc. Providingpropersupportandretention.d. Providingcorrectocclusalrelations.e. High technical skill and care.ConventionalCompleteDenturesTheseareconstructedafterextractionofallnaturalteethonacompletelyhealed-upalveolarridge.ImmediateDentureThisdentureisconstructedbeforetheextractionofteeth(some)andinsertedimmediatelyafterextractionofthosenaturalteeth.Thesedenturescanbecompleteorpartial.OverDentureThis is a complete denture and kept over the retainednaturaltooth-usuallylower3rdmolar.ImplantDentureThiscompletedenturetakessupportfromthestudlikeprojectionsthroughthemucosa,whicharetheverticalcomponentsofmetallicframeworkburiedinthealveolarbone.Tissue Borne Partial DentureThisdentureissupportedverticallyonlybythemucous membrane.Tooth Borne Partial DentureThis denture is supported vertically only by the teeth.DisjunctDentureThisisatwopartpartialdenture,onepartistoothborne,andanotherpartistissueborne,bothactingindependently.InterimDentureThisisatemporarypartialdenturewornbythepatientwhilethepermanentdentureisgettingready.Transitional DentureThis is a temporary denture worn by the patient andtowhichextrateetharebeingaddedasthepatientgoesonloosingnaturalteeth.TreatmentDentureThisisatemporarypartialdenturewornbythepatient as a part of treatment plan until the conditionsarefavorablefortheconstructionofpermanentpartialdenture.ClasplessDentureThisisapartialdenturewithoutclaspbutretainedby another arrangement, which engages the undercutontheproximalsurfacesofabutmenttoothnexttothesaddle.SpoonDentureThisisamaxillarypartialdenturecarryingoneortwoanteriorteethandapalatalspoonlikesectionnotincontactwiththegingivalmarginsoftheteeth.Fig.2.6: Maxillarycompletedenture(occlusalview)A.Chrome-cobaltbasePart 1Prosthodontics 23SectionalDentureThis is a two part partial denture, the path of insertionand removal for both the sections is not one and thesame,butonesectionfrombehindandanothersectionfromfrontandthenbothgetslocked-up.EveryDentureThis partial maxillary denture designed by Mr Everyis completely tissue borne, makes use of full palatalcoverageforsupport.MaxillofacialProsthesisThis is a prosthodontic appliance, which replaces anyof the lost natural part of the human face (Nose, Ear,Eyeball,Skinofface,Bone,etc.)withorwithoutartificialteethattachedtoit,inordertorehabilitatea badly mutilated patient following a major surgeryontheface.ObturatorIsadentalappliancemadetocloseacleft(gap)inthehardandsoftpalate,toimprovespeech.WordOriginandMeaningFromLatin-Obturare=Toclose,Tostop.Gunning SplintThis is an edentulous dental appliance in one or twoparts,shapedlikeocclusalregistrationblocksbutmadeofacrylicresinforthepurposeofsplintingfractured jaws until bone union takes place.FullCrownThis is a entirely metal cast crown on premolars andmolars,usedasretainertoabridge.ThreequartercrownalsoknownasCarmichaelpartialveneercrownisashellcrown,whichcoversallsurfacesoftoothexceptlabialorbuccalbecauseofestheticreasons.Pinlay Type 3/4th CrownThis crown makes use of additional pins, which fits,intoholesdrilledinthetoothparalleltothegrooveforretention.Pinledge Type 3/4th CrownThisisasimilartopinlaytype3/4thcrownexceptthatpinsaresituatedattheedgeoftooth.DifferencebetweenApplianceandDentalProsthesisAppliancehasnoteethattachedtoitbutitisusedforsomeotherpurposeandiswornbythepatientasapartoftreatment.ForExamplePeriodontalsplint.Cast metal cap splintsOrthodonticappliances.Space maintainer.Sportsmouthguards,Nightguards.Appliancetostophabitslikethumbsucking,snoring,etc.Fluoridecustomtray,Bleachingtrays.Dentalprosthesiscarriesteethonitandtheyarecalleddentures.Nondental prosthesis are maxillofacial prosthesis,obturator.ScopeandLimitationsofProsthodonticsProsthodontics is the major routine work undertakenbyadentistineverydaydentalpractice.Inoldendays public thought of dentist as a Tooth puller andtooth maker. But a modern dentist does much morethanthat,andscientificallytoo.Ifoneappreciatesthe importance of teeth for chewing a food and thereby ones general health; for appearance and there byits impact on the morale of the patient, and for speech,it goes without saying that dentures are a must for apatientwhohaslostnaturalteeth.Now a days it is very common for people to loosenaturaltoothforonereasonortheother.Thereforedemandfordentureswillbemore.Makingacomplete denture is a science as well as art. Makingpartial dentures is a skill. Both these involve clinicalwork(bydentist)andlaboratorywork(bytechnician) and both must be done with utmost care.Allinall,scopeforprosthodonticsiswideningdaybydaybecauseofavailabilityofbettermaterials,instruments and techniques. Implant dentures are thelatestinthiswideningscopeofworks.Howevertherearelimitationstooasinallfields,becauseofconditionsprevailinginthemouthwhicharenotfavourable,healthofpatientandlackoftechnicalskill etc. However Good dentures are a thing of beautyand joy forever.Part 124 Essentials of Prosthodontics3Retention and Stability(COMPLETEDENTURES)DIFFERENCEBETWEENNATURALTEETHANDDENTURES(ARTIFICIALSETOFTEETH)Naturalteeth Artificialsets(Denture)Rootsareembeddedinsockets Therearenorootstoteethofofboneandtheretheystayfirm. dentures- so no embedding. Thewholesetasoneunitjustsitson the ridge.Periodontalmembraneisfirmly Thereisnoattachmenttobone-attachedbetweenboneofalveo- sothesetissubjectedtolusandrootoftoothandso movement.thereisnomovement.Dislodgingforcesdonotaffect Dislodging forces affect denture.teeth,situationissimilartoa Situationislikeapostjustpostduggedanderectedinthe madetostanduprightontheground. groundwithoutdigging.Mainfunctionsofnaturalteeth- Mainfunctionsofdenturestooe.g.,mastication,estheticsand aresimilartonaturalteeth-butspeecharedonesatisfactorily itcannotbesatisfactoryiftheduetofirmandstableteethin dentures are not firm and stablethejaw. overthejaw.DEFINITIONSRetention1. Retention is the ability of the denture to remain incontactwithitssupportingtissues.2. Retentionisresistancetoverticaldisplacementtowardstheocclusalsurface.3. Retentionmeansadenturemuststayfootwhereitisplacedtorest.4. Retention means denture must not be loose in themouth.5. Retention is that quality in denture that resists theforces of gravity, adhesiveness of foods and forcesformedduringopeningthejaw.6. Retention is resistance to displacing forces, whichactonthedenture,resultinginamovementtowardstheocclusalsurface.Stability1. Stabilityisabilityofthedenturetoremainstationaryinrelationtoitsbonysupport.2. Stabilityisresistancetoleverageandhorizontaldisplacement.3. Stabilitymeansthedenturemustnotmovesidewayswheninfunction.4. Stability means the denture must not move aboutin the mouth.5. Stability is the quality of denture to be constantlyfirmandsteadyandnotsubjecttochangeofpositionwhenforcesareapplied.6. Stability is an absence of movement of the dentureinanydirectionotherthantowardstheocclusal.RetainingForcesontheDenture1. Adhesion.2. Cohesion.3. Atmosphericpressure4. Co-ordinatedactionoffacialandtonguemuscle.5. UseofundercutsDisplacingForcesontheDenture1. Forceactingontheocclusalsurfacesandincisaledges,e.g.Stickyfood.2. Muscularforcesactingontheperipheryorpolishedsurface.3. Extensionofperipheryintononelasticmucosa.4. Suddenentryofairbetweendentureandoralsupportingtissues.AdhesionThisisattractionbetweendis-similarmolecules(substances)Inthecaseofdentures-dis-similarmoleculesarea. Denturefittingsurfaceb. Mucous membrane.Part 1Retention and Stability 25These two different surfaces when in contact therewillbeadhesion.ToIncreaseAdhesiona. Intimate and uniform contact of the denture againstthe tissues on which it rests. This in turn is broughtaboutbygoodimpressiontechniqueandcloseadaptationofdenturebasetothesurfaceofthecast.b. Widertheareaofcontact,betterwillbetheadhesion.Thisinturndependsupongoodimpression,whichregistersallofdenturefoundationindetail.Greatertheareacoverage,greaterwillbetheresistancetobitingforces.Inthecaseofmaxillaitisgoodbecauseofpalate,but in the case of mandible it is not good becauseofitshorseshoeshape.CohesionCohesionisattractionbetweensimilarmolecules(substances).Whenadisplacingforceactsonthedenture,thecohesive force in the saliva acts to preserve the intactmeniscusattheperiphery.Thisreducesthefluidpressurewithinthesalivabelowatmospheric,andthisdifferenceinthedisplacingforceandforceinsaliva,helpstoretainthedenture.IntactMeniscusattheperipherybringsaboutperipheralseal(Fig.3.1).Meniscusonthepolishessurfaceofthedenturebringsaboutfacialseal.(MeniscusfromGreek-Maniskos,mene,meaningmoon,whichgetsacrescent (curved) shape some time, just like a curvedliquid surface in a test tube due to capillarity).Thisperipheralsealmustencirclethewholeoffittingsurfaceofthedentureinordertogetbestofretention.Thiscanbeachievedbya. Post dam at posterior border of maxillary denture.b. Shaping the buccal and labial surface of denturesin such a way that they maintain an elastic contactwith lip and cheek tissues.c. By muco compressive impression technique.POST DAMThis is done to compress the tissues of the soft palateimmediately behind the posterior border of the hardpalate.Theposteriorborderoftheupperdentureshould be just on the immovable part of the soft palate(Fig.3.2).Definition of peripheral seal: This is a close adaptationbetweensulcusreflexionanddentureperiphery.Ifthisintimatecontactismaintainedthedisplacingforceswillnotdisturbthedentureandtherebyretentionissecured.Peripheralsealpreventstheentryofairbetweenthedentureandtissues.ATMOSPHERIC PRESSUREFauchardwhenhemadehisfirstdentureheknewnothingofatmosphericpressureasameansofretentionofmaxillarydenture.Hisupperdenturewasintheformofhorseshoeshapejustlikemandibular denture and the dentures were retainedbysprings.FortyyearsafterFauchardsdeath,asatisfactory spring-less maxillary denture was madeby James Gardette of Philadelphia in 1800 and he isknownasthediscovereroftheuseofatmosphericpressurefortheretentionofmaxillarydenture.Fig. 3.1: Retention of maxillary complete dentureA. Atmosphericpressure(high)atthepolishedsurface,B.Fittingsurfacewithlowpressure,C.IntactmeniscusofslivaryfilmFig.3.2: LocationofposteriorborderofmaxillarydentureA. Hard palate, B. Maxillary denture, C. Soft palate (Im-movable),D. Soft palate (movable), E. Vibrating linePart 126 Essentials of ProsthodonticsWhenthemaxillarydentureisinplaceonthepalate, partial vacuum is formed on the fitting surfaceofdentureduetotheexpulsionofairfromthere.The atmospheric pressure on the polished surface ismorethanthepressureonthefittingsurface.Thisimbalanceinpressureholdsthemaxillarydentureupinplaceincontactwiththemucousmembrane and thus retained. Cohesive forces in thesalivaandadhesiveforcesbetweendenturesurfaceand mucous membrane also help in better retentionof the maxillary denture against the force of gravity,etc(Fig.3.3).Other factors that help in the retention of dentureare:a. Balancedocclusion,whichpreventsrockingofdenturesduringfunction.b. Muscularexercisesdonebypatient.c. Undercuts in tuberosity and lingual pouch areas.However,themandibulardentureisretainedalmostentirelybymechanicalforces.StabilityisAchievedby1. Avoidingleverage.By placing the teeth in such a position relative totheridge,whichismostfavourabletoresistloading,i.e.bysettingtheposteriorteethoverthe ridges or by suitably tilting the occlusal plane.Set the posterior teeth in Natural Zone. The areaNaturalzonewasdescribedbySirWilliamKelseyFry.2. Resistingleverage.Byadequatepaddingtopreventanairleakandbymakingflangesofproperdepth.3. Avoiding horizontal drag or inter cuspal locking.By balanced functional occlusions.Smooth cuspal clearance.Absenceoflockedbite.InShortDentureretentiondependsonclosestadaptationorfittothemosteffectiveshapeofthedenturefoundationoverthegreatestpossibleareatogetherwithmaximumreductionofdislodgingforces.CONCLUSIONForbetterretentionandstability.1. Thedenturebasemustcoverthelargestareapossible.2. Thedentureperipherymustextendonthecompressible tissues and must form a seal.3. The tissue surface of denture must lie in continuousand intimate contact with the mucosa.ThusImpressionsurfaceofdentureisretainer.Occlusal surface of denture is balancer.Polishedsurfaceofdentureisstabilizer.Therefore;Mostimportantstepsare;1. Accurateimpression.2. Correctjawrelation3. Proper occlusion and finish.Fig.3.3: UseofatmosphericpressureE.g.:Thelizardwalksonthewallwithoutfallingdown.When the lizard presses its feet on the wall, air is expelled from thefittingsidesofitsfeetandbecomeslesspressurearea.Highatmospheric pressure on the external surface of feet keeps the lizardonthewallwithoutfallingdown.This sameprincipleisinvolvedinhowamaxillarycompletedenturestaysontheupperjaw.Part 1PreprostheticSurgery 274PreprostheticSurgeryDEFINITIONThisisasurgicalprocedureundertakenbeforetheconstructionofcompletedenturetoconvertunfavorabledenturefoundationintofavorableone.Contraindicationstopreprostheticsurgery.1. Veryoldpatient2. Psychologicalpatient.Aim of Preprosthetic Surgery1. Toobtainreasonablysatisfactoryalveolarridge-withoutundercuts.2. To obtain uniformally covered mucous membrane.3. Toremoveorreshapefreniandothersofttissueinterferingfactorsinthesulcus.4. Togetsatisfactorydepthofsulcus.How to Avoid Some of the Surgical Procedures?1. Bycarefullyplanningtheextractionofteeth,becausemakingofsatisfactoryartificialdenturestartswiththeextractionofteeth.2. Removingallsharpbonyspiculesatthetimeofextractionofteeth.3. Avoidingbonyundercuts.4. Bycompressingthelabialorbuccalwalloftheextractionsocketsimmediatelyafterextractionoftoothwithfingerpressure.5. Small tori mandibularis can be removed at the timeofextraction.Type of Surgical Procedures1. Onteeth.2. Onbone.3. Onsofttissues.Surgical Procedures on Teeth1. Buriedretainedrootsareremoved.2. Impactedteethareremoved.3. Overerupted,unopposedtoothisremoved.However,impactedmaxillary3rdmolar,andmaxillary canine are not removed if there is no otherpathologicalconditionsassociatedwiththem.SurgicalProceduresonBoneThiscanbeeither;a. Alveoloplastyorreshapingthealveolarridge.b. Alveolectomyorremovingpartofthealveolarbone.Thesearedoneto,Bonyexostoces;Knife-edgeridges;LargeTuberosities,LargeMylohyoidRidge,UndercutRidge,HighLowerridgeintheanteriorregion,Prominent premaxilla,Maxillarytori.ReductionofLargeMaxillaryTuberosityIt may be only the soft tissue or soft tissue as well asbonetoberemoved,dependingupontheclinicalfindings.Twoangulatedincisionsaremadeoverthetuberosity; the width between the incisions dependsupontheamountoftissuetoberemoved.First, soft tissue between the incisions is removedandifnecessaryboneisremovedwithchisel.Remainder of the tuberosity is shaped with rongeursorbonefiles(Fig.4.1).ResectionofMylohyoidRidgeThisisdonetodeepenthelingualsulcus.Theprocedureinvolvesexposingthemylohyoidridgeby making two incisons; detaching the muscle fromtheboneandmylohyoidridgeisresectedanditschippedpartisremoved;thenboneissmoothenedwith vulcanite bur and finally suturing the flap.Part 128 Essentials of ProsthodonticsProminent Genial TuberclesThese are dissected out by antero-posterior incision.Afterdetachingthemucoperiosteumandmuscletendons,theflapisretractedforwardandupwardsothattheprojectingbonecanberemovedbybursandchisel.Bonefilesarethenusedtosmooththecutsurface.Thegenioglossusmuscleisre-transplanted above the geniohyoid muscle and heldtherewithasuturepassingbelowthelowerborderofthemandibletothechin.ReductionofProminentMaxillaThiscanbedonebytwomethods.1. Byintercorticalalveolectomydonesoonafterextractionofteeth.2. By labial alveolectomydone after the gums havehealedinthismethodlabialcorticalboneisremovedandtheridgeisreshaped.InterCorticalAlveolectomyThealveolarseptabetweenthecorticalplatesareremovedsothattheoutercorticalplatecanbecollapsedtoreducetheprotrusionofthealveolarprocessbybringingitintocontactwiththepalatalplate.ExcisionofExostosesThisoftenoccursinmultipleformandcreateundercuts in the ridge, which prevent proper dentureconstruction.Afterasuitableincision,themucoperiosteumisdetachedandretractedtoexposethebonyprojections, which are then removed with rongeurs.Removal of Mandibular TorusThisisremovedbytheuseofosteotomeorsharpchisel. Usually one blow is sufficient.Maxillarytori:Smalltoriarenotremovedbutarerelieved.Largetorusisremovedbyanexperiencedoralsurgeonbecauseofthedangerofperforatingthehardpalate(Fig.4.2).SurgicalProceduresonSoftTissuesSofttissueabnormalitieslike;a. GingivalhypertrophyCausingfolds.b. Flabbyridges.c. Wrongattachmentoffreni.d. Palatalhypertrophy.e. Papillomatosis.GingivalHypertrophyDentureGranulomasThese are excised by sharp dissection since these arepedenculated, the hypertrophied part is grasped withapairofAllisforcepsandpulledawayfromitsattachmentandexcised.Thewoundleftout,neednot be sutured, but covered with base plate containgZincoxideeugenolpaste.Bysuturing,thedepthofsulcuswillbelessened.Thesegranulomasmaybeattached buccally, lingually or on the alveolar ridge.These are due to ill-fitting dentures and lack of oralhygiene.FlabbyRidgesThese are soft, movable gingival ridges without bonysupport. These are found mainly in the anterior partof the maxillary jaw due to excessive occlusal traumawhichcausesboneresorption(Fig.4.3).Fig.4.1: Reductionofenlarged,fibrousmaxillarytuberosityA. Elliptical incision, B. Removal of wedge shaped tissue,C. Undermining the mucosa, D. SutureFig. 4.2: Removing enlarged torus palatinusA. Torus, B. IncisionPart 1PreprostheticSurgery 29RemovingFlabbyRidgeMakeanincisiononeachsideoftheflabbyfoldextending from one side to the other. All that flabbytissue is dissected away. Then the gingival edges aresuturedtoclosethewound(Fig.4.4).Frenoplasty:Tocorrectlowattachmentoflabialfrenum.Maketwoincisionsoneithersideofthefibrousmucousmembrane(notinperiosteum)only.Thenthecentralfibrousbandisdissectedout.Undercutthe mucous membrane on either side and then mucousmembraneissuturedtoperiosteumSurgeryForSulcusExtensionThisprocedureisnecessaryincaseswherethereisadvancedatrophyofalveolarprocessresultinginnosulcusatall.Suchconditionpresentsgreatdifficulty in denture construction. To over come thisproblemmanymethodshavebeensuggested,like;a. Reconstructthealveolarridge.b. Replacingthelostbone.c. Deepening the sulcus.SulcusExtention-(DeepeningtheSulcus)Thisisonlypossibleifsomealveolarboneremainsoriftheheightofthebasalboneisadequate.Theproblem is more in the case of mandible because it isflatonmanyoccasions.Thereforecarefulclinicalexamination and X-ray study is necessary before thesurgery.Muscularattachmentsinboththejaws;positionof the maxillary sinus, location of mandibular canal,mentalforamen,allplayapartinthesesurgicalprocedures.Therearemanysurgicalproceduresnamedafterthepersonwhohasdoneit.EpithelialInlayThisisyetanothermethodofdeepeningthesulcusbyskingrafts.Principlesofthemethod:1. Skingraftisobtainedfromhairlessarea.2. Thingraftisbetterthanthickone.3. Thereshouldbesufficientbloodsupplyintherecipientarea.4. Infectionshouldnotoccur.5. Graftplacedonlywhenbleedinghascompletelystoppedattherecipientarea.6. Graft is held and immobilized under pressure byadentureorbysomeotherappliance.Knife-edge-ridge-SmootheningThisconditionoccursmoreoftenintheloweranterior region below the full lower denture. Patientscomplainofinabilitytousethedentureduetosoreness. To treat this condition, simple alveolectomyFig. 4.3: Removing maxillary flabby fibrous tissueA. Incisions, B. Fibrous tissue, C. Mucosa, D. StitchesFig. 4.4: Removing mandibular flabby fibrous tissueA. Fibrous tissue, B. Area after removal, C. StitchFig. 4.5: Removing knife edged(A) mandibular ridge and suturing (B)Part 130 Essentials of Prosthodonticsis not advised, instead excision of the mucoperiostumovertheridge,smootheningtheunderlyingbonegentlyandcoveringthemucousmembranegraft(Fig.4.5).FrenectomyThis procedure is necessary in few patients with largefrenum,whichwouldinterferewithupperdenturefit.Bestdoneseveralweeksbeforeimpressionsaretaken.Afterlocalanesthesiaisgiven,upperlipisgently pulled away from the alveolar bone, and thenclampthefrenumasfarupasthereflectionofthelabialmucosa,withanarteryforceps.Thenwaitaminute or so. Then the frenum is excised by cuttingup on each side of the frenum while it is still clampedin the beaks of the forceps. Allow the lip to fallback.Underminethemucosaoverthealveolarridgeslightly.Suturethewoundinthelipaswellasthemucosaoverthealveolarbone.Removethesuturesafterfivedays.Part 2Making of Cast and Model 335Making of Cast and ModelDEFINITIONSCastisapositive,dimensionallyaccuratereplicaoforalsoftandhardtissuesofeitherthemaxillaryormandibularjawsandusedfortheconstructionofdental appliances, which fit on the soft tissues of theoralcavity.Model is a positive, dimensionally accurate replicaof oral soft and hard tissues but used as study model,orforpatienteducationortodemonstratetothepatient about the progress and out come of treatmentascomparedtotheoriginalcondition.TYPESOFCASTS/MODELSPreliminary castIs one, which is made on preliminaryimpressionandusedtomakespecialtray.ThisisconstructedwithplasterofParisforeconomicreasons(Fig.5.1).WorkingcastIsone,whichismadeonfinalimpressionandusedtomakedenture.Itiscons-tructedwithdentalstonebecauseitmustbehard,strongandresistanttobreakageandabrasion(Fig.5.2).Modelscanbeasfollows;1. Modelmadeatthebeginningoftreatment.2. Modelmadeattheendoftreatment.Most commonly used cast and model materials.1. Fordentureswithnonmetallicdenturebasea. PlasterofParisb. Dentalstone.2. Fordentureswithcastmetalbase.a. Investmentb. Divestment.IDEALPROPERTIESOFCAST/MODELMATERIALS1. Shouldsettoaverystrongandhardmass.2. Should maintain dimensional stability while andaftersetting.3. Shouldnotwarpordistort.4. Shouldproduceallthefinestdetailsofimpression.5. Shouldhaveconvenientsettingtime.6. Shouldnotbreakorgetdamagedduringlaboratoryprocedures.7. Should be compatible with all types of impressionmaterials.8. Shouldhavecolourcontrastsothatitisnotdamagedduringcarving.9. Shouldberesistanttosurfaceabrasionandchipping.10. Should be easy to manipulate and economic.Fig.5.1: Edentulousplastercasts(preliminary)A. Mandibular, B. MaxillaryFig.5.2: Edentulouscastsofdentalstone(workingcasts)Part 234 Essentials of ProsthodonticsNECESSITYOFCAST/MODELThis represents the true parts of patients jaw or teethand on these, dental appliances are fabricated in thelaboratoryintheabsenceofthepatient,andfittedtothepatientsjawsatalaterdate.Thereforeitisessential that cast must be accurate if the end product(denture)tobeaccurate.Cast/Models are made from an impression of theoraltissues.Accurateimpressionmeansaccuratecastmeansaccuratedenture.Impression making is a clinical procedure and thedentistmustbeskillfultodothis.Castmakinganddenturefabricationisalaboratoryprocedureandthe technician must be equally skillful to produce anaccuratedenture.MAKINGACASTEdentulouspreliminarycastcanbemadeentirely,i.e.impressionpartaswellasbase,withplasterofParis.Butdentulousandpartiallydentulouscastshould be made with dental stone to prevent fractureofteeth.Similarlyallworkingcastsmustalsobemadewithdentalstone.However,impressionareaofcastwithdentalstoneandbasewithplasterofPariscanbeanotherchoiceifonedesires.PRELIMINARYBEFORECASTINGAllimpressionscomingfromclinicshouldbecarefully washed under room temperature tap water.Excesswateronthesurfaceoftheimpressionisshaken off. If it is dentulous impression blow off airfrom teeth area. Keep the impression on the workingbenchwithasupport,oneundertheheeloftheimpressionandanotherunderthehandleoftheimpression. For support one can use wooden end ofplasterknife.Outerbordersofimpressionmustnotbedamaged.Impressionsofcompound,ZOEpaste,Alginate,andElastomersdonotrequireapplicationofseparatingmediumtotheimpressionsurface.ButimpressionmadewithimpressionplasterofParismustandshouldhaveseparatingmediumappliedto the impression surface to prevent adhesion of bothimpression plaster and casting plaster. Soap solutionor 60 percent solution of sodium silicate in water canbeusedasseparatingmedium.Nowadaysplasterimpressionsarerarelymade.CompoundImpressionsofEdentulousJaws:Boththemaxillary and mandibular impressions can be pouredsimultaneouslyifoneisexperienced;ifnot,oneimpressionatatimeshouldbepouredandbasemade.MixingPlasterofPariswithWaterToolsrequired-Clean,flexible,smoothrubberorplasticbowl.Straight,broad,rigidstainlesssteelspatula,Water measuring cup, or jar.BalanceorscaletoweighplasterpowderMixingbowl should not contain any traces of previous mix,ifitdoes,itaffectsthesettingtime.ThewaterpowderratioforplasterofParisforthis purpose is 50 ml of water to 100 gm of plaster.ForpouringoneimpressionatatimebyDoublepour method (Inverting method) 25 ml of water and50gmofpowderissufficientforthefirstmix.Therefore25mlofroomtemperaturewaterisfirsttaken in mixing bowl. Then 50 gm of plaster is addedin increments to the water. Each increment of plasterisshiftedintothewaterandoneshouldwaitforeach increment to be soaked in water before addingnextincrement.Tapthebowlgentlyonceortwice.Thenstartmixing,firstbygentlestirringtowetallthe powder particles and to break down the powderlumps. Then mix vigourously by rubbing against thesideofthebowlforaboutaminutetoasmooth,homogenouscreamymix.Removingairbubblesisvery important during mixing and this can be donebytappingthebowlgentlyeverynowandthenorby using automatic vibrator. Thus mixed mass shouldlook shiny, glossy and cream like. Whipping actionshould not be employed while mixing.DoublePourTechniqueorInvertingMethod:Smallamountofthusmixedplasterisfirstplacedonthepalatalvaultareaofmaxillaryimpressionorintheanteriorregionofthemandibularimpression,andallowedtoflowslowlyintoallareasofimpressionbymildvibrationandbytiltingthetraythissideandthatside.Thetrayistheninvertedandtappedontheedgesoftherubberbowl.Thiswillensureathinandthoroughcoatingofimpressionsurface,whichisfreefromairbubbles.Thisfirstlayerofcoatingisveryimportantandshouldbeperfectbecause it is this what makes the future surface of acast. This procedure can be repeated once more. Thenthewholeimpressionisfilledtothelevelofitsborderswithplastermix.Thusfilledimpressionislaidasidewithasupportunderthehandleandattheheelofthetraywithplasterlookingup.PlasterPart 2Making of Cast and Model 35intheimpressionisallowedtosetandwhenset,fewcriss-crossmarkingsaremadeonitwithwaxknife(Fig.5.3).IIndMix:Thistime2to3mllesswaterisusedforthesame50gmofplaster,inordertogetratherthickmix.Placeallthatmixonaporcelaintileorglass slab and shape it into a square mass of about an inch thick to make a base for the cast. Now invertthe impression filled with previous mix on this squaremass of second mix. Slowly shake the impression toandfrosothatboththeplasterscomeincontactevenly.Whiledoingthis,keeptheimpressionlevelbyholdingthehandleparalleltotheporcelaintile.Thenshapethesidesallaroundtheimpressionbyusingaspatula.Assettingproceeds,theexcessisremovedwithplasterknife.Allowforsettingfor45minutestoonehour(Fig.5.4).SeparatingtheCastfromImpressionThewholeunit,i.e.castandimpressionalongwithtray is placed in hot water at a temperature requiredtosoftenthecompound-say55to600C.Whenthecompound is soft, lift it up all along the buccal areaandthenpalatalorlingualarea.Allthisshouldbedone very carefully without causing any damage tothecast.Donttrytoremovethecompoundimpressionbeforeitissoftened.Alltracesofcompound on the surface of cast should be removedcarefully.Making Working CastThis is made following the final impression made byusingaspecialtraywithZinc-oxideEugenolimpression paste. As usual, the procedure is basicallysame,exceptthatthistimedentalstoneisusedtomake a cast.Washtheimpressionundertapwaterandshakeoff excess water. Mix dental stone with water powderratioof100gmofstoneto30mlofwater.For1stmix take 15 ml of water and 50 gm of stone.No need of separating media to be applied to theimpression surface. After filling the impression withdental stone of first mix, there is a choice for the 2ndmix; to make a base-one can use dental stone or else,plaster of Paris can be used.Separating the cast from ZOE impression: The whole unitalongwithtrayisimmersedinnearboilingwaterforfewminutes.Thiswillsoftenthepaste,whichmakes it easy to separate the cast. While doing this,holdthewholeunitwithatowelandbyusingaround end of wax spatula, lift the impression try allalong the outer periphery of the impression. All tracesofZOEpasteleftonthecastshouldberemovedcarefully.MakingaDentulousorPartiallyDentulousCastForthis,impressionsareusuallymadewithAlgi-nate,(IR-ReversibleHydrocolloid)whosemainFig. 5.3: Making of castby double pour method Fig. 5.4: Making of cast by double pour (Inverting method)Part 236 Essentials of Prosthodonticsdisadvantageisdistortionifnotcastedreasonablyquickly. Impression shrinks due to drying and swellsduetoimmersioninwater.Botharebad.Thereforecasting immediately is the best method. In case, if itis not possible to cast immediately or for some hours,thentheimpressionsarewrappedinadampclothand kept in a polythene bag and seal the bag.Withtheseimpressionsalso,thereisnoneedofseparatingmediumtobeappliedtotheimpressionsurface. Excess alginate beyond the posterior borderofthemaxillaryimpressionsarecutawaycarefullywith a sharp knife. Impression is washed under tapwater, and excess water shaken off. Blow the air outoftheteethareaoftheimpression.Supporttheheelandhandleoftheimpression,while being kept on the bench.OnceagainDoublepour/Invertingmethodisemployed to make a cast by using dental stone.Forthe1stmix50gmofDentalstoneismixedwith 15 ml of water. For second mix to make a base50gmofstoneismixedwith12mlofwatertogetrather thicker mix. While pouring the 1st mix, it is allthemoreimportanttoensurethattheteethareasareproperlycoatedwithoutentrapmentofair.Remaining steps too should be done carefully becauseoftheflexibilityofthematerial.SeparatingtheDentulousCastfromtheImpressionThe presence of teeth in the cast necessitates this steptobedonewithutmostcare,topreventfractureofteeth.Removetheexcessstoneallaroundtheperiphery of the impression. Holding the impressionwiththetrayuplooking,insertaninstrument(e.g.straightendofwaxspatula)betweenthetrayandthealginateoneithersideoftheimpressionandwithdraw the instrument. This will separate the trayfrom the impression material. Separated tray is keptaside.Thenthealginatematerialisliftedfromthebuccal and labial sides section-by-section and peeledoffcarefullywithoutcausinganydamagetotheunderlyingteeth.Boxing an Impression to make a CastThis is a method in which the impression is convertedintoakindofboxbyattachingastripofwaxallaround it and pouring plaster of Paris or dental stoneintoit.Theadvantageofthismethodisthatitpreventspressurebeingfallenonimpressionwhilebeing casted and also base is made automatically.Method: Bead or roll of carding wax is first attachedjust below the periphery of the impression all around.It is sealed with hot wax knife. The lingual space ofmandibularimpressionisclosedbyasheetofmodelling wax and it is attached to the bead in thatarea. Than a sheet of modelling wax of about 4 cm inheightisencircledaroundtheimpressionandfastenedtothebeadofwaxbyhotwaxknife.Sealtheboxproperlyandtestitbyplacingsomewaterintoit.Watershouldnotleakout.Impressionofplaster of Paris, compound, ZOE paste can be easilyboxed because wax beading will stick to the borderseasily.AlginateandElastomericimpressionarenotsuitable for boxing since wax will not adhere to them.Onceaproperlyboxedandsealedimpressionisready, one time mixing of plaster or stone is done insufficientquantity.Atfirstsmallamountofmixispouredintotheboxandgentlytappedorvibratedto make it flow into all areas of impression. This firstcoatingmustbesmoothanduniform.Thentherestofthemixispouredintotheboxfully.Thusfilledboxofimpressionisallowedtosetbyplacingasupportatbothendsoftheimpression.Onceplasterorstoneisset,peeloffthestripofwaxandthe beading all around the impression (Figs 5.5 and5.6).TrimmingCast/ModelMethoda. Handtrimming.b. Byusingmodeltrimmer.Fig. 5.5: Boxing an impressionA.WaxbeadPart 2Making of Cast and Model 37Hand trimming must be done before the cast setstoohard.Byusingplasterknifewithapalmgripand thumb support away from the sharp cutting edgeofknife,buccalandlabialexcessesareremovedwithout encroaching the full depth and width of sulci.Posteriorborderofthemaxillarycastbeyondthehammularnotchandbeyondtheretromolarpadincase of mandibular cast are trimmed and made flat.On such a flat surface the cast should stand upright.Buccal and labial sides are made round. Tongue spaceofthemandibularcastismadeflatandlevelfromone side to another. Base also must be flat and levelfromsidetoside.Excessbeyondthemaxillarytuberosityandretromolarpadisremoved.Inanycasesulcusandotheranatomicalfeaturesmustnotbedamagedorreduced(Fig.5.7).Trimming by using model trimmer. Same principles asin hand trimming are to be followed. But the dangerinthiscaseisexcesstrimmingduetoimpropercontroloverthespeedofthemachine.Excesstrimming especially at periphery of the cast must beavoided.Continuouswatercirculationisnecessaryduringtrimming.TRIMMINGSTUDYMODELSThesemodelsmustbeestheticandmadeattractive.Therefore shape is given during trimming. Maxillarycastispointedanteriorlyandhas3flatsurfacesatthesides.Mandibularcastismaderoundinfrontand has two flat surfaces at the sides. Both casts haveflatposteriorsurface,whichisatrightangletothemidlineofthecast.Thustrimmedcastsaredriedand dusted with French chalk to make them smoothandattractive.DuplicationofCast/ModelThis is a method to make another cast/model withoutmaking another impression of mouth but by makingan impression of the existing cast/model.Thisisrequiredfor,a. Tosavesurgerytimeb. Investmentduplicatecastforcastmetalworki.e.,castpartialdentureconstructionc. Recordpurpose.Method: Select a suitable stock tray that fits accuratelytotheexistingcast.Soak the cast in cold water for 5 minute.Traymustbeperforated.Mix alginate impression material.Makeimpressionofthecast.Removewhenset.Washundertapwater.Pourdentalstoneintothisimpressionandmakecast.SeparatethecastwhenstoneissetTrimthecast.Materials to produce a rubber mould of cast. With whichany number of cast can be made.1. Latexrubber2. PVC (Poly vinyl chloride)CONCLUSIONCast making is a skillful procedure and must be donecarefully and slowly. Proper manipulation of gypsumproductsisessential.Always make a base to all types of casts.Takeextracarewhiletrimmingtoavoidfractureofbaseorteeth.All impressions must be casted immediately or atleastasearlyaspossible.Fig.5.6: Boxinganimpression A.BoxingwaxFig.5.7: EdentulousplastercastsA. Mandibular, B. MaxillaryPart 238 Essentials of Prosthodontics6Making Special TraysThesearealsoknownasCustomtrays,Individua-lizedtrays,Tailormadetrays.Stocktraysarenecessarytomakepreliminaryor1stimpressioneven though these impressions are not accurate. Butthere is no choice, because patient has come to us forthe first time. Stock trays are like readymade shirts,whichwillfittomostpeoplebutarenotexact.Aspecial tray is like made-to-measure shirt, which willfit exact and to only one person for whom it is made.Specialtrayismadeonacastobtainedfrompreliminaryimpressionofthepatient.Main use of Special TrayTomakesecondaryorfinalimpressionofthejaw.DefinitionofspecialtrayItisacorrectlyfittingtraymadeonpreliminarycast.Requirement of Special Tray1. Mustbestrongandrigid.2. Musthavesmoothandroundborders.3. Musthaveprovisiontoretaintheimpressionmaterialonitssurface.4. Itshandlemustbefirmlyattachedandconvenientlyplaced.5. Must not distort during and after impression ismade.6. Flangesofthetraymustnotbeadoptedintoundercuts.7. Posteriorborderofmaxillarytraymustbe1/8of an inch beyond the junction of hard and softpalate.Andmandibularposteriorbordermustcoverretromolarpads.8. Bordersmustnotimpingeonthemuscleattachmentandshouldhaveproperreliefforfrenalattachments.9. Bordersoftrayshouldbelittleshortoftheperipheraloutlines.10. Bordersmustneverbeoverextended.Types of Special TraysA.Close fitting special trayThis type of tray has notmuchroomforthethicknessoftheimpressionmaterials. The impression material is in thin layerasinwashimpression.ZOEpastegivessuchimpressionbecauseofitsthinviscosity(Fig.6.1).B. Spacer special tray or loose fitting special tray.Thesetrays have space for thicker consistency impressionmateriallikealginateandthickconsistencyZOEpaste(Fig.6.2).What can be used as Spacer?a. Modellingwax:One sheet thickness for thick consistency ZOE pasteimpression.Twosheetthicknessforalginateimpression.b. Piece of thick canvas.Materials for Making Special TrayA.Nonmetallic1. Shellac base plate.2. Nonbrittleimpressioncompound.3. Acrylicresin.i. Coldcured.ii. Heatcured.Fig.6.1: Maxillaryspecialtray(shellac)A. Base plate adaption with rolled borders, B. Tray with handlePart 2Making Special Trays 39B. Metallic1. Softalloyoftinandlead.2. Plumberssolder.What can be used to make a handle to the tray?a. Same material as the trayb. Metalwire.Whatcanbeusedtoretaintheimpressionmaterialinthetray?a. Perforationsb. Special adhesive solutionc. Cottonwoolthreadsspreadoverthesurfaceoftrayandfixedwithstickywaxat3to4points.Shellac Special TrayThiscanbemadequicklyandthereforecommonlyusedasaspecialtray.But,becauseitisfragileandbreakableonemusthandlethisverycarefully.Types of Shellaca. Plainb. Alluminium filled (Fig. 6.3).MethodOutlinetheperipheryofthetrayonthecast.DustthecastwithFrenchchalk.Adaptonethicknessofbase plate wax to the cast and cut it little short of theperipheraloutline(TwothicknesswaxsheetforAlginateimpressions)DustthewaxsurfacewithFrenchchalk.Softenthe Shellac base plate over the flame uniformly andadaptittothecast.Inthecaseofanmaxillarycastfirstadaptitatthepalatewiththumbpressure.Inthecaseoflowercastadaptitovertheridgefirst.Resoftentheunadaptedareasofbaseplatesectionby section and thus complete the adaptation all overtheridge;buccal,labialandlingualareasofcast.Fingerpressureisusedtoadaptthebaseplate.Cut away the excess base plate beyond the sulcusand posterior border by sharp hot knife or by scissorsorbyusinganarrowbladedfineteethedsaw(Figs6.4and6.5).Resoften the borders and complete the adaptation.Filetheborderstotheperipheraloutlineofthecast.Smoothen and make the borders round with sandpaper.Labhandpiececanalsobeusedforthis.TomakehandleleftoverpiecesofShellacarejoinedtooneanothertoproperthicknessandsizeofhandleandshaped.OneendofthisisheatedandattachedtotheadaptedShellacataconvenientplace.Thentheattachedbordersofthehandlearesealedwithhotwaxspatula.Whencooledthehandlemustbefirm in place. Piece of impression compound also canbeusedtomakehandle.IfoneisusingZOEpastefor final impressions it will adhere to the dry surfaceoftheimpressiontrayandsothereisnoneedofFig.6.2: Acrylicspacerspecialtrays1. Maxillary, 2. Mandibular (A. Occlusal stops, B. Perforations)Fig.6.3: MaxillaryspecialtraysA. Made of alluminium filled shellac, B. Made of plain shellacFig. 6.4: Base plate (shellac) adaptationPart 240 Essentials of Prosthodonticsperforations.Ontheotherhand,ifalginateisthefinalimpressionmaterial,perforations(holes)aredrilledintothebaseplatewitharoundburorbypiercingahotinstrumentintothebaseplate(Fig.6.6).Spacer wax is removed only after border mouldingbutbeforethefinalimpressionmaterialisloadedintothetray.Closefittingshellacspecialtray(withoutspacer)canalsobeusedwhileusingZOEpasteasfinalimpressionmaterialAcrylic Resin Special TrayAdvantagesMorerigidandstrong,unbreakable,donotdistort.Self Cure (Cold Cure) Resin TrayMethodsa. Sprinkler(saltandpepper)methodb. Doughmethoda. Sprinkler (Salt and Pepper) MethodOutline periphery of tray on the cast apply separatingmedium (cold mould seal) to the cast surface.Wait for it to dry. Apply Vaseline to your fingerslightly.Adaptoneortwothicknesssheetsofbaseplatewaxasspaceroverthecasttotherequiredoutlineforbasalseatarea,i.e.,overthecrestoftheridgeandlittleontothebuccalandlingualsides.Posteriorpalatalareaandretromolarpadnotcovered. Apply separating medium again- this timetothesurfaceofthespacerwax.Cutintothewax2 to 3 mm square openings, one in the canine regionand another in the molar region of both sides of thecrest of the ridge. (These provide bumps in the trayand act as occlusal stops and space for the impressionmaterialtospreaduniformly)Twodispensers,onecontaining acrylic self cure polymer whose flow fromthe opening can be controlled as desired; and anothercontainingcoldcuremonomerliquidwhichcanbedispensedindrops,areessential.Startfromthebuccalselfofmaxillarytuberosityor retromolar buccal self of one side and continue toanotherside.Firstplaceadropofmonomerinthearea, then immediately sprinkle some polymer overit.Repeatthissequenceoverandoveragainuntil2-3mmthicknessofresinisformed,wholebuccaland labial areas of both sides are covered with resin,whichcanbepressedlightlyandsmoothenedwithfingersbeforeitpolymerise