001. Blahoua, Z. and Neuman, M. Physical Factors inthe Retention ol Dentures. J Prosthet Dent25:30-5,1971.
002. Nikoukari, H. A study ofposterior palatal seals with varans tql4lql-b4l!. J Prosthet Dent34:605-613, 1975.
003. Sidney I Silvennan, DDS. Dimensions aqddisplacement pArcr!! qllh! pa!t!9Il!t!I4!4!ql
!9a1. J Prosthet Dent 25.4'70-488, 19'll.
004. Hardy, l.R. and Kapur, K.K. Poslerior border scal - Its rationale and importance. J ProsthetDent 8:386-397, 1958.
005. Stcphen calzier, BS, Drvid N Fincll, DDS, MA. and Larry L Hamon. DDS. Postcriorpe4plq4!!94! d 1 {ion related to hcight ofmaxillary ridse. J Prosthet Dent 43:5{)8 510, 1980.
006. Laney W. and Gonzalez J. The maxillary--del1jll9.ti!!-palalaLlg! u-ptdirtalleal.JADA 80:1 1 82-l 1 87, 1969.
007. Millsap, C. Thc pa$9!ior palatal seal . DCNA: Nov 1964;663-6'73.
001i. Winland, RD aid Young JM. Maxillarv complete denture plsltrrie!]qldt4lllql-yadlliQ!!in size. shapc a!!Lle!al[e!. J Prosthet Dent 29:256-261,1973.
009. Avant, W. E. A comparison of completlellg4lllqba$lbqtdlgilif&Igltlypss-a!-pa$starp4lqtal$4L J Prosthet Dent 29:484-493, 1973.
010a- Jacobson, T. E. and Krol, A. J., A contemporarv view oflhe f'actors involvcd in completedenture retention. stabiljty. and supporl.Parl I: Retention. J Prosthct Dent 49:5- 1 5, 1983. 4contemporary revicw ofthe tu !-ab!'hry,lqtdjuppa4Part II. Stability. J Prosthet Dent 49, 165-172, 1983. A contemporar-v review ofthc factorsinvolved in complete dentures. Part l l l : Support. J Prosthet Dent 49:306-113. 19113.
01 l. Chen, M. Reliabilitv oi the Fovea Palatini lbr Deteminine the Postedor Border ofdreMqrll!ly_De!!u9. i Prosthet Dent 43:133-137. 1980.
012. Firtell, D. et al. Postcrior I'alalal Seal Dislortion Rclatcd to Proccssinq -femperature. JProsthet Dent 45:5911-601, l98l.
013. DL Johnson, DDS, MEd, ar,d MG Duncanson, Jr., DDS, PhD. l he olastic posbalataldenture seal. Quint lnt l8:457-462, 1987.
014. Barco MT, et al. Ihe ellect ofrelininq on the accwacy and stability ofnaxillarv cornpletedentures- An in vitro and in vivo study. J Prosthct Dcnt 42: l'7-22.197t).
015. Ettinger:, R.1., Scandrett, F.R. Thc Postcrior Palatal Seal. A rcvicrv. Aust Dent J 25: 197-200. 1980.
017. Naylor, w.P. and Rcmpala, J.D. 'fhe Posterior Palatal Seal - Its Forms and Functions (l andllL Quintcssencc ofDcntal Technology, l0:41'7-422 dnd 489-492, July/August 1986.
Complete dentures may sufl'er liorn a lack ofproper border extension, but ronc arc moreimpoftant than the posterjor ljmit and thc posterior palatal seal on maxillary complete dentures.The postcrior bordcr is terminated on a sud'ace that contiDues and is movable in varying degrcesand not at a turn oftissue as aae the other denture borden.
DelicieDcies ofthe distal border may bc in thc lcngth ofthe dcnture base, or the depth oftheposterior palatal seal or both. Thcsc errors may lead to inadequate retention due to the lack ofpenphual seal. (Millsap 1964).
The purpose ofthis seminar is to discuss the factoN associated with complctc dmturc rctention,the importance of the posterior palatal scal, its location, design, placement of and processinginlluence.
II. Historical review
1883: Ames and the Greene brothers introduced atmospheric pressure as a means ofdcnturcretmtion iurd recommended the use off'unctional denture borders as opposcd to passivc bordersin the l'abication ofcomplete denturcs.
1 886: Wilson desc bed adhesion as thc primary dctcrminant irl dcnturc retcntion.
1907: Grccn brothcrs " Modeling compound"
1920: Hall revivcd intcrcst in the use ofatmospheric pressure as a reteitive factor by interpretingand dcmonstrating the functional denture borde6.
z-
1948. Stanitz uscd a lab model to suggest that atmospheic pressurc is in cquilibrium with lluidprcssurc exefied on molecules within a capilJary tubc with a liquid level in a container as well asthe attraction of two glass slabs. -fhcsc models explained how lluid film contributed to dentnrcrctention.
l95l: Craddock describcd thc gripping action ofthe buccinator muscle on the buccal flange ofthe mandibular dcnture and also coined the telm "pear shaped pad".
1962: Stamoulis believed that atmospheric pressure conrbincd with intimate tissue contact andperipheral seal comprise the most critical rctcntivc forces.
1964: Fish discussed deteminants ofretentjon and diffcrentiated between tissue, polished, andocclusal surl'aces and how each permits thc dcntist to incorporate mechanical, biologic, andphysical l'actors ofthe dentue retcntion.
Denture retention: (definition) Thc rcslstance in the movement of a denture away from its tissucfoundation especially in a vcrtical direction. A quality o1-a denture that holds it to thc tissuefbu[dation and /or abutment teeth. GPT-7
Wlrat are fivc factors ofretention? ( -Blaliova, Ilardy, Jacobson)
. Adhesion
. Cohesion
. I ter.facialsur.face rcnsion
. Atmospheric pressure
. Mechanical locking into undercuts ( NP(iDS denture syllahus).
Describe the di{ference betlvccn adhesion and cohesion: ( B/aiova, Hardv, Jacobson)
Interfacial surfacc tension: is a resistance to separatjon by thc film ofliquid between the denturebase and supporting tissues. It combines the actions ofadhesion and cohesion and is similar tocapillary action.
When is interfacial surface tension most effective? When lhe salivary lilm is very thin, thcrc is aperf'ect adaptation ofthc dmture base and the soli tissues are firmly attached to undcrlfng boneand not distortcd.
What cffcct does distance between the denture basc and thc mucous menrbrane have on retentionand what is it called? Blahova pg 232. "Capillary attraction".
?
HamullrNotch: ifnot cxtcndcd properly can cause a lack ofrelention. It is lbrmed by thcpterygoid hamulus ofthe sphenoid bone, the plaanidal process ofthc palatinc bonc, and therraxillary tuberosity. This trougl is the lateral indication for completing the posterior palatalseal. Its displncement relates to thc actron ofthe pterygomandibular raphe. What tendon/musclcis {iequeltly activc in this rcgion'l Tendon ofthe tensor levator palatini musclc bchjnd thchamular notch and vcrtical tendinous slips ofthe intemal pterygojd rnusclc.
what el}'ect ofthe Massctcr lnuscle have on the denture base? The nuscle activitv will cffect themandibular dcnture base contour on the posteior lateral aspcct.
What are the intersection ofmuscles oflacial cxDrcssion that comprise the morliolus?Jacobson/ltuol Part II Pg 169
How docs thc buccinabr muscle contibute?
The supcrior fibers ofthe buccinator muscle act to scat thc maxillary denture, the middle fiberscontrol the bolus offood and the infcrior fibers contribute to mandibular denture stability.
Lingual vestibule: It may not be possiblc to achieve a border seal without a correct liDgualflange, which is dividcd into three areas. What are they? See denture syllabus pg I7 &Jacobson,4<rol pg 14.
Stability is increased when extendine thc lin{ual flanqes into the vestibules as tar as pe$illqThese llanges ores€nt "favorable incDlace.
l. Antcrior lintaual =sublineual crescent arca. Influcnccd mainly by the genioglossus muscle(retention) which raise and protrudc the tongue.
2. Middle vestibule :mylohvoid area: (stability) Mainly influenced by the mylohyoidmuscle. which acts to raise the {loor ol the mouth.
3. Distolinzual vestibule :lateral throat form or rctromvlohyoid fossa. Bounded allteriorlyby the mylohyoid muscle, latcrally by the pear shaped pad, posterolaterally by thcsuperior constrictor, postcromedially by the palatoglossus nuscle and mcdially by thetongue.
The posterior Iimit ofthe mandibular denturc is dctcrmincd mainly by what two muscles?Palatoqlossus and the supgtiellelltlgtel
Ifa patient present with a chiefcomplaint of a sore throat what might be the contnbuing t'actor'l
SuDerior constrictor
I
Bxplain why viscosity is the only factor in denture retention that is dependent upon time andwhat can the patient do to overcome such occvtences? Blahata Pg 233
Peripheral seal and atmospheric pressure: The peripheral scal is attained by positive contact ofthe entir€ pcrimeter ofthe denture base to thc rcsilient tissues that outline the basal seat. Howmany pounds ofatmospheric pressurc are needed to dislodge a denture?
14.7 pql Jacobson patl I pg 7.
How did Jacobson describe this phenomenon? (film thickness pg 8)
Hardy dcscribed the lactors goveminS dcnture retention. briefly, give examplcs ofeach. pg 387.
. Physical factors?
. Physiologic factors?
. Psychological factors?
. Mcchanical factors?
. Surgical factors?
What is REALEF mean and how does this contributc to denture retention?
Resilient and like effect.
Anatomic landmarks and muscles affecting denture bordcrs.
What are critical anatomic arcas that influence maxillary denture retention, stability and support?
Maxillary arch Mandibular arch
1. Hamular notches retention Buccal shelf- suppofi2. Soli palate rctention Retromolar pad - support3. Posterior palatal seal - retention Rctromylohyoid space - stability4- Hard palate Support, retention Sublingual lbld - stability5. Buccal vestibule retcntion, stability
Posterior Palatal Seal
I. Purpose ofthe posterior palatal seal
The posterior palatal seal is looated at the posterior border ofthc dcnturc. It has bcen dcfincd as
an arca ofsofi tissue along thejunction ofthe hard and soil palate on which prcssurc, withinphysiologic limits oftissues, can be applied by a denture to aid in its retention. * Summarize thefunctions ofthe posterior palatal seal- Millsap, llfti ger
1 . To make the sunken distal border less noticeable to the tongue2. Aids in compcnsating for dimensional changcs in curing3. The proximity ofthe tissue contact prevcnts food from getting under the denture base4. Fim contact with the tissue ofthe soft palate reduces thc tcndency to gag5. The thickened area provides added strength across the denture6. To provide retention
ll. The location of the posterior palatal s€al and identifying structures
Dcscribe the vibrating line and its location? ranev, Naylor Pg 419
"Thc vibrating line is the imaginary line across the posterior part ofthe palate marking thedivision betwem movable and immovable tissues ofthe soft palatc and can be idcntificd whcnthe movable tissues arc active".
Why is the location ofthe vibrating line or the "ah" line critical and what muscle plays a majorpafl in its movement when the patient says "ah"? Naylor pg 419 (Levator veli pirlatini)
Saying "ah" will cause thc cause th€ soff palatc to lift. The vibrating line is not a line but an arca.This area is used to lblTn the post palatal seal.
Movement ofthe vibrating line in the midline involves a thin, firm, tendon like band. Name thistendon and what it suppods. Zdnel Pg 1 183.
Thc linc usually forward ofthc vibrating or thc "ah' line is called the? Valsalva line. Whei thepatient attempts to blow air through the nose what occurs'l ( soft palatc drops lrom thc airpressure)
Describe ihe lbvea Palatinae: -Iy'a.//or pg 420
6
Can the fovea palatinae be used to accuately locate the poste or palatal seal rrea?
iiardy attribuled some denturc failure to improperly locating the hamular notchcs. Describe thetechnique hc uscd.
" He suggcsted the use ofa "T" burnisher to idcntily thc notch since the instrument will drop intothe notch and identily it without question .
The posterior border and the posterior palatal scal are two ofthe mosi critical areas for maxillarydenture retention. What classification rvill help designate the shape ofthe soft palate anddescribes the amount ofpostcrior tissue that will accept the postcrior palatal seal? Millsap pg 666
. House's Palatal Tlroat form:
. Class L 5-13mm distal (more than 5mm ofmovable tissue availablc) Ideal for retention
. Class II: 3-5mm distal (l-5mm ofmovable tissue availablc) Good retention
. Class III: 3-5rnm anterior (less than lmm ofmovable tissue available) Poor retention
. Class III difhculties are in tissuc movement, tlpically present in high vaultcd patients,and because ofthe small arca for the posterior palatal seal.
III. Designs ofthe posterior palatal seal
Descdbe six ofthe most common Posteior palatal seal configuration described by Winland andYoung. Sec Ettingcr pg 198.
l. A bcad postcrior palatal seal2. A double bead postenor palatal seal3. A butterfly posterior palatal seal4. A buttcrfly posterior palatal seal with a bead on the posterior limit5. A butterfly posterior palatal seal with the hamular notch area cut to half the depth ofa #9
bur6. A postcrior palatal seal constructed jn rcfcrcncc to House's classilication ol palatal
forms;
How did Silverman place the posterior palatal seal on the maxillary cast?
The cast was scored as follows: A pcncil line was scribed liom the hamulus to hamulus midwaybctween the anterior and posterior flexion lines. A grcove was madc in thc cast along the line toa depth of 1-2mn. A shallow scratch indrk was placed on thc antcrior flexion line, iuttl theposte or flexion line was scored io a depth onc halfthat ofthe midscore line. The entire sealarea was scraped so that the antenor scgmmt on the cast sloped liom the scratch mark anteriorlvto the deepest portior at the rnidline. The depth ofthe cast scraping diminishcs from the midlineto the posterior vjbrating line.
What was thc cffect ofthe scraping? To allow the seal area on the denture to slightly displace ihesoft palate with a convex surfacc.
Which postcrior palatal s€al configuration may be used in codunction with the classilied thrcatform? Naylor pg 490
IV. Techniques used to achieve the posterior palatal scal (I.aney)
l. Functional lmpression - Class lll; to compensatc bccause thcre is so much movement2. Arbitrary (semi lunctional) Combination ofboth techniques3. Empirical Scoring cast
Describe the technique that Millsap used for rccording the posterior palatal seal area.
l. Use of Iowa wax or Korecta Wax No. 4.2. Mark landmarks with indelible pencil and reinsert impression3. Palpatc scal arca.4. Apply wax and insert at moderate pressure and allow to cool for scvcn minutcs without
pressure, then apply moderate pressure lbr live miDutes.5. Check to see wax is touching il1 a]l areas, add as needed.6. Trim to indelible pencil )ine.
Distortion of acrylic resin
What wcrc Johnson's findings as to the distortional opcning of the posterior palatal seal?
In test groups of small flat and large V-shaped palate, the distortional opcning ofthe postpalatalperiphery decreased as the size and thickness ofthew denture base was increased. Distortionalopenings along the posterior palatal border ofU-shaped and V-shaped palates were greatest atthe midline and €xtended laterally two thirds ofthe distancc from thc midlinc to thc hamularnotcn,
Whaf did he recommend? That the postpalatal seal should be deeper in the central part ofthepalate and extend to the hamular notch to compensate for acrylic distortion
During processing ofthe dcnture what may contribute the most to acrylic distortion?
Heat activation and cooling. It is assumcd that thc g)'psum materials, the metal flask and thepositive pressure all combine to compensate for pollanerization shrinkagc. Thc magnitudc oftheremaining linear shrinkage is attributed to thermal changes, which occur after the plastic assumesthe physical prcperties ofa solid. Linear sh.inkage is estimated about 0.44% and by volume hasbccn statcd to bc up to syo. (varics according to author)
Cure Cycie: 165 F for E hrs. 2"d stage at 212 F for lhr. bcnch cool I hr. soak room tcmp water %hr-
Monomer boils at 213.4F = porosity. lftemperatue dses too quickly what may occur to the thinareas ofthe denturc base'J Dentue syllabus
( Stone acts as a hcat sink by pulling the heat away from the thin denture base areas. The thiDarcas ofthe dmture base never reach activation tcmperature of 157 F.
Abstracts
33-001. Blahoua, Z. and Neuman, M. @. JProsthet Dcnt 25: 30-5,1971.
PurBelg: Presents a model ofmechanisms involved in denture retention.Discussion: None ofthe physical factors for retention can be totally explaincd. However, they allcommonly and intricately participate at the moment ofdislodgnlcnt. Rctcntion is enhanced by heelasticity ofthe mucous membranes ofthe basal seat area and by a good border seal which keepsspace betwccn dcnture and mucosa as small as possible-
Physical factors that influence rct€ntion:
adhcsion (the bond between mucosa mcmbranes and the dentue) and cohesion (thcmolecular bond between saliva or water) were claimed negligiblc.Negative atmospheric pressure under the denture was not valid because of imperl-ect sealand th€ prcsence ofsaliva.The authors claimed capillary action was the most important. The narower the spacebetween the denture and mucosa, the more retention occurs.Viscosity ofsaliva was responsible for initial rctcntion; as quality over time increascs,retention dccreases. lt also helps prcvcnt dislodgment ofthe denture.
4_
).
l .
1.
The Model: Biting or sucking forces deform elastic tissue under the dcnturc which whendelbrmed allows for capillary action retention. As tissues rctum to nafural state lutd salivaincrcases, rctention begins to fail. It is necessary for a denture, from time to time, to be pushedback against (dcform) the mucosa membranc to maintain retentiol.
33-002. Nikoukari, II. A study ofposterior palatal seals with varving palatal forms. JProsthet Dcnt 34: 605-6f3, 1975.
Purpose:'l'he study was desjgncd to measure the dimension and displacement patterns oftheposterior palatal seal in diffcrent palatal shapes. The effccts ofdifferent materials on thedisplace ent oftissue in the posterior palatal area were also evaluated.
M9!hsd! 44d \1!1!441!: Three patients with differing palalal shapes (deep, nedium, and flat)were selected- lmpressions wcrc made ofthe maxillary arch with plastcr of Paris to provide arecord ofthe palate in an almost nondisplaceable position. Permanent bases were made on thccasts by adapting baseplate wax; llasking and processing heat cured clear acrylic rcsin. The distalextcnsion ofthe bases was determined by having the patients say "Ah" ar'rd marking the posteriorlimit ofmovement ofthe palatal tissue. Ihe anterior extent and dcpth ofthc posterior palaial sealwas determined by palpation wilh a ball bumishet. Thc bases were used to make inpressions of
q
the posterior palatal seal area with ZOE paste. low-fusing n'lodcljng compound (green) andKorccta wax #4. The impression materials wcre applicd in varying amounts as indicated by theamount ofdisplacement ofthe tissuc in the bumisher palpation iridls. The impressions $ ercboxed and poured in stone and two additional pours were made ofthc bascs without theimpressions ofthc posfcrior palatal seal area. One ofthese sen'cd as a rcproduction oftheoriginal cast and the other one had the postcrioa palatal scal cut into it using an arbitrury methodas dcscribed by Neill and Nain1. Measurcmcnts ofthe casts were made usi|1g a penetrometer.Results: 'fhe results indicated that thc tissue displacement caused by ZOE was less than that ofthe other two materials in all thrce types ofpalatal shape. The compound had thc highestdisplacement rcadings and the Korecta wax was second for all thrce palate types. lhe arbitrarymcthod showed that the highest readings wcrc locatcd on the posterior border ofthe posteriorpalatal scal area, whereas, in the other mcthods thcre were midway between the anterior andpostcrior borclers. This discrepalcy was due to the rounding ofthe imprcssion material adjacentto the vibrating lille and lack ofmore distal suppofi.Conclusions: It was concludcd that the best posterior palatal seal can bc achicved by using greenmodeling conpound or Korecta wax #4. The posterior bordcr only should be scraped on the castto account for the roulding ell'ect describcd. No apparent changes oftissue displacement wcrcfound in diflerent palatal shapes. Thc width ofthe posterior palatal seal area was found to b€greatest in the patierlt with tbe flat palatal shape and the least jn tbc paticnt with the deep palatalshape. It \r'as also found that the {lat palatal shape has a vibrating linc located {arther posteriorly.This agccs with earlier studies ofSwenson and Tcrkla that the direction ofthe vibrating lincvarics according to palatal shape. Thc higher the vault. the more abmpt and forward is thcvibratiig line. h a mouth with a flat paldtdl vault, the vibrating linc is usually farther posteriorlyand has a gradual cunature, affording a broader fostcrior palatal seal area.
33-003. Silverman, Sidney L Dimensions and displacement patterns of the posterior palatal
!Sd. J Proslhcl Denl 25:,170-488. ls? l .
Purpose: To test the h)?othcsis that retention and stability ofa complctc maxillary denture willbe increascd by cxtcnding th€ posterior denture border bcyond the vibrating lineMatcrials and Methods: 92 dentures wcrc cxamincd for a period of two years afier completion.Thc findings describe the degree and frequency ofmodification oldenture length and thccondition ofthe solt palate morphology during the reexamination pcriod. Thc clinical procedurelbr making thc imprcssion is given in the article. Affcr thc impression is made, the halnularprocesscs are marked as is the anterior flexion linc. This line is ma*ed twice, once with abruptvigorous burst ofsaying ah and oncc more with briefburst of soll speech sayiDg ah. On themaster cast a shallow scratch mark was mitde on the anteioa flexion linc and a scratch rnark halfas deep was madc on the line rnore posterior. The dcpth ofthc cast scrapping diminished liomthc midline to the posterior vibrating linc. Thc cast were measured in many respectsResults: No signilicant diff'erence was found between the iiterhamular prccess distancc and thesagittal distance or in any othcr correlation. The data indicate only that thcre is a second flexionline that can be clinically obscrvcd and recorded posterior to the fovea-oricntcd flexion lineand that patients can tolcrate and use prostheses that are cxtcnded to this second post€riorflexion linc-qqllguqia!]icompletc maxillary dentures can be extended for an avcragc distance of 8.2 mm
l0
dorsally to the vibrating line. The impression technique described in thc article is critical to itssuccess.
33-004. Hardy, I.R. and Kapurr K.K. Posterior border seal - Its rationale and importance. JProstbct Dcnt 8:386-397, 1958.
Purpqlg: Evaluate the factors governing complete denfurc retention.Factors Goveming Retention:
A. Physical
l Adhesion and cohesion- perpendicular dislodging forces.2. Interfacial surface tension and atmospheric pressurc- lateml torque and horizontal
dislodgment forces. Camot be used to achieve retention alone, due to failurc in cases ofxerostomia and patients with thick rcpy saliva.
B. Physiologic
l. Physical condition2. Degree oftissue tone3. Quality and quantity ofsaliva4. Condition ofmucosa and submucosa5. Neuromuscularcontrol6. Ridgecharacteristics7. Ridge relaiionship
C. Psychologic
I. lntelligence2. Expectation3. Apprehension or fear of embafassment4. Gagging
D. Mechanical
L Occlusion2. Leverage3. Contour of denture bases
E. Surgical
1. Implant dentures2. Ridge extcnsion
PSSleItgI f3]44Nq41: Tle posterior palatal scal crcates a partial vacuum that will not opcratecontjnuously, but only when horizontal and tipping forces are in place. The vacuum is unlikely to
l l
do any damagc to do any damage to the supportinS or border tissues. Excessive border sealdcstroys the supporting tissues due to heavy pressure and the inte 'erence with vascular supply.
A. Advantages
Provides a close contact ofthe denture with the mucous membrane which prcvcnts foodfiom getting undemeath the denture.Diminishes or eliminates gagging.Supplics sunkcn distal borders which are less conspicuous to the tongue.Supplies a thick border to counteract denture warpage.
2.3.1.
B.
c.
1.
2.
t .
Tcchniqucs
l Functional- final impression is border molded in the PPS area with soft stick compoundor wax, pcrformcd by the patient.
2. Semifunctional- border molding is done by the dentist.3. Empirical- PPS is developed on the cast by grooving thc cast to thc dcsired depth.
Methods
Prcper impression poured. Cast trimmcd and a single thick pink base plate wax is adaptedto the cast into thc bordcr roll area, labially and buccally. A hard occlusion rim is adaptedto this base.Itatient uses an astringent mouthwash to rcmovc saliva and instructcd to say "Ah". Amark is done at the point were there is little or no movement ofthe soft tissue, invariablyit will includc thc fovea palatini. lt has the disadvantage that it will olien deprive thedentist ofthe use of.-.
33-005. Galzier, Stephen, BS, Firtell, David N. and Harmon, Larry L. !q$9I!gI-p9I!pIgI4!seal distortion related to heisht ofmaxillarv ridsc, J Prosthct Dcnt 43:508-510, l9{10-
Purpelg: To determinc thc relationship ofdimensional change in the region ofthe posteriorpcripheral seal to maxillary ridge height. Also to detemine the efl'ect porcelair and acrylic tccthmight have on distortion of acrylic resin in the same area.Materials and Methods: An original cast with an initial ridge height of4 mm was designed.Additional mastcr casts were made inc.easing the rklge height 1.5 mm each time up to 12.5 mm.Scvcn sets of four cast each were made. Two sets received porcelain teeth and two sels rccqvcdacrylic teeth. The denture bases werc processed and scparation bctwccn thc cast and denturebases was measured with an optical micromctcr.Rcsults: Thc rcsults arc charted in two tables in the afticle.Conclusion: A statistically significant positive relationship exist between ridge height ola castand dimensional changes in the posterior periphcral scal rcgion ofits dcnturc base. As the ridgeheight increases so does thc dimensional change in posterior peripheral seal region. l here was norclationship bctwccn the use ofporcelain or acrylic teeth and any dimensional change in theposterior peripheral seal region.
IL
33-006. Lancy w- and Gonzal€z J. @palatal seal, JADA 80:1182-1187, 1969.
lupgtet To cxaminc thc need for palertal reliefin a ma,rillary dcnturc and to examine thel'ablication ofthc posterior palatal seal.Mcthods & Materials:'fhe arlicle presents thc opinions and clinical experience (]1-the authors, asrvell as reviewing the anatomical considerations ofa maxillary denlule.Discussion: The reliefofthe palatc and the posterior palatal seal should be cvaluatcd by thedentist and should not bc left up to the laboratory technician. According to the authors, mostmaxjllary dcnturcs do not require relief. The posterior palatal seal must be properly placed anddesigned to enhance border seal and incrcasc stability- This phase ofdenture fabrication iscxtremely impofiant to the success ofthc denture and the health ol the patient.
'l he posterior border ofthe denture is bome by the palatine aponeurosis. Thc hamular notch islbrmed by the pterygoid hamulus, the pyramidal process ofthe palatinc bone, and the maxillarytubercsity. Thc tcnsor vcli palatini muscle is active in the arca posterior to the tuberosity, al1d itsmedial cxtension onto the laferal palate lnay bc affectcd by the vertical tendonous slips ofthcintcmal pterygoid muscle.
Limited el$ticity over tbe antcrior part ofthe hard palate and in the arca ofthc antenorpalatine foramen may contribute to the denture producing parosthcsia, pain, or a burningsensation- lfpalatal reliefis desired, jt should be kept to a minimum.
A technique ofscribing the mastcr cast by traurslerring the posterior bordcr ofthc dcnture isdescribed. The use oftin foil to provide relief is described. A functional as well as arbitrary sealarc lnentioncd. Scribing the cast no more than two thirds ofthe displacement ofthe cljnicalpalpated area is recornmended.Conclusion: The posterior palatal seal is an essential f'eature in the rctcntion ofthe maxillarydenture. Whcn propcrly placed, it enha[ces border seal and increases stability.
33-007. Millsap, C. @. DCNA: Novr964i 663-613.
Purpelg: Review the andtomy and thc physiology to accurately determine the posteior limit forthe palatal seal.Discussion: The purposc is to allow movenent against the lelding tissuc and maintain aposterior bordcr seal as the denturc moves with torquc producing forces. Other purposes includc:compcnsates for dimensional changes, prcvents food from getting beneath the denturc, rcduces
Sagging, adds strength, and lcss noticeable to the tongue.
A!a!p!lty: Antcrior soft palate contains the palatine aponeurosis and is lined by non-keratinizedtissue. Thc submucosa is loose and contains mucous glands- The palatine aponeurosis is lbrmcdby the expanded tenclons ofthe tensor palatine muscles covered with a thick layer ofglands.Location o1': Locate the hamular notch $ ith a mirror by sliding ovcr thc tubcrosities and markwith an indeliblc pcncil. The vibrating lille is located at thejunction ofthc movable tutdirnmovable soft palate. lt is not always syrnmctrical and is thinner in the midline. Mark with anindclible pencil. The vibratiDg linc is always on the soft palate.Palatal Throat lbnns:
Ilow. flat vault in thc hard Dalate.
ts
II-a medium width posterior palatal seal.lll-high vault in the hard palate.
Techniques lbr recordingl
a. Use oflowalvax or Korecta Wax #4.b. Mark landmarks as noted above and rcjnscrt impression.c. Palpate seal area.d. Apply wdx and insert at modffate pressure and allow lo cool for seven minutes.e. Check to se€ wax is touching in all areas, add as needed.f. Trim to indclible pencil line.
33-008. Winland, RD ard Young JM. @Variations in size. shaD€ and location, J Prosthet Dent 29:256-261, 1973.
Purpose: To review thc various types ofposterior palatal seals and their construction as taught inour dental schools.Discussion: A questionnaire was sent to 53 dcntal schools in the United States and Pucrto Rico.Therc were 47 responses completed and retumed.
Included in the questionnaire were questions about the tlpe and mcthod ofconstructing aposterior palatal seal in their maxillary complete d€ntutcs.Conclusions: Although there was much variety, it was found that most schools taught thcbuttedlv cast technique and constructed q4g. Therewas also vanation as to Ebg! the postedor palatal seal was developed, liom as early as thc finalimprcssion, to as late as the linal processing ofthe denture.
Also during linal impressions, mod€ling plastic was used prcdominantly to functionally placesoft glandular tissues in the post€rior palatal seal area.
Most ofthc dcntal schools used Swenson's Complete Dentures (Boucher).
The authors state that no matter what techniquc was used, the most impollant thing to rcmemberwas !qql, ie. to seal out air and food, and to seal in partial pressure.
33-009, Avant, W. E. A comparison of complete dcnture bases havins different tvpes ofposterior palatal seal. J Prosthet Dent 29:484-493, 1973.
!uD9!9: The purpose ofthe study was to deteminc if a posterior palatal seal is necessary forcomplete dcnture retention iuld ifaltering thc t)?e and location ofthat seal affects rctcntion-Mcthods and Materials: An appamtus was designed to test the retention ofcomplete dentures byapplying a verlical dislodging force extraorally to a rod attached to the denture base- The lbrcewas measured using a push-pull dynanorneter. Tlrrcc mcn and two women wete chosen assubjccts for the study. Each had relativcly firm ridges and no postedor undercuts. A master castwas made from a plaster lina) imprcssion. The master cast was duplicated four times usingreversible hydrocolloid. The master cast had no posterior palatal scal inscribed and theduplicated casts had four diffefent types ofpostcrior palatal seals inscribed-
Cast A had a V-shaped grcove across thc palate about 2mm anterior to tlre vibrating lineextending through the pterygomaxillary notches. Cast B had a V-shaped groove as in cast A and
I'f
also grooves forming a loop on both sides ofthe median palatine raphe. Cast C had an angle-shaped groovc carvcd across the palate and thrcugh the pterygomaxillary notches. fhe groovewas deepest (1.0 to L5mm) at the vibrating liI1e and played out completely as it slopedanteriorly. It was widest on each sidc ofthc pdatc on each sidc ofthc palatc bctwcen thetuberosity and the raphe and narrowcst at the mcdian raphe and pterySomaxillary notches. I hetissue was palpatcd with a ball bumisher to determine the outline lbr the anterior border. Thismcthod has been described by Swensoll. Cast D was prepared in a manner simi]ar to cast Cexcept that an arc-shaped groove was used and a V-shaped groove placed in the deepest part ofthe arc-shaped groove.
Identical denture bases wcre constucted on the five casts. The rod was attached to the dentuebases by mcans ofwircs that had been placed in the bases with a jig to insure that the wircs werein thc samc position in each denture base. Each patient was tested wearing each ofthe five basesto determine the amount offorce required to dislodge the base. Each denture base was tested fivctlmes.Bglulb: A posterior palatal seal is necessary for optimum retention ofmaxillary completedentures. Each tlpe ofscal that was tested increased ret€ntion el|ctively.'Ihe posterior palatalscal uscd on cast C was the most effective for three ofthe five patients and a very close secondfor the other two-Conclusions: A poslerior palatal seal is necessary for optimum rctcntion. Altcring thc type ofpalatal seal allects retention. Each t)?c ofscal used in the study increased the retentioneffectivcly. No onc t)?c ofposterior palatal seal that was tested proved to be superior in allsubjects. However, the angle-shaped posterior palatal seal was the most €llective ofthc fourdesigns tested.
33-010a. Jacobson, T. [, and Krol, A, J. @comDlete denture retention. stability. and support,Part I: Retention. J Prosthet Dent,l9:5-15, 1983.
Purpose: Evdluate the principles, factors and thcir intcractions, that mablc us to analyze andselect procedures that lcad to dcnture fabrication.Definition of Propcrties: Retention is the resistance to displacement of the denture base awayfrom the ridge. Stability is the rcsistance to horizontal and rotational forces. Support is thcresistance to vefiical movement ofthe denture base toward the ridpc.Definition of Retention Factors:
l. Adhesion- attraction bctwecn unlike forces.2. Cohesion- attraction between molecules ofthe same mateial.3. lnterlacial sudace tensioll- refers to the lbrces involved in maintainjng the attraction oftwo intimately contacted objccts, by virtue ofa thin fluid filrr in bctwccn them. Alsodefined as the force that maintains the surface continuity of a fluid.4. Gravity- sclf explanabry.5. lntimate tissue contact-close adaptation olthe denture base to the underJfng soft tissues-6. Border seal-involves the irrtimatc contact ofthc dcnturc borders with thc surroundingtlssucs.7. Atmospheric pressure- physical lactor ofhydrostatic pressure due to the weiglt oftheatmosphere on the earlh.
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8. Neuromuscular control-ref'ers to the t'unctional lbrces exerled by the muscles ofthepatient, that can alTect retention. Older patients have more difficulty in adjusring to ne$dentures. due to the progressivc atrophy oftheir neurological systems.
Clinical Observations: Measwemonts madc above sea level showed a decrcase in denturerctcntion- With a 70o% dccrcasc in ahrospheric pressurc, a 50o/o dccrcase in retention was noted.The presence ofdissolved gases or air in saliva, serves to decrease the cffcctivencss ofthcatmospheric pressure. 'l:herelbre the presence ofperlbrations in a PPS. reduces the retention ofthe denture.
Clinical Impliealiqls:
L Impression mateial with adequate flow propedies should be used to avoid unevenpressure dunng impressron making.2. A slight gcncralized prcssure on the soft tissucs is desirable.3- Elimination of full arch reliefspacers in the tray.4. Use ofnonperlbrated trays can lead to inaccurate recordings.5. Recovery ol abused oral tissues obtained by not allowing patients to wenr their prosthesesfor a ninimum of48 hrs prior to inpression taking.
Anatomical Influences on Maxillarv Dcnturc Retention: Highly tapered palatal vaults and therctrozygomatic space (buccal space), represent a problem in maintaining border scal.Anatomic Inlluences on Mandibular Denture Retention: The mandibular denture presents themajor problcm with rcgard to rctcntion. Reasons includc : movablc floor ofthc mouth, whichcauses difficulty in establishing border seal, and lack ofideal ridge height and conformation,which minimizes denture stability.
Adequate seal can be obtained by gcntly compressing the tissues ofthe Iateral wall oftherctromylohyoid fossa lingual to thc retromolar pad and tucking thc distolingual flange laterallyagainst the mucosa overlfng the superior constrictor muscle superiorly and the loose connectivetissue ofthe mandible inf'eriorl y.
The contour and inferior extension ofthc lingual flange are dependent on the action andanatomy ofthe mylohyoid muscle. The most difficult region in which to obtain a bordcr scal isthe anterior lingual border. The mylohyoicl muscle acts anteriorly as well as posteriorly to raisethe floor ofthe mouth. The superior fibers ofthe genioglossus muscle attach to the superiorgenial tubcrclcs and function in dcprcssing thc body ofthe tongue. Activation ofthe inferiorfibers serve to protect thc tongue.Clonclusion: Some techniques recommend the extension ofthe zurterior lingual flangesublingLrally. The flange is exteided infedorly to contact the highest level ifthe floor ofthemouth. Thc flangc can then be cxtcndcd lostcriorly to contact the sublingual folds and thereforeestablish a seal when the tongue is at rest.
Another technique involves adding additional softened border molding matcrial to thc innersurlace ofthe previously molded anterior lingual area and reseating the custom tray-
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33-010b. Jacobson, T. E. and Krol, A. J, @completc denturc retention. stabilitv. and suooort. Part IL Stability. J Prosthct Dent ,19,
165-t72. 1983.
I'urDose: Discuss the factors that contribute to denture stability.Relationshrpla] DqllrqBqq !ql!>us!
A. Mandibular lingual flange: The most desirable featwe ofthe lingual slopc ofthemandible is that it approaches 90" to the occlusal planc. The extent ofthe contact ofthelingual flange with the lilgual ridgc slope is thereby dictated by the firnctional mobility ofthe floor ofthe mouth. Any flange extension below the mylohyoid ridge must inclinemedially away from thc mandible, to allow fbr the mylohyoid muscle contraction-B. Residual ridge anatomy:
L Rcsidual height and confomation- large , squarc, broad ridgcs offcr a greater resistdnceto lateral forces than do snall, narow tapcrcd .idges.2. Arch form- square or tapcrcd arches tend to resist rotation ofthe prcsthesis better thanovoid arches.3. Palatal vault- a steep vault may enhance stability by providing gcatcr surface area ofcontact, and long inclines approaching a right anglc to thc dircction ofthe lbrce.
Relationship ofthe Extemal Surface and Orofacial Musculature:
A. lnlluence oforofacial musculature: The basic geometric design ofthe denture baseshould be tdangular. To direct a seating action on the nandibular denturc, thc tongue shouldrest against a lingual flange, irclined medially away from the mandiblc and somewhatconcave. The degree ofinclination dcponds on the balance ofthe muscular lbrces o1-thetongue as opposed to the mylohyoid and superior constrictor muscles. Cenerally, the buccaland labial flangcs ofthe maxillary and mandibular dentures should be concavc to permitpositive seating by the cheeks and lips. The primary muscles ofthe lips and cheeks are theorbicul:ris ods and buccinator musclc, rcspcctively.B. lmportance ofmodiolus: The modiolus or tendinous node is an anatonic landmark nearthe comer ofthlr mouth that is formed by the intersection of sevetal muscl€s ofthe cheeksand lips. These include the orbicularis oris, buccinator, caninus, triangularis, andzygomaticus muscles. None ofthcse muscles have more than one bony attachment, so th€ydepend on the modiolus for isometric contraclions. The denture must be designed as topermit thc modiolus to function lieely.C. Techniques: Neutral zone- theory that statcs thc beliefthat muscles should lunctionallymold not only to the border but to thc cntire polished surface.
Theories ofOcclusion:
A. Semianatomic or anatomic teeth: ls thought to minimize localized stress conccntrationand latcral dislodging lorces by ensuring multiple points ofcontact, to dist.ibute lunctionalocclusal lbrces-B. Lingualized occlusion: Providc limited range ofexcursive balance and a directing offbrces to the lingual side ofthe lower ridge during working-side contacts. Such concept may
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minimizc horizontal strcss and control the lcvcrage induced by ecccntnc tooth contacts.C. Neuromuscular: Patients are instructed to chew in centric relation contacts, bilaterally.
Tooth Position and Occlusal Plane: Anterior and posterior teeth should be placed as close aspossible to their original in the mouth. A nandibular occlusal plane that is too high ciur result inreduced stability, because the lateral tilting forces are magnified as the plane is raised. Anelevated occlusal plane prcvents thc tolrguc from rcaching ovcr thc food table into the buccalvcstibulc. Various anatomical landmarks should be used to determine an accqrtablc lcvcl oftheocclusal plane, such as: Stensen's duct and the retrornolar pad.Conclusion: Severe retrognathic or prognalhous ridge relationship can be renedied only to alimited extent through prosthetic treatment. The stability factor involves tissue, occlusal, andpolished surfaces ofthe danture.
33-{ll0c. Jacobson, T.E, and Kiol A.J. A contemporarv review oI the factors involved incomplete dentures. Part III: Support, J Prosthet Dent 49:306-313, 1983.
Purpe!9: Study thc rclationship betwcen the denturc base and the supporting tissues.Nature of Supportinq Tissues:
A. Sofl tissucs: Idcally soft tissues should be firmly bouncl to coftical bone, containing aresilient layer ofsubmucosa, arld be covered by keratinized mucosa. Keratin is ascleroprotein prcsent in the stratum comeum and is the cnd product ofepitheljaldegeneration. Excessive tmuma to ihe mucosa beneath n denture base calr lead to abnoma]tissue changes such as development ofparakeratin, localized hlperkeratosis, and epithelialulceration or necrosis. The fatty and glandular tissuo work as a "hydraulic cushion".B. Bone factor: Thc bone factor appears to be related to local anatomic and physiologicvariations within and between individuals. At the present time bone factor can only bedetermined by comparing the paticnt s response to bone stress( extractions, surgery) or byradiographic observation.
Tension placcd on bone on areas ofbone attachment tend to preserve the quality ofthebone and sometimes results in bone deposition. Cortical bone is more resistant to rcsorptionthan cancellous or medullary bone. Sharpey's fibers cnsurc tensjon on bone, minimizing theresorptive changcs othcrwise be the normal rcsponse ofbone to prcssurc. Thcreforc akeratinized masticatory mucosa lirmly bound to underlying cortical bone through a variablezone ofconnective tissue and submucosa \vith associated muscle attachments that providesthe ideal denture-bea.ing tissuc.
Anatomic Considemtions:
A. Mandibular considerations: The primdry stress bearing arens oflhe mandible must includethe pear-shaped pad and the buccal shell'. The pear-shaped pad is the most distal extent ofthekcratinjzed nasticatory mucosa of thc mandiblc. Thc junction ofthc rctromolar pad and thcpcar-shaped arca demarcate the extension ofthe denture base.'I'he pear-shaped area isassocidted with the muscle attaclments ofthe buccinator, superior const ctor, and temporaltnuscle. The muscle attachmcnts and the ovcrlying mucosa provide a stress-bearing area. Thcothcr rcgions ofthc mandible are not usually essential in providing dcnturc support.
6
B. Maxillary considerations:l. Keratinized masticatory mucosa overlies a submucosal layer everywhere except at themidiinc suturc.2. The submucosa contains fatty alld g]alldular tissue.3. Dense connective tissue traverse the mucosa, except the midline raphc which has littleor no submucosa.4. The cortical bone ofthc hard palate (palatine process and the horizontal processes ofthe palatine boncs), rcsists resorptive changes.5- The tensor veli and the levator palatini may provide the source oftension thatcountemct the pressure resorption.6. The crest ofthe ridge has a layer ofthick keratinized tissue, dense fibrous connectivetissue between mucosa and bone that acts as a resilient liner. The underlying bone rscanccllous bonc which is subject b resorptive changes.7. The ronaining facial slopes ofthe maxillary fidge are not essential in the denturesuppofi.
RelicfRcsions: Tissues susceptible to resorption should not be subjected to functional prcssures:
l. most maxillary and mandibular ridge crcsts,2. regions of thin mucosa dircctly ovcr hard cortical bone, these include; midline raphe, tori,exostoses, and thc mylohyoid ridge,3. rcgions ofmucosa overlying neurovascular bulldles such as the incisive papilla, and thcmental lbramen-
Practical Considerations: A tnrly mucostatic or prcssurc frcc imprcssion is virtually impossible toachieve. The fluid implession materiai contained in a rigid tray inevitably causes some tissuecompression. According to Pascal's laws ofhydrostatics, the pressure exerted on a confincd fluidwill transmit evenly throughout the lluid. Unfortunately, the fluid in oral tissucs is not confined,the tissue llLrids can move fieely jr rcsponse to stresses placed on them.
Selective pressure imprcssions provide equal distribution ofpressure to the suppofiing tissuesduring function. It has some disadvantages so, the ideal technique for impression taking shouldincorporate both pressure-liee and selective-prcssurc proccdures.Conclusion: Selection ofthe regions that should provide primary and secondary supporl dependson the anatomic variations unique to each patient.
Pumose: To irvestigate the reliability ofthc fovca palatjni as anatomic landmarks fordetennining the posterior border ofthc maxillary denture.Methods and Matcrials: 101 subjects were screened lbr the study. 72 of these had fovea palatinilocated one on each side ofthe palate. The vibrating lire (determined by the "blow mcthod") andthe lbvea palatini ofthe 72 patients with "idcal" fovca palatini wcre markcd with an indeliblepencil. The dislaDce bctwccn thcse two marks were then measured by two observers. Eachoperator rnadc thrcc mcasurements on each patient. The measurements made by each operator oncach subject were averaged separately and used as dala in compiling the statistical analysis for
t1
the study.Rcsults: Among the 72 "ideal" subjects, l8 had lbvea palatini whose location coincided with thevibrating line. None ofthe subjects had lbvea palatini located anterior to the vibrating line lurdremaining 5,1 were posterior to the vibrating linc. Thc diffcrcnce in the mear values recorded bythe two observers was 0.05mm. Thc authors concludcd that this diffcrence was probably notimportant from a clinical standpoint since existing techniques and instruments for determiningthe vibrating line do not permit precision greater than 0.5mm.Conclusions:
l. lhe nose blowing method appears to be an accurate method lbr locating the lbvea palatiniand the vibrating line.2. Seventy percent ofthe subjects had two fovca palatini.3. When present, the fovca palatini of257o of subjccts lay dircctly on thc vibrating line.4. ln 7% ofsubjects, the fovea palatini were located within l-2 mm posterior to thevibrating line, in 18.8% within 2-3 mm, in 27.1% within 3-4mm, ir l6% within 4-5 nrm,in 4.9% within 5-6 mm. md in L47u more than 6 mm posterior 1() the vibrating line.5. The fovea palatini are unreliable guidcs for locating the centu pofijon ofthc postcriorborder ofthe n'raxillary dcnturc.
33-012. Firtell, D. et al. Posterior Palatal Seal Distortion Related to Processine
IglllpSIellllg. J Prosthct Dcnt 45:598-601, 1981.
Purpose: The objectives ofthis study were (l) to determine the eff'ect ofprocessing temperatureon the accuracy oflit of a complcte maxillary dcnturc and (2) to dctcnninc thc accuracy of aspecial acry1ic resin proccsscd in boiling water and it to pol),methyl methyacrylate processed byconventional procedures.
Retention lbrces are at a maximum when the distance between the denture surl'ace andsupporting tissue is at a minimum. Thc grcatcr thc hcat obtaincd during proccssing, thc grcaterwill bc thc shrinkage and the resultant strain within the processed material. A lower temperaturethan suggested stalldard may produce less distortion of the denture base.Methods & Materials: A maxillary cast will minimal undcrcuts was duplicated 33 timcs. Thrccde3nture bases werc thcn proccssed at each temperature from 135 F to 180 F in 5 degre€incrcmcnts for a total of30 dmture bases. 3 denture bases were processed using a special acrylicthat was cured at 212 F for minutes. Afier denture recovery and storage in a humidor, the castswere trimmed and dried, and the distance between each cast at its denfure base was rncasured atthe midline with an optical micromcter with a tolerance of0.005 inches.Conclusion: It has been noted that a di{Lrence in 4 degrees C in the processing temperaturecould make a dif-lerence of60 degrces C within the acrylic resin. Shrinkage and distorlion can bereduced by decreasing the amount ofrnonomcr. Proccssing conventional heaFcurcd acrylic rcsinat temperatures at or bclow that recornmcnded by the manufacturer produccd no significantdistortion ofthc material at the posterior peripheral area. When the processing temperature wasraised above the recommended tenperature of 163 degees F, the distonion at the poste orperipheral seal became sigrilicant. thc special acrylic, dcsigncd to bc processcd at 212 dcgrccs F,showcd sigrificantly less distortion than conventional acrylic prccessed at or below conventionaltemperatures. However. the overall strength can be debated. There is a possibility that a lowprocessing temperature can produce weakened materials because ofthe formation ofshoder
zo
molecular chains- the increased distortion in dcnturc bases processed at higher temperatures isthought to be associatecl with nore rapid polynerization.
Pumose:'l'o determine the effcct that variations in palatal fbl.rn, sizc, and dcnture thickness haveon distortion observcd along the peripheral border in the palatc ofa maxillary denture.Materials and Mcthods: Master cast werc made for fivc test specimens; flat, medium U shapcd,medium V shaped, large U shaped, and large V shaped. liwo additional smaller sizcs for eachshape were also made for a total of l5 master cast. Three dif'ferent thicknesscs ofdenture baseswere produced on the master cast. The distofiion along lhe posterior palatal edge ofthe castbeginning at the n dljnc and measured every three millimetcrs was rccorded.
BgsqLlq None ofthc individual variables displayed a high d€gree ofcorelation with theposterior palatal openings. More distortion was cvident in thin maxillary dentures as opposed tothick ones. Distoftion along the posterior palatal border showed that flat contours producedopcnings extending across the arch from hamular notch to hanrular notch. tJ shaped irnd Vshaped palatal opelings tcndcd to tenniiate in the area ofthcjunction ofthe middle alrd crestalthird ofthe posterior palatal periphery.Conclusion: A postpalatal seal that is dccpcr in the central paft ol the palate and extcnds to thehamular notch is recomrnended for tJ and V shaped parlate lbnns. Extcnding the seal at least tothe crest ofthe hamu!ar notch or beyond is recommended fbr flat palate ft)rms.
33-01,1. Barco lUT, et al.complete dentures- An in vitro and in vivo studv. J Prosthct Dcnt 42: 17-22' 1979.
Purpelg: To determine ifheat-curcd maxillary denture base after relir'ring is more accurate thanupon its removal lion the flask. Also, ifan improvement in fit ofthc order thaf is achieved bythe relining procedurc is reflected in the stability ofthe denture in lunction.Discussion: An in vitro, as well as in vivo study was conducted here.
'Ihere was an increased distortion of heat-curcd denture bases with teeth as compared tothose without teeth. The rationale here is that the teeth arc hcld filmly in place by the g)lsuminvestment, and thc polynerized acrylic resin ofthc base locks to the teeth. When thermalshrinkage ofacrylic resin occurs, thc tceth are held into place. and this probably induces complexstrcsses in the denture base. whcn the denture is deflasked, relaxatr'on occurs. which results indistortion ofthe basc. whcn no teeth are present, the resin shrinks against the master cast.
The lab data clearly shorvcd that a better fitting denture can be made by relining thehcat cured denture lvith an autopolymcrizing resin prior to delivery. This study did notshow a signilicant reduction jn the amount ofdenture movement aftcr rclining(although therewas some). thjs may bc duc to the small sample size offivc patients.
It was possible to rcducc thc size ofthe posterior palatal scal without jeopardizing the stability oflhe denturc.
33-015. Ettinger:, R.1., Scandrett, l'.R. The Posterior Pala iew. Aust Dent J25: 197-200. 1980.
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The poste.ior palatal seal area is described and its anatomical borders are defined- The methodsused to achieve a seal are (l) scraping the cast, (2) a selective loading impression technique, and(3) a physjologjcal impression technique. Each method is described and its problems aredr'scusscd. The authors bclicvc that the physiological impression tcchniquc usiDg wax rcquircsthc lcast amount ofskill and experience to master (:ompetently.Posterior palatallg4l_dgti4ql an drex of soft tissue along the junction ofthe hard and soli p:rlateon which pressure, within the physiologic ljmjts ofthe tissues, can be applied by a denture to aidin its retention.Fur')ctions ofthc Posterior palatal seal- (1) to provide retention, (2) to prevcnt food from gcttingunder the denture base, (3) to diminish gagging, (4) to make the sunken distal border lessconspiouous to the tongue, and (5) to supply a thick border to counleract denture warpage due todimensional changes during the curing process.Teclniqlg! f1) Scraping cast techniquc- donc chairsidc, it is an educated guess by the clinician(2) selectjvc loading tcchniquc- dcpends on making an itrpression ofthc cdcntulous maxillaundff constant load and laking into account the varying tissue densities ofthe mucosa, effectivebut requires skill anrl experience. (3) Physiologic technique- uses x mouth temperatureimpression wax to create the poste or palatal seal, advatltages are that it can be developed insteps and that it can be coffected.Conclusions- thc most common problem associated with lack ofretention ofthc maxillarycomplcte denture is a faulty posterior palatal senl. Many dentures do not cover the tuberosities,nor do they extend into the pterygomaiillary nolches, while others arc extended too farposteriorly past the vibrating line.
A carcful cxamination ofthe patient's tissues helps to delineate the anatomical boundaries oftheposterior palatal seal area so that an adequate sexl can be established.
Purpele: To compare the djmensional changc of a ncwer continuous-injection technique u'ith astandard trial-pack tcchniquc as determined by measuring the posterior palatal border opening.Methods and Materials: Ten high and ten llat maxillary casls made liom masters moulds pouredin dental stone. Ten of the acrylic resin bases (high vault, n:5; llat vault, n:5)were process bythe standard trial-pack techniquc (TPT) using a commcrcial product designcd for this purposc.Tte othcr group of 1{) acrylic rcsin bases was processed by a continuous-injection technique(CIT). Measurements were marle after deflasking, trimming and polishing, and alter immersionin room temperature water lbr I h, I day and I week.Resuhs: Results showed that the flat vault had largcr opcnings for both proccssing tcchniqucs,cxccpt for thc trial pack tcchnique at deflasked locations I L and {).Conclusion: lt was concluded fhat the continuous-injection technique showed smallerdimensional changes compared with the standard trial-pack technique, and that these changeswere influenccd bv oalate shaoc and immcrsron ln watcr-
33-017, Naylor, w.P. and Renrpala, J.D.The Postcrior Palatal Seal - lts Forms andFunctions (l and II). Quintcsscncc of Dental Technology, 10:. 117-122 and 489-,192,Jul-v/August l9tl6.
LZ-
PurBe!!: Thc authors providc insight and instruction in the evaluation ofthroat form, design andprenaratiun of lhe Pr,sterior Palalal Seal.Dj!g!!qiq4: The posterior palatal seal (PPS) is generally regarded as an important contributor tomaxillary complete denturc retention. A well designed and properly placed PPS serves severalfunctions.
L Helps maintain the peripheral seal.2. Prevents the ingress ofair and food which could dislodge the dentur€.3. Helps compensate for dimensional changes that occur during the curing ofthe acrylicrcsin.4- May reduce gagging by maintaining firm contact with the tissues ofthe soft palate.5- lncreases the thickness ofthe acrylic resin at the posterior border and strcngthens thedenture.6. May make the distal border ofthe denture less noticeable to the tongue by applyingpressure to the tissues ofthe palate.
The development ofan appropriate design lbr the PPS requires an assessment ofthe palatalthroat form, tissue displaceability, and the role ofindividual anatomic landmarks in establishinga dcnturc scal. The following stqrs can act as a guidc to diagnose the PPS deign.
I - Determine the palatal throat form. House Class 1, 2 or 3-2- Assess and note any unusual anatomical features-3. Evaluate the status of key anatomical features, i.e. hamular notches, fovea palatine, etc-
Posterior palatal seal preparation is an integral pa.t ofthe maxillary complete denture fabricationrequiring assessmcnt ofphysiological and technical pammeters. In thc case ofpatients witheither a House Class 1 or 2 throat fom, the clinician may have a choice for the placement ofthearea ofgrcatest depth. A patient with a House Class 3 has limited options because it is the leastfavorablc ofthe threc classes bccausc of limited space for the placement ofthe PPS.
It is important to point out that there is no singlc PPS dcsign for all patients.
