RPD Review

RPD REVIEW LECTURE D R . W R S U A RE Z , M P H TOOTHFIXER24

REMOVABLE PARTIAL DENTURE REMOVABLE PROSTHESIS DESIGNED TO REPLACE MISSING TEETH AND TO RESTORE CONTOURS IN A PARTIALLY EDENTULOUS A R C H E S

Goals of RPD RPD service  



Elimination of oral of oral d disease isease and healt of oral/ p araoral Preservation of healt health h and health h of oral/ paraoral structures R estoration estoration of oral of oral functions that are comfortable, esth esthetically pleasing pleasing and and do do not interfere w interfere w ith ith patients oral functions

Indications of RPD RPD service Long edentulous span eed  Nee d to contour tissue contours bsence of a of adequate p equate perio eriod dontal supp support ort  A natomically com natomically comp promised romised abutments  A  Nee eed d for cross arch arch stabilization  Distal extension nterior nterior esth esthetics  A ge ge  A  Ease of plaque plaque removal 

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If secon f second d molar is missing and and is not to be to be rep replaced laced, it is NOT is NOT consid considered ered in the classification ( classification (in in cases of missing opposing pposing 2nd molar & molar & is not to be to be rep replaced) laced)

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Surveying 19

in REMOVABLE PARTIAL PROSTHODONTICS

Dr.. Walte Dr Walterr R. Suar Suarez,MP ez,MPH H

A dental cast surveyor has een de!ined as an instru"ent instr u"ent used t# deter"ine deter "ine the relative $arallelis" #! t% t%# # #r "# "#re re sur! su r!ac aces es #! th thee teeth #r #ther $arts #! the cast #! a dental arch& 20

Ai"s ' #(ectives #(ectives #! sur surveying) veying) 1.

Locate proximal tooth surfaces that are or can be made parallel to act as guiding plane surfaces.

2.

Locate and measure undercuts for mechanical retention.

3.

Identify areas interferences.

4.

Determine the most advantageous path of insertion/ disl di slod odge geme ment nt co cons nsiist ste ent wit ith h est sth het etic ic re requ quiire reme ment nts. s.

21

of

potential

hard

or

soft

tissue

Ai"s ' #(ectiv #(ectives Delineate elineate the h heig eigh ht of of contour contour of of tthe abutment 6. D and identify and entify tthe areas of of un und dercut that must red re duce uced d, blocke blocked d out or or p preserve reserved d.

teeth teeth be avoi avoid ded,

Hel elp p in in p planning lanning restorative restorative p proce roced dures . 7. H 8. R ecord ecord the most ideal cast cast p position osition for future reference.

9. E Establis stablish h a formal formal p plan lan for for RPD RPD design design an and d the required require d mout mouth h pre prep paration.

22

An unde!u" #$ %&'ed ()en ")e *+$e &% +n &*e!" #$ $'+--e ")+n #"$ "&

Undercut Area 23

Types of undercuts Tooth Undercuts (Proximal undercuts)

Soft Tissues or bony Undercuts(on lingual side of ridge) 24

Types of undercuts

�� blocked ed �� … shld be block 25

Prof. Dr. !."enugo

Path of Insertion(P.I) P.I Is The Direction in Which a Restoration/Prosthesis Restoration/Pros thesis Moes !rom the Point of Initial "ontact With the Su pporting Teeth to the Terminal Resting Position Where the #cclusal Rests Are Seated and the Denture $ase Is I s in "ontact With the Tissue Path of Remoal(P.R)' Reerse of the Path of Insertion The Direction of Moement of the Restoration/Prosthesis Restoration/Pro sthesis !rom Its Resting Position to the %ast "ontact With the Supporting Teeth&. 26

Post Is More Readily Remoed by Application of !orce ear Its Top Than by Applying Same !orce earer round %eel 27

Dental Surv Sur vey eyor or

28

Ney

Survey Sur veyor or

Prof. Dr. !."enugo

Jelenko Jelenk o Sur Survey veyor or

Surveying Tools *- Analyzing Rods

,- "arbon Mar-er 3-

Undercut auge +- Wax Trimmer

29

Prof. Dr. !."enugo

Analyzing Rod

30

"arbon Mar-er

31

Undercut auges

32

Undercut auge

33

Undercut auge

34

Prof. Dr. !."enugo

Wax

35

Trimmer

Prin Pr inccip iplles of of Surve Surveyi yinng

The Prosthesis oes Smoothly Into Place Without Interference After Analyzing the Proximal Tooth Surfaces and Ma-ing the ecessar y Alteration 36


%ocation of the Undercut Area "an $e The %ocation "hanged by " "ha han ngin ing g th the e Tilt

37


The location of the undercut area can be changed by tilting the cast anteriorl anteriorly or lateral 38

Prof. Dr. !."enug opal.

Princ Pri ncip iple less of Survey Surveyin ing g A "ast in a Tilted Relationship Represents a Path of Placement Toard the Side of the "ast That Is Tilted Upard 39

Selection Selec tion of the Pa Path of Inser Insertion tion

Tilting the "ast to'

"reate Suitable Undercuts 0ualize Undercuts on both Sides of the Arch Place the "lasp Tips in a $etter sthetic Position. Undercut Areas Should $e Present at $oth 1ero Tilt and the e Tilt ross Inclination of the "ast to "reate Apparent Undercuts Should $e Aoided 40

onsid en surveying cast Consi derations wh when 

  

Determine the RELATIVE PARALLELISM of toot of tooth h surface to act as GUIDING UIDING PLANES Determine INTERFERENCES etermine INTERFERENCES Determine d etermine desirable esirable / und undesirable UNDERCUTS esirable UNDERCUTS Determine p etermine pat ath h of insertion of insertion wh whic ich h w ould ould permit permit placement of com of comp ponents w onents w ith ith the best ESTHETIC best ESTHETIC ad vantage

ath Pat h of dis disp placement 

Direction along wh along whic ich h the RPD dislo dislod dges A l w w ays p ays per erp pen end dicular to occlusal plane ransferred d to surveyor, it is neutral or zero zero d degree egree tilt tilt (K (K rol) rol)  Transferre und dercuts shoul ould d be be p present resent wh when en at zero zero d degree egree tilt  Desirable un 

Tripoding the Cast 43

Scoring the Cast

MAJOR #ONNE#$OR!

#omponents of a typical

RPD

1. Ma%or connector 2.

Minor

connector

3. Rests 4. Direct retainers 5.

Indirect retainers &for distal di stal extensions'

6.

Denture base

MAJOR #ONNE#$OR! 





(nit of the partial denture that connects the parts of the prosthesis located on one side of the arch w/ those of the opposite side (nit of partial denture to w/c all other parts are directly or indirectly attached #hief functions includes &1' &1'unification unification of prosthesis parts) &2'distribution of applied force throughout the arch to selected teeth and tissue * &3' &3'minimi+e minimi+e torque to teeth



Ma%or

connectors must be RIGID) to enable transfer of functional forces of occlusion from artificial teeth) to denture base) to supporting teeth and tissues within the arch for optimum stability (cross arch stabilization) stabilization)



,lexible ma%or connectors will %eopardi+e supporting oral structures) manifested by traumatic damage to periodontal support of abutment teeth) in%ury to residual ridges) impingement of underlying tissue

Location * design of ma%or connectors 

!hould not impinge on movable tissues



Avoid



-ony * soft tissue prominences should be avoided during placement * removal



Relief

impingement of gingival tissues

provided beneath ma%or connector to avoid impingement of tissues &elevated median palatal suture) inoperable tori'



Relieved

* Located to prevent impingement impingem ent of tissues as distal extension denture rotates in function

Margins

of ma%or connector ad%acent to gingival tissues should be located far enough to avoid impingement



In mandible) mandible) atleast atleast 4mm below gingival gingival margins margins



In maxilla) atleast 6mm away from gingival margins and parallel to the mean curve of free gingival margins

Intimate contact bet contact bet w een een connector and and supp supporting orting tissues adds support, ort, stability & dds to the supp & retention of denture A void void rugae crest if possible possible Posterior limitation of maxillary of maxillary major major connector should ould be just be just anterior to the vibrating line

R(LE: 

$ry to avoid adding any part of denture framework to an already convex surface. surface . Rather try to use existing contours * embrasures. All components should be tapered where they %oin convex surface

Mandibular

ma%or connectors

LING( AL - AR 

Preferred

mandibular ma%or connector design except in cases where &1' &1'floor floor of mouth is high) &2'extreme lingual tilt of anterior teeth) &3'inoperable &3' inoperable tori



Indicated if there is sufficient space between the elevated lingual sulcus * lingual gingival tissue

ingual B ar Lingual Bar 

Half pear pear shape w ith ith greatest bulk greatest bulk at at inferior bord border wh er while ile sup superior bor erior bord der is tap tapered ered to w ard ard gingival tissue

Located ocated above moving tissue but tissue but as far belo far belo w the gingival tissue as p as possible ossible ( (min min 4 4mm mm))  Made of reinforce of reinforced d 6-gauge 

LING(OPL A$E INDI# A$ION!: 

When

the space available for lingual bar is limited &high lingual frenum'



In class I cases w/ excessive resorption of residual ridge



,or stabili+ing periodontally weaened teeth



,uture replacement of one or more incisor

Rule

No comp component should ould be adde dded arbitrarily or arbitrarily or conventionally . Eac Each h comp component should ould be adde dded for a good good reason & reason & to serve a definite definite p pur urp pose

Reason .

1

2. 3. 4. 5. 6.

for adding component

Support pport against horizontal orizontal rotation Stabilization against h R etention etention Preservation of healt health h of tissues of tissues Esth sthetics Patients comfort

the dentist alone is responsible for the choice of design & must have good reasons



Upper Upper bor bord der follo w the natural curvature of sup supracingular surfaces of teet of teeth h and and not be not be located located above the midd middle le third ird of lingual of lingual surface, excep except to cover the interp interproximal spaces to contact p contact points oints

inguop Linguo plate Half pear pear shape forms the inferior bor inferior bord der and and rovides rigid rigidity provid  Ideally Ideally sshould ould have have a terminal rest at each each end end  A ll ll gingival crevices and and dee deep p embrasures must be must be blocked blocked out p out parallel arallel to p to pat ath h of placement placement to avoid avoid gingival irritation and and w edging effect on teeth teeth 

!(-LING( AL - AR



 

Indicated if height of floor of the mouth is less than 6mm * does not allow placement of bar 4mm below gingival margins #an be used if lingual lingual frenum frenum does not interfere interfere #ON$RAINDI# A$ION!: &1'lingual tori) & 2'high frenum frenum attachment attachment)) &3'high &3'high elevation elevation of floor of the mouth during functional movements) &4'severe lingual tilt of anterior teeth

c co on nuous RE$ AINER INDICATION: When When linguop linguoplate is ind indicated icated but the axial alignment of anterior of anterior teeth teeth w ould ould require excessive blockout of inter of interp undercuts proximal und

#ON$RAINDI# A$ION!: 

!evere lingual teeth of lower anteriors



Wide

diaste diastema ma betwee between n lower lower anterio anteriors rs

# ARA#$ERI!$I#! * LO# A$ION 

$hin) $hin) narrow narrow&3m &3mm' m' metal metal strap strap on cingula cingula of anteriors)



!calloped to follow interproximal embrassures0



!uperior border tapered to tooth surface



!hould have rests on terminal end

L A-I AL - AR

INDI# A$ION!: 

When

lingual inclinations of remaining premolar * incisors cannot be corrected) preventing the placement of lingual bar



!evere lingual tori cannot be removed



!evere or abrupt lingual tissue undercut

MAXILL ARY MAJOR #ONNE#$OR!

!INGLE P AL A$ AL !$RAP INDI# A$ION!: 

!hort span) bilateral edentulous spaces on posterior area in tooth supported cases



#an be rigid w/out ob%ectionable bul and interference with tongue



DO NO$ connect anterior replacement to distal extension with single palatal strap for reason of torque and leverage (needs bulk to resist torque and provide adequate vertical vert ical support and horizontal stabilization)

# ARA#$ERI!$I#! * LO# A$ION 

Anatomic

replica form



Anterior

border follows the valleys between rugae as nearly as possible at right angles to median suture line



Posterior

border at right angle w/ median suture

line 

!trap should be atleast 8mm wide



#onfined w/in an area bounded by 4 principal rest

,INI!ING LINE!: 

No

farther than ,mm medial from imaginary line contacting lingual surfaces of principal abutment and teeth to be replaced



,ollow curvature of arch

MAJOR #ONNE#$OR INDI# A$ION! 

#lass I * II arches w/ adequate abutment * ridge support



Long edentulous span in class II mod m od 1



#lass I" arches



Presence

of inoperable tori that do not extend posteriorly to hard -soft tissue %unction

# ARA#$ERI!$I# * LO# A$ION  Parallelogram shaped * open in center  8-10mm anterior * posterior straps  Lateral palatal straps & 7-9mm' broad * parallel to curve of arch minimum of 6mm from gingival crevice of remaining remaini ng teeth



Anterior

strap: anterior border NO$ placed farther anteriorly than anterior rests * never closer than 6mm from lingual gingival crevice0 follows the valley valleys of rugae at right right angle angle to to median palatal palatal suture



Anterior

connector maybe extended anteriorly to support anterior tooth replacement



Posterior

strap placed as far posteriorly as possible (to avoid interference to tongue) but anterior to the line of flexure formed by %unction of hard and soft palate



Anatomic

replica or matte surface

P AL A$ AL PL A$E

$YPE

A re re thin, broa in, broad d, contoured contoured palatal palatal coverage covering  covering  or more of har hard d palate palate Use anatomic rep replica for uniform thickness & ickness & strength strength

n ca ons o s ng e roa pa a a ma or connector

     

#lass 1 arches w/ little vertical ridge resorption " or ( shaped arches !trong abutments More teeth in arch than 6 anterior teeth Direct retention not a problem No interfering tori

# ARA#$ERI!$I# * LO# A$ION 

Anatomic

replica form



nterior Anterior

border border follow follow valley valleys s of rugae at right right angle to median suture line as possible * not extend extending ing anterio anteriorr to occlusa occlusall rest rest or indire indirect ct retainers



Posterior

border located at %unction of hard * soft palate) not extending onto soft palate) at right angle to median suture line0 extended to pter ptery ygoma gomaxil xillar lary y notch notches es

#O"ERAGE

In most instances wh instances where ere only some only some or all anterior teeth teeth remain lass 2 w / large p large posterior osterior mod modification & ification & some Class 2 anterior missing Class 1 w / 1-4 premolars premolars & & some anterior remaining w remaining w / poor poor abutment supp support, ort, excessive vertical resorp resorption of resi of resid dual rid ridge, d ge, direct irect retention d retention difficult ifficult to obtain No torus

!INGLE P AL A$ AL - AR 

Most

widely used yet the least logical



NO$ RIGID ENO(G



$o have rigidity for cross arch stabili+ation) it must have bul



#hoice would depend on the si+e of denture bearing areas that are connected

(-! APED

P AL A$ AL

#ONNE#$OR

Least d east desirable esirable from p from patients atients & & mech mechanical standp standpoint oint ( (lacks lacks rigid rigidity ) never be used used arbitrarily Shoul Should d never be Use sed d only in only in situation wh situation where ere +n"e#& "ee") +e "& *e e-+!ed / #n&e+*-e "&# e0"end "& ")e &$"e#& -#'#" &% &% ")e )+d +-+"e A ny ny portion portion of connector of connector extend extending anteriorly from princip rincipal occlusal rest must be must be supp supporte orted d by in by ind direct retainer



Anterior

border must be ept atleast 6mm from ad%acent teeth



If in any case) it contact teeth) it must be supported by rest in a properly prepared rest seat

PRIN#IP AL O-JE#$ION!

$O (!E O, (-! APE



It lacs rigidity0 rigidity0 may induce torque to abutment



Designs will not provide good support * may permit impingement of underlying tissue when sub%ected to loading



-ul to enhance rigidity results in increase thicness in areas most frequented by tongue

 

Antero-posterior Not rigid enough

palatal bar

!hould be buly to be rigid and provide support and stability but will interfere with tongue function

-eading of maxillary cast 

$erm used to denote the scribing of a shallow groove on cast outlining the palatal ma%or connector



Accomplished



Groove



!lightly rounded preferred than v -shaped

using a cleoid carver

not exceed 0.5mm width/depth

Purpose

of beading



$o transfer the ma%or connector design to investment/ duplicate cast



$o provide a visible finish line for the casting



Ensure

intimate contact of ma%or connector w/ selected palatal tissues

MINOR CONNECTORS

Minor connectors Unites major connectors w connectors w ith ith oth other p er parts arts of t of the denture  A rises rises from the major connector  May be be continuous w continuous w ith ith some p some parts arts of t of the denture 

Functions .

1

2.

To transfer functional stress to abutment abutment) (prost (prosth hesis to abutment) To transfer the effects of retainers, of retainers, rests & rests & stabilizing comp components to the rest of t of the denture denture (abutment to p to prost rosth hesis) esis)

orm & Form & location 

  

Must h ust have ave sufficient bulk sufficient bulk to to be be rigid rigid & effective Located ocated in embrasures, not on convex surface Pass vertically ass vertically from from major connector ard lingual surface tap tapering Thickest Thickest to w ard to w ard ard contact area



Minor connector should ould form a righ right angle w angle w / major connector

Gingival crossing be crossing be abrup abrupt 2. Cover as little gingival tissue as p as possible ossible .

1

 

Shar Sharp p angles should ould be avoid avoided Spaces Spaces should ould not exist ( exist (avoi avoid d food food entrap entrapment) ment)

Minor connector that contacts guid guiding p ing plane lane of abutment: abutment: PRO!IMAL PLATE)





Must be ust be w w ide enough enough to use guid guiding p ing plane lane to the fullest (2 fullest (2/3 /3 of distance distance bet bet w een een cusp cusp tip tips of abutment 2/3 of lengt of length h of enamel of enamel cro w n

Minor connector: connector: of frame w ork ork where acrylic denture enture Portion of frame where acrylic d base w base w ill be ill be attach attached  Designed esigned to be to be comp completely imbe letely imbedd ddeed into the denture base enture base 

Finis inish hing lines Junction of minor of minor connector (d connector (denture enture base base attach attachment) ment) w ith ith the major connector should ould be a butt ty pe joint but joint but w w /out /out appreciable ppreciable bulk bulk  A ngles ngles formed formed should ould not be not be greater than mechanical 9"degrees 9"degrees to ensure the strongest mech connection (und undercut) ercut) 



Mand andibular minor connector for d for distal istal extension base extension base should ould extend extend posteriorly posteriorly about 2/3 of t of the length length of e of edentulous rid ridge & ge & have have elements bot elements both h on buccal on buccal & lingual

Tissue sto stop ps 







Integral p ntegral part art of minor of minor connector d connector designe esigned d for retention of acrylic of acrylic d denture enture base base Provid rovide stability to stability to frame w ork ork during during transfer and and processing processing Prevent d revent distortion istortion of denture denture d during uring acrylic processing Shoul Should d engage buccal engage buccal & lingual slop slopes of resid residual rid ridge for stability

G LINES FINISHING FINISHIN Junction of major of major and and minor connector  Not greater than 9" an 9" degrees degrees  For the thickness of denture denture base base resin 

inish Finis hing lines 

Located ocated 2mm 2mm me med dial from an imaginary line imaginary line that w at w ould ould contact the lingual surface of missing p missing posterior osterior teeth teeth





Direct retainer arm tap tapers from tip tip to finish finishing line Finish inish line at junction at junction of I bar I bar d direct irect retainer arm & arm & minor connector for d for denture enture base base attach attachment ( if if w/out finish lines flexing of clasp arm could create cracks in denture base)

Finis inish hing lines location Minimizes inimizes bulk bulk of of resin resin . M 2. R estores p estores palatal alatal contours 3. E En nhance speec eech h 4. contribute to natural feeling for for p patient atient 1

RE!$!

* RE!$ !EA$!

PR#STH#D#TI"S ,

RE!$ Any



unit of partial denture that rest on a tooth surface that serves to provide ertical support



Rests

should always always be located on tooth surfaces &abutments' that are properly prepared &rest seat'



Designated by the tooth surface prepared to receive them



Rest

should restore the surface of the tooth before rest seat preparation

A l w w ays ays remember that the most effective resistance can be can be p rovid if the tooth tooth is stressed stressed along provi ded if t its long axis. Therefore, Therefore, prosth rosthesis frame w ork s ork should ould engage the tooth tooth in a manner that encourages axial load loading” “

,unctions of rests 

rovide PRIMARY P(RPO!E: P rovide R PD PD



Maintain



 

vertical support for

components in their planned position aintains establishe established d occlusal occlusal relationship relationships s by Maintains preventing settling of denture Prevents impingement of soft tissues Directs Directs * distribute distributes s occlusa occlusall load to abutmen abutmentt teeth

,unctions of rests 

Assist

in distributing load over several teeth



Prevent



Direct food away from tooth contacts * embrasure



Provide

extrusion of unopposed abutment lingual bracing on anterior teeth

Requirements/ 









design consideration

!ufficient thicness of metal to prevent fracture especially at the %unction of rest and minor connector c onnector &1.5mm for chrome cobalt) 2mm for gold' al ong the Placed on surfaces which would direct forces along long axis of teeth &should not be placed on inclined planes' !hould be extended to as close to the center as feasible to promote axial direction of forces Placed in rest seats with smooth and rounded line angles which Rest seats should be on enamel or on restoration which will resist fracture and distortion di stortion when sub%ected to occl occlus usal al forc forces es

,orm of occlusal rest * rest seat 

Outline

form should be rounded triangular in triangular in shape w/ the apex toward the center of occlusal surface

,orm of occlusal rest 

!hould be as long as it is wide. -ase - ase of triangular shape at marginal ridge should be atleast 2.5mm for both molars * premolars


Marginal

ridge of abutment must be loered to

permit sufficient sufficient bul of metal for strength * rigidity. Reduction

of about

*.2mm is usually necessary


,loor of occlusal occlusal rest should should be apical apical to to the marginal ridge * should be concave or spoon shaped. #aution not to create sharp edges or line angles

,orm ,o rm of oc occl clus usal al re rest st 

Angle

formed by occlusal occlusal rest * vertica verticall minor connector where it originates should be less than 90degrees to direct forces along long axis

of rest rest more than an 9"d egrees Floor of 9"degrees

xtend Exten ded occlusal rest In mesially tipp tippeed abutment to: to: further tipp tipping ing (1) minimize furth (2) ensure that forces are d are directe irected d along the long axis of toot of tooth h 



R est est should ould extend extend more than h an half alf of of tthe mesiod mesiodistal w istal w idth of toot of tooth h, 1/3 buccoling /3 buccolingual ual w w idth, and and minimum 1mm thickness of metal, of metal, round rounded w ith ith no und undercuts or sharp arp angles

Intterproxim In ima al/ emb mbrrassu surre occ cclu lus sal rest 

Rest

seat are prepared as individual indi vidual rest seats but preparation are extended farther lingually

Reason

(1)avoid avoid interp interproximal w roximal w edging by ging by frame frame w ork ork food a w ay from ay from contact area (2) shunt food

Lingual rests on canines * incisors 

!ufficient space must be present or created to avoid interference



Root

form) root length) crown inclination) incli nation) crown root ratio must be considered



Lingual Lingual rest rest more preferred preferred than than incisal incisal rest for for it is nearer the hori+ontal axis of rotation2less tendency to tip tip tooth tooth more estheticall esthetically y acceptable acceptable



Lingual rest are usually indicted for m maxillary axillary canines &sometimes mx central' for they have a gradual lingual incline * prominent cingulum



Lingual rest seat in enamel enam el of mandibular anteriors are unsatisfactory for they lac enamel thicness

Lingual rest seat prepared on enamel



!lightly rounded v shaped on %unction of middle * gingival 3rd



Apex

of " directed incisally

Lingual rest seat 

Prepared

using inverted cone then progressing to round end



Eliminate



Rest

seat should be prepared only on enamel * highly polished



lways Always

consider the predetermined path of insertion



,loor of rest should be toward the cervical not on axial



#are not to produce undercuts

all line angles

Lingual rest seat on cast restoration 

$he most satisfactory from standpoint of support



Done by preparing in wax pattern before casting

Incisal rests * rest seats 

Placed

at incisal incisal angles of anterior anterior tooth tooth * on prepared rest seat



Least desirable



Predominantly

used as auxiliary rest or as indirect in direct

retainers 

More



May

applicable for mandibular canines

produce some orthodontic movement due to leverage

Inci In cisa sall re rest sts s * res restt seat seats s 

ounded ed Round

notc notch h in inc incisa isall angl angle e or on inc incis isal al edge edge w/ deepes deepestt portio portion n apical apical to to incisal incisal edge edge



Notch



Approximately 2.5mm

should be bevele beveled d both both labially labially * lingually lingually

* 1.5mm deep

wide

Full incisal rest 

Use sed d wh when oth other suitable p suitable placements lacements of incisal of incisal rests and and rests seat are not available



Patient

should be well aware of location) form * esthetic impact “topography of any rest should be such that it restores the topography of the tooth too th existing before rest seat is prepared”



Rest

seat preparation always must follow proximal preparation. Never precede it

DIRE#$ RE$ AINER! PR#STH#D#TI"S ,

,orces acting to displace displ ace prosthesis prosthesis from tissue 

,orce of gravity acting on maxillary m axillary prosthesis



Action

of adherent foods when mouth opens during chewing



,unctional forces acting acting across the fulcrum line

Retention

of denture bases



ADE!ION: attraction

of saliva to denture *



tissues #OE!ION: attraction of molecules of saliva for each other



A$MO!PERI# PRE!!(RE: dependent

on border seal * result in i n partial vacuum beneath denture base



hysiologic Physiologic

molding of tissues around the polished surface of denture



ffect Effect

of gravity on mandibular denture

Direct retainer Any



unit of removable partial denture that engages an abutment in such a manner as to resist displacement of prosthesis away from basal seat tissues



#an be accomplished by &1'frictional means &2'by engaging a tooth in undercut lying lying cervically to its height of contour

Removable



partial denture retention

PRIMARY RE$EN$ION: accomplished

mechanically by placing retaining elements on abutment teeth 

!E#OND ARY ARY RE$EN$ION: provided by intimate relationship of denture base * ma%or m a%or connector &maxillary' w/ underlying tissues



Engagement

of an attachment mechanism on dental implant

-asic principles of clasp design



EN#IR#LEMEN$



More

than180 degrees in the greatest circumference of tooth should be engaged

-asic principles of clasp design 

Occlusal

rest designed to prevent cervical movement

of clasps 

Retentive

arm should be opposed by reciprocal/stabili+ing arm &!tabili+ing and reciprocating components must be rigidly connected bilaterally for reciprocation of retentive elements'


Amount

of retention should be the minimum necessary to resist reasonable dislodging force



#lasp on abutments ad%acent to distal extension must be designed so as to avoid direct transmission of tipping * rotational forces to abutment &act lie stressbreaers' 

Proper

location of retentive end in relation to rest



(se of more flexible clasp arm


(nless guiding plane will positively control the path of removal) retentive clasps should be bilaterally opposed



$he path of escapement for each retentive arm must be other than parallel to the path of removal


Reciprocal

elements of clasp should be located at the %unction of gingival and middle mi ddle 3 rd of crown &the terminal end of retentive arm placed pl aced at gingival 3 rd'

,unctions of reciprocal arm 

Provide

stabili+ation * reciprocation against action of retentive arm



Located so that denture is stabili+ed against hori+ontal movement &only if rigid reciprocal arm) rigid minor connector) connector) rigid ma%or connector'



May

act as an indirect retainer &if it rests in suprabulge

of abutment anterior to fulcrum line

Extracoronal

direct retainers

(ses mechanical resistance to displacement by components placed on external surfaces of abutments #lasp type type retainer

Extracorona xtracoronall 

direct retainers

,unction * position of clasp assembly parts

#omponent ,unction part

Location

Rest

"ertical support

Occlusal)

Minor

!tabili+ation

Proximal

!tabili+ation

Occlusal

Retention

Gingival

connector #lasp arms

lingual) incisal

surface from marginal ridge to %unction of middle * gingival 3rd 1/3 of crown

1/3 of crown in measured undercut

-asic categories of clasp design 

#ircumferential clasp arm : approaches retentive undercut from occlusal surface



-ar clasp arm: approaches retentive undercut from cervical

#lasp designed to accommodate functional movement 

RPI



RP A



-ar #lasp 

Designed to address concern of lever in distal extension cases

#lass I RPD A distal distal extension acts as a long effort arm arm across across the distal distal rest (fulcrum fulcrum)) to cause the clasp clasp tip tip to (resistance arm arm)) to engage tooth tooth und undercut:::: ercut:::: RESULTING RESULTING TO TIPPING TIPPING AND TOR#UING TOR#UING OF ABUTMENTS whic which h is greater w greater w ith ith stiff clas stiff clasp p and and increased increased denture denture base base movement abutments: STRATEG STRATEGIES to minimize effect on abutments:  Mesial rest conce concep pt: change fulcrum & fulcrum & resistance arm location arm:: minimize effect of lever of lever  Use flexible arm

-ar clasp &roach clasp' 

Arise

from denture base or metal framewor * approaches the retentive undercut from gingival direction



#lassified base on shape of retentive terminal &I) A) $) modified $) or Y'



,orm has little significance as long as it is : &*'mechanically * functionally effective) &, & ,'covers as little surface as possible) & 3'displays 'displays as little little metal as possible

RPI



&rest) proximal plate) i -bar'

Mesiocclusal rest w/ minor connector placed on mesiolingual embrassure but not contacting ad%acent tooth

RPI 

Proximal plate: a distal guiding plane is prepared extending from marginal ridge to %unction of middle * gingival 3rd to receive proximal plate

RPI 

Proximal

plate: buccolingual width of guiding plane is determined by proximal contour of tooth



Proximal

plate plus the minor connector supporting the mesial rest will provide reciprocation

RPI 

I-bar : located on gingival 3 rd of facial surface in 0.01inch undercut



$apered to its terminus) w/ no more than 2mm of tip contacting abutment



Approach

arm located

atleast 4mm from gingival margin

RP A



Modification

of RPI when abutment demonstrate contraindication to RPI &severe lingual/ buccal tilt) severe tissue undercut) shallow vestibule' * desirable undercut is located in gingival 3 rd of tooth away from extension base area

Indications of bar clasp 

!mall degree of cervical undercut & 0.01in' which can be approached in from gingival



Abutment

for tooth supported partial denture or tooth supported modification areas 7-17



Distal extensions



In cases where esthetics must be considered

contraindications 

Deep cervical undercut or severe tooth */or * /or tissue undercut



!hallow vestibule



xcessiv essive e Exc

buccal buccal or lingual lingual tilt of abutmen abutmentt

#ombination clasp 

#an be used to reduce the effect of #lass I lever in distal extension through the use of flexible component resistance arm



#onsist of wrought wire retentive clasp arm * cast reciprocal cast arm

Advantages



,lexibility



Ad%ustability



Esthetic



Minimum



Less service fatigue failure than casted



#an be used on wea abutments ad%acent to distal extension

retentive retentive arm than c -clasp tooth surface covered

(ses of combination clasp : 

Abutment

tooth ad%acent to distal extension base with only mesiogingival mesiogingival undercut



Large tissue undercut



Wea

abutments

Parts

of a #IR#(M,EREN$I AL clasp assembly



Minor

connector



Principal



Retentive



Reciprocal

rest arm arm

#ircumferential clasp 

Most

logical to use on tooth supported cases except in cases when undercut can be approached better w/ bar clasp or esthetics

Disadvantages of c -clasps 

More



Occlusal

approach may increase the width of occlusal surface



More

metal display than bar clasp especially in mandibular arch



alf round form prevent edgewise ad%ustment to increase or decrease retention 

tooth surface covered than with bar clasp

Disadvantages Disadvantages can be minimi+ed by proper mouth preparation

-asic form of c-clasp 

#onsist of buccal buccal and lingual lingual arm originati originating ng from from a common body



#ORRE#$ ,ORM: one retentive arm opposed by a non-retentive reciprocal arm

Ring

clasp



Modification

of circumferential wherein it encircle nearly all tooth from its point of origin



(sed only when proximal undercut cannot be approached by other means (ex.distobuccal or distolingual undercut cannot be approached directly from the occlusal rest area or with tissue undercut preventing the use of bar clasp)



NE"ER be

used as an unsupported ring &always have supporting strut on nonretentive side'

Ring

clasp

-ac action clasp 

Modification

of ring clasp w/ same disadvantages and no advantages



Difficult to %ustify its use

Embrassure





clasp

In class II or class III partial denture w/ no edentulous spaces on opposite side !ufficient space must be provided in occlusal 3 rd to mae room for a common body) yet contact area is not eliminated



istorically has high degree of fracture if abutment not properly prepared



(sually need to protect abutment &crown'

Embrasure

clasp



!hould always always be used w/ double occlusal rest to avoid interproximal wedging (can cause separation of teeth resulting to food impaction and casp displacement)



!hould have 2 retentive * 2 reciprocal arms either bilaterally or diagonally opposed

Multiple 









2 opposing

clasp

circumferential clasp %oined at the terminal end of 2 reciprocal arms (sed when additional retention is needed usually in tooth supported aybe used for multiple clasping when entire half of Maybe arch are to be replaced (sed when retentive areas are ad%acent to each other Disadvantage: 2 embrassure approach

Angle 

A triangle

of cervical convergence

of light visible between tooth * surveyor

blade



eight of contour : a line encircling the tooth at its greatest diameter in respect to path of placement



(ndercut: portion of tooth that lies between ht of contour * gingiva

,actors that determine the amount am ount of retention of clasp $ooth factors factors



!i+e of angle of cervical convergence &depth of undercut' undercut'



ow far into the angle of cervical c ervical convergence the clasp is placed



Prosthesis

 

factors

,lexibility ,lexibili ty of clasp c lasp arm 

#lasp length



#lasp relative diameter



#lasp cross-sectional form or shape



Material

used



Retentive

clasp arm must be located so that they lie in the same sam e approximate degree of undercut on each abutment tooth

INDIRE#$ RE$ AINER!

$ooth supported partial denture &#lass III' 

Movement

of partial denture toward ridge prevented primarily by rests placed on abutments at each end of space



Movement

of base away from tissues is prevented by activation of passive direct retainers &clasp'



ori+ontal * longitudinal rotational prevented by stabili+ing component on primary abutment

Distal extension &#lass I * II') #lass #l ass I" * Extensive class III 

Movement

toward ridge will be proportionate to &1'quality of tissue) & 2'accuracy * extent of denture base) &3'total functional load applied



Movement

away from ridge occur &1'rotational movement about an axis) & 2'displacement of entire denture

Indirect retainer

Denture movement/ rotation 

,(L#R(M LINE: is an imaginary imaginary line passing passing through teeth * component parts of denture) around w/c the denture slightly rotates when sub%ected to forces directed toward or away from residual ridge

,ulcrum line in #lass I 

One

passing through the most posterior abutments

,ulcrum line in class II 

Is diagonal passing through the abutment on distal extension side * the most posterior abutment on the other side

,ulcrum line in class I" 

One

that passes through the two abutment ad%acent to the single edentulous space

,ulcrum line in cLass III 

,ulcrum line is determined by considering the weaer abutment (with poor prognosis and will eventually be lost) as nonexistent and consider though if posterior is not present



In #lass III with nonsupporting anterior teeth) the ad%acent edentulous area is considered to be tissue supported end

Indirect retainer 

Rigid

part of partial denture located on definite rest seat on opposite side of fulcrum line that resist denture rotation



Placed

as far as possible from distal di stal extension extension base &to provide the best leverage possible against lifting of distal extension base' on a prepared rest seat on a tooth capable of supporting it

Indirect retainer principle

Example

#lass I case

,actors influencing effectiveness of indirect indirect retainers 

Principal

occlusal rest on primary abutment teeth must be held in their seat by retentive arm of direct retainer



Distance from fulcrum line 

length of distal extension base



location of fulcrum f ulcrum line



how far beyond fulcrum line the indirect retainer is placed

,actors influencing the effectiveness of indirect retainers



Rigidity

of the connectors supporting indirect retainer. retainer. &all connectors must be rigid if indirect retainer is to function'



ffectiveness Effectiveness

of supporting tooth surface &IR must rest on properly prepared rest seat and no slippage'

Indirect retainer placement

,unction of Indirect retainer 

$o effectively activate the direct retainers to prevent movement of distal extension base away from the tissues

Auxiliary

functions of indirect retainers



May

act as an auxiliary rest to support portions of ma%or connector facilitating stress distribution



May

provide the first visual indication for the need to reline extension base

,orms of indirect indi rect retainers all are effective in proportion to their support and distance from the ( all fulcrum line)



Auxiliary

occlusal rest



#anine rest



#anine extensions from occlusal rest



#ontinuous bar retainers * linguoplates



Modification



Rugae

areas

support

DEN$(RE - A!E #ON!IDERA$ION!

,unctions of denture base 

!upport artificial teeth



$ransfer of occlusal forces to supporting structures



Add



!timulation by massage of underlying tissues of residual ridge

to the cosmetic effect of denture

Denture base in tooth supported RPD that replaces an anterior teeth 

Provide

desirable esthetics



!upport and retain artificial teeth to provide masticatory efficiency and assist in transferring occlusal forces directly to abutment through rests



Prevents

vertical and hori+ontal migration of remaining natural eeth



Eliminate



!timulates underlying tissues

undesirable food traps

Distal extension denture base 

Must

contribute to denture support

(minimize

functional movements & improve stability)



Maximum support from ridge can be obtained by broad accurate denture base that evenly spread load over area available avail able for support

Ways

to accomplish maximum support



5nowledge of limiting lim iting anatomic structures



5nowledge of histologic nature of basal seat areas



Accuracy

of impression



Accuracy

of denture base fit

 

highly variable for every patient! the ability to control functional displacement of distal extension base is a determination that is unique for each individual

!nowshoe principle

broad coverage furnishes the best support with with the least load per unit area" “

!upport is the primary consideration when designing denture base with esthetics) stimulation) * cleanliness secondary

Acrylic

vs

Metal

denture base



if there is need for future relining) use acrylic denture base material



RPD

fabricated after extraction) use acrylic denture base material



In tooth supported RPD &class III') metal m etal denture base can be used

#haracteristic of an ideal denture base material 

Accuracy

* adaptation to tissues w/ minimal m inimal volume

change 

Dense non irritating surface capable of receiving * maintaining good finish



$hermal conductivity



Low specific gravity0 gravity0 lightweight



!ufficient strength0 strength0 resistance to fracture * distortion

Ideal denture base material 

#an be easily ept clean



Acceptable



Potential



Low cost

esthetic

for future relining

at this time ideal denture material does not exist" “

Metal

bases



#an be used for tooth supported cases



DI! AD" AN$ AGE: Difficult to ad%ust and reline



AD" AN$ AGE!:

1.

Gingival

2.

Accuracy

3.

Good

4.

$hermal conductivity

5.

Weight

stimulation * permanence of form

tissue response * bul

Nail

heads

Need 

Loss of occlusion 



to reline

ave the patient bite on a gauge tapping in centric occlusion

28 wax

and

Evidence

of rotation on a fulcrum line w/ indirect retainers lifting from their seats as distal extension base is pressed against the ridge

6If occlusal occlusal contact contact is lost without without evidence evidence of denture rotation rotation with stability of denture base satisfactory reestablishing occlusion is the remedy rather than relining7

!tressbreaers 

Device that allow some movement between denture base or its supporting framewor * direct retainers



Process

of separating the action of retaining elements from the movement of denture base



A5 A stress

equali+er

!plit type stressbreaer

!tressbreaers 

Whatever

the the design) the purpose is to dissipate vertical stresses



Eliminate



#onsideration on health of abutment at the expense of health of residual ridge

hori+ontal stability

Advantages

of stressbreaers

Minimi+ed



forces transmitted to abutment) alveolar support is preserved



Possible

to obtain stress balance between abutment * residual ridge



Intermittent pressure from denture massage mucosa



If relining is needed) but not done) abutments are not damaged quicly



!plinting of wea tooth posible

Disadvantages of stressbreaers 

More



"ertical * hori+ontal forces are concentrated on ridge) increasing possible ridge resorption



Reduce



More

difficult to fabricate * is more costly

/ eliminate effect of indirect retainers

complicated design) not very well tolerated by patients * spaces act as food trap



,lexible connectors if not properly handled are prone to distortion) slight distortion bring more stress to abutment



Repair

* maintenance m aintenance are difficult) costly * frequently required

Advantages  

 



of rigid design

,ramewor is easier * less costly to mae Possible equal distribution of stress to abutment * ridge Less frequent need for relining Indirect retainers * other rigid components com ponents could provide rotational * hori+ontal stabili+ation Less danger of distortion

Disadvantages of rigid design 

If direct retainers are not properly designed) torque will be applied to abutment



If relining is needed but not done) abutment may be loosened * suffer periodontal damage

,actors influencing support of a distal extension base ( ridge ridge support will depend on the following factors)

1.

#ontour * quality of residual ridge

2.

Extent

3.

$ype * accuracy of impression

4.

Accuracy

5.

Design of partial denture framewor

6.

$otal occlusal occlusal load applied applied

of denture base coverage of fit of denture base

ome T on RPD Some Tiips on RPD design design 



No comp component of partial partial d denture enture should ould be adde dded arbitrarily or arbitrarily or conventionally . Eac component Each h comp should ould be adde dded for a good good reason and and to serve a definite p efinite pur urp pose Try to ry to avoid avoid adding dding any part part of partial partial d denture enture frame w ork to ork to an alread alread y convex y convex surface, R surface, R ateh atehr, try to use existing contours and and embrasures for the location of com of comp ponents p onents parts arts of t of the frame w ork ork . A ll ll comp components should ould be tap tapered ered where where they join join convex surface

From the analysis of t of the facts d facts derive erived d from the atient w ork u ork up, diagnostic and oth other d er diagnostic iagnostic patient w diagnostic cast and aid aids, d s, determine etermine the location of t of the abutment teeth teeth whic which h could could hel help p share the load load l w w ays be ays be a w are are of t of the fulcrum lines ( lines (axis axis of  A rotation) rotation) 





These w These w ould ould determine determine the p position osition of of tthe d direct irect an and d in ind direct retaines

O bserve rules on p on placing lacing the comp components

yOu mAy nOw wAKe up !!!

RPD Review

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