Retention

What is an RPI called

Stress relieving clasp system

What is adhesion

Surface forces of saliva on denture and mucosa

How can clasps be made

in wrought metal and incorporated into the denture base or be included as part of the cast denture base

What is direct retention

looking at vertical displacemtn if denture along CPD and inserted nd removed 9 can be same or diff

clasps -

aesthetics dont put clasps on anetrior

What 3 things does the efficiency of clasps depend on

-clasp material -cross sectional thickness and shape -length of the clasp

How can retention be gained (3)

1. mechanical - clasps 2. Muscular forces- shape of the denture 3. Physical forces - coverage of the mucosa

Length of clasp

15 mm from origin to head - for 0.25mm undercut

Mechanical Retention" What is a clasp?

A metal arm that, when is position contacts the tooth preventing the removal of the denture base metal arm that flexes, reforms then returns to where is starts. can be made by wrought metal ( bend into place) or can be cast using lost wax technique.

What is meant by term retention

A term used to describe the RESISTANCE of a denture to LIFTING AWAY from the tissues (VERTICAL DISLODGING FORCESs)

What can be said about the modulus of elasticity of Co Cr and Au

CoCr twice than that of Au less modulus of elasticity so more rigid wrought - greater elasticity

What are the two classification of retention

Direct and indirect direct- resistance to VERTICAL displacement of the denture indirect - Resistance to ROTATIONAL displacement

Direct retention

Direct retention: Close to the base, adjacent to abutment teeth where retainers will be will done on shape of teeth and undercuts. Guide planes advantages over clasps: nothing that can reform, clasps will eventually will be ditressed and exceed portportional limit permanantly. Guide planes indicate you will modify teeth to create parallell surfaces.

What is mechanical retention

Engage tooth undercuts ( below bulbous part of tooth)

What retention is used fro acrylic dentures

Frictional - mucosa bourne mmovement of denture during function. contact points between replacement teeth and natural abutments are maintained to provide frictional resistance by the inclusion of wire stop of the last standing teeth(prevents distal movement of natural teeth) note: wire is not a clasp muscular- Uses the forces of associated muscles acting on the non-impression surface of the denture (DENTURE SHAPE)

What is retention

HOW WILL DENTURE BE RETAINED opposite of support how denture stays in patients mounth how it prevents gravty from making denture prevent food falling out if cavity

What clasp is used for a gingivally approaching clasps (infrabulge inferior to the bulbosity)

I bar clasps (most commonly utilised, best to use this only )

What is alternate?

In some cases it may be appropriate to consider altering the path of insertion along the proximal surfaces of teeth that is different to the common PATH OF INSERTION (90o to the occlusal plane) will provide frictional resistance etention. dreviate from CPD and alter path of insertion and removal so you can utilise undercut areas at COD to keep anterior saddle in place. can provide frictional resistance- can have parallel surfaces on abutment teeth

What are the five indirect retainers

Major connectors minor connectors rest saddle denture base

Guidelines of retention

Not saddle - 1 tooth missing and two adjacent teeth dont need to clasp both - minimal retention - one at each side of arch ideally - triangle - use combination use guide planes and guide surfaces can use combination of retention methods

What are the different types of clasps, according to where they are approaching

OCCLUSALLY approaching (approaches undercut from occlusal side of undercut) GINGIVALLY approaching (crosses the gingival margin)

What does RPI stand for - explain

R(rest occlusal) - Mesial of tooth rounded on the impression surface Proximal plate ( adjacent to saddle) has a guide surface of 2-3 mm undercut permit movement I bar clasp ( gingivally approaching) greatest prominence of the tooth clasp

What is atmospheric pressure

Resistance to displacing forces

What if there are no undercuts?

most commonly - Teeth may be prepared by the addition of composite on the tooth to create an undercut. • The composite build up must be carefully done to ensure the undercut is not too great otherwise the clasp may de-bond the composite from the tooth while engaging the undercut eg may have to use se stainless steel

Indirect

res particularly reeavnt if you have a free end saddle or kennedy classII . here you have to give good thought to retention

What can be said about the porportional limit of stainless steel and CoCr and AU

stainless steel higher value than both Co Cr or Au

Define indirect retention

the resistance to ROTATIONAL displacement of the denture According to the british society of pros- it is the retention obtained by the extension of a partial denture base to provide the fulcrum of a class II lever. (The retainers providing direct retention lie between the fulcrum and that part of the denture which is subject to the displacing force).

What type of material should be chosen for the clasps

think of material default: cobalt chrome .25 undercut have clasp arm 15mm in length abutment tooth thats is short and narrow and no 15 mm length then cant use cobalt chrome, think of more flexible material ( will require deeper undercut eg stainless steel ) if you have tooth that is ceramic crown - use wrought stainless steel clasp. * A metal must be chosen taht will have a suitable MODULUS of ELASTICITY

What is the RPI stress relieving system

The RPI is a stress relieving clasp system that is commonly adopted for DISTAL extension removable partial denture. The RPI stress relieving clasp system is used in free-end saddle designs to prevent stress on the last abutment tooth. kenendy class I and class II, first described bt kratochvil modified by Krol in 1973 The components makes up the RPI - Mesial rest Proximal guide plate Gingivally approaching I bar clasp

What is muscular retention

The action of the surrounding musculature on the shape of the non impression surface ( polished surface ( of the denture) . It is the patients muscular control eg not approschong in tongue space, so tongue keeps denture in place and not expelling the denture

What is the RPI stress relieving clasp system used

Used in free end saddle designs to prevent stress on the last abutment tooth

What is physical retention

( denture will be sitting in hard tissues , pdl, where it is on contact with these tissues have form of adhesion and cohesion of the saliva that can help keep denture in place. bigger the surface are better the adhesion and cohesion and better the retention, however also think about patient saliva) residual alveolar ridge, hard palate, ;lingual sa. consider adheson , cohesion and atmospheric pressure, closeness of adaptation ,extent ( area covered) of denture base

What is reciprocation

Any clasp sitting in patinet mouth is passive ]onky active at insertiona dn removal deforms over bulbosity and then jumps back to rest, applies some hirizontal load onto tooth, if load left unchecked, the tooth will move and the class will no longer be retentive. so for every clasp and retainer, needs to be some form of reciproaction on other side of same tooth to prevent it moving- thats what retentive clasp does.

What are the option of materials you can use for clasps

Cast cobalt chromium cast gold alloy ( expensive cast titanium wrought stainless steel wrought gold alloy wrought cobalt chrome

Direct retention

as close as possible to saddle have surbey lines, spaces denture cant go into these undercuts .

What non metal materials can be used to make clasps and what are the advantages and disadvantages associated with this

acetyl resin (polyoxymethelene) - advantages : appearance , engage deep undercut disadvantage- thick and bulkier , not adjustable , cost

where should a clasp be placed to prevent effective as a reatiner

below the bulbous part of the tooth ( undercut ) This bulbous part of the tooth requires identification , achieved by surveying

How are clasps designed to- how is retention with clasps achieved?

by engaging undercut areas of the tooth. A flexible clasp arm deflects over the bulbous portion of the tooth to passively engage the undercut . Tnhe claps arms deforms over the bulbosity,. once in oatinets mouth, sitting passively and only comes into action when patient removing it or bieng dislodged. When chewing / masticating clasps should do nothing.

How can retention be achieved

by mechanical means, muscular and physicals means (kratochvi) any portion of the prosthesis that contacts the teeth and prevents removal of the prosthesis muscles are also involved

What are the clasp axis equal to

clasp axis= axis of rotation

What is reciprocation

clasp comes down deforms and springs back .during the duration of deformation , the reciprocal is in contact tooth , this is only way to prevent tooth moving ad losing retention . *- As part of the clasp assembly each clasp unit will have an opposing element to the retentive clasp arm to prevent pressure form the clasp acting on the tooth.

Summary

cobalt chromium claso - 15mm long , 1.25 mm undercut if it is less- consider gingivally approaching for premolar and anterior teeth DO NOT - no occlusal for anterior and premolars as you can not get length do not engage a deeper undercut as denture can be inserted and nor removed.

What is direct retention and indirect retention

direct - reisistance to vertical displacement of denture indirect - reistancse to rotational displacement of denture

What is cohesion

forces withing the saliva , viscosity

What are the types of occlusally approaching clasps (suprabulge)

utilised on molar teeth -Ring CLASP ( not rest as it has gap which allows for material to flex and engage in undercut) . goes right round ring of tooth - Circumferential clasp - (2 clasp arms- only 1 goes below survey line and engages in undercut other arm is reciprocal arm that does not engage in undercut, stays above survey line ) - single arm clasp - same as circumferential clasp but does not have reciprocal arm ( stays above survey line and undercut)

when do you consider tilting to decuate CPD

where anterior saddle more than 3 or more teeth missing but always start with CPD denture cannot come out , , eliminate areas of soft tissue undercut so still place clasp posteriorly

Frictional retention

will prevent denture from being dislodges during friction make the guide planes - bigger are- greater digree of friction better retention

What should clasps be used in conjunction with to work most efficiently

with a rest (supporting component)