removable partial denture Tearm in

Prosthesis:-Is the replacement of an absent part of the human body by

some artificial part such as an eye ,nose ,and ear.

Prosthodontics:-is the branch of the dental art that treats with the

replacement of missing dental and oral tissue

Prosthetic :-the art and science of supplying artificial replacement for

missing part of human body .

Dental prosthesis :-an artificial device that replaces one or more is

missing teeth .

Abutment :-is a tooth ,a portion of an implant that serves to support and

–or retain prosthesis.

Retainer:- is defined as any type of device used for the fixation

,stabilization or retention of prosthesis.

Edentulous :-without teeth .

Dentulous :- a condition in which natural teeth are present in mouth.

Partial denture :-a dental prosthesis which restores one or more ,but less

than all of the natural teeth or associated parts and which is supported by

the teeth and- or mucosa ,it may be removable or fixed .

Removable partial denture :-a dental prosthesis which artificially

supplies teeth and associated structures in a partially edentulous jaw and

which can be removed from the mouth by the patient .

Saddle :- the part of denture which rests on and covers the edentulous

areas and carries the artificial teeth and gum work.

We have 2 forms of edentulous areas (saddle area ):-

1-Bonded edentulous area (bonded saddle ):-is defining as the edentulous

areas having remaining natural teeth found at both ends.

2-Free end extension(free-end saddle ):-an edentulous areas having

remaining natural teeth (anteriorly ) only and other end free(posteriorly ).

Guiding plane :-vertical parallel surfaces of abutment teeth oriented so

as to contribute to the direction of the path of placement and dislodgment

of the R.P.D.

Types of partial denture :-

1-fixed partial denture :-is prosthesis replacement of one or more missing

teeth cemented or attached to the abutment teeth .

2-Removable partial denture :-is prosthesis replacement of one or more

missing teeth that can by the patient, the R.P.D. divides for:-

A-Heat acrylic resin partial denture .

B-chrome cobalt partial denture

C-flexible partial denture

Indications of R.P.D. :-

1-distel extension situation .

2- long span

3-after recent extraction s

4-need for effect

5-Excessive loss of residual ridge

6-Economic consideration

The objective of R.P.D.:-

1-To improve masticatory function

2-To restore esthetic and speech

3-Topreserve remaining teeth and supporting structure (prevent and

deviation of the teeth and from normal position )

4-Restore health and comfort to the patient

5-To have proper occlusion

Disadvantages of R.P.D.:-

1-Damage to soft tissue and natural teeth due to either poor denture

design or lack of patient care .

2-Increse plaque accumulation which will lead to change in its

composition

Advantage of chrome cobalt R.P.D.:-

1-Accurate adaptation and

2-abrasive resistance

3- computable with underlying tissue

4-lessbulk

5-lessfood accumulation

6-incresed weight in lower jaw lead to increased stability

7-good thermal conductivity

Disadvantage

1-difficult relining and rebasing

2-special equipment required

3-more expensive

4-incresed weight lead to increased gravity to upper denture and lead to

un stable to the denture

R.P.D. –Lec 2

A.T.Enas

Classification of R.P.D.

1-according to the load distribution :-

a-tooth borne partial denture :-is partial denture which entirely supported

by teeth .

b-tissue borne partial denture :-is partial denture which entirely supported

by mucosa and underlying tissue .

c-tooth –tissue borne partial denture :-is partial denture which entirely

supported by both mucosa and tooth

2- according the edentulous area (Kenndy classification ):-the kennedy

method of classification was originated by Dr.Edwared Kennedy in 1925.

a-class I:- bilateral edentulous areas located posterior to the natural

teeth.

b-Class II:-a unilateral edentulous area located posterior to the

remaining natural teeth .

c- class III:-a unilateral edentulous area with natural tooth

remaining both anterior and posterior of it .

d-Class IV:-a single ,but bilateral (crossing the midline )edentulous

area located anterior to remaining natural teeth .

Modification areas :- any bonded edentulous areas other than those

determining the basic classes of Kennedy classification and

designing by the number .

.Phases of R.P.D

-Special tray fabrication using the study model ,resurveying the master

cast.

Block out and relief the master cast.-

-The block out master cast must be placed in a water bath contain piece of

plaster or stone (slurry) at a maximum temperature of 38°C for 5-10

minutes before duplication, so that the cast will not etched because the

water already contains calcium sulfate, and to allow the escape of any air

trapped beneath the relief wax on the master cast.

-Duplication the master cast by agar-agar to produce a refractory cast

from investment material.

-Dipping the refractory cast in Bee's wax and drying in oven, to make the

cast surface smooth and dense, and to facilitate the adhesion of wax and

plastic patterns to the refractory cast ,form the wax pattern on the

duplicated cast according to the establish design, wax and plastic pattern

(readymade) are used to form the pattern of the removable partial denture

framework; these patterns are available in a variety of shape, size, and

thickness.

-Spruing of the wax framework, to provide an entrance or channels to the

mold space and to serve as a reservoir of metal during casting procedure,

and to allow the gases to escape out of the mold cavity to avoid porosity

of the framewok.

-Investing the refractory cast with its wax framework in the ring and

pouring of investment material in the casting ring to form a mold.

-Wax elimination by burn out the refractory cast with its wax framework

in high temperature furnace, to eliminate the wax pattern leaving a cavity

in the mold, to drives off the moisture in the mold, to expand the mold to

compensate shrinkage (contraction) of metal on cooling.

Melting the metal in the centrifuge, and casting the metal to occupy the-

space left from the wax elimination

-Cooling of the ring and opening of the mold to obtain the metal

Framework.

Finishing and polishing of the framework.-

Checking of the metal framework on the master cast..-

Mounting the casts on the articulator, setting of teeth and waxing.-

Flasking, wax elimination, packing, and curing. -

- finishing, and polishing.

Lec3. M.S.C Enas

Ideal component of R.P.D.

1-Major connector

2-minor connector

3 rest

4-clasp

5-direct retainer

6-indirect retainer

-Major connector :-is plate or bar used to join the units of the

prosthesis located on the one side of the upper and lower arch with those

on the opposite side of the dental arch either directly or indirectly

attached .

Function of Major connector :-

1-connect all the component of the prosthesis .

2-provide indirect retention .

Requirements of major connector :-

1-rigidity a major connector should not be flexible it should be rigid

enough uniformly distribute the occlusion forces acting on any portion of

the prosthesis without undergoing distraction .

2- it should be provide vertical support and protect soft tissue

3-it should be comfortable to the patient .

4-it should not allow any food accumulation .

Type of major connector :-

1- Maxillary major connector .

2- mandibular major connector.

-maxillary major connector :- it should be fulfill the following

additional requirement :-

1- a beading (rounded thick border )should be given to the margin

of the maxillary major connector to provide a seal with the soft

tissue in their margins (prevent the entry of small food particles

between the denture and the soft tissue ) the beading is created by

making a 0.5 to 1 mm groove on the master cast.

Type of maxillary major connector :-

1- simple platelet bar :-

-it is a bar running across the palate ,it has a narrow half –oval

cross section .

-it can not be used in anterior to the premolar region due to

interference to the tongue .

-can be used only 1-2 teeth to be replaced on each side because

it has poor vertical support .

-it can be used only in Kennedy classIII.

2-Single palatal strap :-

-it should be at least 8 mm wide for provide adequate rigidity .

-it can be used in Kennedy class III ( bilateral short span

edentulous spaces ).

3-Antero –posterior palatal bar :-

- it is a combination of an anterior palatal strap and a posterior

palatal bar.

-the anterior strap is narrow than a conventional palatal strap .

-the posterior bar is a half -oval like single palatal bar .

The strap and the bar are connected by two longitudinal

elements along the lateral slopes of palatal giving a circular

configuration provide rigidity (it more rigid and strong ).

-it is indicating in case with palatal tori ,and long edentulous

span.

4- Antero –posterior palatal strap :-

-used when numerous teeth are to be replaced and a torus is

present .

-rigid due to a circular configuration .

5-U-shaped (horse shoe )palatal connector :-

- Used when many anterior teeth are to be replaced .

- used in presence of tori .

6- complete palatal coverage :-

-it covers the entire palatal

-used when many posterior teeth are replaced .

-anterior border should be 6 mm away for the gingival margin or extend

up to the cingula of the anterior teeth.

- the posterior border should be extend to the junction of the hard and

soft palate .

-a slight border seal can be obtained by giving a beading posteriorly , the

beading helps to prevent food accumulation between the palatal and

major connector .

-it can be constructed by using :-

1-all cast matel

2-acombination of a matel and acrylic ,here the matel extend over the

anterior half of the palatal while the acrylic covers the posterior borders

of the matel contain small projection (mesh work) for retention with

acrylic .

Mandibular major connectorTypes of lower major connector:-1-Lingual bar 2-lingual plate3-sublingual bar 4-lingual bar with singulum bar5-singulum bar 6-labial bar

1-lingual bar :-characteristics and location:-1-half –pear shape in cross section with the broadest portion of the bar is located inferiorly .2-superior border tapered to the gingival tissue that will minimize interference with tongue .3-superior border located at least 4mm inferior to the gingival margins 4-there must be a minimum of 8mm vertical clearance from the floor of the mouth to the gingival tissue 5-lingual bar should be placed as inferior as possible so that movement of the tongue not restricted 6-the height and width of lingual bar is 5mm.

Advantage :-1- It is easy to fabricate.2- It has mild contact with oral tissue and no contact with teeth

Indication :-1-when the vertical height of lingual alveolar sulcus must be minimum 8mm

Contraindication :-1-presence of mandibular tori2-high frenal attachment 3-depth of the lingual alveolar sulcus is less than 8 mm

2-lingual plate :-Characteristic and location :-1- Half –pear shape of a lingual bar from the inferior border that provides the greatest bulk and rigidity.2- A solid piece of metal extended interproximatly to the height of contact point above the middle third of lingual surface of mandibular anterior teeth .3- Superior border is scalloped and has intimate contact with the teeth ,this produces a knife edges margin

-: Indication

in cl I and cl II cases when most posterior teeth are lost and additional-1 indirect retention is required and there is excessive vertical ridge. resorption. when there is no space for lingual bar-3. whene one or more incisor teeth have to be replaced in the future-3

-: Advantage most rigid and stable than lingual bar-1 provides indirect retention when rests are provided on the premolar-2 additional tooth replacement can be easily added-3

-: disadvantage.decalcification of tooth structure due to food and plaque accumulation-1

Irritation of oral mucosa-2. Coverage more tooth and tissue than lingual bar-3

3-sublingual bar :--where the height of the floor of the mouth in relation to the free gingival margins will be less than 6 mm.2-can be used in apposition of lingual plate if the lingual frenum does not interfere .3-presence of an anterior lingual undercut that would require blockout for conventional lingual bar .Contraindication :-1- Presence of lingual tori 2- High frenal attachment

4-cingulum bar (continuous bar ):-A cingulum bar located on or slightly above the Cingular of the anterior teeth .Indication:-1-when wide diastima exist between the lower anterior teeth .2-presence of mandibular tori .3-whene there is sever lingual undercut .

5-dobule lingual bar (lingual bar and cingulum bar ):-It consist of two lower major connector which are connected together by minor connector from both side ,the superior part is cingulum bar and the inferior part is lingual bar . this type combine between the characteristic of two major connectors that from it ,the upper bar is half oval ,2-3 mm high and 1mm thick .

Indication :-1-when indirect retention is required .2-when contact with remaining mandibular anterior teeth is indicated , but open embrasure exist .

Advantage :-1- It contributes to horizontal stabilization of the prosthesis .2- Cover less than tooth and tissue surface .3- More rigid than lingual plate .4- Provide indirect retention .

Disadvantage :-1-complex in design .2-tendency to trap food debris .3-generally ,un comfortable to the patient because there are four edges exposed to the tip of the tongue .

6-labial bar :-Characteristics and location :-1-it runs across the mucosa on the facial surface of the mandibular arch .2-it display a half –pear shape when viewed in cross section .3-it is longer than a corresponding lingual bar , double lingual bar or lingual plate , so to ensure rigidity , the height and thickness of a labial bar must be greater than those described for lingual bar .

Indication :-1-when large lingual tori cannot be removed .2-when lingual indication of remaining mandibular premolar and anterior teeth cannot to connected .3-whene sever lingual tissue undercut is present .Contraindication :-1- When other lingual major connector can be used .2- Facial alveolar ridge undercut .3- Presence of facial tori .4- High facial muscle attachment (space less than 3 mm)

Disadvantage :-1-poor esthetics .2-tendes to distort lower lip .

Lec 7 Partial denture Msc .Enas

Direct retainer

Is defining as :-any unit of removable dental prostheses that engages on

abutment tooth to resist displacement of the prosthesis away from basal

seat tissue .

Classification :-

1- Intra –coronal retainer :-with the contour of the crown e.g

.precision attachment .

2- Extra –coronal retainer outside the contour of the crown e.g.

clasp

1- Extra –coronal retainer :- it engage the external surface of the

tooth ( abutment tooth )in an area cervical to its greatest convexity

e.g. clasp assembly )

Clasp :- the part of RPD that act as a direct retainer and –or

stabilized for a prosthesis by partially contacting an abutment tooth

.

Part of extra coronal retainer :-

1- Rest :-function is a vertical support

2- Minor connector :- function is stabilizing by acting through

guide planes placed on the proximal surface of the abutment

tooth

3- The proximal plate :-extending from the prepared marginal

ridge to the middle and gingival third of the abutment tooth .

4- Clasp arms :-function as stabilizing ,retentive and reciprocating

units .

Requirement of design clasp :-

1- Support :-resistance to gingival displacement (occlusal rest )

2- Bracing (stabilization );-resistance to lateral movement

(reciprocal arms ,minor connector )

3- Reciprocation (reciprocal action ):-each force exerted on the

tooth by the clasp arm(retentive arm )must be opposed by an equal

balancing force normally .

4- Passivity ;-when the clasp is in its placed on the tooth ,it should be

at rest and exerted no force .if aretentive function as only activated

when a dislodging force is applied on the RPD

5- Retention ;-retentive arms located in undercuts on the abutment

Factor that determine the amount of retention provide by a

particular clasp arm;-

1- Size of the angle of cervical convergence .

2- How far into the angle of cervical convergence , the clasp terminal

is placed

3- The flexibility of the clasp arm which is produced by ;-

a-the length of the clasp arm

b-the diameter of the clasp arm

c-the cross –sectional form

d-the type of metal used

classification of extra –coronal retainer :-

1- Supra –bulge clasps (akers clasp-circumferential clasp):-the

retentive arm approaches the undercut area from the supra –bulge

direction

2- Infra –bulge clasp (gingivally approaching ,bar clasp):-the

retentive arm approaching the undercut from the infra –bulge

direction ,e.g. bar clasp arm (I,Y,T bar ….)

Types of circumferential clasps (supra –bulge clasps )

1- Circlet clasp

2- Half and half clasp

3- A fish hook or hairpin clasp

4- Embrasure clasp

5- Multiple clasp

6- Ring clasp

7- Combination clasp

1- Circlet clasp (C-clasp ) :-

It’s the most common clasp used for removable partial denture ,the

least complex in design ,it has a rigid reciprocal arm ,arrest a

proximal plate approximately the edentulous area ,and a flexible

retentive arm ending in an undercut of 0.01inch ,it may be used in

canine ,premolars ,and molars .

Advantage :-

1-excelent bracing qualities

2-easy to design and construct

3-lesspotential for food accumulation below the clasp compared to

bar clasps

Disadvantage :-

1- More tooth coverage than bar clasps

2- More metal used is displayed than with bar or combination

clasps

3- Adjustment are difficult or impossible due to yhe half –round

nature of the clasp .

2- Half and half clasp

The half and half clasp are a modification of the circlet clasp are a

modification of the circulate clasp with the reciprocal arm coming from

one direction and the retentive arm from the other .two rests are used for

this clasp .it is used on molars and premolars . this is used in unilateral

denture design because it has dual retention . the retentive tip is placed

into a 0.01 inch undercut .

3- Fish hook or hair pin or reverse action clasp

The fishhook or hairpin clasp is another modification of the circlet

clasp . it is mostly used in the teeth with long crowns .it is rarely

used because so much of the teeth are covered by the retentive arm

. the other difficulty is the lack of flexibility of the retentive tip

because of the bulk of the clasp .

Advantage :-

Allows use of undercut adjacent to edentulous space

Disadvantage :-

1- It only can be used in the tooth with adequate occlusogingival

height

2- There tends to be food accumulation between the upper and

lower clasp arms

3- The upper arm can cause occlusal interference in tight

occlusion of the upper and lower arch

4- Caries prone

5- Not aesthetic

6- A large amount of tooth surface covered that can cause

decalcification and caries

7- Minimum flexibility and cannot be used in distal extension

bases

Type of intra –coronal retainers :-

1- Internal attachment :- it is also known as precision attachment or

key and key away attachment or parallel attachment or slotted

attachment .

Advantage :-

1- Elimination of visible retentive and support component

2- Better vertical support through arrest seat located more favorably

in relation to the horizontal axis of the abutment tooth .

Disadvantage :-

1- Require preparation of abutment

2- require somewhat complicated clinical and laboratory procedure

3- difficult to repair and replace

4- they are effective in proportion to their length and are therefore

least effective on short teeth

5- difficult to place completely within the abutment tooth because of

the size of the pulp

6- they are eventually wear , with progressive loss of of frictional

resistance to denture removal

7- they are considered more costly

2- external attachment (dalbo)

they are indicated for anterior prosthesis in a young patient with

alarge pulp chamber.

It extend outside the normal contour of crown of abutment tooth ,

contain L- shape male portion attached to abutment crown and

female sleeve placed in artificial tooth adjacent to abutment .

Advantage ;-

1- more esthetic

2- resilient

3- easy to insert

disadvantage :-

1- bulky attachment requires more space with in removable partial

denture

2- weak and break easily

3- difficult to replace

3-stud attachment (rotherman )

Which is an attachment that is inside the root that has a ball like structure

coming from it where a component of R.P.D. would come and fits exactly

on top of the ball .

Indication :-

the replacement of a stud attachment is one of personal choice and its

used for over denture .

advantage :-

1- the size of the attachment is small therefore less room is required in

the denture base

2- more versatile

3- can be use on mal –aligned abutment

4- easy to adjust and repair

5- decrease leverage

disadvantage :-

1- it has a tipping effect on the abutment teeth

2- complex design

3- cant be used in cases with limited space

4- expensive

4-bar attachment

These attachment join together teeth or roots and in additional to

providing retention for denture , its indicated when there is bone loss

around abutment teeth , the denture fit over the bar and is connected to it

with one or more sleeve .

Advantage :-

1- rigid splinting

2- cross-arch stabilization

3- it can be used along with other attachment or implants for a

combined fixed – removable prosthesis

disadvantage ;-

1-space requirement

2-Needs frequent soldering

3-difficult to maintain oral hygiene

Partial denture Msc Enas

Types of indirect retainer :-

A-auxiliary occlusal rest

1- Most frequently used

2- Located on the occlusal surface far away from the distal extention

denture base

3- The ideal location is the central incisor ,which is weak ,therefore

bilateral rest on first premolars are effective

4- Rests on premolars do not interfere with tongue movements

5- In kennedy class I bilateral rests on mesial fossa of first premolar

6- Bilateral indirect retainer –an auxiliary rest for major connector

7- When distal abutment on the modification side is poor ( functional

class I )

B- canine extension from the occlusal rest

1- Consists of a finger extension from premolar rest to the lingual

slope of adjacent canine .

2- Applied when the first premolar is the primary abutment

3- It should always use with terminal rests to prevent tipping leverage

as in single cingulum canine rest

C-canine 8rest (cingulum rest or lingual rest )

Used when the mesial marginal ridge of the 1st premolar is too

close to the fulcrum line ,when the teeth are lapped to render the

fulcrum line is inaccessible ,the rest can be more effective by

placing the minor connector more anterior to canine .

D-continuous bar retainers and lingo –palates

Terminal rests are actual indirect retainers ,continues bar retainer or

superior border of the linguo –plate should never be placed above the

middle third of the teeth to avoid tooth movement kennedy class I and II

as they rest on unprepared lingual surface ,they indirectly provide indirect

retention .

E-modification areas :-

The occlusal rest on a secondary abutment in class II modification Iserve

as indirect retainer ,if only one tooth is missing in the modification areas

,occlusal rest on this side should provide support for the unsupported

major connector along with indirect retention.

F-rugae area

Rugua area is firm hence used for indirect retention especially for class I

situations ,it can be used in case of U shaped designs ,less effective than a

tooth –supported

Partial denture M sc. Enas

Indirect retainers

A part of a removable partial denture which assists the direct retainers in

preventing displacement of distal extension denture bases by functioning

through lever action on the opposite side the fulcrum line .

Functions of indirect retainers :-

A- Primary function

Is shifts the fulcrum line away from the point of application of the

force , there by counteracting the lifting force and stabilizing the

denture .

B – auxiliary function :-

1- Reduces the anteroposterior twisting leverage on the principle

abutments especially in the case of an isolated tooth

2- Helps in stabilization

3- Acts as an auxiliary guiding plane

4- Splints the anterior tooth against lingual movement

5- May act as auxiliary rest to support major connector especially in

the mandible

6- May provides the first indication to reline an extension base

7- It counteracts horizontal forces by providing support and stability

to the denture

8- It provides lateral stability of PD by contacting aaxial tooth surface

with the rigid minor connector that is connecting indirect retainer

9- It acts as a third point of contacting the tooth structure to ensure

accurate repositioning of the frame work on the tooth during

rebasing and relining .

Fulcrum line :-

An imaginary line , connecting the retentive points of clasp arms ,

around which the removable dental prosthesis dental prosthesis tends

to rotate when subjected to dislodging forces (sticky food , gravity ,

muscles pull )directed away from or toward the residual ridge .

Types of fulcrum lines :-

1- Retentive fulcrum line

2- An imaginary line connecting retentive points of clasp arms ,

around which denture tends to rotate when subjected to force such

as the pull pf sticky foods

2- stabilizing fulcrum line

An imaginary line connecting occlusal rest , around which denture

tends to rotate when subjected to masticatory forces .

Location of fulcrum lines for different classes of RPD

1- ClassI :-passes through most posterior abutment

2- classII:- passes diagonally through most posterior teeth on one

side and abutment on the distal extension side

3- classIII:- passes through two principle abutments

4- classIV:-passes through two abutment adjacent to the

edentulous space

principle for using indirect retainer

1- more than one fulcrum line may present

2- indirect retianers must be placed as far as possible from distal

extension base ,for better leverage advantage

3- most effective location for indirect retainers is incisor region , but

due to their poor strength canines or premolars are used

4- whenever possible two indirect retianers , closer to fulcrum line are

takento compensate for the compromise in distance

factor affecting the effectiveness of indirect retianers

1- effectiveness of direct retianers

in order to become indirect retainer effective proper functioning of direct

retainer should be present , .the retentive arms of the direct retainer must

hold the principle occlusal rests properly

2-distance from the fulcrum line

a-length of the distal extension base ,if it increase ,an indirect retainer

must place far away from fulcrum line .

b-location of the fulcrum line ,ideally indirect retainer should be located

at a point perpendicular to the midpoint of the fulcrum line

c-distance from the fulcrum line ,indirect retainer is placed as far as away

from the fulcrum line

2- the rigidity of the connector supporting the indirect retainer –it

should be rigid

3- effectiveness of the supporting tooth surface , indirect retainer

should be placed on a definite rest seat . tooth inclines and weak

teeth should not be used for support .

2- infra bulge retainer :-bar clasp (Roach )

Bar clasp originates from the denture framework or a metal base and

approaches the retentive undercut from a gingival direction .

Other bar clasps e.g. T bar or modified T bar do not have a tripping action

since the retentive terminal engage the undercut from an occlusal

direction .

The push type retention of bar clasps is more effective than the pull

retention of a circumferential clasp .

Type of bar clasps :-the bar clasp is classified by the shape of the

retentive terminal into T, modified T,I ,Y or any letter clasp arm .

Bar clasp arms generally are used on the buccal surfaces of teeth in

combination with lingual circumferential clasp arms .

Some types of bar clasps e.g. I bar are push type having a tripping action.

Advantage :-

1- Greater retention than occlusal approaching due to the trip action

2- It is more esthetic than the occlusal approaching clasps .

3- The flexibility of the bar clasp arm can be controlled by its taper

and length

4- Covers less tooth structure than the occlusal apprcaching clasp

(less caries susceptibility )

Disadvantage :-

1- Greater tendency to collect and hold food debris

2- The retentive arm does not contribute to bracing and stability

Contraindication :-

1- When a deep cervical tooth undercut exists

2- When a severe tissue undercut exists

3- When there is a shallow vestibule

4- When there is an excessive buccal or lingual tilt of the tooth

5- When the height of the contour is close to the occlusal surface of

the tooth

Type of the gingivally approaching clasps ;-

1-bar clasp (roach or vertical projection)

Indication :-

1- On abutment for tooth –supported or tooth –mucosa supported

RPD when there is distobuccal undercut

2- In situations in which esthetic is important

Design :-

1-Parts component :- it is usually used as a combination clasp form .

a- Rest

b- Minor connector

c- A cast bar retentive clasp arm

d- A cast circumferential bracing clasp arm

2-It provides unilateral bracing

3-Engages 0.01 inch undercut

4-The shape of the retentive terminal as T,Y,or I classify the bar clasp .

2--RPI system clasp

Indication :-

Commonly used for mucosa born partial dentures

Design :-

It consists of :-

a- mesial rest

b- minor connector:-placed into the mesiolingual embrasure , but not

contacting the adjacent tooth

c- proximal plate contacts approximately 1mm of the gingival

portion of the guiding plane

d- Cast I bar retentive clasp arm located at the mesiobuccal

prominence of the tooth or mesial to it

2-Engages 0.01inch undercut

3-Provides unilateral bracing

4-The proximal plate and the minor connector provide stabilization and

reciprocation

5-During the function ,proximal plate and I bar clasp arm move in

amesiogingival direction disengaging tooth . this distributes more

functional load to the edentulous ridge .

2-Intra –coronal retainer (precision attachment(

This retainer is either cast or attached totally with in restored natural

contours of an abutment tooth

It is typically composed of a prefabricated machined key and key way ,

with opposing vertical parallel walls , which serves to limit movement

and resist removal of the partial denture through frictional resistance .

It is usually regarded as an internal or precision attachment , which

consists of a key and keyway

Note :- the key is attached to the abutment tooth and the key way is

attached to the saddle of the denture .

Advantage :-

1-Labial or buccal clasp arms on canine or premolars are not required so

aesthetic can be better

2-Vertical or horizontal loads are applied more directly to the abutment

teeth than by clasps or rests

3-Efficiency of retention is not affected by the contours of the abutment

tooth

4-Number of components of the denture is reduced and hence tolerance

should be better

5-When used with lower free end saddles posterior movement of the

denture is prevented

Disadvantage ;-

1-Extensive preparation of all abutment teeth is necessary , together with

construction of the necessary crowns or inlays

2-When the crowns of the abutment teeth are small or short , these

attachments cannot be used

3-Teeth with large pulps are at risk owing to the relatively deep

preparation

4-Intracoronal attachment are not normally advised for free end saddle

denture owing to the rigidity of the union between tooth and saddle .

5-High costly

Lec:-6 Msc Enas

Rests and rest seats

Rest : It is a rigid extension of partial denture which rest in (occlusal

,incisal , and lingual surface ) of a tooth to provide vertical support the

removable partial denture and transmit functional forces to the teeth .

Rest seat : It is that portion of the tooth that have been selected and

prepared to receive a rest . The rest that is part of a retentive a rest . The

rest that is part of a retentive clasp assembly is called primary rest . while

rest that is responsible for additional support or indirect retainer is called

secondary rest or auxiliary rest.

Function of rests

The primary function of the rest is to provide vertical support for the

partial denture and :

1. Maintains components in their planned positions

2. Maintains established occlusal relationships by preventing settling

of the denture

3. Prevents impingement of soft tissue .

4. Directs and distributes occlusal loads to abutment teeth .

5. Serve as a reference point for evaluating the fit of the framework to

the teeth

6. Prevent extrusion tipping or migration of the abutment teeth

7. Acts along with its minor connector as an indirect retainer a tooth

tissue supported removable partial denture .

Types of rests

Rest named according where they seated on the tooth surface

1. Occlusal rest .

2. Inter proximal rests (embrasure rest ) .

3. Lingual rest .

4. Incisal rest .

Incisal rest and rest seat

Incisal rests are placed at the incisal angles of anterior teeth and on

prepared rest seats . this type of rest desirable . it may be used

successfully for selected patients when the abutment is sound and

when cast restoration is not otherwise indicated it is used as auxiliary

rests or as indirect retainers .

Incisal rest may be used on a canine abutment it is more applicable to

the mandibular canine due to lack of adequate thickness of enamel on

the lingual surface . this type provid definite support relativity little

loss of tooth structure and little display of metal . An incisal rest is

prepared in the from of a rounded notch at the incisal angle of canine

or on the incisal edge of an incisor with approximately 2.5 mm wide

and 1.5 mm deep so that the rest will be strong without having to

exceed the natural contour of the incisal edge .

Occlusal rest

This rests are placed on the occlusal surface of the tooth should extend

more than one –half the mesiodiatal width of the tooth should be a

proximately one – third the buccolingual width of the tooth and

should allow for .

A minimum of 1 mm thickness of the metal . this type used in

Kennedy class II, modification I , and Kennedy III situation in which

the most posterior abutment is mesially tipped molar Occlusal rest

should de designed and prepared to minimize further tipping of the

abutment and to ensure that the forces are directed down the long axis

of the abutment . occlusal rest preparation should be rounded with no

undercuts or sharp angles .

Inter proximal rests (embrasure test )

One or two occlusal rests on interproximal rests adjacent teeth every

seat must be prepared as individual occlusal rest with exception that

the preparation must be more lingually .

Lingual rests

In spite of the preferred site for an external rest is the occlusal surface

of a molar or premolar , Also an anterior teeth iccasionally must be

used to support an indirect retainer or an auxiliary rest . A canine is

much preferred over an incisor for this purpose because it is placed

closer to the horizontal axis of rotation ( tipping axis) of the abutment

and therefore will have less of a tendency to tip the tooth . In addition ,

lingual rest are more esthetically acceptable than are incisal rests .

When canine is not present , multiple rests that are spread over several

incisor teeth are preferable to the use of a single incisor . Root form ,

root length , inclination of the tooth , and ratio of the length of the

clinical crown to the alveolar support must be considered when the

site and from of rests placed on incisors are determind . Lingual test

sometimes may be placed in an enamel seat at the cingulum or just

incisally to the cingulum . This type of rest is usually confined to

maxillary canine that have a gradual lingual incline and a prominent

cingulum . In a few instances . such a rest may be placed on maxillary

central incisors . when the lingual slope of the mandibular canine is

usually too steep for an adequate lingual rest seat to be placed in the

enamel .

Rest seat preparation a slightly rounded V is prepared on the lingual

surface at the junction of the gingival and the middle one third of the

tooth . The apex of the V is directed incisally , the floor of the rest seat

should be to ward the cingulum rather than the axial wall . all line

angles must be eliminated and the rest seat must be prepared within

the enamel and must be highly polished . A predetermined path of

placement for the denture must be kept in mind when the resr seat in

prepared .

Lec :-5 Msc. Enas

Minor connector

Its components that serve as the connecting link between major connector

or base of a removable partial denture and other component of the

prosthesis such as the clasp ,indirect retainer ,occlusal rest or cingulum

rests .

Functions:-

1-primary function joining other units of the prosthesis and denture base

to the prostheses .

2-transfer functional stresses to the abutment teeth .

3-transfer the effect of retainer, rest ,stabilizing components throughout

the prostheses .

4-distributes the stresses that occur against certain components of partial

denture to other component .

5-distribution forces on the edentulous ridge and the remaining teeth .

Form and Location :-

1-sufficient bulk to be rigid .

2-minor connector contacting axial surface of abutment teeth should not

be located on convex surface ,instead should be located on the embrasure

3-should conform to the interdental embrasure .

4-should be thickest toward the lingual surface ,tapering towards the

contact area.

5-deepest part of interdental embrasure should have been blocked out to

avoid interference during placement and removal .

6-when a minor connector contacts tooth surface on either side of the

embrasure in which it lies ,it should be tapered to the teeth .

7-minor connector should be wide enough to use guiding plane to the

fullest advantage .

8-when it gives rise to clasp arm it should be tapered .

Types of minor connector :-

1-join the clasp assembly to the major connector .

2-join director retainers or auxiliary rest to the major connector .

3-join the denture base to the major connector .

4-serve as an approach arm for a vertical projection or bar type .

Finishing line :-

Its an undercut area at the junction of major and minor connector in the

ladder area that will from an angle not greater than 90 degree its done to

prevent chipping away of acrylic resin that supporting artificial teeth by

forming a step .

If the finishing line is located on the outer surface of major connector ,it

is called external finishing line ,if it is located on the inner surface , it

called internal finishing line .

Type of finishing line :-

1- Vertical finishing line :- it is the finishing line at the junction of

the ladder area and major connector in free end extension cases

(class I and class II) in mandibular arch , and class IV mandibular

arch with labial bar major connector .

2- Horizontal finishing line :- it is the junction of major connector and

ladder area and it extends horizontally forming an undercut area

that support acrylic resin that carrying artificial teeth , this type of

finishing line is detected in all maxillary partial denture cases and

in class III mandibular cases .

Surveying

Surveying:-an analysis and comparison of the prominence of intraoral

contours associated with the fabrication of the prostheses

Dental surveyor :-an instrument used in the construction of removable

partial denture to locate the contours and relative position of the abutment

Survey line :-a line drawn on a tooth or teeth of a cast by means of a

surveyor for the purpose of determining the position of the various parts

of a clasp

Objective of the surveying :-

1-to design a RPD such that it is rigid and flexible component are

appropriately positioned to obtain good retention .

2-to determine the path of a prosthesis such that there is no interference to

insertion along this path .

3-to make the height of contour of the area above the undercut

4-to make the survey lines (height of contour of a tooth )

5-to make the undesirable undercut into which the prosthesis should not

extend.

Parts of surveyor :-

1-surveyer platform :-it is a metal plate parallel to the floor where a cast

holder can be placed .it forms the base of the base of the surveyor on to

which all the other components are attached and supported .

2-cast holder ,surveying table :-it is a stand placed over the surveying

platform .this stand has a base and a table to a place a cast.

3-vertical arm :-it arises vertically from the surveyor platform .it

supported the superstructure (horizontal arm the surveying arm )

4- horizontal arm :-it extend horizontally from the top of the vertical arm

.it is designed to support the surveying are it is free end

5- surveying arm :- it extend vertically from the free end of the horizontal

arm . it is parallel to vertical ,it can be move upward and downward . the

lower end of this arm has a mandrel into which tools used for surveying

can be locked in .

6-surveying tools :-these are tools attached to the mandrel of the

surveying arm and are used for surveying .there are of different types e.g.

analyzing rod ,carbon marker ,wax trimmer and undercut gauge .

tools of the surveyor

1-analyzing rod :- it acts like atangent to the convex surface of the object

being surveyed tool ,it helps to analyze the location of the height of

contour .the presence and absence of favorable undercuts for a particular

path of insertion .

2-carbon marker :-it is used for marking the survey line on the cast . in

ney surveyor the carbon marker is circular in cross section but in jelenko

surveyor it is triangular .

3-wax trimmer :- they can be attached to the mandrel of the surveying

arm .they are used to directly trim the excess wax while surveying wax

patterns and also to eliminate and block out undesirable undercut parallel

to the path of insertion

4- undercut gauge :-a gauge is a high precision instrument used to

measure the liner dimension of any structure .undercut gauge are used to

measure the depth and location of the undercut gauge are used to measure

the depth and location of the undercut on the analyzed tooth in three

dimensions .

Types of surveyor :-

1-ney surveyor (widely used )

2- jelenko surveyor

3- willams surveyor structure of these surveyors is basically similar with

mild difference from one another ,generally the willams surveyor is more

flexible

Blocking out the master cast

After the master cast has been surveyed and establishment of the path of

placement and the location of undercut areas on the master cast, any

undercut areas that will be crossed by rigid parts of the denture (which is

every part of the denture framework except the retentive clasp terminals)

must be eliminated by blockout.

Blockout:- It is the elimination of the undercut areas that will be crossed

by rigid parts of the denture except the retentive clasp terminals; this step

was done on the master cast before duplication.

Deep areas in the palatal rugae and interdental spaces should also be

blocked out. This facilitates subsequent removal from the duplicate

mould. Blocked out areas are carefully reduced to a minimum using a

parallel carver (until the carver comes into contact with the tooth).

Types of blockout of master cast

1-Parallel blockout: - Parallel blockout is necessary for areas that are

cervical to guiding plane surfaces and over all undercut areas that will be

crossed by major or minor connectors. Hard inlay wax may be used

satisfactorily as a blockout material. It is easily applied and is easily

trimmed with the surveyor knife. All guiding plane areas must be parallel

to path of placement, and all other areas that will be contacted by rigid

parts of denture framework must be made free of undercut by parallel

blockout.

Sites of parallel blockout

.

.

.

.

d by minor connectors or

linguoplates.

.

2 - Shaped blockout (Ledges for clasp arms):- For locating clasp patterns

may or may not be used. However, this should not be confused with the

actual blocking out of undercut areas that would offer interference to the

placement of the denture framework.

Wax ledge for reciprocal clasp arm as cervical as possible also ledge for

location of retentive clasp arm, ledge is applied below the survey line

around the abutment teeth. Wax ledges on buccal surfaces of premolar

and molar abutments have been duplicated in refractory the cast for exact

placement of clasp molar pattern and the premolar wrought wire clasp.

Sites of shaped blockout

to locate the wax patterns for clasp

arms.

3 .Arbitrary blockout:- Such areas are the labial surfaces and labial

undercuts not involved in the denture design and the sublingual and

distolingual areas beyond the limits of the denture design. These are

blocked out arbitrarily with hard baseplate wax, but because they have no

relation to the path of placement, they do not require the use of the

surveyor.

Arbitrary block out is done to:

duplication.

removed.

Sites of arbitrary blockout

.

denture

framework.

work.

design.

n the refractory cast.

Purpose of relief

t tissue impingement resulting from rotation of the denture

framework.

.

.)

Tissue stops:- Tissue stops are represented as (2 mm x 2 mm) square cut

in the relief wax over the ridge in distal extension areas. Tissue stops are

integral parts of minor connectors designed for retention of acrylic resin

bases. They provide stability to the framework during the stages of

transfer and processing.

Preparing the finishing margins (Beading):- The finishing

margins of the transversal connector marked on the model are ground to a

maximum depth of 0.5 mm with a 1 mm round bur. This increases the

suction of the denture. The prepared finishing margins

Relieving the master cast

Relief:- It is the procedure of placing wax in certain areas on the master

cast before duplication, to create a raised area on the refractory cast.

Purpose of relief

framework.

.

.)

Tissue stops:- Tissue stops are represented as (2 mm x 2 mm) square cut

in the relief wax

over the ridge in distal extension areas. Tissue stops are integral parts of

minor connectors designed for retention of acrylic resin bases. They

provide stability to the framework during the stages of transfer and

processing

Preparing the finishing margins (Beading):- The finishing

margins of the transversal connector marked on the model are ground to a

maximum depth of 0.5 mm with a 1 mm round bur. This increases the

suction of the denture. The prepared finishing margins .

Duplication of master cast

Refractory cast: It is a cast made of material that will withstand high

temperature without disintegration when used in partial denture casting

procedure; it has an expansion to compensate for metal shrinkage. The

refractory cast has been made of investment material.

On the duplicated cast the metal framework may be fitted without danger

of fracture or abrading the surface of the original master cast. The

investment material is used for making the refractory cast; the type of

investment depends on the type of alloy used.

a- Gypsum bounded investment is used for low heat alloys as type IV

gold alloy.

b- Phosphate bounded investment is used for high heat alloys as

vitallium, palladium

and Co-Cr alloy.

Objectives of duplication

.

fracture or abrading

the original master cast.

Duplication procedure :-

1-Mount master cast to the middle of the flask base with sticky wax.

Ensure that there is a uniform gap (approx. 1 cm) between the model and

the edge of the sleeve so that the silicone mold has adequate stability.

Seat body of flask.

2 - Prepare silicone or agar we two types of duplication materials

a- For the duplicating silicone (irreversible material) is mixed bubble free

in a vacuum mixer according to the manufacturer‘s instructions for use.

b- or using agar ( reversible hydrocolloid that are capable of being reused

up to four times, they may be prepared and stored in an automatic

duplicating machine. The clean colloid can be used by cutting it into

small pieces, reheated in this double boiler to a fluid consistency, then

tempered to a working temperature, it will be cooled enough to flow

easily without melting the blocked out wax (63°C)

3 - Filling the flask with silicone or agar

4 - After hardening remove the master cast from the agar mold. Ensure

that no wax sections are left in the duplicate mold.

5 - Spray the duplicate mold with silicone wetting agent to avoid bubbles

forming in the investment model. The Cr-Co investment is mixed bubble

free in a vacuum mixer according to manufacturer‘s instructions.

6 - Poured the investment slowly into the duplicate mold with the aid of a

vibrator. It is important to use the correct oscillation mode for the

material at the optimum level of vibration to ensure that the model is

poured without bubbles. The model can be carefully removed after the

investment has set.

Wax pattern

Wax pattern: Its waxing the removable partial denture framework should

be accurately shaped and duplicate the anatomic landmark of the partial

denture .

The technique of casting into a mold created by making first A wax

pattern on the investment cast, then surrounding it by additional

refractory material, which is heated to eliminate the pattern metal, is then

cast´into the resulting mold to form the metal framework .

Requirements of wax pattern material:

1 .The wax pattern must be conform to the exact size, shape, and contour

of the appliance, which is be constructed.

2 .No dimensional changes should take place in the wax pattern .

• Materials used in making pattern (wax and plastic)

There are two methods of making a wax pattern

1 .Free hand waxing methods :

By flushing the wax on the cast, it is made by adding melting wax on the

cast with warm spatula until the desired thickness and shape are

established, free hand methods require much more skill in making the

wax pattern on the cast similar to the outline and any errors that may be

occurs will appear in the cast

2. Ready-made wax pattern:

Plastic forms applied to the cast and seal in place with adhesive liquid,

this method preferred because make fabrication more accurate faster and

make finishing much simple . Preformed clasp patterns assure that clasp

will have the proper taper and resiliency.

This method make the procedure more easily and more accurate but it

require:

1. correct selection of the pattern

2. Careful handling of the pattern( mo pattern magdstrated by Finger

pressure)

3. Cutting the pattern according to the size needed.

4. Should be firmly adapted to the refractory cast.

Procedure of making wax pattern:

1-Waxing the major connectors :-

Used either casting sheet wax or ready-made wax the wax should not

be stretched altering their thickness

May need adding wax according to the type of major connector to give

the correct form of the connector and to have adequate thickness for

finishing .the wax should be well adapted on the refractory cast & sealed

through its course because if not the pattern may be dislodge during

investing resulting investment material seeping under the pattern and

cause framework not adapted inside patient mouth .

2 - Waxing the minor connector :-

The minor connector should be made perpendicular to the major

connector crossing to the embrasure of the teeth and try to follow its

contour without excessive bulk that would cause interference with tongue

3 .Waxing The rest :-

The rest should be waxed-before the clasp arm. The occlusal restore

filled with inlay wax and carving with spoon shape of a macron

instrument .

Rest formed less bulky that will not interfere with occlusion of the

opposing teeth and the rest should be broad and strong to allow sufficient

support to the framework to resist chewing and biting forces

4 - Waxing of the clasp:

The waxing of the clasp is the most difficult step in the waxing

procedure and requires some of experience and skill .

Making ledge of the clasp on the master cast facilitate the clasp

waxing pattern procedure.

In the waxing of the clasp we should avoids any sharp comer in the wax

by adding a slight amount of wax to give it a rounded effect. The size of

the clasp depends on the contour and size of the tooth.

The approximate size of molar clasp at the junction of the truss arm is

(2mm) and( 2 mm) in width, tapering is (1mm)toward the free end for

flexibility and( 12 mm) length.

6- Waxing the finishing line:- (shoulder(

The finishing line made of one gage round wax wire and lay on the

lingual side of palate, then sealed to the saddle on both inner and outer

edges .

The inner edge is sealed with heated spatula without added wax, and

the outer side of the finishing line may be flamed but do not flame the

inner side because the finishing line can easily destroyed by the heat of

the flame.

After completed the wax pattern flamed it lightly to smooth the wax

,the flame should lightly because excessive flaming causes flow the wax

over the cast lead to melting the wax pattern.

When this occurs the excess must be removed without marring

(abrasion) the cast..

Partial dentures vary in design, a broad outline on the refractory cast

one of the essential point help to produce a good wax pattern

The first step is to outline the framework design on the investment cast

with a soft pencil to avoid marring (abrasion) of the cast. Used the master

cast as a guide.

The difference between mandibular and maxillary refractory cast is:

before duplicated the maxillary master cast that a bead line is placed in

the master cast around the edge of maxillary major connector this beads

line transfers and duplicated to the refractory cast, in the waxing around

wax is placed in the bead line, the wax extended above the surface cast is

removed .then the casting wax is adapted the same way in (No, 1(

In mandibular cast, the lingual bar pattern is placed using line drawn

on the cast as a guide .be sure that the lingual bar is a minimum of (3

mm) from the marginal gingiva of all the teeth including the abutment

teeth.

The plastic retention (or ladder) placed should always extend over the

crest oه

f the ridge to prevent midline fracture of the denture base .

The clasp pattern are next placed into position and adapted, the tip of

the clasp is always adapted first.

(Spruing) • Sprue: Channel or hole through which plastic or metal is poured or cast into reservoir and then into a mold. • Sprue channel: is the opening leading from the crucible to the cavity in which the frome work is to be cast. • The purpose of the spruing: 1. For leading the molten metal from the crucible to mold

cavity „so they should be large enough to accommodate the entering steam and for proper shape to locateitin to the mold cavity as quickly as possible.

2. Providing reservoir of molten metal from which the casting may draw during solidification thus avoid porosity due to shrinkage.

The three important rules for spruing of the cast: 1. The sprue should be large enough that the molten in them

will not Solidfy until after the metal in the casting proper has frozen (8-12) gauge round wax is usually used for multiplespruing or removable partial denture casting.

2. The sprues should be lead into the mold cavity as directly as possible and still permit a configuration that will induce a minimal amount of turbulence into stream of molten metal.

3. Sprues should leave the crucible from a commen point and be attached to the wax pattern at its bulkier section. That is, no thin section of casting should intervene between two bulky , un sprued portions .

Notes: One of the more important sources of difficulty in casting

is the entrapment of gases in the mold cavity before they have a chance to escape.

If the sprue channels contain sharp right- angle truns, great turbulence is induced, which is calculated to entrap such gases and solead to faulty castings.

The sprue channels should make long radii and easy truns, and also enter the mold cavity form a direction designed to prevent splashing at this point.

The sprues should be attached to the bulky points of the wax pattern.

There are two basic types of sprues: 1. Multiple. 2. Single. 1. Multiple sprue: the majority of the removable partial denture casting required multiple spruing using (8-12) gauge round max shapes for the main sprues. And (12-18) gauge round wax shaped for auxiliary sprue.

In mandibular sprued wax pattern. Three 8-gauge sprues attached to lingual bar and three 12-gauge sprues attached to denture base minor connector and direct retainer assemblies are joined at central sprue hole in investment cast.

2. Single sprue: a. Must be attached to the wax pattern so that the direction of flow of the molten metal will be parallel to the long axis of the single sprue.

b. In the removable partial denture the use of single sprue the use is limited to those maxillary frame work in which because of the presence of platal plate impossible to locate multiple sprues.

Figure For a maxillary 8gauge spnues or a single main sprue incated posteriorly can be used. When a single main sprue is used, additional

sprues can feed critical regions for casting completeness rk, either muleiple • Disadvantage of single sprue: Single sprue the use is limited to those maxillary frame work in which because of the presence of platal plate impossible to locate multiple sprues centrally. • The material used in procedure of spruing: 1. Major sprue. 2. Fannel or plastic sprue. 3. Vent wax use to escape thegases. • Some important points to remember in multiple spring are as follows:

1. Use a few sprues of large diameter rather than several smaller sprues.

2. Keep all sprues as short and direct as possible. 3. Avoid abrupt changes in direction. 4. Avoid T- Shaped junctions as much as possible. 5. Reinforce all junction with additional wax to prevent v-

shaped sections of investment that right break away and be carried into the casting.

* There are two method of spruing: 1. Direct method. 2. Indirect method. 1. Direct method: used in the upper and lower casts in which

we have a reservoir and sprue originate from it to the thickest portion of the patterns.

2. Indirect method: used in the lower cast commonly because we need to make a hole in the base of the cast. The reservoir will be below the cast. The main sprue enters through the hole and from it multiple spruing originated. It cannot be used in upper cast in case of palatal plate major connector.

Soldering and welding

Soldering : is the process of joining 2 pieces of metal by solder material,

the main material used for soldering are

A. Solder

B. Flux

This union is mechanical union not chemical union .

Solder : is that inter mediate material used to joint together individual

pieces like wire and clasp

Types of solder : we have two types

a) Hard solder : are those material having high melting point

b) Soft solder : are those material having low melting point

Properties of solder :

1- Should be flow easily and smooth

2- The melting point should be lower than that of metal to be soldered

3- Its color should be mach the color of metal to be soldered.

4- It must be resist oxidation and corrosion by oral fluids

5- The physical properties of the solder should be compatible with

metal to be jointed .

Flux : Is that material which is applied during soldering in order to

dissolve metallic oxide and protect the wire from further oxidation .

Properties of flux :

1- Its melting point should be lower than of solder

2- It must be able to dissolve metallic oxides

3- It should be easily removed after solering

Anti flux : Is that material used to control the solder, prevent its flowing

where it is not necessary like (grafet ) lead pencil may be used as anti flu

Rules of soldering ( process of soldering(:-

1- The pieces should be cleaned

2- The pieces should be closed to each other

3- The solder must be heated to its melting point

4- The temperature should be controlled to avoid overheating and

prevent annealing of wire .

5- Using flux to avoid oxidation

How we can control temperature during soldering :

1- Making a fine needle pointed flame this save the residual metal

from annealing and oxidation

2- Using a wet cotton role to cause the wire to prevent annealing

3- The wires are quinined in cold water immediately so that no times

is allowed for the heat to be travel along the wire

Welding : it is a process by which two pieces of stainless steel wire can

be joint together by passing highly electrical current under pressure and

low voltage .

The electrical current increase the heat between the two pieces which lead

to melting surface of two pieces which lead joined the end together if

pressure applied in orthodontic we used machine called ( spot welding

machine )

Investing

Means the process of covering , or enveloping the wax pattern with a

suitable investment material before casting .

Purposes of investing:

1 – provide the mold cavity for casting the metal and give the mold a

smooth surface .

2 – this investment material provide the strength to hold the force exerted

by entering stream of molten metal

3 – it provides an avenue of escape of gases entrapped in the mold cavity.

4 – compensate for the dimensional changes of metal alloy from the

molten to the solid cold state .

Procedure:

By using orofilm on the wax pattern to keep it smooth and reduce wax

tension so that the investment material can adhere , we put the refractory

cast in the casting ring that should be lined with Vaseline to help in

removing the investment the ring .

Then , we put the ring on a vibrator and we start pouring the investment

material after we would mix according to manufacturer instruction and

would continue pouring ,until the ring is filled but we shouldn’t close the

opening of the sprue with the investment material , then we leave it until

its set . in this case it is called the muffle .

That it is ready for burn out step .

Burn out :

Place the muffle in a cold furnace , the furnace used either electrical or

gas furnace and should have thermostatic regulator . the muffle should be

placed the furnace upside down ( inverted ) to get rid of any carbon

residue result from wax vaporization because if it remain it will effect the

cobalt –chromium alloy properties and make it hard and brittle , the

temperature then gradually raise from 0-900 to 110c for 1-2 hr , then

maintain at this temperature for about 30 minute to ensure uniform heat

penetration .

Procedures of burn out:

1 – it vaporize and eliminate the wax pattern leaving a cavity in the mold.

2 – drive off moisture in the mold .

3 – it expands the mold to compensate for contraction of the metal on

cooling .

Casting:

The method of casting will vary depending on the alloy and equipment

being used the machine types are different according to the type of force

used to inject the molten metal into the mold cavity and also they are

different according to the method of melting the metal .

According to the type of forces we have two types :

1 – center fugal force .

2 – gas pressure force either by air pressure or other gases as nitrogen gas

or organ gas .

According to the method of metal melting also we have two types :

1-by electrical induction .

2- by oxygen acetylene torch ( blow torch)

In this method the flame consist of three zone .

1 – mixture zone .

2 - reducing zone .

3 – pin point end .

For all method we put ingots of the metal into the crucible that is suitable

for the chromium cobalt and then start melting the metal that pass into

stages which are :

1 – sandy stage .

2 – ashy stage .

3- Shinny stage .

Which is the right time of shooting the metal from the crucible to the

mold then remove the muffle from the casting machine and leave it on the

bench side until it is cooled then we remove the frame work from the

investment by using wooden hummer .

Finishing:

After removal the frame work from the investment

1 – we should sand blast the frame work and sprues to free them from

investment residue and the oxide layer ( sulpher oxide ) which is grayish

brown layer .

2 – cutting the sprue by cutting dish .

3 – smoothing , peripheries by stone burs .

4 – remove excess of cobalt chromium frame work by acid ( ortho

phosphoric acid ) used in electro polishing machine then we should

wash the frame work in water .

5 – finally we polished the frame work by rubber point

After complete finishing and polishing , the frame work should be

checked on the master cast before we send to the dentist to be checked

inside the patient mouth .