SELF EVALUATION

• Name and define different types of undercuts.

• Name different types of clasps, relate them to a survey line and their approach.

• Define an occlusal rest and its function.

• What is tripoding and its purpose?

• Advantages of an RAPD compared to an Acrylic RPD.

• Components of a RAPD, list them.

• Define RPI and its advantages.

• Major connectors and their use.

• Minor connector and its purpose.

• Relief wax and its purpose.

• RAPD design.

• Purpose of analyzing, surveying and waxing or blocking out.

• Purpose of a refractory model.

• Purpose of a working model.

• Why construct a RAPD.

• Guiding planes and proximal plates.

• The difference between support and retention.

• Purpose of reciprocation.

• Once a refractory model has been poured and re-surveyed, what is the next step?
• Where should tripod marks not be placed? Why?

• Name two types of direct retainers.

• What must every retainer have opposing it?

• Read revision on spruing for prac. Exam.

• What is a fulcrum line?

• Indirect retention, define it and give an example (diagram)

Topics to be covered today:
• Identifying landmarks
• Principles of RAPD design in relation to RAPDs
• Advantages and disadvantages of a RAPD compared to a Fixed Partial Denture
• Advantages of a RPI design compared to a Lingual plate design
• Advantages of a RAPD compared to an Acrylic partial denture
• Relief wax



IDENTIFYING LANDMARKS ON DENTAL MODELS RELATING TO DESIGN OF RAPD

• Remaining natural dentition
• Incisive papilla
• Gingiva
• Frenum
• Sulcus
• Rugae
• Saddles
• Occlusal surfaces (natural teeth)
• Cingulum surfaces (natural teeth)
• Incisal edges (natural teeth)








Principles of RAPD design

All RAPD’s must be designed to "preserve & maintain what remains".

The following principles must be followed when designing partial dentures.


(1) The denture must be passive, i.e. exert no force when not in function. Otherwise it may act as an orthodontic appliance and cause unwanted tooth movements.

(2) The denture must be comfortable without comfort it will fail.

(3) The denture must be aesthetically pleasing to the patient. If not, it will fail.

(4) The design of free-end saddle dentures must compensate for the slight movement, which occurs during the function to minimise the trauma caused to the remaining oral structures.

(5) With the above principles in mind, the design should be as simple as
possible. A simple design aids in the maintenance of oral hygiene.



ADVANTAGES OF A RAPD COMPARED TO A FIXED PARTIAL DENTURE

1. Help maintain remaining natural teeth in their position (stabilize mobile teeth).
2. Easily cleaned-both denture and oral cavity.
3. Easily repaired or additions made.
4. Initial cost less expensive than a fixed partial prosthesis.
5. Enables free-end edentulous area to be restored to function.
6. Restores lost appearance (aesthetics) and speech (phonetics).
7. Natural teeth do not have to be prepared
8. Cost





DISADVANTAGES OF AN RAPD COMPARED TO A FIXED PARTIAL DENTURE



1. May cause damage to supporting tissue and teeth;
Trauma to the gingival margins.
• The denture base fitting too close into the gingival area.
• Food packing between the denture and the natural teeth.
• By the contour of the natural teeth being disturbed by clasps which stop the flow of food away from them.

2. Cause caries by harboring food. This will depend on the age of the patient, their oral hygiene and the denture design.

3. Loosen teeth by leverage. This can be caused by the clasps “gripping” teeth tightly or poor positioning of in direct retention.

4. Traumatised palate. Caused by the denture base movement over the palate.







ADVANTAGES OF RPI SYSTEM COMPARED TO A LINGUAL PLATE DESIGN

• Less mucosal coverage (comfort)
• Aesthetically pleasing (position of I bar)
• Less lateral forces on abutment teeth
• Self cleansing







Advantages of a RAPD compared to an Acrylic RPD.

• More rigid
• Stronger
• Thinner
• Choice of many designs
• Transfers temperature better
• Better fit




Relief wax.


The purpose of relief wax is to make a space between the metal casting and the mucosa, the reasons this is done is as follows:

• To relieve the bar of the bar clasp from continuously rubbing and irritating the mucosa.
• To provide retention for the denture acrylic by spacing the mesh of the casting from the mucosal saddle areas. The space will be filled with acrylic and therefore no space will be present once the denture is finished.





Outcomes:
You should now be to:
• Identify land marks on a dental model relating to RAPD design
• List the advantages of RPI compared to Lingual plate design
• List the advantages and disadvantages of s RAPD compared to FPD
• List the principles of RAPD design
• List the advantages of a RAPD compared to a Acrylic partial denture
• Explain the purpose of relief wax

 

Power point only

Topics to be covered today are:
• RPI design
• It s advantages compared to Lingual plate design

The RPI System.

RPI stands for:
– Rest.
– Plate (proximal).
– I bar clasp.

Mesial Distal

The RPI system of clasping is used to minimize the denture caused stresses on the abutment teeth, In particular with cases with free end saddle(s). The system aims to have as little an impact as possible on the remaining teeth. For that purpose, the RPI system is normally used with the “skeletal design” option for a particular partial denture. The skeletal design has very limited coverage on the lingual surfaces of the remaining natural teeth. Added to that, the RPI system places very little metal parts of the denture on the abutment teeth surfaces. That keeps the gingival margins of the natural teeth exposed to the self cleansing actions of the tongue and saliva.

The mechanics of the RPI also aim to exert minimal amount of torquing (tilting) forces on the abutment teeth. The placement of rests and their positioning makes a marked difference to the way a denture will behave under load. Normally, we would place the rest on the mesial side of the abutment in the case of a free end saddle denture. A rest placed on the distal side of the abutment leads to greater amount of rotation of the major connector. More importantly, it can cause the clasp to act as an extracting tool. Or even worse, the whole denture can slip off the tooth in a distal direction, causing great injury to the oral tissues.

The proximal plate is usually limited to the distal width of the tooth. It provides the mesio-distal stability to the denture; As well as the limit of the saddle where the acrylic and teeth are fixed. The proximal plate can also provide a certain degree of retention by mean of friction (without engaging an undercut). These plates are also a major component determining the path of insertion, and giving the clasps their effectiveness in the undercuts they engage.

The I bar clasp is utilized to provide direct retention and better aesthetics because of its minute surface area coverage. If the clasp crosses the gingival margin at a right angle (90°), then its interruption of that margin is confined to a very small distance (1-2mm). Its impact on the tooth itself is also very small, leaving almost negligible areas for food traps and germ harboring.

These three components of the RPI system when connected to a major connector rigidly will provide a very low impact, low maintenance mean of stability retention and support.

OUTCOMES:
• Define and explain RPI in relation to a RAPD.
• List the advantages of the RPI design compared to a Lingual plate design.

Topics to be covered today are:
• RAPD designing

Designing of RAPD.

Principles of design:

1- Mark all saddles.

2- Mark the closest possible rests to provide support to each saddle.

3- Determine all possible fulcrum lines for each saddle.

4- For each fulcrum line draw the load lines.

5- Find possible retention points on the opposing side of fulcrum line.

6- Consider the suitability of each of those spots (teeth) for direct retention.

7- Consider the type of direct retainer suitable for the given tooth.

8- Consider indirect retention.

9- Determine the type of major and minor connectors to link all the components. Keeping in mind rigidity, support, hygiene and patient comfort.

Outcomes
• You should now be able to design a RAPD using the above procedures.

 

3051 L Cast Metal Alloy Removable Partial Denture

Topics to be covered today are as follows:
• Proximal Plates, definition
• Purpose of a Proximal Plate

Proximal Plates

Proximal plates are metal extensions, on one or the two ends of a saddle, that will fit closely on the mesial and/or distal guiding surfaces of the abutment teeth.

The proximal plate should be flat and thin (0.5mm) unless they form part of a minor connector. They should extend bucco-lingualy to just short of the buccal aspect of the tooth. By keeping them short they should not show out of the acrylic after the finishing of the denture.

The proximal plates in conjunction with the major connector define the path of insertion of a denture. That is why it is essential at the survey and block out stage to have a complete block out of undesirable undercuts. That block out should be done with minimal amount of wax. Leaving the blocked out surfaces parallel, and all the areas of a tooth above the survey line should be cleaned from any remaining wax.

The proximal plates will:

1- Establish and maintain the path of insertion. By sliding against the guiding planes of the teeth
2- Define the proximal borders of a denture saddle.
3- Provide stability for the denture.
4- Can provide a certain degree of retention.
5- May provide rigidity to occulsal approaching clasps

Outcomes:
• You should now be able to define and explain proximal plates and their purpose in relation to a RAPD.

Topics to be covered today are:
• Fulcrum line
• Indirect Retention

The fulcrum line

Definition: The fulcrum line is a longitudinal axis of rotation around that a partial denture may turn when forces are applied to one of its various saddles.

A saddle may have one or more fulcrum lines affecting its movements. In the case of tooth born saddle the fulcrum line is formed by the two rests closest to it. In the case of free end saddles, a fulcrum line may be formed by the crest of the residual ridge, as well as surrounding rests.
The occlusal forces (mastication or dislodging) on one side of the arch cause lifting forces on the opposing side of the arch. This results in a tilting or twisting action around the given fulcrum line for that force. This rotation is counteracted by:

1- Rigid connectors.
2- Direct retainer design.
3- Denture base coverage (support and indirect retention).
4- Denture tooth placement.
5- Contour of the denture base.

INDIRECT RETAINERS.

If a removable partial denture is not supported by natural teeth at each end of the edentulous saddle area, some provision must be made for the prosthesis to resist rotational forces that are exerted. This may also apply to long span bounded saddles (anterior especially).
Rotational movement around the fulcrum line, either toward the tissue or away from the tissue, may occur as forces are applied to the denture base. Movement toward the supporting ridge will be limited by the amount of compressible mucosa, or the amount of bone resorbption since the prosthesis was made. This movement to the ridge can only be controlled by accurate denture base adaptation. An indirect retainer does not control this movement.
Movement also occurs away from the tissue. This movement may be caused by sticky foods or other matter lifting the denture base; the tongue or buccinator muscles when they are activated by speech, mastication or swallowing. Gravity may also exert dislodging forces on a maxillary prosthesis. The reason for the use of the indirect retainer is to counter the movement produced by these forces.
The indirect retainer in free-end prosthesis uses the mechanical advantage of leverage by moving the fulcrum line farther from the force. The indirect retainer may contribute to the support and stability of the prosthesis.

FACTORS INFLUENCING INDIRECT RETAINERS.

Several factors influence the effectiveness of the indirect retainer.
The greater the distance between the indirect retainer and the fulcrum line, the more effective will be the indirect retainer. A line projected at right angles from the fulcrum line and ending at a tooth that is capable of supporting a suitable rest will indicate the most effective location for the indirect retainer. The longer this line, the more favourable will be the result.
In order for the indirect retainer to provide any function, the direct retainer must prevent lifting of the denture base and the rests. This lifting is one of displacement and not of rotation. The indirect retainer does not resist displacement.
An indirect retainer must be rigid. A flexible indirect retainer will allow greater movement than a rigid one.
The indirect retainer is most often an auxiliary rest. If incisor teeth are to be used for an indirect retainer, it should be as a group and not individually as they are not capable of withstanding pushing forces individually.

Outcomes
You should now be able to define and explain a fulcrum line and indirect retention in relation to a RAPD.

 

Introduction
Topics to be covered today are as follows:
• Direct retainers (component of a RAPD)
• Components of a clasp unit
• Requirement of a clasp
• Spruing
DIRECT RETAINERS
A direct retainer is a unit of a removable partial denture that engages a standing tooth in such a manner as to resist displacement of the prosthesis. This may be achieved by frictional means or by engaging a tooth undercut lying cervically to the height of contour.
There are two types of direct retainers. They are; Intra coronal retainer. Extra coronal retainer.
INTRA CORONAL RETAINER
This consists of two units, male and female. One of which is built into the crown of an abutment tooth. The other unit is attached to the removable prosthesis. The male insert is machined to precisely fit into the female receptacle. When dislodging forces are applied, a binding or wedging action results and acts to retain the prosthesis.
EXTRA CORONAL RETAINER
An extra coronal retainer is a clasp, which operates on the principle of resistance of metal to deformation. For a clasp to be retentive, it must be placed in an undercut area of a tooth, where it is forced to deform when a vertical dislodging force is applied.
The amount of retention can be varied by the depth of clasp placement in the undercut. The flexibility and thickness of the clasp arm are also variables that may affect the amount of retention achieved. A clasp’s flexibility can also be increased or decreased by alteration of the length of the clasp arm.
The areas used for extra coronal retention must be an undercut in relation to the path of insertion or there will be no retention of the prosthesis. Dislodging forces tend to unseat the prosthesis at right angles to the occlusal plane.

There are two types of clasps;
(a) Circumferential (supra bulge)
(b) Bar Type or Vertical Projection. (infra bulge)
1. CIRCUMFERENTIAL
Circumferential clasps approach the undercut from the occlusal aspect of the height of contour. The retentive terminal third should be pointed toward the occlusal surface, never toward the gingiva. This helps produce a curved clasp and results in greater flexibility.
The retentive tip should terminate at the mesial or distal line angle of the tooth, never in the centre of the buccal or lingual surface.
The clasp arm should be kept as low on the tooth as possible. (depth of the undercut)
This will give greater mechanical advantage against a lever action on the tooth than if it were positioned near the occlusal surface. Also the lower the clasp position, better aesthetics are possible.
This type of clasp may also be referred to as a suprabulge clasp.
2. BAR TYPE OR VERTICAL PROJECTION
These clasps approach the undercut from the cervical or gingival margin. The flexibility of the bar clasp may be controlled by the taper and length of the approach arm. The greater the length and the more the taper, the more flexible the clasp. The approach arm must be tapered uniformly along its length and diameter.
The approach arm of a bar clasp must not impinge on the soft tissue it crosses. The approach arm should cross the gingival margin at a 90-degree angle.
COMPONENTS OF A CLASP UNIT
1. Rest.
The part of the unit that lies on the occlusal, lingual or incisal surface of a tooth and resists the movement of the clasp toward the mucosa. It is essential that this be rigid.
2. Body.
The part of the unit that connects the rest and the shoulders of the clasp to the minor connector. It must be rigid and lie occlusal to the height of contour (circumferential only).
3. Shoulder.
That part of the unit that connects the body to the clasp terminals. The shoulder must lie occlusal to the height of contour and provide some stabilization against horizontal forces (circumferential only).
4. Reciprocal Arm.
A rigid non retentive clasp arm placed occlusal to the height of contour on the opposing side of the tooth to the retentive arm. It should, where possible, resist the tipping force applied to the tooth by the retentive arm as it passes over the height of contour. The arm also helps stabilize the prosthesis against lateral movement. It can also contribute to vertical support as it is occlusal to the height of contour.
5. Retentive Clasp Arm.
The part of the unit comprising the-shoulder, which is not flexible, and is located occlusal to the height of contour and the retentive terminal (circumferential only).
6. Retentive Terminal.
The only component of the unit to lie cervical to the height of contour. This portion is flexible and provides the direct retention (approximately a third of the clasp arm) (circumferential only).
7. Minor Connector,
The part of the clasp that joins the body of the clasp to the remainder of the framework. It must be rigid.

8. Approach Arm.
The component of a bar or vertical projection clasp that runs across the mucosa connects the retentive terminal and the framework. It may be slightly flexible.
REQUIREMENTS OF A CLASP
All clasps must be designed so that they satisfy the following requirements:

(1) RETENTION.
The function of the retentive arm is to provide retention for the prosthesis against dislodging forces. The retentive arm is considered to have three functional requirements;

(i) The terminal third is flexible and engages the undercut (circumferential only).
(ii) The clasp arm has a limited degree of flexibility.
(iii) The proximal third, or shoulder, is rigid and must be positioned occlusal to the height of contour(circumferential only). The amount of retention that a clasp arm provides depends on the flexibility of the clasp arm, the depth that the retentive terminal extends into the undercut, and the amount of clasp arm that extends cervical to the height of contour.
The amount of retention used should always be the minimum necessary to resist reasonable dislodging forces. The retentive undercut has three dimensions;
• The buccolingual depth - measured by using an undercut gauge and is significant as it determines the amount of undercut available.
• The distance between the height of contour and the retentive tip. This affects the clasp arm length and flexibility.
• The mesio-distal length of the clasp arm cervical to the height of contour. The longer this distance the more flexible the clasp. This will place more importance on the bucco-lingual depth.

(2) SUPPORT.
The function to resist displacement of the clasp in a gingival direction. The prime support unit of a clasp is the rest. Other units positioned occlusal to the height of contour will provide some support, e.g. reciprocal arm.
(3) STABILITY.
Stability is resistance to horizontal displacement. All clasp components, except the retentive terminal, contribute to this function in varying degrees. The reciprocal and bracing sections of a clasp unit provide equal amounts of stability. A cast clasp offers more stability than a wrought clasp because of its perfect adaptation.
(4) RECIPROCATION.
The reciprocal arm opposes the retentive arm and resists horizontal forces exerted on the tooth by the retentive arm. In addition, it provides stabilization. The reciprocal arm must be rigid and the same diameter throughout. It is positioned occlusal to the height of contour. It must also be the same or greater in thickness than the retentive clasp it is opposing.
(5) ENCIRCLEMENT.
Each clasp unit should be designed to encircle more than 180 degrees of the tooth. This may be continuous as in a circumferential or broken as in a bar type clasp. This helps prevent tooth movement by the application of forces.
(6) PASSIVITY.
The retentive function should only be activated only when dislodging forces are applied. Continual force applied to the tooth by a clasp unit will create pain and discomfort for the patient.

Spruing of RAPDs

Introduction:
The sprue is an opening leading from the pattern to the crucible. The sprues serve the purpose of transporting the molten metal to the pattern cavity. They should be large enough to accommodate the molten metal and of a shape to prevent, or minimize turbulence. The sprues also provide a reservoir of molten metal from which the casting may draw during solidification.

There are three factors that will, have a profound effect. They are:

 The sprue size
 The sprue length.
 The sprue configuration

The following points should be observed when a pattern is to be sprued:

1. Sprues should be as short, and direct as possible to allow the metal immediate access to the pattern whilst molten.
2. The sprue should be positioned so as to allow the metal to flow into the body of the pattern and to minimize splashing effects.
3. Where possible, the sprues should be attached to the thickest portion of the pattern, to allow feeding of the metal to thinner areas. Care should be exercised to avoid finishing margins, clasps, rests etc.
4. The sprue should be smooth surfaced throughout its length to minimize turbulence. Any uneven surfaces should also be avoided at the junction to the pattern and crucible.
5. As few sprues as the pattern will allow should be used to avoid turbulence.
6. Sprues should lead from a single central crucible.
7. Abrupt changes in direction should be avoided.
8. Avoid thin diameter sprues - minimum of 3mm pattern sprues. Use wax or plastic
9. The base of the crucible former should be above the highest point of the cast. The sprue can have a deal of influence on the property of the cast metal.

Outcome
You should now be able to:
• Explain a direct retainer and its purpose in relation to a RAPD.
• Name two types of retentive clasps and their relation to a survey line.
• List and explain components of a clasp unit.
• List and explain the requirements of a clasp.
• Explain the purpose and requirements of spruing in relation to a RAPD

INTRODUCTION: The topics to be covered today are:

• Minor Connectors (types and their function as a component of a RAPD)
• Rests (types and their function as a component of a RAPD)

MINOR CONNECTORS.

The primary function of the minor connector is to join other units of the prosthesis to the major connector. It is also responsible for distributing the stresses that occur against certain components of the denture to other portions of the denture and the edentulous ridges. The minor connector should not be bulky but must be rigid, so that all forces may be distributed and to help stabilize the removable partial denture.

There are four types of minor connectors:

1. Those that join the clasp assembly to the major connector. These support the active component of a partial prosthesis - the retentive clasp. If the minor connector is located on a proximal surface of a tooth adjacent to edentulous areas, it should be broad buccolingually to provide strength but thin mesiodistally to minimize encroachment on the saddle area. This will enable the artificial teeth to be positioned closely to the abutment tooth to achieve satisfactory aesthetics. If the clasp assemblies to be placed on a non-abutment tooth, the minor connector must be positioned in the lingual embrasure between the two teeth. Using this triangular space for the metal results in sufficient, bulk without encroaching on tongue space.

2. Those that join indirect retainers or auxiliary rests to the major connector. These should be positioned at right angles to the major connector but gently curved at their junction to avoid sharp corners. It should be designed into the lingual embrasure between teeth to disguise bulk as much as possible.

3. Those that join the denture base to the major connector. This is the mesh or latticework over the edentulous saddle areas. They must be strong enough to anchor the denture base; interfere as little as possible with the arrangement of artificial teeth and be rigid enough to resist breakage or flexing. The edentulous saddle areas must be relieved to provide a space between the ridge and the mesh to enable the acrylic denture base to encase the mesh for anchorage. (mechanical retention)
4. Those that serve as an approach arm for a vertical projection or bar-type clasp. This is the only minor connector not required to be rigid. It supports a direct retainer that engages an undercut from the gingival margin and must be relieved from the tissue to avoid injury, to the patient.
RESTS.
Vertical support for a removable partial denture is provided by a unit of the prosthesis - the rest - being placed upon the occlusal surface of the teeth. Forces applied to the prosthesis should be directed as near as possible down the long axis of the natural tooth so that the stresses can be absorbed by the fibers of the periodontal ligament or supporting bone.
In an all-tooth supported removable partial denture, all the forces are transferred to the natural teeth whereas only a portion of the forces are transferred to the natural teeth on free-end saddle dentures
The rest that is a component part of a direct retainer unit is referred to as a primary rest. Additional rests that are incorporated into the prosthesis are referred to as secondary rests.
Apart from transferring the forces of occlusion from the denture base to the standing teeth, the rest acts as a vertical stop, preventing injury and over displacement of the soft tissue under the denture base.
The rests must maintain the clasps in their designed position on the surface of the teeth to prevent the loss of retention and to maintain occlusal relationship between the prosthesis and the opposing dentition.
Auxiliary, or secondary rests are placed anterior to the fulcrum line to prevent the unsupported free-end denture base from lifting away from the edentulous ridge. In this manner the rests are acting as indirect retainers.
The primary role of Primary rests is to prevent vertical movement of the prosthesis toward the tissue and maintain the denture in its correct position. Lateral forces are far more damaging in free-end saddle prosthesis. Supporting teeth are capable of withstanding vertical forces, but lateral forces of much less magnitude can be destructive. (tooth-tissue bourne)
Rests may be used to prevent the ingress of food between the denture base and the proximal surface of an abutment tooth.

In some situations, a rest may be used to help establish a more acceptable occlusal contact. In situations where inclined teeth produce a slight loss of occlusal contact the rest maybe built-up to re-establish the occlusal relationship.

Rests are designated by the surface of the tooth on which they are to be located. They are:

a. Occlusal rest.
b. Lingual, or Cingulum rest.
c. Incisal rest.

(a) Occlusal Rest.
Located on the occlusal surface of molars and premolars. The size should be (approx.) half the buccolingual width and a quarter the mesiodistal width of the tooth on which it is to be seated. Rest seats may be prepared by the Dentist, therefore they need to be filled to the dimensions of the preparation. The occlusal rest is used to provide vertical support of a removable prosthesis.

(b) Lingual or Cingulum Rest.
Primarily used on anterior teeth. They have the advantage over the incisal rest in that it is closer to the center of rotation of the tooth. This will result in less leverage being exerted. The lingual rest can be hidden from view and be less annoying to the tongue than incisal rests. Lingual rests are used when they are on abutment teeth or when a site for an auxiliary rest is required.

(c) Incisal rests.
These are placed at the incisal edges of anterior teeth. They are predominantly used as auxiliary rests or as indirect retainers on a mandibular or maxillary prosthesis.
At all times a rest must be rigid. Any movement or flexing of the rests will cause destructive forces to be transmitted to the supporting teeth and mucosa.

OUTCOME:

• You should now be able to list types, define and explain a Minor Connector in relation to a RAPD.

• You should also be able to list types, define and explain a Rest in relation to a RAPD.

INTRODUCTION: The topics to be covered today are:
• Components of a RAPD
• Major Connectors:
• Types
• Function
• Indications for their use
COMPONENTS OF REMOVABLE PARTIAL DENTURES.
A removable alloy partial denture is made up of six structural elements, each of which plays a role in restoring function and preserving the remaining oral structures. The six structural units are:
1. Major connector.
2. Minor connector.
3. Rests.
4. Direct retainers.
5. Indirect retainers.
6. Denture base.

Each component parts name is descriptive of its function and they are the same for both the maxillary and the mandibular removable partial dentures.
MAJOR CONNECTOR.
The Major connectors primary function is to unite the various structural elements of prosthesis. All other parts of the partial denture are attached to it either directly or indirectly. The function of a maxillary major connector varies beyond this point to a mandibular major connector.
A mandibular major connector has a very limited capacity to provide support, but may contribute to indirect retention in comparison to a maxillary major connector.
Major connectors must posses the following five qualities:
1. Rigidity.
2. Provide vertical support and protection of the soft tissues.
3. Provides means of obtaining indirect retention where indicated.
4. Provide an opportunity of positioning the denture bases where needed.
5. Maintain patient comfort.
The first requirement of a major connector is rigidity. This allows stresses that are applied to the partial denture to be distributed effectively over the entire supporting area, including the teeth, underlying, bone and soft tissue. Other components of a partial prosthesis can only be effective if the major connector is rigid. Flexibility allows forces to be concentrated on individual teeth or edentulous ridges causing damage to those areas.

Major connectors must avoid impingement of the free gingival margin. The major connector must never terminate on gingival tissue because the marginal gingival is susceptible to injury from pressure.
The border of the major connector should run parallel to the gingival margin. If the gingival margin must be crossed, it should be at right angles to the margin to produce the least possible contact with soft tissue.
Patient comfort should be considered when designing the major connector and food traps must be avoided where possible.
The selection on a particular type of major connector will depend on the following:
(a) The need for support.
(b) The number and location of teeth to be replaced.
(c) The number of clasps.
(d)The need for indirect retention.
(e)The need for horizontal stabilization.
The selection of any particular connector will depend on the need for support, the number and location of teeth to be replaced and the number of clasps. Additional factors to be considered are:
• The presence of lingual tori.
• The need for indirect retention.
• The need for stabilization of infirm teeth.
• The mental attitude of the patient.

MANDIBULAR MAJOR CONNECTORS.
Because of space limitations caused by the height of the floor of the mouth, the position of the lingual frenum, or the presence of mandibular tori, mandibular major connectors are usually long and narrow.
In contrast to maxillary major connectors, mandibular major connectors are relieved from the soft tissue. For all tooth-supported removable partial dentures a minimum of relief is required because the prosthesis tends not to move. Free-end saddle prosthesis requires more relief because they tend to rotate during function.
TYPES OF MANDIBULAR MAJOR CONNECTORS.
The selection of a particular type of mandibular major connector will depend on the need for indirect retention and horizontal stabilization.
There are four types of mandibular major connectors:
1. Lingual Bar.
Half pear-shaped bar that follows closely the contour of the lingual surface of the alveolar ridge.
Indications for use: Used when there is no requirement for indirect retention or stabilization of weak teeth.

2. Lingual Plate.
Half pear-shaped bar with a thin solid area of metal extending upward onto the lingual surface of the teeth.
Indications for use: Used to aid in the stabilization of weakened anterior teeth. It may also be extended onto premolars for stabilization. May be used to increase indirect retention and to help prevent the deposits of calculus on the lingual surface of the teeth. When insufficient space is available for a lingual bar, lingual plating may be used.
3. Double Lingual Bar.
Half pear-shaped bar (lingual bar) with half oval bar on the lingual surface of the teeth. This bar on the lingual of the teeth is more commonly referred to as a continuous clasp.
Indications for use: Commonly referred to as a continuous clasp. Primarily used to provide or increase indirect retention. Also used instead of lingual plating when large interproximal embrasures occur.
4. Labial Bar.
Half pear-shaped bar that lies across the labial mucosa.
Indications for use: There is a very limited application for this type of connector. There are two circumstances when it maybe used to advantage.
1. When lingual tori are so large that an adequate lingual bar is not possible.
2. When mandibular anteriors and/or premolars are so severely inclined lingually that proper positioning of a conventional design is not possible.

OUTCOME
You should now be able to define and explain types, function and indications for use of a mandibular major connector. Also you should be able to list the components of a RAPD.

INTRODUCTION: The topics to be covered today are:
• Components of a RAPD
• Major Connectors:
• Types
• Function
• Indications for their use
COMPONENTS OF REMOVABLE PARTIAL DENTURES.
A removable alloy partial denture is made up of six structural elements, each of which plays a role in restoring function and preserving the remaining oral structures. The six structural units are:
1. Major connector.
2. Minor connector.
3. Rests.
4. Direct retainers.
5. Indirect retainers.
6. Denture base.

Each component parts name is descriptive of its function and they are the same for both the maxillary and the mandibular removable partial dentures.
MAJOR CONNECTOR.
Major connectors primary function is to unite the various structural elements of a prosthesis. All other parts of the partial denture are attached to it either directly or indirectly. The function of a maxillary major connector varies beyond this point to a mandibular major connector.
The maxillary connector, in addition to the primary function contributes substantially to the support of the prosthesis. The mandibular connector has a very limited capacity in support, but may contribute to indirect retention.
Major connectors must posses the following five qualities:
1. Rigidity.
2. Provide vertical support and protection of the soft tissues.
3. Provides means of obtaining indirect retention where indicated.
4. Provide an opportunity of positioning the denture bases where needed.
5. Maintain patient comfort.
The first requirement of a major connector is rigidity. This allows stresses that are applied to the partial denture to be distributed effectively over the entire supporting area, including the teeth, underlying, bone and soft tissue. Other components of a partial prosthesis can only be effective if the major connector is rigid. Flexibility allows forces to be concentrated on individual teeth or edentulous ridges causing damage to those areas.
Major connectors must avoid impingement of the free gingival margin. The major connector must never terminate on gingival tissue.
In maxillary castings the border of the major connector should be at least 6mm to 8mm from the gingival margin of the teeth and in the mandibular it should be at least 3mm from the gingival margin.
Patient comfort should be a consideration when designing the major connector and food traps must be avoided where possible.
The selection on a particular type of major connector will depend on the following:
Maxilla -
(a) The need for support.
(b) The number and location of teeth to be replaced.
(c) The number of clasps.

MAXILLARY MAJOR CONNECTORS.
A maxillary major connector should have a prepared seal along all borders that contacts soft tissue (food line). This seal forms a beading that will slightly depress the soft tissue. The food line (or seal) is scribed into the master cast to a depth of 1mm and width of approximately 1.5mm. The food line prevents food debris from collecting under the major connector. The extra thickness provided by the seal enables the metal to be tapered into the tissue surface without loss of strength. Usually, an intimate contact between the palatal soft tissue and the connector is required so there is no relieving of the tissue.
It also provides a point where the casting should be finished.

TYPES OF MAXILLARY MAJOR CONNECTORS.
The selection of any particular connector will depend on the need for support, the number and location of teeth to be replaced and the number of clasps. Additional factors to be considered are:
• The presence of palatal tori.
• The need for indirect retention.
• The need for stabilization of infirm teeth.
• Phonetic considerations.
• The mental attitude of the patient.

There are six types of maxillary major connectors.
1. Single Posterior Palatal Bar.
Narrow, half-oval in shape with its thickest point at the centre. The bar is gently curved and should not form a sharp angle at the junction with the denture base.
Indication for use.
Very limited use, usually when one or two teeth are missing on one side of the arch only. Where there is minimal need for palatal support and minimal interference with phonetics.
2. Palatal Strap.
Wide (minimum 8mm), thin band of metal that crosses the palate in an unobtrusive manner.
Indication for use
Suitable for use when only one or two teeth are being replaced on either or both sides of the arch, and the denture is to be tooth borne. There is minimal need for palatal support but more than a palatal bar. Also there is minimal interference with phonetics using this type of major connector.
3. Double Palatal Bar (A-P Bar).
Anterior portion is narrower than palatal strap. Posterior portion similar to single posterior palatal bar. This configuration gives the effect of a circle.
Indication for use.
Used when the anterior and posterior abutments are widely separated and full palatal coverage is not desirable e.g. tori palatinus. Offers very good rigidity.

4. Horseshoe.
A thin band of metal running along the palatal surfaces of teeth and extending onto palate.
Indication for use.
There are three principle applications. When several anterior teeth are being replaced. When a toris palatinus is present and does not allow for posterior coverage, or when mobile anterior teeth require stabilizing.
5. Closed Horseshoe (Anterioposterior Palatal Strap).
Similar to horseshoe with palatal strap connecting both sides of the arch posteriorly.
Indication for use
Generally indicated when numerous teeth are to be replaced and when a toris palatinus is present. When periodontaly weakened teeth require stabilizing. This is structurally strong and rigid.
6. Complete Palate.
The posterior border extends to the junction of the soft and hard palate. It is similar to a full denture, the difference being that it is made of an alloy instead of acrylic.
Indication for use
Indicated when all posterior teeth are to be replaced bilaterally. Also when anterior teeth require replacement along with bilateral free-end saddles. When flat or mobile ridges are present, the palate can offer stabilization for the prosthesis, if a patient has well developed muscles of mastication and complete mandibular natural teeth, heavy occlusal forces can be anticipated. A complete palate will offer support against vertical displacement.

OUTCOME
You should now be able to define and explain types, function and indications for use of a maxillary major connector. Also you should be able to list the components of a RAPD.

Topics to be covered today are as follows:
• Steps in waxing and constructing a RAPD (notes)
• Slideshow on waxing a RAPD
• Video on waxing a RAPD

Steps in the construction of R.A.P.D.

 Place master model on survey table
 Analyse master model (as per design on schedule H or Work Order)
 Tilt Survey table to reduce or eliminate undesirable undercuts, minimise and equalise desirable undercuts. And determine the path of insertion.
 Tripod master model.
 Survey. Use undercut gauges (0.25mm, 0.5mm, 0.75mm) to determine depth of undercuts.
 Draw design on master model.
 Block out undesirable U/Cs, gingival margins, bar clasp arms, saddle areas. Cut or scribe in food/ finish line on maxillary models.
 Place relief wax over saddle areas.
 Have the model checked
 Soak in tapped water for a minimum of 10 mins (upside down).
 Duplicate using a duplicating flask and hydrocolloid. Let the hydrocolloid set for 40 minutes to 1 hour.(bench cool only)
 Pour model with refractory material. Not stone.(be sure to use correct W/P ratios)
 Place plastic sprue former in the duplicate if needed
 Let the refractory material set for 30 mins.
 Remove refractory model from hydrocolloid, and place in the drying oven for 40 mins at 230°C.(don’t forget to wash the hydrocolloid and return it)
 While hot dip the refractory model in the hardening resin for 5 secs. Drain it and place back into the oven for 2 minutes.
 Remove from oven and leave to bench cool in the casting room
 Trim if necessary with the Dry Trimmer only
 Place refractory model back on the survey table, use tripod markings and re-establish the tilt.
 Re-survey and transfer (draw) design onto refractory model from master model.
 Proceed with the wax up of the metal partial denture.

Waxing up of RAPD

RAPD’s framework is waxed up on the refractory model.

1- Laying down of major connector:
- Start with the acrylic finish lines; fill them up to the level of the relief wax (at least).
- Flow wax in the narrower sections Thicken them up and give them more strength.
- Flow wax in the minor connector areas. Those are the ones leading to rests and clasps.
- Fill up the food/finish line with maxillary cases.
- Lay the stipple over the whole major connector area and cut it to the limit of the design. And seal it down.

2- Lay down the mesh for acrylic attachment.

3- Position and lay down all clasps correctly. (Direct retainers and reciprocators)

4- Join all the different components of the RAPD with hot wax (rests clasps saddles) and proximal plates. With the mandible wax up the tissue rests.

5- Position the profile wax around the saddle areas following the contour of the relief wax.(acrylic metal finish lines)

6- Shape and clean up all the waxed up sections of the RAPD. (Remember that it is much easier to cut and shape wax than it is to do metal)

7- Sprue the finished wax up.

Outcomes
You should now have the knowledge to:
• Produce a refractory model
• Wax up a RAPD

WELCOME BACK TO RANDWICK TAFE

MY NAME: PETER POULIKAKOS

EMAIL: peter.poulikakos@tafensw.edu.au

I AM AT RANDWICK TAFE ON MONDAYS ONLY .

THE UNIT OF COMPETENCY
THAT I WILL BE TEACHING YOU IS:

Construct cast metal alloy removable partial denture framework
HLTDT509B

1st PRACTICAL EXAM WILL BE HELD IN WEEK 16
THEORY EXAM AND 2ND PRACTICAL EXAM IF NEEDED WILL BE HELD IN WEEK 18

YOU MUST PASS BOTH THEORY AND PRACTICAL EXAMS EACH MODULE

WEEK 1

Topics to be covered today are:
• RAPD definition
• Objectives of a RAPD
• Terminology
• Slideshow overview of RAPD construction

Removable Alloy Partial Denture: Is a denture that replaces one or more but not all natural teeth. It is made of metal (gold, Titanium or Cobalt Chromium alloy) that is removable by the patient.

OBJECTIVES OF RAPD DENTURE CONSTRUCTION

When a person is edentulous or partial dentate, dentures are constructed to restore:

• FORM
• FUNCTION
• AESTHETICS

FORM – Restoring supporting tissues to their correct position
FUNCTION – Restoring the ability to masticate and /or talk.
AESTHETICS –Restoring ones appearance to a desirable standard

When a person is missing one or more of their natural teeth there may be one or more problems that occur –
1. Over eruption of teeth
2. Tooth drift
3. Facial muscle collapse
4. Reduction in face height (occlusal vertical dimension)
5. Loss of certain sounds during communication (phonetics)

1) Over eruption
When natural teeth are not in centric occlusion they may proceed in a vertical direction, therefore over erupting beyond the occlusal plane.

2) Tooth drift
When a tooth or teeth are extracted the remaining teeth on either side may begin to move horizontally, this movement of the natural teeth is termed TOOTH DRIFT.

3) Facial muscle collapse
When a person is missing a number of anterior teeth the lip loses its support from those teeth, therefore the labial contour has changed. The same may occur when a number of posterior teeth are missing. This gives the appearance that the face has collapsed.

4) Reduction in face height
When a person is missing many teeth and centric occlusion is absent, they tend to over close, therefore the OVD is not sufficient.

5) Phonetics
When anterior teeth are missing certain sounds are difficult to reproduce.
1. V sounds
2. TH sounds
3. F sounds
This is because certain sounds need the tongue to be in contact with the anterior teeth, and anterior teeth to contact the lip.

A RAPD should be constructed with the above objectives taken into consideration. Also a RAPD should not cause further damage to the remaining dentition and oral structures.

GLOSSARY OF TERMS

DENTAL SURVEYOR: A parallelometer used to analyse and survey a cast prior to designing a prosthesis.

SURVEY TABLE: An adjustable table that holds a model. The table has a tilt top so the cast can be tilted to various angles. Note: used with the DENTAL SURVEYOR

ZERO TILT: The occlusal plane as near to the horizontal as possible when positioned on the survey table.

TILT: The position of the cast on the survey table relative to the horizontal plane.

ANALYSING: The process of tilting the cast on the survey table to try and reduce or eliminate undesirable undercuts and maximise desirable undercuts. (using a non-marking analyzing rod)

PATH OF INSERTION: The plane or angle in which the prosthesis is inserted and withdrawn from the patient's mouth.

TRIPODING: Three widely spread separate marks, all on the same plane scribed into a cast to relocate the cast in that given plane.

SURVEYING: Is the procedure of locating and outlining the greatest circumference or contour of the teeth and associated structures in relation to the path of insertion of a removable partial prosthesis.

SURVEY LINE: A line on a tooth that identifies the maximum bulbusness (height of contour). A carbon rod is used in conjunction with the dental surveyor to mark the survey line.

HEIGHT OF CONTOUR: A line encircling a tooth to designate its greatest circumference; the line encircling a tooth at its greatest bulge or diameter with respect to a selected path of insertion.

GUIDING PLANES: The surfaces of the natural teeth that guide the prosthesis into position (path of insertion)

UNDERCUT GAUGE: An instrument used in conjunction with a dental surveyor to measure the depth of an undercut from the height of contour (survey line). It identifies the location for retentive clasp terminals.

UNDERCUT: The area on a tooth between the height of contour (survey line) and the gingiva.

DESIRABLE UNDERCUT: An area of tooth surface below the height of contour (survey line) suitable for the location of a direct retainer.

RETENTIVE UNDERCUT: Same as desirable undercut.

UNDESIRABLE UNDERCUT: An area of a tooth surface or tissue region below the height of contour (survey line) that would be detrimental to the insertion of the prosthesis.

RETENTION: Resistance to dislodgment.

CLASP: A component of a partial prosthesis that partly encircles abutment teeth and helps retain, support and stabilise the prosthesis in the mouth.

DIRECT RETAINER (CLASP): A unit of a removable partial prosthesis that engages a desirable undercut on a natural tooth in such a manner as to resist displacement of the prosthesis in a vertical direction.

CIRCUMFERENTIAL CLASP: Approaches the survey line on a tooth from the occlusal aspect of the height of contour.

BAR TYPE CLASP: Approaches the survey line on a tooth from the cervical or gingival margin aspect of the height of contour.

RECIPROCATION: That part of the denture that opposes the lateral forces on natural teeth created by direct retainers.

SUPPORT: Resistance to displacement in a vertical direction or in a direction parallel to the long axis of the natural teeth. (usually supplied by the rests or denture base).

RESTS: Are metallic lugs or projections in a removable partial prosthesis which lie on the occlusal or incisal surfaces of natural teeth. Their principal function is to resist vertical displacement of the prosthesis.

Outcomes
You should now be able to:

• List and explain the objectives of a RAPD
• Define terms relating to a RAPD (glossary of terms)