REMOVABLE PARTIAL DENTURE (RPD)

An RPD is an appliance which restores a partial loss of natural teeth and tissues, and which receives its retention and support from the natural teeth and/or from the mucosa

As the level of dental awareness in a community increases, there is likely to be a decrease of total edentulism and an increase in patients seeking treatment for partial edentulism. Reasons for seeking treatment any vary but the predominant one is to improve appearance.

If the total integrity of the arch of teeth is impaired by loss of one or more teeth, there may be a variety of sequelae. It is important to be aware not only of the possible consequences, but also their biological significance, for this will determine the necessity for tooth replacement. Some of the consequences are as follows

The most common reason why patients seek treatment. This depends on the value place on the appearance of missing teeth in any given community or society as well as the economic ability to provide a denture service.

The effect of the anterior tooth loss on a variety of speech sounds. Sibilants (s, sh sounds), and labio-dental sounds are the most obvious of these

Teeth are subjected to continuous forces of eruption, both in a vertical and mesial direction. The whole system is designed that way to provide compensating mechanisms for tooth wear, however this compensating mechanisms are only obvious when there’s tooth loss. Teeth may continue to erupt into a gap until they contact the ridge. Teeth on either side of a gap may tilt towards the gap .

4. Abnormal sites for food stagnation because of spaces between the teeth, this leads to increased plaque accumulation resulting in caries and periodontal disease.

5. Damage to remaining teeth due to increased tooth wear

6. Alveolar resorption

7. Loss of support for soft tissues

8. Psychological disturbance eg decreased smiling and a decreased sense of self worth

‘Our objective should be the perpetual preservation of what remains rather than the meticulous replacement of what is missing’ M.M.De Van

• Despite the litany of events outlined above they do not always occur, and not all of them at the same degree. For this reason, it is not always necessary to replace every missing tooth.

• In the absence of an opposing tooth, an opposing force will still be generated, usually by the tongue and during swallowing. This implies therefore that all gaps are not supposed to be filled except there’s is a sound biological and functional need.

One aspects to consider is just how many teeth or occluding units are needed for adequate function? It has been suggested that an arch extending to the second premolars (shortened dental arch) is more adequate for normal functional demands placed on dentition subjected to a modern diet.

• Apart from these biological considerations, there are other contraindications relating more to the patient as a whole. This would include;

1. The patient’s own attitude towards the type of treatment recommended by the dentist

2. Their ability to maintain their teeth and partial dentures in state that would not contribute to further deterioration

3. Their general medical condition, age and life expectancy.

4. financial implications

The most important of these is the ability of the patient to maintain a healthy mouth, where plaque is controlled, excessive and/or frequent sugars are not consumed, and the susceptibility to dental disease is therefore extremely low. Where this is not the case, the introduction of a foreign object “RPD” with many other surfaces for the accumulation of plaque, place the health of the teeth and periodontium at further risk.

Determinants of success• Case selection• Plaque control• How the denture is supported• Rigidity of the design• Avoidance of gingival coverage• Occlusal relations• Simplicity of design• Regular maintenance

As a direct result of examination and diagnosis the design of the removable partial denture must originate on the diagnostic cast so that all the mouth preparations may be planned and performed with a specific design in mind.

This may be influenced by many factors, such as;

1. Which arch is to be restored with the RPD and if both, a consideration of their relationship to one another, including the following:

a. Orientation of the occlusal plane

b. Space available for restoration of missing teeth

c. Occlusal relationship of the remaining teeth

d. Arch integrity e. Tooth morphology

2. Response of the oral structures to previous stress, periodontal condition of the remaining teeth, and the need for splinting, which may be accomplished either by means of fixed restoration or by the design of the denture framework.

3. Whether the denture will be entirely tooth supported. If one or more distal extension bases are involved, the following must be considered:

a. Clasps designs that will best minimize

the forces applied to the abutment teeth during function

b. Secondary impression method to be used

c. Need for indirect retentiond. Need for later rebasing, which may

influence the type of base material to be used

4. Need for abutment tooth modification or restorations, which may influence the type of clasps arms to be used and their specific designs.

5. The type of major connector indicated, based on existing and correctable situations.

6. Materials to be used, both for the framework and the bases.

7. The type of replacement teeth to be used, which may be influenced by the opposing dentition.

8. Patient’s past experience with a removable partial denture and the reasons for making a new denture. E.g. inability to tolerate denture

• It must spread the forces which will act on it evenly over the supporting tissues to a degree within their physiologic limit and be adequately retained in position in the mouth during all the normal functional movements.

• It must prevent the dental arch from collapsing by preventing the teeth from drifting and tilting into edentulous spaces. It must also cause the minimum amount of damage to soft and hard tissues.

It must maintain the health of previously unopposed teeth by restoring their function and preventing over eruption

It must restore masticatory efficiency and appearance and comfortable to wear.

Design of partial the denture framework should be systematically developed and outlined on an accurate diagnostic cast after surveying.

To develop the design the following are considered;

1. How the partial denture is to be supported i.e tooth/mucosa/both/implants.

• In an entirely tooth-supported partial denture the most ideal location for the support units (rests) is on prepared rest seats on the occlusal,cingulum or incisal surface of the abutment adjacent to each edentulous space.

• It is also important to evaluate the potential support that an abutment tooth can provide, consideration should be given to(a) periodontal health; (b)crown and root morphologies; (c)crown-to-root ratio; (d) bone index area (how tooth has responded to previous stress);(e) location of the tooth in the arch; (f) relationship of tooth to other support units (length of enedtulous span)(g) the opposing dentition.

Diagram showing ideal distribution of abutment teeth in the arch.

• In mucosa supported partial denture, support must come from the edentulous ridge areas. Consideration must be given to;

(1)the quality of the residual ridge, which include the contour and the quality of the supporting bone (how the bone has responded to previous stress) and quality of the supporting mucosa;

(2) the extent to which the residual ridge will be covered by the denture base;

(3) the type and the accuracy of the impression registration;

(4) the accuracy of the denture base;

(5) the design characteristics of the component parts of the partial denture framework;

(6) the anticipated occlusal load

• In tooth-and –mucosa supported partial denture, the above considerations for tooth and mucosa support must be given.

Denture base areas adjacent to the abutment teeth are primarily tooth supported. As you proceed away from the abutment teeth, they become more tissue supported. Therefore it is necessary to incorporate characteristics in the partial denture design that will distribute the functional load equitably between the abutment teeth and the supporting tissues of the edentulous ridge

Locating support units (rests) on the principal abutment teeth and designing the minor connectors that are adjacent to the edentulous areas to contact the guiding planes in such a manner that they disperse the functional load equitably between the available tooth and tissue supporting units will provide the design with controlled distribution of support.

•Where long bounded saddles are present in a maxillary denture, there are often better made mucosa supported to avoid the risk of overloading the abutment teeth.

•The presence of multiple bounded saddles in a maxillary denture often indicates the desire for mucosa support to avoid over complexity i n denture design.

•With bounded saddles in the mandible it is advisable to use tooth support to prevent trauma to the mucosa

•In a mandibular denture, it is desirable that the bounded saddles be made tooth supported; this is because of the limited area of mucosa which is available in the mandible to provide support

2. The second step is to connect the tooth and tissue support units.

The major connectors must be rigid so that the forces applied to any portion of the denture can be effectively be distributed to the supporting structures. Minor connectors arising from the major connectors make it possible to transfer functional stress to each abutment tooth through its connection to the corresponding rest and also to transfer the effect of the retainers, rests and stabilizing components to the remainder of the denture and throughout the dental arch.

3. The third step is to determine how the partial denture is to be retained.

Retention is defined as the quality inherent in a denture that resists the vertical forces of dislodgement (e.g. Gravity, adhesive food, forces associated with the opening of the jaws).

This is accomplished by mechanical retaining elements (clasps) being placed on the abutment teeth and major connectors (maxillary) with the underlying tissue

The key to selecting a successful clasp design for any given situation is to choose one that will;

(a) avoid direct transmission of tipping or torquing forces to the abutment (b) accommodate the basic principles of clasp design by definitve location of component parts correctly positioned on the abutment tooth surfaces(c) provide retention against reasonable dislodging forces

(d) be compartible with the undercut location, tissue contour, and esthetic desires of the patient. Location of the undercut is the most important single factor in selecting a clasp. Undercut location, however, can be modified by recontouring or reestoring the abutment tooth to accommodate a clasp design better suitated to satisfy the criteria far clasp selection.

4. The fourth step is to connect the retention units to the support units.

If direct and indirect retainers are to

function as designed, each must be rigidly attached to the major connector. The criteria for selection, location and design are the same as those indicated for connecting the tooth and tissue support units.

5. The fifth step in this systematic approach to design is to outline and join the edentulous area to the design components.

Components of RPDs

• Saddles• Rests• Clasps• Major connectors• Minor connectors

Kennedy Classification of Partially Edentulous Arches

Rests• Any unit of a partial denture that rests upon a tooth surface to provide vertical support for the denture

Functions of Rests• Transmit occlusal forces to teeth alongtheir longitudinal axes• Maintain correct occlusal relationship ofthe denture base to the abutment teeth• Prevent trauma to the gingiva• Provide some lateral stability• Prevent ingress of food between abutmentteeth and denture base

Occlusal rest seat

Cingulum restseats

Incisal rest seat

TYPES OF CLASPS•Occlusally approaching clasps.... Examples; circumferential clasp, ring clasp, back action clasp, embrassure clasp, reverse-action/hairpin clasp, multiple clasp

• Gingivally approaching clasp....Examples I- Bar, T- Bar, L-Bar

TYPES OF MAJOR CONNECTORS•MAXILLARY MAJOR CONNECTORS

1.Palatal bar2.Palatal strap3.U-Shaped palatal connector4.Anterior –posterior palatal bar5.Combination anterior and posterior palatal strap connector6.Palatal plate

• MANDIBULAR MAJOR CONNECTORS

1. Lingual bar2. Sublingual bar3. Lingual bar with sub lingual

bar (continuous bar)4. Lingual plate5. Labial bar

ADDITIONAL CONSIDERATIONS INFLUENCING DESIGN

1.USE OF SPLINT BAR FOR DENTURE SUPPORTwhen the edentulous span is too large to ensure adequate support from other teeth, other methods must be used.An anterior splint bar may be attached to the adjacent abutment teeth in such a manner that a fixed splint results, with a smooth, contoured bar resting lightly on the gingival tissues to support the RPD.

However in a distal extension situation, because of the vertical rotation of the denture, caution must be exercised to form the splint bar so that excessive torque will not accrue to its supporting abutments. The proximal contours of the abutments adjacent to the splint bars should be parallel to the path of placement. This serves three purposes:

•It permits a desirable arrangement of artificial teeth•It aids in resisting horizontal rotation of the restoration•They act as guiding planes to direct the partial dentures to and from its terminal position.The splint bar must be positioned antero-posteriorly just lingual to the residual ridge to allow an esthetic arrangement of artificial teeth. The resulting partial denture will have esthetic advantage of removable anterior replacements and stability from the underlying splint bar.

•INTERNAL CLIP ATTACHMENTInternal clip attachment differs from the splint bar in that the internal clip attachment provides both support and retention from the connecting bar. Internal clip attachments are also commercially available in various metal alloys and durable nylon.

Retention is provided by one of the commercial preformed metal or nylon clips, which is contoured to fit the bar and is retained in a preformed metal housing or partially embedded by means of retention spurs or loops into overlying resin denture base.

The internal clip attachment thus provides support, stability and retention for anterior modification areas and may serve to eliminate both occlusal rests and retentive clasps on the adjacent abutment teeth.

•OVERLAY ABUTMENT AS SUPPORT FOR A OVERLAY ABUTMENT AS SUPPORT FOR A DENTURE BASEDENTURE BASE

Every consideration should be directed to Every consideration should be directed to preventing the need for a distal extension preventing the need for a distal extension RPD. In many instances it is possible to RPD. In many instances it is possible to salvage the roots and portions of the crown salvage the roots and portions of the crown of a badly broken down molar thru of a badly broken down molar thru endodontic treatment. endodontic treatment. A periodontically involved molar, otherwise A periodontically involved molar, otherwise indicated for extraction, may sometimes be indicated for extraction, may sometimes be salvaged by periodontal and endodontic salvaged by periodontal and endodontic treatment accompanied by reduction of the treatment accompanied by reduction of the clinical crown almost level with gingival clinical crown almost level with gingival tissues.tissues.

In another situation, an unopposed molar In another situation, an unopposed molar may have overly erupted to such an extent may have overly erupted to such an extent that restoring the tooth with a crown is that restoring the tooth with a crown is inadequate to develop a harmonious inadequate to develop a harmonious occlusion. Also a molar that is grossly occlusion. Also a molar that is grossly tipped anterior such that it cannot serve as tipped anterior such that it cannot serve as an abutment unless the clinical crown is an abutment unless the clinical crown is reduced drastically. Such teeth should be reduced drastically. Such teeth should be considered for possible support for an considered for possible support for an otherwise distal extension base. otherwise distal extension base. Endodontic treatment and preparation of Endodontic treatment and preparation of the coronal aspect of the tooth as a slightly the coronal aspect of the tooth as a slightly elevated dome-shaped abutment often elevated dome-shaped abutment often offer an alternative to distal extension offer an alternative to distal extension base.base.

•USE OF A COMPONENT PARTIAL TO GAIN USE OF A COMPONENT PARTIAL TO GAIN SUPPORTSUPPORT

A component denture is a RPD in which the A component denture is a RPD in which the framework is designed and constructed in framework is designed and constructed in separate parts. The tooth support separate parts. The tooth support components is individually fabricated, and components is individually fabricated, and the 2 are joined with high impact acrylic the 2 are joined with high impact acrylic resin to become a single rigid functioning resin to become a single rigid functioning unit..unit..