The proponents of this concept believe in recording the edentulous
ridge in functional form either by using functional impression
technique or by functional reline method.
• During the functional impression, the mucosa covering the
edentulous ridge gets displaced to its functional form.
• Direct retainers and retentive clasp designed with minimum
retention and number of direct retainers is also minimum.
• Denture fabricated with functional impression compresses the soft
tissues even at rest. This can lead to excessive residual ridge
• When the partial dentures are at rest, the artificial teeth will be
positioned slightly above the plane of occlusion because of the
rebound of the compressed tissues.
FIGURE 17-5 Dentures made with functional impression
compress the soft tissues even in rest state.
• Functional loading has a physiological stimulating effect on the
• For proper vertical movement of the partial dentures from rest to
functional position, this direct retainer should be minimum in
• Simplicity of designing and fabrication results in lightweight
• Less forces are transmitted on the abutment tooth.
• There are greater chances of premature contacts.
• It is difficult to produce effective indirect retention.
• Greater forces are transmitted to the edentulous ridge.
• There are chances of premature contact, as the teeth will be
positioned slightly above the plane of occlusion.
This concept advocates wider distribution of stresses by the prosthesis
using additional rests, clasp assembly and broad denture base. The
partial dentures feature maximum coverage of the teeth and the soft
FIGURE 17-6 Removable partial denture made with broad
• Less concentration of stress
• Greater resistance to lateral stresses
• Less expensive in fabrication
• Increased horizontal stabilization
• Because of wider coverage, difficult to maintain oral hygiene
Factors which influence the amount of stresses on the abutment
Factors which influence the amount of stresses on the abutment tooth
Length of edentulous span: Greater the length of the edentulous span,
greater will be the length of the denture base and thus more forces
will be transmitted to the abutment tooth.
Form of residual ridge: Broad, well-formed ridges provide better
support and stability to the prosthesis than thin knife-edged ridges.
Also, firmly bound healthy keratinized mucosa is capable of
resisting the functional stresses better than the loose, atrophic and
Clasp quality: More flexible the clasp, greater lateral and vertical
forces will be transmitted to the residual ridge. More flexibility of
the clasp, lesser will be force transmitted to the abutment.
Length of the clasp: Flexibility of the curved clasp is better than the
straight one. Flexibility of the clasp is directly proportional to the
• Passively fitting clasp exerts less stress on the abutment tooth than
• The framework should be completely seated in order to ensure that
the retentive clasp will be passive.
• Disclosing wax can be used to seat the framework completely.
Clasp material: Greater the rigidity of the clasp material, greater will
be the stress transmitted to the abutment.
• Cast clasp will exert more stress on the abutment
• As the cast clasp has greater rigidity in comparison
to the gold clasp, it should be made of smaller
Tooth surface: Intact enamel offers less frictional movement to the
clasp arm than full veneer crown or restoration.
• Greater stress will be created on the tooth restored
with gold or cast metal rather than with tooth
Occlusion: Deflective or disharmonious occlusal contact and the type
of opposing occlusion influence the amount of force on the
• Type of the occlusion and the area of the denture
base determine the amount of stress transmitted
onto the abutment tooth and the residual ridge.
• Partial denture opposing complete denture will be
subjected to less occlusal stress than if opposed by
• The occlusal load should be applied in the centre on
the residual ridge, both anteroposteriorly and
buccolingually. Usually, the second premolar and
the first molar are the best areas to bear the
Design considerations in controlling stress in an RPD.
The following are the design considerations which are important in
controlling stresses in an RPD:
Direct retention: The retentive clasp arm transmits most of the
leverages forces to the abutment tooth. Clasp retention should be
kept to the minimum but without compromising on the retention of
• Retention is enhanced by accurately fitting and
maximal coverage denture base.
• Retention by frictional control is enhanced by
creating guiding planes on as many teeth as
• Properly extended partial denture can aid in better
neuromuscular control by the patient, therefore,
contributing in retention of the prosthesis.
Clasp position: The position of the clasp in relation to the height of
contour influences the amount of stress on the partial denture. The
number of clasps used is governed by the classification.
Quadrilateral configuration: It is indicated in Kennedy class III cases
with a modification space on the opposite side. A retentive clasp is
placed on all abutment teeth adjacent to the edentulous space (Fig.
Tripod configuration: It is indicated in Kennedy class II cases with a
modification space on the opposite side. All the abutment teeth on
both sides are clasped to result in tripod configuration (Fig. 17-8).
Bilateral configuration: It is indicated in Kennedy class I cases
without any modification space. The retentive clasp is located on
abutment on both sides adjacent to the edentulous space (Fig. 17-9).
Clasp design: Circumferential clasp originating from the distal
occlusal rest and engaging into the mesiobuccal undercut should be
avoided in distal extension cases, as it produces harmful leverage
forces on the abutment tooth. Reverse circlet clasp can be used.
• Bar clasp is indicated in distal extension cases when
distal undercut is located. It should never be used
when there is mesiobuccal undercut.
• It is advantageous to place the mesial rest more
anteriorly than the distal rest because of better
• T clasp with disto-occlusal rest and rigid
circumferential reciprocating clasp is thought to
produce least stress on the abutment tooth.
Splinting: Splinting of two or more teeth helps in distributing the
stress over a larger area of support, as it increases the periodontal
• For splint to stabilize teeth in the arch in the
buccolingual direction, it should extend across the
Indirect retention: It is essential in distal extension cases.
• It resists the rotation of the prosthesis.
• It is usually located anteriorly and perpendicular to
• It should be located as far anteriorly as possible to
provide long lever arm. Also, the indirect retainers
should be located in definite rest seat in order to
transmit the forces along its long axis.
• It also contributes to the stability and support of the
Occlusion: Harmonious occlusion minimizes the stress on the
abutment teeth and the residual ridges.
• The buccolingual width of the artificial teeth should
be reduced in order to minimize stress on the
abutment and edentulous ridge.
• Steep cuspal inclines should be avoided.
• Posterior teeth should have sharp cutting surfaces
Denture Bases: The denture base should be extended over wider ridge
area in order to distribute the stresses.
• Denture base flanges should be made as long as
possible in order to stabilize the denture against
• Denture base should be accurate and closely fitting,
as this will ultimately reduce the stresses
transmitted to the abutment teeth.
• Selective pressure impression technique is useful in
reducing stresses on the ridge and the abutment.
Major connector: It should be rigid.
• In mandibular arch, lingual plate design can
effectively support periodontally compromised
teeth and can distribute stresses to the remaining
teeth, if supported by the rests at the distal
• In maxillary arch, the complete palatal design
contributes to stability, support and retention of the
prosthesis. This helps in distributing the functional
forces over wide surface area, thereby reducing the
amount of forces on the abutment and the ridge.
Minor connector: It joins the clasp assembly to the major connector
and the guide planes on the abutment tooth.
• It provides horizontal stability to the partial denture
• Because of its contact with abutment tooth, it
stabilizes the tooth against lateral stresses.
• In order to minimize the stresses on the abutment
teeth, guide planes should be prepared on
Rests: It helps in directing the stresses along the long axis of the teeth.
• It provides support to the prosthesis.
• It should form an acute angle with the
perpendicular line passing through the long axis of
• In distal extension cases (class I and class II), rest
seat should be saucer-shaped to allow freedom of
movement of the rest within the rest seat. The
action is similar to the ball and socket joint.
• More the number of teeth with rest seat, lesser will
be the stress transmitted to each abutment tooth.
FIGURE 17-8 Tripodal configuration in Kennedy class II
FIGURE 17-9 Bilateral configuration in Kennedy class I
Design considerations in distal extension partial
Design consideration in a distal extension cases (Kennedy class I and
• Properly contoured and closely fitting denture base is important to
restore function and appearance.
• Accurate fitting of the framework against the guide planes.
• Simplest type of clasp design should be selected.
• Selected clasp should possess a good stabilizing quality and should
• These should be strategically positioned so that these can best
In Kennedy class I situation, two retentive clasp arms are required,
one each on the terminal abutment.
• In case retentive undercut is located in the distobuccal region, a bar
• If the retentive undercut is located in the mesiobuccal region,
wrought wire clasp should be used.
• The reciprocal or the bracing arm should always be rigid.
In Kennedy class II situation, the prosthesis should have three
• On distal extension side, the terminal abutment has one retentive
• On the tooth supported side, one clasp is placed as far anterior and
one clasp is placed as far posterior.
• If modification space is present, retentive clasp is placed on teeth,
both anterior and posterior to the edentulous space.
• Rests should be placed next to the edentulous space.
• Rest seat should be prepared so that the functional forces are
directed along the long axis of the tooth.
• Teeth which can provide maximum support should be selected.
• Rest seat should be saucer-shaped which should not have any sharp
• Rest should freely move in the rest seat in order to release the
stresses which otherwise would have been transferred to the
• It should be located as far anterior to the fulcrum line as possible.
• Two indirect retainers are indicated in class I situation and usually
one is indicated in class II situation.
• It should be prepared with positive rest seats which can direct the
forces along the long axis of the tooth.
• Lingual plate can act as an indirect retainer, if supported at both
• It should always be rigid and should not impinge on the gingival
• In maxillary major connector, support should be derived from the
• In mandibular major connector, extensions into the lingual surface
of the teeth should be used in order to increase rigidity and
distribute the lateral stresses.
These should be rigid and should be positioned such that they
increase the comfort and cleanliness.
• A harmonious occlusion is desired without any interfering contact.
• Artificial teeth should be arranged such that they minimize the
stresses produced by the prosthesis.
• To minimize the stress, fewer teeth with reduced buccolingual
• Teeth with sharp cutting edges and sluiceways are
• For better mechanical advantage, the teeth should
• The centric relation should be coincided with the
• Denture base should have broad coverage to distribute the stresses
• The tissues are recorded in functional form using a selective
• The form and contour of the denture should be highly polished.
Design consideration in tooth-supported partial
Tooth-supported partial denture is included in Kennedy class III
situation. The components of the partial denture should be designed
after surveying the master cast on the surveyor.
• The location of the retentive undercut is not critical as in distal
• The abutment teeth are not subjected to harmful stresses during
• Quadrilateral configuration of the clasps should be ideal.
• Simplest type of clasp design should be selected.
• The reciprocal arm should always be rigid.
• Rests are usually placed next to the edentulous ridge.
• The rests provide support to the prosthesis.
• These are usually not required.
• If posterior abutment is not clasped, the requirements are similar to
Major, minor connector and occlusion.
These should be rigid and design consideration similar to distal
• Functional impression is not needed here.
• Extension of the denture base depends on factors such as comfort
and aesthetics of the patient.
In class IV situation, the aesthetic need may necessitate the
placement of the teeth more anterior to the crest of the ridge. This may
result in transmission of harmful leverage forces on the abutment
teeth. In order to minimize the stresses on the abutment:
• As many teeth as possible should be retained.
• Labial alveolar process should be preserved.
• The edentulous span should be small.
Quadrilateral configuration of the clasp system is desirable. The
broad palatal type of major connector is preferred. In case of extensive
edentulous space, functional impression is indicated.
Biomechanical problems associated with
extension base RPDs and their remedies
Biomechanical problems in distal extension partial dentures
• The distal extension partial denture can be subjected to a number of
movements on functional or parafunctional loading.
• The movements are dependent on the quality of supporting
structures, accuracy and extent of the denture base and the
magnitude, direction, duration and frequency of the functional
• Possible movements of the partial dentures can occur:
• About an axis through the most posterior abutment
• Around the longitudinal axis formed by the crest of
• Around the vertical axis located near the centre of
Rotation about the axis through the most posterior abutments
• On the application of the functional load, the rotation of the distal
extension partial denture occurs around the line joining the occlusal
rests which is called the axis of rotation or the fulcrum line.
• The amount of rotation of the denture base depends on the
resiliency of the mucosa covering the residual alveolar ridge and the
accuracy of the adaptation of the denture base.
• Movement of the denture base in opposite direction is resisted by
the action of the retentive clasp arm of the terminal abutment and
• The indirect retainer should be placed as far as possible from the
distal extension base to afford the best possible mechanical
• The denture base should cover as large area as possible in order to
reduce the load per unit area.
• The occlusal rests should be placed mesially on the abutment tooth
in order to move the arc of movement of the saddle more
• Effect of clasping is that more the rigidity of the clasp, greater the
leverage on the tooth and less the load on the alveolar ridge;
whereas, more the flexibility of the clasp, less leverage on the tooth
Rotation around the longitudinal axis formed by the crest of the
• Fulcrum line extends posteriorly distal to the terminal abutment.
• It passes along the crest of the ridge to its posterior extent on the
• In class I situation, there are two fulcrum lines around which lateral
movement of the partial denture can occur.
• The lateral movement of the extension base can occur due to the
inclined plane of the cusp of the posterior teeth.
• The steeper the cusp, more will be the lateral load.
• The anatomy of the residual ridge will play a significant role in
resisting lateral movement of the denture base.
• Flat ridge with movable submucosa will offer less resistance to
lateral movement as compared to well-formed ridge with firmly
• Cast clasp transmits more rotational or lateral force on the abutment
tooth in comparison to the wrought clasp.
• However, the wrought clasp will convey more lateral stress on the
residual ridge in comparison to the cast clasp.
• Lateral loads are also exerted on the denture by the adjacent facial
and lingual musculature during swallowing.
Rotation around the vertical axis located near the centre of the
• The rotation of the prosthesis is along the vertical axis located near
• When vertical forces are acting on the denture base, most of the
periodontal ligament fibres are activated.
• If lateral forces are applied to the denture base, only part of the
periodontal fibres will be activated and this will result in harmful
• This rotation is resisted by the stabilizing component of the partial
denture such as the reciprocal clasp and the minor connectors.
• Stability component on one side of the arch acts to stabilize the
partial denture against the horizontal forces applied on the opposite
• To minimize the movement, the arms of the three-arm clasp should
brace the tooth completely on its buccal and lingual surfaces.
• The minor connector should be made rigid.
• The magnitude of the stress on the abutment will be greater, if the
clasp is made of cast alloy than with wrought alloy.
• The magnitude of stress will be less on the ridge posteriorly, if the
clasp is made of cast alloy than with wrought alloy.
Methods of stress control in RPD
Methods of controlling stress in RPD are:
(i) Reduce the load on the abutment and the ridge
(ii) Distribution of load between the teeth and the residual ridge
• By varying the connector between the clasp and
• Combination of rigid connection and bar clasp
• Combination of rigid connection and Akers’ clasp
• By anterior placement of the occlusal rest
(iii) Distributing the load widely
• Over more than one abutment tooth on each side
• Over the maximal area of the edentulous ridge
Reducing load on abutment and the ridge
• By reducing the buccolingual width of the teeth
• By reducing the number of teeth on the denture base particularly the
• Broad coverage of the denture base
• This ensures decreased load on the ridge and abutment teeth,
thereby increasing the chewing efficiency.
Distribution of load between the teeth and the
Distribution of load between the teeth and the ridge is done by
varying the connection between the clasp and the denture base.
Stress breaking: It provides a certain degree of movement between the
clasp unit and the denture base.
• Most of the load here is borne by the ridge rather
Combination of rigid connection and the bar clasp: The resiliency of
the portion of the bar clasp which contacts the abutment tooth
depends upon its length, cross-section and the type of alloy used.
• Greater the resiliency of the clasp, lesser will be the
horizontal and lateral stresses borne by the
Combination of rigid connection and the Akers’ clasp: Here there is
more load on the abutment tooth and less on the ridge.
• To reduce the stress, saucer-shaped rest seat should
be prepared in distal extension cases.
Disjunct denture: In patient with severe gingival recession and
periodontically weakened teeth, a two-part denture called disjunct
• The denture consists separately of tooth-borne and
mucosa-borne segments which act independently
of each other on the supporting tissues.
By anterior placement of the occlusal rest
• By doing so, the stresses on the saddle is changed from class I lever
system to the favourable class II lever system.
• This ensures even distribution of stresses on the ridge and less stress
• This principle is utilized in RPI system and the balance of force
• Wider load distribution over the teeth takes place by anterior
placement of the rest on the abutment.
• Broad coverage of the denture base reduces the load over the
Stress breaker is defined as ‘a device or system that relieves specific dental
structures of part or all of the occlusal forces and redirects those forces to
other bearing structures or regions’. (GPT 8th Ed)
Stress breaker is a device which allows movement between the
denture base and the clasp assembly.
• Role of stress breaker is to distribute the load between the ridge and
• Both the vertical and horizontal components of the forces are
• The vertical component of the force is to the greater extent
distributed to the edentulous ridge and to lesser extent to the
• The horizontal or lateral forces acting on the stress breaker sadly are
greatly distributed to the edentulous ridge and not to the abutment
• The magnitude of harmful lateral torquing forces on the abutment
• Since the edentulous ridge bears greater amount of horizontal and
lateral forces, it is more likely to show signs of greater resorption.
• Stress breakers are usually indicated for periodontally compromised
abutment teeth, where it is desirable to distribute the stresses over
the edentulous ridge rather than the teeth.
• Poorer the condition of the teeth, more flexible connection between
the ridge and tooth is desired and vice versa.
• Horizontal or lateral forces acting on the abutment teeth are
• It is possible to seek a balance of stress between the abutment and
the ridge by proper selection of the flexible connector.
• Intermittent pressure on the denture base massages the mucosa.
• Splinting of the weak teeth by the denture is possible despite the
movement of the distal extension base.
• Concentration of horizontal and vertical stresses leads to increased
• Effectiveness of the indirect retainer is reduced or eliminated.
• Repair and maintenance are difficult.
• There are chances of wear of the attachments.
• The spaces between the components can attract food lodgement.
Precision attachments are defined as ‘an interlocking device, one
component of which is fixed to an abutment or abutments, and the other is
integrated into a removable dental prosthesis in order to stabilize and/or
Classification of the precision attachments
According to Alan A. Grant and O.A. Wesley:
On the basis of site of attachment to the abutment tooth:
(i) Class 1: Coronal attachments – divided into extracoronal
attachments and intracoronal attachments
(ii) Class 2: Root-face attachments – divided into stud attachments and
According to H.W. Prieskel (1979)
On the basis of shape of attachments:
(i) Intracoronal attachments – frictional type
• Semiprecision attachment (custom-made)
(ii) Extracoronal attachments – projection units
(iv) Bar attachments – bar joints
(v) Auxiliary attachments – screw units
Function of precision attachments
• Labial or buccal clasp arm is eliminated.
• These are aesthetically superior.
• These direct the forces along long axis of the teeth.
• These can provide effective reciprocation.
• Tooth supported partial dentures
• To break stress in distal extension cases
• To stabilize unilateral saddles
• When few remaining teeth are present
• When splinting of teeth is indicated to aid in their stabilization
• For superior aesthetics, since there is elimination of the clasp.
• In case of teeth which are narrow buccolingually and have short
• In a patient with poor oral hygiene.
• In a patient with high caries index.
• In case of teeth with large pulp horns.
• In case of decreased patient dexterity.
• In case of inadequate space for the attachment.
• In case of compromised restorative and endodontic treatment.
• It has better mechanical advantage, as it directs the forces along the
• Force applications are closer to the fulcrum line.
• In distal extension cases, there is decreased stress to the abutment
• In comparison to the clasp, the attachments are less bulky and are
more aesthetic and lead to less food stagnation.
• It has complexities of design, procedures for fabrication and clinical
• Minimum 4–6 mm of occlusogingival abutment height is required to
incorporate attachment without overcontouring.
• Anatomy of the tooth – limited faciolingual tooth width.
• Wearing of attachment components is a disadvantage.
The primary aim of restorative dentistry is to preserve the complete
dental arch. It may not be possible or affordable for majority of the
elderly patients; therefore, the concept of shortened dental arch (SDA)
Definition: SDA is an arch with reduction of teeth starting posteriorly,
mostly in the permanent molars.
This concept was first developed by A.F. Kayser (1981). The concept
suggests that the minimum number of occluding pairs of teeth
(anterior and the premolars) are required to provide satisfactory oral
functional demands of the patient.
The number of occluding pairs can vary according to age and other
factors illustrated in Table 17-1.
FACTORS ON WHICH OCCLUDING PAIRS VARY
Age Functional Level Occluding Pairs
40–80 II – Suboptimal 10 (SDA)
70–100 III – Minimal 8 (ESDA) extreme
Note: ESDA, extreme shortened dental arch; SDA, shortened dental arch.
• Spatial relationship between the maxillary and mandibular arch
• Periodontal condition of the anterior teeth
• Adaptive capacity of the TMJ
• Progressive caries/periodontal disease confined mainly to the
• Periodontal condition of the anterior and premolars favourable
• Financial and other limitation to the restoration of dental arch
• Class III and severe class II skeletal relationship
• Alveolar support of remaining teeth is markedly reduced
• Excessive or abnormal wear of existing teeth
• It results in simplification of oral hygiene maintenance.
• It results in enhanced prognosis of the remaining teeth.
• No support from the edentulous ridge.
• Gillett Bridge consists of a partial denture which utilizes the Gillett
clasp system. It is composed of an occlusal rest which is notched
deep into the occlusal axial surface with a gingivally placed groove
and a circumferential clasp for retention. The occlusal rest is
custom-made with a cast restoration.
• Angle of gingival convergence is located apical to the height of
contour on the abutment tooth.
• Every denture is an all acrylic type of dentures which restores
multiple edentulous spaces in the maxillary arch. There is minimal
contact between the acrylic teeth and the abutment teeth to reduce
the lateral stresses. The posterior most teeth are bounded by the
wrought clasp which aids in retention and prevents distal tipping of
• Embrasure clasp is best used in Kennedy class II cases.
• Dr A.J. Fortunati was first to use dental surveyor.
• Surveyor is essentially a parallelometer which is used to determine
the relative parallelism of two or more surfaces of the teeth or other
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