Forces acting on RPD

Edentulous area 1)Quality of ridge support

2)Type of mucosa Healthy mucosa capable of bearing greater functional loads Soft, flabby, displaceable mucosa little vertical support of denture allows excessive movement of denture Accurate impression allow for better fit and less displacement

3) Length of edentulous span:

Longer edentulous span longer denture base greater force transmitted to abutment teeth Retain a Posterior abutment to serve as vertical support, even as an overdenture abutment Improved patient service

The Periodontal Support of the Abutment Teeth

Splinting two or more teeth increases the periodontal ligament area and distributes applied loads more effectively

The Periodontal Support of the Abutment Teeth

• Splinting : • removable prosthesis: consists of clasping more

than one tooth on each side of the arch and using additional rests for increased support

• fixed splinting is possible.

Fibers of periodontal ligament are

arranged such that their resistance to

vertical forces is much greater

than that to horizontal forces

Tissues are adapted to

receive and absorb forces

within their physiological

tolerance

The magnitude and intensity

The duration

The direction

The frequency

of these forces

The Ability Of living tissues

To Tolerate Forces Is Largely Dependent Upon

POSSIBLE MOVEMENTS OF THE PARTIAL DENTURE

Vertical forces acting in gingival direction tending to move the denture towards the tissues

I- Tissue-ward movements

Vertical forces acting in gingival direction tending to move the denture towards the tissues

Properly designed supporting rests Broad accurately fitting denture bases in distal extension partial

dentures.

Rigid major

connectors

II- Tissue-away movements

Vertical forces acting in an occlusal direction tending to displace and lift the denture from its position

Direct retention is obtained through:

• Mechanical means (the most important)

• Physiologic means (muscle action and neuromuscular control

• Physical means (play a

minor role in RPD

Mechanical retention is obtained through:

• Frictional fit • Engaging undercuts • teeth undercuts • tissue undercuts

From: • Direct Retainers

•Active I-Bars • Indirect Retainers

•Rests on the other side of the axis of rotation from the extension base

Indirect retainer (rest)

Extension Base

Horizontal movements A) Lateral movements

.

Horizontal forces developed when the mandible moves from side to side during

function while the teeth are in contact

Bracing Resistance to Lateral Movement of the Partial Denture This Function Is Mainly Provided By: Bracing clasp arms placed at or above the survey line of the tooth. Minor connectors in contact with axial (vertical) surfaces of abutment teeth Proximal plates Adequate extension of the Flanges

From:

• Guide planes

• Bracing clasp arms

• Lingual plates

• Rests

• Denture bases

Active I-bar

Reciprocation

I-bar

BRACING AND STABILIZATION

Reciprocation

• It is the resistance to the orthodontic-like force applied by the retentive tip of RPD during insertion and removal

Horizontal movements B) Antero-posterior movements

.

Horizontal movements B) Antero-posterior movements

Forward movement of the upper denture could be resisted by:

Anterior natural teeth bounding the edentulous space.

Palatal slope. Maxillary tuberosity. The backward movement of the

lower denture could be resisted by:

The slope of the retromolar pad. The natural teeth bounding the

saddle area. Proximal plates.

8.Case with missing mandibular 45678

unilateral classified as class:..........,and the type of major connector used in this case is..............

9.In the previous case the clasps used are

............in edentulous side ,while ...................on the other side.

IV- Rotational movements

Rotational movements are due to the variation in compressibility of supporting structures, absence of distal abutment at one end or more ends of denture bases, and

/or absence of occlusal rests or clasps at any end of the base

1-Rotation of all bases around a longitudinal axis parallel to the crest of the residual ridge(tipping)

2-Rotation about an imaginary perpendicular axis near the centre of dental arch (FISH-TAIL MOVEMENT)

3-Rotation of the extension denture base around transverse fulcrum axis:

(Torque)

A) Rotation of the denture base towards the ridge around the fulcrum axis joining the two

main occlusal rests

B) Rotation of the denture base away from the ridge around the fulcrum axis joining the retentive tips of the most

posterior clasps Retentive/Rotational line.

Stability:- Is the Resistance of Partial Denture to Tipping (Rocking torsional forces)

Stability is obtained through:

• Providing adequate bracing • Broad base coverage • Rigid major connector • Balanced contact between upper and lower

teeth

Prevent rotation of the free end saddle around the fulcrum line

INDIRECT RETAINERS

Class I Lever:

fulcrum: between E and R

E

R

Free end saddle partial denture