Week 6 - Surveying of models and design of partial dentures

Question 1

What are survey lines

Answer 1

markings or lines made on the denture model to find:
- widest part of the tooth
- hard and soft tissue undercuts - implication for denture base extension
- determine the path of insertion
- help determine placement and type of direct retainer (clasp)
- Aids contouring wax patterns for milled crown construction
- used to assist with blocking out undercuts

Question 2

Why is a path of insertion important

Answer 2

• creates a fixed pathway for seating and removing the denture
• allows the effective use of guide planes and contact with the guide planes
• ensures that components function as designed
• clasps do not exceed their design capability
• improves patient ease of use and comfort
• reduces tooth wear

Question 3

What is a lever

Answer 3

Simple machine consisting of a bar that pivots at a fixed point, called a fulcrum

Question 4

What is a first class lever

Answer 4

In the first class lever the fulcrum is located between the input force and the load.

Question 5

What is a second class lever

Answer 5

where the load is located between the fulcrum and the input force

Question 6

What is a third class lever

Answer 6

where the input force is between the fulcrum and the load

Question 7

the greatest movement occurs in what type of prosthesis

Answer 7

tooth tissue supported prosthesis

Question 8

the movement towards tissue depends on

Answer 8

1. quality of tissue
2. accuracy and extent of denture base
3. Applied functional load

Question 9

what type of rotation is this

Answer 9

rotation around fulcrum line passing through the most posterior abutment teeth

Axis: A horizontal line passing through the most posterior abutments.

Movement: The denture base moves toward or away from the tissue (tipping).

Question 10

what type of rotation is this

Answer 10

rotation about a longitudinal axis formed by rest of residual ridge

Axis: Runs front-to-back, usually along the residual ridge.

Movement: One side of the denture moves up while the other moves down.

Question 11

what type of rotation is this

Answer 11

Rotation around a vertical axis located in the center of the arch

Axis: A vertical line through the center of the denture.

Movement: The denture twists side to side.

Question 12

What are the 2 types of supported RPD

Answer 12

1. tooth-tissue supported RPD
2. tooth supported RPD

Question 13

Movement of the base towards tissue is resisted by what (for tooth tissue supported RPD)

Answer 13

residual ridge

Question 14

Movement away from the tissue (fulcrum rotation) (for tooth tissue supported RPD)

Answer 14

direct retainers
stabilizing components
indirect retainer

Question 15

Movement along the longitudinal axis is resisted by what (for tooth tissue supported RPD)

Answer 15

• major and minor connectors
• rigid part of the direct connector

Question 16

Rotation around the vertical axis and horizontal movment is resisted by what (for tooth tissue supported RPD)

Answer 16

• stabilizing elements on the axial surfaces of abutment teeth such as minor connectors and reciprocal clasps

Question 17

What are biomechanical considerations in tooth supported RPD

Answer 17

• movement towards tissue is prevented by rests and rigid parts
• movement away from tissue is prevented by direct retainers and stabilizing components
• movement along longitudinal axis is prevented by rigid part of direct retainer and major connector
• rotation around vertical axes, horizontal movement is the only existed movement, which should be resisted by employing stabilizing elements placed in axial surfaces of abutments such as minor connectors and intracoronalrests

Question 18

For tooth supported RPD what resists the movement towards tissue

Answer 18

• rests
• rigid parts

Question 19

For tooth supported RPD what resists movement away from tissue

Answer 19

• direct retainers
• stabilizing components

Question 20

For tooth supported RPD what resists movement along the longitudinal axis

Answer 20

• rigid part of the direct retainer and major connector

Question 21

For tooth supported RPD what resists rotation around vertical axis

Answer 21

horizontal movement is the only existed movement, which should be resisted by employing stabilizing elements placed in axial surfaces of abutments such as minor connectors and intra coronal rests

Question 22

What are biomechanical considerations for acrylic partial dentures

Answer 22

• Maximum coverage of basal support area to distribute masticatory/vertical forces
• lateral and rotational forces counteracted by base against alveolar ridge, palate, abutment teeth
• clasps provide retention against dislodgement forces
• base provides reciprocation

Question 23

What is a recommended RPD design order

Answer 23

1. Saddles
2. rests
3. clasps
4. indirect retention
5. bracing
6. reciprocation
7. connectors

Question 24

How are saddles used

Answer 24

• For class 1 or 2

Question 25

What are considerations for placement of rests

Answer 25

- main function = transmit load from the denture down long axis of supporting teeth - should be on each side of a saddle - prevent occlusal interference

Question 26

What are considerations for use of free end saddle rests

Answer 26

- class 1 or 2 - placed medial on abutment teeth - improves leverage - improves force distribution along long axis - reduced risk of distal tipping

Question 27

What are considerations for use of guide surfaces

Answer 27

- guide surfaces are parallel axial surfaces on abutment teeth - they limit the path of insertion of a denture benefits - increase stability - allow a reciprocating component to maintain continuous contact with a tooth as the denture is displaced occlusally

Question 28

What are considerations for use of clasps

Answer 28

- claps provide direct retention - they should not provide bracing, because it should be passive until the denture begins to lift/drop - only the last 1/3 should be under the undercut - clasps need reciprocation - clasps should always be supported with a rest

Question 29

What are the steps in designing a partial denture

Answer 29

1. identify saddle areas and teeth to be replaced. identify rest positions 2. the above information allows you to identify Kennedy classification 3. using survey information, identify the position of clasps and find best undercuts. Design clasps to fit these undercuts 4. bracing and reciprocation 5. add major and minor connectors

Question 30

How is RPD design applied to class 1

Answer 30

- requires only 2-4 clasps - rests should be placed to the adjacent endentulous space(s)

Question 31

How is RPD design applied to class 2

Answer 31

- 3 retentive clasps - the distal extensions ide should be designed with the same considerations as class 1 - the opposite side of the arch should have 2 retentive clasp arms (one as posteriorly as possible and one as anteriorly as possible but not on incisor - tripod configuration but if possible 4th clasp to get quadrilateral config) - the major connectors should be a palatal plate for upper for lower there is not much choice

Question 32

where should indirect retainers be located

Answer 32

opposite the distal extension base and as far from the fulcrum line as is practical

Question 33

how many indirect retainers for class 1

Answer 33

2

Question 34

how many indirect retainers for class 2

Answer 34

1

Question 35

what are direct retention considerations for class 3

Answer 35

because these prostheses are entirely tooth borne the transmission of harmful forces to the abutment teeth and residual ridges can be minimized

Question 36

what are the clasp considerations for class 3

Answer 36

trilateral/quadrilateral positioning of direct retainer is ideal

Question 37

what are the rest considerations for class 3

Answer 37

when possible they should be positioned adjacent to the edentulous space

Question 38

what are the indirect retention considerations for class 3

Answer 38

usually not required

Question 39

what are the denture bases considerations for class 3

Answer 39

coverage of the residual ridge areas should be determined by appearance comfort and avoidance of food impaction - probably horizontal strap

Question 40

what are the considerations for class 4

Answer 40

- quadrilateral configuration of direct retainers ideal - ideal quadrilateral configuration of clasping may preclude the need for additional indirect retainers - major connector should be rigid and broad palatal coverage should be used in the maxillary arch