Dalhousie RPD Manual

Question 1

What is the definition of a retainer?

Answer 1

Component of a rpd that provides both support and retention

Question 2

4 treatment objectives of an rpd?

Answer 2

1. Preserve remaining teeth and supporting structures
2. Restore esthetician and phonetics
3. Restore and or improve mastication
4. Restore health, comfort, and quality of life

Question 3

Guiding planes are most effective when? (5 points)

Answer 3

1. Are parallel
2. Include more than one common axial surface
3. Are directly opposed by another guiding plane
4. Are placed on several teeth
5. Cover large surface area (long and/or broad)

Question 4

How long should guiding planes be?

Answer 4

At least 1/2 to 1/3 of of the axial height (minimum 2mm in height)

Question 5

What are the 3 effects of guiding planes on retention and stability?

Answer 5

1. Guiding planes maintain retention
2. Guiding planes minimize the need for retention (frictional retention minimizes need for direct retainers)
3. Guiding planes stabilize teeth (most effective in class 3)

Question 6

In what cases would we want longer vs shorter guiding planes? Why?

Answer 6

Class 3 longer guiding planes

Class 1 and 2 shorter guiding planes (because loading of denture base causes rotation of rest seat. Shorter guiding planes allow rotation into the gingival relief area and prevent the immediate torquing of the tooth)

Question 7

2 ways of modifying height of contours and why ?

Answer 7

1. Lowering height of contour
   - eliminates tooth interferences where rigid elements are placed
   - improves esthetics (retentive arms are more gingival)
2. Raising height of contours
   - only time is when there is no retentive undercut present or when it is too close to fgm

Question 8

3 ways of raising height of contour?

Answer 8

1. Preparing retentive undercut (inferior border of prep at least 1mm from Gingiva)
2. Place composite resin
3. Combination of preparing undercut and placing composite resin

Question 9

6 functions of rests?

Answer 9

1. Direct forces along long axis of tooth
2. Prevent denture base from moving cervically and impinging gingival tissues
3. Maintain planned clasp-tooth relationship
4. Prevent extrusion of abutment teeth
5. Provide positive reference seats in rebasing and/or impression procedures
6. To serve as an indirect retainer by preventing rotation of partial denture (class 1 or 2 only)

Question 10

What is the shape of an occlusal rest seat?

Answer 10

Rounded triangular shape

Question 11

How wide should an occlusal rest seat be?

Answer 11

Approximately 1/3 buccal-lingual width

Question 12

How much bulk should be present for an occlusal rest?

Answer 12

1-1.5 mm minimum to prevent fracture

Question 13

What should the angle be between the rest and minor connector?

Answer 13

Less than 90 degrees which helps direct occlusal forces along long axis of tooth.

SHOULD BE A POSITIVE REST SEAT (less than 90mdegrees). Explorer won’t slide off top of rest seat

Question 14

What occurs if the rest seat is not positive?

Answer 14

Occlusal forces are not directed along long axis of tooth and permits movement of the clasp away from the tooth and orthodontic movement of the tooth

Question 15

What shape should the floor of the rest seat be? Why?

Answer 15

Concave or spoon shaped to prevent horizontal stresses and torque on the abutment tooth

Question 16

Why should a cingulum rest seat not be prepared too high or low?

Answer 16

Too high - much of lingual surface will need to be reduced to obtain sufficient width. May also interfere with occlusion

Too low - much of cingulum will need to be reduced to obtain sufficient width, enamel is also thinner in this area and could result in dentinal exposure

Question 17

Why is a lingual rest always preferred to an incisal rest?

Answer 17

Because a lingual rest is placed near the centre of the tooth and is less likely to tip the tooth

Question 18

What are 3 functions of a major connector?

Answer 18

1. Unification
2. Stress distribution
3. Cross-arch stabilization

Question 19

What is a more rigid alloy? (Chrome-cobalt vs. Gold; cast vs. Wrought metal)

Answer 19

Chrome-cobalt > gold

Cast>wrought metal

Question 20

4 requirements of a major connector?

Answer 20

1. Rigidity
2. Non-interfering with soft tissues
3. Food impaction
4. Unobtrusive

Question 21

What is the shape, size, and position of a lingual bar?

Answer 21

Shape
- flat on tissue side and convex on tongue side (like 1/2 a pair shape)
Size
- occlusal-gingival width (4-6mm)
- thickness (1.5-2mm)
Position
- inferior border should be as low as the lingual Frenum
- superior border should be 1.5-2mm or more below fgm
- in distal extension cases, when alveolar ridge bone loss occurs, lingual bar may impinge on soft tissues, to prevent this a wax spacer (1 thickness of 30 gauge wax) should be placed underneath when it is being waxed for casting

Question 22

What are 3 reasons why a lingual bar could not be used?

Answer 22

1. High floor of the mouth
2. Large lingual frenum
3. Lingual Tori

Question 23

In what case would we use a labial bar on the mandible?

Answer 23

When there is extreme lingual inclination of remaining teeth and there is no way to use a lingual bar without interfering with tongue movements.

Question 24

What maxillary major connector is best used with torus palatinus?

Answer 24

Anterior-posterior palatal strap

Question 25

Give 5 cases where a full palatal plate should be used?

Answer 25

Maximum tissue support is required 1. Long distal extensions 2. 6 or less anterior teeth remain 3. Abutments are periodontal involved 4. Edentulous areas covered with flabby tissue 5. Shallow palatal vault

Question 26

When would a palatal strap(or bar) not be used? Why?

Answer 26

Never be used in distal extensions or for replacement of anterior teeth because it needs to be made bulky for rigidity

Question 27

When should an anterior palatal plate (u shaped or horse shoe palatal connector) be used? What is its major downside?

Answer 27

Only used where the torus palatinus prevents use of other connectors. Huge downside is you must have bulk in the rugae area where the tongue requires freedom. Also in distal extension cases there is lots of movement and may cause irritation to residual ridges

Question 28

Compare and contrast the 2 types of grid work minor connectors that connect denture bases and teeth to the major connector?

Answer 28

Mesh grid work - flatter - more potential rigidity - less retention for acrylic if openings are too small Lattice gridwork - better retention - can interfere with setting of teeth (if struts are made too thick or poorly positioned)

Question 29

How much relief is required to allow acrylic resin to flow under gridwork minor connectors? When should relief be provided under gridwork next to the abutment tooth? Why?

Answer 29

Usually 1mm of relief 1.5-2mm from abutment. This allows a metal to tissue contact immediately beside the abutment tooth which is preferable over acrylic because it wears less, is less pours, thus allowing better hygiene.

Question 30

What type of junction should there be between gridwork and the major connector? Why?

Answer 30

Should be in the form of a butt joint with a slight undercut (angle formed must not be greater than 90mdegrees). This provides max bulk of resin at the junction and prevents creation of weak, thin feather edges which can easily fracture or distort

Question 31

What type of wax blockout would we use for the small space below a proximal plate and it’s respective guiding plane?

Answer 31

Zero degree block out with wax

Question 32

How far should gridwork extend dismally in the mandible?

Answer 32

2/3 of the way from the distal abutment to the retromolar pad (but not on the ascending portion of the ridge!)

Question 33

How far should the gridwork be extended distally in the maxilla? What about the major connector?

Answer 33

2/3 the length to the Hamular notch (but the major connector should extend all the way to the hamular notch to merge with acrylic

Question 34

How far should the junction of the maxillary major connector and gridwork be from the lingual surface of a tooth?

Answer 34

Approximately 2mm

Question 35

Why should mandibular distal extensions have a tissue stop at their posterior limit?

Answer 35

Without a tissue stop the framework can be bent or displaced during pressure packing of the acrylic. If this occurs, the framework could resume its shape after deflating and the denture would lift off the tissue. Rocking of the denture base and clasp apparatus would result and occlusion would be high.

Question 36

How much should a direct trainer encircle a tooth?

Answer 36

Greater than 180 degrees

Question 37

Do we need stress releasing clasps in class 3 and 4 pds?

Answer 37

No because there is no rotation as there would be in class 1 and 2

Question 38

Rank the 4 direct retainers for tooth borne rpds (class 3 and 4)

Answer 38

1. Circumferential clasp 2. Ring clasp 3. Embrasure clasp 4. C clasp (hair-pin clasp)

Question 39

Rank the 3 clasps used for class 1 and 2?

Answer 39

1. RPI (proximal plate, medial rest, I bar) 2. RPA (same thing as rpi but instead of I bar you use wrought wire clasp) 3. Combination clasp (same thing as a circumferential clasp but retentive arm is wrought wire instead of cast)

Question 40

How far should the approach arm of an I bar be from the fgm?

Answer 40

3-4 mm

Question 41

What are 3 forms of indirect retainers for class 1 and 2’s?

Answer 41

1. Auxiliary cingulum rest 2. Auxiliary occlusal rest 3. Continuous bar retainers or lingual plates

Question 42

How far should external finish lines be from lingual surface of denture teeth?

Answer 42

2mm