Biomechanics

Question 1

_____ FPD:

• -1 or 2 missing teeth
• -2 abutments

Answer 1

Simple FPD

Question 2

\_\_\_\_\_\_ FPD:
--3 or more missing teeth
--Missing Canine
--1,3, or greater than three abutments
Splinted, pier, cantilever
--Non-parallel abutments
--Combined anterior and posterior FPD

Answer 2

Complex FPD

Question 3

Abnormal stress created by_____ and _______ create material

failure and tooth failure

Answer 3

torque and leverage

Question 4

What are the 4 Problems caused by bending and deflection?

Answer 4

• Fracture of Porcelain
• Connector breakage
• Retainer loosening and subsequent caries
• ”Unfavorable” tooth or tissue response

Question 5

The ______ is directly proportional to the cube of

the length of its span.

Answer 5

deflection

Question 6

The deflection is directly _______to the cube of

the length of its span.

Answer 6

proportional

Question 7

Greater span/ interabutment space = _____ deflection

Answer 7

Greater deflection

Question 8

_______ varies inversely by the cube of its

height (thickness).

Answer 8

Deflection

Question 9

Deflection varies inversely by the cube of its

________

Answer 9

height (thickness).

Question 10

The higher the occluso-cervical thickness of the connector, the _____ the FPD flexure

Answer 10

Less flexure

Question 11

–FPD flexure is ______ to connector width

Answer 11

proportional

Question 12

Is the width or height of connector more important to decreasing FPD flexure?

Answer 12

height

Question 13

For PFM, what is the minimum height for connector?

Answer 13

3-4 mm

Question 14

For ceramic FPDs, what is the minimum connector height needed?

Answer 14

4 mm

Question 15

Use a bridge material with _____ yield strength (Yield strength refers to an
indication of maximum stress that can be developed in a material without
causing plastic deformation.)

Answer 15

high

Question 16

_______ refers to an
indication of maximum stress that can be developed in a material without
causing plastic deformation.)

Answer 16

(Yield strength

Question 17

Abutments and retainers in FPD receive ____ dislodging forces
than a single crown

Answer 17

greater

Question 18

Occlusal force on
pontics can cause
______
torque.

Answer 18

Mesial-Distal

Question 19

Forces at an oblique
angle or outside the
center of the restoration
cause _______

Answer 19

F-L torque (around

M-D axis of rotation) .

Question 20

Grooves / boxes ______ to dislodgement.

Answer 20

increase resistance

Question 21

Is stress more favorable on the max or mand arch to stabilize and decrease likelihood of fracture?

Answer 21

Mand arch

Question 22

Canine replacing FPD is not a good idea in ____ arch?

Answer 22

Max arch

Question 23

\_\_\_\_\_\_\_ help stabilize the prosthesis by distributing forces over 
more teeth (do not necessarily increase retention).

Answer 23

Double abutments

Question 24

Double abutments help stabilize the prosthesis by distributing forces over 
more teeth (do not necessarily \_\_\_\_\_\_\_ )

Answer 24

increase retention).

Question 25

An edentulous space on both sides of a lone free-standing abutment

Answer 25

Pier Abutment:

Question 26

Cause of failure in Peir Abutments is most often a _______ -Prosthesis flexure creating movement of teeth -Tensile stresses between terminal retainers and abutments; intrusion of abutments under loading -Differences in retentive capacities between abutments (relative to size)

Answer 26

loosened retainer

Question 27

-Stresses can be concentrated around the abutment teeth and between retainers and abutment preps -Slight movement in non-rigid connectors can minimize the transfer of stress from the particularly loaded segment to the rest of the FPD

Answer 27

Non-rigid connectors

Question 28

``` If a non-rigid connector is placed on the _____ side of the retainer on a middle abutment, movement in a mesial direction will seat the key into the keyway. ```

Answer 28

distal

Question 29

If a non-rigid connector is placed on the _____ side of the middle abutment, mesially-directed movement will un-seat the key.

Answer 29

mesial

Question 30

- Indications: - Pier abutment FPD - Long span FPD with multiple abutments - Non-parallel abutments – Tipped molar - Planning for failure

Answer 30

Non-Rigid Connectors

Question 31

- Contraindications: - Long span FPD with two abutments - Excessively mobile teeth - Unopposed teeth

Answer 31

Non-Rigid Connectors

Question 32

-Long axes of abutment teeth should converge by no more than _____ (maximum angle of tilting) if FPD is made.

Answer 32

25o - 30o

Question 33

-Generally poor abutments -Mesial wall must be over-reduced / overtapered (↓ resistance) -Distal adjacent tooth may intrude on the path of insertion Mesial surface may need re-contouring or restoration or extraction Consider orthodontic uprighting (3rd molar extraction)

Answer 33

Tilted molars

Question 34

-Non-axial loading (horizontal) because of a tilted molar often leads to ________

Answer 34

proximal crestal bone loss

Question 35

-Places abutment in better position for preparation -Distributes forces under loading through long axis of tooth (helps prevent/eliminate mesial bony defects) -Enables replacement of optimum occlusion -Requires EXCELLENT communication and treatment planning skills to educate patient. Often extra 1-2 years of ortho prior to bridge placement. And then maybe an implant would be better?

Answer 35

Molar uprighting (orthodontic movement)

Question 36

If a molar is tilted, where would you have to reduce more occlusally for occlusion to be harmonious?

Answer 36

Distal

Question 37

``` -Allows slight movement - short span -Keyway in distal of premolar to avoid intrusion of molar (mesial seating action) -Must prepare box in distal of premolar preparation ```

Answer 37

Non rigid connector used to accommodate a tilted molar

Question 38

If a non rigid connector is used, where should grooves/boxes be placed for retention of the FPD?

Answer 38

Facial and lingual surfaces

Question 39

``` – does not involve distal wall -3/4 crown rotated 90o Used in case of tilted molars Requirements: -Caries-free distal surface -Low incidence of caries -Even marginal ridge height -Short span length ```

Answer 39

Proximal Half Crown

Question 40

``` Full crown preparation and coping with path of insertion in long axis of tooth. Full coverage crown compensates for discrepancy in paths of insertion. Must over-reduce molar to accommodate the thickness of coping and crown. WHY would you do this? Design for failure Protect tooth (reduced fracture of crown of tooth with bridge stresses ```

Answer 40

Copings

Question 41

``` Primarily only for patients contraindicated for implants. Why? -Removing tooth structure on two teeth. -Occlusal forces create guarded prognosis Criteria : -Replace only 1 tooth, and have at least 2 abutments Criteria for abutment teeth: -Long roots w/ good configuration -Long clinical crown -Resistance form for preparations O-C height for connectors w/o impinging on interdental papilla -Favorable crown:root ratio and healthy periodontium ```

Answer 41

Cantilever

Question 42

What are the 3 types of forces that can result from a cantilever placed in high occlusion?

Answer 42

Down, toward abutment or oblique twisting forces

Question 43

-Only the canine should be used as a solo abutment (Why?) Long Root, Esthetics easier, occlusal forces more lateral and therefore protective of pontic. -A Rest can be placed on mesial of pontic against a rest prep in a restoration in the distal of the central incisor or slight wrap-around of proximal contact. -Good clinical crown length / orthodontic position is necessary

Answer 43

Replacing lateral incisor

Question 44

Replacement of _______ using cantilever - Use full veneer retainers on the 2nd premolar and 1st molar. - Limit occlusion on the pontic.

Answer 44

First Premolar

Question 45

``` -For premolar cantilevers for premolars, ______ used to support premolar cantilever pontic -Either cemented or bonded. ```

Answer 45

Mesial rest

Question 46

What’s the 2 biggest problems with this type of restoration (mesial rest for PM cantilever?? -

Answer 46

OCCLUSION and Caries

Question 47

-Unfavorable prognosis!! -Extreme leverage forces generated by posterior position -Occlusal forces place tensile stress on 2o retainer

Answer 47

First molar cantilever

Question 48

``` If absolutely necessary: -Pontic size small (premolar) -Light occlusal contact; no excursive contact -Pontic and connector need maximum O-G height for rigidity -Good crown:root ratio of abutments -Clinical crowns - maximum preparation length and resistance form ```

Answer 48

Cantilever first molar indications

Question 49

-Lateral incisor abutment -Why is this negative? -Severe vertical overlap -Why is this negative? -Repeated de-cementation with this particular case. -Why would this keep happening? What other options could you have done here to replace #9? -Conventional bridge from #8-#10 -Single implant -What else??

Answer 49

Central incisor cantilever