lecture 2 - biomechanics

Question 1

Application of mechanical principles on biological tissues while studying the biology from a functional viewpoint and then using these principles to design a stable prosthesis.

Answer 1

Biomechanics in Prosthodontics

Question 2

*The RPD and their associated structures are subjected to various forms of stress. Their ability to resist them depend on:

• __________________ and frequency of the Stress (Force) being applied onto the denture and denture bearing areas
• Capacity of these areas to resist these forces/stress
• Changes due to resistance over time
• The type of Resistance Generated:
  1. Tooth based
  2. Tooth and Tissue based

Answer 2

Direction, Duration, Magnitude

Question 3

Types of Stress (Force) acting on an RPD within the oral cavity:

Answer 3

1. Vertical -
   a) Displacing Force
   b) Dislodging Force
2. Horizontal
3. Torsion

Question 4

Resistance to stress can be divided into: (2)

Answer 4

1. Tooth based resistance contributes mainly to resisting Horizontal Stress (direct retainers)
2. Tooth-Tissue based resistance contributes to resisting Vertical Stress and Torsion (major connectors and indirect retainers)

Question 5

FACTORS CONTRIBUTING TO THE AMOUNT OF STRESS ON THE RPD: (5)

Answer 5

• The length of edentulous span (example: Kennedy Classification III usually exhibit no lever action)
• Quality of Ridge Support (example: Wider ridges disperse more stress due to the Snow Shoe Principle)
• Quality of Oral Mucosa (example: Healthy mucosa are able to withstand much greater force than weak flabby mucosa)
• Clasp Design (flexibility, length and material used)
• Occlusal Harmony

Question 6

PRINCIPLES OF MECHANICAL FORCES
(ACCORDING TO MCCRAKEN): (6)

Answer 6

• Lever
• Wedge
• Inclined plane
• Screw
• Pulley
• Wheel and axle

Question 7

MECHANICAL FORCE PRINCIPLES TO BE CONSIDERED WITHIN THE ORAL CAVITY: (3)

Answer 7

1. Lever Principle (Further divided into Orders I, II and III)
2. Inclined Plane Principle
3. Wheel and Axle (Rotation)

Question 8

There are 3 types of mechanical lever action based on:

Answer 8

1. The position of the fulcrum
2. The location of the load along the fulcrum line.
3. The area from which the effort to displace is exerted.

Question 9

• Example of 1st Order Lever Action

o In _____________________ where There is Distal Extension. If there is bone Resorption of the residual alveolar ridge under the distal extension, it will result in an effort leading to first order lever movement along the fulcrum line.

Answer 9

cantilever type of Removable Partial Denture

Question 10

Equation of First Order Lever Action (Class I):

Answer 10

Resistance - left and above
Fulcrum - middle and under
Effort - right and arrow down

Question 11

Equation of Second Order Lever Action (Class II)

Answer 11

fulcrum - left and below
resistance - middle and above
effort - right and arrow up

*nakaanggat yung distal extension ng denture

Question 12

• Example of third order Leveraction:

o Usually seen in the ___________________. Upon consuming sticky food, the food exerts pulling effort on the prosthetic teeth while the natural teeth and retainers exert counteracting forces from both sides.

Answer 12

tooth supported RPD

Question 13

third order Leveraction (class iii) equation

Answer 13

effort - left and arrow down
resistance - middle arrow up
fulcrum - right

Question 14

The rest will ‘slip off’ the inclined rest seat
However, _________ the rest seat will aid in the retention of the direct retainer on the tooth surface and resist horizontal forces

Answer 14

flattening
INCLINED PLANES

Question 15

WHEEL AND AXLE PRINCIPLE: (ROTATION)

The Partial denture can rotate along one of 3 planes: (A-C)

And along one of 3 axes: (1-3)

Answer 15

A. The Saggital plane
B. The Frontal plane
C. The Horizontal Plane

1. Saggital axis
2. Vertical axis
3. Horizontal axis

Question 16

The basis of the principle is to distribute stress/forces onto as large an area as possible in order to counteract the stresses applied to a partial denture.

In order to overcome the forces acting against the RPD, the prosthesis must take full advantage of all the primary and secondary stress bearing areas.

Answer 16

SNOW SHOE PRINCIPLE