Biomechanics II Flashcards
Define force (2)
- any interaction that, when unopposed, will change the motion of an object
- Push or pull
Force only exists as a result of …. (2)
- an interaction
- When the interaction ceases, the two objects no longer
experience the force
Define vector
When a physical property has both magnitude and direction its called a vector quantity
A force vector is characterized by…? (4)
- Magnitude
- Line of action
- Point of origin
- Sense
What is force component intensity?
- Force magnitude (amount of force applied)
- Length of segment
What is force component origin?
Where the vector of the force starts
What is force component direction?
Line of action of the force
What is force component sense?
Directions a vector may point
Units of force? (3)
- Newton
- Kilopond
- Dyne
Formula for force?
F= mass*acceleration
What is a newton?
- Is equal to 1 kilogram meter per second squared.
- Force required to accelerate an object with a mass of 1 kilogram 1 meter per second per second. 1 kg.m.s^-2
What is a kilopond?
Force exerted by a mass of 1 kilogram at the standardized
value of the acceleration due to Earth’s gravity, 9.80665 meters per second per second
What is a dyne?
The force required to accelerate a mass of one gram at a rate
of one centimetre per second squared. 1 g⋅cm/s2
1g = ____ oz
0.035 oz
1oz = _____ g
28.35 g
1N = ____ oz
3.596 oz
1oz = ____ N
0.278 N
What is a dinamometer?
slide 10
What are the forces (in a force system) with different characteristics acting together in the body? (5)
- Muscular contraction (cheeks, lips, tongue)
- Occlusion and mastication
- Forces of eruption
- Growth forces
- Orthodontic forces
What is a resultant?
A resultant is the only force that replaces them in a forcce system
What are the different types of resultants? (3)
- Same firection and sense
- Same direction and opposite sense
- Same origin and different direction
What are the resultants of the same direction and sense? (2)
- Intensity: addition of F
- Sense: sense of the F
What are the resultants of the same direction and opposite sense? (2)
- Intensity: subtract the smallest from the biggest
- Sense: sense of the bigger F
What are the resultants of the same origin and different direction?
Parallelogram method: resultant of 2 forces
What is the center of mass of a free body? (2)
- The point through which an applied force must pass to move it linearly without any rotation
- Center of mass is the free objects “balance point”
What is the center of resistance? (2)
- It is the equivalent balance point of a restrained body
- Point on the tooth when a single force is passed through it, would bring about its translation along the line of action of the force
Center of resistance depends on? (3)
- Root length & morphlogy
- Number of roots
- Level of alveolar bone support
What happens when there is a force through the centre of resistance? (2)
- Pure translation
- Gresion
What happens when there is a force to a distance of centre of resistance? (3)
- Translation + rotation
- Version
- Moment of force
Whats a version movement?
Slide 17
What is a gresion movement?
Slide 17
What is the centre of resistance related to the mouth?
Center of mass modified because the tooth is restrained by alveolar bone and periodontal ligament.
Localization of the centre of resistance in relation to the mouth? (3)
- Depends of root length and heigth of alveolar bone
- Single-rooted healthy teeth: coronal third with middle third (root)
- Multi-rooted: 1-2mm apical from bifurcation
Factors affecting centre of resistance? (3)
- Number of roots
- Degree of Alveolar Bone loss
- Degree of Root Resorption
What is the moment of force? (3)
- If the line of action of a force does not pass through the centre of resistance
- The force will produce traslation + rotation (inclination)
- Vector intensity depends on the distance from the centre of resistance
- M = F*D
What is couple? (5)
– Two forces equal in magnitude and opposite in direction
– Effect: pure rotation
– 2 parallel F (not in the same direction)
– Same intensity
– Opposite sense
Can we act through the centre of resistance of teeth to produce pure translation? why? (2)
- No
- Need to use a combination of forces so that the resultant passes through the centre of resistance
What’s newtons third law? (3)
– Action-reaction
– When one body exerts force on another, the latter exerts an equal (intensity) and opposite (sense) force on the first
- Forces may displace other teeth
What is intraoral anchorage (3)
• RESISTANCE TO UNWANTED TOOTH MOVEMENT
• Anchorage value of a tooth is proportional to the
surface area of the root
• The tooth with larger root surface area requires
greater force to move
Specific anchorage values of teeth
Slide 27
What is absolute anchorage? example? (2)
- Appliances gaining anchorage from extraoral structures - extraoral appliances
- (ex. head gear)
What does the dentoalveolar unit consist of? (5)
- Alveolar bone
- Cementum
- Periodontal ligament
- Gingiva
- Neurovascular plexus
Alveolar bone cell fraction? (2)
- Osteoblasts
* Osteocytes
Alveolar bone extracellular fraction? (4)
Organic matrix
» Collagen (70%)
» Other protreins(5%)
» Water
Inorganic matrix
» Hydroxyapatite crystals(70%)
Properties of alveolar bone? (7)
Subject to the action of forces Inmature bone Great cell number Plenty irregular collagen Low calcification More radiolucent Cancellous bone
Maintenance of thickness of alveolar bone? (2)
• In an ideal treatment, the attachment level is
maintained
• Resorption and deposition of bone maintains its
thickness in the facial and lingual side irrespective
of the type of movement the tooth has undergone
on the alveolar bone
What is radicular cement? (2)
• Mineralized connective tissue
• Same embryologic origin that alveolar bone and
periodontal ligament
How is radicular cement similar to bone tissue? (4)
– Grows by apposition
– Has Lamellae
– Cells in lacunae
– Less ability to remodel (resorption/apposition)
What is the cell fraction of radicular cement? (2)
- Cemento blasts
- Cementocytes
What is the extracellular fraction of radicular cement?(3)
- Organic 23%: collagen fibers
- inorganic 65% : HA crystals
- water 12%
Osteoclasts & cementoclasts? (3)
– Multinucleated cells (8-60) that resorpt bone or
cement (lysosomes)
– Stem from blood monocytes
– NOT local cells
What is teh periodontal ligament?
- network of parallel collagenous fibers
- Vascularized
- insterstitial fluid
What cells are in the periodontal ligament? (4)
Undifferentiated mesenchyme cells:
- fibroblasts
- osteoblasts
- cementoblasts
Describe the nerve endings in periodontal ligament? (3)
– Unmyelinated
– Pressorreceptors
– Proprioceptors
Thickness of normal PDL ?
0.5 mm
Collagenous fibres of PDL connects …? (2)
the cementum and lamina dura
the PDL fibers run at an angle attaching…
farther apically on the tooth than on the adjacent alveolar bone
PDL space is filled with…
fluid derived from vascular system
Cellular elements in the PDL? (6)
- Fibroblasts
- Osteoblasts
- Osteoclasts
- Cementoblasts
- Cementoclasts
- Nerve endings
What does a fibroblast do?
produce and destroys collagen fibers
What does a osteoblast do?
Produce new bone
What does a osteoclast do?
Aids in bone resorption
What does a cementoblast do?
Forms new cementum
What does a cementoclast do?
removes cementum
What do the nerve endings in the PDL help with?
is vascular and aids in proprioception
Characteristics of periodontal ligament? (5)
- Functional organized fibers
- Engaged in incompressible fluid
- Hydraulic behaviour
- Alveolar deformation: piezoelectricity
- Proprioceptors
Periodontal Ligament functions? (5)
• 1. Links tooth to bone
• 2. Receives and transmits forces of mastication
– Deforms or distorts alveolar bone
– Piezoelectric signals
• 3. Eruptive movements
• 4. Active stabilization of tooth position
• 5. Dynamic potential to modify tooth position
What is pascals law?
a pressure change occurring anywhere in a confined
incompressible fluid is transmitted throughout the fluid such
that the same change occurs everywhere
What is pascals law in relation to the PDL space?
Filled with fluid (derived from vascular system). A fluid-filled chamber with retentive but porous walls = shock absorber
Physiologic response to heavy pressure against a tooth: <1 sec ? (3)
- PDL fluid incompressible
- alveolar bone bends
- Piezoelectric signal generated
Physiologic response to heavy pressure against a tooth: 1-2 sec (2)
- PDL fluid expressed
- tooth moves within PDL space
Physiologic response to heavy pressure against a tooth: 3-5 sec (3)
- PDL fluid squeezed out
- tissues compressed
- immediate pain if pressure is heavy
What happens during the 2nd second of the physiologic response to heavy pressure?
Fluid exits through pores of the lamina dura
What happens during the 3rd second of the physiologic response to heavy pressure?
Tooth advances in the sense of force
What is piezo electricity?
Electric charge that accumulates in certain solid materials (such as crystals and biological matter such as bone, DNA and various proteins) in response to applied mechanical stress
Whats the piezoelectric effect? (3)
• When a force is applied to a crystalline structure (like bone or collagen), a flow of current is produced that quickly dies away • When the force is released, an opposite current flow is observed • The piezoelectric effect results from migration of electrons within the crystal lattice JM
What are the tooth movement theories? (2)
- Bioelectric theory
- Pressure - tension theory
What is the bioelectric theory?
Dental movement produces changes in bony metabolism controlled by electric signals generated when alveolar bone distorts
What are the electric signals associated with the bioelectric theory? (3)
1. Mechanical stress (piezoelectricity)
2. Flow of current (fluids)
3. Altered Cell resting potential
What is piezoelectricity in relation to the bioelectric theory?
- potential created by mechanical stress
- very fast decay
- equal signal in opposite direction once its stops acting
- HA crystals and collagen fibers (Bone & PDL)
What is positive piezoelectricity?
resorption
What is negative piezoelectricity?
apposition
What happens when the piezoelectricity is electronegative? (2)
- in concavity
- bone opposition/formation
What happens when the piezoelectricity is electropositive? (2)
- in convexity
- bone resorption
What is the flow of current in relation to the bioelectric theory? (3)
- Ionic potential generated by flow of fluids
- When PDL fluid exits through pores of lamina dura of alveolar bone
- Generated flow of fluid creates a flow of electric current
What is the alteration of cell resting potential in relation to the bioelectric theory? (4)
– Cell membrane patency (permeability) of calcium is
modified
– Altered membrane potential creates bioelectricity
– This is transducted into a biological response that
leads to bone remodeling
– Occurs in osteoblasts, fibroblasts and osteoclasts
What are the specific physiological changes that occur when there is alteration of cell resting potential? (6)
- mechanical stress
- protein activation
- closed calcium channel opens
- increase in intracellular cAMP & PGE2 & Ca2+
- activated cell secreted cytokines
- Cytokines cause bone formation/resorption & increase of collagen, collagenase & decrease of TIMP
What happens within the first hour of chemical regulation of OTM? (2)
Increase in:
- Prostaglandin E & IL1
- cytokines & NO
What happens after 4 hour of chemical regulation of OTM?
increase in cAMP
What is the chemical mediator for differentiation?
cAMP
What do prostaglandins stimulate in regards to bone?
Osteoblast & osteoclast
What does cAMP do? (3)
– Adenosine Monophosphate
– Second messengers
– Activates cell differentiation
What does prostaglandin E do? (2)
– After 4h of sustained pressure:
Increases concentration in PDL
– Stimulates osteoclast and osteoblast
activity
How long does it take to initiate orthodontic
tooth movement?
Minimum of 4 to 6
hours of continuous force
A removable appliance
worn for less than 4-6 hours is ….
of no use
Maximum efficiency of a removable appliance is ..?
if it is worn 24/7
What is the pressure tension theory?
Dental movement is caused by cellular changes done by chemical messengers created by altered blood flow through PDL
What are the steps for pressure-tension theory? (8)
- Force on tooth
- Change of position in the PDL socket
- Compression or stretching of PDL fibers
- Flow alteration in PDL vessels
- Modification of O2 content
- Biochemical changes
- Release of mediators and active substances
- Cellular activation
What happens when there is deformation with the pressure - tension theory? (2)
- PRESSURE AREA: reduced blood Flow:
resorption - TENSION AREA: increased blood Flow:
apposition
How does resorption activity occur with the pressure-tension theory? (3)
- pressure side
- compressed periodontum and blood vessels
- resorption activity
- tension side
- collagen fiber stretching
- osteoblast activation
- bone apposition
Look at slide 64
do it
