Physiology of Tooth Movement and Appliances Overview Flashcards
What are the two main categories of tooth movement and their definitions?
- Physiological:
Tooth Eruption
Mesial drift - Orthodontic:
Movement in response to an externally generated force
What is the fundamental physiological basis of orthodontics?
If an external force is applied to a tooth, the tooth will move as the bone around it remodels
- This bony remodelling is mediated by the periodontal ligament (PDL)
- A tooth without PDL or that is ankylosed will NOT move
- Cementum is more resistant to resorption than bone, though some root resorption after orthodontics should be expected
What are the three main theories for control of orthodontic tooth movement, and what is important to know about the bioelectric theory?
- Bioelectric/Piezo-electric theory
- Pressure-tension theory
- Chemical messenger theory/Mechano-chemical theory
Regarding the bioelectric theory:
Piezo-electric currents are generated when crystalline structures like bone are deformed
Once thought to be the primary mechanism for tooth movement
Now considered less significant as these currents are short-lived and very small
Explain the pressure-tension theory in detail.
The pressure-tension theory states that:
In areas of compression, bone is resorbed
In areas of tension, bone is deposited
This creates a pattern of bone remodeling that allows tooth movement
What are the key components of the mechano-chemical theory?
- Mechanical effects cause cell shape changes leading to:
Production and release of cytokines
Release of prostaglandins
Release of other chemical messengers - Blood flow changes:
Decreases in compression areas
Increases in tension areas - Changes in O2 and CO2 levels stimulate release of biologically active agents
- Cell-mediated interactions activate osteoblasts and osteoclasts
strain is sensed by the PDL cells via Integrins ( in their cell walls)
What is the role of the osteoblast in controlling orthodontic tooth movement?
Osteoblasts control movement in two ways:
In areas of tension:
- Flatten to cover the osteoid layer, preventing osteoclast access
- Secrete collagen and proteins forming organic matrix
- Secrete hydroxyapatite crystals to form new bone
In areas of compression:
- Bunch together and expose the osteoid layer
- Allow osteoclast access to resorb bone
- Send signals (e.g., RANKL) to recruit and activate osteoclasts
- Release Osteoprotegerin (OPG) to regulate osteoclastic activity
Describe the step-by-step cascade of cell interactions within the periodontal ligament during orthodontic tooth movement.
Initial step:
Cytokines activate osteoblasts to produce:
Prostaglandins (PGE-2)
Leukotrienes
Secondary messenger activation:
PGE-2 and leukotrienes cause osteoblasts to produce intracellular (secondary) messengers
Secondary messenger effects:
The intracellular secondary messengers trigger production of:
Receptor Activator of Nuclear factor Kappa-B-Ligand (RANKL)
Colony Stimulating Factor (CSF)
Interleukin-1 (IL-1)
Amplification loop:
IL-1 itself increases the production of more RANKL
Final effects:
RANKL and CSF cause blood monocytes to fuse and form multinucleated osteoclasts
RANKL stimulates these osteoclasts to become active and resorb bone
Key cellular players involved:
Fibroblasts
Macrophages
Osteoblasts
Osteoclasts
Osteocytes
Blood vessels
What are the three main types of orthodontic appliances?
- Removables (URA)
- Functionals
- Fixed
What are the six types of tooth movement possible with orthodontic treatment?
- Tipping
- Bodily movement
- Intrusion
- Extrusion
- Rotation
- Torque
What are the optimum force levels for different types of tooth movement?
Tipping: 35-60g
Bodily movement: 150-200g
Intrusion: 10-20g
Extrusion: 35-60g
Rotation: 35-60g
Torque: 50-100g
What are the key points about functional appliances and mandibular positioning?
effects on facial growth
The mandible is postured away from its normal rest position
Facial musculature is stretched, generating forces transmitted to:
Teeth
Alveolus
Effects on facial growth may include:
- Restriction of maxillary growth
- Promotion of mandibular growth
- Remodeling of the glenoid fossa
For Class II Division I cases, what are the clinical effects of Twin Block functional therapy?
skeletel, dental, additional
Skeletal change (30%):
Growth of mandible
Restraint of maxilla
Dentoalveolar change (70%):
Retroclination of upper teeth
Proclination of lower teeth
Additional effects:
Mesial migration of lower teeth
Distal migration of upper teeth
Combination achieves Class I
What specific type of tooth movement is tipping?
Movement characteristic: Tooth tips around its center of rotation
Creates areas of pressure and tension in PDL
Most basic form of tooth movement
What is bodily movement with fixed appliances and what force is needed?
Force required: 150-200 grams
Key characteristics:
- Allows tooth to retain normal periodontal ligament width
- Maintains stability
- Entire tooth moves in same direction without changing inclination
- Creates parallel movement of root and crown
- Results in even distribution of force along root surface
How does intrusion work with fixed appliances and what force is recommended?
Force required: 10-20 grams
Characteristics:
- Pressure on supporting structures is evenly distributed
Bone resorption occurs particularly at: - Apical area
- Alveolar crest
Requires very light forces to avoid root damage
Movement is in apical direction
What are the characteristics of extrusion with fixed appliances?
Tension is induced in the supporting structures
Bone deposition is necessary to maintain tooth support
Movement is in occlusal direction
Generally considered one of the more predictable movements
How is rotation achieved with fixed appliances?
Requires force couple (two forces)
Can be achieved using:
- Stretched elastic modules
- Stretched elastic chain
Movement occurs around the center of rotation
Often requires overcorrection
What is torque movement and how is it achieved with fixed appliances?
Torque (Root uprighting):
Force required: 50-100 grams
Characteristics:
Uses force couple to achieve root movement
Changes inclination of tooth
Center of rotation is near the crown
Most complex type of tooth movement
Requires precise bracket positioning and wire engagement
What are the five main factors affecting response to orthodontic force?
- Magnitude
- Duration
- Age
- Anatomy
- Drugs/medications
What are the histological changes that occur with light forces during orthodontic movement?
1.Hyperaemia within blood vessels (both pressure and tension sides)
2.Pressure side:
Increased osteoclastic activity
Resorption of lamina dura
3.Tension side:
Increased osteoblastic activity
Deposition of osteoid
4.PDL reorganizes
5.Results in slow tooth movement
What happens histologically with moderate to high forces?
1.Pressure side:
Cell-free areas (HYALINIZATION)
Occlusion of blood vessels
Increased osteoclastic activity
2.Tension side:
Increased endosteal vascularity
Hyperaemia of blood vessels
3.Period of STASIS followed by:
SUDDEN movement of tooth (“CLUNK”)
Healing of PDL
What is the threshold concept in relation to force duration?
- Force magnitude plotted against duration (hours/days)
- There is a threshold level around 50-100 units
- Duration affects the force required
- Relationship between force and duration follows a curved pattern
- Forces must be maintained for certain durations to achieve movement
What are the excessive force effects and their manifestations?
Unwanted side effects include:
- Pain
- Tissue changes:
Necrosis
Undermining resorption leading to permanent changes - Root resorption:
Significant if greater than 1/3 root length lost - Anchorage loss
- Possible loss of tooth vitality
- Histological effects:
Extensive lateral root resorption (RR)
Undermining resorption (UR)
PDL necrosis
What are the potential deleterious effects of orthodontic force?
- Pain and mobility
- Pulpal changes
- Root resorption
- Loss of alveolar bone support
- Relapse
What is the ideal rate of tooth movement and typical treatment duration?
Ideal movement: One mm of tooth movement per month
Typical treatment time: 24 months for fixed appliances
How do different medications affect orthodontic tooth movement?
- Prostaglandin Inhibitors:
Corticosteroids and NSAIDs (aspirin, ibuprofen, naproxen)
Low dose, short duration generally doesn’t significantly affect movement - Other prostaglandin inhibitors:
Tricyclic anti-despressants
Methylxanthines
Phenytoin
Some tetracyclines
Can theoretically decrease tooth movement - Bisphosphonates:
Used in osteoporosis treatment
Specifically inhibit osteoclast-mediated bone resorption
Which of the following cytokines does not promote osteoclastic resorption of bone?
a. Osteoprotegerin
b. Interleukin - 1
c. Prostaglandin E2
d. Colony Stimulating Factor
e. RANKL
a
Which of the following force ranges would be most appropriate to apply when trying to intrude teeth with a fixed appliance?
a.150-200g
b.10-20g
c.100-150g
d.50-100g
e.35g -60g
b
Which of the following is NOT a factor which can influence the rate of tooth movement?
a.Direction of force
b.Age of the patient
c.Duration of force
d.Anatomy of bone in the area
e.Magnitude of force
a
Which of the following tooth movements can be carried out using a removable appliance?
a.Tipping
b.Rotation
c.Extrusion
d.Intrusion
e.Root uprighting / torquing of teeth
a
With regards to the mechanism by which bodily orthodontic tooth movement takes place during fixed appliance treatment, which of the following statements is true:
a.Bone is laid down in response to compression of the periodontal ligament on the same side of the tooth as the direction of intended tooth movement
b.Bone is removed in response to tension of the periodontal ligament on the same side of the tooth as the direction of intended tooth movement
c.Bone is laid down in response to tension of the periodontal ligament on the opposite side of the tooth to the direction of intended tooth movement
d.Bone is laid down in response to compression of the periodontal ligament on the same side of the tooth as the direction of intended tooth movement
e.Bone is removed in response to compression of the periodontal ligament on the opposite side of the tooth to the direction of intended tooth movement
c