Anchorage Flashcards
Define anchorage
Source of resistance to the forces generated in reaction to the active components of an appliance
What is Newton’s third law of motion?
Equal and opposite reaction to the force(s) are generated (e.g. by the active component)
List the types of anchorage
Simple
Compound
Reciprocal
What is simple anchorage
Active movement of a relatively smaller tooth using a larger tooth (root surface area is accounted)
What is compound anchorage
Two or more teeth used to move one tooth
What is reciprocal anchorage
Two groups of teeth pitted against each other causing reciprocal movement of both groups
List the factors to consider when planning anchorage
Space requirements Type of movement required Number of teeth that need to be moved The distance of movement Root surface area of teeth Occlusal interdigitation Bone quality
Which tooth movements require more anchorage?
Bodily movement requires more than tipping
How does the number of teeth being moved affect anchorage?
The more teeth being moved, the greater the anchorage demand
How to overcome excess anchorage when moving multiple teeth?
- Consider moving a few teeth at a time (conserving anchorage)
How does the distance of movement required affect anchorage?
The greater the distance of movement, the greater the anchorage demand and the higher the risk of unwanted movement
How does root surface area affect anchorage?
Large root surface area = the greater the demand
Anchorage can be lost if the force applied exceeds the threshold for movement of the anchor teeth
How to increase root surface area of anchorage units to prevent unwanted tooth movement?
Increase the number of anchor teeth (this increases the overall root surface area)
How does interdigitation affect anchorage?
Anchor teeth with good interdigitation may increase anchorage by reducing mesial movement of the anchor unit
How does bone quality affect anchorage?
- Maxilla is less dense therefore threshold for movement of upper teeth is lower (requires more anchorage)
How can the teeth be moved to increase anchorage?
- Anchorage can be increased by moving roots closer to the cortical plate
What is the limitation of moving the roots closer to the cortical plate?
Increased risk of root resorption
What are the types of intraoral anchorage? give examples -
- Use of teeth (as many teeth as possible, differential extraction)
- Intermaxillary traction (elastics)
What extraction pattern allows greater anchorage
- As anterior as possible (As this leaves more posterior teeth to act as anchorage units)
How should extractions in crowded dentitions be approached in relation to anchorage?
- Extract as close to crowding as possible to reduce the amount of tooth movement required (this reduces the risk of anchorage loss)
What is the differential extraction pattern in class II and EXPLAIN
Upper 4s - aids OJ reduction and corrects canine relationship
Lower 5s - prevents retraction of LLS and corrects molars
What is the differential extraction pattern in class III and EXPLAIN
Upper 5s and lower 4s
Camouflages and retroclines the LLS
What is intermaxillary anchorage?
Anchorage from one arch used to reinforce anchorage in the other via elastics
What can headgear be used for?
- Extra oral anchorage
- Extra oral traction
What is extra oral anchorage?
Posterior teeth held in position to prevent unwanted mesial movement of anchorage unit
What is extra oral traction?
Distal forces applied to posterior teeth, allowing distal movement
How much force is required for EOT and EOA?
EOT - 500g
EOA - 200-250g
What are the types of force in headgear
- Force below occlusal plane (Cervical pull)
- Force above occlusal plane (high pull headgear)
- Along curve of Spee (combination pull)
When is cervical pull headgear used and why?
- Pts with reduced vertical dimensions
- This action extrudes upper molars and increases vertical dimensions
When is high pull headgear used and why?
- Pts with increased vertical dimensions
- It intrudes upper buccal segment and aids vertical maxillary development
Why is combination pull commonly used?
It does not affect vertical dimensions
List the components of headgear
Tooth attachment (facebow)
Headcap/neck strap
Elastic component
Headgear safety mechanisms
