Spring Flashcards
What are the different components of a removable appliance?
Active components
Retentive components
Baseplate
Anchorage
Which components should be designed first and why?
Active components (because the other components will be influenced by the active components)
What 6 things will an ideal spring do?
- Apply the correct force over a good range
- Move tooth in the right direction
- Be difficult to position incorrectly
- Be resistant to accidental damage
- Be a-traumatic
- Be hygienic
What are the 3 parts of the palatal retractor?
The arm = not normally straight -> usually sits around the tooth
Coil = extension of the arm
Tag = mechanical retention - the only portion that goes within the acrylic
What is this part?
A guard
The horizontal wire stops distortion in the mouth
Why do we have an eyelet on the end of the arm?
To stop damage to patient
Which factors determine the force applied by a spring?
- Length of the spring
- Thickness of a wire
- Elastic modulus of the wire
- Degree of activation
What force do we want the force of a tooth moving spring to apply?
A low force over a good range of movement
What does doubling the length of a wire do to a spring?
Reduces the stiffness by a factor of 8
What does doubling the radius (thickness) of a wire do to a spring?
Increases the stiffness by a factor of 16
What does a lower elastic modulus of wire do to a spring?
Lowers the stiffness (listen to 9mins 30)
What does doubling the activation of a wire do to a spring?
Doubles the force of the spring
What does the loop in a palatal spring do?
It adds length (reduces the force for a given deflection) (listen to 10 mins = slide 15)
What force does an ideal palatal retractor apply and what activation does it have?
Force: 20-40 gm (cN) = moves tooth gently & physiologically
Activation: 3mm
Typically for a canine which wire is used to make sure it is the right thickness and elastic modulus?
0.5mm stainless steel
What happens if the spring is activated too much (>3mm)?
It may self- insert on the wrong side of the tooth (tooth width) and will apply too much force
How do you activate a palatal retractor?
What can help ensure the correct amount of activation?
Marking the acrylic (on baseplate and bend the wire to this mark)
In which direction will the tooth move to the point of contact?
The tooth will move at right angles to the point of contact
What is a common incorrect tooth movement?
Point of contact slightly too palatal = rotation and buccal movement
What is a common adjustment that can be used to prevent this rotation?
What movements are palatal springs clinically used to achieve?
Mesio-distal movement of canines, premolars and molars
When moving a premolar which thickness of wire do we use?
Thicker wire (the extra force can be taken due to the wider root)
Which other orthodontic springs exist?
The buccal canine retractor (X3)
Z springs
T springs
Auxillary springs (Screws)
When is the buccal canine retractor used and what are the 3 types?
For moving buccally placed canine teeth :
- Self supporting
- Sleeved
- Reverse loop
What is the self supporting retractor?
A buccal canine retractor = 0.7mm stainless steel wire n.b there’s not very much sulcal depth in this region (if too long = trauma)
What are the advantages of the self supporting retractor?
Quite stiff = good control of spring position
What are the disadvantages of the self supporting retractor?
Activation of stiff wire = high force levels
Sits high in sulcus and can traumatise the mucosa
How much are self supporting retractors activated by?
1mm only
What is a sleeved buccal retractor?
The same as the self supporting retractor but the non active part is sleeved = thick and stiff
0.5mm in tubing
How are the self supporting retractors and sleeved buccal retractor activated?
What are the advantages of the sleeved buccal retractor?
Flexible with 2mm activation
Good control
What are the disadvantages of the sleeved buccal retractor?
High in sulcus (can traumatise mucosa)
How much are sleeved buccal retractors activated by?
2mm
What can happen if the sleeved buccal retractor is too high?
Ulcer
What design can be used to make it lower?
= less trauma but stiffer
What is the reverse loop buccal retractor?
Coil is above the tooth two behind the moving tooth
0.7mm stainless steel
How is the reverse loop buccal retractor activated?
‘curl and cut’
What are the advantages of the reverse loop buccal retractor?
Short vertically (less traumatic)
Good lateral control of the spring position (relatively short range of movement -> can only bend a few times before it breaks)
What are the disadvantages of the reverse loop buccal retractor?
Stiff (short range)
How much is a reverse loop buccal retractor activated by?
1mm (more than this applies huge pressure to tooth)
What does the reverse loop buccal retractor look like when passive and active?
What type of spring is this?
z spring
What movement to z springs achieve?
Push teeth labially
If you have a cross bite (upper incisors behind lowers) how do we use a z spring to treat this?
But z spring behind upper incisors and use blocks so no horizontal interference -> can use single spring contacting two teeth to move them but two individual springs is more adjustable
What are the advantages of z springs?
- Flexible with 1-2mm activation on a single tooth spring and 3-4 mm activation on a double tooth spring
- Quite easily adjustable
What are the disadvantages of z springs?
- Displaces the appliance = requires very good retention i.e. cribs and labial bows
How are z springs activated?
What type of spring is this?
T spring
What movement does a T spring achieve?
Pushes teeth buccally
What are the purpose of the loops on the T spring?
Give the wire extra length = reduces the pressure put on the tooth
How are T springs activated?
Pulled away from acrylic
What are the advantages of T springs?
- Easily adjustable
- Good for buccal segment teeth
What are the disadvantages of T springs?
- Displace the appliance and need good retention
- Limited range of action
What movements can screws achieve (with a crib)?
Mesio-distal movement and for expansion
How do screws work?
Patient tightens/ loosens activation wheel once each week = 0.25 mm activation
How can screws be used for distal movement?
n.b. need lots of retention to keep it in place
What is important in screws?
Done by patient themselves = should not be able to do it incorrectly = wrong movement!
