Removable Appliances Flashcards
What is the prevalence of removable appliances?
2%
What is the prevalence of fixed appliances?
9%
What are the uses of a removable appliance?
To hold teeth in a particular position, for simple tooth movements, and expanding dental arch
What are examples of simple tooth movements?
Tipping of a single tooth/multiple teeth and intruding/extruding either lower incisors/posterior teeth
What are the types of tooth movement?
Tipping, intrusion/extrusion, bodily movement, and rotation
What are different forces required for?
Type of movement and root surface area of teeth to be moved
What are the components of removable appliances?
Retention, active component, anchorage, baseplate
What clasps are use for retention of removable appliances?
Adams clasp, Southend clasp, and labial bow
What is the Adams clasp made of?
0.7 mm stainless steel
What is the Southend clasp made of?
0.7 mm elgiloy
What is the labial bow made of?
0.7 mm stainless steel
What is the main difference between stainless steel and elgiloy?
Elgiloy is a cobal chrome alloy
What is stainless steel also known as?
18:8 steel
What percentage of the population are allergic to nickel?
15%
What is nickel free wire made of?
Copper/Vanadium
What is used to tighten the crypt of a clasp?
Spring formers
What are the active components of removable appliances?
Springs, orthodontic screws, pistons, magnets, elastics, acrylic blocks/planes
What are springs used for?
To move teeth buccally, palatally, and mesially/distally
What two types of springs are commonly used for buccal/labial tooth movement?
T spring and Z spring
How are T spring and Z spring activated?
1st visit use a pair of spring formers to pull spring away from baseplate 3-5mm and subsequent visits use a pair of spring formers to pull wire along direction of movement desired 2-3mm
What two types of springs are used for distal and palatal tooth movement?
Palatal finger spring and canine spring
What are palatal finger springs used for?
To move UR3 distally
What are palatal finger springs made of?
0.5 mm stainless steel with coil and guard
What are canine springs used for?
To move UL3 palatally
What are canine springs made of?
0.7 mm stainless steel
Why are palatal finger springs usually made with a guard?
To prevent wire impinging palatal mucosa and preventing free movement of spring
Where should palatal finger spring rest?
3/4 of the way up mesial incline on canine before insertion
What is used to expand laterally/mesio-distally?
Orthodontic screws
How are orthodontic screws activated?
Turn screw twice a week Wednesday and Sunday
What does each turn of an orthodontic screw do?
Expands 2 plates apart by 0.25mm to 0.5mm per week
Why are pistons not used too often?
Active component can get clogged and therefore inactive
Why do attracting magnets work better than repelling ones?
Repelling magnets lack a specific direction
Why do magnets need to be well-encased avoiding contact from oral fluids?
Potentially toxic
What can elastics be used to do?
Bring down unerupted teeth and also reduce increased overjets with anterior spacing
What is anchorage?
Resisting unwanted tooth movement
What are the two broad types of anchorage?
Intra-oral and extra-oral
What is intra-oral anchorage?
Reciprocal, simple, temporary anchorage devices (TAD’s)
What is extra-oral anchorage?
Headgear
What is reciprocal anchorage?
Either bring teeth together/pushing apart
What is simple anchorage?
Root surface area of tooth to be moved (canine) should be significantly less (1/3 or more) than anchor unit (2nd premolar and molar) baseplate can also be considered as contributing to anchorage
What does a flat anterior bite plane do?
Disengages upper and lower molars and premolars which allows them to erupt increasing facial height and a posterior rotation of mandible and intrudes lower incisors with some degree of proclination/retroinclination which depends on whether lower incisors are proclined/retroclined relative to FABP
What is it important to measure when designing a flat anterior bite plane?
Overjet and add 3mm so that lower incisor will hit bite plane
What do flat anterior bite planes usually have a height of?
1/3, ½, 2/3’s of upper incisal height
What do posterior bite planes do?
Disengages upper and lower incisors which allows them to erupt and increase overbite and encourage a reduced face heigh and forward rotation of mandible
Why should posterior bite planes be at least 3mm thick?
To minimise breakages
What does force needed to move teeth depend on?
Root surface area, number of teeth being moved, type of movement desired and size of anchorage unit
What is force measured in?
Centinewtons (CN) (one hundredth of a newton)
What is 1CN in grams force?
1.02
What is needed to 1 Newton of force required to accelerate?
1 kilogram of mass at rate of 1 metre per second squared in direction of applied force (N=KG M/S2)
What should force also be considered in relation to?
Root surface area and/or mass of tooth
What is force defined as?
A change in motion of a tooth/stress induced in a stationary ankylosed tooth
How is magnitude of force calculated?
By multiplying mass of body and its acceleration
What is force influenced by in orthodontics?
Deflection of spring, radius of wire, and length of wire
How is force calculated?
Force = deflection x radius4/length3
What happens to force if the length of wire is doubled?
Decreased by a factor of 8
What happens to force if the thickness of wire is doubled?
Increased by a factor of 16
What is the pre-clinical checklist of fitting a new appliance?
Make sure patient details on laboratory documents match patients, check original orthodontic design against appliance made, does appliance fit model well, are there any pimples/sharp pieces of acrylic on base plate, check for plier marks on retentive components and thickness of baseplate
What may badly marked wires/over polished/thin baseplates lead to?
Early fracture/components part of removable appliance
What is the clinical checklist of fitting a new appliance?
Explain what you are going to do to patient, show them appliance, fit appliance, if it is loose adjust retentive components, ask patient to remove and insert a few time to ensure they understand correct procedure for insertion and removal, once they are confident you can then adjust active components, provide patient with an information leaflet on how to look after appliance provide contact numbers if any problems arise, appliance should be worn nearly full-time and only removed to clean teeth and appliance after meals, appliance should be removed in contact sports and swimming and kept in a rigid box in a safe place, and arrange a review appointment for 4-6 weeks
