removable appliances Flashcards
How do RA work?
Tip teeth
Move blocks of teeth
influence eruption of opposing teeth
Why do RA only tip teeth?
Because they have only a single point of contact and applies a force which tilits a tooth about its fulcrum
Why can removable appliances move blocks of teeth?
because they are connected via a baseplate so more efficient than fixed appliances
How can RA affect the eruption of opposing teeth?
Flat anterior guide plane
Buccal capping
When is a flat anterior guide plane useful?
overbite reduction
When is buccal capping useful?
intruding posterior teeth
What are the problems arising from just tipping teeth?
aesthetics
occlusal fit
What are the advantages of removable appliances?
removed for tooth brushing palatal coverage increases area for anchorage less risk of iatrogenic damage used as a passive retainer transmits forces to blocks ofteeth
What are the disadvantages of removable appliances?
appliance can be left out only tiliting movements possible affects speech intermaxiliiary traction not possible lower appliances less tolerable inefficient for mutliple tooth movements
Why are RA less succesful in the lower arch?
less tolerated as appliance encroaches on the tongue space
Less space
Less retention due to less undercut
Less sulcus depth for buccal springs
T/F RA can perform vertical movements?
F
T/F the movements of teeth in RA are less precise?
T
T/F RA cannot derotate a tooth?
T
When are RA most commonly used now?
Space maintainence retainer tooth over the bite bite opening arch expansion functional appliances simple tooth movements
What are the advantages of an acrylic baseplate?
Can provide an anterior and posterior bite plane
accomadate a screw
gives anchorage from palatal vault
How can you be sure the patient is wearing the removable appliance?
speech has improved confident in removing and replacing wear facets has become loose/passive gingivitis on palate teeth have moved
What are the components of RA?
Active components
retentive components
base plate
anchorage
Which component should be designed first?
Active
When should extraction be done, before or after the RA is fitted? and why?
after (as a general rule)
because patient may decide once RA fitted that they do not want to continue with the treatment
AND
if there is a delay in time between extracting the tooth and fitting the RA the the space will close
What is the most commonly used active component?
spring
What is the relationship between F and othodontic springs?
F proportional to dr^4/l^3 and elastic modulus d is deflection r is radius l is length
What are example of active components on removable appliances?
springs
bows
screws
WHat are the three types of springs used as buccally?
self supporting
sleeved
reversed loop
What is the type of spring used as a palatal springs?
palatal spring
What is the diameter of the wire used in the self supporting retractor and how mich do dou you activate it by?
0.7mm
activate 1mm
What are the advantages of the self supporting retractor?
still
good control of spring positions
What are the disadvantages of the self supporting retractor?
stiff so provides a high force
high in sulcus so damages mucosa
WHat are the advanatges of the sleeved buccal retractor?
flexible and good control
What are the disadvanatages of the sleeved buccal retractor?
high in sulcus so can traumatise mucosa
How thick is the sleved buccal retractor and by how much do you activate it?
0.5mm ss wire
2mm activation
What are the advanatges of the reverse loop buccal retractor?
it is short vertically so less traumatic
good lateral control of spring position
What are the disadvanatges of the reverse loop buccal retractor?
it is stiff
short range of action
How thick is the wire in the reverse loop buccal retractor and how much do you activate it by?
0.7mm
activated by 1mm
Which springs push teeth labially?
z springs
Which springs push teeth buccally?
t springs
How thick is the wire on the z springs?
- 5/0.6/0.7
0. 5mm used for single tooth
How much do you activate z springs by?
single tooth: 1-2mm
double tooth: 3-4mm
WHat are the disadvanatges to Z springs?
displaces the appliance so need good retention
WHat are the advanatges of z springs?
easy to adjust
vary degree of activation depending upon the amount of teeth needing to move
How do you activate z springs?
activate by turning 45 degrees in direction of movement
When are T srprings needed?
buccal segment teth
What are the advanatges of T springs?
easy to adjust
What are the disadvanatges of T springs?
displaces the appliance so need good retention
Limited range of action
What is so special about screws?
only means in a RA that can the tooth being retained can also be moved
WHen are screws used?
mesio-distal movement
expansion
correcting x bite
How do you activate T springs?
by pulling away from he acylic
How do you activate a screw?
turn 0.25mm/week
Why can you only activate a screw by 0.25mm?
this is dependant upon the space of the pdl
if you were to exceeed this, you would crush the pdl and this would cause cessation of movement
What feature is designed after active components?
retention
WHat is retention?
the resistance to movement away from tissues
How do we retain on posterior teeth?
adams clasp
How do we retain on anterior teeth?
Southend clasp (BEST RETENTION)
Labial bow
Adams clasp
WHat is the size of the wire used on adams clasps?
- 7mm ss wire
0. 6mm ss wrire can be used on premolars too
What is the size of wire used on southend clasp?
0.7mm ss wire
What is the size of wire used on a labial bow?
0.8mm ss wire
What are the components of an adams clasp?
a bridge
two arrowheads
two flyovers
two tags
How do adams clasps gain retention?
by engaging into the undercut beneath the maximum bulbosity of the tooth
What are the advantages of using adams cribs?
E/O traction tubes can be soldered onto them
Double cribs can be used to straddle two teeth
WHat is the purpose of a labial bow?
retention
guidance (canines during retraction)
Active (retract incisors)
retention
where should the labial bow be placed on the crown?
near the gingival sulcus to engage in some undercut
How can labial bows be used for incisor retraction?
split the labial bow
and then re solder once teeth moved
By which direction do teeth move relative to point of contact of spring?
90 degrees to point of contact
Where must the line of force pass through to avoid rotation of the tooth?
must pass through the centre of resistance
When using labial bows as active components, do we need a thin or thick wire?
thin
so it is more flexible
When is buccal capping used in remoable appliances?
occlusal interferences need to be removed to allow tooth movement and where a reduction in the overbite is undesirable
WHat is the name of the appliance used in conjusvtion with head gear?
Nudger appliance
When would you use a nudger appliance?
when you want distal movement of posteror teeth and then move on to fixed appliances
What are the ideal requirements of a spring?
apply the correct force over a good range move the tooth in the right direction difficult to position incorrectly recistant to accidental damage atraumatic hygeinic
what is the stress of wire?
F/unit area
What is the strain of the wire?
deflection/unit length
What is the modulus?
stress/strain
if you double the length of the wire what happens to the stiffness?
it decreases by a factor of 8
What happens if you double the radius of the wire?
the stiffness increases by a factor of 16
What happens to the force upon activation of the wire?
double the activation doubles the force
What is the size wire used for the palatal retractor?
0.5mm
ss
How much force is created with a 3mm activation on the palatal spring?
20-40g
what happens if you activate the palatal spring more then 3mm what happes?
it may self insert on the wrong side
applies too much force
When can you use palatal springs?
for mesiodstal movement of canines premolars and moalrs
What are the forces used to tip teeth?
25-50gms
