Orthodontics Flashcards
what are the elements of a removal appliance ?
active components, retentive components, baseplate, anchorage
which elements of a removal appliance should be designed first ?
active components
what should an ideal spring be like ?
apply the correct force over a good range of movement, move tooth in the right direction, be difficult to position incorrectly, be resistant to accidental damage, be atraumatic, be hygienic
what are the 3 parts of the palatal retractor ?
arm, coil, tag
what is the unction of the tag?
mechanical retention
what factors determine the force applied by palatal springs ?
length of the spring,
thickness of the wire,
elastic modulus of the wire,
degree of activation
how does length affect the stiffness of a wire ?
double the length of wire will reduce stiffness by a factor of 8
how does thickness affect the stiffness of wire ?
double the radius of a wire will increase the stiffness by a factor of 16
how does modulus affect the stiffness of a wire ?
lower modulus means lower stiffness
how does degree of activation affect the force applied by a spring ?
double the activation doubles the force
how much force should a palatal retractor apply ?
20-40gm (cN) with a 3mm activation
what thickness of wore is used to make a palatal retractor ?
0.5mm
what can happen if a spring is activated >3mm ?
self insert on the wrong side of the tooth,
apply too much force
what is the function of a palatal spring ?
mesio-distal movement of canines, premolars and molars
what other orthodontic springs can be used in removable appliances ?
buccal canine retractor, Z springs, T springs, auxiliary springs, screws
what diameter wire is the self supporting buccal retractor made of ?
0.7mm ss wire
what are the advantages of the self supporting buccal retractor ?
stiff so good control of spring position
what are the disadvantages of the self supporting buccal retractor ?
activation of stiff wire provides high force levels,
high in sulcus and can traumatise mucosa
by how much should a self supporting buccal retractor be activated ?
1mm
what diameter wire is the sleeved buccal retractor made from ?
0.5mm ss wire in tubing
what are the advantages of the self sleeved buccal retractor ?
flexible,
good control
what are the disadvantages of the self sleeved buccal retractor ?
high in sulcus and can traumatise mucosa
by how much should a sleeved buccal retractor be activated by ?
2mm
what diameter wire is the reverse loop buccal retractor made of ?
0.7mm ss wire
how is the reverse loop retractor activated ?
curl and cut
what are the advantages of the revere loop buccal retractor ?
short vertically so less traumatic,
good lateral control of spring position
what are the disadvantages of the reverse loop buccal retractor ?
stiff so short range
by how much should the reverse loop retractor be activated ?
1mm
what is the function of Z springs ?
push teeth labially
what are the advantages of Z springs ?
flexible with 1-2 mm activation on a single tooth spring and 3-4 mm on a double tooth spring,
easily adjustable
what are the disadvantages of Z springs ?
displaces the appliance so requires very good retention
what is the function of T springs ?
push teeth buccally
how are T springs activated ?
pull 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 and need good retention,
limited range of action
what is the function of screws ?
mesio-distal movement,
expansion
What are the elements of a removable appliance ?
Active components,
Retentive components,
Anchorage,
Baseplate
What provides retention of a removable appliance on posterior teeth ?
Adam’s clasp
What provides retention for a removable appliance on anterior teeth ?
Southend clasp,
Labial bow
What is an Adams clasp made from ?
0.7mm wire, may be made from 0.6 mm ss wire for premolars
What is a Southend clasp made from ?
0.7 mm ss wire
What is a labial bow made from?
0.8 mm ss wire
what are the functions of the labial bow ?
retention in the mouth,
guidance of canines during retraction,
actively retract the incisors,
retain teeth in corrected position
what are the 2 types of labial bow ?
high labial bow - only suited as active component,
reverse looped bow
where should the labial bow be positioned in order to be retentive ?
placed at bottom 1/3 of incisors in line with the baseplate
how can the labial bow control tooth movement ?
teeth move at right angles to point of contact of the spring,
where the line of force does not pass through the centre of resistance, the tooth will rotate
retract upper canines and reduce overbite,
retract proclined incisors
what type of wire is needed for retention in the mouth, canine guidance and retaining tooth positions ?
stiff, thick wire
what type of wire is needed to retract incisors ?
flexible wire
how does splitting a labial bow aid incisor retraction ?
makes it more flexible
what does a removable appliance do ?
tips teeth, does not move roots
what are the potential problems from just tipping teeth ?
aesthetic, dental health, occlusion
what limitations arise from tipping action ?
mesio-distal in buccal segments,
labio-lingual in class II,
labio-lingual in class III,
mesio-distal in labial segments
what are the limitations of removable appliances ?
tipping, inappropriate for lower arch, vertical movements, inter arch elastics, precision, rotations, multiple tooth movements
what are the current uses of removable appliances ?
space maintenance, retainers, tooth over the bite, bite opening, expansion, other simple tooth movements
what are the advantages of removable retainers ?
all teeth can be retained, partial withdrawal possible, less dental health hazard, oral hygiene, missing teeth can be replaced, responsibility of the patient
what are the disadvantages of removable retainers ?
rotations,
anterior diastemas,
vertical tooth position,
need to be worn
what are the advantages of the acrylic baseplate ?
can provide anterior and posterior bite planes,
can accommodate a screw,
give some anchorage from the plate
what are the functions of screws ?
unilateral or bilateral distal movement,
arch expansion,
anterior cross bite correction
how can you tell if a patient is wearing their removable appliance ?
good speech, palatal gingivitis, wear facets on acrylic, passive springs, confident removal and insertion
