3rd year labs Flashcards
appliance design - URA to retract buccally placed 13 and 23 and reduce OB
A - 13 and 23 buccal canine retractors, 0.5mm HSSW and 0.5mm ID tubing
R - 16 and 26 Adams clasps 0.7mm HSSW, 11 and 21 Southend clasp 0.7mm HSSW
A
B - self-cure PMMA, FAB OJ plus 3mm
appliance design - URA to correct anterior CB 12
A - Z-spring 0.5mm HSSW
R - 16, 26, 14, 24 Adams clasps 0.7mm HSSW
A
B - self cure PMMA, PBP (needs to cover all posterior teeth)
appliance design - URA to retract 13 and 23
A - 13 and 23 palatal finger springs and guards 0.5mm HSSW
R - 11 and 21 Southend clasp 0.7mm HSSW, 16 and 26 Adams clasp 0.7mm HSSW
A
B - self-cure PMMA
appliance design - URA to retract 13 and 23 and reduce OB
A - palatal finger springs and guards 13 and 23 0.5mm HSSW
R - 16 and 26 Adams clasps 0.7mm HSSW, 11 and 21 Southend clasp 0.7mm HSSW
A
B - self-cure PMMA, FAB OJ plus 3mm
appliance design - URA to expand the U arch
A - midline palatal screw
R - 16, 26, 14, 24 Adams clasps 0.7mm HSSW
A - reciprocal anchorage
B - self-cure PMMA, FPBP
HSSW gauge for retentive components
0.7
adams clasp can use 0.6 for deciduous
HSSW gauge for stops
0.7/(flattened)
HSSW gauge for active components
0.5
HSSW gauge buccal canine retractor (supported)
0.5mm sheathed with 0.5mm ID tubing
HSSW gauge Roberts retractor
0.5mm sheathed with 0.5mm ID tubing
unsupported buccal canine retractor
0.7mm HSSW - but too much force so don’t work well - don’t really use
palatal finger spring - pressure exerted by spring depends on
size of coil (3-4mm diameter)
thickness of wire (0.5mm HSSW)
overall length of arm inc coil (approx 20mm)
structure of palatal finger spring in URA
active arm engages contact point, applies distal force
guard/guide wire
active arm on top of coil 2/3 into palate/20mm long
3-4mm coil facing mesially
mechanically retained tag embedded within acrylic
waxed out area allowing free movement of spring within acrylic
action of palatal finger spring
can be used to move any tooth M/D along the line of the arch
palatal finger springs to move molars
0.8 mm
palatal finger spring - importance of position of coil
most important as it influences how efficiently the spring moves the tooth
bisect start finish position for position of coil
advantages of palatal finger spring
provides a light pressure and is well tolerated
several springs can be added if required to retract teeth successively
disadvantages of palatal finger spring
cannot move teeth in a palatal direction so unsuitable for buccally placed teeth
if it was used it may move the tooth further buccally and tend to produce rotation
guard wires
incorporated to prevent displacement/distortion of the spring during wear
guard wires position
place away from coil and shouldn’t impede tooth movement
usually 0.5mm HSSW with slight curve so it follows the shape of the arch
open spring and guard wires
may have guard wire placed on tissue side or either side so in action it slides between the 2
boxed spring and guard wires
can have guard wire on tissue side to prevent the spring from becoming distorted
open palatal finger spring
tissues stay much healthier
baseplate of appliance can be much weaker if >1 spring used
easier adjusting as access with the pliers is easier
advisable to use twin guard wires, open springs more liable to distortion if no guard wires used
boxed/closed palatal finger spring
can lead to proliferation of the tissues into the boxed area - not serious problem as only for about 6m
- any temp modification to underlying mucosa quickly reverts to its normal condition after a short time
baseplate much stronger - greater acrylic coverage
acrylic can be used to guide tooth along line of arch
take care to ensure spring over freely within boxed area and has adequate range of movement
what are wire tags needed for in the baseplate?
mechanical retention
ID tubing function
adds strength and rigidity - prevents distortion in buccal sulcus
why does a z spring need a lot of retention?
produces a lot of displacement force
what are FABPs used for?
correction of an overbite
PBP
prop bite open to allow movement of anterior tooth
cover all posterior teeth or some will overerupt
will go back into position when remove
incisors will act as retainer
if 7s are PE where should baseplate finish?
behind 6s
which teeth will overerupt?
posteriors (incisors don’t)
Adams clasp - what should you check first?
flyover then arrowhead
Adams clasp - if flyover distorts and interferes with occlusion
may not engage into UC
if keep biting - metal fatigue - break - could inhale/swallow
arrowhead could dig into gingiva - ST trauma
midline palatal screw
expands the upper arch
midline palatal screw anchorage
reciprocal anchorage
what should be used with midline palatal screw?
PBP - if deep occlusal digitation could also pull lower teeth out accidentally too
midline palatal screw retention
Adams clasps 4 and 6s - can’t use Southend as would split
midline palatal screw - if just want to expand posteriors
stop acrylic appropriately
midline palatal screw - expand one side more
move division line - larger force on smaller area - will move more
midline palatal screw movment
0.2-0.25mm per week
turn screw 1-2 per week
= 1mm movement per month
SS work hardening
hard wire - draw cold metal through a series of dies of successively smaller diameter
- causes work hardening - gives wire spring properties
further work hardening during bending process of constructing components - utilise to increase spring properties
SS wire fractures causes
overworking
mechanical abrasion
fatigue
weld decay
overworking
bending then straightening the wire at the same point
creates extreme stresses within the immediate area
mechanical abrasion
damaged by burs/stones/crushed
fatigue
repeated straining action e.g. continually strained to engage a deep undercut with an Adams clasp
weld decay
intergranular corrosion created by overheating alloy
causes chromium carbides to ppt at grain boundaries
oral fluids can now access the surface of other metals
= galvanic action - weakens - fracture
18-8 SS composition
72% Fe 18% Cr 8% Ni 1.7% Ti 0.3% C
Cr in SS
corrosion resistant - forms passive oxide film over surface
lowers temp at which martensite forms
Ni in SS
corrosion resistance and strength
Ti in SS
prevents ppt of Cr carbides at grain boundaries when alloy heated during welding or soldering
18-8 alloy form
austenitic
can’t be heat hardened and remains soft unless cold worked
corrosion resistant when cold worked
martensite
principal component of hard steel
formed by quenching from high temps
explain why martensite is harder
cube distorted by interstitial carbon atoms that do not have time to diffuse out during quenching
- creates crystal defects within the material similar to work hardening
- prevent atoms from sliding past one another in an organised fashion - material harder
writing a lab prescription
cross out missing teeth aim active components retention anchorage baseplate
active component
whatever applies force to teeth
retention
resistance to displacement forces
anchorage
resistance to unwanted tooth movement - newtons 3rd law
so only tend to move 1-2 teeth at a time in a URA
functions of baseplate
connector
retention (cohesion adhesion)
anchorage
where should the baseplate extend?
halfway to 7s otherwise gag reflex
baseplate material
self-cure PMMA
- quicker
- more residual monomer (allergy)
- disposable appliances - properties adequate
when should you make the baseplate in heat cure?
if the pt has a known monomer allergy
PMMA liquid
monomer
PMMA powder
polymer
heat cure PMMA advantages
better mechanical properties
can control curing
- easier to work with
more dimensionally stable
IO displacement forces
gravity mastication tongue talking active component
tooth movement aim
1mm per month
reasons for slow tooth movement
relying on bone resorption and remodelling
can cause root resorption/rip PDL
can rip/cut off blood supply - necrosis
more force = more displacement force
increased OJ consequences
trauma risk
aesthetics
functional - biting
avoiding increasing OJ with URA
measure OJ each month - should remain same
baseplate helps to prevent
reasons for tx
oral function
dental health
aesthetics
aims of tx
stability
function
aesthetics
what movement do URAs achieve?
tipping
advantages of fixed
precise control - rotation and controlled root movement possible
multiple tooth movement simultaneously
reduced impingement on tongue space
can’t easily be removed by pt
disadvantages of fixed
OH more difficult
components can be ££
advantages of removable
no OH problems
cheap
simple to adjust if correctly manufactured - less clinical time
palatal coverage increases anchorage
can be adapted to transmit force to blocks of teeth
disadvantages of removable
removable
only tilting
bulky - speech can be initially impaired and can produce increased salivation
need careful removal and insertion to avoid fractures or the appliance becoming deformed
functional
source of force is not contained in the appliance - most passive
constructed so mandible is maintained in a postured position - influences orofacial musculature and dentoalveolar development
growing pts
advantages of Adams clasp
small, neat, unobtrusive
can use on almost any tooth
can clasp PE tooth
highly versatile - can modify
highly retentive
provides a site (bridge) where pt can apply pressure with fingertips during removal
auxiliary springs can be soldered to bridge
can solder hooks or bent in during construction to accept inter-maxillary traction
can solder tubes to bridge of clasp to accommodate facebow for EO traction
how do teeth move?
prolonged force
bone remodelling
controlled by PDL - OC and OB around tooth
compression and tension areas
- causes extra blood flow in both areas increasing cellular activity
desirable pressure
25g/sq cm = 1mm per month
FABP
OJ+3mm - prevents retroclining L incisors
build up of platform of acrylic behind U incisor
reduces OB
get posterior open bite - will sort as lowers tend to continue erupting
remove bite platform then correct OJ
stages in appliance delivery
1 - check right appliance and right pt
2 - make sure appliance is the right design
3 - run finger over to ensure no sharp areas
4 - look for potential signs of damage
5 - try in mouth - look for blanching
6 - check posterior retention
7 - check anterior retention
8 - check and activate active components
9 - show pt correct way to insert and remove, get them to demonstrate it back to you
10 - book review 4-6wks
advice to give pt
will feel big and bulky, but normal, will get used to it
affects speech - lisp - practice reading out loud at home - tongue will adapt
lots of saliva - will pass quickly
will feel tender/pressure/mild discomfort on that tooth - shows appliance is working
wear 24/7 inc mealtimes
take it out to clean with soft brush after every meal
can take off for contact/active sports = protective container
avoid custom gumshields - move teeth back
avoid hard and sticky foods - will damage appliance
be careful with hot food and drink - baseplate can act as insulator
non-compliance will significantly lengthen tx
emergency contact details
z-spring which coils should be activated?
both coils = for straight movement
wire thickness and force
thinner wires - less force
