Midterm Flashcards
PDL occupies how much space?
.5mm
Main cell in PDL
undifferentiated mesenchymal cells that turn into fibroblasts and osteoblasts
collagenous fibers do what?
resist displacement in normal function. They attach to lamina dura and cementum
can orthodontic forces displace sutures?
yes, especially in kids
T/f, as the tooth moves away the PDL moves with it?
T, tooth movement is primarily a PDL phenomenon.
_____ & _____ forces squeezes out PDL fluid causing remodeling of adjacent bone
light, continuous
> 1 second of pressure on the PDL
PDL fluid to compress and alveolar bone bends
1-2 seconds of pressure on PDL causes
PDL fluid expressed, tooth moves within the PDL space
3-5 seconds seconds of pressure on PDL causes
PDL fluid squeezed out, tissue compressed, immediate pain if pressure is heavy.
which area of the mouth is affected by tongue thrusting?
lower anteriors. tongue produces ~10gm and lip produces 5gm
T/F, fibers within the PDL can cause movement themselves?
T, Collagen fibers continue to change even after tooth eruption and can cause extraetruded teeth.
whats hyalinization?
form of tissue degeneration. Denotes a compressed and locally degenerated pdl. Reversible process. Occurs in almost all forms of orthodontics
whats tipping?
simplest form of orthodontic tooth movement. Center of resistance is usually ½ way between the apex and alveolar crest.
strain
internal distortion produced by the load( defined as deflection perunit length)
whats translation?
2 forces applied simultaneously. AKA bodily movement. Has a rectangular diagram
translation requires__ times as much force as tipping?
2
whats intrusion?
one of the hardest movements in orthodontics. You have a very small loading area. This requires very little force. Movement is back into the alveolar bone.
____ hours of force is the minimum for beginning of tooth movement?
6
(on F&D diagram)
elastic limit
space between yield point and proportional limit, Its the greates amount of stress without permanently deforming
force decay
reduction in force magnitude as is seen in springs after a tooth has moved.
3 stages in tooth movement are…
initial compression and alterations in blood flow associated with pressure within the PDL, formation and release of chemical messengers, activation of cells
( on stress-strain diagram)
the more vertical the slope, the more ____ the wire
stiffer
intermittent forces
when magnitude of force drops to zero in one shot. ( like when removing the braces)
stress
internal distribution of the load (defined as force per unit area)
strain
internal distortion produced by the load( defined as deflection perunit length)
load deflection
degree to which a structural element is displaced under a load
3 major properties of water are
strength, stiffness, range
(on F&D diagram)
proportional limit
highest point stress and strain has linear relationship
(on F&D diagram)
yield point
intersection of stress-strain curve with parallel line offset at .1% strain
(on F&D diagram)
elastic limit
space between yield point and proportional limit
(on F&D diagram)
point of arbitrary clinical loading
clinically useful springback
( on stress-strain diagram)
the more horizonal the slope, the more ___ the wire
springier
( on stress-strain diagram)
the more vertical the slope, the more ____ the wire
stiffer
modulus of elasticity
the ratio of the stress applied to a body or substance to the resulting strain within the elastic limit
stationary anchorage
refers to the advantage of putting bodily movement of one group of teeth against tipping of another group.
nickel titanium alloy ( nitinol) properites
provides light force of large range.
Beta-titanium properties
TMA?????
2 different forms of Nitinol
martensitic- stable at low temp and high stress
austenitic- stable at high temp and low stress
what happens when you double the length of Niti wire?
- Cuts strength by ½
- 8X more springy
- 4X the range
what happens when you double the thickness of the niti wire?
- 8X as strong
- 1/16 as springy
- ½ the range
Anchorage
resistance to unwanted movement
what can be used for anchorage?
teeth, palate, head, neck, screws..
reciprocal tooth movement
forces applied to teeth and arch segment are all equal.
Which teeth are better anchors and why?
posteriors because they have a bigger PDL area
reinforced anchorage
you add another tooth into the system to anchor that side more so the other side moves more.
define moment
measure of tendency to rotate an object around some point
Orthodontic pain
caused by ischemic areas in the PDL that undergo sterile necrosis
what should be used for ortho pain?
acetaminophen ( tylenol)
tissue inflammation with ortho treatment
very rare but is usually caused by latex allergy and or nickel from the brackets
what happens when incisor is tipped to far lingually?
vitality is lost via root exposure
what did Rygh and his coworkers discover for root effects?
where PDL necrosis occurs, the underlying cementum is remodeled as well. Root length is decreased( mostly incisors)
what factors play into root resoprtion?
treatment length, and heavy forces
what were elastics made of in the past and what are they made out of now?
gum elastic, it degraded pretty fast so they switched to latex elastics which last 4-6 times as long
ortho magnets
not good. Follow inverse law which means they dont provide consistant force.
define force
a load applied to an object that will tend to move it to a different position in space.
define center of resistance
point at which resistance to movement can be concentrated for mathematical analysis. On a tooth it is at the approximate midpoint of the embedded portion of the root
define moment
measure of tendency to rotate an object around some point
plastic brackets
stain, poor stability, friction between plastic an wire makes it difficult to slide teeth into new positions ( some have metal sliding material but they still suck)
define couple
when 2 forces equal in magnitude and opposite in direction
define center of rotation
point around which rotation actually occurs when an object is being moved
MC/MF ratios and control of root resorption
- A simple way to determine how a tooth will move is to look at the MC/MF ratio
- MF- the moment of the force
- MC- moment of the couple
(MC/MF ratios and control of root resorption)
=0
pure tipping
(MC/MF ratios and control of root resorption)
=1
bodily movement
(MC/MF ratios and control of root resorption)
>1
torque( root apex moves further than crown)
what year did Dr. angle make edgewise appliances?
1928
ribbon arch vest
whent all around the tooth with a vertical slot
edge wise appliance
slot size .22X.28”
horizontal slot
90 degree angle of insertion
what is a good alternative for someone who is allergic to stainless steel brackets? ( it has nickel)
titanium brackets
ceramic brackets
very strong and can cause abrasion problems with enamel ( why they put them on maxillary usually). Very stable but can fracture easily.
first order bends
used to compensate for differences in tooth thickness
o Upper molars should have at least 10 degree offset
o Lower molars should be 5-7 degrees
second order bends
used to position roots correctly mesiodistally
o Also called artistic positioning bends
third order bends
torque bends to position roots in faciolingual direction
o Failure to add third order bends makes the anterior teeth become too upright. Posteriorly buccal cusps of molars would be depressed and lingual cusps elevated
3 types of self ligating brackets
springy latching cap, springy retaining clips, and rigid latching caps.
Save time during ligating but thats it.
customized brackets
- This technology is used to precisely cut each bracket using CAD/CAM so that each slot for each bracket has the appropriate thickness, inclination, and torque needed for positioning that specific tooth.
- Treatment time is reduced in comparison to conventional brackets
- Minor adjustments to wires still needed
lingual appliances
wire bending is done via “wire bending robot”.
2nd molars arent positioned as precisely as others.
what kind of archwires should be used when nickel-titantium and beta titanium wires are needed?
preformed archwires because theyre difficult to bend without special tools.
If both arches are incompatible during beginning of treatment, which arch should you use as a basic guide?
mandiublar
Whats a catenary curve
shape that a loop of chain would take if it were suspended from 2 hooks.
Brader arch form
based on trifocal ellipse. This provides the posterior constriction that the catenary curve does not.
So this is good for 2nd and 3rd molars.
benefits of polymer clear wires
esthetic, as strong as metal, round or rectangular, can be corporated into retainers
AAO recommends children to have their first ortho apt at what age?
7
Reasons: the posterior occlusion is established when the first molars erupt. At the time one can evaluate the antero- posterior n transverse relationships of occlusion, as well as discover any functional shift or crossbites.
TADs
Bone screws
o Mostly titanium due to better biocompatibility than stainless steel.
o Stability- short term and long term is determined by mechanical retention of screw in bone, which depends on bone properties, design of screw, placement technique.
o Long term ( secondarily stability)- defined by biologic union of screw to surrounding bone. Determined by implant surface, bone characteristics, bone turnover, and implant surface mechanical system
• Primary stability
o Decreases over time while secondary increases
what factors into the stability/success of TADs
pitch, lenght, diameter, taper , form of tip.
pitch of screw
how close the threads are. For dense bone you want a tight pitch.
length of screw
the amount of contact with the cortical bone is the main determining factor of stability
diameter of scew
needs to be narrow enough to fit between teeth. ( current scews are 1.3-2mm wide)
form of tip
2 types
thread forming- compasses bone around the threads of the screw as it advances which is better bone to scew contact
self-tapering-
TADs
miniplates are usually placed where?
base of zygomatic arch( but can be elsewhere)
what are the determinates for stability for miniplates?
o Number of screws used- 3 is best, anything more doesn’t add additional stability
o Patient age- failure occurs more often in young pts. Bone maturity doesn’t reach a good level until around age 11
what are some indications for miniplates?
positioning groups of teeth- distalization of entire maxillary or mandibular arch, intrusion anterior and posterior teeth
Growth modification- class 3 elastics, maxillary deficient child
can canine interference cause a posterior crossbite?
you bet it can! This is why its important to make sure the pt is in CO when diagnosing.
what appliace can you use for a mxed dentition patient?
2x4 or 2x6
whats somthing to watch out for when treating someone in mixed dentition?
unerupted teeth
T/F, early treated ortho patients frequently need a phase 2 treatment?
true
In early treated patients, can class 2 or 3 pts be delayed?
class 2 can class 3 needs to be addressed early because there may be skeletal deformities.
which permanent teeth are most commonly missing?
upper laterals and lower 2nd premolars
90% of supernumerary teeth are what ?
maxillary anteriors
what must you watch when using the cross-elastic technique for single posterior teeth?
o Must monitor carefully especially in children with increased lower facial height. When lingual cusp drops down and contacts molar it will make face even longer, 1mm in post is 3 mm in anterior
what % of kids have posterior crossbites?
7.1
how do palatal expanders work?
( w-arches, quad helix) they prevent the fusion of the suture and open it up
can canine interference cause a posterior crossbite?
you bet it can! This is why its important to make sure the pt is in CR when diagnosing.
niti wire in aiding with anterior crossbites
The niti wire pushes the teeth out but doesnt align. This method is good for thumb suckersand tongue thrusters
what appliacne can be used for someone with unilateral maxillary constriction?
W- arch with one side longer than the other. The longer side is the anchored side and the shorter is the one doing the pushing. ( he said both sides moves so its not a good appliance)
how can you adjust a W-arch?
with a 3 pronged plier. It can be adjusted without removal.
which appliace can be used to stopt thumb sucking and tongue thrusting?
thumb crib, this makes a mark on the tongue but will disappear. Its affective in about 85-90% of cases. It does cause hygiene problems becasue it traps food.
whats an example of reminder therapy for thumb suckers.
put a bandaid on their finger
how far should you over correct maxillary constricions?
until maxillary posterior lingual cusps occlude with lingual incline of buccal cusps of mandibular posteriors
You want to retain this for 3 months
how do you fix a single molar thats in crossbite?
cross-elastic with welded buttons on bands
what must you watch when using the cross-elastic technique for single teeth?
o Must monitor carefully especially in children with increased lower facial height. When lingual cusp drops down and contacts molar it will make face even longer, 1mm in post is 3 mm in anterior
what can you do if a cross bite is forming in the anterior area druing mixed dentition?
extract primary cuspids to provide more room. sometime spontaneous correction occurs
removable appliace in aiding anterior crossbites
its a retainer with a double helical fingerspring thats activated 1.5-2mm per month to produce 1mm per month of tooth movement
anterior crossbite with the fingerspring
has bands on the posterior teeth with the helical wire pushing on the anterior teeth. This can be modified into a retainer to maintain the position after treatment.
niti wire in aiding with anterior crossbites
The niti wire pushes the teeth out but doesnt align. This method is good for thumb suckersand tongue thrusters
when does it start to become a problem with tongue thrusters?
as soon as incisors start o erupt. If habit ceases while theyre erupting the incisors autocorrect.
which method provides the best success to stop thumb sucking?
reward system
child must be motivated
parants must be willing to give reward, child must go 3 days without sucking for reward
which appliace can be used to stopt thumb sucking and tongue thrusting?
thumb crib, this makes a mark on the tongue but will disappear
whats an example of reminder therapy for thumb suckers.
put a bandaid on their finger
thumb suckers maxillary incisor are usually tipped ______ and mandibular are ______
facially
lingually
