ORTHO pt 2 Flashcards
what are the two bracket slot sizes most commonly used?
0.018x0.025 inch and 0.022x0.028 inch
the magnitude of the forces generated in the ___ and ___ direction is partly depend on the bracket slot size
faciolingual and occlusogingival
how can the mechanical behavior of a ductile orthodontic wires in tensile loading be analyzed?
in a force-deflection or stress-strain plot
___ is the internal response of a wire to the application of external forces defied as force (load) (F) per cross-sectional area (A)
stress
___ is the deformation or deflection of the archwire as a consequence of the stress and is defined as the dimensional change divided by the original dimension
strain
what are the characteristics of an ideal orthodontic wire?
- high strength
- low stiffness
- high working range
- high fomability
- these characteristics depend on the alloy composition, the crystal structure of the metal, and the manufacturing process
each of the major elastic properties of wires (strength, stiffness, and range) is affected by a change in the ___ and ___ of a wire
-length and cross section
doubling the length of a wire does what to its strength, stiffness, and range?
- decreases strength by half
- makes it 8x less stiff (8x springier)
- gives it 4x the range
doubling the diameter of a wire does what to its strength, stiffness, and range?
- 8x stronger
- 16x stiffer
- working range is decreased by half
for large orthodontic movements (usually during initial stages of orthodontic treatment), wires with a ___ load/deflection rate are desirable because they are able to provide constant low forces as the tooth moves and the appliance is deactivated
low
for minimal tooth movements, such as in maximum anchorage extraction cases or during finishing, a ___ load/deflection rate is desirable
high
the load/deflection rate of a wire is proportional to the ___ of the material
modulus of elasticity
the most flexible wire (with the lowest load/deflection rate) is made of what material?
nickel titanium alloy
the load/deflection rate varies directly with the ___ power of the diameter of a round wire and with the ___ power of the width of a rectangular wire
- fourth
- third
the load deflection rate varies inversely with the ___ power of the length of a wire segment
- third
- increasing the interbracket distance by incorporating loops or helices into the archwire decreases the load/deflection rate
nickel titanium orthodontic archwires offer what two very important characteristics?
- a very low modulus of elasticity
- extremely wide working range
beta titanium wires are frequently known as ___ wires
TMA (titanium-molybnenum alloy)
describe beta titanium wires
- intermediate modulus of elasticity (half that of stainless steel and twice that of nickel titanium)
- excellent resilience, which provides wide working range
- drawback is a high coefficient of friction
- high formability, which allows the clinician to bend the wires and incorporate stops or loops into them if desired
- can be spot-welded
describe the characteristics of stainless steel archwires
- good mechanical properties, excellent corrosion resistance, and low cost
- when compared with NiTi and beta titanium wires, stainless steel wires exhibit the highest elastic modulus (stiffness) and lowest springback
- can be soldered and welded
what is the typical composition of stainless steel wires?
- 18% chromium
- 8% nickel
- (“18-8”)
what component of stainless steel wires give it corrosion resistance?
chromium
preadjusted edgewise appliances (brackets with prescriptions) allow what?
- rotational control
- horizontal control
- mesiodistal tip control
- torque
what is the disadvantage of metal brackets? what are they made of?
- unesthetic appearance of the metal color
- stainless steel
what are ceramic brackets made of?
monocrystalline or polycrystalline ceramics
describe the characteristics of ceramic brackets
- highly esthetic
- prone to fracture during torsional and tipping activations
- increased frictional resistance to sliding mechanics
- may cause abrasion of opposing teeth
___ brackets have a locking mechanism incorporated into the bracket system to hold the archwire in the slot
self-ligating brackets
what is the purported advantage of self-ligating brackets?
- supposedly these systems shorten treatment time by reducing friction and because the wire is efficiently kept engaged in the bracket slot
- these claims are controversial
is banding molar teeth preferred by many clinicians?
yes, although contemporary orthodontic treatment can include bonding of all teeth (including molars)
what are the 3 reasons headgear is used?
- to modify growth of the maxilla
- to distalize (retract) or protract maxillary teeth
- to reinforce anchorage
headgear should preferably be worn how many hours per day?
12-14
with headgear, what force level per side is recommended for orthopedic changes? what about for dental movements?
- 250-500g per side for orthopedic changes
- 100-200g per side for dental movements
what are 5 types of headgear?
- high-pull
- cervical-pull
- j-hook
- protraction (reverse-pull, facemask)
- chin cup
which type of headgear has the objectives of restriction of anterior and downward axillary growth and molar distal movement, intrusion, and control of maxillary molar eruption?
high pull headgear
which type of headgear is used to correct class II malocclusions with deep bite and has the objectives of restricting anterior growth of the maxilla and to distalize and erupt maxillary molars?
cervical pull headgear
which type of headgear is generally used to retract canines and incisors, rather than for orthopedic purposes?
j-hook headgear
which type of headgear is used in patients with class III malocclusions where there is a maxillary deficiency?
protraction headgear (reverse pull, facemask)
which type of headgear is used to correct class III malocclusions resulting from excessive mandibular growth?
chin cup (chin cap)
___ appliances hold the mandible in a protrusive position and transmit the forces created by the resulting stretch of the muscles and soft tissues to the dental and skeletal components to produce movement of teeth and modification of growth
functional
functional appliances are used most commonly to achieve correction of a class ___ malocclusion
II
what is important in the success of functional appliances?
patient compliances (most functional appliances are removable)
a ___ is a fixed (or sometimes removable) functional appliance that consists of a piston and tube device that places the mandible in a forward position as the patient closes the mouth; it is usually cemented or bonded to the maxillary and mandibular arches.
herbst appliance
with the herbst appliance, there is a tendency for the mandibular incisors to ___
procline (flare)
what was the first removable functional appliance developed?
activator
which functional appliance consists of the following: an acrylic body that covers part of the palate and the lingual aspect of the mandibular alveolar ridge with a labial bow that fits anterior the maxillary incisors, and on the acrylic adjacent to the maxillary posterior teeth, facets are cut to allow occlusal, distal, and buccal movement of these teeth. on the lingual aspect of the mandibular posterior teeth, facets allow occlusal and mesial movement
activator appliance
in addition to the effects of activator appliances on the growth of the mandible, these appliances can ___ and control ___
tip anterior teeth and control eruption of teeth in the vertical dimension
which functional appliance has the following characteristics: less bulky than the activator, consists of lingual, horseshoe-shaped acrylic with a wire in the palatal area; facets are introduced into the acrylic to guide the maxillary and mandibular posterior teeth and hold the mandible forward in a postured relationship; a labial bow is present anterior to the maxillary incisors, extending distally, to eliminate the pressure from the buccal musculature
bionator
which functional appliance has the following characteristics: removable or cemented two-part design; interaction between the maxillary and mandibular parts controls how much the mandible is postured forward and how much the maxilla and mandible are separated in the vertical dimension
twin block appliance
which functional appliance is supposedly more easily tolerated by patients because of its two-part design?
twin block appliance
which functional appliance is characterized by the following: consists of oversized stainless steel crowns on the maxillary and mandibular molars, elbows that insert into the tubes on the maxillary crowns, and arms that protrude from the mandibular crowns
mandibular anterior repositioning appliance (MARA, allesee orthodontic appliances, sturtevant, wisconsin)
how does the design of the mandibular anterior repositioning appliance result in anterior force to the mandibular arch and posterior force to the maxillary arch?
the lower arms interfere when the patient attempts to bite down, forcing the mandible to reposition forward into a class I relationship
noncompliant appliances to correct class II malocclusions are indicated in which situations?
- full or cusp-to-cusp molar/canine relationships
- mild to moderate crowding (0-6mm)
- a profile or other characteristics that do not support an extraction treatment plan
what are the two noncompliant appliances?
pendulum appliance and forsus fatigue resistant device (3M unitek orthodontic products, monrovia, california)
which noncompliant appliance is characterized by the following: cemented appliance that consists of an acrylic body to use the palate as anchorage with wire extensions to the maxillary premolars; two springs extending from the posterior portion of the appliance are inserted into lingual molar attachments and are activated to distalize the molar teeth
pendulum appliance
when using the pendulum appliance, what can you do if expansion of the maxilla is also needed?
an expansion screw may be incorporated into the acrylic body in the midpalatal region (appliance is then called a pandex)
which noncompliant appliance consists of a bypass rod, push rod, ball pin, and stainless steel spring module (force module) for each side, with the interarch force deliver system that is efficient in treating class II malocclusions with minimal compliance and breakage problems
forsus fatigue resistant device
describe the force generated by the forsus fatigue resistant device
delivers forward, downward force to the anterior mandibular arch and backward, upward force to the posterior maxillary arch
appliances to correct posterior crossbites:
___ or ___ appliances are used to correct transverse discrepancies by skeletal expansion of the maxilla or by dental expansion; if expansion is carried out at a rate of ___mm/day, it is called rapid palatal expansion/rapid maxillary expansion. slow expansion is carried out at a much slower rate of ___mm/week
- maxillary or palatal expansion
- 0.5mm/day
- 1.0mm/week
what are the types of appliances to correct posterior crossbites?
- hyrax appliance (banded type)
- haas appliance
- hawley-type removable appliance with a jackscrew
- quad-helix and w-arch
- transpalatal arch