Ortho level 3 unit A module 1 2 3 Flashcards
How is a problem list for orthodontics made?
Interview, clinical examination, analysis of records
Then a systematic description is used to classify the problem
What is the purpose of the interview?
To answer 4 major questions:
- Why is this patient seeking treatment, and why now?
- How did things get to be the way they are?
- What, if anything, is likely to change in the near future? (progression of medical condition, and probable growth changes)
- What do the patient and parents expect as a result?
What are the goals of a clinical examination?
Evaluate facial proportions and tooth-lip relationships.
Evaluate the health of oral hard and soft tissues.
Evaluate jaw function.
Determine what diagnostic records are required
How is the face examined during a clinical examination?
First, in the full face view, symmetry and proportion.
Second, in the profile view, a-p and vertical jaw relationships.
Third, in the smile and profile views, lip-tooth relationships and lip support.
How is the health of tissues examined?
The focus should be first on the health of the tissues and on jaw function, not the details of the occlusion.
In the examination of the soft tissues, it is important to examine the amount of attached gingival tissue, in addition to looking for areas of gingivitis/bleeding on probing.
How is jaw function evaluated?
Check for malocclusion
Check for mandibular movements
Which radiograph is always indicated for orthodontic treatment?
OPG
Which orthodontic records are essential for orthodontic diagnosis?
Dental casts
Intraoral and facial photographs
Lateral cephalometric radiographs/tracing
Why are dental casts used?
Necessary to allow measurements in space analysis and to provide a record of pretreatment alignment and occlusion.
To evaluate dental arch symmetry
To evaluate arch width
Why are facial and intraoral photographs used?
To allow evaluation of change.
To identify soft tissue problems. (eg lack of gingival attachment)
What is the function of a lateral cephalometric radiograph in orthodontic diagnosis?
To allow evaluation of response to treatment and to allow greater precision in evaluating jaw and tooth-jaw relationships.
Is there any advantage in having the dental casts mounted on an articulator?
That depends on the individual case. If extensive restorative treatment or maxillary surgery must be planned as part of comprehensive evaluation in an adult, then yes, articulator mounting is indicated. But as a general rule for orthodontics and especially for children, the answer is no. In a growing child, because the relationship of the dentition to the TM joint changes rapidly, the articulated casts quickly become only a historical artifact.
Is a cephalometric radiograph necessary for orthodontic diagnosis?
The cephalometric radiograph makes it easier to define skeletal and dental relationships, but it is not strictly necessary for diagnosis. Problems in jaw relationships and lip support can be detected on careful clinical examination. Yet modern orthodontic treatment almost always requires cephalometric analysis. It’s malpractice to do comprehensive treatment without cephalometrics. Why? Because it is impossible to determine the progress of treatment without being able to superimpose serial cephalometric tracings. You can easily be fooled on clinical examination as to what really is happening. If you didn’t take a pretreatment ceph, a progress ceph is of minimal value.
What is the indication for a P-A cephalometric radiograph in addition to the lateral ceph?
The primary indication for a P-A ceph is jaw asymmetry noted on clinical examination. A P-A ceph is not taken routinely for two reasons: (a) symmetric transverse relationships can be evaluated from clinical records and dental casts, and (b) in contrast to the lateral ceph, evaluating growth and treatment response from serial superimpositions is difficult and inaccurate.
How is 3D imaging done?
3D photographs or 3D video (expensive and not as practical)
MRI (no ionizing radiation and valuable for TMJ evalutation)
CT
What are the disadvantages of CBCT?
Additional expertise needed to evaluate pathological changes revealed by these images.
Radiation exposure. (lower than conventional CT but still quite high)
When is CBCT indicated?
CBCT of the area of impacted teeth now is indicated for most patients,
Full-face CBCT is indicated for skeletal asymmetry.
Other potential reasons for obtaining CBCT are not (yet?) supported by evidence.
What do diagnostic records of orthodontic patients consist of?
Photographs
Radiographs
Dental casts (primary space analysis, available space, etc)
Can occassionally also consist of articulator-mounted casts, CT scans, MRI images, or other data
What information do photographs and digital videos provide to orthodontists?
Photographs primarily provide confirmation and documentation of what was observed clinically. Facial animation, especially on smile, is an important part of evaluating esthetics. Short video clips (as seen in the accompanying image) can be obtained with almost any modern digital camera and incorporated into digital records, and are likely to become a routine part of orthodontic evaluations in the future. The video clips can provide facial views in multiple dimensions as well as a record of lip-tooth relationships on smiling. Careful observation, not frame-by-frame measurement, is the primary method of analysis.
What relationships does a lateral cephalometric radiograph help us understand?
How jaws relate to cranial base
How jaws relate to each other
How teeth of each jaw relate to the supporting bone of the jaw itself
How should a problem list be formed prior to orthodontic treatment?
Note any pathologic problems separately. (highest priority)
Classify diagnostic findings of developmental problems to develop the rest of the problem list with a systematic description
What are the 5 steps of the systematic description approach created by the Ackerman-Proffit classification?
1) Alignment/symmetry of the dental arches
2) Evaluation of dental protrusion/esthetics
3) Transverse skeletal/dental relationships
4) A-P skeletal/dental relationships
5) Vertical skeletal/dental relationships
What question is asked in diagnosis?
What are the problems?
The answer is a description of the problems and their cause.
What is the question asked for treatment planning?
What can be done about the problems?
What are the steps of treatment planning?
1) to separate out the patient’s pathologic problems, which will require other types of treatment, from the developmental problems that are treated with orthodontics
Then the developmental problems are placed in priority order, and the treatment plan is developed by evaluating the possible treatment procedures relative to the patient’s prioritized problem list
How should the treatment planning process be approached?
Consider the possible solutions to each problem, starting with the most important one
Examine the “practical considerations” of interactions among the possible solutions, cost-benefit, necessary compromises, and other factors
Meet with the patient/parent to review alternative treatment possibilities, seek their input, and obtain informed consent
What causes the shock absorber effect seen when a tooth is subject to a heavy load?
The fluid in the PDL space
Why is it still possible to feel pain if you bite something very hard?
When you bite down, the fluid is incompressible, and the first thing that happens is that the alveolar bone bends. The tooth (or teeth) moves relative to the jaw, but not relative to the alveolar bone. After one second or so, the fluid begins to be squeezed out, and at that point the cellular elements begin to feel pressure. If you bite down on what you thought was a peanut and it doesn’t break apart, you probably maintain the force and bite a little harder. If it still doesn’t shatter, you begin to feel pain because the cellular elements are being loaded more as the fluid continues to be squeezed out—and you stop biting.
Why doesn’t the alveolar bone immediately disappear after a tooth extraction?
We know now that bone bending is necessary to maintain normal calcification and remodeling.
How does bone bending generate an electric current?
Bone bending produces an interesting electrical effect, the generation of a piezo-electric current. Force against a crystalline structure (many nonbiologic crystals, but also bone and collagen) mechanically distorts the crystals. This produces a rapid current flow as electrons move to a different location within the crystal lattice, which quickly declines as they reach their new position. When the force that produced bending is removed, the electrons move back to their original position, and a reverse current flow is observed. As you walk down the street, there is a rhythmic current flow with each step. When you chew, the same rhythmic current flow occurs in your alveolar bone and throughout your jaws.
Is the piezoelectric effect important for maintenance of calcification of bones?
No, piezo-electric currents are important for maintenance of calcification of bones that are loaded during function, which very much includes alveolar bone, but are irrelevant for orthodontic tooth movement
What happens when light pressure is applied to a tooth for a sustained period of time?
Tooth is displaced and alveolar bone bends. The bone springs back creating pressure in the PDL and fluid is expressed from the pressure side. Tension is created on the opposite side.
The side with pressure gets less blood supply and cells are distorted, side with tension gets more blood supply and distorted PDL cells leading to chemical messengers that change the position of the tooth.
What happens if heavy force is applied to the tooth?
The blood vessels in that area are totally cut off leading to necrosis of the tissue in that area. (sterile necrosis) after 3 - 5 seconds cytokines and prostaglandins are released..
Which chemical messengers are involved in the progress of tooth movement?
cAMP is released at 4 hours increasing cell differentiation.
After some hours of compression of PDL space, there are no cells in the PDL to differentiate into the osteoclasts and osteoblasts needed for remodeling of the socket. Where are the cells going to come from?
2 answers to this question:
1) Adjacent PDL areas that are not necrotic
2) Bone marrow spaces outside the lamina dura.
If necrotic area is small adjacect areas are the major source. If not bone marrow undergoes undermining resorption.
What is undermining resorption?
Undermining resorption has that name because when there are large necrotic areas in the PDL, it is necessary for osteoclasts to resorb the lamina dura from its underside. The necrotic area sends a chemical signal to stimulate the formation of osteoclasts, but it takes a few days for this to penetrate through the lamina dura into the bone marrow. So instead of 2 days for remodeling to begin, it’s 3-5 days before an osteoclastic attack on the underside of the lamina dura begins.
When does undermining resorption remove lamina dura adjacent to compressed PDL?
7 - 14 days
What is the maximum force that should be applied to avoid undermining resorption?
~50 grams
What is the maximum force that should be applied to avoid undermining resorption when tipping the tooth?
~50 grams
How much force is required for moving the entire tooth forward, torsion, and retrusion?
Moving entire tooth = ~100 grams
Rotation within the socket = ~50 grams
Extrusion/Retrusion = ~50 grams
Torque in which root apex is moved further than the crown of the tooth = ~75 grams
Is intrusion possible?
Extremely difficult and requires an exceptionally light force ~10 grams applied down the long axis of the tooth smaller teeth would require less and larger or multirooted teeth would require more. (PDL should be compressed only at the apex of the root)
What kind of force is best for tooth movement?
Light continuous force is the best way to move teeth, because it is more biologically acceptable and achieves maximum movement.
Heavy continuous force can cause destruction of the lamina dura due to repeated occlusion of blood vessels and no opportunity for repair..
Springs show a decline in force as the tooth moves. How are springs controlled to allow treatment goals to be achieved?
Appointments are made for adjustments. Heavy forces are only acceptable if they decline all the way to zero before the next reactivation appointment.
How frequently should orthodontic appliances be adjusted?
Ideally every 4 to 6 weeks. If it is too frequent there might be heavy continuous force leading to significant tissue damage.
What kind of pain should patient feel with application of an orthodontic appliance?
There should be no immediate pain. Pain would indicate heave pressure.
Several hours later patient should feel a mild aching sensation and teeth should be sensitive to pressure so that biting something hard hurts. Pain usually lasts 2 - 4 days then disappears until the next activation of the appliance.
What effects does an orthodontic appliance have on the dental pulp?
Mild pulpitis usually results.
What effect does orthodontic force have on root structure?
In the absence of necrotic (hyalinized) PDL areas, uncalcified cementum on the root surface protects against osteoclastic attack, but cementum adjacent to a necrotic area is “marked” or stained by adjacent necrotic tissue in the PDL, and clast cells attack this area when the PDL is repaired. Cementum (and dentin if the attack penetrates all the way through the cementum) is removed, and then new cementum is formed to fill in the defect in the tooth root.
What often happens to the root apex during orthodontic movement?
Islands of root structure that are separated from the root surface can form and they can be resorbed and lost. This can often involve the apex.
As a result each year of orthodontic treatment would lead to ~1mm of root length lost.
What are the types of apical root resorption seen in orthodontic treatmetn?
3 types:
Mild to moderate generalized
Severe generalized
Severe localized
How common is severe root resorption?
Very rare, the average dentist is likely to encounter only one or two such cases in a career.
Not necessarily caused by orthodontic treatment
Which teeth are most commonly affected by root resorption?
The maxillary incisors are most commonly affected.
What should be done to ensure that the roots are not undergoing severe root resorption during orthodontic treatment?
It is good practice to take an OPG 6 - 9 months after orthodontic treatment.
What principles should be kept in mind when thinking about growth modification?
1) You can’t modify growth that isn’t happening. That means treatment at a period of rapid growth usually is the best plan, and for practical purposes, it means that the adolescent growth spurt is the preferred time for most growth modification treatment
2) When growth modification is desired, tooth movement almost always is undesirable. Correction of a malocclusion is not a primary goal of growth modification treatment, correction of an improper jaw relationship is.
3) The hours of the day are not created equal relative to growth. In fact, almost all skeletal growth (and tooth eruption) occurs in a critical time period between early evening and midnight. Whatever the growth modification device is, it’s important for it to be worn during these hours—but wearing it all the time may be neither necessary nor desirable.
What is the purpose of restraining maxillary growth?
Excessive maxillary growth contributes to both Class II and long face problems.
How is maxillary growth restrained?
Since formation of new bone as the sutures above and behind the maxilla are pulled apart by soft tissue growth is a major mechanism of growth, a force to restrain growth at the sutures ought to be effective.
A force of 250 grams per side minimum is required.
The force duration should be at least 12 hours per day.
Why is increasing forward growth of the maxilla not as successful as restraining maxillary growth?
The mid-palatal suture is an open straight-line structure in infants and young children. It shows some convolutions in childhood (early mixed dentition)and by late childhood / early adolescence the suture is so interdigitated that opening it requires micro-fractures of the bone spicules along the suture line. After the adolescent growth spurt opening the suture is possible only with surgical assistance.
Can mandibular growth be restrained?
No, for many reasons. The only successful treatment is surgery.
However if done early enough could potentially be effective
What are TADs?
the use of Class III elastics from miniplates at the base of the zygomatic arch to miniplates mesial to the mandibular canines
What is the optimal time for face mask and TAD?
Facemask: Before sutures become so locked up and interdigitated. (6 - 8 years old)
TAD = 10.5 or 11 yo
How effective are TADs?
Very variable in efficacy and long-term outcomes are yet to be understood completely.
What are the main reasons for retention after orthodontic treatment?
- The gingival and periodontal tissues require time for reorganization after the orthodontic appliances are removed;
- The teeth may be in an inherently unstable position, so that soft tissue pressures constantly produce a relapse tendency
- Changes produced by growth may alter the treatment result.
How is the PDL reorganized following orthodontic treatment?
Disruption of the collagen fiber bundles in the PDL and widening of the PDL space are necessary to allow tooth movement to occur. Even if active tooth movement stops, reorganization of the PDL does not occur as long as each tooth is tightly splinted to the one next to it by a heavy archwire. After the braces are removed, reorganization of the PDL takes 3-4 months, and only at that point does the slight mobility that is normal after treatment disappear. During this time the teeth will be unstable against occlusal and soft tissue pressures that can be resisted later. For this reason, every patient needs retainers for at least a few months
What happens to gingival fibers when moved?
Gingival fibers are stretched when a tooth is moved a considerable distance or is rotated significantly. These fibers remodel quite slowly, and are still capable of rotating a tooth back towards its original position even a year after treatment. This becomes a reason for more prolonged retention after correction of severe crowding. For a tooth or teeth that had correction of severe rotations, like the maxillary incisors shown in these images, it is wise to sever the gingival fiber network around them (which must be done carefully to maintain the interdental papillae) before the braces are removed. Without this it can be almost impossible to maintain the rotation correction.
What is long-term stability of tooth position based on?
It is based on how far the tooth has been moved not how their position after treatment compares to population average.
As a general rule (to which there are exceptions), the lower arch can be considered a foundation on which the upper arch rests, so how far the lower teeth were moved is important.
When does continued growth after orthodontic treatment create a problem?
Patients who received growth modification treatment for a skeletal problem. Growth pattern is constant.
Patients without a skeletal problem whose incisors were aligned with some expansion or who had space closure in the maxillary incisor area. A little late mandibular growth in the late teens that occurs after maxillary growth has essentially ceased is to be expected. This has the potential to create lower incisor crowding, even in an individual who never had orthodontic treatment.
What are the measures of strength of a metal wire?
4 measures:
Proportional limit reached when the wire begins to deviate from normal elastic behaviour.
Yield strength when measureable deviation is observed (when elastic limit of material is reached and begins to bend)
Ultimate tensile strength is the point where the material begins to fail
Failure point is where it breaks.
What properties would you want in an elastic material to be used as an orthodontic spring?
Enough strength that the spring didn’t get bent out of shape. That would mean that the distance along the y axis to the yield point should be as large as possible. Note that a spring still works beyond the yield point, but it doesn’t totally spring back to its original position if it’s loaded beyond its yield point.
The best possible springiness. That would mean that the slope of the line should be tilted to the right (i.e., more horizontal), so that the amount of force delivered by the spring would be as constant as possible.
The best possible range. That would mean that the distance along the x axis at the point of permanent deformation should be as large as possible.
Reslience (area under the curve of stress strain until the proportional limit)
Reasonable formability (Distance between elastic limit and the point at which the wire breaks)
How does the size of a wire affect its properties?
The size of a wire obviously would affect its basic properties. The bigger it gets, the stronger but the less springy it will be, and the less range it will have. This means that for orthodontic purposes there are a range of useful wire sizes. You don’t have to memorize those wire sizes—you can always look them up—but you do need to understand that concept. Steel is stronger than gold or titanium, so all other things being equal, smaller steel wires would be used for orthodontic purposes.
What forms do orthodontic springs come in?
Cantilever beams attached only at one end (eg finger spring from removable appliance)
Supported beams attached at both ends (Section of arch wire between brackets on adjacent teeth)
How does size of a wire affect strength?
Doubling the size of wire used to make a finger spring:
increases its strength 8 times: x * 2x3 = 8x strength
decreases its springiness 16 times: x * 2x-4 = 1/16x springiness
decreases its range by half: x * 2x = 1/2x range
How does length of a wire affect its strength?
For a cantilever beam (finger spring), doubling its length:
Cuts its strength in half: x * 2x = ½ strength
Increases its springiness 8 times: x * 2x3 = 8x springiness
Increases its range 4 times: x * 2x2 = 4x range
What kinds of materials violate hooke’s law?
Superelastic materials. These materials have different force/deflection curves from elastic materials.
Why is a superelastic spring useful in orthodontics?
It would deliver the correct force without change over a wide range.
The amount of force they deliver can be changed by releasing a wire from a bracket on a tooth, and then tying or clipping it back into the bracket. (Clinically, that’s rarely important because the plateau is nearly flat anyway, but it’s an amazing property.)
How is superelasticity possible?
Because superelastic materials undergo a phase transition with changes in temperature or internal stress. For a material with a transition temperature close to mouth temperature, stressing it by tying it to irregular teeth literally turns it into a different material than the one you picked up off the counter near the dental chair.
What material is used for superelastic springs?
nickel-titanium-alloy (nitinol)
What are the disadvantages to using superelastic wires?
Almost zero formability. The manufacturer shapes it while forming it by controlling it’s temperature. But practitioner can’t really do the same.
What does the Mc/Mf ratio tell us about the tooth’s movement?
Mc: A pure moment (MC) that would rotate the object but not displace it.
Mf: A force (grams for our purposes, newtons in scientific reports) that is delivered at a distance from the center of resistance. Its magnitude is force x distance (gm-mm).
If Mc/Mf ratio is = 0, tooth tips around the center of resistance.
if 0 < Mc/Mf < 1, Mc=Mf, tooth moves bodily
If Mc/Mf > 1 torque is created so that the root apex moves more than the crown
Why are fixed appliances used for almost all orthodontic treatment, and why is a fixed appliance almost always required if you want to do anything but tip a tooth?
Because it takes 2 points of contact against the crown to create a couple, and a finger spring from a removable appliance gives you only a single point of contact. This produces a force and its moment that causes the tooth to tip around its centre of resistance.
How is a couple produced in the facio-lingual direction and the mesiodistal direction?
A wide bracket creates a couple in the mesiodistal direction
A square wire in a rectangular bracket slot produces a couple in the facio-lingual direction
How does the width of the bracket affect the movement?
The wider the bracket the lower the force because the moment arm across the bracket is longer
What is required for sliding and why?
The wire must be undersized relative to the bracket to prevent friction and the effect of wire contacting both corners of the bracket.
if you want to slide a tooth along an archwire, a wider bracket is better, but friction is not an important factor when an undersized wire is used.
What factors reduce forces of sliding in orthodontic wires?
Friction
Contact of wire with the corners of the bracket.
A smaller wire is often used to counteract friction. This however, will not counteract the contact of the wire with the bracket
What are the 3 types of removable appliances used for modern orthodontic treatment?
Functional appliances for growth modification (for jaws not teeth)
Active plates with finger springs or screws for minor tooth movement
Clear aligners for certain types of malocclusion in adults.
Should springs be added to a functional appliance?
Adding springs to a functional appliance to move teeth is possible, but may be counter-productive. If you’re trying to produce forward growth of the mandible, reducing overjet by tipping upper incisors back and lower incisors forward decreases the amount of overjet reduction from growth that might be achieved.
What does a functional appliance do to growth of the mandible?
It accelerates it for a while but the rate slows down to allow the jaw to reach the size it would have been later in life without treatment.
The reaction of the soft tissues to holding the mandible forward is a backward force against the maxilla that tends to restrict its forward growth (in other words, a headgear effect).
How are clear aligners made?
Clear aligners are “suckdown appliances” produced by vacuum-forming clear thermoplastic sheets over a dental cast.
Who are clean aligners most optimal for?
There is no way to account for growth changes in the dental occlusion with a series of aligners, so Invisalign is just for adults or older adolescents, but the fact that a clear aligner is almost invisible when it’s in the mouth appeals to some adults.
What kinds of tooth movement can be created by invisible aligners?
Almost all types of tooth movement can be produced with clear aligners, so long as you’re willing to bond attachments to some teeth to improve the grip of the aligners. The attachments can be clear plastic, so they too are almost invisible.
How are clear aligners fabricated?
Accurate impressions of the teeth are sent to the Invisalign laboratory, and CT scans are used to develop a digital model
With input from the doctor, the company’s software is used to reposition the teeth in the digital model in a series of steps, with a new digital model for each step
The digital models for each step are used to create a series of stereolithographic casts a suckdown aligner is made to fit each of the casts
What kind of fixed appliance is commonly used in modern contemporary orthodontics?
Rectangular arch wires in a bracket with a rectangular slot (this has gone 5 major changes and changes are continuing to occur)
Why can’t normal restorative bonding material be used for bonding brackets to teeth?
The bonding is too strong and can require removal of enamel to remove the brackets.
When are bands used in modern orthodontics?
Major indication is a need for greater strength, particularly when a heavy force will be encountered.
To support a lingual arch
More generally, bands often are used on first molars and sometimes on second molars in a complete fixed appliance
What were the changes seen in the evolution of orthodontic wires?
Bonded brackets replaced bands
Different brackets used for the same wire instead of bending wires to get the right forces on the teeth. (wires are still bent but much less dramatically)
Self ligating brackets
Custom prescription brackets instead of prescribed straight wires (using 3d scan)
Lingual appliances
What are the types of self-ligating brackets?
Active clip (In an active-clip bracket, the springiness of the clip would add to the springiness of the wire, reducing the force against a tooth during initial alignment.)
Active-passive clip (active initially but then no longer forces the wire into the bracket after position of tooth is correct)
Passive (rigid) clip (has a rigid cap and depends entirely on the springiness of the wire at all stages of treatment)
How are computer fabricated arch wires made?
Custom brackets for each tooth and arch wires that are formed only to the desired arch form are one way to reduce wire bending to a minimum if not totally eliminate it. An alternative approach, now commercially available, is to use “plain vanilla” brackets with no prescription (or any prescription, so long as it is known), and then fabricate the necessary rectangular arch wires with a computer robot.
What are the major issues with using lingual appliances?
Bonding a thin bracket to the variable lingual surfaces of the teeth
Inserting a rectangular wire into a rectangular slot without great difficulty (disturbing the tonsils in doing so is not good!)
Forming the arch wire, which requires major bends to compensate for tooth thickness and careful use of tilt and torque
Computer fabrication has provided solutions to all of these major issues
What is orthodontic anchorage?
The resistance of a tooth to unwanted movement
What is the optimal force for moving a tooth?
The lightest force (and resulting pressure in the PDL) that will produce tooth movement at a near-maximum rate.
How can dental anchorage be arranged so that differential movement can occur?
that could occur only if the pressure in the PDL of the anchor teeth was less than the pressure in the PDL of the tooth you’re trying to move, and if you were on the vertical leg of the tooth movement/pressur graph
Is it good to give force above the optimal force?
No because this causes the anchor tooth to move further and anchorage control becomes impossible.
What is the simplest form of anchorage?
Reciprocal anchorage which occurs when movement of one tooth (eg maxillary central incisor) was pitted against one exactly like it (the other central incisor)
What is reinforced anchorage?
Anchorage where one side of the force exerts more pressure than the other.
What is stationary anchorage?
A strategy to increase the anchorage value is to take advantage of the different loading of the PDL for bodily movement vs. tipping. Since a force is distributed over twice as much PDL area for bodily movement as for tipping, you would move a tooth twice as much as its anchor if the anchor could only move bodily while the movement tooth was allowed to tip. Arranging the force and moments on the anchor unit so those teeth can only move bodily is called “stationary anchorage”.
What is cortical anchorage?
Teeth normally are in medullary bone, which remodels relatively quickly adjacent to a stressed PDL. Cortical bone can and does remodel, but it does so much more slowly. Cortical bone can be used as a more resistant anchor.
What does resistance to sliding lead to?
More force will be needed to retract the anterior teeth and this leads to the posterior teeth moving more anteriorly.
How is the problem of resistance to sliding overcome?
Use less anterior teeth at a time so that the forces move the anterior teeth without mosiving the posterior teeth then add the anterior tooth that has moved back to the anchorage of the posterior teeth.
The alternative is to move segments of wire with the teeth attached, so that there is no sliding of brackets along a wire (image 2). This can be accomplished with loops that form the retraction spring. Then the typical incisor retraction could be achieved in one step, pitting the entire anterior segment against the posterior anchorage. The price of resistance to sliding then becomes clearer: the difficulty of controlling anchorage as teeth slide along an archwire increases treatment time to achieve the desired result.
What is the difference between a determinate and indeterminate force system?
A determinate force system means that you can measure, and therefore determine, the force and moments felt by all teeth. An indeterminate force system means that it is impossible to know exactly what forces and moments are produced.
What makes a force system indeterminate?
The answer is that a one-couple system is determinate, while two-couple systems are indeterminate.
What’s a one-couple system?
Simply a system in which a couple is present at only one place, and a force or forces without a couple are felt elsewhere. Two-couple systems have forces and couples present in at least two places.
Which devices are commonly 1 couple systems?
Removable appliances rarely become two-couple systems—they have enough trouble producing one moment, much less two. So although they are not very efficient, you can at least know what forces and moments are being delivered.
What kind of system is a fixed orthodontic appliance?
A two-couple system is guaranteed if you place a continuous rectangular wire in more than one rectangular bracket. The rectangular wire creates a couple within the bracket in the torque plane of space if there is any twist when it is inserted
How do you set up an appliance for intrusion?
This requires two things: a long span of wire that bypasses some teeth (so that it will deliver the necessary light force), and the absence of a couple where it attaches to the incisor teeth.
Can intrusion be done with a fixed wire appliance?
No it is very difficult to make a one-couple system with a fixed appliance even if you bypass brackets.
How should ankylosed teeth be used?
If it is in a good position then it can act as perfect anchorage in the same way an implant can.
If it is in a bad position then it can prevent correct movement of other teeth leading to movement of other teeth in the wrong direction.
Would it be possible to place a skeletal anchor that, unlike a typical implant for restorative purposes, would be easily removable after its orthodontic use?
The answer to that also is yes. Temporary anchorage devices (TADs) now are coming into widespread use in orthodontics, especially in adults but also in adolescents. The lower age limit for TADs is about age 11. In children younger than that, the bone is not mature enough to maintain a bone anchor.
What are the uses for temporary skeletal anchorage?
Positioning individual teeth when no other satisfactory anchorage is available
Intrusion of posterior teeth to close an anterior open bite
Retraction and intrusion of protruding maxillary incisors
Distal movement of molars (and the entire maxillary or mandibular arch if needed)
How can retraction of maxillary incisors be done with TADs?
Using bone screws in the palate to stabilize a lingual arch that holds the posterior anchor teeth in position
Using bone screws in the alveolar process posteriorly
Using mini-plates placed at the base of the zygomatic arch, with an arm projecting into the vestibule
Where should TAD screws be placed ideally?
In attached gingiva (not alveolar mucosa)
When is intrusion treatment indicated?
To correct an anterior open bite as they are usually caused by posterior overeruption.
