Ortho level 3 unit A module 1 2 3

Question 1

How is a problem list for orthodontics made?

Answer 1

Interview, clinical examination, analysis of records

Then a systematic description is used to classify the problem

Question 2

What is the purpose of the interview?

Answer 2

To answer 4 major questions:

1. Why is this patient seeking treatment, and why now?
2. How did things get to be the way they are?
3. What, if anything, is likely to change in the near future? (progression of medical condition, and probable growth changes)
4. What do the patient and parents expect as a result?

Question 3

What are the goals of a clinical examination?

Answer 3

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

Question 4

How is the face examined during a clinical examination?

Answer 4

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.

Question 5

How is the health of tissues examined?

Answer 5

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.

Question 6

How is jaw function evaluated?

Answer 6

Check for malocclusion

Check for mandibular movements

Question 7

Which radiograph is always indicated for orthodontic treatment?

Answer 7

OPG

Question 8

Which orthodontic records are essential for orthodontic diagnosis?

Answer 8

Dental casts

Intraoral and facial photographs

Lateral cephalometric radiographs/tracing

Question 9

Why are dental casts used?

Answer 9

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

Question 10

Why are facial and intraoral photographs used?

Answer 10

To allow evaluation of change.

To identify soft tissue problems. (eg lack of gingival attachment)

Question 11

What is the function of a lateral cephalometric radiograph in orthodontic diagnosis?

Answer 11

To allow evaluation of response to treatment and to allow greater precision in evaluating jaw and tooth-jaw relationships.

Question 12

Is there any advantage in having the dental casts mounted on an articulator?

Answer 12

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.

Question 13

Is a cephalometric radiograph necessary for orthodontic diagnosis?

Answer 13

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.

Question 14

What is the indication for a P-A cephalometric radiograph in addition to the lateral ceph?

Answer 14

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.

Question 15

How is 3D imaging done?

Answer 15

3D photographs or 3D video (expensive and not as practical)

MRI (no ionizing radiation and valuable for TMJ evalutation)

CT

Question 16

What are the disadvantages of CBCT?

Answer 16

Additional expertise needed to evaluate pathological changes revealed by these images.

Radiation exposure. (lower than conventional CT but still quite high)

Question 17

When is CBCT indicated?

Answer 17

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.

Question 18

What do diagnostic records of orthodontic patients consist of?

Answer 18

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

Question 19

What information do photographs and digital videos provide to orthodontists?

Answer 19

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.

Question 20

What relationships does a lateral cephalometric radiograph help us understand?

Answer 20

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

Question 21

How should a problem list be formed prior to orthodontic treatment?

Answer 21

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

Question 22

What are the 5 steps of the systematic description approach created by the Ackerman-Proffit classification?

Answer 22

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

Question 23

What question is asked in diagnosis?

Answer 23

What are the problems?

The answer is a description of the problems and their cause.

Question 24

What is the question asked for treatment planning?

Answer 24

What can be done about the problems?

Question 25

What are the steps of treatment planning?

Answer 25

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

Question 26

How should the treatment planning process be approached?

Answer 26

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

Question 27

What causes the shock absorber effect seen when a tooth is subject to a heavy load?

Answer 27

The fluid in the PDL space

Question 28

Why is it still possible to feel pain if you bite something very hard?

Answer 28

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.

Question 29

Why doesn’t the alveolar bone immediately disappear after a tooth extraction?

Answer 29

We know now that bone bending is necessary to maintain normal calcification and remodeling.

Question 30

How does bone bending generate an electric current?

Answer 30

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.

Question 31

Is the piezoelectric effect important for maintenance of calcification of bones?

Answer 31

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

Question 32

What happens when light pressure is applied to a tooth for a sustained period of time?

Answer 32

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.

Question 33

What happens if heavy force is applied to the tooth?

Answer 33

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..

Question 34

Which chemical messengers are involved in the progress of tooth movement?

Answer 34

cAMP is released at 4 hours increasing cell differentiation.

Question 35

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?

Answer 35

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.

Question 36

What is undermining resorption?

Answer 36

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.

Question 37

When does undermining resorption remove lamina dura adjacent to compressed PDL?

Answer 37

7 - 14 days

Question 38

What is the maximum force that should be applied to avoid undermining resorption?

Answer 38

~50 grams

Question 39

What is the maximum force that should be applied to avoid undermining resorption when tipping the tooth?

Answer 39

~50 grams

Question 40

How much force is required for moving the entire tooth forward, torsion, and retrusion?

Answer 40

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

Question 41

Is intrusion possible?

Answer 41

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)

Question 42

What kind of force is best for tooth movement?

Answer 42

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..

Question 43

Springs show a decline in force as the tooth moves. How are springs controlled to allow treatment goals to be achieved?

Answer 43

Appointments are made for adjustments. Heavy forces are only acceptable if they decline all the way to zero before the next reactivation appointment.

Question 44

How frequently should orthodontic appliances be adjusted?

Answer 44

Ideally every 4 to 6 weeks. If it is too frequent there might be heavy continuous force leading to significant tissue damage.

Question 45

What kind of pain should patient feel with application of an orthodontic appliance?

Answer 45

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.

Question 46

What effects does an orthodontic appliance have on the dental pulp?

Answer 46

Mild pulpitis usually results.

Question 47

What effect does orthodontic force have on root structure?

Answer 47

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.

Question 48

What often happens to the root apex during orthodontic movement?

Answer 48

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.

Question 49

What are the types of apical root resorption seen in orthodontic treatmetn?

Answer 49

3 types:

Mild to moderate generalized

Severe generalized

Severe localized

Question 50

How common is severe root resorption?

Answer 50

Very rare, the average dentist is likely to encounter only one or two such cases in a career.

Not necessarily caused by orthodontic treatment

Question 51

Which teeth are most commonly affected by root resorption?

Answer 51

The maxillary incisors are most commonly affected.

Question 52

What should be done to ensure that the roots are not undergoing severe root resorption during orthodontic treatment?

Answer 52

It is good practice to take an OPG 6 - 9 months after orthodontic treatment.

Question 53

What principles should be kept in mind when thinking about growth modification?

Answer 53

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.

Question 54

What is the purpose of restraining maxillary growth?

Answer 54

Excessive maxillary growth contributes to both Class II and long face problems.

Question 55

How is maxillary growth restrained?

Answer 55

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.

Question 56

Why is increasing forward growth of the maxilla not as successful as restraining maxillary growth?

Answer 56

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.

Question 57

Can mandibular growth be restrained?

Answer 57

No, for many reasons. The only successful treatment is surgery.

However if done early enough could potentially be effective

Question 58

What are TADs?

Answer 58

the use of Class III elastics from miniplates at the base of the zygomatic arch to miniplates mesial to the mandibular canines

Question 59

What is the optimal time for face mask and TAD?

Answer 59

Facemask: Before sutures become so locked up and interdigitated. (6 - 8 years old)

TAD = 10.5 or 11 yo

Question 60

How effective are TADs?

Answer 60

Very variable in efficacy and long-term outcomes are yet to be understood completely.

Question 61

What are the main reasons for retention after orthodontic treatment?

Answer 61

1. The gingival and periodontal tissues require time for reorganization after the orthodontic appliances are removed;
2. The teeth may be in an inherently unstable position, so that soft tissue pressures constantly produce a relapse tendency
3. Changes produced by growth may alter the treatment result.

Question 62

How is the PDL reorganized following orthodontic treatment?

Answer 62

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

Question 63

What happens to gingival fibers when moved?

Answer 63

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.

Question 64

What is long-term stability of tooth position based on?

Answer 64

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.

Question 65

When does continued growth after orthodontic treatment create a problem?

Answer 65

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.

Question 66

What are the measures of strength of a metal wire?

Answer 66

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.

Question 67

What properties would you want in an elastic material to be used as an orthodontic spring?

Answer 67

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)

Question 68

How does the size of a wire affect its properties?

Answer 68

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.

Question 69

What forms do orthodontic springs come in?

Answer 69

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)

Question 70

How does size of a wire affect strength?

Answer 70

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

Question 71

How does length of a wire affect its strength?

Answer 71

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

Question 72

What kinds of materials violate hooke’s law?

Answer 72

Superelastic materials. These materials have different force/deflection curves from elastic materials.

Question 73

Why is a superelastic spring useful in orthodontics?

Answer 73

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.)

Question 74

How is superelasticity possible?

Answer 74

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.

Question 75

What material is used for superelastic springs?

Answer 75

nickel-titanium-alloy (nitinol)

Question 76

What are the disadvantages to using superelastic wires?

Answer 76

Almost zero formability. The manufacturer shapes it while forming it by controlling it’s temperature. But practitioner can’t really do the same.

Question 77

What does the Mc/Mf ratio tell us about the tooth’s movement?

Answer 77

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

Question 78

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?

Answer 78

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.

Question 79

How is a couple produced in the facio-lingual direction and the mesiodistal direction?

Answer 79

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

Question 80

How does the width of the bracket affect the movement?

Answer 80

The wider the bracket the lower the force because the moment arm across the bracket is longer

Question 81

What is required for sliding and why?

Answer 81

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.

Question 82

What factors reduce forces of sliding in orthodontic wires?

Answer 82

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

Question 83

What are the 3 types of removable appliances used for modern orthodontic treatment?

Answer 83

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.

Question 84

Should springs be added to a functional appliance?

Answer 84

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.

Question 85

What does a functional appliance do to growth of the mandible?

Answer 85

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).

Question 86

How are clear aligners made?

Answer 86

Clear aligners are “suckdown appliances” produced by vacuum-forming clear thermoplastic sheets over a dental cast.

Question 87

Who are clean aligners most optimal for?

Answer 87

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.

Question 88

What kinds of tooth movement can be created by invisible aligners?

Answer 88

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.

Question 89

How are clear aligners fabricated?

Answer 89

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

Question 90

What kind of fixed appliance is commonly used in modern contemporary orthodontics?

Answer 90

Rectangular arch wires in a bracket with a rectangular slot (this has gone 5 major changes and changes are continuing to occur)

Question 91

Why can’t normal restorative bonding material be used for bonding brackets to teeth?

Answer 91

The bonding is too strong and can require removal of enamel to remove the brackets.

Question 92

When are bands used in modern orthodontics?

Answer 92

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

Question 93

What were the changes seen in the evolution of orthodontic wires?

Answer 93

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

Question 94

What are the types of self-ligating brackets?

Answer 94

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)

Question 95

How are computer fabricated arch wires made?

Answer 95

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.

Question 96

What are the major issues with using lingual appliances?

Answer 96

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

Question 97

What is orthodontic anchorage?

Answer 97

The resistance of a tooth to unwanted movement

Question 98

What is the optimal force for moving a tooth?

Answer 98

The lightest force (and resulting pressure in the PDL) that will produce tooth movement at a near-maximum rate.

Question 99

How can dental anchorage be arranged so that differential movement can occur?

Answer 99

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

Question 100

Is it good to give force above the optimal force?

Answer 100

No because this causes the anchor tooth to move further and anchorage control becomes impossible.

Question 101

What is the simplest form of anchorage?

Answer 101

Reciprocal anchorage which occurs when movement of one tooth (eg maxillary central incisor) was pitted against one exactly like it (the other central incisor)

Question 102

What is reinforced anchorage?

Answer 102

Anchorage where one side of the force exerts more pressure than the other.

Question 103

What is stationary anchorage?

Answer 103

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”.

Question 104

What is cortical anchorage?

Answer 104

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.

Question 105

What does resistance to sliding lead to?

Answer 105

More force will be needed to retract the anterior teeth and this leads to the posterior teeth moving more anteriorly.

Question 106

How is the problem of resistance to sliding overcome?

Answer 106

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.

Question 107

What is the difference between a determinate and indeterminate force system?

Answer 107

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.

Question 108

What makes a force system indeterminate?

Answer 108

The answer is that a one-couple system is determinate, while two-couple systems are indeterminate.

Question 109

What’s a one-couple system?

Answer 109

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.

Question 110

Which devices are commonly 1 couple systems?

Answer 110

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.

Question 111

What kind of system is a fixed orthodontic appliance?

Answer 111

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

Question 112

How do you set up an appliance for intrusion?

Answer 112

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.

Question 113

Can intrusion be done with a fixed wire appliance?

Answer 113

No it is very difficult to make a one-couple system with a fixed appliance even if you bypass brackets.

Question 114

How should ankylosed teeth be used?

Answer 114

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.

Question 115

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?

Answer 115

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.

Question 116

What are the uses for temporary skeletal anchorage?

Answer 116

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)

Question 117

How can retraction of maxillary incisors be done with TADs?

Answer 117

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

Question 118

Where should TAD screws be placed ideally?

Answer 118

In attached gingiva (not alveolar mucosa)

Question 119

When is intrusion treatment indicated?

Answer 119

To correct an anterior open bite as they are usually caused by posterior overeruption.