Level III Unit A Learning Objectives - partial fill

Unit A

I - Orthodontic Diagnosis and Treatment Planning

Recognize and evaluate skeletal and dental relationships in all three planes of space

Two main methods of evaluating skeletal and dental relationships : facial form and cephalometric analysis

Facial Form Analysis

01 - Facial Form Analysis 10 6 Orthodontic Diagnosis L4 Level II Unit B Level II Unit B Summary—integrated > Dentofacial Proportions

Cephalometric Analysis

02 - Cephalometric Tracing Techniques 03 - Cephalometric Superimposition 10 6 Orthodontic Diagnosis L4 Level II Unit B Level II Unit B Summary—integrated > Cephalometric Analysis

1. Vertical Plane of Space

Facial Form

• Vertical plane of space can be analyzed in the frontal and profile facial form analysis
• Frontal view
  • Facial Thirds
• Profile view
  • Reassess facial thirds
  • Estimate the mandibular plane angle
    • steep is a long face/open-bite tendency, flat is a short face/deep-bite tendency

Cephalometric vertical proportions Level II Unit B Summary—integrated > Evaluate jaw relationships to the cranial base and each other.

Five main horizontal reference lines

1. S-N, the inclination of the anterior cranial base
2. True horizontal, the visual axis which is drawn perpendicular to the true vertical through the lower border of the orbit (Or)
3. ANS-PNS, the palatal plane
4. Functional occlusal plane, drawn along the occluding surfaces of the posterior teeth
5. Go-Gn, the mandibular plane

In a well-proportioned face the horizontal anatomic planes tend to converge toward a single point.

• If the planes intersect relatively close to the face and diverge quickly as they pass anteriorly the facial proportions are long anteriorly and short posteriorly this is known as : *skeletal open bite *
• If the planes are nearly parallel so that they converge far behind the face and diverge only slowly as they pass anteriorly, there is a skeletal predisposition toward anterior deep bite and the condition is termed *skeletal deep bite *

2. Anterior - Posterior Plane

Facial Form

• A-P relations are obtained from the lateral view facial analysis

• To evaluate draw two lines:

  1. Dropped from bridge of the nose to base of upper lip
  2. Extending from base of upper lip to the point of the chin
  • A convexity in the lines indicates class II jaw relationships

    • 10 degrees , so 190 degrees or more 10 6 Orthodontic Diagnosis

  • A concavity indicates Class III jaw relationships

    • 10 degrees so 170 degrees or less

  • If they are straight it indicates a Class I jaw relationship ideal

**Facial form - Lip and Incisor Prominence

Observe the upper lip relative to a true vertical line through the concavity at the base of the upper lip (soft tissue point A).

• Observe the lower lip relative to a true vertical line through the concavity between the lip and chin (soft tissue point B).
• If a lip is significantly forward of its reference line → protrusive; if behind → retrusive.

When is incisor protrusion "excessive"?

Dental protrusion is judged excessive only when the lips are simultaneously prominent (forward of soft tissue A/B), incompetent (separated at rest by >3–4 mm), and strained on closure.[^1] Lips that touch at rest, or that are separated but not forward of A/B, do not indicate excessive protrusion.

Cephalometric A-P

• Key cephalometric diagnostics for evaluating AP are
  • N - A
    • 0-4 mm normal
  • N - B
    • (-4 - 0 mm normal)
  • ANB angle
    • <1 is class III
    • 1 -5 degrees is class I

    • 5 degrees is class II

  • SNA angle for maxilla in relation to cranial base
    • < 77 is retrognatic
    • 77-85 is orthognaticc (normal)

    • 85 is prognatic

  • SNB angle for mandible in relation to cranial base
    • < 75 is retrognathic
    • 75 - 85 is orthognathic

    • 85 is prognathic

  • Additional measurements include
    • U1 - SN angle
    • L1 - Go-G angle
    • Interincisal angle
    • Po - N perpendicular

Cast/dentition

• Angle classification to describe molar relationship with extended version used to describe dental and skeletal relationships source

3. Transverse plane of space

**Facial Form

• Facial fifths give transverse facial proportions
• want to also look for posterior cross bites

Recognize and quantify the patient’s arch length status

L4 Level II Unit B Workbook Level II Unit B Summary—integrated > Space Analysis 01 - Essentials of Orthodontic Diagnosis > Cast Analysis

• use a tanaka Johnston space analysis form to see the extent of potential crowding
• If a posterior crossbite exists, measuring arch widths can provide insight into whether the upper arch is unusually narrow because of a skeletal problem or a dental problem , or the lower arch is unusually wide

Evaluate the skeletal and arch length considerations, interactions and appropriateness of treatment or non-tretment

02 - Concepts of Orthodontic Treatment Planning

To be completed

Nott enough info in orthoinstruction part 1 or 2?

Recommend treatment or referral of specific problems based upon case evaluation

02 - Concepts of Orthodontic Treatment Planning

To be completed

Nott enough info in orthoinstruction part 2?

II - Biologic Response to Orthodontic force

03 - Biologic Response to Orthodontic Force

Describe the histologic/cellular/vascular response of the supporting structures to force applied to teeth

• The PDL is composoed of a fluid component and of a cellular component
  • the fluid component of the PDL functions as a shock absorber, allowing the tooth to move in the same direction relative to the alvoelar bone. This is because the fluid is non-compressible, thus upon biting the alveolar bone actually bends
  • As fluid is squeezed out, the cellular elements feel pressure, increasing pressure results in the feeling of pain
  • Image 2

Light force application 03 - Biologic Response to Orthodontic Force > Pressure-Tension Effects

• Light pressure application has a different physiological response than heavy
  • 1. Mechanical distortion of cells in the periodontal ligament, which causes release of the contents of some cells
  • 2. A decrease in blood flow in the PDL on the side opposite the direction of force application (where the pdl is compressed) and an increase in blood flow on the other side, where the pdl is unter tension
    • this leads to a change in oxygen and carbon dioxide levles in the PDL
    • Both effects lead to the relase of chemical messengers from affected cells after a few hours, cellular differnetation begins within the PDL, eventually resulting in tooth movement and remodeling of the bony socket
• As Pressure increases, the PDL is increasingly compressed and if the pressure is high enough the blood flow is **cut off **
  • this results in necrosis of the tissue in that area

Sustained heavy Pressure

• sustained heavy pressure results in undermining resorption
• Cells come from two different sources (as local cells become necrotic due to force)
  • From adjacent PDL areas that are not necrotic
  • From bone marrow spaces outside the lamina dura

Discuss the role of biologic electricity in maintenance and turnover of alveolar bone

Bone bending and Electic current

• Rhythmic loading to the alveolar bone (in the form of mastication) produces a piezo-electric current. This stimulates bone deposition.
• When teeth are lost the alveolar bone no generates piezo-electric currents, resulting in decalcification and resorption
• Note that piezo-electric currents are irrelevant for orthodontic tooth movement

Describe the relationship of orthodontic force levels to anchorage

03 - Biologic Response to Orthodontic Force > Force Distribution and Types of Tooth Movement 05 - Orthodontic Anchorage and Controlled Tooth Movement Forms of tooth movement:

• Tipping
• Bodily movement
• Rotation, Extrusion and Torque
• Intrusion

Tipping

• tipping of a tooth occurs when a single force is applied to the crown of a tooth
• Ideal force for tipping is 50g
• Bodily Movement
• Bodily movment is root and crown movmeent in the same direction
• bodily movmenet needs about twice as much force as tipping movements as the area of PDL compression is double
• Ideal force for bodily movement is 100g
• 

Extrusion and rotation

• require the same amount of force as tipping : 50g
• This is due to the fact that root are irregularly shaped and not conical, thus as soo nas a tooth responds to extrusion or rotation it will also tip

Torque

• The type of tooth movement in which the root apex is moved further than the crown of the tooth
• An intermediate force of 75 grams is best for torque

Intrusion

• Successful intrusion is only possible with exceptionally light force
• the optimum force for intrusion is 10 grams (slightly less for small teeth and slightly more for larger/multi-rooted teeth )

Duration of force

• light continuous force is good
• Best timeline for force duration is betweeen 4-8 hours each day
• orthodontic appliances decay in force with movement, thus they need to be re-activated at various orthodontic appointments

III - Mechanical Principles in Controlling Orthodontic Force

04 - Mechanical Principles in Controlling Orthodontic Force

Define and apply the principles of anchorage in appliance design to control and minimize unwanted tooth movement

Elastic Materials

If you want to move a tooth, it’s necessary to use a spring that places a light but prolonged force against it

**Ideal Properties for elastic materials in orthodontics **

• Enough strength that the spring doesn’t get bent out of shape
• The amount of force deliver should be as constant as possible (line tilted to the right in a force/deflection plot)
• The best possible range --- the distance along the x axis at the point of permanent deformation should be as large as possible
• Resilience: the area under the curve up to the proportional limit.
  • resilience gives a good estimate of other mechanical properties and is often used when advertising orthodontic materials **Forms of orthodontic springs **
• orthodontic springs come in two forms
  1. cantilever beams
     • example: fingr spring from a removable appliance
     • cantilever beas are attached only at one end
  2. Supported beams
     • supported beams are attached at both ends

Laws of elasticity in cantilever beams: 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

Laws of elasticity, effects of doubling beam length in all cantilever spring types

• 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

Application of the laws

• You should choose a large wire size to gain strength
• Make the loop of wire longer to gain rainge and obtain springiness

Image 1: To improve its springiness and increase its range, this spring has been lengthened by placing a loop in the wire.	Image 2: The loops in this steel arch wire also add springiness where it is needed in the relatively stiff steel wire.

Describe and recognize different types of removable orthodontic appliances in the following categories

04 - Mechanical Principles in Controlling Orthodontic Force > Contemporary Removable Appliances

A Functional (Orthopaedic) appliances

Goal: To guide the growth of the jaws

• usually used to encourage forward growth of the mandible in children with a class II problem due to mandibular deficiency
• They are usually removable but can be fixed in place
• For class II it brings the mandibular condyles down and forward

Removable Functional appliances

• Activator
• Twin-block appliance
• Frankel appliance
• Hybrid functional

Image 1, Original activator: The activator caused the child to bite forward, and incorporated a spring to keep it from fitting tightly so that the child would have to keep biting to hold it in place—thus “activating” the muscles.	Image 2, Twin-block appliance: The twin block has separate upper and lower components, with a ramp on the lower to bring the mandible forward. A screw for maxillary expansion usually is included in the upper component.
Image 3, Frankel appliance: The Frankel appliance is constructed to hold the lips and cheeks away from the dentition, and incorporates acrylic behind the lower incisors to produce a forward bite.	Image 4, MARA appliance: Fixed functional appliances can’t be removed by the patient. The MARA appliance (right) forces the patient to bite forward in order to bring the teeth together. It is less bulky than the older Herbst design (left) that holds the mandible forward all the time, but it may not be as effective.
Image 5, Hybrid functional: For a patient with a jaw asymmetry, a hybrid appliance like this can be helpful. It has a bionator-type bite block on one side, Frankel-type shields on the other side, and is made using a mandibular position that improves or corrects the asymmetry.

Functional Appliance Effects

• Mainly work to speed up mandibular growth rather than enlarge it.
• The main way they work is to actually restrict maxillary growth
  • Holding the mandible forward is a bacwards force agasint the maxila that tneds to restrict its forward growth
• There also a force to move the lower incisors forward and upper incisors back

B Crozat

C Hawley type

D Clear aligner Therapy

• aka invisalign
• Suckdown appliances
• Used as retainers or as a way to move teeth in adults

Describe and make correct appliance designs of the active Hawley type with specific recommendations for these components

A Active

B Retention

C connector

D reactive or anchorage

Select the correct wire size for active and retentive elements of active Hawley type appliances

Define and explain the biomechanical principles that pertain to orthodontics, specifically the meaning of terms such as “force”, “Moment”, “Fulcrum”, “center of rotation”, and “anchorage” as applied to biomechanics

04 - Mechanical Principles in Controlling Orthodontic Force > Forces and Moments in Tooth Movement

Anchorage: resistance to unwanted tooth movement Moment: A force that is delivered at a distance from the center of resistance

• the center of resistance of a tooth is the middle part of the root, so whenever we apply force onto the crown we also create a “moment of force”
• This moment displaces the crown while tipping the tooth so that it rotates around the center of resistance
• This causes the PDL to be compressed maximally at the root apex on one side and at the height of the alveolar crest on the other side

Pure moment (MC): two equal forces in opposite directions will rotate an obect but won’t displace it

Cancelling out bodily movment Moment of force

For bodily movement the force is 100 gm. If you say the center of rotation is 15 mm from the bracket then you have a 1500 gm-mm MF. Thus the opposite force (MC to cancel MF) would have to be 1500 gm-mm

Defining tooth movement as a ratio of Mc/MF

Image 1: When MC/ MF = 0 (i.e., there is no MC), the tooth tips around its center of resistance, so that the center of rotation and the center of resistance are the same.	Image 2: When MC/ MF is > 0 but < 1, the tooth tips but the center of rotation is moved away from the center of resistance
Image 3: When MC/ MF is 1, the center of rotation is displaced infinitely far away from the center of resistance, and the tooth moves bodily (translates).	Image 4: When MC/ MF is > 1, the root apex moves more than the crown, and the center of rotation is displaced in the other direction

To do anything but tip a tooth you have to have a fixed attachment and 2 points of contact

Demonstrate the relationship between wire size, strength, stiffness and the force produced for a given deflection

Explain the difference between tipping and bodily tooth movement, and how an applied force can produce either

IV Orthodontic anchorage and Controlled tooth Movement

Describe the reaction of a tooth to a single force placed against the crown

Tipping

Describe the reaction of a tooth to a two-force system placed against the as a function of the moment-to-force ratio

Indicate the changes in orthodontic forces and moments needed for successful movement of a tooth that has lost alveolar bone support (as from previous periodontal disease )

05 - Orthodontic Anchorage and Controlled Tooth Movement > Cortical Anchorage

Describe the adaptations in the contemporary edgewise appliance to reduce in-out (first order) bends in arch wires

04 - Mechanical Principles in Controlling Orthodontic Force > Prescription Brackets the Straight-Wire Appliance Varying thickness of brackets

• Different brackets with varying thickness made for different teeth can help reduce first order bends

Describe the adaptations in the contemporary edgewise appliance to reduce angulation (second order) bends in arch wires

changing orientation of bracket slot

• Placing the slot perpendicular to the long axises of the tooth and not parallel to the incisal edge helps reduce 2nd order bends

Describe the adaptations in the contemporary edgewise appliance to reduce torque (third order) bends in rectangular arch wires

changing facio-lingual orientation of the bracket slot to match the desired root orientatoin

• this reduces the need for third order (twist/torque bends)