# **DMD Level 3 Unit A: Biomechanics and Preclinical Orthodontics** ## Orthodontic Seminar * Part 1. Orthodontic Diagnosis & Treatment Planning * Part 2. Biologic Response to Orthodontic Force * Part 3. Mechanical Principles in Controlling Orthodontic Force * Part 4. Orthodontic Anchorage and Controlled Tooth Movement Autosave DMD Level 3 - Unit A - Biomechanics and Preclinical Orthodontics THE UNIVERSITY OF WESTERN AUSTRALIA  Orthodontic Seminar - Part 1. Orthodontic Diagnosis & Treatment Planning - Part 2. Biologic Response to Orthodontic Force - Part 3. Mechanical Principles in Controlling Orthodontic Force - Part 4. Orthodontic Anchorage and Controlled Tooth Movement Labelled diagram: A schematic illustration of a tooth model with a bracket and archwire, demonstrating the mechanical setup for orthodontic force application. **DMD Level 3** ### **Unit A: Biomechanics and Preclinical Orthodontics** # Orthodontic Seminar * Part 1. Orthodontic Diagnosis & Treatment Planning * Part 2. Biologic Response to Orthodontic Force * Part 3. Mechanical Principles in Controlling Orthodontic Force * Part 4. Orthodontic Anchorage and Controlled Tooth Movement Orthodontic Seminar - Part 1. Orthodontic Diagnosis & Treatment Planning - Part 2. Biologic Response to Orthodontic Force - Part 3. Mechanical Principles in Controlling Orthodontic Force - Part 4. Orthodontic Anchorage and Controlled Tooth Movement <div style="width:100%;text-align:center;font-family:LAT2;font-size:20px;color:gold;background-color:red;padding:20px;margin:10px auto;"><strong>Previous Review Seminars</strong></div> # Part 1. Orthodontic Diagnosis & Treatment Planning ## Be sure that you are able to: 1. Recognize and evaluate skeletal and dental relationships in all three planes of space. 2. Recognize and quantify the patient's arch length status. 3. Evaluate the skeletal and arch length considerations, interactions and appropriateness of treatment or non-treatment. 4. Recommend treatment or referral of specific problems based upon case evaluation. IMG: UNIVERSITY OF WESTERN AUSTRALIA LOGO Part 1. Orthodontic Diagnosis & Treatment Planning ### Be sure that you are able to: 1. Recognize and evaluate skeletal and dental relationships in all three planes of space. 2. Recognize and quantify the patient's arch length status. 3. Evaluate the skeletal and arch length considerations, interactions and appropriateness of treatment or non-treatment. 4. Recommend treatment or referral of specific problems based upon case evaluation. The University of Western Australia 1. Recognize and evaluate skeletal and dental relationships in all three planes of space. **Ackerman-Proffit Classification**  1. Recognize and evaluate skeletal and dental relationships in all three planes of space. #### Ackerman-Proffit Classification Labelled diagram: # ALIGNMENT/ASYMMETRY **THE UNIVERSITY OF WESTERN AUSTRALIA**   #### Alignment/Asymmetry A composite dental cast image showing an occlusal view of the upper arch and a frontal view of the maxillary and mandibular teeth in occlusion. A clinical document titled 'Mixed dentition space analysis form' from The University of Western Australia, featuring two diagrams: an upper arch and a lower arch. These illustrations depict dental arches with labeled tooth positions (e.g., A, B, C) to assist in analyzing the alignment and spacing of teeth during mixed dentition. ESTHETIC IMPACT OF MALOCLUSION THE UNIVERSITY OF WESTERN AUSTRALIA ANNIE C. 21Y 6M INITIAL  #### Esthetic Impact of Malocclusion Annie C. 21Y 6M Initial Clinical photo: A composite image displaying three views of a young female patient (Annie C., 21Y 6M) to illustrate the aesthetic impact of malocclusion. The figure includes a frontal view, a left profile view showing facial convexity, and a smiling frontal view. TRANSVERSE RELATIONSHIPS THE UNIVERSITY OF WESTERN AUSTRALIA 6    #### Transverse Relationships 6 A labelled diagram illustrating the measurement of palatal width, showing a top view of dental arches with red arrows indicating two distinct measurements: AB across the upper arch and CD across the lower arch. Labelled diagram illustrating the relationship between palatal width (AB) and intermolar width (CD) in two dental arch configurations. The top portion shows a wider arch where the palatal width exceeds the intermolar width, while the bottom portion depicts a narrower arch where these measurements are more closely aligned. A labelled diagram illustrating transverse relationships between the head and shoulders, featuring a lateral profile of a human figure. Red arrows and lines measure specific distances: 'AB' indicates the width across the upper skull or hairline, while 'CD' measures the distance between the ear tragus. **A-P RELATIONSHIPS** THE UNIVERSITY OF WESTERN AUSTRALIA Class I skeletal pattern Class II skeletal pattern Class III skeletal pattern 7 #### A-P Relationships - Class I skeletal pattern - Class II skeletal pattern - Class III skeletal pattern 7 **VERTICAL RELATIONSHIPS** THE UNIVERSITY OF WESTERN AUSTRALIA **ANNE C.** **12Y 6M INITIAL** **8**   #### Vertical Relationships Anne C. 12Y 6M Initial 8 Lateral view dental cast showing the vertical relationship between the maxillary and mandibular arches in a Class II malocclusion, characterized by the lower jaw being positioned posteriorly relative to the upper jaw. A lateral cephalometric radiograph displaying the skeletal and dental structures of a patient named Anne C. at age 12 years and 6 months (initial). The image includes superimposed horizontal and vertical reference lines used for orthodontic analysis. # Part 2. Biologic Response to Orthodontic Force Be sure that you are able to: 1. Describe the histologic/cellular/vascular response of the supporting structures to force applied to teeth. 2. Discuss the role of biologic electricity in maintenance and turnover of alveolar bone. 3. Describe the relationship of orthodontic force levels to anchorage. Be sure that you are able to: 1. Describe the histologic/cellular/vascular response of the supporting structures to force applied to teeth. 2. Discuss the role of biologic electricity in maintenance and turnover of alveolar bone. 3. Describe the relationship of orthodontic force levels to anchorage. **Biologic Response to Orthodontic Force** 1. Describe the histologic/cellular/vascular response of the supporting structures to force applied to teeth. 1. Describe the histologic/cellular/vascular response of the supporting structures to force applied to teeth. **TIME SEQUENCE -LIGHT** **CONTINUOUS PRESSURE** 1. **MILLISECONDS** - FLUID PRESSURE UP PIEZO-ELECTRIC EFFECT 2. **SECONDS** - FLUID PRESSURE BALANCED 3. **MINUTES** - BLOOD FLOW AFFECTED 4. **HOURS** - CELLULAR DIFFERENTIATION BEGINS 5. **DAYS** - APPPOSITION/RESORPTION TOOTH MOVEMENT **Time Sequence - Light Continuous Pressure** 1. **Milliseconds** - Fluid pressure up, piezo-electric effect 2. **Seconds** - Fluid pressure balanced 3. **Minutes** - Blood flow affected 4. **Hours** - Cellular differentiation begins 5. **Days** - Apposition/resorption, tooth movement **** | **FORCE AGAINST TOOTH** | | :--- | | **BLOOD FLOW CHANGE** | | MECHANICAL DEFORMATION? | | PROSTOGLANDIN RELEASE | | --- | | **STIMULUS TO FORM** | | OSTEODlasts/OSTEOBLASTS | | --- | | **REMODELLING** | | Force Against Tooth | | :--- | | Blood Flow Change | | Mechanical Deformation? | | Prostaglandin Release | | --- | | Stimulus to Form | | Osteoclasts/Osteoblasts | | --- | | Remodelling | 1. Describe the histologic/cellular/vascular response of the supporting structures to force applied to teeth. THE UNIVERSITY OF WESTERN AUSTRALIA 13     1. Describe the histologic/cellular/vascular response of the supporting structures to force applied to teeth. Labelled diagram: This figure illustrates the histologic response of periodontal supporting structures to force applied to teeth, depicting a cross-section of alveolar bone with adjacent lamina dura and tooth roots. Labelled diagram: This illustration depicts the histologic response of periodontal tissues to force, showing wavy collagen fibers on the left and a vertical array of cells (likely osteoblasts or cementoblasts) on the right. It demonstrates how supporting structures react to applied forces through changes in tissue alignment. Labelled diagram: This illustration depicts the histologic response of periodontal tissues to force, showing blood vessels within connective tissue fibers adjacent to a bone structure. Labelled diagram: This figure illustrates the histologic response of supporting structures to force, specifically showing a periodontal ligament (pink wavy fibers) and bone (yellow matrix with vertical osteocytes). It depicts how the fibers remodel or reorient around the tooth surface under stress. | Heavy Pressure | → | Total shut-off of blood flow | → | Sterile Necrosis = hyalinization | | :--- | :--- | :--- | :--- | :--- | | **14** | | Heavy Pressure | → | Total shut-off of blood flow | → | Sterile Necrosis = hyalinization |  Labelled diagram: A cross-sectional view of a vessel or duct demonstrating concentric intimal thickening, where the lumen is significantly narrowed by a layered, fibrous plaque. <blue>**Cells from trabeculae**</blue>  Cells from trabeculae A labeled diagram showing a microscopic view of bone trabeculae. A blue arrow points to specific areas, identifying them as 'Cells from trabeculae' and noting the presence of 'PMN Neutrophils'. Cells from **trabeulae** **Undermining resorption** **17**  Cells from trabeculae Undermining resorption Labelled diagram showing the process of bone resorption, featuring a blue arrow pointing to 'Cells from trabeculae' and red text indicating 'Undermining resorption'. THE PIEZO-ELECTRIC EFFECT Changing the shape of a crystalline material causes an electrical current flow  **The Piezo-Electric Effect** Changing the shape of a crystalline material causes an electrical current flow A photograph of a large, translucent quartz crystal cluster with pointed terminations and visible internal inclusions. Handling 3D Bone Mineralization ... ### 2. Re-establish established bone mineralization - IF CB - -> Trigger PTP/Pt & pCa signals - -> Stop Mesenchymal Stem Cell (MSC) proliferation ```| 2D X-ray OSSIFICATION Center (m. M./mm.) + RhGM - Encloth by bone mineral (Ca2+) ``` #### 3. Re-establish established bone mineralization (Sustained) - IF CB - -> Trigger PTP/Pt & pCa signals - -> Maintain MSC replication - -> *** Maintain mineralization if 1st rate (Crisis avoided) *** **Figure: Piezoelectricity in bone. 29** PIEZO-ELECTRICITY IN BONE **SOURCE** - Bone Mineral - Collagen **EFFECT:** - Rhythmic pulses of electric pulses during function (chewing, walking etc) - Important in order to maintain mineralisation 20  Handling 3D Bone Mineralization ### 2. Re-establish established bone mineralization - IF CB - -> Trigger PTP/Pt & pCa signals - -> Stop Mesenchymal Stem Cell (MSC) proliferation ``` 2D X-ray OSSIFICATION Center (m. M./mm.) + RhGM - Encloth by bone mineral (Ca2+) ``` #### 3. Re-establish established bone mineralization (Sustained) - IF CB - -> Trigger PTP/Pt & pCa signals - -> Maintain MSC replication - -> Maintain mineralization if 1st rate (Crisis avoided) **Figure: Piezoelectricity in bone.** **Piezo-Electricity in Bone** **Source:** - Bone Mineral - Collagen **Effect:** - Rhythmic pulses of electric pulses during function (chewing, walking etc) - Important in order to maintain mineralization A diagram illustrating the concept of piezoelectricity in bone, showing a central structure emitting rhythmic electric pulses. The visual form is a labeled diagram. <img>Graph of charge over time<img>  A line chart plotting 'charge' on the y-axis against 'seconds' on the x-axis. The graph shows a step function starting at zero, spiking sharply upwards at the 1-second mark (labeled 'on'), decaying exponentially back towards zero, then dropping sharply downwards at the 2-second mark (labeled 'off') before recovering. # Time course of events: Heavy biting pressure ### **Milliseconds** Fluid incompressible in periodontal ligament ### **Seconds** Fluid leaking out ### <Minute> Fluid gone: ***Pain*** **Time course of events: Heavy biting pressure** ### Milliseconds Fluid incompressible in periodontal ligament ### Seconds Fluid leaking out ### Minutes Fluid gone: Pain <u>Biologic Response to Orthodontic Force</u> 3. Describe the relationship of orthodontic force levels to anchorage. 23 3. Describe the relationship of orthodontic force levels to anchorage. The image displays a chart of tooth root cross-sections (dental anatomy diagrams) with red numerical values indicating relative anchorage values. Relative Anchorage values 450 533 254 282 194 230 450 475 240 270 200 170 25  Relative Anchorage values 450 533 254 282 194 230 450 475 240 270 200 170 A chart displaying various tooth root cross-sections with red numerical values indicating relative anchorage. The diagram illustrates dental anatomy, showing the structural differences between molar and premolar roots. **Types of anchorage** Simple Reciprocal Reinforced Stationary 26  - Simple - Reciprocal - Reinforced - Stationary **Simple anchorage** 27 **Stationary anchorage** **30**   A labeled diagram illustrating tooth movement in response to light force, featuring a line graph showing 'Post' and 'Ant' positions relative to 'Tooth Movement'. Amount of Tooth Movement Post Ant Heavier force Pressure 32  Amount of Tooth Movement Post Ant Heavier force Pressure Labelled diagram: **2. Describe and recognize different types of removable orthodontic appliances in the following categories:** **(a)** functional appliances; **(b)** Crozat; **(c)** Hawley type; and **(d)** Clear Aligner Therapy. a b c d 34     2. Describe and recognize different types of removable orthodontic appliances in the following categories: - (a) functional appliances - (b) Crozat - (c) Hawley type - (d) Clear Aligner Therapy Labelled diagram: A transparent green removable orthodontic appliance, likely a Hawley retainer or functional appliance, featuring an acrylic plate and metal wires. Clinical photo of an intraoral view showing a removable orthodontic appliance, specifically a Hawley type retainer with a wire framework and acrylic baseplate. Clinical photo: A close-up view of a patient placing a clear, custom-fitted orthodontic aligner over their lower teeth. The image illustrates the application method for Clear Aligner Therapy. 3. Describe and make correct appliance designs of the active Hawley type with specific recommendations for these components: (a) active; (b) retention; (c) connector; and (d) reactive or anchorage. 4. Select the correct wire size for active and retentive elements of active Hawley type appliances. • Lab Bow 0.7—0.8mm • Adams molars 0.7 mm premolars 0.6 mm • Finger spring guarded 0.6mm unguarded 0.7mm • Ball clasp 0.7 mm • C clasp 0.7mm 35  3. 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 4. Select the correct wire size for active and retentive elements of active Hawley type appliances. - Lab Bow: 0.7–0.8 mm - Adams molars: 0.7 mm, premolars: 0.6 mm - Finger spring guarded: 0.6 mm, unguarded: 0.7 mm - Ball clasp: 0.7 mm - C clasp: 0.7 mm Clinical photo of an active Hawley type orthodontic appliance, specifically highlighting the labial bow component. The image shows a yellow resin baseplate with metal wire components, including clasps engaging the molar teeth and a central section likely representing the active or connector element. 5. 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. THE UNIVERSITY OF WESTERN AUSTRALIA ### Centre of Resistance - To complete the description of a force - need to define it in relation to the centre or resistance of the tooth - Burstone –from apex usually 2/3 root and just above furcation on molars 37  5. 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. #### Centre of Resistance - To complete the description of a force, need to define it in relation to the centre of resistance of the tooth. - Burstone – from apex usually 2/3 root and just above furcation on molars. Labelled diagram: A schematic illustration of a molar tooth demonstrating the location of the center of resistance (marked by red dots). The figure depicts both a mesial and distal view, showing the placement of orthodontic brackets and archwires relative to the tooth's root structure. 5. 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. • Moment = Tendency to rotate ✹ 38  5. 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. - Moment = Tendency to rotate THE UNIVERSITY OF WESTERN AUSTRALIA • Couple = Two equal and opposite, non colinear, parallel forces – Pure rotation around center of rotation (CR) - Couple = Two equal and opposite, non colinear, parallel forces - Pure rotation around center of rotation (CR) # How do we apply couples? THE UNIVERSITY OF WESTERN AUSTRALIA 42 #### How do we apply couples? **MOMENT = F x d g.mm** 43 **MOMENT = F x d g.mm** **Uncontrolled Tipping** <div style="border:1px solid black; padding:10px;"> <img src="placeholder_teh_university06.jpg" alt="Dental diagram illustrating 'Uncontrolled Tipping' with tooth model and directional arrows" style="width:100%; height:auto;"> </div> **Uncontrolled Tipping** = Controlled Tipping THE UNIVERSITY OF WESTERN AUSTRALIA 47 = Controlled Tipping The University of WESTERN AUSTRALIA The text on the page is best understood as labels for a diagram illustrating "Controlled Tipping". It involves arrows and symbols indicating forces and movement on a tooth, which is typical of a figure. <!-- Image text --> The text on the page is best understood as labels for a diagram illustrating "Controlled Tipping". It involves arrows and symbols indicating forces and movement on a tooth, which is typical of a figure. Translation THE UNIVERSITY OF WESTERN AUSTRALIA Translation 6. Demonstrate the relationship between wire size, strength, stiffness and the force produced for a given deflection. - Effect of changing wire size - If you **double** the **diameter** of the wire - 8 times as **STRONG** - 16 times as **STIFF** - Will bend ½ as Far  6. Demonstrate the relationship between wire size, strength, stiffness and the force produced for a given deflection. #### Effect of changing wire size - If you **double** the **diameter** of the wire: - 8 times as **STRONG** - 16 times as **STIFF** - Will bend ½ as Far A labelled diagram showing two blue cylinders of different diameters to illustrate the effect of changing wire size. The top cylinder is thinner, and a downward arrow points to a thicker bottom cylinder, visually representing an increase in diameter. 6. Demonstrate the relationship between wire size, strength, stiffness and the force produced for a given deflection. ### The University of WESTERN AUSTRALIA - Effect of changing wire length - If you make a **finger spring twice as long** - 1/2 as **STRONG** - 8 times as springy - Will bend 4 times as Far 6. Demonstrate the relationship between wire size, strength, stiffness and the force produced for a given deflection. #### Effect of changing wire length - If you make a **finger spring twice as long**: - 1/2 as **STRONG** - 8 times as springy - Will bend 4 times as Far 6. Demonstrate the relationship between wire size, strength, stiffness and the force produced for a given deflection. - Effect of changing wire size - If you **double** the **diameter** of the wire - 8 times as STRONG - 16 times as STIFF - Will bend ½ as Far  6. Demonstrate the relationship between wire size, strength, stiffness and the force produced for a given deflection. #### Effect of changing wire size - If you **double** the **diameter** of the wire: - 8 times as STRONG - 16 times as STIFF - Will bend ½ as Far Labelled diagram: This figure illustrates the effect of changing wire size, showing a transition from a thin wire to a thicker wire via a downward arrow. It visually supports the slide's concept that doubling the diameter results in a wire that is 8 times stronger and 16 times stiffer. 6. Demonstrate the relationship between wire size, strength, stiffness and the force produced for a given deflection. - Effect of changing wire length - If you make a **finger spring** twice as long - 1/2 as STRONG - 8 times as springy - Will bend 4 times as Far  6. Demonstrate the relationship between wire size, strength, stiffness and the force produced for a given deflection. #### Effect of changing wire length - If you make a **finger spring** twice as long: - 1/2 as STRONG - 8 times as springy - Will bend 4 times as Far **Part 4. Orthodontic Anchorage and Controlled Tooth Movement** Be sure that you are able to: 1. Describe the reaction of a tooth to a single force placed against the crown. 2. Describe the reaction of a tooth to a two-force system placed against the crown a function of the moment-to-force ratio. 3. 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). 4. Describe the adaptations in the contemporary edgewise appliance to reduce in-out (first order) bends in arch wires. 5. Describe the adaptations in the contemporary edgewise appliance to reduce angulation (second order) bends in arch wires. 6. Describe the adaptations in the contemporary edgewise appliance to reduce torque (third order) bends in rectangular arch wires. Be sure that you are able to: 1. Describe the reaction of a tooth to a single force placed against the crown. 2. Describe the reaction of a tooth to a two-force system placed against the crown as a function of the moment-to-force ratio. 3. 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). 4. Describe the adaptations in the contemporary edgewise appliance to reduce in-out (first order) bends in arch wires. 5. Describe the adaptations in the contemporary edgewise appliance to reduce angulation (second order) bends in arch wires. 6. Describe the adaptations in the contemporary edgewise appliance to reduce torque (third order) bends in rectangular arch wires. # OSCAR Clinical Reasoning exercise OSCAR Clinical Reasoning exercise Design of the Straightwire Appliance THE UNIVERSITY OF WESTERN AUSTRALIA 4. Describe the adaptations in the contemporary edgewise appliance to reduce in-out (first order) bends in arch wires. 5. Describe the adaptations in the contemporary edgewise appliance to reduce angulation (second order) bends in arch wires. 6. Describe the adaptations in the contemporary edgewise appliance to reduce torque (third order) bends in rectangular arch wires.  Design of the Straightwire Appliance 4. Describe the adaptations in the contemporary edgewise appliance to reduce in-out (first order) bends in arch wires. 5. Describe the adaptations in the contemporary edgewise appliance to reduce angulation (second order) bends in arch wires. 6. Describe the adaptations in the contemporary edgewise appliance to reduce torque (third order) bends in rectangular arch wires. This is a frontal radiograph illustrating the design of a straight-edgewise appliance. It shows the most anterior tilted mesial at the extreme vertical edge of the base, demonstrating how the bracket slot is angled to align with the tooth's long axis. 4. Describe the adaptations in the contemporary edgewise appliance to reduce in-out (first order) bends in arch wires. **Precise In/Out Measurements**   4. Describe the adaptations in the contemporary edgewise appliance to reduce in-out (first order) bends in arch wires. **Precise In/Out Measurements** A labelled diagram of a dental arch wire showing the specific in-out bend dimensions (ranging from 1.6 mm to 2.9 mm) required at various points along the curve. A labelled diagram illustrating the specific in-out bend dimensions (measured in millimeters) required for a contemporary edgewise archwire. The figure displays a series of arrows indicating the precise curvature at different points along the wire, with measurements ranging from 1.2 mm to 2.5 mm. 4. Describe the adaptations in the contemporary edgewise appliance to reduce in-out (first order) bends in arch wires. THE UNIVERSITY OF WESTERN AUSTRALIA 56  4. Describe the adaptations in the contemporary edgewise appliance to reduce in-out (first order) bends in arch wires. Labelled diagram: This figure illustrates the concept of 'In/Out' bends in a 7x7 archwire, demonstrating how an archwire is bent inward at the posterior segments and outward at the anterior segments to adapt to the dental arch form. 5. Describe the adaptations in the contemporary edgewise appliance to reduce angulation (second order) bends in arch wires. Standard Angulations 57 <!-- CAPTIONS_JSON_START --> {"BOX_A": ""} <!-- CAPTIONS_JSON_END -->  5. Describe the adaptations in the contemporary edgewise appliance to reduce angulation (second order) bends in arch wires. **Standard Angulations** Labelled diagram: This figure displays a series of tooth models illustrating standard angulations for arch wires. Vertical lines intersect the crown and root axes, with text annotations indicating specific degrees (2° and 5°) relative to a horizontal baseline marked as 90°. ### INSTRUCTIONS: E2 Describe the Adams (cannot describe all limitations and strengths are to be recorded in separate column).  #### Instructions: E2 Describe the Adams (cannot describe all limitations and strengths are to be recorded in separate column). A labelled diagram illustrating the 'Standard Inclination' of teeth relative to a horizontal line. The image displays two rows of teeth with varying degrees of angulation, marked with specific negative and positive angles (e.g., -9°, -7°, +3°) to demonstrate deviations from vertical alignment. ## Case: Transverse Discrepancy and Crossbite Classification ### Question **Scenario:** Evaluating transverse relationships and differentiating between dental and skeletal crossbites using study models and illustrations. **What's shown:** Illustrations comparing a normal palatal width with normal molar inclination, a normal palatal width with excessively lingually tilted upper molars, and a narrow, athrasic upper arch with buccally tilted upper molars. **Consider:** How to differentiate between a dental crossbite and a skeletal crossbite based on palatal width and the compensatory tilting of the upper molars. ### Answer **Observations:** - Normal palatal width with lingually tilted upper molars indicates a dental crossbite. - A narrow, athrasic upper arch with buccally tilted upper molars indicates a skeletal crossbite. - In severe skeletal crossbites, the upper arch may be completely lingual to the lower arch without the ability to compensate via tilting. **Reasoning:** The lecturer explains that if the palatal width (AB distance) is normal but the molars are tilted, the issue is dental. If the palate is narrow (athrasic), the molars may try to compensate by tilting buccally, but the underlying issue is skeletal. **Takeaway:** Palatal width is the key diagnostic feature to differentiate between dental and skeletal crossbites, as dental crossbites occur with normal palatal width while skeletal crossbites involve a narrow upper arch. ## Case: Histological Response to Heavy Orthodontic Forces ### Question **Scenario:** Examining the biological response of the periodontal ligament (PDL) and alveolar bone to orthodontic forces. **What's shown:** An illustration and a histological display using India ink showing the PDL being completely compressed and blood vessels shut off. **Consider:** What happens to the PDL and the subsequent bone turnover when heavy forces completely block the blood supply. ### Answer **Observations:** - The PDL becomes completely squished, leading to sterile necrosis (hyalinization) due to the shut-off of blood vessels. - Differentiated cells for bone turnover can no longer come from the PDL and must come from the bone itself. - This results in undermining resorption, which significantly delays orthodontic tooth movement. **Reasoning:** The lecturer walks through the histological image, explaining that heavy forces cause ischemia and sterile necrosis in the PDL. Because the PDL is necrotic, bone resorption must occur via undermining from the adjacent bone marrow spaces, taking much more time. **Takeaway:** Heavy orthodontic forces can cause PDL necrosis and hyalinization, leading to undermining resorption and delayed tooth movement; therefore, light forces should be used to maintain PDL vitality. ## Case: Anchorage Worked Example for Space Closure ### Question **Scenario:** Planning orthodontic mechanics for space closure following extractions. **What's shown:** A clinical scenario where premolars are extracted to retract the canines and incisors, utilizing the 5th, 6th, and 7th teeth as the anchorage unit. **Consider:** How to quantify anchorage and manage the anchorage unit to achieve the desired retraction of the anterior teeth. ### Answer **Observations:** - The anchorage unit consists of the 5, 6, and 7 teeth, combining their root surface areas to increase resistance to movement. - The desired movement is the retraction of the canines and incisors (the movement unit). - The goal is to minimize the movement of the anchorage unit while maximizing the movement of the anterior teeth. **Reasoning:** The lecturer explains that anchorage is quantified by the root surface area within the bone. By combining multiple posterior teeth, the anchorage unit's resistance is significantly increased, ensuring that the extraction space is closed primarily by the retraction of the anterior segment. **Takeaway:** Anchorage is determined by the total root surface area of the teeth used to resist movement; combining multiple teeth reinforces the anchorage unit to prevent unwanted posterior tooth movement during anterior retraction. ## Case: Transverse Discrepancy and Crossbite Classification ### Question **Scenario:** Evaluating transverse relationships and differentiating between dental and skeletal crossbites using study models and illustrations. **What's shown:** Illustrations comparing a normal palatal width with normal molar inclination, a normal palatal width with excessively lingually tilted upper molars, and a narrow, athrasic upper arch with buccally tilted upper molars. **Consider:** How to differentiate between a dental crossbite and a skeletal crossbite based on palatal width and the compensatory tilting of the upper molars.   ### Answer **Observations:** - Normal palatal width with lingually tilted upper molars indicates a dental crossbite. - A narrow, athrasic upper arch with buccally tilted upper molars indicates a skeletal crossbite. - In severe skeletal crossbites, the upper arch may be completely lingual to the lower arch without the ability to compensate via tilting. **Reasoning:** The lecturer explains that if the palatal width (AB distance) is normal but the molars are tilted, the issue is dental. If the palate is narrow (athrasic), the molars may try to compensate by tilting buccally, but the underlying issue is skeletal. **Takeaway:** Palatal width is the key diagnostic feature to differentiate between dental and skeletal crossbites, as dental crossbites occur with normal palatal width while skeletal crossbites involve a narrow upper arch. ## Case: Histological Response to Heavy Orthodontic Forces ### Question **Scenario:** Examining the biological response of the periodontal ligament (PDL) and alveolar bone to orthodontic forces. **What's shown:** An illustration and a histological display using India ink showing the PDL being completely compressed and blood vessels shut off. **Consider:** What happens to the PDL and the subsequent bone turnover when heavy forces completely block the blood supply.    ### Answer **Observations:** - The PDL becomes completely squished, leading to sterile necrosis (hyalinization) due to the shut-off of blood vessels. - Differentiated cells for bone turnover can no longer come from the PDL and must come from the bone itself. - This results in undermining resorption, which significantly delays orthodontic tooth movement. **Reasoning:** The lecturer walks through the histological image, explaining that heavy forces cause ischemia and sterile necrosis in the PDL. Because the PDL is necrotic, bone resorption must occur via undermining from the adjacent bone marrow spaces, taking much more time. **Takeaway:** Heavy orthodontic forces can cause PDL necrosis and hyalinization, leading to undermining resorption and delayed tooth movement; therefore, light forces should be used to maintain PDL vitality. ## Case: Anchorage Worked Example for Space Closure ### Question **Scenario:** Planning orthodontic mechanics for space closure following extractions. **What's shown:** A clinical scenario where premolars are extracted to retract the canines and incisors, utilizing the 5th, 6th, and 7th teeth as the anchorage unit. **Consider:** How to quantify anchorage and manage the anchorage unit to achieve the desired retraction of the anterior teeth.  ### Answer **Observations:** - The anchorage unit consists of the 5, 6, and 7 teeth, combining their root surface areas to increase resistance to movement. - The desired movement is the retraction of the canines and incisors (the movement unit). - The goal is to minimize the movement of the anchorage unit while maximizing the movement of the anterior teeth. **Reasoning:** The lecturer explains that anchorage is quantified by the root surface area within the bone. By combining multiple posterior teeth, the anchorage unit's resistance is significantly increased, ensuring that the extraction space is closed primarily by the retraction of the anterior segment. **Takeaway:** Anchorage is determined by the total root surface area of the teeth used to resist movement; combining multiple teeth reinforces the anchorage unit to prevent unwanted posterior tooth movement during anterior retraction. Case: Transverse Discrepancy and Crossbite Classification Labelled diagram illustrating the relationship between palatal width (AB) and intermolar width (CD) in two dental arch configurations. The top portion shows a wider arch where the palatal width exceeds the intermolar width, while the bottom portion depicts a narrower arch where these measurements are more closely aligned. Lateral view dental cast showing the vertical relationship between the maxillary and mandibular arches in a Class II malocclusion, characterized by the lower jaw being positioned posteriorly relative to the upper jaw. Labelled diagram: This illustration depicts the histologic response of periodontal tissues to force, showing blood vessels within connective tissue fibers adjacent to a bone structure. Labelled diagram: This figure illustrates the histologic response of supporting structures to force, specifically showing a periodontal ligament (pink wavy fibers) and bone (yellow matrix with vertical osteocytes). It depicts how the fibers remodel or reorient around the tooth surface under stress. Labelled diagram: This illustration depicts the histologic response of periodontal tissues to force, showing wavy collagen fibers on the left and a vertical array of cells (likely osteoblasts or cementoblasts) on the right. It demonstrates how supporting structures react to applied forces through changes in tissue alignment. A chart displaying various tooth root cross-sections with red numerical values indicating relative anchorage. The diagram illustrates dental anatomy, showing the structural differences between molar and premolar roots. ## Case: Identification of Orthodontic Appliances ### Question **Scenario:** Identifying various orthodontic appliances from visual examples. **What's shown:** Images of a functional appliance, an older crossbite appliance with an omega loop and spring, a Hawley-type removable appliance with Adams clasps and a spring, and a clear aligner. **Consider:** Identifying the specific appliances shown and their primary functions or mechanisms of action. ### Answer **Observations:** - The first appliance is a functional appliance. - The second is an older crossbite appliance featuring an omega loop for expansion and a spring for anterior correction. - The third is a Hawley-type removable appliance with Adams clasps for retention and a spring to correct an anterior crossbite. - The fourth is a clear aligner. **Reasoning:** The lecturer points out the distinct features of each appliance, such as the omega loop and spring on the older crossbite appliance, and the specific clasps and springs on the Hawley appliance, linking them to their historical or current clinical uses. **Takeaway:** Recognizing the structural components of removable and functional appliances, such as omega loops, Adams clasps, and springs, helps in understanding their specific clinical applications for crossbite correction and expansion. ## Case: Removable Appliance Design for Anterior Crossbite ### Question **Scenario:** Designing a removable appliance to correct an anterior crossbite of a central incisor. **What's shown:** An image of a removable appliance featuring an Adams clasp, a ball clasp, a Hawley clasp, and a finger spring underneath the acrylic plate. **Consider:** How the components of the appliance provide retention and how the spring is activated to apply force to the incisor. ### Answer **Observations:** - Retention is achieved using an Adams clasp, a ball clasp, and a Hawley clasp. - A finger spring made of 0.6 or 0.7 mm stainless steel wire is located underneath the acrylic plate. - The spring is activated by pulling the wire down towards the cervical part of the incisor. **Reasoning:** The lecturer describes the design, noting that stainless steel is used instead of NiTi because it can be bent to form the spring loops. The clasps balance the retention against the force of the spring to keep the appliance in place during function. **Takeaway:** In removable appliance design, adequate retention via clasps must be balanced against the active force of the spring, and stainless steel wire is preferred for springs because it can be bent to incorporate loops for increased resilience. ## Case: Biomechanics of Tooth Movement and Tipping ### Question **Scenario:** Analyzing the biomechanics of applying an orthodontic force to a bracket. **What's shown:** A diagram illustrating the center of resistance, the point of force application at the bracket, and the distance between them, demonstrating uncontrolled tipping versus controlled tipping with a rectangular wire. **Consider:** How the distance from the center of resistance creates a moment, and how to achieve controlled tipping or bodily movement using rectangular wires. ### Answer **Observations:** - Applying a force at the bracket, which is distant from the center of resistance, creates a moment that results in uncontrolled tipping. - Using a rectangular wire in a rectangular bracket slot produces an opposing moment (torsion) that counteracts the tipping. - This interaction allows for controlled tipping or bodily movement without needing to apply force directly at the center of resistance. **Reasoning:** The lecturer explains that the moment is the product of the force and the distance to the center of resistance. By engaging a rectangular wire, a counter-moment is generated, neutralizing the tendency for uncontrolled tipping and allowing the tooth to move in a controlled manner. **Takeaway:** Because orthodontic brackets are placed at a distance from the center of resistance, applying a single force causes uncontrolled tipping; engaging a rectangular wire creates a counter-moment that allows for controlled tipping or bodily movement. ## Case: Identification of Orthodontic Appliances ### Question **Scenario:** Identifying various orthodontic appliances from visual examples. **What's shown:** Images of a functional appliance, an older crossbite appliance with an omega loop and spring, a Hawley-type removable appliance with Adams clasps and a spring, and a clear aligner. **Consider:** Identifying the specific appliances shown and their primary functions or mechanisms of action.    ### Answer **Observations:** - The first appliance is a functional appliance. - The second is an older crossbite appliance featuring an omega loop for expansion and a spring for anterior correction. - The third is a Hawley-type removable appliance with Adams clasps for retention and a spring to correct an anterior crossbite. - The fourth is a clear aligner. **Reasoning:** The lecturer points out the distinct features of each appliance, such as the omega loop and spring on the older crossbite appliance, and the specific clasps and springs on the Hawley appliance, linking them to their historical or current clinical uses. **Takeaway:** Recognizing the structural components of removable and functional appliances, such as omega loops, Adams clasps, and springs, helps in understanding their specific clinical applications for crossbite correction and expansion. ## Case: Removable Appliance Design for Anterior Crossbite ### Question **Scenario:** Designing a removable appliance to correct an anterior crossbite of a central incisor. **What's shown:** An image of a removable appliance featuring an Adams clasp, a ball clasp, a Hawley clasp, and a finger spring underneath the acrylic plate. **Consider:** How the components of the appliance provide retention and how the spring is activated to apply force to the incisor.  ### Answer **Observations:** - Retention is achieved using an Adams clasp, a ball clasp, and a Hawley clasp. - A finger spring made of 0.6 or 0.7 mm stainless steel wire is located underneath the acrylic plate. - The spring is activated by pulling the wire down towards the cervical part of the incisor. **Reasoning:** The lecturer describes the design, noting that stainless steel is used instead of NiTi because it can be bent to form the spring loops. The clasps balance the retention against the force of the spring to keep the appliance in place during function. **Takeaway:** In removable appliance design, adequate retention via clasps must be balanced against the active force of the spring, and stainless steel wire is preferred for springs because it can be bent to incorporate loops for increased resilience. ## Case: Biomechanics of Tooth Movement and Tipping ### Question **Scenario:** Analyzing the biomechanics of applying an orthodontic force to a bracket. **What's shown:** A diagram illustrating the center of resistance, the point of force application at the bracket, and the distance between them, demonstrating uncontrolled tipping versus controlled tipping with a rectangular wire. **Consider:** How the distance from the center of resistance creates a moment, and how to achieve controlled tipping or bodily movement using rectangular wires.    ### Answer **Observations:** - Applying a force at the bracket, which is distant from the center of resistance, creates a moment that results in uncontrolled tipping. - Using a rectangular wire in a rectangular bracket slot produces an opposing moment (torsion) that counteracts the tipping. - This interaction allows for controlled tipping or bodily movement without needing to apply force directly at the center of resistance. **Reasoning:** The lecturer explains that the moment is the product of the force and the distance to the center of resistance. By engaging a rectangular wire, a counter-moment is generated, neutralizing the tendency for uncontrolled tipping and allowing the tooth to move in a controlled manner. **Takeaway:** Because orthodontic brackets are placed at a distance from the center of resistance, applying a single force causes uncontrolled tipping; engaging a rectangular wire creates a counter-moment that allows for controlled tipping or bodily movement. Case: Identification of Orthodontic Appliances Clinical photo of an intraoral view showing a removable orthodontic appliance, specifically a Hawley type retainer with a wire framework and acrylic baseplate. Labelled diagram: A transparent green removable orthodontic appliance, likely a Hawley retainer or functional appliance, featuring an acrylic plate and metal wires. Clinical photo: A close-up view of a patient placing a clear, custom-fitted orthodontic aligner over their lower teeth. The image illustrates the application method for Clear Aligner Therapy. Clinical photo of an active Hawley type orthodontic appliance, specifically highlighting the labial bow component. The image shows a yellow resin baseplate with metal wire components, including clasps engaging the molar teeth and a central section likely representing the active or connector element. Labelled diagram: A schematic illustration of a molar tooth demonstrating the location of the center of resistance (marked by red dots). The figure depicts both a mesial and distal view, showing the placement of orthodontic brackets and archwires relative to the tooth's root structure. # How do we apply couples? THE UNIVERSITY OF WESTERN AUSTRALIA 42 Tooth diagram with orthodontic bracket A labelled diagram showing two blue cylinders of different diameters to illustrate the effect of changing wire size. The top cylinder is thinner, and a downward arrow points to a thicker bottom cylinder, visually representing an increase in diameter. ## Case: Biomechanics in Periodontally Compromised Patients ### Question **Scenario:** Planning orthodontic mechanics for a patient with periodontal bone loss. **What's shown:** A clinical scenario describing a periodontally compromised patient where alveolar bone loss has occurred. **Consider:** How periodontal bone loss affects the center of resistance and the resulting orthodontic forces required for tooth movement. ### Answer **Observations:** - Bone loss moves the center of resistance apically, closer to the apex of the root. - This increases the distance between the bracket (where force is applied) and the center of resistance. - The increased distance results in a larger moment (couple) for the same amount of force. **Reasoning:** The lecturer explains that because the center of resistance shifts apically due to bone loss, the moment arm increases. To prevent excessive tipping and manage the larger moment, significantly lighter forces must be used compared to a patient with normal periodontal support. **Takeaway:** In periodontally compromised patients, apical bone loss shifts the center of resistance apically, increasing the moment arm; therefore, much lighter orthodontic forces are required to achieve controlled tooth movement. ## Case: Straight Wire Appliance Bracket Compensations ### Question **Scenario:** Understanding the built-in compensations in a straight wire bracket system. **What's shown:** An illustration showing the base of a bracket or tube with specific angulations and compensations for first, second, and third-order bends. **Consider:** How the bracket base incorporates first, second, and third-order bends to eliminate the need for wire bending during initial alignment. ### Answer **Observations:** - First-order bends (buccal-lingual offsets) are built into the base of the bracket or tube. - Second-order bends (mesio-distal inclinations/angulations) are incorporated into the bracket design. - Third-order bends (torque/rotations) are built into the angle of the bracket slot itself. **Reasoning:** The lecturer points out that the "straight wire" concept relies on these pre-built compensations in the bracket base and slot angulation. This eliminates the need for the clinician to place complex first, second, and third-order bends in the archwire during the initial stages of treatment. **Takeaway:** The straight wire appliance system incorporates first, second, and third-order bends directly into the bracket base and slot angulation, simplifying archwire bending and streamlining the alignment process. ## Case: Biomechanics in Periodontally Compromised Patients ### Question **Scenario:** Planning orthodontic mechanics for a patient with periodontal bone loss. **What's shown:** A clinical scenario describing a periodontally compromised patient where alveolar bone loss has occurred. **Consider:** How periodontal bone loss affects the center of resistance and the resulting orthodontic forces required for tooth movement. ### Answer **Observations:** - Bone loss moves the center of resistance apically, closer to the apex of the root. - This increases the distance between the bracket (where force is applied) and the center of resistance. - The increased distance results in a larger moment (couple) for the same amount of force. **Reasoning:** The lecturer explains that because the center of resistance shifts apically due to bone loss, the moment arm increases. To prevent excessive tipping and manage the larger moment, significantly lighter forces must be used compared to a patient with normal periodontal support. **Takeaway:** In periodontally compromised patients, apical bone loss shifts the center of resistance apically, increasing the moment arm; therefore, much lighter orthodontic forces are required to achieve controlled tooth movement. ## Case: Straight Wire Appliance Bracket Compensations ### Question **Scenario:** Understanding the built-in compensations in a straight wire bracket system. **What's shown:** An illustration showing the base of a bracket or tube with specific angulations and compensations for first, second, and third-order bends. **Consider:** How the bracket base incorporates first, second, and third-order bends to eliminate the need for wire bending during initial alignment.    ### Answer **Observations:** - First-order bends (buccal-lingual offsets) are built into the base of the bracket or tube. - Second-order bends (mesio-distal inclinations/angulations) are incorporated into the bracket design. - Third-order bends (torque/rotations) are built into the angle of the bracket slot itself. **Reasoning:** The lecturer points out that the "straight wire" concept relies on these pre-built compensations in the bracket base and slot angulation. This eliminates the need for the clinician to place complex first, second, and third-order bends in the archwire during the initial stages of treatment. **Takeaway:** The straight wire appliance system incorporates first, second, and third-order bends directly into the bracket base and slot angulation, simplifying archwire bending and streamlining the alignment process. Case: Biomechanics in Periodontally Compromised Patients Frontal radiograph of a straight-emgwise appliance, showing the most anterior tilted mesial at the extreme.vertical edge of the base This is a frontal radiograph illustrating the design of a straight-edgewise appliance. It shows the most anterior tilted mesial at the extreme vertical edge of the base, demonstrating how the bracket slot is angled to align with the tooth's long axis. In/Out 7x7 Labelled diagram: This figure illustrates the concept of 'In/Out' bends in a 7x7 archwire, demonstrating how an archwire is bent inward at the posterior segments and outward at the anterior segments to adapt to the dental arch form. Labelled diagram: This figure displays a series of tooth models illustrating standard angulations for arch wires. Vertical lines intersect the crown and root axes, with text annotations indicating specific degrees (2° and 5°) relative to a horizontal baseline marked as 90°. 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