Biomechanics 3(how to achieve various tooth movements)
TLDRIn this informative presentation, Dr. Fong Gum discusses the intricacies of orthodontic treatment, focusing on the calculation and application of couple moments for controlled tooth movement. He explains the formula for calculating moment of couple and how it differs from single force calculations. Dr. Gum further delves into achieving various tooth movements beyond tipping by managing the ratio between applied force and moment of couple. He illustrates this with examples from clinical cases, emphasizing the importance of using the correct wire type and force magnitude for desired tooth movement outcomes, such as translation and torque. The presentation is a valuable resource for understanding the principles behind effective orthodontic force application.
Takeaways
- 📚 The formula for calculating the moment of couple is force multiplied by the distance between the point of force application.
- 🔄 The moment of couple is generated when the force applied on a tooth results in bodily movement rather than tipping.
- 📈 The ratio between the applied force and the moment of couple can dictate the type of tooth movement, such as tipping, translation, or torque.
- 🦷 In a class 2 Division one case with planned extraction of upper first premolars, managing the ratio between the moment of applied force and moment of köppen is crucial for achieving desired tooth movements.
- 🏋️♂️ A 1:10 ratio of force to moment of couple is required for bodily movement of the tooth, as exemplified by canine retraction using a power chain.
- 🔄 When a single force is applied without couple, the tooth will tip until it contacts the bracket at two points.
- 🔧 The use of a rectangular cross-sectional wire in conjunction with rectangular brackets can help generate couple and control root movement.
- 🌀 Twisting a rectangular wire can create two-point contacts and generate couple, leading to controlled tipping and better root movement control.
- 📊 The amount of force required to achieve a specific moment of couple depends on the bracket slot height and the desired force-to-couple ratio.
- 🦷 For pure torque, where the center of resistance and center of rotation coincide, the force-to-couple ratio should be greater than 1:12.
Q & A
What is the formula to calculate the moment of couple in orthodontics?
-The formula to calculate the moment of couple is force multiplied by the distance between the point of force application. If the width of the bracket is 5 millimeters, then the distance is also 5 millimeters. For example, if a force of 50 grams is applied, the moment of couple would be 250 gram millimeters.
Is the formula for calculating the moment of couple different from the one used for a single force?
-No, the formula is the same. The difference lies in how you apply it. For a single force, you calculate the moment at the force arm. For a couple, you calculate moments of both forces separately and then add them up to get the total moment of couple.
How can different types of tooth movements be achieved apart from tipping?
-Different types of tooth movements can be achieved by managing the ratio between the moment of the applied force and the moment of couple. This ratio is detailed in textbooks and varies for different tooth movements, such as tipping, translation, or bodily movement.
What is the recommended ratio of force to moment of couple for bodily movement of teeth?
-For bodily movement of teeth, the recommended ratio of force to moment of couple is approximately 1 to 10. This ensures that the tooth moves bodily along the arch wire, minimizing tipping.
In a Class 2 Division 1 case with planned extraction of upper first premolars, how does the canine react to the force of a power chain?
-Initially, the canine will tip distally due to the force of the power chain. As the force magnitude increases, the two-point contact with the arch wire prevents further tipping, leading to the generation of couple and resulting in bodily movement of the canine.
Why is a heavier wire recommended for canine retraction?
-A heavier wire is recommended for canine retraction because it promotes more bodily movement and less tipping. The thicker the wire, the more force can be applied, increasing the moment of couple and thus facilitating bodily tooth movement.
What is the role of the wire's cross-section in controlling tooth movement?
-The cross-section of the wire plays a crucial role in controlling tooth movement. A rectangular cross-sectional wire, when placed in a rectangular bracket slot and twisted, can generate a couple, leading to controlled tooth movement and root control.
What type of movement can be expected when retracting incisors with a round wire?
-When retracting incisors with a round wire, only retroclination of the tooth can be expected since a round wire cannot generate a couple, leading to uncontrolled tipping.
How does the amount of twist in the wire affect the type of tooth movement?
-The amount of twist in the wire directly affects the type of tooth movement. More twist generates a larger moment of couple, leading to more controlled tipping or even translation if the moment of couple equals the moment of force. The center of rotation also shifts towards the crown with increased twist.
What is the force required to achieve a moment of couple of 500 gram millimeters for an 18 mil bracket system?
-For an 18 mil bracket system, 1100 grams of force is required to achieve a moment of couple of 500 gram millimeters.
What happens when the moment of couple equals the moment of force?
-When the moment of couple equals the moment of force, there will be pure torque, and the center of resistance and center of rotation both lie at the same point, leading to a specific type of tooth movement where the tooth rotates around a fixed point.
Outlines
📚 Calculation of Moment of Couple in Orthodontics
This paragraph discusses the method of calculating the moment of couple in orthodontic treatments, particularly when using fixed appliances. Dr. Fong Gum explains that the formula for calculating the moment of couple is similar to that of a single force, which is the product of force and the distance between the point of force application. The example given involves a 50-gram force applied at a 5-millimeter distance (assuming the bracket width is also 5 millimeters), resulting in a 250 gram-millimeter moment of couple. The paragraph emphasizes the importance of understanding this concept to control tooth movement beyond simple tipping, such as achieving translation or bodily movement of teeth.
🦷 Achieving Various Tooth Movements Beyond Tipping
The second paragraph delves into how to achieve different types of tooth movements apart from tipping by managing the ratio between the moment of the applied force and the moment of couple (Köppen's moment). It references a textbook table that provides ratios for specific tooth movements. The paragraph uses a detailed clinical example of a Class 2 Division 1 case, where upper first premolars are extracted, and the canines are retracted using a power chain. It explains how the initial tipping turns into translation when the force magnitude increases, leading to bodily movement of the tooth. The explanation includes the mechanics of how the force and couple interact, and the importance of using a heavier wire for better bodily movement. The paragraph also clarifies the requirements for translation, which is a 1:10 force-to-moment ratio, and how it changes as the force is increased.
🔄 Understanding Root Movement and Wire Twisting
The final paragraph focuses on the mechanics of incisor movement, particularly when retracting them using a crimped wire and power chain. It explains that the movement is influenced not only by the wire's thickness but also by its cross-sectional shape. The paragraph highlights the need for a rectangular cross-section wire to generate couple and control root movement. It describes how twisting the wire can lead to two-point contacts and the generation of couple, which allows for controlled tipping and root movement. The summary also discusses the impact of the amount of twist on the type of movement achieved and the force-to-moment ratio for different types of tooth movement, such as controlled tipping (1:7 ratio) and pure torque (force-to-moment ratio greater than 1:2). The paragraph concludes with a practical application of these principles in orthodontic treatment planning.
Mindmap
Keywords
💡Couple
💡Moment of Couple
💡Tooth Movement
💡Fixed Appliance
💡Force
💡Bracket
💡Archwire
💡Köppen's Moment
💡Translation
💡Tipping
💡Torque
Highlights
Discussion on applying couples and controlling root movement with fixed appliances.
Formula for calculating the moment of couple is force multiplied by the distance between the point of force application.
The width of the bracket can affect the distance for calculating the moment of couple.
Explanation of how forces and moments of couple can be calculated separately and still yield the same result.
Achieving different tooth movements beyond tipping by managing the ratio of applied force to moment of couple.
Table of ratios for force and moment of couple to achieve specific tooth movements like tipping and translation.
Case example of class 2 division one treatment with extraction of upper first premolars.
Explanation of how canines react to applied force and the generation of couple for controlled movement.
Importance of using a heavy wire for canine retraction to expect more bodily movement and less tipping.
Requirement of a 1 to 10 force to moment of couple ratio for bodily movement of teeth.
Clinical observation of initial tipping followed by translation for tooth movement.
Application of crimpable work to retract incisors and the expected movement.
Influence of wire thickness and cross-section on the movement of incisors.
Necessity of rectangular cross-sectional wire and brackets to generate couple and control root movement.
Mechanics of tooth movement depending on the single force applied and the couple generated.
Calculation of the moment of force and the absence of couple resulting in uncontrolled tipping.
Requirement of a 1 to 7 force to moment of couple ratio for controlled tipping with the center of rotation at the apex.
Increase in the twist of the wire to achieve more root movement and a higher moment of couple.
Explanation of how a higher moment of couple can result in pure torque and shift the center of rotation towards the crown.
Transcripts
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