Mechanics Of Orthodontic Tooth Movement Question And Answers

Mechanics Of Orthodontic Tooth Movement

Question 1. Write a short note on Bodily tooth movement.
Answer. Bodily tooth movement is the most desirable type of tooth movement.

• When both, the crown and root, move in the same direction i.e. either in lingual direction or in labial direction, this is known as bodily movement.
• The force applied for bodily movement is 70 to 120 g and the center of rotation is at infinity.
• On periodontal ligament uniform stress pattern is applied.

 

Read And Learn More: Orthodontics Question And Answers

Question 2. Write short notes on different types of tooth movements.
Or
Write short note on various types of tooth movement.
Answer. Following are the different types of tooth movements, i.e. tipping, translation, root movement, and rotation.

Tipping

Tipping is the simplest form of tooth movement.

• In the tipping type of tooth movement crown moves more as compared to the root.
• It is of two types, i.e. controlled tipping and uncontrolled tipping.

Controlled Tipping

• In controlled tipping, movement of the crown occurs in a single direction while the root shows no movement in the opposite direction.

• The center of rotation lies at the apices of the root.
• In this force required is 35 to 60 g.
• The moment-to-force ratio is in the ratio of 7:1.
• PDL is stressed very little at the root apex. Due to this root movement is prevented.
• In the cervical area stress pattern is more.
• It is used when the excess proclined incisors are to be retracted and roots are at normal position.

Uncontrolled Tipping

• It is done when a single force application is applied to the crown of the tooth.
• In this crown moves in a single direction while the root in another or opposite direction.
• The center of rotation lies between the center of resistance and the root apex.
• PDL is stressed near to root apex over the same side of applied force and at crest of alveolar bone over opposite side.
• It is used when the proclination of incisors is carried out.

Translation

In translation, two forces are applied to the crown of the tooth.

• As translation tooth movement is applied, the crown and root move in the same direction at the same distance.
• Forces applied to pass through the center of resistance of a tooth.
• Pure translation is of three types:
  • Intrusion.
  • Extrusion.
  • Bodily tooth movement

Intrusion

• Intrusion is the bodily displacement of a tooth along its long axis in an apical direction.
• Intrusion tooth movement needs minimum force application.
• The force required for intrusion is 10 to 20 g.
• Force-applied passes via the center of resistance.
• PDL present in the apex gets compressed at a small area.
• Areas of tension are absent.

Extrusion

• Extrusion is the bodily displacement of a tooth along its long axis in an occlusal direction.
• The force required for extrusion is 35 to 60 g.
• PDL present in the apex shows stretched areas.

Root Movement

• It is the opposite of crown tipping and the crown of a tooth should be kept stationary, while the root moves labiolingually or mesiodistally.
• Root movement occurs due to torquing of the incisor and uprighting the tipped teeth.
• Two types of root movements are present i.e.
  • Torque: It leads to the labiolingual movement of the root.
  • Uprighting: It leads to mesiodistal movement of the root with the center of rotation at the incisal edge. Usually, 50 to 100 g of force is required. Here stress is greatest at the apex and decreases gradually to the cervical level.

Rotation

• Rotation is defined as the spinning of the tooth at its long axis.
• It is gained by using a couple.
• Forces become null and momentum remains which causes rotation.
• The force required is 35 to 60 g.
• In cases where correction is done by rotation chances of relapse are too many.
• Rotation is gained by the help of a couple of forces or by the help of a single force and stop.
• Pure rotation is divided into two types i.e.
  • Transverse rotation: Tooth displacements during which the long axis orientation changes are called as transverse rotation. Examples are tipping and torquing
  • Long axis rotation: In this, the angulation of the long axis is not altered. An example is the rotation of a tooth around its axis.
• Generalized rotation: Any movement that is not pure translation or rotation can be described as the combination of both translation and rotation and is known as generalized rotation. This movement is seen in routine clinical practice.