User:Globalorthodontist/Space closure in orthodontics

'Space Closure in orthodontics is done in cases where one or multiple teeth are extracted in a person's mouth. This technique ensures the spaces to be closed via orthodontically, in comparison to placing a dental implant in those spaces. Closing spaces in orthodontics is based on the type of Anchorage (orthodontics) is needed in each case. Different types of anchorage exist in a classification made by Charles J. Burstone.

Loop/Friction-Free Mechanics

Dr. Ray D. Robinson was the first person to advocated the use of loops in orthodontics in 1915. This type of mechanics uses loops in rectangular Orthodontic archwires to create a force to move teeth and allow the spaces to close. The loops are activated by pulling the wire behind the molar tooth and synching or bending it. This concept is based on creating differential moments in the archwire to create the effect. Some of the advantages of loop mechanics include are: force can be delivered constantly over time, amount of force can be controlled by the type or length of wire, various design of loops can result in different amounts of forces delivered. Cases that requires maximum anchorage, individual canine retraction is done with loops instead of bringing all front 6 teeth back.

The types of loops that exists are: T Loop (Burstone), Asymmetric T Loop (Hilgers), Tear-drop Loop, Rickett's Canine Retractor, Retraction spring (Paul Gjessing), Delta Loop (Proffit), Bull Loop, Open Vertical Helix Loop, Omega Loop, Opus Loop (Siatkoski), Rectangular Loop, Closed Vertical Helix Loop, Boxed Loop and Double Keyhole Loop (Almeda).

Moment/Force Ratio

It is important to have the proper moment to force ratio which helps determine the type of tooth movement. According to Burstone and Koenig, several modifications can be done to increase the moment to force ratio delivered to teeth by the orthodontic archwire. Following are the ratios that have been shown by Charles Burstone in the literature.

• Uncontrolled Tipping - 5:1
• Controlled Tipping - 8:1
• Translation - 10:1
• Root Movement - >10:1

Following modifications can be added to the loops to increase the moment to force ratio on a orthodontic archwire.

• Increasing vertical dimension of the loop
• Increasing horizontal dimension in apical part of loop
• Incorporating helix in the loop
• Decreasing interbracket distance
• Placing Pre-activation or Gable bends

Alpha and Beta Moments

Each loop can have alpha (anterior) or beta (posterior) moments on either side of the loop. These moments are created by the alpha and beta bends respectively. The bends are placed either mesial or distal to the loop. If beta moment > alpha moment, increased posterior anchorage is seen by mesial movement of roots along with extrusion of posterior (clockwise moment) and intrusion of anterior (counterclockwise moment). If alpha moment > beta moment, anchorage of anterior segment is increased by distal movement of anterior teeth along with anterior extrusion and posterior intrusion. If alpha moment = beta moment, then no vertical changes occur.

Loop Position

The position of the loop can very depending on the type of tooth movement desire. The closer a loop is to a tooth, the more moment or anchorage a tooth feels and thus less tendency for that tooth to move. The farther away a loop is from a tooth, that tooth will feel less moment and will tend to move a lot more than its counterpart on the other side. I

If a vertical discrepancy that exists between the anterior and the posterior segment, it may tend to deepen the anterior segment which can create a deep bite.

Properties of Wire

Increasing the length of wire in the loop can lead to low amount of force delivered to the teeth. This can be done by adding helices in the loop itself. An example is adding a helix to a vertical closing loop. The type of wire that is used can also have an affect on the force delivered. Using a wire with lower modulus of elasticity can lead to low amount of force delivered to the teeth. Beta-Titanium is a type of wire that can produce low force to the teeth if loops are fabricated out of this wire.

Sliding/Friction Mechanics

In this type of mechanics, the spaces are closed by moving teeth along the archwire. Either elastics or coil springs are used in this type of mechanics to provide the force for the space closure. When the force is applied through the elastics and coil springs, there is friction that is produced between the bracket and the archwire leading to a tooth feeling less force than normal. This is said to have slowed down tooth movement [Citation Needed]. However, there is a archwire present in this mechanics which helps to prevent any tipping and rotations. Methods of space closure in sliding mechanics are discussed below.

Elastomeric Chains

Elastomeric chains in orthodontics were first used in 1960s. Their advantages are that they are inexpensive, can be applied in mouth without removing the wires and no patient compliance is needed in order to use them. Their disadvantages are that they permanently stain, its force decays over time, unhygienic and difficult to clean and they can absorb saliva and water. These elastic chains can usually be applied from a back molar tooth to the hook on the canine bracket in order to close the spaces that exist between canine and 2nd premolar. They can be used in many different designs to close spaces that exist in the mouth.

Coil Springs

The first coil springs were used in orthodontics in early 1930s.

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