Written by Dr. Febin Mary George, BDS | Medically Reviewed by Dr. Shaista Salam, BDS, Dr. Zein El Hammouz, DDS, MFD/RCSI
Elastics are elastomeric rings secured between specific points on the maxillary or mandibular arches to exert pressure and move the teeth into their desired positions. They can be intermaxillary elastics (when used between maxillary and mandibular arches) or intra-arch elastics (when used only on one arch)
Elastics are used in conjunction with clear aligners to improve anchorage. They also increase the predictability and efficiency of certain orthodontic movements.
The biomechanics of elastics is complex, but their proper application can significantly improve the patient's bit and achieve more predictable results.. Many variables influence the biomechanics of intermaxillary elastics such as,
For ease of understanding, let us assume a static environment with no variables except the direction of forces and their relation to the center of resistance for each jaw and interpret the effects of Class II elastics.
If you take a look at the Class II elastics here, the arrows indicate the direction of force at the point of application. The point halfway down between the roots of the premolars will be considered the center of rotation for both the maxilla and mandible. As the point of application of force is away from the center of rotation, a moment force will be created, causing a clockwise rotation in both jaws.
The force created by the elastics is transmitted to the teeth through the clear aligners. The teeth and surrounding bone respond to this force by remodeling, allowing them to move to their new positions.
In the case of class II elastics, both jaws will move downward and backward, increasing the anterior facial height.
There are different types of elastics based on where they are attached and what they are used for.
Elastics can be classified according to force values (usually expressed in ounces) as (1):
They can be classified according to lumen size as (1):
3/16 medium, 3.5 ounces is the most commonly used size of elastics. But it is the responsibility of the doctor to choose the elastic size that is most suited for their case.
According to their use/placement in the arches, elastics can be classified as (1):
Class II elastics in clear aligner orthodontics are placed between the upper canines and lower first molars. They help improve Class II relationships by dentoalveolar compensation or provide anchorage for distal movement of upper dentition and mesialization of the lower posterior teeth.
All the modifications mentioned above are aimed at an anterior placement of the elastics on the maxillary teeth to a more posterior position on the mandibular teeth.
Class II elastics may have a negative impact and may worsen the condition if used in cases like:
Class III elastics are placed between the lower canines and the upper first molars.
Use Class III elastics with care in case of retroclined lower incisors, as retroclined lower incisors can retrocline even further with their use.
Box elastics are intermaxillary elastics placed buccally on maxillary and mandibular premolars and molars.
Triangular elastics are a modification of box elastics placed from the labial surface of a specific tooth to the labial surface of two opposing teeth.
Cross elastics are a different type of box elastics. These elastics clear aligner orthodontics are placed from the buccal surface of premolars or molars to the lingual or palatal surfaces of opposing premolars and molars.
Rotational elastics are intra-arch elastics used to create a force moment around a rotated tooth. They are placed between the rotated tooth's buccal and lingual surface and the adjacent teeth depending on the direction of rotation.
Every clear aligner patient may not require elastics. As a doctor, it is your decision on whether you want incorporate elastics in clear aligner orthodontics, based on the desired tooth movements and case complexity. They can be extremely helpful in addressing severe malalignment issues like Class II or Class III malocclusions, rotations and crossbites.
Elastic bands can be attached to clear aligners in two ways:
Elastics could detach if they are not inserted correctly. Educate and train your patients on how to wear the elastics on their aligners. Although, patients may find it quite tricky in the beginning, assure them that they will be able to place elastics comfortably in due course of time.
They can wear the aligners first and then attach the elastics to the precision cut. Alternatively, they can fix the elastics to the precision cuts then wear the aligners and then fasten the other end of the elastics to the button.
While placing the interarch elastics, care should be taken to place one end on a precision cut (anterior) and the other end on a button (posterior). The stability is higher when both ends of the elastic are placed on buttons. On the other hand, if both the ends are engaged to precision cuts, the chance of the elastic getting dislodged is extremely high.
For clear aligner patients using elastics, these tips may prove helpful:
If you experience any problems wearing elastics with your clear aligners, be sure to inform your doctor and they will fix it for you.
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