Intermaxillary Elastics with Clear Aligners: A Comprehensive Guide

Table of Contents

1. What are elastics?
2. Biomechanics of elastics
3. Types of elastics & their indications
4. How to place elastics? (procedure)
5. Dental care: tips and guidance for patients

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What are elastics?

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.

Biomechanics of elastics

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,

1. How the elastics have been applied
2. The different forces in play and the various points of application
3. The change in the vertical dimension when the patient moves his jaw and
4. The degrading of elastic material under the effects of intraoral fluids.

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.

Types of elastics & their indications

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):

• Light (2 OZ)- 56.7g
• Medium-light (3.5 OZ)- 128g
• Medium-heavy (5OZ)- 141.8g
• Heavy (6.5OZ)- 184g
• Extra heavy (8OZ)- 226.8g

They can be classified according to lumen size as (1):

• 2/16”=1/8”=3.18mm
• 3/16”=3/16”=4.76mm
• 4/16”=1/4” =6.35mm
• 5/16”=5/16”=7.94mm
• 6/16 = 3/8” = 9.5mm
• 8/16”=1/2”=12.7mm
• 10/16”=5/8”=15.8mm
• 12/16”=3/4”=19.1mm

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
• Class III elastics
• Box elastics
• Triangular elastics
• Cross elastics
• Rotational elastics

Clear aligners class II elastics

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.

Modifications

• Upper first premolars to lower first molars- This modification is used only when upper canines are rotated as elastics might interfere with the de-rotation force applied by the aligners.
• Upper canines to lower second molars- This modification is applicable only when lower first molars cannot be used like in cases of missing 6s
• Upper first premolars to lower second molars.

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.

Indications:

• Correction of Class II relationship
• Distalization of upper molars and premolars
• Mesialization of lower molars and premolars
• Correction of midline shift

Class II elastics may have a negative impact and may worsen the condition if used in cases like:

• Reduced overbite
• Increased vertical dimensions
• Gummy smiles
• Retroclined upper incisors

Class III elastics in orthodontics

Class III elastics are placed between the lower canines and the upper first molars.

Modifications

• Lower first premolars to upper first molars- This modification can be used when the lower canines are rotated, and any placement of such elastics on them can counteract the planned de-rotation of these teeth.
• Lower canines to upper second molars - This modification can be used when first molars are absent, or where forces from the elastics can counteract a planned movement on these molars, such as expansion or distal in rotations.
• Lower first premolars to upper second molars.

Indications:

• Correction of Class III relationship
• Mesialization of upper molars and premolars
• Distalization of lower molars and premolars - This is done to create anterior spaces to retract lower incisors for the correction of Class III incisors and anterior cross bite.

Use Class III elastics with care in case of retroclined lower incisors, as retroclined lower incisors can retrocline even further with their use.

Rectangular Box elastics

Box elastics are intermaxillary elastics placed buccally on maxillary and mandibular premolars and molars.

Indications:

• Help with posterior teeth extrusion to close the posterior open bite
• Settling the bite at the end of aligner treatments

Triangular elastics

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.

Indication:

• Aids in single tooth extrusion (for instance, a high maxillary canine)

Cross elastics

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.

Indications:

• Correction of posterior crossbite
• Correction of scissor bite

Rotational elastics

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.

Indication:

• Helps in rotational movements of severely rotated teeth

Does your patient need clear aligner elastics?

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.

How to place elastics? (procedure)

Elastic bands can be attached to clear aligners in two ways:

1. Precision cuts- These are hook-like cuts created on the aligner itself, and the elastics are passed through these cuts.
2. Buttons- These are small prefabricated fixtures made of metal or ceramic material that can be bonded to the teeth' buccal or lingual/palatal surfaces. Aligners are trimmed in predefined areas to facilitate the cementation of these buttons.

Class II elastics

• Precision cuts are usually placed on the anterior teeth (upper canine) for enhanced esthetics and buttons are placed on the posteriors (lower molar). This is the default Eon Aligner protocols, but the doctor can specifically ask for buttons on both anterior and posterior teeth if the patient is compliant, since buttons are more retentive than precision cuts.
• Loop the elastic around the button and extend it to hook it onto the precision cut.

Class III elastics

• A button is placed in the upper molar, and a precision cut is on the lower canine.
• Take the elastic, secure it around the button, and attach it onto the precision cut in the lower canine.

Cross elastics

• If teeth are in crossbite, the buttons are placed on the lower first premolar and molar's buccal surfaces and the palatal surfaces of the upper first premolar and molar.
• Start by placing the elastics on the palatal buttons on the upper teeth and stretch to attach them to the lower teeth' buccal buttons.
• Cross elastics can be used to correct scissor bite also. The position of the buttons depends upon the case, but generally, they would be on the buccal surface of the upper premolars and molars and on the lingual surface of the lower premolars and molars.

Box elastics

• For this one, the buttons are placed on the upper and lower premolars and molars.
• You can start by attaching the elastic to the upper and lower first premolars and then to the molars or vice versa.

Triangular elastics

• These elastics are used to extrude teeth or settle the bite at the end of clear aligners treatment. Usually, the buttons are placed on three different teeth, in a triangular shape; for example, the lower first premolar, lower canine, and upper canine
• You should loop your elastic around the upper tooth button and then stretch it to engagge the lower buttons.

Rotational elastics

• Making cutouts on both the buccal and lingual surfaces of the same tooth will weaken the aligner, so cutouts are made on one side (usually lingual). And on the other surface (labial), we add rotational attachments.
• For the de-rotation, the rubber bands are wound around the buttons or precision cuts.

Reasons elastics could detach

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.

Dental care: tips and guidance for patients

For clear aligner patients using elastics, these tips may prove helpful:

1. Elastics must be worn daily for at least 22 hours a day.
2. Elastics need to be changed everyday ideally.
3. Sticky food should be avoided.
4. Regular checkups with doctors should not be missed.

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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