Dr. An: Reflection on Molar Distalization in Clear Aligner Orthodontic Treatment

Under the wave of digitization, there is a rapid advancement in dental technology. In the field of orthodontics, clear aligner technology has been developing rapidly. Due to its speed, aesthetics, and comfort, it has been highly sought after and gradually become the mainstream method for correcting dental malocclusions. However, there are still many aspects of its development and application that require further discussion and exploration.

Today, we have invited orthodontist An Boyu to discuss some thoughts on the molar distalization using clear aligners.

What is molar distalization?

The molar distalization refers to sequentially moving the posterior teeth distally to provide space for aligning or retracting the teeth in the anterior region. Simply put, when the anterior are crowded, space is needed for alignment, and this space is created by moving the molars away to provide space for the dental arch or anterior teeth.

In traditional orthodontics, there are roughly three methods for achieving the molar distalization: headgear, removable orthodontic appliances, and micro-implant anchorage.

Briefly, here's how they work: 1. Headgear requires wearing them for over 10 hours a day; 2. Removable appliances need to be bonded inside the mouth; 3. Implant anchorage requires a surgical procedure.

The disadvantages of traditional orthodontic tools for molar distalization include low comfort,  poor compliance of the patient, poor effectiveness, and complexity of operation. Among them, there is a possibility of implant anchorage coming off, which lowers patient acceptance.

What are the advantages of molar distalization in clear aligner treatment?

Convenience, speed, efficiency, high comfort, and ease of patient compliance.

Let's first talk about the anchorage in invisible orthodontic treatment for molar distalization. During clear aligner treatment, any force applied to the teeth to move them will inevitably produce an equal and opposite force supporting the corrective movement of the teeth, and this is called anchorage.

What are the indications for molar distalization?

The indications for molar distalization in clear aligner treatment are as follows:

1.       Class II malocclusions with mild protrusion, especially division 2 malocclusions, are suitable for clear aligners;

2.       Mild Class III malocclusions;

3.       Molar teeth with root distal inclination and crown mesial inclination;

4.  The posterior area of the molars can accommodate the amount of molar distalization, and it is necessary to assess whether there are wisdom teeth and can be extracted upon patient consultation;

5.       Mild to moderate crowding of the dental arch.

How to determine the limits and contraindications of molar distalization?

Treatment should be tailored to the individual patient's situation, and a preliminary assessment of the space for molar distalization should be made to ensure that the movement occurs within the bone, while also considering the morphology of soft tissues to avoid excessive movement causing periodontitis.

In terms of contraindications, careful consideration should be given to whether it can be performed, mainly including:

1.       Obvious lack of space between the posterior molars;

2.       Presence of wisdom teeth, and the patient refuses extraction;

3.       Severe crowding of anterior teeth or crowding exceeding 6mm, making it impossible to obtain sufficient space solely through distalization;

4.       Molar teeth with significant distal inclination of the crown;

5.       Second molars have not erupted or have insufficient eruption height;

6.       Associated temporomandibular joint disease;

7.       High-angle cases, to avoid clockwise rotation of the mandibular plane, leading to opening.

Can molar distalization be used in adolescent orthodontics?

In adolescent orthodontics, molar distalization needs to be analyzed according to specific circumstances, paying attention to:

1.       Perform molar distalization when the second molars erupted;

2.       Appropriately accelerating the wearing efficiency of clear aligners;

3.       For adolescent orthodontic cases, attention should be paid to the space behind the molars, taking into account growth and development trends.

The selection of adolescent orthodontic cases needs to consider the development of dental roots, overall treatment time, the need for molar distalization, and whether it will affect growth and development. During the treatment process, attention should be paid to the eruption of second molars, and re-taking impression may be necessary after second molar occlusion.

How to ensure that molar distalization is achieved in invisible alignment?

It mainly includes the following five aspects:

1.       Movement staging design

Reasonable movement sequence is crucial. Tooth movement methods include sequential movement, translation movement, and individualized movement. It is recommended to use sequential movement to effectively protect anterior tooth anchorage.

Sequential movement means that no more than two teeth can be distalized simultaneously on one side. For example, when the second molar tooth 7 is moved distally, after tooth 7 has moved into place, tooth 6 is moved, followed by tooth 5, achieving the treatment goal in sequence.

2.       Anchorage design

When planning molar distalization, attention should be paid to anchorage design, including:

a)       Use sequential movement to protect anchorage;

b)       Coordinate intermaxillary traction (class 2 traction, class 3 traction); appropriate traction can effectively protect anterior tooth anchorage and prevent anterior tooth proclination;

c)       Implant anchorage, pay attention to the timing of implantation.

The timing of auxiliary traction is when the first molar distalization begins. Additionally, when implant anchorage is used, if the anchorage is still insufficient, patient compliance is poor, and the patient's revisit interval is relatively long, auxiliary implant anchorage or extraction design can be considered from the beginning of treatment.

The insertion site for temporary anchorage devices (TADs) is between the maxillary tuberosity and the external oblique line of the mandible, in the interdental space between teeth 56 and 67.

In summary:

a)       Molar distalization using only invisible aligners (single-jaw molar distalization <1.5mm);

b)       Auxiliary intermaxillary traction is needed for molar distalization (single-jaw molar distalization <3mm);

c)       Auxiliary implant anchorage is needed for molar distalization (single-jaw molar distalization >3mm or double-jaw molar distalization >2.5mm).

3.       Attachment design

When planning the molar distalization, attention should be paid to attachment design, including:

a)       It is recommended to place attachments in the premolar and canine areas to enhance retention;

b)       In the posterior tooth area, the size and type of attachments should be determined based on the size of the crown and the axis of the tooth. Rectangular attachments can be considered, placed near the buccal side, taking care not to interfere with the jaw;

c)       To place attachments in the canine area for control (root control and tooth axis control), it is recommended to consider optimizing root control attachments.

4.       Anterior torque design

When planning the molar distalization, attention should be paid to the design of anterior torque, including:

a)       In the early stage of molar distalization, due to the reactive force of anterior tooth anchorage, there is a risk of anterior tooth proclination, and a small amount of negative torque can be designed to prevent this risk. Class 2 Division 2 should avoid this design (sagittal direction).

b)       After obtaining space, anterior teeth begin to align and retract. To counteract the extrusion caused by retraction, a small amount of intrusion compensation is needed to achieve control of anterior overbite (vertical direction).

c)       During follow-up visits, pay close attention to whether there is a loss of torque in the anterior teeth. During the retraction phase, prevent lingual inclination and pendulum effects in the anterior teeth. Severe cases can lead to bone window or bone fracture near the roots.

How to avoid the above situations? There are two methods: add appropriate overcorrection to prevent lingual inclination and pendulum effects during anterior teeth retraction; for individual anterior teeth that need torque control, power ridges can be added to assist in root control movement.

5.       Overcorrection design

When planning the molar distalization, attention should also be paid to overcorrection design, including:

a)       Design for maxillary molar distal movement: anterior teeth overjet 1mm, overbite 0mm;

b)       An additional 1mm overcorrection can be added during molar distalization;

c)       When designing expansion, the posterior teeth can be expanded another 0.3mm on the basis of normal overbite and overjet, with negative torque designed for maxillary molars.

These are some considerations and methods for achieving molar distalization in clear aligner treatment. By carefully planning and implementing these strategies, orthodontists can effectively address the challenges and achieve successful outcomes in orthodontic treatment.