Invisalign aligners are designed to apply forces to the teeth, allowing for various types of tooth movement. In some cases, these forces alone are sufficient to straighten your teeth without the need for attachments. For example, tipping the crowns of your teeth or rotating the incisors rarely require attachments.
While aligners can accomplish many tooth movements, complex movements and rotations often require attachments. In fact, the presence of attachments significantly improves aligner retention and orthodontic teeth movement.
Trying to correct significant misalignments without attachments can be challenging and frustrating for both the patient and the clinician. In such cases, the Invisalign provider is expected to come up with an appropriate attachment design in the diagnosis and treatment planning process.
Tooth Movements that require Attachments
There are some instances when attachments need to be incorporated in your Invisalign treatment plan to enable certain tooth movements. These include
Premolars, with their small contact surface and round shape, typically require attachments for rotational movements. Attachments provide the necessary grip and stability to effectively rotate these teeth.
Aligners can use neighboring teeth as anchorage to create an extrusive force. However, this mechanical process is less effective without a firm attachment on the crown surface of the tooth being extruded. Attachments play a vital role in facilitating the extrusion of most teeth.
Bodily movement or translation of teeth requires a high moment-to-force ratio and substantial anchorage. While aligners can deliver forces, achieving significant translation often relies on attachments. Optimized or vertical attachments can enhance the moment-to-force ratio, allowing for effective tooth translation.
4. Mesial Tooth Movement
Moving posterior teeth, such as a second molar, mesially (towards the front) can be challenging due to limited crown height. Attachments may not generate enough moment for substantial mesial translation. In such cases, alternative approaches like fixed appliances may be more effective.
When intruding teeth, attachments are typically unnecessary as aligners can easily develop intrusive forces. However, it’s important to consider the potential extrusion of anchorage teeth during intrusion. Attachments may be required to stabilize anchorage teeth and prevent unwanted extrusion.
Factors to Consider When Designing Invisalign Attachments
Designing appropriate attachments is crucial in Invisalign treatment to ensure effective tooth movement and achieve desired outcomes. By addressing specific questions, clinicians can define and design attachments that best suit the planned direction of tooth movement and fulfill their intended functions.
Here are the questions that your Invisalign provider will use to design your Invisalign buttons:
1. What is the planned direction of tooth movement?
Understanding the intended direction of tooth movement, whether it’s mesial (towards the front), distal (towards the back), extrusion (moving teeth upwards), or intrusion (moving teeth downwards), helps determine the type and placement of attachments required for optimal results.
2. What is the function of the attachment?
Attachments serve different purposes in Invisalign treatment, such as providing anchorage or delivering an active load to facilitate specific tooth movements. Clarifying the function of the attachment aids in designing the appropriate shape, size, and placement of the attachment.
3. Which is the active surface of the attachment?
Identifying the active surface of the attachment is crucial for estimating the amount of force and couple generated by the programmed recoil of the aligner. The moment-to-force (M:F) ratio, the plane of the force system, and the underlying root structure influence the path of tooth movement. Attachments help control individual tooth movement as aligners tie the arch together.
4. Is it feasible for an active load from an aligner to produce the desired tooth movement?
Assessing the feasibility of achieving the desired tooth movement solely with an active load from the aligner is essential. Severe crowding may require additional interventions like tooth extraction, arch expansion, or enamel stripping to avoid undesirable lip protrusion. Evaluating the feasibility helps determine if attachments are necessary and guides treatment planning.
5. Is the active force parallel to the direction of tooth movement?
When the active force from the aligner is parallel to the desired direction of tooth movement, surface attachments are a wise choice. Aligning the force and movement direction enhances the effectiveness of attachments in guiding tooth movement.
Case Examples: Do you need Attachments?
a. Deep-bite Attachments
In cases of deep bite, upper incisor intrusion and lower incisor intrusion or buccal segment extrusion are potential solutions. Attachments are not typically required for incisor intrusion, but they are needed on premolars serving as anchorage. The attachments can be conventional for retention or optimized for both extrusion and retention.
b. Molar-Intrusion Attachments
Intruded molars generally do not require attachments as their occlusal surfaces are sufficient for delivering axial loads. However, adjacent premolars may need attachments to resist the resulting extrusive loads. Conventional attachments for retention or optimized attachments for extrusion and retention can be utilized on premolars.
While aligners can achieve many tooth movements, there are situations where attachments become necessary for optimal results. Rotation, extrusion, translation, mesial tooth movement, and intrusion are some examples where attachments play a vital role in facilitating effective tooth movement. Attachment selection and placement are important considerations in the treatment planning process to ensure successful outcomes in Invisalign treatment.