Optimized vs. Conventional attachments

Attachments are not always necessary for tooth movement with clear aligners, but they may be used to enhance the effectiveness and predictability of them. Optimized attachments, specifically those designed by Invisalign, can provide precise biomechanical forces to facilitate desired tooth movements. Or this is what they tell to us.

Placing optimized attachments can be relevant in certain cases because they are combined with SmartForces. However, it is important to note that the decision to use optimized attachments depends on the specific treatment plan and the individual patient's needs, and some studies did not found statistically significant differences in tooth movements between Invisalign's optimized and conventional attachments.

Regarding one of the latest articles of Karras et al, where they analyzed the differences between optimized attachments and conventional on two types of tooth movements: rotation of canines and premolars, and extrusion of incisors and canines, the results obtained with both types of attachments were very similar. These movements were chosen because they are reported to be the least accurate with aligners.

If we review the study in detail, even though there are no statistically significant differences between them, they found that optimized attachments had a higher mean accuracy than conventional attachments for both rotation and extrusion. The authors suggest that this may be because most of the conventional rotation attachments used were rectangular and 3 mm long, which are typically larger than optimized attachments. A larger attachment provides a greater surface area for the aligner to push on, thus improving efficacy. Therefore, optimized attachments may still be preferred by some orthodontists due to their potentially higher accuracy and smaller size.

However, it is important to note that despite the larger size of conventional attachments, the study did not find a statistically significant difference in accuracy compared to the smaller optimized attachments. Therefore, while attachment size may play a role, it does not appear to be the sole determining factor in the effectiveness of attachments.

The study mentions several factors that can affect the predictability of tooth movement with aligners. These include:

• The location, size, orientation, and beveling of conventional attachments.
• Other minor simultaneous movements occurring in different planes of space, which can compromise the predictability of the studied movements.
• The anatomical characteristics and size of the teeth.
• The inability to account for certain variables, such as periodontal support, conventional attachment features, simultaneous tooth movements, and patient compliance.
• Existing mobility and altered periodontal support, which may have influenced results, along with general periodontal status and bone density ranging from patient to patient.
• The fact that most clear aligner systems, including Invisalign, do not take into account a tooth's root length, angulation, and center of resistance when planning movements.

In essence, when we are planning tooth movements with clear aligners, we should consider these factors to improve the predictability of treatment outcomes. The better we understand and assimilate these variables, the better we will be able to control each case and solve the problems that may arise during the treatment.

Efficacy of Invisalign attachments: A retrospective study. Karras T et al. Am J Orthod Dentofacial Orthop 2021;160:250-8.