Clear aligners are the rage in orthodontics today. You can’t watch a TV show, view social media, or listen to the radio without being exposed to an advertisement for some type of plastic aligner system that offers you a new smile. The biggest company in this market is Align Technology who produces Invisalign. They have a huge advertising budget and their aligners have become a household name like Kleenex and Band-Aids. New patients come to my office every day asking for me to straighten their teeth with Invisalign because they don’t want anything glued to their teeth. Many are surprised when I explain that although Invisalign doesn’t use brackets and wires, there are still tooth-colored “attachments” that must be glued to the teeth to achieve a successful outcome. What are attachments and why are they necessary?
Plastic aligners use a series of clear plastic shells that are shaped so that they sequentially guide the teeth into their desired positions. Two fundamental principles must be remembered about aligners. First, plastic can only push, it cannot pull. For a tooth to move in any desired direction, there must be a surface against which the aligner can push. Second, for a tooth to remain engaged in the aligner (to “track”), there must be an undercut or purchase point that allows the plastic to grip the tooth. Some teeth have natural undercuts because they are round or bulbous in shape (primarily the back ones). Other teeth are more triangular or pyramidal in shape (the front ones). For all movements except intrusion (pushing the teeth towards the gums), attachments are necessary to create the required pushing surfaces and undercuts. These movements include tipping, rotating, and lengthening the teeth.
To create pushing surfaces and undercuts, orthodontists construct “attachments” or bumps on the teeth using tooth-colored composite (the same material used to repair chipped teeth). The size, shape, number, and location of these attachments is determined by the anatomy of the teeth and the desired movements. Although visible up close, most attachments are invisible to the naked eye at normal conversational distances (about 3 feet). Orthodontic attachments provide the same function for clear aligners as brackets do with conventional braces. They are just handles on the teeth. I tell my patients to think of their attachments as the brackets and the plastic aligners as their wires.
Some patients are adamant that they don’t want to have anything glued to their teeth. Unfortunately, trying to make certain movements without attachments is scientifically impossible. Imagine an upper lateral (second tooth from the center) that needs to be longer to look straight. Without an attachment to provide an undercut, the tooth will remain its original length no matter how well the aligner is designed or worn. Additionally, making the aligners tighter on a tooth in hopes that it will move with the plastic actually causes the opposite effect (the tooth will actually move up rather than down). Think of how a watermelon seed squirts through your fingers when you squeeze it to pick it up. Similarly, if the plastic aligners are programmed to tip a pyramidal shaped tooth without an undercut, the tooth will actually slide UP the aligner rather than move with it.
Attachments glued to the teeth are necessary for accurate, predictable orthodontic movements. I wish there was a way to move teeth successfully without them using aligners, but as of 2018 one does not exist.