TAD is short for “Temporary Anchorage Device“. TADs are also known as “Micro-implants” which are distinct from “Mini-implants” or “Dental Implants”. A TAD is first and foremost “Temporary”. It is not meant to reside in a patients mouth forever – it will be removed at the end of treatment or when it has served its purpose. Basically, a TAD is something that an orthodontist can place to provide skeletal anchorage for orthodontic tooth movements and remove once those tooth movements are accomplished. What is anchorage? Anchorage refers to the orthodontic principle that whenever we push or pull teeth into a new position we’re always constrained by at least two things: biologic limitations (primarily the amount and relative position of surrounding bone) and also Newton’s 3rd Law (“for every action there is an equal and opposite reaction”).
If you imagine a patient in braces and a wire connecting two adjacent teeth (see images above and below), we can understand that when the wire is moving one tooth one way the “equal and opposite forces” (Newton’s 3rd law) are going to attempt to move the adjacent tooth the opposite way. What happens if we don’t want that opposite movement to occur? Obviously we would need to resist these forces. One of the ways we can resist these unwanted tooth-movement forces is to use the surrounding bone to “anchor” the tooth in its existing position – much like how a boat is anchored against a current or the prevailing winds and tides that would displace it from its position in a harbor. The boat is connected to something more rigid and stable than itself – the rocky/sandy surface underneath it. A tooth can be “anchored” to a more rigid and stable surface by being connected to the surrounding bone just like a boat is anchored to the rocky/sandy surface underneath it (thus the term “anchorage”).
In the following image we see the “equal and opposite forces” at play. On the left (image “A”) we see a patient in full braces with a canine (or eye-tooth as they’re sometimes called) much higher than the adjacent two teeth. The archwire that connects these 3 neighboring teeth will have a natural tendency to help the high canine to erupt downwards (purple arrow which is what we want – good!) but also pull the adjacent teeth up to meet the canine (green arrows – unwanted tooth movements). We see the resultant tooth movements on the right in image “B”. You can imagine this result after 1-3 months of archwire influence over these 3 teeth. The adjacent teeth will naturally rise to meet the canine as it comes down towards the rest of the teeth. This type of phenomenon is sometimes referred to as the “rollercoaster effect” as the archwire will eventually resemble the undulating track of a rollercoaster. If we needed this canine tooth-movement to be controlled and focus on moving the canine only we could use a TAD to anchor one or both of the adjacent teeth to the bone to resist these unwanted tooth movements and allow primarily for the desired eruptive canine tooth movements (erupting the canine into its proper position).
The same “equal and opposite forces” principles can be seen in play on the lower arch where a spring is attempting to make space for the lower canine to erupt into position. We see that the spring will exert its influence on both the front teeth (blue arrow – pushing them forward) as well as the premolar (orange arrow – pushing it back to meet the molar). If these two tooth movements are desired then all the better! If we can’t afford to allow the front teeth to move forward (say we already suffer from recession or lack of supporting bone) then we should consider anchoring to the surrounding bone to help resist this unwanted tooth movement. Similarly, if we cannot afford for the premolar to move backwards (say there’s no space or we want to preserve that space for a future dental implant that will support a crown or bridge) then we should consider a TAD to anchor the tooth in this location.
These are some very simplistic examples of where a TAD may be beneficial from a clinical perspective. There are many other different uses including pushing or pulling directly off the TAD itself or using the TAD to overcome nearly-closed sutural connections between two different halves of an upper jaw bone. The image below shows an expander (which is typically used for patients younger than 16 years old) being applied to a young adult via the addition of skeletal anchorage. Four TADs anchor the expander to the two halves of the upper jaw and allow the expander to overcome the nearly-fused sutural connections of both halves of the upper jaw. Now we can provide expansion to patients as old as 25-28.
