Temporary anchorage devices (TADS) are also known as mini screws and are used to facilitate the movement of teeth through what is called Skeletal Anchorage. TAD appliances are placed directly into the jaw bone then teeth are pulled towards the TAD via elastic or spring traction. Prior to the introduction of TADS, orthodontic tooth movement required the use of other teeth to pull or push from (Tooth Borne Anchorage) or the use of extra oral appliances such as headgear (Extra Oral Anchorage). Unfortunately there is a limit to how effective a tooth or group of teeth is in providing adequate anchorage even when extra oral anchorage is employed as these teeth tend to drift towards the teeth being moved. This is termed loss of anchorage.
Much of the current literature is dominated by TADS and their application to Orthodontic treatment. The idea of skeletal anchorage has been around for 25+ years however the procedures to place the fixation appliances were often complex, or the materials used for the appliances were not biocompatible. In the 1990's the use of small, threaded titanium screws resulted in a resurgence of interest from the orthodontic profession as it appeared that a simple, yet effective method for providing skeletal anchorage had arrived. Like many medical discoveries, it would take time to gain approval for use and to gain acceptance from the profession. Today, the use of skeletal anchorage is utilised by much of the orthodontic fraternity as a safe and simple method to improve treatment mechanics.
A simple example of the use of a TAD to improve treatment outcome is the closure of space. Conventional tooth borne mechanics would involve bracing the teeth adjacent to the space and pulling toward each other. The result would be that teeth from both sides of the gap would move into the space. We can improve the direction of movement by bracing more teeth on one side and making a bigger anchor to pull from however there is no way to completely eliminate undesired movement (loss of anchorage).
If it is essential to close the space by bringing the large molars forward with NO backward movement of the front teeth then some form of skeletal borne anchorage is required. In this case, a TAD is placed into the bone forward of the gap and then used to pull the back teeth forward with a spring.
The use of TADS has created the ability to move teeth more predictably and often in directions that were previously impossible to routinely achieve.
Method of Placement
Like most minor surgical procedures, a sterile environment is required. Chlorhexidine solution is applied to the area where the TAD will be placed prior to local anaesthesia. The amount of anaesthetic delivered is about 1/3 that normally given for a filling. The TAD is taken from a sterile container, placed into a driver (similar to a screwdriver) and then screwed through the gum and into the bone. The time taken to place the screw is approximately 20 seconds-add to that 5 minutes for the delivery of the anaesthetic and a couple of minutes to place the spring, most single TAD placements can be carried out within a normal orthodontic adjustment appointment. Simple home care reduces the risk of any post-placement complications.
I have regularly asked patients of their experiences during and after placement and the consensus is that it is less trouble than a filling with minimal discomfort once the anaesthetic wears off. Once the TAD is no longer required, it is easily unscrewed and usually without the need for anaesthetic. For those interested, placement of the screw is similar in feel to screwing a small wood screw into soft pine wood -pretty simple.
Occasionally screws loosen before they have achieved their goals and need replacement. There is rarely a contraindication to immediate replacement.
If your orthodontist recommends the placement of a screw(s), this would be on the basis that it will assist in producing the best result possible. If you have concerns or queries, discuss these with the orthodontist prior to treatment.
If you would like more information, the link to the manufactures site is as follows: http://www.ormco.com/index/ormco-products-vector. Several YOUTUBE videos are available by searching for "miniscrews".