Conventional fixed appliances
The twin bracket is the basic design of all classic fixed appliances. The orthodontic archwire is tied onto the bracket using 4 points, namely the four corners of the bracket.
By default, this bracket is wide to accommodate the tie wings. The orthodontic archwire is held in place either by elastomeric ligatures or metal ligatures. The insertion and removal of an orthodontic archwire take definitively longer than with self-ligating brackets.
The right image shows twin brackets, probably Ormco Mini Diamond®, coming from a transfer case of another orthodontist. The picture was taken without the wire. This bracket, wider than 4 mm, thus fills half of the visible surface of an incisor which varies between 8 and 9 mm in width.
The use of metal tie wire to hold the orthodontic archwire in place gave the idea to Steven Spielberg of a memorable scene from the Poltergeist movie released in 1982 and well represented by our patient who was willing to take part of an amusing reenactment.
This bracket has only two tie wings instead of four and the archwire is thus tied centrally onto the bracket. It is thus designated as a point attachment tie or single tie. This bracket is not much used nowadays, but I have happened to come across a few transfer cases with this type of brackets. It is a little narrower than the twin bracket, but the metal and elastomeric ligatures do not make it very appealing.
This bracket is practically no longer used nowadays.
To convince ourselves, we only need to put side by side 2 pictures of the same patient with his Attract™ brackets and his new SPEED™ brackets. These pictures were taken in 2002 and correspond to a time when I was using regular SPEED™ brackets. I now use mini SPEED™ brackets on the 4 incisors (see page on Appliances). Notice the yellow-brown color of the elastomeric ligatures.
Clear twin brackets
The Clarity™ bracket is 4.25 mm wide compared to 2.5 mm for a regular SPEED™ bracket. It is part of the family of “invisible” brackets. The matt appearance of the bracket depends on the polycrystalline structure of the material used. The presence of an elastomeric chain and metal ligatures adds to the visual cluttering.
I let you judge by yourself the more or less mitigated benefit that a clear ceramic bracket offers compared to a SPEED™ bracket. The left picture shows a patient whom the Clarity™ brackets were changed for SPEED™ brackets.
These polycrystalline brackets are harder than enamel and, as a result, when they are used in the mandibular arch and a tooth gets in contact with a bracket, the enamel of the tooth wears out instead of the bracket.
Smoking, which is known to be the best way to put nicotine on teeth, is generally not recommended with any bracket. It is very visible in this case.
On the left, a close-up view of the Inspire™ bracket which is carved in crystal (imagine a Corning Ware™ dish top). The structure is said to be monocrystalline which gives it a great transparency compared to the polycrystalline structure used for the Clarity™ and SmartClip SL™ brackets.
One of the major disadvantages of clear brackets, either they are monocrystalline or polycrystalline, is their extreme weakness (they break easily). The red arrows show 2 broken wings. The bracket thus needs to be replaced and this can delay the evolution of the treatment significantly.
Another disadvantage is the interface between the orthodontic archwire which is in stainless steel and the crystal. It’s a little like sliding a metal file against a window. There is friction and this friction slows down the movement of the tooth on the wire.
On the right, an Inspire™ smile. Notwithstanding the transparency of the bracket, there is always the orthodontic archwire, the metal ligatures and in this case, the surgical posts engaged in the wire between the brackets.
In the same way as previously, nothing is better than comparing 2 kinds of brackets in the same patient. These 2 pictures were taken during the same session at a 45-minute interval. The brackets were changed because it was impossible to finish the treatment with the Inspire™ brackets whereas it was done in 6 weeks with SPEED™ brackets.
The material used to make the Spirit™ bracket is a polycarbonate resin in which a metal slot is inserted. This slot (green arrow) allows a better stiffness of the interface with the orthodontic archwire. Despite this addition which was, for that matter, taken up for the Clarity™ brackets, the stiffness of the polycarbonate is not sufficient to submit the torsional movements efficiently when they are necessary.
Another disadvantage is that polycarbonate wears out and for this reason, it cannot be used in the mandibular arch, because chewing forces and food will damage the wings completely at the corners of the bracket.
The elastomeric chain (blue arrow) used to hold the orthodontic archwire in place and to close the interdental spaces changes in color with the ingested food. This explains the yellowish appearance around the brackets on the picture of the smile on the left.