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CERAMIC BRACKETS

CERAMIC BRACKETS


Ceramic braces are the same size and shape as metal braces, except that they have tooth-colored or clear brackets that blend in to teeth. Some even use tooth-colored wires to be even less noticeable.

Pros : Less noticeable than metal braces; move teeth much faster than clear plastic aligners (Invisalign)

Cons : More expensive than metal braces; Brackets can stain easily if patients don't care for them well

Ceramic braces are well-suited for many patients without severe misalignments. Your orthodontist will let you know if you're a good candidate for these braces after they examine your teeth. They'll also let you know if your treatment time will be extended by choosing these braces.



POLYCRYSTALLINE & SINGLE-CRYSTAL CERAMICS

Polycrystalline brackets are manufactured by blending aluminum oxide particles with a binder so that the mixture can be molded into a shape from which a bracket can be cut. The molded mixture is heated to temperatures in excess of 1,800°C to burn out the binder and fuse the particles together. This fused part is then machined with diamond cutting tools to provide the slot dimensions and other critical tolerances. The machined bracket must be heat-treated to remove surface imperfections and relieve stresses created by the cutting operations.

Optical properties and strength are incompatible for polycrystalline ceramics. The larger the ceramic grains, the greater the clarity or translucency. However, the material tends to become weaker when the grains reach a size of about 30 microns. Polycrystalline brackets begin as aluminum oxide particles of about .3 microns, which are fused to produce ceramic grains of 20-30 microns. Heat treatments after machining must be carefully controlled to prevent further grain fusion, which could detract from physical properties.

PHYSICAL PROPERTIES


Little information has been generated on the physical properties of the finished products

1. They do not account for the geometry of the various brackets, cross-sections, and designs.

2. They do not include variations in manufacturing processes.

3. They do not consider the influences of stress rate on brittle failure.

4. They may not be clinically significant in terms of orthodontic use.

Both single-crystal and polycrystalline brackets resist staining or discoloration from any chemical substance likely to be encountered in the mouth. Unfortunately, the same cannot be said for elastic ligatures. And, because aluminum oxide is chemically inert, it cannot be directly adhered to by the acrylic materials used for orthodontic bonding.


Two different mechanisms are presently being used for bonding ceramic brackets: a mechanical retention via indentations and/or undercuts in the bracket base, and a chemical bonding using an adhesive intermediate.
Laboratory testing of mechanical retention indicates that adhesive-to-bracket bond strengths are less than those of equivalent-size foil/mesh metal brackets.
Chemical bonding, a more recent development, is used for "A"-Company's Starfire and Unitek's Transcend ceramic brackets. Glass is added to the aluminum oxide base and treated with a silane coupling agent.
Using a no-mix or one-step bonding material with ceramic brackets is probably contra-indicated. The no-mix materials contain higher concentrations of amine polymerization accelerator to achieve rapid setting. Therefore, the materials tend to discolor more than those of a two-component mixture. The no-mix systems were designed for thin glue lines and mesh bases, and the larger mechanical grooves and indentations in the mechanically retained ceramic bases may exceed their capability. Also, the polymerization shrinkage of no-mix systems could be too great for these relatively large undercuts and indentations.

Debonding ceramic brackets that use a mechanical interlock does not appear to offer any new difficulties. The archwire is left in place, and each bracket is removed with a pin and ligature cutter or a pincer-type bond removal plier. The principle of applying a slow, peeling force at the bracket base still applies. Compressing the wings together--the least traumatic method for metal twin brackets--will only result in a brittle fracture of the ceramic bracket.
Plastic placement caps are offered with several of the ceramic brackets to assist in identification and alignment. Some practice is required--preferably on a model or typodont--to become familiar with each manufacturer's design. Depending on the clinician's bonding expertise, the placement caps may not be too helpful in height and angulation positioning.
Steel or elastic hook ligatures can be used with care. However, stress induced by steel ligatures can cause brittle failure.