Claude G. Matasa

Adhesion and its ten commandments

Despite the fact that retention has been widely discussed in many specialty papers, there is still a lack of information regarding it. The author of the following article happens to have been both a designer or orthodontic adhesives for a major manufacturer and a principal scientist of a Fortune 200 company (in charge of adhesion projects like the substitution of riveting through bonding for airplanes and advanced composites metal/plastics). Based upon his experience, hes trying to relate knowledge which is common in the bonding industry to the needs of the orthodontist.

Bracket angulation as a function of its length in the canine distal movement

The slot angulations that are built into currently manufactured brackets are the same as those recommended more than 20 years ago. Because of a continuous trend toward miniaturization, the bracket slot length has diminished considerably, fact that should have had an impact on the characteristics of the slot. This impact has not yet taken place. A decrease in the overall bracket size and the shortening of the slot length invite unaccounted tooth rotation, which happens when an attempt is made to adhere to traditional angulations. If only a pure translation of a tooth is wanted, such a rotation becomes undesirable. To reduce its action, power arms are used. Unfortunately, these do not solve the problem. Indeed, to overcome this effect, a modification of the values of standard angulations is needed. To illustrate the point, maxillary canine retraction is considered, because it is both common and involves an already high bracket slot angulation. With standard solid mechanics and statics, new angulations are proposed as functions of the bracket slot length and arch wire rigidity. In addition, an estimation of the minimum useful size of the slot is made.

Metal strength of direct bonding brackets

Because the strength of direct bonding brackets is both important and difficult to measure, a related property, microhardness, has been investigated. Twelve popular U.S. brands of direct bonding brackets have been tested with a Vickers-Hanemann microhardness apparatus. The tests have shown a consistently wide difference in hardness between brands, the highest values being exhibited by those using the precipitation hardened steel known as PH 17-4, and the lowest by those using the austenitic 316L. As the first steel proved to be significantly less corrosion resistant than the last one, it seems that today there are too few attachments that are both strong and chemically resistant.