Straight Arch Research Articles

Evaluation of the straight arch wire concept

A n increasing number of orthodontists who work with some sort of edgewise technique are changing their armamentarium of conventional edgewise brackets to a more sophisticated system that allows them to work with arch wires that are unbent except for the basic arch form (straight arch wire). Hence, an increasing number of orthodontic supply companies promote such systems. They carry different names, but all of them ultimately have the same goal-to reduce the time needed by the orthodontist to bend arch wires. (The first company who used and promoted such a system on a large scale called it “the straight wire appliance.“) By looking more closely at the different systems, the orthodontist might detect a rather large variation in the built-in features from one company to another and even within a company’s own system. Many companies claim to have developed-in close cooperation with outstanding clinicians-the ideal system that allows the user to work with no bends (other than the arch form) or with a minimal number of bends. The buyer of any such system, however, should remember that he can buy only the brackets (prewelded on bands or on direct bonding pads) but not the skills of the clinicians who helped the company to develop its system. What might work in one clinician’s hand might not work in another’s. This article seeks to offer the clinician a better understanding of what to expect from the straight arch wire concept and what to consider in the purchase of a straight arch wire system. I believe that a straight arch wire system-correctly applied-can actually help to decrease chair time.

A return to large nonresilient straight arch wires

A return to large nonresilient straight arch wires

Treatment of unerupted incisors

Various orthodontic methods of bringing unerupted central incisors to the line of occlusion have been discussed. Those mentioned here included the use of a straight arch wire, an arch wire with double horizontal loops, threaded pins inserted in the incisal edges, and twisted brass wires around the necks of the unerupted teeth.

Force distribution in splinted anterior teeth

For splinting periodontally involved upper anterior teeth, a straight arch form usually does not afford as favorable a prognosis as a curved arch form. A curved arch splint places the center of rotation posterior to the central incisor area. Occlusal pressure here in a curved arch form causes the splint to revolve about the center of rotation. Since this center is distal to the application of force, the stress applied to the periodontal support in the central area is more apical in direction than in a straight line splint. In the latter case the center of rotation passes through all the teeth in the apical third and causes a tipping movement. Occlusal force at the end of a curved splint also affords a more equitable distribution of stress to the other abutments. In a straight line splint the teeth toward the midline receive less stress from the horizontal rotation. In a natural dentition there is usually more torque on the upper than on the lower anterior teeth. This is true whether there is a fairly deep or a shallow vertical overbite. In a lower anterior curved arch splint, occlusal pressure in the central incisor area causes the splint to rotate around the center of rotation, which passes near the apical third of the canines. The teeth in the central area have stress exerted on the periodontal support in a more apical direction than in a straight arch splint. When we have a fairly deep overbite case with a curved arch, there is less torque on the lower splint than when there is shallow overbite. This is due to the line of force passing closer to the center of rotation in the deep overbite case, producing less torque. The reverse is true for the upper curved arch splint with a fairly deep overbite, which produces more torque than a shallow overbite.