Force degradation of closed coil springs: an in vitro evaluation.

This in vitro study was designed to determine the force degradation of closed coil springs made of stainless steel (SS), cobalt-chromium-nickel (Co-Cr-Ni) and nickel-titanium (Niti) alloys, when they were extended to generate an initial force value in the range of 150 to 160 gm. The specimens were divided into two groups. Group I included SS, Co-Cr-Ni, and two nickel-titanium spring types (Niti 1 and Niti 2), 0.010 x 0.030 inch with an initial length of 12 mm. Group II was comprised of SS, Co-Cr-Ni, and Niti 3 0.010 x 0.036-inch springs, with an initial length of 6 mm. A universal testing machine was used to measure force. A pilot study determined the extension required for each spring type, so that the initial force was in the range of 150 to 160 gm. Initial force was recorded, and then the springs were extended to the respective distances at 4 hours, 24 hours, 3 days, 7 days, 14 days, 21 days, and 28 days resulting in a total of eight time periods. Between the time intervals, all springs were extended to the same initial extension on specially designed racks and stored in a salivary substitute at 37 degrees C. Means and standard deviations of force values, percent force loss, and mean extension were statistically analyzed. All springs showed a force loss over time. Of the total, the major force loss for most springs was found to occur in the first 24 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of friction between ceramic brackets and orthodontic wires of four alloys.

The purpose of this investigation was to determine the frictional resistance offered by ceramic brackets used in combination with wires of different alloys and sizes during in vitro translatory displacement of brackets. Findings with ceramic brackets were also compared with outcomes of treatment with stainless steel brackets. Stainless steel, cobalt-chromium, beta-titanium, and nickel-titanium wires of different cross-sectional sizes were tested in medium-twin monocrystalline ceramic brackets with both 0.018-inch and 0.022-inch slot sizes. The wires were ligated into the brackets with elastomeric modules. Brackets were moved along the wire by means of an Instron universal testing machine, and frictional force was measured by a compression cell and recorded graphically on an xy recorder. Wire friction in the ceramic brackets increased as wire size increased, and rectangular wires produced greater friction than round wires. Beta-titanium and nickel-titanium wires were associated with higher frictional forces than stainless steel or cobalt-chromium wires. These findings follow the same general trends as those found with stainless steel brackets; however, wires in ceramic brackets generated significantly stronger frictional force than did wires in stainless steel brackets.

Evaluation of friction between edgewise stainless steel brackets and orthodontic wires of four alloys.

This investigation was designed to determine the effects of wire size and alloy on frictional force generated between bracket and wire during in vitro translatory displacement of bracket relative to wire. Stainless steel (SS), cobalt-chromium (Co-Cr), nickel-titanium (NiTi), and beta-titanium (beta-Ti) wires of several sizes were tested in narrow single (0.050-inch), medium twin (0.130-inch) and wide twin (0.180-inch) stainless steel brackets in both 0.018- and 0.022-inch slots. The wires were ligated into the brackets with elastomeric ligatures. Bracket movement along the wire was implemented by means of a mechanical testing instrument, and frictional forces were measured by a compression cell and recorded on an X-Y recorder. beta-Ti and NiTi wires generated greater amounts of frictional forces than SS or Co-Cr wires did for most wire sizes. Increase in wire size generally resulted in increased bracket-wire friction. The wire size-alloy interaction on the magnitude of bracket-wire friction was statistically significant (p less than 0.005). With most wire sizes and alloys, narrow single brackets were associated with lower amounts of friction than wider brackets were. The levels of frictional forces in 0.018-inch brackets ranged from 49 gm with 0.016-inch SS wires in narrow single brackets to 336 gm with 0.017 x 0.025-inch beta-Ti wires in wide twin brackets. Similarly for 0.022-inch brackets, frictional forces ranged from 40 gm with 0.018-inch SS wires in narrow single brackets to 222 gm with 0.019 x 0.025-inch NiTi wires in wide twin brackets.

An evaluation of the shape-memory phenomenon of nickel-titanium orthodontic wires.

This investigation was undertaken to quantitatively analyze the shape-memory phenomenon of wires made of seven commercially available nickel-titanium alloys. The shape memory was determined by calculation of the percent shape recovery that occurred when the wire of each alloy was first plastically deformed below its TTR and then heated to a temperature above its TTR. The findings indicate that: 1. The mean percent recovery ranged from 89% to 94% for Ni-Ti, nitinol, Orthonol, Titanol, Sentinol Light, and Sentinol Medium alloys. The Sentinol Heavy alloy showed a mean recovery of 41.3%, which was significantly less than that of the other alloys. 2. It appears that Sentinol Heavy wire showed relatively less percent recovery because its TTR was close to room temperature. This resulted in minimal plastic deformation, because the alloy recovered its original length almost immediately, and this also indicates the importance of a proper TTR. It was concluded that the TTR should be reasonably higher than the oral temperature for clinical application of the shape-memory phenomenon of nickel-titanium alloys. 3. The heat-recovery temperature was kept to 300 degrees F in this study for maximum possible recovery. Although the results indicate that the recovery was around 90% for most alloys tested, future studies are required to determine the shape recovery at or just above oral temperature.

An in vitro evaluation of bond strength of three glass ionomer cements.

The purpose of this study was to determine the bond strength of three commercially available glass ionomer cements when used to bond mesh-backed medium twin (0.130 inch) brackets to enamel surface. Three different enamel surface conditions, which included use of pumice, pumice and polyacrylic acid, and pumice followed by acidulated phosphate fluoride, were also tested to determine their effect on the bond strength. In addition, bond strength of one composite resin was compared with those of glass ionomer cements. The teeth were bonded with all the materials according to manufacturers' instructions. Each specimen was embedded in Super-Die with the bonded facial surface exposed. A surveyor was used to align the teeth in the stone uniformly for all specimens. A special bracket holder was used to hold the brackets precisely under the wings during debonding. An Instron universal testing machine was used to measure the force required for bond failure. To stimulate oral conditions, the direction of pull was so designed that it included an element of torsional stress along with tensile force. The findings indicate that a large variation existed between the bond strengths of all materials tested. The bond strength of glass ionomer cements was significantly less than that composite resin. However, the bond strength of at least one glass ionomer cement appears to be adequate for clinical use. The different surface preparation before bonding did not significantly affect the bond strengths of glass ionomer cements. Further investigation is required to test the bond strengths of glass ionomer cements clinically.