Polyphenylene polymers as esthetic orthodontic archwires.

INTRODUCTION: There is continuing interest in an esthetic, effective labial archwire. In this study, we evaluated the potential of new, high-strength polyphenylene polymers to fill this need. METHODS: Polyphenylene (Primospire, Solvay Advanced Polymers, Alpharetta, Ga) polymer was extruded into wires with clinically relevant round and rectangular cross sections. Tensile, flexure, spring-back, stress-relaxation, and formability characteristics were assessed. Arch forms and secondary shapes were formed. RESULTS: Smooth wires with consistent cross-sectional dimensions, high spring-back, and good ductility were produced. Forces delivered were generally similar to typical beta-titanium and nickel-titanium wires of somewhat smaller cross sections. The polyphenylene wire did experience stress relaxation for up to 75 hours. The force magnitudes place polyphenylene wires in the category of an alignment or leveling wire. High formability allowed shape bending similar to that associated with stainless steel wires. CONCLUSIONS: Polyphenylene polymers could serve as esthetic orthodontic archwires; further study is warranted.

Viscoelastic properties of an aesthetic translucent orthodontic wire.

The objective of this study was to evaluate the time-dependent viscoelastic properties of an aesthetic orthodontic archwire. The wire is based on a recently developed translucent polyphenylene thermoplastic, whose rigid molecular structure provides high strength. While the wire has good instantaneous mechanical properties, over time all polymers may relax so it is important to understand the potential impact of the relaxation on orthodontic force systems. Four samples of 0.020 inch round and six samples of 0.021 × 0.025 inch rectangular wire were loaded in tension to a range of initial stresses, and relaxation of the stress was monitored for 7 days. Sixty-three additional samples were maintained in edgewise bracket pairs with vertical displacement for up to 6 weeks. The deformation of these wires was measured immediately after removal from the brackets and for 2 days as the samples recovered. Tensile stress decayed about 10-30 per cent over 24-48 hours depending on the initial stress. The relaxation behaviour was proportional to the initial tensile strain and therefore these data were combined into a single curve using regression. Deformation of the samples placed in the bracket pairs increased with increasing vertical displacement and time, evaluated with analysis of variance, but 19-100 per cent of the deformation was recoverable. The force systems from polyphenylene wires could vary with time and activation, but this behaviour is predictable.

A Tensionable Suture-based Cerclage Is an Alternative to Stainless Steel Cerclage Fixation for Stabilization of a Humeral Osteotomy During Shoulder Arthroplasty.

INTRODUCTION: Fixation of periprosthetic humeral fractures is most commonly obtained with steel-based wires or cables; however, disadvantages with these constructs are numerous. Suture-based cerclages offer the advantage of easy handling, less radiographic interference, and risk of metallosis, as well as decreased risk of cutting into the soft humeral bone. Therefore, the purpose of this study was to compare a suture-based cerclage to a stainless steel wire cerclage (SSWC) for stabilization of the humerus during shoulder arthroplasty. METHODS: In part I of the study, SSWC fixation was compared with single-looped tape cerclage and a double-looped tape cerclage (DLTC) fixation. In part II, a subsidence test was performed on 12 cadaveric humeri. After an osteotomy, the humeri were secured with either a SSWC or DLTC. Subsequently, a metal wedge was introduced into the humerus to simulate the stem of a shoulder arthroplasty. RESULTS: In part I, load to 2-mm displacement was significantly higher for the DLTC construct compared with the SSWC construct (2,401 ± 483 N versus 750 ± 33 N; P < 0.0001). Load to failure was 935 ± 143 N with the SSWC, 1,737 ± 113 N with the single-looped tape cerclage, and 4,360 ± 463 N with the DLTC constructs, and all differences were statistically significant (P < 0.05). In part II, load at 20-mm subsidence was higher for the DLTC (320 ± 274 N) compared with the SSWC (247 ± 137 N), but no significant difference was observed (P > 0.05). However, gap displacement at 20 mm subsidence was significantly lower with the DLTC construct (0.33 ± 0.31 mm versus 0.77 ± 0.23 mm; P = 0.009). Load to failure was higher with the DLTC construct compared with the SSWC construct (4,447 ± 2,325 N versus 1,880 ± 1,089 N; P = 0.032), but the final gap displacement did not differ significantly (DLTC 5.23 ± 6.63 mm versus SSWC 6.03 ± 8.82 mm; P > 0.05). DISCUSSION: A DLTC has higher load to failure and trends toward lower gap displacement compared with a SSWC. The DLTC construct may therefore be a viable alternative for fixation of periprosthetic fractures or osteotomies of the humeral shaft during shoulder arthroplasty.