Tight Placement of Erich Arch Bar While Avoiding Wire Fatigue Failure

Objective:  The Erich arch bar is an important surgical device to secure occlusion for jawbone fracture treatment including open and closed reduction, prior to temporomandibular joint and maxillofacial reconstructive surgery, and occasionally skeletofacial deformity correction. The main concern for placement of the Erich arch bar is time consumption during surgery due to a trial and error approach to wire tightening.  The objective of this research was to determine the number of wire twists needed to acquire ideal Erich arch bar tightness before wire fracture (fatigue failure) in relationship to the different distance and angle at which the surgeon grasps the wire with the wire holder. Using this multi-variable clinical experiment, these data were used to present oral and maxillofacial surgeons with a primary clinical guide to aid in the application of Erich arch bars.    

Methods:  This experiment was designed to mimic surgical placement of an Erich arch bar using a plastic mandibular model with 24- and 26-gauge surgical wire.  Wire was twisted clockwise under calibrated handheld force of 28 Newtons to close the air-loop between surgical wire and Erich arch bar.  Four groups were tested and compared depending on wire distance between arch bar and wire holder tip (5mm, 10mm) and the degree at which the wire was held relative to the axis of the tooth (45 degrees, 90 degrees). This procedure was designed to assess the relationship among number of wire twists, arch bar tightness, and wire fatigue failure.  Clinical judgment of Erich arch bar tightness at each number of twists was measured using a visual analog scale with 4 options: no tightness, moderate tightness, tightness, and wire fracture.  Tightness was defined as the point at which the Erich arch bar was completely immobile due to twisting.  After reaching arch bar tightness, a wire shearing test was done using an oscillating movement to test wire strength.  Scanning electron microscopy was then used to assess microscopic wire fatigue.

Results:   24-gauge wire held at 10mm, 45 degree twisting reached tightness in significantly fewer twists (4.38 ± 0.07, n=30 for all groups) compared to those twisted at 90 degrees (4.87 ± 0.05) as determined by unpaired t-test (p<0.05).  In contrast, 24-gauge wire held at 5mm showed no significant difference between number of twists to tightness (p=0.21).  For 26-gauge wire held at 5mm, 45 degree twisting reached tightness in significantly fewer twists (3.30 ± 0.05) compared to those twisted at 90 degrees (3.50 ± 0.05, p<0.05). For 26-gauge wire held at 10mm, 45 degree twisting reached tightness in significantly fewer twists (5.10 ± 0.05) compared to those twisted at 90 degrees (5.23 ± 0.05, p<0.05).  SEM results also showed wire twisted to tightness, wire fatigue due to over-twisting past tightness, and wire strength by wire shearing test.

Conclusions:  When placing an Erich arch bar, holding the wire at a 45 degree angle 10mm from the arch bar results in a tight fit with fewer twists and can withstand more twisting without breaking when compared to a wire held at a 90 degree angle.  Once the arch bar has reached tightness from twisting, additional twisting and shearing forces will weaken the wire, leading to fatigue failure.  This is the first study to utilize scanning electron microscopy to evaluate the wire fatigue during Erich arch bar placement.  The findings of this study may guide efficient arch bar placement with appropriate tightness while avoiding wire fatigue failure.

References:

1. Dingman, Reed O., and Paul Natvig. Surgery of Facial Fractures. Philadelphia: W.B. Saunders, 1964. 124-132.

2. Fonseca, Marciani, and Turvey. Oral and Maxillofacial Surgery. Second ed. Vol. II. St Louis, MO: Saunders, 2009. 139-160.