Ex Vivo Biomechanics of a Bilateral Type I/Bilateral Interdental Pin and Acrylic External Fixator Applied to the Canine Mandible


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Virginia Tech


Bilateral mandibular ostectomies were performed between premolars 3 and 4 in 10 adult canine specimens. A type I external fixator incorporating a full interdental pin was placed stabilizing a 0.5 cm fracture gap. Four different pin configurations were tested in dorsoventral bending five separate times on each of the ten mandibles: 1) intact mandibular bodies with fixator; 2) ostectomized mandibular bodies and complete fixator; 3) ostectomized mandibular bodies with the caudal pins of the rostral fragment cut; 4) ostectomized mandibular bodies with all pins of the rostral fragment cut. The full interdental pin remained intact in all configurations. Total stiffness and gap stiffness were then determined for each fixation geometry on a materials testing machine.

The mean total stiffness(Nm/rads) for the four configurations was 1) 1543.6, 2) 301.6, 3) 290.5, 4) 267.0. The mean gap stiffness(Nm/rads) for the right hemimandible was: 2) 2041.1, 3) 1763.5, 4) 1679.9. The mean gap stiffness of the left hemimandible was: 2) 2110.8, 3)1880.1, 4)1861.1. There was no gap stiffness for the first configuration since a fracture gap was not present.

Two-way ANOVA was performed on the gap stiffness and the total stiffness. There was a significant decrease in total stiffness between intact mandibles and ostectomized mandibles regardless of external fixator configuration. However, there was not a significant difference in total stiffness or gap stiffness among the different external fixator configurations applied to ostectomized mandible. External fixator configurations with only the full interdental pin engaging the rostral fragment were as stiff as configurations which had two or four additional pins in the rostral fragment for the applied loads. External fixators for rostral mandibular fractures may be rigidly secured with rostral fragment implants applied extracortically avoiding iatrogenic trauma to teeth and tooth roots.



External Skeletal Fixation, Mandible and Fracture, Canine