Objective—To determine total stiffness and gap stiffness
of an external fixation system in a canine
mandibular fracture gap model incorporating a full
interdental pin as the only point of rostral fixation in a
bilateral type-I external fixator.
Sample Population—10 canine mandibles.
Procedure—Bilateral mandibular ostectomies were
performed between premolars 3 and 4. A type-I external
fixator incorporating a full interdental pin was
placed to stabilize a 0.5-cm fracture gap. Four pin configurations
(intact mandibular bodies with fixator;
ostectomized mandibular bodies and complete fixator;
ostectomized mandibular bodies with caudal pins
of rostral fragment cut; ostectomized mandibular bodies
with all pins of rostral fragment cut) were tested
in dorsoventral bending 5 times on each mandible.
The full interdental pin remained intact in all configurations.
Total stiffness and gap stiffness were determined
for each configuration on a materials testing
Results—Total stiffness of intact mandibles was significantly
greater than that of ostectomized mandibles,
regardless of external fixator configuration. However,
total stiffness and gap stiffness were not significantly
different among different external fixator configurations
applied to ostectomized mandibles.
Conclusion and Clinical Relevance—External fixator
configurations with only the full interdental pin engaging
the rostral fragment were as stiff as configurations
that had 2 or 4 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. (Am J Vet