Summary
In order to study the modifying effects of functional appliances on the mechanical
environment of the temporomandibular joint (TMJ), we characterised the structure of
the mandibular condyle subsequent to an experimental functional appliance intervention.
Eight, four-month-old, castrated male Merino sheep, were randomly allocated to experimental
and control groups (n = 4 in each group). Forward mandibular displacement was induced
with an intraoral appliance. The study period was 15 weeks, during which time fluorochromes
were administered to all of the animals. Midsagittal sections of the TMJ were selected
for analysis and trabecular anisotropy was estimated using bone histomorphometry.
Only the experimental group demonstrated that the trabecular bone in the central condylar
region was less anisotropic when compared to the subchondral region. Also, the variation
in trabecular anisotropy of the central condylar region was found to be smaller in
the experimental group. The collagen fibre orientation was analysed under polarised
light as the proportion of the dark or bright fibres observed in regions which existed
before, and regions which formed during the experiment, as determined by the fluorochrome
labels. In the experimental group, more bright collagen fibres were found in the most
superior region of the mandibular condyle when compared with the controls. These results
suggested that the experimental functional appliances changed the orientation and
pattern of the mechanical forces acting on the mandibular condyle, and possibly increased
the magnitude of the lateral functional forces applied to the most superior part of
the condyle during such treatments.
Keywords
Sheep mandibular condyle - growth modification - collagen fibre orientation - trabecular
anisotropy
