the occlusal situation. For this reason, maintaining or restoring functional stress to the canine pillar area may be considered essential as a prophylactic measure. Cosmetic advantages are also de-rived from maintaining the volume of the canine pillar. Superficially, the pillar is convex and supports the naso-mental crease. When the bone behind this crease recedes (10), the crease deepens.

The zygomatic pillar begins in the region of the first molar (11). It continues upward, flaring outward to follow the zygoma. In the body of the zygoma, the pillar trifurcates to pass supraorbitally (12), infraorbitally (13), and over the zygomatic arch (14).

Of the three maxillary pillars, the zygomatic pathway curves most extremely. Its base forms the lateral wall of the maxillary sinus. When balanced functional stimulation is maintained in the area of the first molar, the lateral wall has a significant core of spongy bone (15). Disuse atrophy or trauma can thin the wall significantly, until the bone over the sinus becomes eggshell-thin (16) — an inappropriate site for a subperiosteal strut.

The zygomatic pillar area is particularly susceptible to some-
times dramatic dropping of the sinus. In most adults, the lowermost
point of the sinus lies between the first molar and second bicuspid.
Lack of functional stimulation to the area leads to the rather rapid
dropping of the sinus when a single tooth is lost, or the draping
of the sinus over the roots of teeth that have lost their antagonists.
The pterygoid pillar begins in the sockets of the second and
third molars (17) and ascends backward over the tuberosity, across
the palatine bone anchoring the pterygoid process to the maxilla,
and onto the pterygoid process of the sphenoid bone. This particu-
lar pathway is noteworthy because its base involves the maxillary
tuberosity, a core of spongy bone that defines the most posterior
extent of the sinus. Even after disuse atrophy leads to extensive
alveolar bone loss, deflected stress may maintain enough spongy

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