The face-bow is a mechanical device (fig. 8-15)
used to duplicate the position of the maxilla to an
articulator. The face-bow rests on the patient's face
and a wax bite plate is inserted into the oral cavity to
record the patient's bite. Several types of face-bows are
available for use.
Impression trays hold the impression material in
place while it sets. The impression may include a
portion of the arch or the entire arch. Generally, the
impression tray is shaped to match the natural contour
of the arch. The two basic types of trays are stock and
custom trays. With either type, the tray used for the
mandibular impression differs from the maxillary tray
because it allows free tongue movement.
Stock trays come in many sizes for both the
maxillary and mandibular arches. As figures 8-16 and
8-17 illustrate, stock trays may be rimlocking or mesh.
Both stock trays are available in regular, edentulous,
and orthodontic styles. Generally, the size of a tray
will be identified on the handle tray.
Rimlock trays are easily identified by a rim that
resembles a metal wire soldered along the inner part of
the tray at the edge of the outer borders. The maxillary
impression tray has a U-shaped wire soldered to a
palatal area on the tray. Semiliquid impression
Figure 8-17.Maxillary and mandibular mesh stock trays.
material flows into the undercuts (ledges) formed by
the rim and sets (hardens). This locks the material in
Use liquid tray adhesive or the spray type on
impression trays to ensure that the impression material
does not separate from the tray. Stock trays are used for
hydrocolloid impression materials. Unless disposable,
stock trays must be cleaned and sterilized after each
Custom trays are made in the dental laboratory
from tray acrylic. Since custom trays are made for
individual patients, you must have a dental cast of the
patient's teeth. The fabrication of custom trays is
discussed later in this chapter.
Figure 8-16.Maxillary and mndibular rimrock stock trays.