Impression Procedure

2. MAKING THE PRELIMINARY
IMPRESSION
 An edentulous stock tray is selected that will provide
for approx 5 mm of bulk of impression material over
the entire basal seat area.
 Posteriorly the retromolar pads should be covered by
the tray.
 The tray is raised anteriorly for observation of the
relation between the lingual flanges and the lingual
slope of the lower residual ridge.
 Any areas of under extension need to be corrected
using soft boxing wax before the impression is made.

3.  Before making the preliminary impression, it is advisable to
practice placing the tray in position and to rehearse the
patient.
 Patient is asked to open the mouth halfway, and the tray is
rotated into the mouth in the horizontal plane using the
handle until it is centered over the residual ridge, with the
tongue raised slightly so that it is positioned in the tongue
space of the tray.
 Tray is seated gently by alternating pressure from an index
finger on either side of the tray in the first molar region and
the tongue in relaxed position.
IRREVERSIBLE HYDROCOLLOID
 Tissue surface and borders of the tray are painted with an
adhesive material to ensure that the irreversible hydrocolloid
adheres to the tray.
 The loaded tray is then loaded positioned in the mouth in a
manner similar to that during the practice session.

4.  Once the material has set, the cheeks and lower lip are lifted
away from the borders of impression and the tray is removed
from the mouth in one motion.
IMPRESSION COMPOUND
 Impression compound is used for making the priliminay
impression, the technique is the same except the borders of
the tray are not modified by wax.
 No need to use a tray adhesive.
 Impression compound has high viscosity and thus it is easy
to displace the mylohyoid muscle while making the
impression.
 Preliminary impression has been removed from the mouth
the borders of the custom tray should be identified.

5. CONSTRUCTION OF CUSTOM TRAY
 Wax spacer approx 1mm thick is placed over the crest and
slopes of residual ridge.
 The buccal shelf on each side is left uncovered so that the
custom tray contacts the mucous membrane in the region of
the buccal shelves.
 It helps in positioning the tray correctly in the mouth and to
place additional pressure on this primary stress-bearing area
when final impression is made.
 The custom tray should be 2 to 3 mm thick with an anterior
handle centered over the labial flange in the position of
anterior teeth.
 Achieved by using either a stepped handle of sufficient
height to avoid distortion of the lower lip or a straight handle
approx. 20mm in height.

6.  Anterior handle is used to carry the tray into the mouth and
position it over the residual ridge.
 Posterior handle is used as finger rests to complete the
placement of the tray and to stabilize its correct position.

7. REFINING THE CUSTOM TRAY
 When the custom tray is removed from the preliminary cast,
the wax spacer is left inside the tray which allows the tray to
be positioned correctly on the residual ridge.
 For the border moulding to be carried out successfully space
must be created for the border moulding material.
 Flanges of the custom tray should be reduced until they are
approx. 2mm short of limiting structure.
 Border moulding can be achieved using either an
Incremental technique with stick tracing compound or a
One-step technique with a rubber material such as polyether
impression material.
 When using an incremental technique stick tracing
compound is added and molded initially along the border of
the labial flange, followed in turn by each buccal flange.

8.  Lingually the same sequence is followed, anterior lingual
border is molded first, followed by the left and right
posterior lingual extension including the retro molar pads.
 Irrespective of the method used the following border
molding movements are carried out by the dentist:
1) Labial flange is molded by lifting the lower lip outward,
upward and inward.
2) The region of the buccal frenum, the cheek is lifted
outward, upward, inward, backward and forward to
stimulate movement of frenum.
3) Posteriorly the cheeks are pulled buccaly to ensure that the
cheek is not trapped under the tray and then the cheek is
moved upward and inwards.
4) Anterior lingual flange is molded by asking the patient to
protrude the tongue and to push the front part of the
palate.

9. 5) Protruding the tongue determines the length of the lingual
flange of the tray in this region.
6) Protruding the tongue activates the mylohyoid muscle,
which raises the floor of the mouth. This helps the dentist
to determine the length and scope of lingual flange in
molar region.
7) If the border molding builds up on the inside of the tray, it
must be removed otherwise it may interfere with the
action of mylohyoid muscle.
8) Distal end of lingual flange is molded by asking the patient
to protrude the tongue. This action activated superior
constictor muscle which supports the retromylohyoid
curtain.
9) The patient is then asked to close as dentist applies
downward force on the impression tray. This records the
contraction of medial pterygoid muscle on retromolar
curtain.

10. 10) Finally the patient is asked to open wide. If the tray is too
long a notch is formed at the posteromedial border of
retromolar pad, indicating encroachment of tray on
pterygomandibular raphe and is adjusted accordingly.
11) Final border molded tray should be so formed that it
supports the cheeks and lip in the same manner as the
finished denture will do.
12) The lingual surface of the tray should be shaped so that it
guided the tongue in the same position it will occupy in the
final denture.

11. PREPARING THE TRAY TO SECURE THE FINAL
IMPRESSION
 Space now must be provided for the final impression
material-otherwise the borders will be over extended and the
mucous membrane displaced.
 Wax spacer is removed from the inside of the tray along with
any border molding compound flow over it.
 Any excess material on the outside of the tray is removed
and approx. 0.5mm of border molding material is removed
from around the border.
 Finally small holes can be drilled through the tray, approx
10mm apart, in the center of the alveolar groove and over
retromolar pads, this will provide the escape ways for the
final impression material and relieve the pressure over the
crest of alveolar ridge and retromolar pads when the final
impression is made.

12. MAKING THE FINAL IMPRESSION
 A good final impression cannot be made unless a properly
fitting tray is in correct position on the residual ridge.
 This procedure must be practised before making the final
impression.
 Tray is rotated into the mouth in horizontal plane using the
anterior handle until its over the residual ridge.
 The patient is asked to raise the tongue slightly and the tray
is moved downwards towards its final position.
 The index finger of each hand are placed on top of the
posterior handles and with alternating gentle pressure the
tray is seated until the buccal flange come in contact with the
mucosa covering the buccal shelf.
 Tray held steadily and not moving on residual ridge the
borders of the impression are formed.

13.  Once the dentist and the patient is familiar with the
procedure the final impression material of choice(zinc oxide
eugenol paste) is mixed according to the manufacturer’s
instructions and evenly distributed within the tray.
 All borders must be covered.
 The tongue must be kept forward touching the upper lip
while the impression material sets.
 When the final impression has set the tray is removed from
mouth and inspected for acceptability.
 If it needs to be remade the impression material is removed
carefully preserving the border molding.

14. BOXING IMPRESSION AND MAKING THE
CAST
 A wax is developed around the borders of final impression to
preserve the shape of the periphery and to simplify making
casts, this procedure is called Boxing.
 The technique is same as in the upper impression with the
addition that tongue space is filled with a sheet of wax that is
attached to the superior surface of boxing wax.