lec-5- prosthodontics 2nd class Dr:reem
Special tray and final impression
Special tray ( Individual or custom tray) :An individualized impression
tray made from a cast recovered from primary impression. It is used in making
a final impression. رمي شهاب امحد.م.م
طب الاس نان
On the primary cast , special tray is constructed -as edentulous لكيةshow
ridge – جامعة تكريت
variations of shape & size, some have flattened ridges & other have bulky
ridge, So stock tray can fit the ridge only in an arbitrary manner, so special tray
is constructed.
Fig: Special tray
Advantages of special trays:
1- Economy in impression material ( used less impression material required in
special tray).
2- More accurate impression.
3- Special tray provides even thickness of impression material. This minimize
tissue displacement & dimensional changes of impression material
4- The work with special tray is more easier & quicker than modifying stock
tray to provide accurate impression.
5- Special tray is more accurately adapted to the oral vestibules, this helps in
better retention of denture.
6- Special tray are less bulky than stock tray which is more comfortable for the
patient.
lec-5- prosthodontics 2nd class Dr:reem
Materials used in construction of special tray:
1-cold cure acrylic
2-shellac base plate
3-light cure acrylic
رمي شهاب امحد.م.م
4- heat cure acrylic (rarely)
جامعة تكريت – لكية طب الاس نان
Types of special tray:-
1-spaced tray with wax(with or without stoppers)
2-closed fitted special tray without wax.
Fabrication of special tray with cold cure acrylic
1-The cast should be soaked in water.
2-Severe undercuts should be blocked out using wax.
3-The borders of the special tray and the relief areas should be
marked.
4-The borders of the tray marked on the cast are grooved deeper
using a carver ,this act as guide to trim the tray later.
lec-5- prosthodontics 2nd class Dr:reem
هIn closed fitted special tray For spaced special tray
1 5 رمي شهاب امحد.م.م
5-application of separating 5-adapting the wax نان طب الاس
spacer, جامعة تكريت – لكية
should
medium on study cast about 2mm thick, the posterior palatal
seal on the cast is not covered with the
6-using the cold cure acrylic tray wax spacer
material
6-on the crest of the ridge ., wax should
be cutted2 on canine and2 on molar
area about 2-4mm and is called
stoppers
In order to stabilize the impression tray
during impression making
7-application of separating medium
8- using cold cure acrylic
lec-5- prosthodontics 2nd class Dr:reem
رمي شهاب امحد.م.م
جامعة تكريت – لكية طب الاس نان
Fig:application of wax with stopper(spaced special tray)
Criteria for Special tray construction
1- The impression tray must not impinge upon movable structures.
2- The borders must be under extended (2mm) .
3- The posterior limits of the impression tray should be slightly over- extended
to ensure inclusion of the posterior detail for development of the post-dam area
in upper tray.
4- The tray should be rigid & of sufficient thickness that it will not fracture
during its use.
5- The tray must have a handle for manipulation & the handle must not
interfere with functional movement of the oral structures.
6- The tray must be smooth on its exposed surfaces, and should have no sharp
corner or edges which would injury the patient.
Final or Secondary impression: It is a negative likeness or registration
of the entire denture bearing, stabilizing area and border seal area of the
mandible & maxilla for the purpose of fabricating a prosthesis.
lec-5- prosthodontics 2nd class Dr:reem
The final impression is made with special tray and it is used for making master
cast which must be poured with stone material.
Master cast (definitive or final cast):A replica of the tooth surfaces,residual
ridge areas and \or other parts of the dental arch and \or facial structures used
to fabricate a dental restoration or prosthesis. رمي شهاب امحد.م.م
جامعة تكريت – لكية طب الاس نان
Materials used for final impression:-
1-zinc oxide eugenol impression material
2-Alginate impression material
3-elastomers impression material(polysulfide, polyether and silicon
light body)
4-impression wax
Boxing impression and making the casts:-
Boxing: is the enclosure of an impression to produce the desired size & form of
the base of the cast & to preserve desired details
Boxing impression can be used for primary & final impression for complete
denture. This procedure cannot usually be used on impression made from
hydrocolloid materials (e.g. alginate) because the boxing wax will not adhere
to the impression material & the impression material (alginate) will be
distorted.
Advantages of boxing
1- To facilitate pouring the impression with plaster or stone.
2- Produce the desired size & form of the base of the cast (adequate thickness
of the cast).
3- Preserve desired details &borders of the impression
4- In the lower impression, reproduction of the lingual borders & tongue space
easier.
MATERIALS USED FOR BOXING
lec-5- prosthodontics 2nd class Dr:reem
1- Beading wax: a strip of wax is attached all the way around the outside of
the impression approximately (1-2 mm) below the border &sealed to it with
wax knife.
2- Boxing wax : a sheet of wax is used to made the vertical walls of the box &
it is attached around the outside of the beading wax strip so thatامحد رمي شهاب
it does not.م.م
alter the borders of the impression, the width of the boxingنان
wax الاسis
طبabout
يت – لكية جامعة تكر
10-15
mm.
3- Base plate wax: a sheet of wax can be used to fill the tongue space
in the
lower impression that is sealed just below the lingual border of the
impression
Artificial stone is mixed according to manufacturer s direction and sufficient
stone is poured into the final impression so that the base of the cast will be
from 10-15mm in thickness .The cast is called master cast
Boxing procedure
Special tray making final impression
pouring with stone
Making master cast(accurate details)
lec-5- prosthodontics 2nd class Dr:reem
رمي شهاب امحد.م.م
جامعة تكريت – لكية طب الاس نان
Fig:- Master cast
