Functional impression technique Dr. Dalaya M V
Sep 11, 2014
Functional impression technique
Dr. Dalaya M V
Introduction The distal extension removable partial denture does
not have the advantage of total tooth support One or more bases are extensions covering the
residual ridge for a portion of its support The distal extension removable partial denture
should also obtain some retention from its base Indirect retention to prevent the denture from lifting
away from the residual ridge, should also be incorporated in the design
Whereas the tooth- support base is secured at either end by the action of a direct retainer and supported at either end by a rest, this degree of support and direct retention is lacking in the distal extension restoration
Since the ridge must supply some support for the partial denture functional / dual / physiologic impression technique is used
To equalize as much as possible, the support derived from the edentulous area and that received from the abutment teeth
The impression of the teeth should be made in its anatomic form
Normally teeth do not change position under function to any measurable degree
The impression of the soft tissue, on the other hand, must be made in such a manner as to record the tissues in a functional form
Factors influencing the support of a distal extension base Support from the residual ridge become
more important as the distance from the last abutment increases and will depend on the following several factors:
Contour and quality of the residual ridgeExtent of residual ridge coverage by the
denture base Type and accuracy of the impression Accuracy of the fit of the denture baseDesign of the partial denture frameworkTotal occlusal load applied
Functional impressionsThe form of the residual ridge
recorded under some loading, whether by occlusal loading, finger loading, or the consistency of the recorded medium, in specially designed individual trays is called the functional form
This is the surface contour of the ridge when it is supporting a functional load
Functional impressionsThe objectives of any functional impression
technique are: ◦ Equalize as much as possible the support
derived from the edentulous area, and that received from the abutment teeth
◦ Provide maximum support for the removable partial denture base, thereby distribute the load over as large an area as possible
◦ Direct more occlusal forces to the primary stress bearing regions of the ridge which are more capable of withstanding the forces
◦ Minimize movement of the base which would create leverage on the abutment
Methods for obtaining functional impressionI. Mclean's and Hindel's
physiologic impressionII. Fluid wax method III. Functional reline method
Mclean's and Hindel's physiologic impressioni. Mclean’s physiologic impression The residual ridge that supports a distal
extension base is recorded in its functional or supporting form, and then related to the remainder of the arch by an overall hydrocolloid impression
First impression is held in position with finger pressure
For this impression technique, a selectively relieved acrylic individual tray with modeling plastic occlusion rim is constructed on a diagnostic cast of the arch
Free flowing zinc oxide impression material is used to make an impression in the tray over the distal extension base only
The patient applies steady biting forces during setting of the impression
Then an overall hydrocolloid impression of the dental arch is made with a full arch tray, while the first impression is held in position with finger pressure
ii. Hindel’s Physiologic impression technique
The main change introduced to Mclean's original technique was that the impression of the edentulous ridge was not recorded under biting forces, but was an anatomic impression of the ridge at rest
Made with a free flowing zinc oxide eugenol paste(tray with no occlusion rim)
To establish the relationship between the teeth and the mucosa to a displaced state, a perforated full arch tray that has been provided with two circular openings in the region of the first molar is used
Special tray with no occlusal rim
Overall impression tray with 2 holes in the molar region
As the hydrocolloid second impression is being made, finger pressure is applied through the holes in the tray, to the first anatomic impression
This pressure should be maintained until the alginate impression has hardened
The finished impression will be a reproduction of the anatomic form of the ridge and the surfaces of the teeth
The two are related to each other, as if masticating forces are taking place on the denture base
Fluid wax functional impression technique, Altered cast, split cast impression techniqueAn impression of the displaced edentulous
ridge is made by using an impression tray attached to the metallic framework
The master cast is then altered to accommodate the new ridge impression, for this reason the technique is often referred to as the altered cast or split cast technique
The term fluid wax is used to denote, waxes that are firm at room temperature and have the ability to flow sufficiently at mouth temperature
They prevent over displacement of the tissues and permit equalization of pressure
Fluid wax functional impression technique, Altered cast, split cast impression techniqueThe frequently used fluid waxes are Iowa wax and
Korrecta was No. 4The procedure for making this impression requires
the construction of an individual acrylic tray attached to the acrylic resin, minor connector of the framework
The tray is selectively relieved for the lower arch since, the crest of the ridge is not considered to be a pressure bearing area
The undersurface of the tray is relieved In addition holes are drilled opposite to the residual
ridge and retromolar pad to allow escape of excess impression material as the impression is being made
After softening the impression wax in a water bath, the wax is painted on the tissue surface of the tray, the tray is seated in the patient’s mouth
Patient maintains his mouth half open for about 5 minutes with the dentist’s three fingers placed on the two principal occlusal rests and the indirect retainer
So that the relationship between the partial denture framework and teeth is maintained
The framework is held in its terminal position as the impression is being made
The peripheral extensions are developed by tissue movements
Cheek is moved downward, outward, and upwardFor the distobuccal border the patient must move
to a wide-open-mouth position, to activate the masseter muscle fibers and pterygomandibular raphe, and produce the desired border anatomy
For proper lingual extension, the patient must thrust the tongue into the cheek opposite to the side of that being border molded
The distolingual extension is obtained by having the patient press the tongue against the lingual surface of the anterior teeth
The tray is removed and the wax examined for evidence of tissue contact
Where tissue contact is present the wax surface will be glossy, and where there is no contact the surface will be dull
If needed, additional wax is painted on the areas not in contact with the tissues
After the impression evidences complete tissue contact, and the anatomy of the border limiting structures is evident, a new cast is poured as soon as possible to prevent distortion of the wax impression
Edentulous regions of the master cast are eliminated
Framework and impression are returned and noted to avoid displacement during boxing and pouring procedures
Functional reline methodThis procedure is accomplished before the
insertion of the partial denture, or it may be done later for the purpose of perfecting the fit of the denture base to the residual ridge because of bone resorption
The partial denture is constructed on a master cast made from a single impression usually irreversible hydrocolloid
At the time of denture insertion, a space is provided on the tissue surface of the denture base to allow room for the impression material
Functional reline methodThin layer of modeling compound is painted
on the tissue surface of the denture base, and borders
Modeling compound is tempered in water bath and placed in patient's mouth
This procedure is repeated until base seat tissues are not displaced in the patient's mouth and framework is correctly positioned
Borders are perfected by manipulating cheeks, and having patient form lingual borders by tongue movement
Functional reline methodBorders of compound are shortened, and
whole inside of impression are relieved with exception of buccal region
The final impression is made with free-flowing zinc oxide paste or rubber base
The patient must maintain the mouth in a partially open position while the border modeling, and impression are being accomplished
As in all reline procedures, occlusal discrepancies must be corrected after the denture base has been processed.