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.