Impression making in Complete Denture

Impression making in Complete Denture

By- By-

Prof Geeta Rajput Prof Geeta Rajput

Prosthodontics Prosthodontics

Dr.Z.A.D.C Dr.Z.A.D.C

A.M.U Aligarh.

A.M.U Aligarh.

INTRODUCTION

• Complete denture impression procedures are

perhaps one phase on which much has been spoken about. The literature on the subject shows a persistent disagreement ever since 1850.

• Much of this confusion results from the fact that

many impression procedures have been developed on empirical basis.

• Many have used the available knowledge of functional and histological anatomy for the development of their procedures, but the variation in these techniques indicate a wide difference in interpretation of the foundation of dentures.

• Whatever the method used it is generally agreed that good impressions are basic for the construction of a good denture.

-M.M. Devan

“Ideal impression must be in the mind of the dentist before it is in his hand. He must literally make

the impression rather than take

it”

Definitions

Impression -a negative likeness or copy in reverse of the surface of an object; an imprint of the

teeth and adjacent structures for use in dentistry;

Preliminary impression - a negative likeness

made for the purpose of diagnosis, treatment planning, and/or the fabrication of a custom impression tray

Final impression - the impression that represents

the completion of the registration of the surface

or object

Basic Requirements

• Knowledge of facial & oral anatomy

• Knowledge of basic and reliable technique

• Knowledge and understanding of materials

• Skill and Patient management

Anatomical landmarks in Anatomical landmarks in

Maxilla Maxilla

Limiting structures:

Labial frenum Labial vestibule Buccal frenum Buccal vestibule Hamular notch

Posterior palatal seal area

Supporting structures

Primary stress bearing areas :

• Hard palate

• Posterolateral slopes of the residual alveolar ridge

Secondary stress bearing areas :

• Rugae

• Maxillary tuberosity Relief areas :

•

Incisive papilla

•

Cuspid eminence

•

Mid palatine raphae

•

Fovea palatine

Anatomical landmarks in Anatomical landmarks in

mandible mandible

Limiting structures :

Labial frenum Labial vestibule Lingual frenum Buccal frenum Buccal vestibule

Alveolo lingual sulcus Retromolar pad Pterygomandibular raphe

Supporting structures :

• Buccal shelf

• Residual alveolar ridge Relief areas :

• Mylohyoid ridge

• Mental foramen

• Genial tubercles

• Torus mandibularis

Objectives of impression Objectives of impression

making making

PRESS

- Preservation of the alveolar ridges.

- Retention - Esthetics.

-Stability.

- Support.

-

Preservation of the Preservation of the

alveolar ridges alveolar ridges

M.M. De Van’s dictum “It is more important to

preserve what already exists than to replace what is missing”.

• Not to use heavy pressure

• Covering as much of the supporting areas as

possible - minimize the possibility of soft tissue abuse and bone resorption.

Retention

Retention of a denture is that quality inherent in the dental prosthesis acting to resist the forces of dislodgment along the path of placement

•

It depends upon factors that produce

attachment of the denture to the mucosa.

•

Resists the adhesiveness of foods, the force of gravity and the forces associated with the

opening of the jaws

Factors affecting retention of dentures 1. Anatomical factors

2. Physiological factors 3. Physical factors

4. Mechanical factors 5. Muscular factors

1)Anatomical factors

• Size of denture bearing area - Retentive force is directly proportional to the area covered.

• Quality of the denture bearing area- Displaceability of tissues

2)Physiological factors

• Saliva and its quality

3)Physical factors

• Adhesion

• Cohesion

• Interfacial surface tension

• Capillarity and capillary attraction

• Atmospheric pressure and peripheral seal

4)Mechanical factors

• Retentive springs

• Undercuts

• Magnetic forces

• Denture adhesive

• Suction chambers and suction discs

5)Muscular factors

• The muscles apply supplementary retentive forces on the denture.

• It is most effective in the neutral

zone.

Oral and facial musculature

•

Denture bases must be properly extended to cover the maximum area possible

•

The occlusal plane must be at the correct level

•

The arch form of the teeth must be in the neutral

zone

Stability

The quality of a dental prosthesis to be firm, steady or constant, to resist displacement by

functional horizontal or rotational stresses.(GPT-9)

• Relationship of the denture base to the underlying bone

• Attained by more intimate contact of labial

and buccal flanges with the labial and buccal

slopes and of the lingual flanges with the lingual

slopes of the ridge.

To be stable; a denture requires

• Good retention

• No interfering occlusion

• Proper tooth arrangement

• Proper form and contour of the polished surfaces

• Proper orientation of the occlusal plane

• Good control and coordination of the patient's musculature.

Support

• The resistance to vertical forces of mastication and to occlusal or other forces applied in a direction

toward the basal seat.

• Enhanced by selective placement of pressures that are in harmony with the resiliency of the tissues that

make up the basal seat.

Primary support area:- area of edentulous ridge that are at right angle to occlusal

forces & usually do not resorb easily .

• Maxillary:- a)posterior ridge b) flat areas of the palate

• Mandibular:- a)buccal shelf area b)Posterior ridge c)pear shaped pad

Secondary supporting area:- area of

edentulous ridge that are greater than at right angle to occlusal forces ;

Also the area of dentulous ridge that are at right angle to occlusal forces but tend to

resorb under load.

• Maxillary :- anterior ridge ,rugae & all ridge slopes

• Mandibular:- anterior ridge & all ridge slopes

Esthetics

• Prime concern of patients

•

Thickness of the denture flanges

•

Thicker denture flanges are preferred in long- term edentulous patients - labial fullness.

• Impression should perfectly reproduce the

width and height of the entire sulcus for the

proper fabrication of the flanges.

Classification of impressions

A. Based on the theories of impression.

1. Pressure theory- Mucocompressive 2. Minimal pressure- Mucostatic

3. Selective pressure

B. Based on the position of the mouth while making the impression.

1. Open mouth 2. Closed mouth

C. Based on the method of manipulation for border moulding.

1. Hand manipulation

2. Functional movements

MUCOCOMPRESSIVE IMPRESSION MUCOCOMPRESSIVE IMPRESSION

TECHNIQUE TECHNIQUE

• Also known as definite pressure impressions.

• Because denture retention is tested most during mastication, many dentists formerly considered it essential for the tissues to remain in contact with the denture during chewing.

•

It was logical to them to make impressions that would press the tissues in the same manner as

chewing forces, thus ensuring

contact during chewing stroke.

•

However, dentures made from such impressions did not fit well at rest,

because tissues so distorted tend to rebound.

•

Furthermore, these abused tissues

will not be able to long maintain

the shape that they assumed on

the day of impression.

• Many of the proponents of pressure

impressions advocate the use of closed mouth techniques.

• But closed mouth technique do not allow for adequate muscle trimming of the

periphery.

• Very often dentures made with closed

mouth technique are over-extended and must be arbitrarily trimmed.

The materials used for this technique include impression compound, waxes and soft liners.

Mucocompressive Technique

• ADVANTAGE:

Good retention during function.

DISADVANTAGES:

1 : Dentures do not fit well at rest because tissues so distorted tend to rebound to its former contour. This results in premature contacts.

2 : Pressure is sufficient to interfere with the blood supply to the tissues of basal seat &

eventually cause resorption of the residual ridge.

Due to constant pressure on the tissues, mucosal tissue reaction is seen.

3 : Dentures are in occlusal contact for only a relatively short period of time & the

constant pressure even at rest , even if equal may overstress the tissues.

The total time during 24 hours associated with directs functional occlusal force

application to periodontal tissue is 17.5 minutes .

4 : Closed mouth technique does not allow for adequate muscle trimming of the

periphery. Dentures made are often

overextended & must be arbitrarily trimmed.

MUCOSTATIC IMPRESSION MUCOSTATIC IMPRESSION

TECHNIQUE TECHNIQUE

• Also known as minimal pressure impressions.

• Addison in 1944 described this technique and attributed this

to Page.

• The main point of the mucostatic principle concerned Pascal’s law, which states that pressure on a confined liquid will be transmitted through the liquid in all

directions.

•

According to this concept, the

mucosa being more than 80 percent

water, will react like a liquid in a closed vessel and thus cannot be compressed.

•

According to the principle of

mucostatics, the impression material should record without distortion, every detail of the mucosa so that the

completed denture would fit all minute elevations and depressions.

•

Mucostatics further demanded that a metal base be used rather than the

dimensionally stable acrylics.

• The adherents of the mucostatic principle considered interfacial surface tension as the only important retentive mechanism in complete dentures.

• The mucostatic principle ignores the value of dissipating masticatory forces over the large possible basal seat area.

Mucostatic Impression Mucostatic Impression

Technique Technique

• ADVANTAGES:

1:Tissue health is preserved and maintained.

2: Suitable to areas where the residual ridges are sharp, thin & flat flabby ridges.

Disadvantages Of Mucostatic Technique

• 1: Inadequate support :

Ridge tissues are not uniformly displaceable

& a base made from a mucostatic

impression will result in the firmer areas

bearing greatest part of pressure & the more displaceable areas giving little (less) support.

This condition is undesirable from viewpoint of bone preservation & comfort.

2 : Lack of Peripheral Seal:

The impressions made by mucostatic

technique does not displaces even the soft tissues at the borders. This results in lack of border seal.

3 : SHORT FLANGE LENGTH :

The impressions made with non-pressure

technique were significantly under extended.

The flanges of the dentures are shorter. Short flanges do not support the lips and cheeks.

Selective pressure impression

• It is an impression technique that combines pressure over certain areas and little pressure over others.

• The technique utilizes a preliminary compound

impression that is generously relieved over the midline and incisive papilla areas.

• The final impression is taken in plaster , which acts as a wash and also records the relieved areas with minimal pressure while the ridge areas are undergoing

considerable presssure.

• Thus the papilla and midline sections of

the denture will not make contact with the mucosa when the denture is not in

function, but by the same token, they will not bear heavily when the patient is

chewing.

• This principle of impression making is based on the belief that the mucosa over the

ridge is best able to withstand pressure

,whereas covering the midline is thin and contains very little submucosal

tissue.(Boucher,1951)

Combines the principles of both pressure and minimal pressure techniques

Tissue preservation + mechanical factor of achieving retention with minimum pressure, which is within the physiologic limits of tissue tolerance

Philosophy of the selective pressure technique

• Certain areas of the maxilla and

mandible, are by nature better adapted for withstanding extra loads from the

forces of mastication.

• These tissues can be recorded under slight placement of pressure while other tissues must be recorded at rest

Boucher divided basal seat area into

different zones according to capacity to withstand masticatory loads without

undergoing resorption.

Primary stress bearing area

Secondary stress bearing area Relief area

Advantages

•

Technique considers the physiologic functions of the tissues of the basal seat, and therefore appears more sound and appealing.

Disadvantages

•

Some feel that it is impossible to

record areas with varying pressure.

•

Since some areas are still recorded

under functional load, the denture still faces the potential danger of

rebounding and loosing retention

Open-mouth Impressions

Impressions are made with the tray that is held by the dentist

Advantage

Preferred because the operator can see whether muscle trimming is done properly

Closed-mouth Impressions

•

Supporting tissues are recorded in a functional relationship

•

Wax occlusion rims that are made on preliminary casts.

•

Border molding and the final impressions are completed

•

McMillan - tongue movements are more forceful

when teeth are together.

Advantage:- Saving of time Disadvantage:-

• Tendency for overextensions

• Problem of limited space between the tuberosity and pear shaped pad

• No control over the amount of pressure during the final impressions

• Soft tissues – displaced- rebound

• Bone resorption

Steps in impression making

1. Examination and conditioning of the patient and the mouth.

2. Seating of the patient

3. Selection of impression material 4. Selection of the impression tray

5. Selection of impression technique 6. Making the preliminary impression 7. Constructing the primary cast

8. Fabricating the custom tray 9. Border molding

10.Making the final impression

Examination and conditioning of Examination and conditioning of

the patient and the mouth the patient and the mouth

• Inflammation of the mucosa

• Distortion of denture-foundation tissues

• Excessive amounts of hyperplastic tissue

• Insufficient space between the upper and lower ridges

Impression material

Classification

• Elastic

1. Reversible hydrocolloid 2. Irreversible hydrocolloid

3. Rubber impression materials a. Polyether b. Silicone

• Non-elastic

1. Gypsum products

2. Metallic oxide pastes 3. Impression compound

Based on Prosthodontic use

Preliminary impression materials :

1. Impression compound 2. Alginate Final impression materials:

1. Plaster of paris,

2. Zinc oxide-eugenol paste, 3. Irreversible hydrocolloid,

4. Silicone, polysulfide, polyether,

SELECTION OF THE IMPRESSION TRAY SELECTION OF THE IMPRESSION TRAY

A device that is used to carry, confine, and control impression material while making an impression

(GPT-9).

Classification of impression trays

Bases on whether they are prefabricated or individualized

1)Stock trays

2)Custom trays

Depending on the presence or absence of holes or perforations A. Perforated

B. Non-perforated

Depending on whether they are meant for dentate or edentate individuals

A. Dentulous trays B. Edentulous trays

C. Combination trays

Points to be considered during Tray Selection

•

There should be at least 5

mm clearance between the stock tray and the ridge.

•

With the stock tray in

position in the mouth, the handle of the tray is tilted downwards and the

posterior border of the tray is observed. The tray should

extend over the tuberosity

and the hamular notch.

The tray should be neither too large nor too small. In both cases a distorted impression will result.

• If the tray is too large, it will distort the

border tissues by pulling them away from the bone.

• If the tray is too small, the border tissues will collapse inwards towards the residual ridge thus reducing support for the denture.

Seating of the patient

Position of the operator for

maxillary impression

Position of the operator

for mandibular impression

Preliminary impression making Preliminary impression making

:Maxillary :Maxillary

• Practice positioning of the tray

• Labial frenum - guide.

• Anterior fingers - 1st molar region

• Adhesive - silicone putty material or alginate

• Impression compound

Border molding

Labial and buccal vestibules Coronoid process

Impression poured - Plaster

Primary impression : Primary impression :

Mandibular Mandibular

Posterior extent of tray – retromolar pad

Tray loaded with material and catered over the ridge with tongue slightly raised

Alternating pressure on molar region with index finger

Functional movements done to get the border

limit

Constructing the custom tray

• Outline for the wax spacer is drawn on the cast

• Posterior palatal seal area on the cast is not covered with the wax spacer –

maxilla

• Buccal shelf not covered - mandible

• Baseplate wax approximately 1 mm in thickness is placed on the cast

• Self-curing acrylic resin tray material - uniformly adapted over the cast

• Tray thickness - 2 to 3 mm

• Resin handle is attached in the anterior region of the tray

Spacer design

Roy Mac Gregor recommends placement of a sheet of metal foil in the region of incisive papilla and mid palatine raphae

• Neill recommends

adaptation of 0.9 mm casing wax all over

except PPS area

• Boucher recommends placement of 1 mm

base plate wax on the cast except PPS area

• Morrow, Rudd, Rhoads

recommends to block out undercut areas with wax, and placement of 3 tissue stops equidistant from each other

• Sharry recommended Base plate wax adapted over

whole area, four stops 2mm width cut from wax : cuspid and molar region- extend

from palatal aspect of ridge : mucobuccal fold

Border molding

•

Border molding is the process by which the shape of the borders of the tray is made to conform accurately to the contours of the buccal and labial vestibules

•

Manipulation of the border tissues, against a moldable impression material

•

Borders of the tray are molded to a form that

will be in harmony with the physiological action

of the limiting anatomical structures

Border molding may be carried out in

sections either recording one part of the

border at a time or recording all parts of the borders simultaneously.

Recording all of the borders simultaneously has two general advantages:

1. The number of insertions of tray is reduced.

2. Developing all borders simultaneously avoids propagation of errors caused by a mistake in one section affecting the borders contours in another.

Polyether impressions materials are well suited for simultaneous molding of all borders.

Stick impression compound is ideally suited for carrying out border molding in sections

Final Impression

Preparing the tray to secure the final impression:

1. Reduce the borders on the tray that protrude through the polyether.

2. Remove any material that extends internally within the tray more than 6mm.

3. Remove the relief wax.

4. Reduce the thickness of labial flange to approximately 2.5 to 3mm from one buccal frenum to another.

5. Make the final impression in silicone, metallic oxide paste, or rubber base.

References References

• Zarb G, Hobkirk JA, Eckert SE, Jacob RF, editors.

Prosthodontic treatment for edentulous patients. 13th ed.

St. Louis: Elsevier Mosby; 2013 pp 161-179

• Sheldon Winkler, Essentials of complete Denture

prosthodontics, 2nd edition,2012, AITBS Publishers, India, pp 88-105

• Sharry .J.J, Complete denture Prosthodontics, 3rd edition, Mc Graw Hill company, pp 191-210.

• Rudd and Morrow, Dental lab procedures, Complete

dentures, 2nd edition, 1986, Mosby Publications, USA, Pp 9 - 89

• Nair KC, A primer on complete denture fabrication, 1st edition, 2013, Ahuja publication, India Pp 67-77

• Zimmer I.D. and Sherman, H. An analysis of the development of complete denture impression techniques. J Prosthet dent 46: 242-249, 1981.

Thank-you