Postpalatal seal area is defined as ‘the soft tissues area at or beyond the

junction of the hard and soft palates on which pressure, within physiological

limits, can be applied by a complete denture to aid in its retention’.

It lies in the area of the soft palate and provides the peripheral seal

to the denture. The seal prevents air between the denture and the

tissues and helps in resisting the horizontal and torquing forces.

The histological content of this area consists of a thick submucosa,

containing glandular tissues, which allows displacement of the tissues

without impairment.

Functions of PPS

• Aids in retention

• Reduces gag reflex

• Reduces food accumulation between the posterior aspects of the

denture

• Reduces patient discomfort

• Compensates for polymerization shrinkage

PPS can be divided into two separate areas on the basis of

anatomical boundaries, which are as follows:

(i) Postpalatal seal: This extends medially from one tuberosity to

another.

(ii) Pterygomaxillary seal: This extends laterally from one hamular

notch to another and 3–4 mm anterolaterally approximating the

mucogingival junction.

The PPS lies between the anterior and posterior vibrating lines (Fig.

4-9).

FIGURE 4-9 Posterior palatal seal.

Anterior vibrating line

It is an imaginary line located at the junction of the attached tissues

overlying the hard palate and the movable tissues of the immediately

adjacent soft palate. The anterior vibrating line is cupid bow shaped

due to the projection of the posterior nasal spine.

Methods to locate anterior vibrating line

The Valsalva manoeuvre: In this method, both the nostrils of the patient

are held firmly and the patient is asked to gently blow through the

nose. This positions the soft palate inferiorly at its junction with the

hard palate.

Visualization method: This can also be located by asking the patient to

say ‘ah’ in a short vigorous burst and visualizing the area.

Posterior vibrating line

This is an imaginary line at the junction of the aponeurosis of the

tensor veli palatine muscle and the muscular portion of the soft palate.

Posterior vibration line is visualized by asking the patient to say ‘ah’

in a short burst in normal, unexaggerated fashion. It marks the distal

most extension of the denture base.

Techniques to Record PPS

(i) Conventional approach

(ii) Fluid wax technique

(iii) Arbitrary scraping of master cast

Conventional approach

• ‘T’ burnisher is used to locate the hamular notch.

• An indelible pencil is used to extend a line from hamular notch on

one side to the other.

• The patient is instructed to say ‘ah’ in short burst.

• The mark is placed at the junction of movable and nonmovable soft

palate.

• This mark is transferred to master cast.

• The cast is scraped to a depth of 1–1.5 mm in resilient areas and 0.5–

1 mm in less resilient area.

• The scraping should taper progressively.

Fluid wax technique

• The procedure followed is similar as described above, except that

special waxes, such as Iowa wax or Korecta wax, are used.

• After secondary impression, these fluid waxes are applied in the

posterior seal region.

• Various head and tongue movements are made to record posterior

palatal seal.

Arbitrary scraping of master cast

• It is the least accurate method and should not be followed.

• Cast is arbitrarily scraped by the dentist.

Biological considerations in

mandibular impressions

The available denture-bearing area for the edentulous mandible is

only 14 cm2

, whereas that of the maxilla is around 24 cm2

.

The basal seat of the mandible is different from the maxilla in terms

of size and form.

The anatomical landmarks in mandible can be studied as follows

(Fig. 4-10):

FIGURE 4-10 Anatomic landmarks of the mandibular arch.

Supporting Structures

(i) Primary stress-bearing area

• Buccal shelf area

• Pear-shaped pad

(ii) Secondary stress-bearing area

• Residual alveolar ridge

Buccal shelf area

• It extends between the mandibular buccal frenum and the anterior

border of the masseter muscle (Figs 4-10 and 4-11).

• Its boundaries are as follows:

• Medially by the crest of residual ridge

• Anteriorly by the buccal frenum

• Laterally by the external oblique ridge

• Distally by the retromolar pad

• It is covered by a layer of cortical bone and lies at right angles to the

vertical occlusal forces

• It is covered by mucosa with submucosal layer containing

buccinator fibres and glandular fibres.

• Buccinator fibres run along the buccal shelf in anteroposterior

direction and portion of the denture base lies directly on the muscle

without displacement.

• Width of the buccal shelf area:

• 4–6 mm

• 2–3 mm (in case of narrow mandible)

• As it lies at right angles to the occlusal forces, it serves as primary

stress-bearing area.

FIGURE 4-11 Location of buccal shelf region.

Pear-shaped pad

• It is the distal most extent of keratinized masticatory mucosa of the

mandibular ridge.

• It is formed by scarring pattern after third molar extraction.

• The term was coined by F.W. Craddock.

• The retromolar pad lies distally to the pear-shaped pad.

• Distal border of the mandibular impression should extend to the

junction of retromolar pad and pear-shaped pad.

• Buccinator, superior constrictor and temporal muscles are attached

to it.

• Muscle attachment and overlying keratinized mucosa provide

stress-bearing region that is relatively resistant to resorption.

• It is considered as the primary stress-bearing area (T.R. Jacobson

and A.J. Kroll).

Residual alveolar ridge

• The crest of the ridge is covered by fibrous connective tissue.

• The underlying bone is mostly cancellous without any muscle

attachments.

• The submucosa, if loosely attached, makes the soft tissue movable,

thereby making the denture construction difficult; however, if

firmly attached it provides good support.

• Ridge crests are considered as secondary support areas (Fig. 4-10).

Limiting structures

Labial frenum

• It contains a band of fibrous connective tissue which attaches the

orbicularis oris muscle (Fig. 4-12).

• Frenum is active and quite sensitive.

• It should be carefully relieved to avoid soreness and provide

adequate seal.

FIGURE 4-12 Location of labial and buccal vestibule.

Labial vestibule

• This extends from the labial frenum to the buccal frenum on each

side (Fig. 4-12).

• Related muscles are orbicularis oris and mentalis.

• The depth of the flange is determined by the mucolabial fold.

• The extent of the flange in this area is limited because the muscles

are inserted close to the ridge crest.

• If the flange is thick and the mouth is wide opened, the orbicularis

oris narrows the sulcus which in turn displaces the denture.

Buccal frenum

• It is a fold or folds of mucous membrane extending from the buccal

mucosa to the slope or the crest of the residual ridge (Fig. 4-12).

• It may be single or double, broad U-shaped or sharp V-shaped.

• It overlies the depressor anguli oris.

• Relief must be provided in the denture base to avoid dislodgement

of the denture.

Buccal vestibule

• It extends from the buccal frenum to the retromolar pad area (Fig. 4-

12).

• It is bounded by the residual alveolar ridge on one side and the

buccinator muscle on the other.

• The extent of the vestibule is influenced by the buccinator muscle

and the distobuccal border at the end of the buccal vestibule is

influenced by the action of masseter on the buccinator.

• Buccinator muscle extends from the modiolus to the

pterygomandibular raphe and attaches to the buccal shelf region.

• Because its fibres run horizontally, it has seating effect on the

denture Fig. 4.3.

• Contraction of the masseter alters the shape and size of the

distobuccal end of the lower buccal vestibule.

• Masseter pull is recorded by asking the patient to exert the closing

force, in which the operator applies the force in opposite direction.

Lingual frenum

• It is a fibrous band of tissue that overlies the centre of the

genioglossus muscle (Fig. 4-12).

• It is an extremely resistant and active frenum.

• It is usually a narrow single band of tissue but may be broad.

• Relief is needed in this area of the impression as well as in the

finished denture because inadequate clearance may result in pain or

displacement of the denture.

• A high lingual frenum is called a tongue-tie and should be

corrected, as it affects the stability of the denture.

Alveololingual sulcus

• It is the space between the residual ridge and the tongue and

extends from the lingual frenum to the retromylohyoid curtain (Fig.

4-13).

FIGURE 4-13 Alveololingual sulcus.

• It is divided into the following three areas:

(i) Anterior vestibule referred to as the sublingual

crescent area or the anterior lingual fold

(ii) Middle vestibule referred to as the mylohyoid area

(iii) Posterior vestibule or the distolingual sulcus

Anterior region

• It extends from the lingual frenum to the premylohyoid fossa, where the

mylohyoid ridge curves below the sulcus.

• Length and width of the border are important in maintaining the

seal of the lower denture.

• Position of the tongue is important in maintaining this seal.

• It is influenced indirectly by the mylohyoid muscle.

• The lingual border of the impression in the anterior region should

extend down to make contact with the mucosa of the floor of the

mouth when the tip of tongue touches the upper anteriors.

• The anterior lingual flange will be shorter than the posterior lingual

flange.

Middle region

• It extends from the premylohyoid fossa to the distal end of mylohyoid

ridge, curving medially from the body of the mandible.

• This curvature is caused by the prominence of the mylohyoid ridge

and the action of the mylohyoid muscle.

• The length and width of the flange are determined by the

membranous attachment of the tongue to the mylohyoid ridge.

• The lingual borders are formed when the mylohyoid muscle is

functional.

• The middle of lingual flange should slope medially towards the

tongue, which helps in three ways as follows:

• The tongue rests over the flange, thereby stabilizing

the denture.

• This provides space for raising the floor of the

mouth without displacing the denture.

• The peripheral seal is maintained during the

function.

Posterior region

• This is the distolingual vestibule, also referred to as lateral throat form

or retromylohyoid fossa.

• Posterior lingual flange usually extends more inferiorly than the

anterior lingual flange.

• The border of the lingual flange in this region assumes the typical ‘S’

shape because of the projection of mylohyoid ridge towards the

tongue and the existence of retromylohyoid fossa at the distal end

of the sulcus.

• The distal end of the lingual flange is called the retromylohyoid

eminence and its contour lies below the level of retromolar pad.

Retromolar pad

• It is an important structure which forms the posterior seal of the

mandibular denture (Fig. 4-10).

• The denture should include the retromolar region.

• It aids in stability by adding another plane to resist the movement of

the denture base.

• It is a triangular soft pad of tissue at the distal end of lower ridge.

• It consists of pterygomandibular raphe, fibres of superior constrictor

and buccinator muscle, fibres of temporalis tendon and some

glandular tissues.

Relief areas

Mylohyoid ridge

• It extends along the lingual surface of the mandible.

• Anteriorly, the ridge lies close to the inferior border of the mandible,

whereas posteriorly it flushes with the superior surface of the

residual ridge.

• Thin mucosa over the ridge should be relieved to avoid trauma.

• The lingual flange should be properly shaped and extended during

the impression making to ensure proper border seal.

Mental foramen

• It lies between the first and second premolar region.

• Severe resorption of the bone may result in mental foramen lying at

the crest of the ridge.

• Relief should be provided to avoid paraesthesia of the lip.

Torus mandibularis

• It is a bony prominence usually found at the first and second

premolar region.

• It is covered by a thin mucosa and should be relieved to avoid

soreness of denture.

• It is surgically removed if large and interferes with the denture

retention and stability.

Primary impression

Definition

Primary or preliminary impression is defined as ‘a negative likeness

made for the purpose of diagnosis, treatment planning or the fabrication of a

tray’.

This is the first step in fabricating complete denture prosthesis for a

patient.

For this purpose, an impression tray is used.

Impression tray: It is defined as ‘a device that is used to carry, confine

and control impression material while making an impression’ or ‘a receptacle

into which suitable impression material is placed to make a negative likeness’.

Classification (Lavere and Treda [1976])

Impression trays are of two types: (i) stock trays and (ii) custom trays

(i) Stock trays are further classified as follows:

Type A: Disposable and nondisposable

Type B: Metallic and nonmetallic

Type C: Perforated and nonperforated

• Rim lock trays: Thickened flange edges for

mechanical retention.

Rim lock trays can be of two types on the basis of type

of dental arch:

(a) Edentulous

(b) Dentulous

(ii) Custom trays are also called special trays or final impression trays or

individualized trays.

Ideal requirement of impression trays

• Tray should be rigid.

• It should be dimensionally stable.

• It should be smooth to avoid injury to mucosa.

• It should provide uniform space for impression material.

• It should not distort the vestibular area.

Points to consider during tray selection

• Stock tray should have 5–6 mm of space between the ridge and the

tray.

• Tray is placed in mouth by centring the labial notch of the tray over

the labial frenum.

• Once the tray is anteriorly positioned, it is observed posteriorly for

extension.

• A slightly oversized tray is always selected.

• The tray should not be too large or too small.

Functions of the tray

• To support the impression material in planned contact with oral

tissues

• To allow the placement of additional stress in selected regions of the

residual ridge while recording other regions in an undisplaced state

• To support the impression material when removed from the mouth

so that a cast can be poured

Principles of Impression Making

• Impression should extend to cover all the basal seat area.

• Borders should be in harmony with the anatomical and

physiological limitations of oral tissues.

• Border moulding should be performed.

• Selective pressure should be applied on the basal seat during

impression making.

• Proper space should be provided for the impression material.

• Guiding mechanism should be provided for correct positioning of

the tray.

• Tray and final impression should be made of dimensionally stable

material.

• External shape of the final impression should match the external

surface of denture.

• Oral tissues should be in healthy state.

• Impression when removed from the mouth should not damage the

soft tissues.

• Sufficient space should be available for the impression material in

the impression tray.

Primary cast

Primary cast is defined as ‘a positive likeness of a part or parts of the oral

cavity for the purpose of diagnosis and treatment planning’.

Requirements of a primary cast

• The surface should be smooth, dense and free of voids.

• It should cover all the area which provides denture support.

• Wall of the cast should be parallel or diverging outwards but should

never be converging inwards.

• Tongue space should be smooth.

• Occlusal table should be parallel to the floor.

Uses of primary cast

• To measure the depth and extent of undercut

• To evaluate the size and contour of the arch

• To determine the path of insertion of the denture

• To perform a mock surgery

• To educate the patient

• To determine the requirements for preprosthetic surgery

Custom tray

A custom tray or special tray is defined as ‘an individualized

impression tray made from a cast recovered from a preliminary

impression. It is used in making a final impression’.

Ideal requirements of a custom tray

• It should be dimensionally stable on the cast and in the mouth.

• It should have an excellent fit.

• The tissue surface should be free of voids or projections.

• It should be rigid in thin sections, especially in the palatal or lingual

flange region.

• It should not warp or flow.

• It should be easy to remove and should not react with the

impression material.

• It should be 2 mm short from the sulcus to provide space for the

green stick compound.

Materials used for fabrication

• Self-cure resin

• Shellac

• Vacuum-formed thermoplastic resin

• Vacuum-formed polystyrene

• Type II impression compound

Adapting relief wax

• Relief wax is adapted over relief areas in the maxillary and

mandibular casts.

• Relief is provided to prevent any excessive pressure on the

nonstress-bearing areas.

• It is 2 mm in thickness and can vary depending on the quality of the

tissues.

Spacer thickness and design

• A wax spacer is then placed within the outlined border to provide

space for the impression material in the tray.

• It also ensures that the loaded tray is not too bulky and allows the

ease of placement in the mouth.

• A planned relief is designed to carry out the impression procedure

best suited for the patient.

• This depends on the tissue tonicity and on the difference in the

displaceability of tissues in every patient and in different buccal

areas of the same patient.

• In addition, the special circumstances that sometimes occur in a

given clinical situation may indicate the use of different shaped

spacers.

• The technique by A.R. Halperin suggests that peripheral relief

provided by the spacer so that a uniform space for border moulding

material and correct positioning of tray are achieved.

• Some areas that are routinely relieved in selective pressure

technique are incisive papilla, mid-palatine raphe in the maxilla and

the crest of the ridge in the mandible.

• Baseplate wax, approximately 1 mm thick, is placed on the cast

within the outlines to provide space in the tray for the final

impression material.

• The PPS area is not covered with the wax spacer and in the lower

area the buccal shelf area is left uncovered.

• In addition to this, tissue stops can also be placed in the wax spacer.

Method of fabrication

• Eliminate undercuts with a thin coat of wax and paint the cast with

tin foil substitute and allow it to dry.

• The acrylic resin can be adapted on the cast by sprinkle-on method

or by dough method.

Sprinkle-on method

• In this method, the powdered polymer is shifted on the cast and is

saturated with the liquid monomer until a uniformly thick tray is

formed.

• The tray might be too thick or too flexible.

• It might be too thin over the ridges and too thick over the palates.

• It is important that the tray is 2–3 mm thick.

• Remove the tray only after complete polymerization has taken

place.

• Afterwards, the handle is placed on the tray, which could be a

stepped handle or an angulated handle.