Post on 06-Apr-2015
BIOLOGICAL CONSIDERATION IN MANDIBULAR IMPRESSION PROCEDURES
BY SARAVANAN .T.T 1ST YEAR PG
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.
DEFINITIONS
IMPRESSION A negative likeness or copy in reverse of the
surface of an object . – gpt 8
An impression can also be defined as an imprint of the teeth and adjacent structures for use in dentistry. - gpt 4
COMPLETE DENTURE IMPRESSION A complete denture impression is a negative registration
of the entire denture bearing, stabilizing and border seal areas present in the edentulous mouth
PRELIMINARY IMPRESSION A preliminary impression is an impression made for the
purpose of diagnosis or for the construction of a tray
MUCOUS MEMBRANE
MUCOUS MEMBRANE
The bones of the upper and lower edentulous jaws are covered with soft tissue, and the oral cavity is lined with soft tissue known as mucous membrane.
The denture bases rest on the mucous membrane, which serves as a cushion between the bases and the supporting bone.
The mucous membrane is composed of two
layers
Mucosa
Submucosa
The mucosa is formed by the stratified
squamous epithelium and a subjacent
layer of connective tissue known as the
lamina propria.
• The submucosa is formed by connective
tissue.
It may contain glandular , fat , or
muscle cells and transmits the blood
and nerve supply to mucosa.
• The thickness and consistency of
submucosa are largely responsible for the
support that the soft tissue affords the
denture, since in most instances the
submucosa makes up the bulk of the
mucous membrane.
• In a healthy mouth the submucosa is firmly
attached to the periosteum of the
underlying bone of the residual ridge and
will usually successfully withstand the
pressure of the denture.
HISTOLOGY OF THE MUCOUS MEMBRANE COVERING CREST OF THE RESIDUAL RIDGE
BONE
PERIOSTEUM
SUBMUCOSA
MUCOSA
CLASSIFICATION OF
ORAL MUCOSA:
•The oral mucosa is divided in three catogories depending on its location in the mouth •Masticatory mucosa•Lining mucosa•Specialized mucosa
The masticatory mucosa covers the
crest of the ridge
the residual attached gingiva firmly adherent to the
supporting bone
hard palate.
It is characterized by a well defined keratinized
layer on its outermost surface subject to changes in
thickness.
The specialized mucosa covers the dorsal surface
of the tongue. This mucosal covering is keratinized.
The lining mucosa is generally devoid of the
keratinized layer. It is found to cover the :
mucous membrane of lips, cheek
vestibular spaces
alveolingual sulcus
soft palate
ventral surface of the tongue and,
the unattached gingiva found on slopes of
residual ridge.
BIOLOGICAL CONSIDERATIONS
The considerations for the mandibular impressions are generally similar to that for those of maxillary impressions and yet there are many differences owing to the following facts: The basal seat of mandible is different in
size and form from the maxillary counterpart.
The submucosa in some parts of mandibular basal seat contains anatomic structures different from those in the upper jaw.
The nature of the supporting bone on the crest of residual ridge usually differs between the two jaws.
The presence of the tongue complicates the impression procedures for the lower denture.
The available area of support from an
edentulous mandible is 14 cm2 while the
same for the edentulous maxilla is 24cm2 .
The supporting and the peripheral sealing
areas will be in contact with the dentures
fitting or impression areas. The support for
the mandibular denture is derived from the
body of mandible.
The landmarks can be broadly grouped into:
Limiting structures:
Labial frenum Labial vestibule Buccal frenum Buccal vestibule Lingual frenum Alveololingual sulcus Retromolar pads Pterygomandibular raphe.
Supporting structures:
Buccal shelf area Residual alveolar ridge
Relief areas:
Crest of the residual alveolar ridge Mental foramen Genial tubercles Torus mandibularis.
BUCCAL SHELF AREA The area between the
mandibular buccal frenum
and the anterior edge of the
masseter is known as the
buccal shelf.
It is bounded medially by
the crest of the residual
ridge , anteriorly by the
buccal frenum , laterally by
the external oblique line and
distally by retromolar pad.
The buccal shelf forms the primary support for the mandibular denture as it is made primarily of cortical type of bone.
The buccal shelf area can range from 4-6 mm wide on an average mandible to 2-3 mm or less in narrow mandible.
The buccal shelf is very wide and is at right angles to the vertical forces of occlusion. For this reason it offers
excellent resistance to such forces.
Crest Of The Mandibular Ridge The crest is covered by the fibrous
connective tissue, but in many mouths the underlying bone is of cancellous type without a cortical bony plate covering .
The fibrous connective tissue is favorable for resisting the externally applied forces, such as the denture. However, with the underlying cancellous bone this advantage is lost .
Labial Frenum:
This is single narrow band but may
consist of 2 or more bands.
The activity of this area tends to be
vertical so the labial notch on the denture
should be narrow.
Buccal Frenum:
This is usually in the area of 1st pre molar.
The oral activities in these area are
horizontal as well as vertical (ex. Grinning
and puckering) thus needing wider
clearance.
The contour of the denture will be little
narrower in this area due to the activity of
depressor anguli oris muscle.
Labial Vestibule:
It is the sulcus between the buccal
frenums.
The major muscle in this area is orbicularis
oris whose fibers are mainly horizontal
thus overextension in this area should be
avoided.
Buccal Vestibule:
The buccal vestibule extends from the
buccal frenum posteriorly to the outside
back corner of the retromolar pad and
from the crest of the residual alveolar
ridge to the cheek.
Pear Shaped Pad: The retromolar pad as
described by Sicher is the soft
elevation of mucosa that lies
distal to the third molar.
It contains loose connective
tissue with an aggregation of
mucous glands and is
bounded posteriorly by the
temporalis tendon , laterally
by the buccinator, and
medially by the
pterygomandibular raphe and
the superior constrictor.
Lingual Vestibule:
It can be divided into three areas
anterior vestibule/sublingual crescent
area/ anterior sublingual fold
the middle vestibule/ mylohyoid area
the distolingual vestibule/ lateral throat
form/ retromylohyoid fossa
Anterior lingual vestibule
This extends from the lingual frenum to
where the mylohyoid ridge curves down
below the level of sulcus. Here a
depression the premylohyoid fossa can be
palpated.
This is mainly influenced by the
genioglossus muscle, lingual frenum and
some part by anterior portion of sublingual
glands .
Middle vestibule:
This is the largest area and is mainly influenced by mylohyoid muscles and somewhat by sublingual glands.
The mylohyoid muscle is the largest muscle in the floor of the mouth whose principal function occurs during swallowing. Its intra oral appearance is misleading because the membranous attachment makes the muscle appear to be horizontal when contracting.
Sears has shown that at maximum contraction the fibers are still in a downward and forward direction so that a denture can be extended below the muscle attachment along the mylohyioid ridge.
The average mylohyoid border is 4-6 mm beyond the mylohyoid ridge in fair to good ridge it is about 2-3 mm . If the ridge is flat it is often advantageous to make mylohyoid border thicker (4-5mm or more).
Distolingual vestibule:
The lateral throat form is bounded anteriorly by mylohyoid muscle, laterally by pear shaped pad, posterolaterally by superior constrictor, posteromedially by palatoglossus and medially by tongue.
The so called “s” curve of the lingual flange of the mandibular denture results from stronger intrinsic and extrinsic tongue muscles, which usually place the retromylohyoid borders more laterally and towards the retromylohyoid fossa, as the oppose weaker superior constrictor muscle.
The posterior limit of the mandibular denture is determined mainly by the palatoglossus muscle and somewhat by weaker superior constrictor muscle this is area is called posterior/ retromylohyoid curtain.
Neil described this area and noted that the
denture could have three possible lengths,
depending on the tonicity, activity, and
anatomic attachments of the adjacent
structures-
Class I throat form: The horizontal border is usually 2-3 mm thick, but a thicker border of 4-5 mm should be used for better seal if the ridge is flat. The retromylohyoid curtain area should be thinner, about 2-3 mm, and very rounded and smooth.
Class II throat form is about half as long and narrow as class I and about twice as long as class III.
Class III lateral throat form has minimum length and thickness. The border usually ends 2-3 mm below the mylohyoid ridge or sometimes just at the ridge.
BASIC REQUIREMENTS FOR IMPRESSION MAKING
Knowledge of Basic anatomy Knowledge of basic reliable technique Knowledge and understanding of
impression materials Skill Patient management
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OBJECTIVES OF IMPRESSION MAKING
1) RETENTION2) STABILITY3) SUPPORT4) ESTHETICS5) PRESERVATION OF REMAINING
STRUCTURES
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