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1. BIOLOGIC CONSIDERATIONS OF MANDIBULAR
EDENTULOUS FOUNDATION
Total area of usable support in the mandible is less
compared to that of maxillae. So the mandible is less capable of
resisting occlusal forces than the maxillae and much care is
essential to take advantage of the available support in the
mandibles.
Total width of bony foundation and mandibular basal seat
becomes greater in the molar region as resorption continues. The
reason is that the width of the inferior border of the mandible from
side to side is greater than the width of the mandible at the
alveolar process from side to side.
Supporting structure: Support for lower denture is provided
by the mandible and soft tissues overlying it, some parts of the
mandible are more favourable for this foundation than others.
1) Crest of the residual ridge:
- Usually has a cancellous type of bone without a good
cortical bone plate covering it. The crest of the ridge

2. may be sharp, thin or even contain larger nutrient
canals.
- So under these circumstances it cannot be utilized for
bearing primary stresses.
2) Buccal shelf area:
- Area between the mandibular buccal frenum and
anterior edge of masseter muscle.
- Bounded medially by the crest of the residual ridge,
anteriorly by buccal frenum, laterally by external
oblique ridge and distally by retromolar pad.
- It represents an area of compact bone which is at right
angles to the direction of vertical occlusal forces.
- This is the primary stress bearing area and should be
occupied correctly in the primary impression.
- It takes the occlusal load off the sharp narrow crest of
the residual alveolar ridge.

3. 3) Mylohyoid ridge:
- Begins near the posterosuperior aspect of the alveolar
process on the medial side of the mandible. It is a
prominent ridge inclined anteroinferiorly through the
molar area. It may continue to the symphysis.
- Soft tissues often hide the sharpness of the mylohyoid
ridge which can be found by palpation.
- Mylohyoid is attached all along the ridge. Anteriorly
the muscle attaches close to the inferior border of the
mandible and posteriorly it may flush with superior
surface of residual ridge.
4) Mental foramen area:
- In greatly resorbed mandibles, the mental foramina
lies on or near the crest of the residual ridge. This can
result in impingement of blood vessel and nerves if
relief is not provided in the denture base. Pressure on
mental may cause numbness of lower lip.

4. LIMITING STRUCTURE
1) Labial Frenum
- It contains a band of fibrous connective tissue with no
muscular element.
- It is influenced by the perioral musculature i.e.
orbicularis oris.
- The frenum is quite sensitive and active and must be
carefully recorded to maintain a seal without causing
soreness.
2) Buccal frenum
- It connects as a continuous band through the modulus
at the corner of the mouth and to the buccal frenum
attachment in the maxilla.
- It is underlined with depressor anguli oris muscle.
- So the impression must be functionally trimmed to
have the maximum seal and yet not so great an
extension as to displace the denture when the tip is
moved.

5. 3) Buccal vestibule
Boundaries:
Anteriorly : Buccal frenum
Posteriorly : Massetric notch.
Medially: alveolar mucosa of the ridge.
Laterally : Buccal mucosa
- This area remains an important esthetic consideration
because when smiling the dark space BUCCAL
CORRIDOR should be visible.
4) Masseter muscle region of masseteric notch area
- It is immediately lateral to the retromolar pad and
continues anteriorly into buccal vestibular sulcus, it
accommodates the mesial border of the masseter
muscle.
- Often when the mouth is opened wide, border of the
denture in this area cuts into the tissues.
- So it should be recorded with the mouth slightly
opened wide.

6. 5) Retromolar pad
- It represents the distal limit of the mandibular
denture.
- It is also called as pear shaped body.
- It is a soft tissue pad which contains:
 Glandular tissue.
 Buccinator fibres enter it from buccal
side.
 Fibres of superior pharyngeal constrictor
enter it from lingual side.
 Pterygomandibular replace enters the pad
at its top back corner.
6) Lingual Border anatomy
- The border tissues in this region because of their
peculiar lack of immediate resistance are early
distorted when impressions are being made. Such over
extensions over a long period of time will cause tissue

7. soreness or dislodgement of denture by tongue
movements.
Sublingual gland region:
In the premolar region on the lingual side of the ridge, the
sublingual gland rests above the mylohyoid muscle. When the
floor of the mouth is raised, the gland comes quite close to the
crest of the ridge, thus preventing the development of a long
flange in the anterior region.
Alveolingual sulcus
- It is the space between the residual ridge and the
tongue and extends from lingual frenum to the
retromylohyoid curtain.
- It can be divided into 3 regions:
1) Anterior region: Extends from the lingual frenum to the
place where the mylohyoid ridge curves down below the
level of the sulcus.
The lingual border of the impression in this anterior
region should extend down to make definite contact with the

8. mucous membrane of the floor of the mouth when the tip of
the tongue touches the upper incisors.
2) Middle region: Extends from the premylohyoid fossa to the
distal end of the mylohyoid ridge.
When the mylohyoid muscle and tongue are relaxed, the
muscle drapes back under the mylohyoid ridge. If an
impression were made these conditions, the muscle and
other tissues in the region would be trapped under the ridge
when the tongue is placed against the upper incisors.
This can be avoided when the part of the lingual flange
of the tray is shaped to slope inward towards the tongue and
the final impression is made with a very soft impression
material in addition the slope of the lingual flange provides
space for the floor of the mouth to be raised during
functions.
3) Posterior region: It is called retromylohyoid space.
- It extends from the end of the mylohyoid ridge to the
retromyolohyoid curtain.

9. - It is bounded on lingual side by anterior tonsillar
pillar, at the distal end by retromylohyoid curtain and
superior.

10. - It is bounded on lingual side by anterior tonsillar
pillar, at the distal end by retromylohyoid curtain and
superior.