bio consideration in mand impressions.ppt

Macro and micro

1. Biologic considerations of
mandibular impressions

2. contents
 Why good impressions are necessary ?
 Mandible-the bone
 Sequelae to tooth loss
 Anatomy of supporting structures
 Macroscopic
 microscopic
 Anatomy of limiting structures
 Macroscopic
 Microscopic
 Discussion
 Conclusion

3. Why good impressions are
necessary ?
It is very important that the new dentures fit when placed
initially in the mouth.
Good impressions are basic to the needs of a contended
denture wearer .
Most dentures examined by prosthodontists have woefully
inadequate bases .

4. Mandible-the bone
The only mobile bone forming
lower 1/3
rd
of the face .
Suspended from cranium at the
two TMJs.
Body of mandible carries alveolar
process superiorly supporting the
mandibular denture.

5. Maxilla vs. mandible
Denture bearing area 14 sq. cm.
Sub mucosa thin and loosely attached, becomes more
displaceable with resorption .
Bone cancellous –more prone to resorption .
Tongue, strong, muscular and mobile .
Decreased support because of resorption pattern .

6. Sequelaeto tooth loss
Alveolar process resorption
pattern –bony foundation shorter
vertically and narrower
buccolingually.
Bone foundation width > molar
region .
RRR lingual → buccal .
Alveolar process resorption
produces low ant. curve and high
post. curve.

7. Macroscopic anatomy of
supporting structures
Crest of residual ridge
The buccal shelf
Shape of supporting structures
•Flat mandibular ridges
•Mylohyoid ridge
•Mental foramen
•Genial tubercles
•Torus mandibularis

8. Crest of residual ridge
Keratinized mucosa and
submucosa variably
attached to periosteum .
Firmly attached mucosa
provides good soft tissue
support .
Underlying bone
unfavorable as it is often
cancellous

9. The buccal shelf
Area between mandibular buccal
frenum and the anterior edge of the
masseter muscle .
Total width of the bony foundation
greater in this region .
Mucous membrane less keratinized
and loosely attached with thicker
submucosa.
Insertion of inferior buccinator
muscle fibers .
Underlying cortical bone at rt. angle
to vertical occlusal forces .
Favorable as primary stress bearing
area.

10. Shape of supporting structures
Original size and consistency
General health
Forces developed by surrounding musculature
Severity and location of periodontal disease .
Forces accruing from wearing of dental prosthesis .
Surgery during removal of teeth .
Period of edentulousness .
Influencing factors

11. Flat mandibular ridges
Muscles in close proximity to
labial crest .
Concave bearing surface
►placement of tissues by
impression.
Impingement of buccinator
muscle fibers .

12. Mylohyoid ridge
Overlying soft tissues conceal the
hardness .
Anteriorly the mylohyoid muscle
attachment lies close to the
inferior border of the mandible .
Posteriorly following resorption
lies flush with superior border .
Relief advised over sharp or
irregular mylohyoid ridge.

13. Mental foramen and genial tubercles
Resorption causes mental
foramina to lie in proximity to
ridge crest .
Relief necessary as mental nerve
and blood vessels may get
compressed .
Pressure on mental nerve causes
numbness of lower lip.
Genial tubercles also become
prominent with increased
resorption .

14. Torus mandibularis
Bony prominence usually found
bilaterally and lingually in the
premolar region .
Usually located midway between
alveolar ridge crest and floor of
the mouth .
Mucous membrane layer covering
is extremely thin .
Surgical removal preferred as
relief compromises denture seal .

15. Macroscopic anatomy of limiting
structures
Labial vestibule
Buccal vestibule
Masseter muscle region
Distal extension of mandibular impression
Lingual border
Mylohyoid muscle
Retromylohoid fossa
Sublingual gland region
Alveololingual sulcus

16. Labial vestibule
Runs from labial frenum to buccal
frenum .
Length and thickness influenced
by muscle insertion e.g. mentalis .
Depth determined by muco-labial
fold .
Mandibular labial frenum gives
attachment to orbicularis oris
muscle.
Impressions always narrowest in
the mandibular anterior region .

17. Buccal vestibule
Impression is always widest in
this region .
Lower buccinator muscle fibers
attached to buccal shelf and
external oblique ridge .
External oblique ridge does not
govern the buccal flange
extension .
Buccinator muscle fibers run ║ to
the border .
Initiallymore resistance is offered
in this region .

18. Masseter muscle region
Distobuccal corner of the denture
must converge rapidly to avoid
displacement .
The anterior masseter muscle
fibers lie outside the buccinator
muscle fibers .
The distobuccal corner encounters
the affect of the masseter
depending on shape of mandible .
the size of masseter muscle
influences its action on buccinator

19. Distal extension
Limited by ramus, buccinator,
pterygomandibular raphe,
superior constrictor muscle and
retromolar fossa .
Desirable extension slightly
lingual to these prominences.
Retromolar pad must be covered
to perfect the border seal .
Denture base must extend approx.
⅔rd over the retromolar pad .

20. Lingual border
Lingual tissues exert less direct
resistance and distort easily hence
overextensions result in this
region .
Denture flange should be parallel
to the mylohyoid muscle when
contracted .
In the posterior region the lingual
flange can go beyond mylohyoid
attachment till the mucolingual
fold for border seal .

21. Retromylohyoid fossa
Area posterior to mylohyoid
muscle .
Lingual flange in this fossa
not influenced by the
mylohyoid muscle .
The denture border should
extend posteriorly to contact
the retromylohyoid curtain
when tip of tongue contacts
upper residual ridge.

22. Sublingual gland region
In premolar region sublingual gland rests above mylohyoid
muscle .
Sublingual gland may be pushed down and laterally by
resistant impression material .
Sublingual gland area should be shaped to slope in toward the
tongue .
Lingual frenum should be recorded in function as it comes
close to ridge crest.

23. Alveololingual sulcus
Considered in three regions
Anterior region
lingual border should reach
floor of mouth when tongue
tip touches upper incisors .
Premylohyoid eminence
Middle region:
Middle of lingual flange is
made to slope toward tongue
below level of mylohyoid
ridge.
Provides space for floor of
mouth while maintaining seal
in mucolingual fold.
Tongue rests on top of flange
stabilizing the lower denture.

24. Posterior region:
Flange passes into
retromylohyoid fossa .
Turns laterally toward
ramus obtaining typical S
form of lingual flange.

25. Microscopic anatomy of supporting
structures
Crest of residual ridge
Mucosa –cornified
keratinized epithelium
Submucosa-loose or firmly
attached .
Bone –cancellous , spongy
trabeculae
Buccal shelf
Mucosa –loosely attached
and less keratinized
Submucosa-thicker than in
ridge crest .
Bone –compact bone
composed of haversian
systems .

26. Microscopic anatomy of limiting
structures
Vestibule
Mucosa –thin and
noncornified
Submucosa –loosely
arranged connective tissue .
Alveololingual sulcus
Mucosa –thin and
noncornified
Submucosa –anteriorly
contains sublingual gland
Retromolar pad
Mucosa –thin , noncornified
Submucosa –glandular
tissue, buccinator and sup.
Constrictor fibers ,
pterygomandibular raphe and
temporalis tendon .
Register impression in
resting position

27. Discussion
Good impressions without tissue trauma
require proper tray selection .
Careful and minimal insertions should be done
to avoid irritation to angle of the mouth .
Old dentures must not be worn as tissue
recovery is delayed in elderly .
Physiologic muscle trimming should be
performed to develop border seal .

28. Conclusion
Scientific knowledge of denture supporting and
influencing structures helps in meticulous
fabrication of satisfactory dentures .
A knowledge of the relevant tissue anatomy also
enables the clinician to honor M. M. De Van’s
dictum “it is more important to preserve what
already remains than to replace what is
missing .”