Stability and support in

complete denture
Dr\ Ahmed Nafady
 STABILITY:
vDefinition of stability
ØThe quality of a denture to be firm, stable or constant and to resist displacement by
functional stresses & not to be subject to change of position when forces are applied.
vThe various factors that affecting the stability are:
1-Vertical height of the residual ridge 2-Quality of the impression
3-Occlusal rims 4-Arrangement of the teeth
5-Contour of the polish surface 6- Shape of the palatal Vault
7- Retention 8- Proper relief

üWidth of the occlusal table >>must be less than normal teeth >> to get good stability
and retention.
1) Vertical height of the residual ridge
Ø The residual ridge should have sufficient vertical height to obtain good stability.
Ø Highly resorbed ridges offer the least stability.

2) Quality of the impression:

Ø An impression should be as accurate as possible. The impression surface should be smooth
and duplicate all the details accurately.
Ø It should be devoid of voids and any rough surfaces. The impression should not warp on
removal.
Ø The impression should be dimensionally stable and the cast should be poured as soon as
possible.

3) Occlusal plane:
Ø The occlusal plane should be oriented parallel to the ridge .
Ø If the occlusal plane is inclined then the sliding force may act on reduce its stability.
Ø The occlusal plane should divide the inter arch space equally
4) Teeth arrangement (balanced occlusion and neutral zone):
Ø The position of the teeth and their occlusion play an important role in the stability of the
denture.
Ø Balanced occlusion facilitates the even distribution of force across the denture.
Ø Absence of the balanced occlusion may produce unbalanced lever type of force of any
one side of the denture leading to loss of stability.
Ø The teeth in the denture should arrange in the neutral zone.
Ø Neutral zone: the potential space between the lips and cheeks on one side and the tongue
on the other. Natural or artificial teeth in this neutral zone are subjected to equal and
opposite force from the surrounding musculature""
5) Contour of the polished surface;
Ø The polish surface of the denture should be harmonious with the oral structures.
Ø They should not interfere with the action of the oral musculature.

6) Shape of palatal vault

Ø A steep palatal vault may enhance stability by providing greater surfaces area of contact &
long inclines approaching.
Hard palate:
ØHard palate can be classified as:
1 -U-shaped: ideal for both retention and stability.
2-V-shaped: retention is less as the peripheral seal is easily broken.
3-Round: reduced resistance to lateral and rotator force.
ØStability decreases with
1-Loss of vertical height of the ridge
2- Increase in the movement of flabby tissue.
Support:
ØThe resistance to the forces of mastication, occlusal forces & other
forces applied in a direction towards the denture bearing area.
ØInitial denture support is achieved by using impression procedure
that provide optimal extension & functional loading of the supporting
tissue
 Nature of the Supporting tissue
The soft tissues should be
1- In the edentulous person, the mucosa covering the hard palate and the crest of the residual
ridge, including the residual attached gingiva, is classified as masticatory mucosa. It is characterized
by a well-defined keratinized layer on its outermost surface that is subject to changes in thickness
depending on whether dentures are worn and on the clinical acceptability of the dentures
2- The submucosa is firmly attached to the periosteum of the underlying supporting bone and will
usually withstand successfully the pressures of the dentures. (The thickness and consistency of the
submucosa are largely responsible for the support that the mucous membrane affords a denture
because in most instances, the submucosa makes up the bulk of the mucous membrane.
ØWhen the submucosal layer is thin, the soft tissues will be non-resilient, and the
mucous membrane will be easily traumatized.
Ø When the submucosal layer is loosely attached to the periosteum or it is inflamed or
edematous, the tissue is easily displaceable, and the stability and support of the
dentures are adversely affected)
3- Covered by keratinized mucosa.
Nature of the Supporting tissue
ØHard tissue should be Relatively resistance to remodeling & resorptive
changes.
ØConsideration must be given to the maintenance of alveolar ridge height in
the conventional complete denture patient.
ØMinimizing the pressure in those regions most susceptible & directing the
forces toward those regions relatively resistance to resorption can maintain
healthy residual ridge.
ØThere are two types of osseous tissue that form bones.
1) Cortical bone: It is harder, stronger and stiffer than cancellous bone
2) Cancellous bone: is less dense, softer, weaker, and less stiff. It typically occurs at
the ends of long bones
 Mandibular anatomical consideration:
1-Buccal shelf area
The surface of the mandible from the residual
alveolar ridge or alveolar ridge to the external
oblique line in the region of the lower buccal
vestibule. It is covered with cortical bone.

• Buccal shelf area is the primary support area for

the mandibular denture because
1) it's usually covered by mucosa with an
intervening sub mucous layer containing glandular
connective tissue & buccinators muscle fibers
2) It is parallel to occlusal plan.
3) It lined by cortical bone.
 Mandibular anatomical consideration:
2-MANDIBULAR RESIDUAL RIDGE
• It is covered by a keratinized layer and is attached by its
submucosa to the periosteum of the mandible. The extent
of this attachment varies considerably. In some people,
the submucosa is loosely attached to the bone over the
entire crest of the residual ridge, and the soft tissue is
quite movable. In others, the submucosa is firmly
attached to the bone on both the crest and the slopes of
the lower residual ridge.
• The ridges crests are reserved as secondary support
areas.
1) The lack of the muscle attachment
2) Presence of cancellous bone
 MAXILLARY ANA TOMIC CONSIDERATION
1) Horizontal portion of the hard palate is considered as primary stress bearing area It has keratinized
masticator mucosa overlies a distinct Sub mucosa layer everywhere

2) In the region of the medial palatal suture, the submucosa is extremely thin, with the result that the mucosal
layer is practically in contact with the underlying bone. For this reason, the soft tissue covering the medial palatal
suture is non-resilient and may need to be relieved to avoid trauma from the denture base.

3) In the area of the rugae, the palate is set at an angle to the residual ridge and is rather thinly covered by soft
tissue. This area contributes to the stress-bearing role, though in a secondary capacity. The submucosa covering
the incisive papilla and the nasopalatine canal contains the nasopalatine vessels and nerves

4) CREST OF MAXILLARY RIDGE

• The crest of the edentulous ridge is an important area of support. However, the bone is subject to resorption,
which limits its potential for support, unlike the palate, which is resistant to resorption. Because of this, the
ridge crest should be looked on as a secondary supporting area, rather than a primary supporting area. The
inclined facial surface of the maxillary ridge provides little support,
• Although the peripheral tissues should be contacted to provide a border seal
• The configuration of the bone that provides the support for the maxillary denture varies considerably with each
patient.
Crest of the ridge Median palataine raphae
Stress bearing areas in Maxilla and Mandible

v Primary stress bearing area v Secondary stress bearing area

ØIn Maxilla ØIn Maxilla
Horizontal portion of the hard • Area of the Rugae
palate • CREST OF MAXILLARY RIDGE

ØIn Mandible ØIn Mandible

Buccal shelf area Crest of mandibular ridge
 Factors that influence the form and size of the
supporting bone include
(1) Its original size and consistency;
(2) The person’s general health;
(3) Forces developed by the surrounding musculature;
(4) The severity and location of periodontal disease (a frequent cause of tooth loss).
(5) Forces accruing from the wearing of dental prostheses.
(6) Surgery at the time of removal of the teeth.
(7) The relative length of time different parts of the jaws has been edentulous. In addition, a number of anatomical
features influence the shape of the hard palate and residual ridge.
• Methods used for improving the retention stability and support, these are described
in the following.
a) Dental implants improve the support, retention and stability of a full or partial denture reducing the slip and
movement while speaking or eating
b) Mini-implants have become a common treatment option for improving retention of lower dentures