Denture base
Denture base:is the part of denture that rests on the foundation tissues and to which teeth are attached.
Functions:
Support and retention of denture teeth 1-
2-Receive the functional force from occlusion and transfers it to supporting oral structures or tissues.
3-Improving esthetics by reproducing natural looking contours.
4-Stimulation of underlying tissue of residual ridge.
Denture bases are either : A- Tooth supported R.P.D.bases
B-Tooth-tissue borneR.P.D.bases
Materials :
1. Acrylic Resin Bases
2. Metal Bases
1. Acrylic Resin Bases Acrylic resin bases are the most common types used in removable partial dentures. They should be routinely used in distal extension cases to allow for relining of the base to maintain mucosal support. Acrylic resin should make a butt joint or slightly undercut joint with the major and minor connectors. If the resin is brought to a feather edge, it will distort, break or separate from the framework, causing injury to the underlying soft tissues.
Disadvantages: a. dimensional stability less than metal bases - warpage b. lower strength than metal - long spans c. porous - hygiene d. low thermal conductivity
Advantages: a. ability to reline the base as the supporting tissues change b. esthetically superior to metal bases c. ease of repair
Tooth supported R.P.D.Bases when replace anterior teeth must perform following functions:
1-Provide Desirable esthetic2-Support and retention of denture teeth in such away that provide masticatory efficiency and assist in Receive the functional force from occlusion and transfers it to abutment teeth through rests.
3-Prevent horizontal and vertical migration of remaining natural teeth.
4-Eliminate undesirable food traps.
Stimulate underlying tissues. 5-
Distal Extension R.P.D.BASE
1-The most important is to contribute in the support of denture as minimizing functional movement and improving prosthesis stability. As the distance from abutment teeth increased, the support from underling tissues become increasingly importance.
Tooth supported R.P.D.Bases
2-esthetic
3--Stimulation of underlying tissue of residual ridge.4--Eliminate undesirable food traps.
Ideal denture base material
Requirements:
1-accuracy of adaptation to tissue with minimal volume change.
2-dense non irritant surface capable of receiving and maintaining a good finish.
3-thermal conductivity
4-low specific gravity
5-sufficient strength
6-easily kept clean
7-esthetic acceptability
8-potential for future relining
9-low initial cost
The snowshoe principle
2. Metal Bases Metal bases can be used wherever acrylic resin bases are used. However, the esthetic result can be compromised unless the metal can be veneered with sufficient thickness of acrylic. Where single tooth replacements are placed, there is often insufficient room to fabricate a retentive grid work. A full metal base is often used in these instances. When this type of base is used, denture teeth are attached to the framework with acrylic resin via beading or retentive posts on the metal surface. In some rare instances, a tooth-bounded edentulous span may exist that is too small for placement of a denture tooth. When this type of edentulous space is encountered, it is metal, if it will not compromise esthetics can be completely filled with the framework . Metal bases cannot be relined, so they are generally not used for tooth-tissue borne removable partial dentures, or in areas where teeth have been removed within 12 months .(resorption will still be occurring at an increased rate and relining will be usually be required).
Beaded metal base for single tooth replacement
Metal filled edentulous space Retentive posts can be particularly useful in anterior regionsAdvantages of Metal Bases
1-Accuracy and Permanence of FormCast metal bases, whether of gold, chrome, or titanium cast more accurately than denture resins but also can maintain their accuracy of form without changes in the mouth
This fact is that an additional posterior palatal seal may be eliminated entirely when a cast palate is used for a complete denture, as compared with the need for a definite post-dam when the palate is made of acrylic-resin
are not subject to distortion by the release of internal Accurate metal casting strains, as are most denture resins. Because of its accuracy, the metal base provides an intimacy of contact that contributes considerably to the tension retention of a denture. Sometimes called interfacial surface
Metal Bases
Permanence of form of the cast base is also ensured because of its resistance to abrasion from denture cleaning agents.
The metal bases, particularly the harder chrome alloys, withstand repeated cleaning without significant changes in surface accuracy.
2- Comparative Tissue Response
Clinical observations have demonstrated that the inherent cleanliness of the cast metal base contributes to the health of oral tissues when compared with an acrylic resin base. Perhaps some of the reasons for this are the greater density and the bacteriostatic activity contributed by ionization and oxidation of the metal base.
For this reason, a metal base is naturally cleaner than an acrylic-resin base.
Thermal Conductivity 3-
Temperature changes are transmitted through the metal base to the underlying tissues, thereby helping to maintain the health of those tissuesFreedom of interchange of temperature between the external influences tissues covered and the surroundingsolid foods, and inspired air)(temperature of liquids,contributes much to the patient’s acceptance of a denture and may help avoid the feeling of the presence of a foreign body.
4-Weight and Bulk
Metal alloy may be cast much thinner than acrylic-resin and still have adequate strength and rigidity.In the mandibular arch, the weight of the denture may be an asset with regard to retention, and for this reason a cast gold base may be preferable .
extreme loss of residual alveolar bone may make it necessary to add fullness to the denture base to restore normal facial contours and to fill out the buccal vestibule to prevent food from being trapped in the vestibule beneath the denture. In such situations an acrylic resin base may be preferable to the thinner metal base.
In the maxillary arch, an acrylic resin base may be preferable to the thinner metal base.
To provide fullness in the buccal flanges and for esthetic reasonIn areas of the tongue and cheek need maximum room, thinness of metal bases is desirable. .
Methods of Attaching Denture Bases
Acrylic-resin bases are attached to the partial denture framework by means of a minor connector designed so that a space exists between the framework and the underlying tissues of the residual ridgeThus after casting, the portion of the retentive framework to which the acrylic-resin base will be attached will stand away from the tissue surface sufficiently to permit a flow of acrylic-resin base material beneath its surface.
Relief of at least a 20-gauge thickness over the basal seat areas of the master cast is used
The design of the retentive framework it should be located both buccally and lingually its effective rigidity and strength when it is embedded in the acrylic resin base. It should also be free of interference with future adjustment, should not interfere with arrangement of artificial teeth, and should be open enough to avoid weakening any portion of the attached acrylic-resin. restoration
Metal teeth Occasionally, a second molar tooth may be replaced as part of the partial denture casting.
It is usually done when space is too limited for the attachment of an artificial teeth
metal teeth made of chrome alloys are difficult to adjust and are objectionably hard for use as occlusal surfaces. Therefore they should be used only to fill a space and to prevent tooth extrusion.
Flange Extension 1. Denture bases for tooth-tissue supported partial dentures (Class I and II) should be extended to provide the greatest available surface area for support and retention, without over extension or impingement on movable border tissues
2. Tooth supported partial dentures (Class IIIand IV) need not necessarily be extended maximally, since most of the support for these dentures comes from the teeth. 3. Maxillary distal extension denture bases should terminate in the hamular notches
4. Mandibular distal extension denture bases should. terminate on the retromolar pad.
. 5. Occasionally, the path of insertion can cause the denture flanges to impinge on the mucosa above undercut portions of the residual ridge, when the partial denture is being seated. it is usually preferable to shorten the flange, rather than relieving the internal surface. If the internal surface is relieved significantly, a space will exist between the denture base and the tissues when the denture is fully seated. Food may become trapped in the space and work its way under the partial denture .
Deep lingual undercut Do not relieve internally Shorten flange (difficulty seating, pain) (food trap) (maintain usable undercut) for retention