Metallic and plastic denture base materials used for partially edentulous cases
Denture base: that part of removable partial denture that rests on oral mucosa and to which teeth are attached.Types of denture Base material:
(1) metal, and (2) plastic.1-Metal denture base materials:
- Chrome cobalt
- Stainless steel
- Gold alloy
- Titanium
2- Plastic denture base materials:
-acrylic
-polystyrene
-valplast
Metal denture base materials
The fitting surface of this dental base is entirely metal, prosthetic teeth are attached to the metal base with a plastic base or by cementation to a retentive post .
Indications
1-Tooth supported partial denture (class III or IV and modification ) where furture bone resorption is not anticipated.
2-Inadequate inter arch space.
3-High occlusal forces – deep bite.
4- Acrylic allergy.
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).
Advantages
1-Accuracy and Permanence of Form: metal alloys cast accurately and maintain their accuracy.
2-Intimacy of contact contributes to retention.
3-Thermal conductivity :Temperature changes transmitted through metal to the underlying tissue help to maintain health of the tissue. Thermal conductivity may be decreased if plastic is processed onto the metal base.
4-Good soft tissue response due to its high density and
bacteriostatic activity contributed by ionization and oxidation of metal.
5-Weight and bulk : the metal bases can be cast thinner than resin bases while maintaining adequate strength.
6-Less porous: so they are easily cleaned
7- Resistant to abrasion.
Disadvantages
1. less esthetic.
2-Trimming is difficult and hence overextension must be avoided.
3- Difficult to reline .
4-Difficult to correct underextensions.
5-Cannot be used to support lips, cheek and make up for lost bone.
Plastic denture base:
Acrylic resin bases are the most common types used in removable partial dentures , they have the plastic material in contact with edentulous ridge. It is used more frequently than the metal base. This material is not ideal in every respect and it is the combination of virtues rather than one single desirable property that accounts for its popularity and usage.They should be routinely used in distal extension cases to allow for relining of the base to maintain mucosal support .
Indications for acrylic resin denture base:
1-Distal extension base partial denture (tooth- tissue supported edentulous space).
2-Long span edentulous ridges.
3-Contour restoration (extreme loss of residual alveolar bone _fullness of denture base to restore facial contour )
4-Where esthetic is a primary concern.
ADVANTAGES
1. Ability to reline the base as the supporting tissues change.
2. Easy to fabricate, adjust, finish and polish, and repair.
3. Plastic is more esthetic than metal.
DISADVANTAGES
1. More strength in bulk, so space for artificial teeth may be reduced. Cannot be used when inter-arch space is less.
2. Less fatigue and abrasion resistant so may break with use.
3. Can distort due to internal strain release.
4-More plaque accumulation.
5-Can irritate soft tissue.
6-Poor thermal conductivity.
Flexible denture material
It was first introduced by the name of valplast and flexiplast to dentistry in 1956.
Advantages
1-Improved esthetic.
2-Used in areas of deep undercuts.
3-Comfort to patient.
4-stress breaking function.
5-Biocompatibility.
6-Accuracy.
Disadvantages:
1-Difficult to reline and rebase.
2-Difficult to repair.
3-Prone to staining.