prosthodontic seminar

1. Presented by :-
Dr. Ahmed Salih
B.D.S

2. Contents
Definition of denture base
Requirements
Functions
Types
a,Plastic
b,Metal

3. Definition –
Is that part of the removable partial denture which rests
on oral mucosa and to which teeth are attached.

4. REQUISITES FOR IDEAL DENTURE BASE
• Accuracy of Adaptation To Tissues With Low Volume Change
• Dense non irritating surface capable of receiving &
maintaining a good finish.
• Biologically Compatible with tissues
• Thermal conductivity
• Low specific gravity – Lightness in mouth
• Esthetics

5. • Dimensional stability
• Sufficient strength – Resistance to fracture /distortion
• Resist deformation
• Self cleansing
• Low Cost
• Potential for future relining

6. Functions –
Esthetics
Support and retain artificial teeth
Assist in transfer of occlusal forces directly to
abutment teeth by rests.
Prevent vertical and horizontal migration of
remaining natural teeth.
Eliminate undesirable food traps.
Stimulates the underlying tissue.

7. Types –
Plastic
Acrylic
- hot cure
- cold cure
- light cure
- pour and cure
Polystyrene
Valplast
Metal
Gold
Co-Cr
Titanium
Vitallium

8. Metal Denture base

9. Metal Base-Indications
Tooth supported partial dentures
Inadequate interarch space
Structural details
Designed with optimum extension
Thinner base than plastic resin
Avoid sharp margins

10. Metal Base - Advantages
• Accuracy & performance of form
• Comparative tissue response
• Thermal conductivity
• Weight & Bulk

11. Comparitive tissue response-
Inherent cleanliness of cast metal base contributes to
health of oral tissue.
Bacteriostatic activity – ionization and oxidization of
metal base.
Metal base naturally cleaner than an acrylic resin
base.

12. Thermal conductivity-
Temperature changes transmitted though
metal to the underlying help to maintain
health of that tissue.
Patients acceptance.
Denture resins – insulating property

13. Weight and bulk-
Metal alloy may be cast thinner than acrylic resin and
still have adequate strength.
Certain situations demands use of acrylic denture
base-

14. Metal Base-Disadvantages
• Esthetics
• Enhancement of retention not possible – lack of weight
of metal base
• Relining difficult
• Restoration of normal facial contour can not be
achieved

15. Acrylic denture base

16. Acrylic denture base- Indications
Extension base partial denture
Long span edentulous ridges
Relining
Contour restoration

17. Porosity
Two types of porosity are recognized :-
-Contraction porosity
-Gaseous porosity
Contraction porosity :- occurs because the monomer contracts by
some 20% of its volume during processing .
-gaseous porosity :- occurs due to the exothermic reaction of
polymerization which could make the temperature of the resin to
rise above 100c which is the boiling temp. , if this temp. is
exceeded before the polymerization process is completed ,
gaseous monomer will be formed which is the cause of gaseous
porosity.
It can be avoided by alllowing the temp. to be raised in a slow and
controlled fashion.
-polymerization should be carried out slowly to prevent gaseous
porosity and under pressure to prevent contraction porosity.

18. Mechanical properties :-
The tensile strength of acrylic resin is typically no more than 50
mpa , the elastic modulus is low , the flexure modulus being in the
region of 2200 – 2500 mpa .
When this is combined with lack of fracture toughness , it perhaps
not surprising that dentures are prone to fracture .
An alternative approach for strengthening of acrylic dentures is
incorporation of fibers so as to produce a fiber – reinforced
composite and these include :- carbon fibers , aramid ,
uhmpe ( ultra high molecular weight polyethelene ) and the glass
fibers.

19. Physical properties
-Thermal conductivity :- acrylic has low coefficient of thermal conductivity , from
a patient point of view , it will isolate the oral soft tissues from any sensation of
temperature.
-Coefficient of thermal expansion :- its quite high about 80 ppm / c , in general
it does not present any problem except that there is possibility that porcelain teeth set
in denture base resin may gradually loosen and lost due to different expansion and
contraction.
-Water sorption and solubility :- resin molecule absorbs water due to its
polar nature , in practice this helps to compensate for the slight processing shrinkage .
-Biocompatibility :- acrylic is highly biocompatible and patients suffer few
problems , nevertheless some patients will show an allergic reaction and this is most
probably associated with the various leachable components in the denture such as any
residual monomer or benzoic acid .

20. Valplast
1950,s
Valplast – flexible base resin ideal for partial
dentures.
Esthetic yet fully functional alternative to traditional
cast metal based removable partial dentures.

21. Biocompatible nylon and thermoplastic resin-flexibility and
stability.
Color, shape and design of valplast partials blend seamlessly
with natural appearance of gingiva making prostheses
nearly invisible.
Strenght of valplast resin doesn’t require a metal
framework-eliminates metallic taste.
Enables partial to be fabricated thin enough with non
metallic clasps.

22. Adequate occlusal clearance b/w arches for tooth
placement.
No tooth preparation required.
Vitallium combination-better support and clasp
esthetics

23. Need for relining
Distal extension base differs from toothsupported
base-made of material-relined.
Acrylic resin denture base materials that can be
relined are generally used.

24. Loss of support - distal extension bases- changes in
residual ridge-loss of occlusion-heavy occlusal
contact b/w remaining natural teeth.
Relining necessary.
Rotation of fulcrum line with indirect retainers lifting
from their seats as distal extension base is pressed
against ridge tissue-relining

25. Loss of occlusal contact and rotation-relining.
Loss of occlusal contact with no evidence of rotation
-restablish occlusion.
Loss of support assessed clinically-hydrocolloid,
wax,tissue conditioning material.

26. References
Carr A B, Mc Givney G P, Brown D T, Major connector in
McCraken’s Removable partial Prothodontics. 11th ed, st louis:
Mosby; 2008
Stewart K L, Rudd K D, Kuebker W A, Major connector in Stewart’s
Clinical Removable Partial Prosthodontics. 2 nd, Chennai; 2004
Miller E L, Grasso J E, Major connector in Removable Partial
Prosthodontics. 2nd ed, Baltimore: Williams & Wilkins; 1979
 Development of in vivo measuring system of the pressure
distribution under the denture base of removable partial
denture. J Prosthodont Res. 2009 Jan;53(1):15-21

27. YOU !!