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

Contents Definition of denture baseRequirementsFunctions Types a,Plastic b,Metal

Definition –

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

•Accuracy of Adaptation To Tissues With Low Volume Change

• Dense non irritating surface capable of receiving & maintaining a good finish.

• Thermal conductivity

• Low specific gravity – Lightness in mouth

• Esthetics

• Biologically Compatible with tissues

REQUISITES FOR IDEAL DENTURE BASE

• Dimensional stability

• Resist deformation

• Low Cost

• Self cleansing

• Potential for future relining

• Sufficient strength – Resistance to fracture /distortion

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.

Types – Plastic Acrylic - hot cure - cold cure - light cure - pour and cure

Polystyrene Valplast Metal Gold Co-Cr Titanium Vitallium

Metal Denture base

Tooth supported partial dentures

Inadequate interarch space

Structural details

Designed with optimum extension

Thinner base than plastic resin

Avoid sharp margins

Metal Base-Indications

• Accuracy & performance of form

• Comparative tissue response

• Thermal conductivity

• Weight & Bulk

Metal Base - Advantages

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.

Thermal conductivity-

Temperature changes transmitted though metal to the underlying help to maintain health of that tissue.

Patients acceptance.Denture resins – insulating property

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-

• Esthetics

• Enhancement of retention not possible – lack of weight of metal base

• Relining difficult

• Restoration of normal facial contour can not be achieved

Metal Base-Disadvantages

Acrylic denture base

Acrylic denture base- Indications

Extension base partial denture

Long span edentulous ridges

Relining

Contour restoration

PorosityTwo 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.

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.

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 .

Valplast 1950,sValplast – flexible base resin ideal for partial

dentures.Esthetic yet fully functional alternative to

traditional cast metal based removable partial dentures.

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.

Adequate occlusal clearance b/w arches for tooth placement.

No tooth preparation required.

Vitallium combination-better support and clasp esthetics

Need for reliningDistal extension base differs from

toothsupported base-made of material-relined.

Acrylic resin denture base materials that can be relined are generally used.

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

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.

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. 2nd, 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

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