denture base considerations

Definition Requirements Functions Types a,Plastic b,Metal Tooth supported partial denture base Distal extension denture base Methods of attaching denture base Methods of attaching artificial teeth Relining Stress breakers

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 Compactable with tissues

• 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 thru rests. Prevent vertical and horizontal migration of

remaining natural teeth. Eliminate undesirable food traps. Stimulates the underlying tissue.

Types – Plastic Acrylic Polystyrene Valplast Metal Gold Co-Cr Titanium Vitallium

Tooth supported partial dentures

Inadequate interarch space

Structural details

Designed with optimum extension

Thinner base than plastic resin

Avoid sharp margins

• Accuracy & performance of form

• Comparative tissue response

• Thermal conductivity

• Weight & Bulk

Accuracy and permanence of form-

Cast more accurately than denture resins and maintain their accuracy of form without change in mouth.

Internal strains released later to cause distortion not present.

Need for an additional pps eliminated entirely. Accuracy –metal base provides intimacy of

contact-retention of denture prostheses. Such intimacy-not acrylic resin bases.

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.

Pts 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-

Xtreme loss of residual alveolar bone-fullness to denturebase to restore facial contours.

To provide fullness to fill a max vestibule Esthetics

• Esthetics

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

• Relining difficult

• Restoration of normal facial contour can not be achieved

Acrylic denture base- Indications

Extension base partial denture

Long span edentulous ridges

Relining

Contour restoration

Adequate bulk & strength - junction of base & minor connector

Tissue stops at extension base frame work

Placement of Base –

Placement over crest ridge- Resin breakage

Buccal/lingual of crest ridge

1950,s Valplast – 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

TYPES

Tooth Supported Partial Denture Base

Distal Extension Partial Denture Base

In tooth supported prostheses denture base is primarily a span b/w 2 abutments supporting artificial teeth.

Occlusal forces transferred to abutments-Rests.

Prevent horizontal migration of all abutment teeth in partially edentulous arch and vertical migration of teeth in opposing arch.

Support of the denture. Support critical to goal of minimizing functional

movt and improving prostheses stability. Max support obtained – broad accurate denture

bases-occlusal load equitably. Support – gross size and cellular characteristics of

residual alveolar ridge. Snow shoe principle-broad coverage furnishes the

best support with least load per unit area is principle choice for providing max support.

Support –primary consideration

Esthetics,stimulation of underlying tissue,and oral cleanliness-secondary importance.

Relining necessary in tooth supported denture base.

Tooth – supported bases made soon after xn should be of material that permits relining.

Primary retention for RPD –mechanically by placing retaining elements on abutment teeth.

Secondary retention-intimate relationship of denture base and major connectors.

Retention of denture bases as a result of following forces-

Adhesion –attraction of saliva to denture and tissue.

Cohesion –attraction of molecules of saliva for each other.

Atmospheric pressure-border seal. Physiological molding of tissue around polished

surface of the denture. Effect of gravity on mandibular denture.

Acrylic resin bases-attached to partial denture frame work-minor connector designed b/w framework and underlying tissue.

Relief 20 guage thickness-basal seat. Plastic mesh patterns in forming retentive

framework less satisfactory than open pattern.

12-14 guage half round wax and 18 guage round wax-ladder like framework rather than mesh pattern.

Designing retentive framework –bucally lingually-strengthen acrylic resin base-minimize distortion of

base-stress Not interfere with teeth arrangement-future

adjustment

Metal bases –cast as integral parts of partial denture framework.

May also be assembled and attached to framework with acrylic resin.

Plastic Mesh Pattern

Open Lattice

BEADS & NAIL HEADS

• Porcelain/ Resin Artificial Teeth with Resin

• Porcelain/ Resin Tube Teeth & Facings Cemented Directly to Metal Bases

• Resin Teeth Processed Directly To Metal Bases

• Metal Teeth Cast With Frame Work

• Chemical Bond

Mechanically retained. Posterior teeth retained by acrylic resin in their

diatoric holes. Ant teeth retained by acrylic surrounding their

lingually placed retention pins. Acrylic resin teeth retained by chemical union

with acrylic resin of denture base.

Attachment of acrylic resin to metal base – nail head retention,retention loops or diagonal spurs.

Any junction of acrylic resin with metal should be at an undercut finish line.(mech retention)

Every attempt should be made to prevent separation and seepage which results in discoloration and uncleanliness.

Denture odors are frequently caused by accretions at the junction of acrylic resin with metal.

Separation occurring b/w acrylic resin and metal can eventually lead to some loosening of acrylic resin base.

Some disadv of this type of attachment are- Difficulties in obtaining satisfactory occlusion. Lack of adequate contours for functional tongue and

cheek contact. Unesthetic display of metal at gingival margins.

Modification of this method is attachment of ready made acrylic resin teeth to the metal base with acrylic resin of same shade(pressing).

Particularly applicable for ant replacements.

Procedure- Labial index of the position of teeth is made. Lingual portion cut away or post hole prepared. Subsequently tooth is attached to denture with

acrylic resin of same shade. For best occlusal relation jaw relation records made

with denture casting in mouth. Tube teeth preferred. Teeth are ground to fit the ridge with sufficient

clearance beneath for metal base. Casting completed and tried. Teeth ground to harmonious occlusion.

Occlusal relation established in mouth and transferred to articulator.

Teeth can be carved or processed in acrylic resin of proper shade.

Long,short,wide or narrow teeth may be created when necessary to fill spaces.

Occlusion on acrylic resin teeth may be restablished to compensate for wear or settling by reprocessing new acrylic resin or using light activated acrylic resin.

Occasionally a second molar tooth may be replaced as part of partial denture casting.

Space too limited for attachment of an artificial tooth. Because metal particularly a chrome alloy is abrasion

resistant area of occlusal contact should be held to min to prevent damage to peridontium of opposing tooth.

Should be used only to fill a space and to prevent tooth extrusion.

Recent developments-direct chemical bonding of acrylic resin to metal frame works.

Investing alveolar and gingival tissue replacement components can be attached without the use of loops,mesh or surface mechanical locks.

Section of metal framework-roughned with abrasives-treated with vaoporized silica.

Acrylic resin bonding agent applied-thin layer of acrylic resin.

Triochemical coating accomplishes a second method of fusing a microscopic layer of ceramic to metal.

Sandblasting metal framework with silica particle (Rocatec-plus).

Silane added to ceramic-chemical bond b/w silicate layer and denture base acrylic resin.

Denture base acrylic resins formulated with 4-Meta are also available and provide mechanism of bonding acrylic resin to metal.

Distal 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.

Acrylic resin bases – distal extensions

Min and harmonious occlusion,and accuracy with which base fits the underlying tissue influences trauma occuring under function.

Absence of trauma-ridge integrity.

Best indication for metal distal extension bases-ridge that supported a previous partial denture.

Tissues remain healthier beneath a metal base than a acrylic resin base –thorough Rx planning-pt education-care of denture bases.

Highest pressure was on the residual ridge crest. The pressure distribution varied along with the design of the occlusal rest.

“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”

In distal extension situations-rigid connection b/w denture base and supporting teeth account for the base movt without causing tooth or tissue damage.

Stress on abutment teeth and residual ridge minimised-broad coverage,harmonious occlusion,direct retainers.

2 types of clasp assembly-distal extensions-stress breaking design.

Retentive clasp arms-engage undercuts on abutment tooth-tissueward movt- min leverage to abutment.

Tapered,wrought wire retentive clasp-flexibility. Act as stressbreaker b/w denture base and

abutment tooth. Another concept of stress breaking-separating

action of retaining elements from denture base

Stress breakers effectively dissipate vertical stresses.

It is the rigid nature of conventional RPD that allows satisfaction of requirements of support,stability and retention.

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