Selection of denture base and teeth for rpd /certified fixed orthodontic courses by Indian dental academy

SELECTION OF DENTURE BASE AND TEETH
FOR REMOVABLE PARTIAL DENTURE

INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

• CONTENTS
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
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


Introduction
Definition
Functions of denture base
Ideal requirements of denture base materials .
Denture base materials used in fabrication of RPD.
Denture Base resins.
Advantages & Disadvantages
Metallic denture base materials
Advantages & disadvantages
Fabrication of distal extension denture base



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

Attaching Resin denture base to major connector
Teeth selection
Different artificial teeth
Anterior teeth selection
Posterior teeth selection
Attaching teeth to denture base
Review of literature
Summary & Conclusion
References.

•

INTRODUCTION


 DENTURE

BASE
 The part of a denture that rests on the foundation
tissues and to which teeth are attached.


•FUNCTIONS OF TOOTH SUPPORTED DENTURE BASE



Provide desirable esthetics.



Support the artifial tooth .



Prevent vertical & horizontal migration of remaining natural teeth.



Eliminate undesirable food entrapment.



Stimulate the underlying tissues.


• FUCTIONS OF DISTAL EXTENSION DENTURE BASE


Contributes to the support of the denture & improves stability of the
prosthesis .



Esthetics by attaching the teeth & restoring the lost facial contours.



Stimulation of the underlying tissues.



Cleanliness maintenance.



Secondary retention by intimate contact between the denture base &
the major connector with the underlying tissues

•IDEAL REQUIREMENTS OF


Bio- compatible.



Accurately adapt to the underlying tissues



Adequate Physical & Mechanical properties



-Sufficient strength to resist distortion & fracture
-Dimensional stability
-Low specific gravity,
-Good thermal conductivity
-Easy to finishing & polishing
-Should not absorb oral fluids
-In soluble in oral fluids.



Ease of fabrication & repair.



Potential for future relining , rebasing.



Esthetically acceptable ,color stability.



Odourless.



tasteless



Easy to clean the prosthesis.



Long shelf life.



Cost effective.

• DENTURE BASE MATERIALS


Acrylic resin



Metallic


•HEAT ACTIVATED DENTURE BASE RESIN


COMPOSITION:



POWDER
1) Poly(methyl methacrylate)
2) Initiator- Benzoyl peroxide-0.5- 1.5%
3)Plasticizer- Dibutyl pthalate
4) Pigments
5) Opacifiers
6)Inorganic particles- glass fibers & alumina.

 LIQUID


Non polymerized methyl
methacrylate



Inhibitor – Hydroquinone
0.003%-0.1%.



Cross linking agent – Glycol
dimethacrylate-1 to 2% by
volume.



HIGH IMPACT STRENGTH
MATERIALS



Reinforced with butadiene styrene
rubber



The rubber particles are grafted to
methyl methacrylate to bond to the
acrylic matrix



POUR TYPE RESIN
Composition similar
particle size smaller







RAPID HEAT POLYMERIZED RESIN



Altered initiator system



LIGHT ACTIVATED



Urethane dimethacrylate matrix with acrylic copolymer



Microfine silica fillers




Photo initiator - Comphorquinone
Polymerized with a visible light of 400 to 500 nm

FIBER –REINFORCED POLYMER


Glass, carbon/graphite, aramid and ultrahigh molecular wt
polyethylene have been used as fiber reinforcing agents.



Metal wires like graphite has minimal esthetic qualities.



Fibers are stronger than matrix polymer thus their inclusion
strengthens the composite structure.



The reinforcing agent can be in the form of unidirectional, straight
fiber or multidirectional weaves.

•MECHANICAL PROPERTIES



PMMA&PVA posses adequate tensile & compressive strength .



Transverse strength is the combination of tensile & compressive
strength proportional limit, elastic modulus .



PVA has 7to 10%of Elongation ,is an indication of toughness &
permit larger deformation .



Proportional limit should be sufficiently high to withstand
masticatory forces.



Impact strength –. Rubber reinforced acrylic more impact strength.



Rubber reinforced acrylic resin possesses adequate fatigue strength
to withstand the smaller cyclic stresses during mastication.



Fracture toughness of rapid heat cure resin is better than
conventional & high impact resin.



Hardness KHN of denture base acrylic is low so care should be
taken while polishing, cleaning.


• ADVANTAGES


Easy adjust & polish.



Reling & rebasing is possible .



The weight & bulk is more than cast alloys.



Denture base contours for functional tongue & cheek movements.



In mandibular arch weight of the denture contributes for retention.



Esthetics, tinting..



Processing



Cost

• DIS ADVANTAGES


Adaptation not as accurate as cast metal alloy.



Abrasion resistance..



Acrylic resin bases tend to accumulate mucinous deposits



So meticulous cleanliness maintenance required.



Thermal conductivity



Weight & Bulk



It should be min. 2mm in thickness

to obtain adequate rigidity &

strength .


•METALLIC DENTURE BASE MATERALS REMOVABLE
PARTIAL DENTURE


High Noble casting alloys- Au- Ag- Cu -Pd



Predominantly base metal alloys
* Co-Cr-Mo
* Co- Cr –W
* Ni-Cr –Mo
* Ni-Cr –Mo-Be
* Cp-Ti
* Ti-Al-V

•


As early as 1949 it was estimated that nearly 80% of all partial
denture appliances were cast from Co-Cr alloys.



Principle elements –Cr, Co, Ni -82 to 92%.



COMPO SITION :



COBALT-CHROMIUM -ALLOYS
- Cobalt- 60%




- Chromium -25% to 30%
OTHER COMPONENTS :
Mo,Al,W,Fe,Ga, Cu, Si, C, Pl.









COBALT-CHROMIUM-NICKEL
- Co-50%
- Cr-25%
- Ni-19%
Other constituents
- Mo-3.7%
- C -0.2%
NICKEL CHROMIUM- MOLYBDENUM ALLOYS :
- Ni - 70%
- Cr - 16%
Other constituents
- Al –2%
- Be –0.5%
- Mo,W, Mg, Co, Si, C.



Chromium :
Tarnish and corrosion resistance and stain less properties.



Cobalt and nickel :
In general cobalt and nickel are interchangeable .



Cobalt increases the elastic modulus ,strength and hardness more
than Nickel does.





OTHER ALLOYING COMPONENTS :
Carbon : increases the hardness of Co based alloys.



Molybdenum : (3% to 6% )
Contributes to the strength of the alloy.



Aluminium :
Forms a compound with Ni ,which increases the tensile and the
yield strength of the alloys.



Berylium :
About 1% lowers the fusion temperature range of the alloy by about
100 degrees C.



Silicone and Manganese :
Increase the fluidity and castability of these alloys.



Nitrogen :
If present contributes to the brittle qualities of these alloys .

•TITANIUM ALLOYS








High purity titanium (99 wt %) with O,C ,N,H atoms dissolved
interstitially.
It undergoes an allotropic transformation from hexagonal to body
centered crystal structure when the temperature is raised to 882 +/ 2 degree.
4 types – Alpha
- Near alpha
-Alpha – Beta
-Beta
Cp Ti available in 4 different grades (ASTM)



Titanium alloy- Ti- 6V – 4Al



Vanadium is the beta phase stabilizer with the BCC
structure.



Al alpha phase stabilizer



Most commonly used is alpha – beta alloy. [strength > Cp
Ti.]

• TYPE IV GOLD ALLOY




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
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



Composition :
Au - 69%
Ag – 12.5%
Cu -10%
Pd – 3.5%
Pt – 3%
Zn,Sn,Fe,In, Ga for balace.
ALLUMINIUM ALLOY
Al – 99.95 wt %
Mg – 3.5%

MECHANICAL PROPERTIES
Metal Type

Yeild
Strength
(Mpa/Ksi)

Tensile
Strength
(Mpa/Ksi)

Elongation
(%)

Hardness
(HV)

Elastic Modulus
(GPa/Ksi x 103 )

Co- Cr (A )

710/103

870/120

1.6

432

224/32.4

Ni – Cr (B)

690/100

800/116

3.8

300

182/26.4

Co – Cr – Ni
(c)

470/68

685/99

8.0

264

198/28.7

Fe – Cr ( D)

703/102

841/122

9

309

202/29.3

Type IV Gold

493/71.5

776/112

7

264

90/13

CP Ti

344/50

345/50

13

210

103/14.9

Ti – 6V- 4 Al

870/126

925/134

5

320

117/17


ADVANTAGES OF METALLIC DENTURE
BASE


Accurate adaptation & permanence of the form



Abrasion Resistance.



Comparative tissue response
-Inherent cleanliness
-greater density & bacteriostatic activity contributed by the
ionization & oxidation of metal base.




Thermal conductivity .



Better patient acceptance.



Weight & Bulk



Metal alloys can be casted much thinner..



Maintains & prolongs the health of supporting tissues.


DIS ADVANTAGES


Relining & rebasing difficult.



Difficult to adjust.



It cannot be used whenever restoring the normal facial contours is
required for esthetics.



Special equipment required.



More expensive.




INDICATIONS:



1) Risk of fracture of resin denture base.



2)RAR atrophy



2) More room for the tongue functioning is required.



3) Patient allergic to resin.



4) Satisfactorily healed ridges.

• THE METAL- ACRYLIC RESIN BASE


Consists of cast metal base
that fits the RAR & acrylic
resin attached to it to retain
the teeth.


•FABRICATION OF DENTURE BASE IN DISTAL
EXTENTION RPD


Distal extension RPD depends…



Extensions of the denture base



Kaire has shown that maximum coverage of denture
bearing areas with large wide denture base is of utmost
importance for with standing the vertical & horizontal
stresses.

•SELECTIVE PRESSURE IMPRESSION METHOD
By this method the soft tisuses over the primary
supporting areas are recorded to provide support to the
denture base under functional load.
 Denture base closely adapted in the region of buccal shelf
area .
 lightly adapted to the crest of the ridge.



•METHODS OF ATTACHING THE DENTURE BASE


Minor connector joins the denture base to the major
connector.



Relief of at least 20 guage is provided beneath the
retentive frame work for the acrylic to flow.



Should not interfere with teeth arrangement.



Any junction of acrylic resin with metal should be at an
undercut finishing line.

•TYPES OF MINOR CONNECTORS


1) Open construction

2) Mesh construction
 3) Bead, nail head & wire
constructions



CHEMICAL BONDING


Direct bonding of acrylic resin to metal framework.



Sections of metal frame work meant for supporting the
replacement teeth is roughened with abrasives & treated
with vaporized silica coating.



Acrylic bonding agent is applied.



Thin film of acrylic resin applied to act as substrate for
teeth replacement or acrylic resin tissues replacement




Tribochemical coating
Method for fusing microscopic layer of ceramic to metal.



Sandblasting the metal framework with special silica particle
material .



Silica is attached to the framework by impact.



Silane is added to this ceramic like film to form chemical bond
between silicate layer & acrylic resin.



Denture base acrylic resins formulate with 4-META provide
mechanism of bonding acrylic resin to metal.

•SELECTION OF THE PROSTHETIC TEETH


Teeth replacement is important to reestablish the lost
facial contours, phonetics, masticatory function.


• IDEAL PROSTHETIC TOOTH SHOULD SATISFY
FOLLOWING REQUIREMNT


Pleasing appearance to satisfy the esthetic requirement.



Easily adaptable to any edentulous space.



Easy for attaching to the prosthesis.



Easy to modify the shape & size as per requirement & repolish
restore the original polish.



Color stability.




Resistance to blanching, distortion ,crazing.



It should have enough strength to bear occlusal load.



Adequate resistance to wear.



Capable of articulating with teeth of any occlusal pattern or
material without causing adverse effect to either.


• TYPE OF ARTIFICIAL TEETH


Acrylic resin teeth



Porcelain teeth



Metal tooth



Acrylic resin teeth with occlusal restorations



Custom denture tooth.


•ACRYLIC RESIN TEETH


Strength adequate to withstand the occlusal load.



Chemical bonding with acrylic denture base.



Low abrasion resistance



Absorbs stain.



Impact resistance greater than porcelain.



Shape & size can be modified.




Easy to polish.



Dose not cause the wear of the opposing natural teeth or gold
restorations.



Low heat distortion temperature .



Cold flow or permanent deformation under pressure below their
elastic limit.

• CHARECTERISTICS OF PORCELAIN TETH


More esthetics than acrylic resin teeth.



Strength more than acrylic teeth .



Brittle chips off or fractures easily



Good abrasion resistance



It can cause wear of the opposing natural teeth or gold restorations.



Impervious to stain.




Clicking sound.



Difficult to trim & adjust so cannot be used in inadequate interarch
space.



Mechanical bonding with the acrylic denture base so percolation
may occur



High heat distortion temperature .



No permanent deformation under forces of mastication.


• THE INTERCHANGEABLE FACING








It is a strongest type of anterior teeth replacements.
Indicated in
Single tooth replacements preferred especially in anterior region
In severely decreased inter ridge space.
- Deep bite.
- Bulbous alveolar ridge such that the retention latice work of
the metal frame work is restricted.
When more strength is required in anterior teeth replacement.
Sometimes used for replacing maxillary I premolar.



Advantages



When contours of the RAR altered by resorption the
interchangeable facings can be refitted.



Disadvantages



Esthetically not good.


•THE POST OR PRESSED ON TOOTH


Esthetics better than the Interchangeable facings.



Strength better than denture tooth but less than
interchangeable facing.



Requires adequate amount of interarch space .



Most commonly used to replace maxillary canine.


• METAL TOOTH


It is the tooth of choice for posterior tooth replacement.



Strength more than any other prosthetic tooth.



The frame work is of the Co- Cr then tooth should not be occluded
heavily with the opposing gold restoration .



Indicated in



Edentulous space measuring about 3to8 mm. Decreased mesio distal
width by mesial drifting of 2nd molar .




Gold occlusal surfaces.



Amalgam occlusal
surfaces


• THE SELF CLEANSING PONTIC


The self cleansing occlusal surfaces which
is an integral part of the metal frame work
thus the potential areas of food entrapment
are eliminated & permitting saliva to flow
under & around pontic.



Used to replace the single posterior tooth
with extensive alveolar ridge atrophy.



When the adjoining teeth have drifted ,
rotated.

•SELECTION OF ANTERIOR TEETH FOR REMOVABLE
PARTIAL DENTURES


FACTORS TO BE CONSIERED



Size



Shape & form



Texture



Color



Material


•DENTOGENIC CONCEPT
 Dentogenics is the art, practice & technique of creating the illusion
of natural teeth in artificial denture & is based on the elementary
factors suggested by the sex, personality & age of the patient.


Considering the sex factor
- Feminine characteristics select the mold that is more
rounded & incisal edges altered by grinding procedures which
gives more softer appearance.
- Masculine characteristics select mold , followed
by grinding of incisal edges to make more squarish.



Consideration of age factors in prostodontics is to maintain the
conformity between the restoration & patients physiological age.



As age advances natural teeth show wearing & similar aging effects
are produced in artificial teeth by characterization.



Considering the personality factors



Personality spectrum – Delicate, Medium pleasing , Vigorous .



The mold should be in harmony with the personality of the
individual.



Age, sex & personality are inseparable & interdependent.

• SIZE OF THE TOOTH


Measuring the dimensions of the corresponding tooth on the
opposite side of the arch.



Pre – extraction records – Photographs, Study casts, radiographs.



Extracted teeth of the patient.



Edentulous space



In multiple anterior teeth replacement the space is measured.



Increased space in edentulous area as seen in patients with large
diastema between the central incisors. Then two central incisors are
placed with overlapping the teeth or reshaping it as lateral incisor.

• LENGTH OF THE TOOTH










Visibility of incisal edges & high lip line guide in the selection of
the length of the anterior tooth .
Visibility of the upper anterior depends on
1) Age
-Young patients 2 to 3 mm of upper central incisor
may be visible .
-Elderly – fraction of a mm of tooth.
2)Length of upper lip
- Short upper lip- half the length of crown of the central
incisor may be visible.
3) Over bite – More of the upper anterior teeth may be visible.
High lip line – the maximum excursion of upper lip in function.

Length of C.I = Chin to hair line distance / 16
 By Dr. M.M.House



• WIDTH


METHODS



1) Canine eminences
Line marked on the distal aspect of canine eminence on
the cast gives the mesio –distal width of upper anterior
teeth



2)Bizygomatic width
Breadth of all upper anterior teeth Bizygomatic width / 3.3
Width of
upper C.I = Bizygomatic width / 16



3) Cranial circumference
The horizontal circumference of the cranium about plane passing through
glabella & most prominent point on the occipital bone is said to be 10 times the
width of six anterior teeth



Corner of the mouth.
The distal surface of the natural upper canine is positioned at the corner of
relaxed mouth ..



Width of the nose
The parallel lines extended from the lateral surface of ala of nose onto the
properly contoured upper occlusal rim will give an indication of position of cusp
tip of upper canine teeth .




Lateral surface of nose
The line passing from the lateral surface nose, through the center
brow line. Lateral aspect of ala & extended on to the occlusal rim ,
gives an indication of the position of distal aspect of canine tooth.



Incisive papilla
Line parallel to coronal plane & passing through the incisive
papilla passes through the cusp tips of cuspid.


• SHAPE OF THE TEETH


The shape of the teeth should be in
harmony with the patients face.



J. Leon Williams – the shape of crown
of upper central incisor corresponded to
the outline form of the face.



Classified Face form
– Square
_Tapering
_Ovoid


• SHADE SELECTION


Artificial tooth shades should be selected according to the
physiological color changes seen in progressively aging ,
undiseased tooth.



Methods
- The tentative selection of the anterior teeth is arranged on a
plastic tooth selector & held on the side of the patient’s face
-Under the lip with more exposed tooth to observe the size in
relation to the patient’s face.
-The ‘ SQUINT TEST’.

•TEXTURE OF THE TOOTH


The artificial teeth should incorporate the features like
imbrication lines, wear facets, hypoplastic areas to
harmonize with the adjacent natural teeth.


SELECTION OF THE POSTERIOR TEETH
 The

form of the posterior teeth is important for the
preservation & maintenance of the health of the
residual alveolar ridges.














SIZE:
MESIODISAL DIMENSION :
In tooth supported RPD the space between the distal surface of
mesial abutment & mesial surface of the distal abutment teeth
should be considered.
In distal extension RPD the space between the canine & the
anterior end of the retromolar pad is considered.
OCCLSOGINGIVAL DIMENSION:
Available inter arch space determines the length.
Esthetics should be in harmony with adjacent natural teeth.




BUCCOLINGUAL DIMENSION.



The BL space available for artificial teeth is limited by the cheek &
tongue tissues , load bearing capacity of the supporting tissues.



Relatively narrow in BL direction are indicated to enhance the
sloping form of the flanges , permit surrounding tissues to function
to maintain the stability of the denture.



Narrow occlusal surfaces with proper escape ways for food
thought to direct the less force during function to supporting
structure


•FORM OF POSTRIOR TEEH


Determined by the cuspal inclines & arrangement of remaining
natural teeth.



Deep over bite cases the high cusped teeth should be used to
achieve occlusal balance.



In RAR atrophy the non anatomic teeth are used .


 SHADE

SELECTION
 In harmony with the remaining natural teeth .




METHODS OF ATTACHING THE ARTIFICIAL
TEETH TO THE DENTURE BASE


Porcelain or Resin tube teeth & Facings cemented
directly to Metal Bases


Teeth are altered & set prior to
completion of frame work.



Disadvantages



Difficulty in obtaining the satisfactory
occlusion.



Lack of adequate contours for
functional tongue & cheek contact.



Unaesthetic display of metal at the
gingival margin.

Pressing on a Resin tooth


Modification..



Teeth is selected & labial index of the position of the
teeth is made.



Post hole prepared on lingual portion.



Tooth attached with acrylic resin of the same shade.











Resin Tube or side groove teeth is selected
before waxing the denture frame work.
Hole is drilled on the ridge lap area.
The tooth is ground to fit the ridge with
sufficient clearance for the metal base.
45 degree bevel is placed around the base
of tooth to accommodate the boxing of
metal.
Lingual collar is created.

RESIN TEETH PROCESSED DIRECTLY TO
METAL BASES



The recess is carved in the wax pattern.
Occlusal relationships established



The teeth is carved & processed in acrylic
resin of the proper shade.



Advantages



Better attachment to the metal base.



Unusually long, short, narrow, wide teeth
may be fabricated.



Braided helical Post.



Posterior tube teeth.


•REVIEW OF LITERATURE
A study was conducted by Anthony & Peyton (1962) He
compared the dimensional accuracy of self cure & heat
cure acrylic resin , Cr- Co alloy .
 He concluded that self cure acrylic resin dentures were
of accurate fit followed by heat cure, Cr- Co . Because
of the fewer processing strains.



A study was conducted by Donald , Lundquist in (1963)
He compared the accuracy of fit of denture bases made
of PMMA & Al.
 He concluded that the fit of accuracy of cast Al alloy
dentures were better than the PMMA.





A study was conducted by Anthony De Furio and Daniel H. Gehl
(1970) to determine the amount of force required to dislodge
maxillary dentures made from Al ,Au alloy and acrylic resin.



He concluded that the chrome cobalt and Al alloy bases gave
retention values which were significantly higher than those
obtained with the acrylic resins and gold alloy bases




A study was conducted by Frank E. Pulskamp in (1979)
He compared the two dimensional accuracy of Type iv
Gold alloy, Ni-Cr, Co-Cr alloys.



He concluded that Type iv gold alloy showed least
cross arch & antero posterior expansion than Co-Cr.


A study which was conducted in dept of prosthodontics by Dr.Gautam
Shetty under the guidance of DR. N.P.PATIL Sir The main
objective of the study were :
1. To compare the fit of Al alloy (7010)denture base
and base metal alloy denture base.

with acrylic

2. To study the effect of anodization and electroplating on the
resistance to corrosion.
3. To compare the flexure strength of aluminum alloy with that of
resin and base metal alloy .


RESULTS :


The results indicated the accuracy of fit of aluminium was better
than base metal alloy and superior than acrylic resin



Anodized Al showed better resistance to corrosion resistance than
that electroplated and that without any surface treatment.


•SUMMARY & CONCLUSION


REFERENCES


Applegate The partial denture base. J.P.D:1955:5:636:648.



Anthony & Peyton Dimensional accuracy of various denture base
materials J.P.D: 1962:12:61-81.



Craig’s Restorative dental materials ,11th edition.



David Watt, MacGregor’s Designing Partial dentures.



Donald An alluminium alloy denture base material. J.P.D :
1963:13:1:102.



Grant & Jhonson’s Removable denture prosthodontics, 2nd edition.



Earnest Miller’s Removable prosthodontics 2nd edition.



Frush ,Fisher, Ronald introduction to Dentogenic Restoration ,J.P.D
1955:586:595



Frush How dentogenics interpretes the personality factor,
J.P.D:1956:441
Frush How dentogenics interpretes the sex factor, J.P.D :1956:160



Frush, Fisher Age factor in Dentogenics 1957:7:5



Frush Dentogenic s Its practical application. 1959:9:6:914.



Jhon Cornell Physical properties of denture bae materials J.P.D :



1960 :10:516.


McCracken’s Removable partial prosthodontics, 11th edition.



Philip’s Science of Dental Materials, 11th edition.



Stewart’s Clinical Removable partial prosthodontics, 3rd edition.

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Selection of denture base and teeth for rpd /certified fixed orthodontic courses by Indian dental academy

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