1.
ABUTMENT SELECTION
IN
FIXED PARTIAL DENTURES
PRESENTED BY:
Dr. Anshul Sahu
2nd Year
PG Student

2.
CONTENTS
1. Introduction
2. Diagnostic Casts
3. Radiographic Examination
4. Factors influencing Abutment selection:
a. Crown length
b. Crown Form
c. Crown – root Ratio
d. Periodontal ligament Area
e. Root Configuration
f. Root Proximities

3.
f. Periodontal examination.
g. Long- Axis Relationship
h. Arch Form
i. Span Length
j. Unrestored Abutments
l. Endodontically Treated Abutments
m. Rigidity of Prosthesis
n. Margin Location

4.
o. Occlusal Anatomy
p. Pontic Tissue Contact
q. Available Tooth Structure
r. Age of Patient
s. Vitality testing of the pulp
t. Long term Abutment Prognosis

5.
5. Special Problems
a. Pier Abutments
b. Tilted Molars Abutments
c. Canine replacement fixed partial denture
d. Abutments for Cantilever FPD.
6. Questionable abutments
7. Summary & Conclusion
8. References

6.
INTRODUCTION
• Fixed partial dentures transmit forces through the abutments to
the periodontium. Failures are due to poor engineering, the use of
improper materials, inadequate tooth preparation, and faulty
fabrication. Of particular concern to prosthodontist is the
selection of teeth for abutments. They must recognize the forces
developed by the oral mechanism, and resistance.
• Successful selection of abutments for fixed partial dentures
requires sensitive diagnostic ability. Thorough knowledge of
anatomy, ceramics, the chemistry and physics of dental materials,
metallurgy, Periodontics, phonetics, physiology, radiology and the
mechanics of oral function is fundamental.

7.
DEFINITION
• A tooth, a portion of a tooth, or that portion of a dental implant
that serves to support and/or retain a prosthesis.
(GPT 9)

8.
DIAGNOSTIC CASTS
 A life size reproduction of the parts of the oral cavity and or facial
structures for the purpose of study and treatment planning.
 Articulated diagnostic casts are essential in planning fixed
prosthodontic treatment.
 To accomplish their intended goal, they must be accurate
reproductions of the maxillary and mandibular arches made from
distortion free alginate impressions.
 The diagnostic casts should be mounted on a semiadjustable
articulator with a face bow after bite registration.

9.
RADIOGRAPHIC EXAMINATION
• Periapical and bitewing films are most important in selection of
abutment teeth. On occasion additional views, such as TMJ radiographs
for patients with TMJ dysfunction and panoramic radiograph can also be
useful.
• Radiographs provide information that cannot be determined clinically
and however are not a primary source of diagnostic information.
• An intraoral radiographic examination reveals:
• Remaining bone support
• Root number and morphology (long, short, slender, broad, bifurcated, fused,
dilacerated etc.) and root proximity.
• Quality of supporting bone, trabecular patterns and reactions to functional
changes.
• Width of periodontal ligament spaces and evidence of Trauma From Occlusion

10.
• Areas of vertical and horizontal osseous resorption and furcation invasions
• Axial inclination of teeth(degree of non parallelism if present)
• Continuity and integrity of lamina dura.
• Pulpal morphology and previous endodontic treatment with or without post
and cores.
• Presence of apical disease, root resorption or root fractures.
• Retained root fragments, radiolucent areas, calcifications, foreign bodies or
impacted teeth.
• Presence of carious lesions, the condition of existing restorations, and
proximity of carious lesion to the pulp.
• Proximity of carious lesions and restorations to alveolar crest.

11.
• The functional demand on the tissue of one person may be quite
different from those of another. The tissue response and tolerance
vary among individuals; therefore no two abutment teeth will
react exactly the same under similar conditions.
• An understanding of the favorable indications and reasonable
limitations of abutments for fixed partial dentures is essential.

12.
FACTORS INFLUENCING ABUTMENT
SELECTION
• The choice and number of abutments are determined
by a combination of load- bearing ability of the
abutment teeth plus the forces and stresses to which
these will be subjected. The number of roots, their
shape, length, alignment, and bone height has a direct
relation to the load- bearing capacity of teeth. The
shorter, more tapered the root and lower the bone
level, the less satisfactory the tooth will be as an
abutment.

13.
a. CROWN LENGTH
• Teeth must have adequate occlusocervical crown length to
achieve sufficient retention. Teeth with short clinical crowns often
do not provide satisfactory retention unless full – coverage
preparations are used or additional length is achieved through
periodontal surgery.

14.
b. CROWN FORM
• Some teeth have tapered crown form, which interferes with
preparation parallelism, necessitating full coverage retainers to
improve their retentive and esthetic qualities.
Ex: include anterior teeth with poorly developed cingulam and
short proximal walls and mandibular premolars with poorly
developed lingual cusps and short proximal surfaces. Also, some
incisors poses very thin highly translucent incisal edges making
use of partial coverage retainers esthetically unacceptable.

15.
c. CROWN – ROOT RATIO
Definition:
Physical relationship between the portion of tooth within
alveolar bone compared with the portion not within the
alveolar bone, as determined by radiograph. (GPT-8)
• This ratio is a measure of the length of tooth occlusal to the
alveolar crest of bone compared with length of root embedded
in bone.
• The optimum crown- root ratio for tooth to be utilized as a
fixed partial denture abutment is 2:3. A ratio of 1:1 is the
minimum ratio that is acceptable for a prospective abutment
under normal conditions (such as number of teeth being replaced,
tooth mobility and overall periodontal health is good)

16.
Optimum C: R ratio is 2:3 A ratio of 1:1 is minimum
in FPD abutment that is acceptable

17.
 Biomechanical concept:
Represents Class I lever :
• Crown -> Effort arm. (E)
• Root ->Resistance arm. (R)
• Centre of rotation of tooth -> Middle of root that is embedded in
alveolar bone
Loss of alveolar bone: Chance of harmful lateral increases.
• Crown portion (effort arm) : Increase.
• Root portion (resistance arm) : Decrease.
• Centre of rotation moves apically.
E=1 R=2

18.
d. PDL AREA AND SURFACE AREA
• This is an important point in the assessment of abutment’s
suitability from a periodontal standpoint.
Root surface area or the area of periodontal ligament attachment of
the root to the bone
 Large teeth  Greater surface area  Better ability to bear
added stress.
 Periodontal disease  Loss of supporting bone  Lesser
capacity to serve as
abutment.

19.
• Tylman in 1970 stated that 2 abutment teeth could support 2
pontics.
• ANTE suggested in 1926 that it was unwise to provide a FPD
when the root surface area of the abutment was less than the root
surface area of the teeth being replaced; this has been adopted
and reinforced by other authors (Johnston, Dykema) in 1971 as
ANTE’s LAW. This rule was based on the engineering principles
used for designing bridges
• ANTE’s LAW – Irwin H. Ante (Toronto, Ontario Canada)
Is an eponym in FPD Prosthodontics for the observation
that the combined pericemental area of all abutment teeth
supporting a FPD should be equal to or greater in
pericemental area than the tooth or teeth being replaced

20.
Combined root surface area of II
premolar& II molar (A2p+A2m) is
greater than that of I molar being
replaced (A1m)
Combined root surface area of I
premolar and II molar (A1p+A2m) is
approx. equal to that of the teeth
being replaced (A2p+A1m)
The combined root surface area
of the canine & the second
molar is exceeded by that of
the teeth to be replaced. A fixed
partial denture would be a poor
risk in this situation

21.
Average root surface area (Jepsen 1963)

22.
• Factors Modifying ANTE’s LAW
Condition Existing Probable modification in ANTE’s LAW
1. Bone loss from periodontal disease Increase the number of abutments.
2. Mesial or distal tipping or changes in axial
inclination.
Increase the number of abutments.
3. Migration (bodily movement)of abutment
teeth decreasing M-D length of
edentulous area.
Decrease the number of abutments used (less
pericemental support required)
4. Less than favorable opposing arch
relationship producing increased occlusal
load.
Increase the number of abutments used for
support.
5. Endodontically restored abutment teeth
with root resections.
Increase the number of abutments
6. Arch form situations creating greater
leverage factors.
Increase the number of abutments.
7. Tooth mobility created after osseous
surgery.
Increase the number of abutments(splinting
procedure)

23.
e. ROOT CONFIGURATION
Roots that are broader
labiolinguallly than they are
mesiodistally are preferable to
roots that are round in cross –
section.
Multirooted posterior teeth
with widely separated roots will
offer better periodontal support
than roots that are short
converge,

24.
• A tooth with conical roots can be used as an abutment if all other
factors are optimal.
• Irregularly shaped, multiple, divergent roots offer better
prognosis.
• A well aligned tooth will provide better support than a tilted one.
Alignment can be improved with orthodontic treatment.

25.
f. ROOT PROXIMITIES
• There must be adequate clearance between the roots of
proposed abutments to permit the development of physiologic
embrasures in completed prosthesis.
• Malpositioned anterior teeth and the mesiobuccal roots of
maxillary molars often present unfavorable root proximities
where desired embrasure form is not possible.
• Solution to root proximity: Selective extraction or root
resection procedures

26.
g. PERIODONTAL DISEASE
• Healthy periodontal tissue is prerequisite for all fixed
restorations.
• Abutment with bone loss needs careful assessment:
• Conical shape of roots: with 1/3rd of root length exposed, ½ of the
supporting are is lost.
• Lengthened clinical crown leads to greater leverage force.
• Successful fixed prosthesis with severely reduced periodontal
support, is assured when periodontal tissues have been returned
to excellent health, and long term maintenance has been ensured,
otherwise results will be disastrous.

27.
• Periodontal assessment
An examination of the periodontal tissues should be made. The
aim is to provide a basic screening of the tissues and to obtain an
indication of the treatment requirements of the patient.
• Mobility
• Recession
• Pocket
• Furcation

28.
h. LONG AXIS RELATIONSHIP
• The architecture of periodontal ligament is such that forces are
withstood best when they are directed along the long axis of the
tooth.
• A severely inclined tooth will not withstand forces as well as one
that is erect.
• Inclined tooth as abutment: Shorter edentulous span with less
occlusal force.
• Common path of insertion for all retainers:
 Conventional FPD: Less then 25° inclination.
 Resin-bonded FPD: Less then 15° inclination mesio-distally and
same plane facio-lingually.
Evaluation: Diagnostic casts with a dental surveyor.
Radiographs.

29.
i. ARCH FORM
• When pontics lie outside the interabutment axis line, the pontics
act as a lever arm, which can produce a torquing movement.
 Common problem in replacing all four maxillary incisors.
• Solution:
 Additional retention in opposite direction from the lever arm and at a
distance from the inter-abutment axis equal to the length of the lever
arm.
 The first premolars sometimes are used as secondary abutments for a
maxillary four pontic canine-to-canine FPD

30.
AB- fulcrum line
FG- the distance the pontics extend
anteriorly to fulcrum line.
CD – counterbalancing retention by
including the I premolars as abutments

31.
j. SPAN LENGTH
• In addition to the increased load placed on the periodontal ligament by a
long span fixed partial denture, longer spans are less rigid.
• Bending or deflection varies directly with the cube of the length and
inversely with the cube of the occlusogingival thickness of the pontic.
• Compared with a fixed partial denture having a single tooth pontic span,
a two tooth pontic span will bend 8 times as much. A three tooth pontic
will bend 27 times as much as a single pontic.

32.
Disadvantages of Longer pontic span:
Potential for producing more torquing forces abutment.
Less rigidity

33.
• To minimize flexing caused by long and/or thin spans:
• Pontic designs with a greater occluso-gingival dimension
• The prosthesis may also be fabricated of an alloy with higher yield
strength, such as nickel-chromium
• Double abutment
Retainers on secondary abutments must be at least as retentive as the
retainers on the primary abutments. As the retainer on secondary
abutments will be placed in tension when the pontic flexes, with
primary abutment acting as fulcrum.

34.
k. UNRESTORED ABUTMENTS
• An unrestored, caries free tooth is an ideal abutment. It can be
prepared conservatively for a strong retentive restoration with
optimum esthetics.
• In an adult patient, an unrestored tooth can be safely prepared
without affecting the pulp as long as the design and technique of
tooth preparation are wisely chosen.

35.
l. ENDODONTICALLY TREATED ABUTMENTS
• Teeth in which the pulpal health is doubtful should be
endodontically treated before initiating fixed prosthesis.
• Although a direct pulp caps maybe acceptable, risk for a simple
amalgam or composite resin, a conventional endodontic
treatment is normally preferred for cast restorations, especially
where the later need for endodontic treatment would jeopardize
the overall success of treatment.
• Such endodontically treated teeth serve well as abutment with
post and core foundation for retention and strength. Sometimes
its better to remove badly damaged tooth rather than attempting
endodontic treatment.
• Can not be selected for cantilever FPD.

36.
m. RIGIDITY
• The lack of sufficient rigidity in a fixed prosthesis is a frequent
cause of failure. Rigidity is obtained by use of the proper
materials arranged in the correct shape form and thickness in
regard to the forces acting upon them.
• Excessive occlusal forces cause loosening of prosthesis through
flexure or can induce ceramic fracture. The force can also cause
tooth mobility, particularly in presence of decreased bone
support.
• Flexure can cause damage to the abutments and may result in
eventual loosening of the retainers, and fatigue of the metal. The
induced stresses must not exceed the yield strength of the alloy.

37.
n. MARGIN LOCATION
• Sound tooth enamel cannot be improved biologically or
esthetically. Therefore when conditions permit, margins of
restorations should be kept away from the gingival tissues. The
most accurate margin for any restorative material irritates the
gingiva when it is extended beneath the free margin.

38.
o. OCCLUSAL ANATOMY
• Natures own anatomy and contour should be recreated in all
restorations.
• Has an indirect influence on the loads transmitted.
• Ridges and grooves increase the sharpness and shearing action of
teeth and reduce friction between opposing surfaces by keeping
the contacting area to minimum.
• Permits the most efficient mastication of food, thus reducing the
load transmitted.
• Attrited teeth need more muscular power and longer and more
masticatory strokes in order to chew food enough.

39.
Factors affecting occlusal forces:
 Degree of muscular activity.
 Habits such as bruxism.
 Number of teeth being replaced.
 Leverage on the bridge.
 Adequacy of bone support.
Results of excessive occlusal forces:
 Loosening of prosthesis through flexure.
 Ceramic fracture.
 Tooth mobility (In presence of decreased bone support).

40.
 Replacement strategies:
 Buccolingual width of pontic should harmonize with
buccolingual dimension of natural unmutilated teeth, and
recreate the normal buccal and lingual form to the height of
contour.
 The total meso-distal width of the cusps of abutment should be
equal or exceed that of pontics.

41.
p. PONTIC TISSUE CONTACT
• The tissue contacting the surfaces on the pontic should be
convex, smooth and free of porosity. The area of contact should
be minimal, free of pressure and thought of as having saliva
contact rather than tissue contact.

42.
q. AVAILABLE TOOTH STRUCTURE
• The size, number and location of carious lesions or restorations in
tooth affect whether full or partial coverage retainers are
indicated.
• Extensive defective restorations or fractures require intentional
endodontic therapy or post and core fabrication to provide a
sufficiently retentive and resistant form to the preparations.
• Crown lengthening maybe indicated to expose sound tooth
coronal to biologic width when caries, restorations fractures are
in proximity to alveolar crest.

43.
r. AGE
• Fixed Partial Denture is usually contraindicated adolescents ,
Because:
• Teeth are not fully erupted.
• Excessively large pulp horns.
Treatment options:
 Space maintainer: Holds abutment and opposing teeth in
position.
 Minimal tooth reduction: Prosthesis considered temporary
and remade when pulp size permits.

44.
s. VITALITY TESTING OF THE PULP
• Vitality of the tooth may be tested using either electrical or
thermal stimulation. Electrical testing will require a charge to be
applied to the tooth. The charge is generated by a machine and
the patient becomes part of the circuit when the tip is applied to
the tooth.
• Thermal stimulation may be through either cold or heat, but cold
stimulation is preferred. This is done using a ice stick or a pledget
of cotton wool soaked in ethyl chloride, which will give a quick
response. However, a more intense cold stimulus can be provided
by use of dry ice.
• This way the prospective abutment teeth are tested for pulp
vitality, if pulp in non- vital it should be endodontically treated
before using as abutment for a FPD

45.
t. LONG TERM ABUTMENT PROGNOSIS
• When there is some question of the ability of remaining supporting
structures to accept additional occlusal forces, the bilateral bracing
afforded by a removable prosthesis may be advantageous.
• Also a tooth with sufficient loss of periodontal support and
questionable long term prognosis may be best treated with a
removable prosthesis.
Overloading of abutments:
• The ability of abutment teeth to accept applied forces without
drifting or becoming mobile must be estimated and has a direct
influence on prosthodontic treatment plan.
• These forces are severe during Parafunctional grinding and clenching
and need to be eliminated during restoration of damaged dentition.

46.
SPECIAL PROBLEMS
• PIER ABUTMENTS/ INTERMEDIATE ABUTMENTS
Definition:
A natural tooth located between terminal abutments that serve to
support a fixed or removable partial denture.

47.
Completely rigid restoration: Contraindicated..
1. Physiologic tooth movement:
 Faciolingual  56 to 108μm.
 Intrusion  28μm.
Independent in direction and magnitude:
 Tendency for prosthesis to flex.
 Stress concentration around abutments.
2. Arch position of abutment:
Forces transmitted to terminal retainers as a result of middle
abutment acting as a fulcrum, causes failure of weaker retainer.
3. Disparity in retentive capacity:
Retention: Smaller anterior tooth < Larger posterior tooth.
Dislodgement of anterior retainer

48.
• The use of a non-rigid connector has been recommended to
reduce this hazard. It Broken stress mechanical union of retainer
and pontic.
• key way : Distal contours of pier a abutment
• Key: Mesial side of the distal pontic

49.
 Advantages:
• Movement prevents the transfer of stress from segment being
loaded to the rest of the FPD.
• Transfers shear stress to supporting bone rather then
concentrating it in connector.
• Minimize mesio-distal torquing while permitting them to move
independently.
 Disadvantages:
• Not preferred in teeth with decreased periodontal attachment.
• Supraeruption of key and posterior unit when opposed by RPD
or no teeth and anterior three unit by natural teeth.

50.
• TILTED MOLARS ABUTMETS
• Discrepancy in long axis of molar and premolar makes it
impossible to achieve common path of insertion.
• 3rd molar tipped with tilted 2nd molar prevents complete
seating of FPD

51.
 ADJUSTMENT FOR TILTED MOLAR:
 If the encroachment is slight, the problem can be remedied by
restoring or recontouring the mesial surface of the third molar
with an overtapered preparation on the second molar.
 If the tilting is severe, other corrective measure will have to be
followed. The treatment of choice is uprighting of the molar by
orthodontic treatment.
 A proximal half crown can be used as a retainer on the distal
abutment.

52.
• CANINE REPLACEMENT FIXED PARTIAL DENTURE
 This is a problem because often the canine lies outside the
interabutment axis. The abutments are the lateral incisor, usually
the weakest in the entire arch and the first premolar, the weakest
posterior tooth. A FPD replacing maxillary canine is subjected to
more stress than that replacing a mandibular canine since forces
are transmitted outward on the maxillary arch.
 So the support from secondary abutments will have to be
considered.
 Edentulous spaces created by the loss of canine and any
contiguous teeth is best restored with Implants.

53.
• ABUTMENT SELECTION FOR CANTILEVER FPD
 Cantilever FPD is one that has an abutment or abutments at one
end only, with the other end of the pontic remaining unattached.
This is a potentially destructive design with the lever arm created
by the pontic.
 Abutment teeth for cantilever FPDs should be evaluated for
lengthy roots with a favourable configuration, good crown root
ratios and long clinical crowns.
 Generally, cantilever FPDs should replace only one tooth and have
at least 2 abutments.

54.
QUESTIONABLE ABUTMENTS
• CLASSIFICATION
• General Disorder:
Mineralization
 Amelogenesis Imperfecta.
 Dentinogenesis Imperfecta.
 Hypocalcification.
 Ectodermal Dysplasia.
 Discolouration due to drugs like Tetracycline.
 Flouridosis.
 Internal resorption .

55.
• Congenital & growth deformities:
• Malformed dentition.
• Malposed teeth.
• Skeletal disparities of Maxillo-mandibular relationships.
• Oligodontia.

56.
• Local problems:
• Polycarious tooth.
• Periodontally involved teeth.
• Occlusal plane correction.
• Endodontically treated teeth:
• Previously treated teeth.
• Currently treated teeth.
• Tilted teeth.
• Wasting Diseases

57.
• TREATMENT STRATEGY:
 Abutment with generalized mineral disturbance:
• Full coverage restoration.
• Success depends on supporting tissue response.
 Congenital and growth deformities:
1st line of treatment:
• Orthodontics.
• Interceptive periodontics.
• Restorative dentistry.

58.
 Malposed teeth:
• Judicious tooth reduction.
• Orthodontics for minor tooth movement: Requires periodic occlusal
adjustments.
• Telescopic crowns
 Occlusal plane correction: Supra-erupted teeth
• Intentional RCT.
• Reduction to satisfactory occlusal plane.
• Tooth preparation to receive retainer.
• Construction of opposing prosthesis.

59.
 Polycarious tooth: No contraindication.
• DMF >3
• Clinical approach to uncontrolled caries:
• Caries control program.
• Endodontic and periodontic consultation.
• Cast metal restoration where indicated after amalgum restoration.
• Recall visits strictly maintained.

60.
Periodontally involved teeth:
• Review the reason for the condition.
• Periodontal treatment before caries control.
• Loss of periodontal support: Splinting may compensate.
Mobility:
• Due to Primary TFO: Occlusal correction.
• Due to Secondary TFO: Splinting.
Furcation involvement: ( Class III)
• Open and closed root debridment.
• Filling the furca with polymeric ZOE cement or GTR.
• Root amputation and hemisection.

61.
SUMMARY AND CONCLUSION
In the above discussion various guides have been
suggested for selection and construction of fixed
partial dentures that should withstand the forces of
oral function with maximum service. Abutments bear
the stresses of mastication and the choice of abutment
influences the prognosis of treatment.
In a concluding note the importance of selecting a
suitable abutment for a fixed partial denture cannot be
overemphasized. It forms the preliminary treatment
planning for fixed partial dentures whose proper
selection and preparation aids in long term durability
of the restoration.

62.
REFERENCES
Shillingburg. Fundamentals of Fixed prosthodontics. 3rd ed.
Tylman’s Theory and practice of fixed prosthodontics. 8th ed.
Rosenstiel, Land, Fujimoto. Contemporary Fixed prosthodontics.
3rd ed.
Jhonston’s modern practice in fixed prosthodontics. 4th ed.
Colin R. Cowell. Inlays, crown and bridges. A clinical handbook.
4th ed.
Glossary of Prosthodontic Terms. JPD 2005;94.
Crown root ratio : Its significance in restorative dentistry. JPD
1979;42.
The prosthodontic concept of crown-to-root ratio: A review of the
literature. JPD 2005;93.

63.
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