A BRIEF INTRODUCTION REGARDING THE SELECTION OF ABUTMENT TOOTH/TEETH IN FIXED PROSTHODONTICS.ALL THE CONTENTS ARE TAKEN FROM THE BIBLE OF FIXED PROSTHODONTICS,SHILLINGBERG

1. ABUTMENT EVALUATION
Dr. VIGNESH R, BDS

2. CONTENTS
• INTRODUCTION
• SELECTION OF ABUTMENT TEETH
• SUMMARY
• REFERENCES

3. INTRODUCTION
• Every restoration must be able to withstand the constant
occlusal forces to which it is subjected. This is of particular
significance when designing and fabricating a fixed partial
denture, since the forces that would normally be absorbed by
the missing tooth are transmitted, through the pontic,
connectors, and retainers, to the abutment teeth. Abutment
teeth are therefore called upon to with- stand the forces
normally directed to the missing teeth, in addition to those
usually applied to the abutments.

4. SELECTION OF ABUTMENT
TOOTH
• A tooth can be used as an abutment if it is;
1. VITAL
2. ENDODONTICALLY TREATED(and
asymptomatic)

5. Abutment teeth should not be-
1. A teeth that is pulp capped in the
process of preparing tooth should not be
used before they are endodontically
treated.
2. A mobile tooth.

6. • The periodontal tissues should be healthy
and free from inflammation.
• The roots and the supporting structures
should be evaluated for 3 factors;
A. crown-root ratio
B. root configuration
C. periodontal ligament area

7. CROWN-ROOT RATIO
• The optimum crown root
ratio- 2:3
• minimum acceptable
ratio- 1:1

8. ROOT CONFIGURATION
• The roots that are
broader labiolingually
than mesiodistally are
preferable to roots that
are circular in cross
section.
• multirooted posterior
tooth with widely
separated roots will offer
better periodontal
support than roots that
converge,fuse or are
conical.

9. PERIODONTAL LIGAMENT
AREA
• Larger teeth have a greater surface area and are better
able to bear added stress.
• the areas of root surfaces of the various teeth have been
reported by Jepsen and are shown below;

10. ANTE’S LAW
• THE ROOT SURFACE AREA OF THE
ABUTMENT TEETH SHOULD BE EQUAL
TO OR SURPASS THAT OF THE TEETH
BEING REPLACED.

12. BIOMECHANICAL
CONSIDERATIONS
• Longer spans are less rigid.
• bending or deflection varies directly with the
cube of the length and inversely with the
cube of occlusogingival thickness of the
pontic.

13. deflection with span length
deflection with thickness

14. • SPECIAL PROBLEMS;
• Pier abutments;
• Rigid connectors between pontics and retainers are the
preferred way of fabricating most fpd’s.
• an fpd with the pontic rigidly fixed to the retainers
provides desirable strength and stability to the
prosthesis while minimising the stresses associated
with the restoration.
• the most commonly used non-rigid design consists of a
t-shaped key that is attatched to the pontic,and a
dovetail keyway placed within a retainer.

15. nonrigid connector is placed on the
distal side of the retainer
nonrigid connector is placed on the
mesial side of the retainer

16. when a mandibular molar tilts mesially,
there is a discrepancy between the long axis
of the molar and that of a premolar
this fpd will not seat because the tooth
distal to fpd intrudes on the path of
insertion

17. orthodontic appliance for uprighting
a tilted molar
fpd using a proximal half crown as a
retainer on a tilted molar abutment

18. fpd using a telescope crown and
coping as a retainer on a tilted molar
abutment.
a non rigid connector on the distal
aspect of the premolar compensates for th
inclination of the tilted molar

19. CANINE REPLACEMENT FPD
“A fixed partial denture replacing a
maxillary canine is subjected
to more damaging stresses than
that replacing a mandibular canine
because the forces are directed
outward and the pontic lies farther
outside the interabutment axis”
“A fixed partial denture
replacing a mandibular canine
has a more favorable prognosis
than that replacing a maxillary
canine because the forces are
directed inward and the pontic
will be closer to the
interabutment axis.
.

20. CANTILEVER FIXED PARTIAL DENTURE
“ Forces applied to the pontic of a
routine fixed partial denture are
transmitted to both abutment teeth.”
“Forces on the pontic of a cantilever
fixed partial denture tend to tip the
fixed partial denture or the abutment
tooth.”

21. “Cantilever fixed partial denture
replacing a maxillary lateral incisor,
using the canine as the abutment.”
“A cantilever pontic can be used to replace
a first premolar if full veneer retainers are
used on the second premolar and first
molar abutments.”
“Forces on a full-size molar cantilever
pontic place great stress on the mesial
abutment.”
“Cantilever fixed partial denture
replacing a mandibular first molar,
using both premolars as abutment
teeth. To minimize stress on the
abutments, the pontic is the size of a
premolar rather than a molar.”

22. SUMMARY
• Success of a prosthesis depends on many foundational
steps taken to prepare it.Proper handling of the abutment
teeth is one of the most important foundational steps that
either enhances or detracts from the eventual value of the
prosthesis.
• when conditions are proper like crown contour,retention,and
criteria of good preparation techniques and design are
met,sound abutment considerations will be strong link in the
success of the prosthesis.
• selecting a suitable abutment forms the preliminary
treatment planning for FDP,whose proper selection and
preparation aids in long term durability of the restoration.

23. REFERENCES
• Fundamentals of fixed prosthodontics-4th edition - Shillingberg,Jr,