Abutment evaluation /Fixed orthodontics teaching

INDIAN DENTAL ACADEMY
Leader in continuing dental education
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contents
Need for evaluatioN
factors to be coNsidered
while abutmeNt evaluatioN
 selectioN of abutmeNt teeth
 coNclusioN
 refereNces

Need for evaluatioN
 Abutment--It is any tooth, root or implant
which gives attachment and support to the
fixed partial denture.
 Abutment teeth are important to withstand
the forces normally directed to missing teeth
and those usually applied to itself.

aN importaNt step iN
treatmeNt plaNNiNg
 Identification of patient needs
 Deciding what type of prosthesis
 Decision to remove any teeth or not
 Treatment of symptoms
 Stabilization of deteriorating conditions such
as dental caries, any periodontal disease
 Definitive therapy and occlusal adjustment
 Fixed prosthodontics---ABUTMENT
EVALUATION
 Follow up www.indiandentalacademy.com

factors to be coNsidered
while abutmeNt
evaluatioN

crowN-root ratio
 It is a measure of the length of tooth occlusal to
the alveolar crest of bone compared with the
length of root embedded in the bone.
 Optimum crown-root ratio for tooth to be used
as an abutment is 2:3
 Ratio of 1:1 is the minimum ratio acceptable .
 Cases where ratio greater than 1:1 is possible- -if
opposite dentition is made up of artificial teeth

 -if opposing dentition is composed of
periodontally mobile teeth instead of sound
teeth…

Root configuration

PDL AreA
 Larger teeth have greater surface area and
are better able to bear added stress,
 When supporting bone has been lost because
of periodontal disease, the involved teeth
have a lessened capacity to serve as
abutments
 TYLMAN- two abutment teeth could support
two pontics

 The root surface area of abutment teeth had to
equal or surpass that of teeth being replaced with
pontics --by Ante in 1926
 According to this law, one missing tooth can be
successfully replaced if the abutment teeth are
healthy
 Example – patient has lost first molar and second
premolar
- Four unit FPD is an acceptable risk as long as there
is no bone loss from periodontal disease
ANTe’S LAW

Ante’s law

 Because second molar and first premolar
abutments have root surface areas
approximately equal to those of missing teeth
 If first molar and both premolars are missing
,then FPD is not considered a good risk because
the missing teeth have a greater total root
surface area than the potential abutments
LIMITATION:
Teeth with considerably reduced bone support
can be successfully used as fixed partial denture
abutments if oral hygiene is maintained

SeLecTION Of AbuTMeNT
TeeTh
 Replacement of single missing tooth
 Replacement of several missing tooth
 Replacement of special situations-
 Pier abutment
 Cantilever FPD
 Canine FPD
 Mesially tilted molar

rePLAceMeNT Of SINgLe MISSINg
TOOTh
1. Cantilever FPD
Example- lateral incisor pontic attached only to
an extra coronal metal ceramic retainer on
canine
2. Long term prognosis of single abutment
cantilever is poor as it induces lateral forces on
supporting tissues leading to tipping , rotation
or drifting of the abutment
- It can be resisted by multiple abutments teeth
or using implant supported prostheses

ASSeSSMeNT Of
AbuTMeNT TeeTh

eNDODONTIcALy TreATeD
AbuTMeNTS
 Used along with post and core foundations
for retention and strength.
 It can fail by 2 reasons:
1. If roots are short or
2. coronal tooth structure is less

Unrestored AbUtments
 Unrestored abutment better than – prepared
tooth
 In case of prepared tooth prepare
conservatively with optimum esthetics
 In adult patients unrestored tooth can be
safely prepared without jeopardizing the pulp
as long as the design and technique of tooth
preparation are wisely chosen

mesiAlly tilted second
molAr
TREATMENT :
1.UPRIGHT orthodontically
2.Space maintainer at the time of extraction
3.If cannot be corrected, it has been seen that
less than 25 degree inclination can be
accommodated
4.Designing with non rigid connector
if parallel path of insertion is not obtained

replAcement of
severAl missing teeth

overloAding of AbUtment
teeth
 Forces due to parafunctional grinding and
clenching should be eliminated for a perfect
abutment.
 Well formed ridge/Moderately resorbed ridge
with favorable loading with respect to
magnitude, direction.

direction of forces
 Ideally a well fabricated FPD can distribute
forces directing them in the long axis of
abutment teeth
 Potentially damaging lateral forces can be
confined to the anterior teeth Where they are
reduced by long lever arm?????

root shApe And
AngUlAtion And root
sUrfAce AreA
1. Divergent root > conical roots
2. Single root with elliptical cross section > circular cross
section
3. Well aligned tooth > tilted tooth
Root surface area—ante’s law

periodontAl diseAse
 Horizontal bone loss from periodontal disease
LEADS to loss of PDL supported root surface area
o Example- because of conical shape of most roots,
when one third of the root length has been exposed,
half the supporting area is lost
 Center of rotation moves apically
 Lever arm increases – increased magnifying forces
on supporting structure
 Because of greater leverage associated with
lengthened clinical crown

Span length
 Excessive flexing under occlusal loads can
cause failure of a long span leading to
1. Fracture of porcelain veneer
2. Breakage of retainer or a connector
3. Unfavorable soft tissue response
 LONGER THE SPAN ,GREATER THE
FLEXING
 Deflection varies directly with cube of length
of pontic and inversely with the cube of
occluso gingival thickness of pontic

Span length

Replacing Multiple
anteRioR teeth
 Problems with appearance and need to resist
laterally directed tipping forces
 In case of mandible, if a lone incisor remains, it
should be extracted and only canine can be used as
abutment
 IN case of maxilla, both canine and premolar are
used as abutments as because of the curvature of
the arch, forces directed against a maxillary pontic
will tend to tip the abutment teeth
 In case of anterior bone loss, FPD cannot be used
as it does not support missing tissues

concluSion
 An abutment tooth is always evaluated so
that it can bear forces of both missing teeth
and those on itself.
 Whenever possible ,an abutment should be
a non mobile, vital tooth, if not then it
should be endodontically treated and should
possess good amount of coronal structure for
retainer and surrounding tissues should be
healthy .

RefeRenceS
 Fundamentals of FPD by Herbert .shilinburg
page(85-101)
 Contemporary fixed prosthodontics by
Stephen.rosenstiel page(82-102)

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Abutment evaluation /Fixed orthodontics teaching

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