Prosthodontics

Planning fixed partial dentures for severely misaligned abutments

Gabriel R. Zuckerman*

Abstract fVhen the abtttment teeth of a fixed partial denture are severely mlmligned.
insertion ofthe pmsthesis becotnes tnore difficult. Some ofthe tnethods
traditionally recomtnended to overcome the probletns associated with this situation
are examitied. Otie design that simplifies treatment and improves the prosthesis is
suggested. (Quintessence hit 1996:27:527-532.)

Clinical relevance commit the time and funds necessary for this extended
and extensive treatment, requiring the coordinated
A segmented fixed partial denture design with an services of an orthodontist and a restorative dentist.
extracoronal interlocking attachment made from
prefabricated plastic patterns is tnore esthetic and A Itered path of insertion
requires less tooth reduction than do traditional It is possible to prepare the molar abutment with a path
designs recommended for ftxed partial dentures on of insertion that is compatible with the premolar prep-
severely misaligned abutments. aration, but this approach has several disadvantages.
The retention and resistance of the molar prepared
under these conditions are severely compromised,-"'*
and the risk of creating a mechanical exposure ofthe
Introduction mesial pulp horn ofthe molar is increased. Further-
more, the mesial marginai ridge ofthe third molar, if
Placement of a fixed partial denture (FFD) can be present, would interfere with insertion ofthe prosthe-
complicated by misaligned abutment teeth. Ideaily, the sis (Fig 2).
long axes ofthe abutment teeth of an FPD shouid be
parallel to one another. When the abutment teeth are
severely misaligned, the design for the proposed Mesial half-crown retainer
prosthesis must be modified. Careful platining prior to Rosenstiel et a!^ and Shillingburg et ai- have recom-
treatment is necessary if the prosthetic result is to be mended the use ofthe mesial half crown as a retainer
predictable and successful. Misalignment is most for tilted molars (Fig 3). A mesial half-crown retainer
frequently encountered when a mandibular first molar has several disadvantages:
is to be replaced after the second and third molars have 1. The mesial half crown cannot be used if the molar
drifted and tilted mesially and lingually (Fig I ). has previously been restored on the distal surface.
2. Preparation ofthe molar could resuit in exposure of
Traditional procedures the mesial pulp horn.
3. The patient may object to the use of a cast-metal
Orthodontics
restoration.
Use of orthodontic treatment to upright the mesially 4. Caries occurring on the unrestorcd distai surface of
tipped molar has been suggested.'- Aithough this the second molar abutment after insertion ofthe
approach is ideal, patients are often reluctant to prosthesis jeopardizes the restoration.
Shillingburg et al- have suggested use of a complete
* Private Practice, East Nonhpon, New York. coping with retentive grooves and a teiescopic mesial
Reprint requests: Dr Gabriel R. Zuekerman, 1199 Fifth Avenue, East halfcrown for the molar retainer {Fig 4). A retainer of
Northporl, New York 11731. this design requires more tooth reduction and could

Quintessence International Volume 27, Number 8/t996 527

Fig 1 The missing mandibular first molar has allowed Fig 2 Three-unit FPD with rigid connectors. The prosttie-
second and third molars to tilt mesially. Note the severe sis will not seat because the distal margin of the molar
misalignment between the long axes of the second pre- retainer engages the mesial marginal ridge of the third
molar (A) and the second molar (B), molar during insertion. Note the proximityof the mesial pulp
horn to the mesial axial wall of the molar preparation.

Fig 3 Three-unit FPD with rigid connectors. The second

molar abutment has been prepared for a mesial half-crown
retainer with facial and lingual grooves for added retention.
Note the proximity of the mesial pulp horn to the mesial axial
wall of the molar preparation.

Fig 4 fr/ghíí Three-unit FPD with full coping and telescopic

mesial half crown on the molar abutment.

result in pulpal exposure or an overcontoured retainer. advocated. The literature contains a variety of seg-
Preparation of the tooth for the complete-coverage mented prosthetic designs recommended to overcome
coping would be excessively tapered. Even if retention the problems associated with insertion of an FPD
between the mesial half crown and the coping were when the abutments are divergent,
ideal, retention ofthe coping to the abutment tooth Shillingburg et a|- have suggested the use of a
might fail because of the excessively tapered tooth segmented FPD with a nonrigid attachment between
preparation,^-^ the second premolar retainer and pontic. This design
requires tooth preparation ofthe premolar with a box
Segmented FPD on the distal surface to accommodate the female
The use of a segmented FPD, in which each section of component of a nonrigid connector (Fig 5), Tooth
the prosthesis has its own path of insertion and there is preparation of the premolar to accomrnodate this
a mechanical interlock between segments, has been connector could jeopardize the pulp and the retentive

528 Quintessence International Volume 27, Number 8/1996

Fig 5 Segmented FPD witb nonrigid connector between Fig 6 Segmented FPD with an interlock between the
premolar and pontic. Excessive tooth reduction ¡s required second molar retainer and the ponfic. Excessive tooth
to accommodate the female section of the interlock on the reduction is required on the mesial surface of fhe second
distal surface of the premolar retainer. molar abutment to accommodate the female portion of fhe
interlock.

properties ofthe preparation. The ocelusal surface of

the nonrigid attachment is visible on the occlusal
surface ofthe anterior retainer and can be cosmetically
objectionable to the patient. It is also possible to
design the prosthesis so that the female component of
the nonrigid connector is on the mesial surface ofthe
molar retainer (Fig 6)- However, the preparation of
the molar abutment to accommodate this configura-
tion increases the risk of pulpal exposure and com-
promises the retention ofthe molar preparation,
O'Connor et a!^ have proposed a segmented FPD
with a split pontic containing a nonrigid connector
The nonrigid connector is oriented parallel to the path
of insertion ofthe molar retainer. The gingival half of
the pontic is connected to the distal surface of the Fig 7 Segmented FPD with a split pontic containing a
premolar retainer and contains the male component of nonrigid connector.
the nonrigid cormector. The occlusal half of the pontic
is attached to the molar retainer and houses the female
component ofthe nonrigid connector (Fig 7). This
complex design is time consuming to produce and,
when completed, results in an unesthetic display of
metal at the base of the pontic.
Moulding et al^ have advocated the use of a
segmented FPD with a nonrigid cormector between
Alternative procedure
the premolar retainer and the pontic. The male
component ofthe connector is inverted and placed on A segmented FPD with a nonrigid connector between
the distal surface ofthe premolar retainer, parallel to the pontic and the molar retainer can be designed
the path of Insertion ofthe molar retainer (Fig 8), without the disadvantages of the previously described
When the nonrigid connector is positioned in this prostheses. The male portion of tbe nonrigid connec-
location, there is an unsightly display of the metal tor can be placed on the mesial surface of the molar
guiding planes of the connector, and a large gingival retainer and oriented parallel to the path of insertion of
embrasure is created below the connector the premolar retainer (Fig 9 ), The female section ofthe

Quintessence International Volume 27, Number 8/1996 529

Fig 8 Segmented FPD with a nonrigid connector. The Fig 9 Segmented FPD with the maie portion of tiie
premolar has the maie portion of the inleriock on its distal interiook on the mesial surface of the second molar retainer
surface. Note the iarge gingival embrasure between the The tooth preparation of the second molar is retentive hut
premolar and the pontic. without r^sii oi pulpal exposure.

Fig 10 (left) Design and dimensions of PDC components.

Fig 11 (below) ivtale portion of the PDC on tfie mesiai axiai

wail of the moiar retainer. (1) Guiding piane; (2| crest of
ridge; (3] gingival end of male PDC contoured to ridge.

Size 1mm) A B C D E F

Smail 70 2.8 2.0 6.7 2.4 23

i_arge ao 3.5 2.5 7.0 3.0 33

nonrigid connector is located under the pontic in the Dovetail Connector (PDC} attachments (Fig 10). The
anterior segment ofthe prosthesis. PDC attachments are designed so that the mating
This design is ideal for metal-ceramic restorations. surfaces of male and female components restrict the
Both abutments are prepared for metal-ceramic com- movements of the two segments of the FPD to ore
plete yeneer crowns with a path of insertion parallel to plane. If the vertical height for the connector is limited,
their long axes. This allows the dentist to prepare the the PDC components may be reduced in height about
teeth with maximum retention and minimal risk of 40% and still remain effective.
pulpa! exposure.
The male and female components of this nonrigid Disadvantages
connector are manufactured in two sizes and are listed Use of this design for FPDs with long spans should be
in the catalogs of denial supply dealers as Plastic ayoided, particularly when the connector has beeti

530 Quintessence internationai Voiurne 27, Number 8/1996

 Zuckerman

Fig 12 Molar preparation with palh ot insertion along ¡ts Fig 13 Molar retainer with male porlion of the PDC on Ihe
long axis. mesial surface. The nonrJgid conneotor is aligned parallel to
Ihe path ol insertion of the premolar preparation.

Fig 14 Anterior section ot FPD placed over the PDC and Fig 15 Completed prosthesis atter insertiorî.
on the premolar abutment.

reduced in height. Slight movement of the abutment to 4. The guiding plane of the connector is located in the
which the pontics are rigidly connected can produce contact area between the molar retainer and the
excessive muvement between the components of the pontic. The gingiva! end of the connector is
nonrigid connector. contoured to establish even contact with the crest of
Another disadvantage of this design is that the the ridge (Fig 11).
iaboratory costs for a segmented FPD are higher than 5. The female pattern of the PDC is piaced over the
the cost of a rigidly assembled FPD. Furthermore, male pattern. A wax pattern for the pontic is made
most laboratory technicians are unfamiliar with this over ihc female pattern. The gingival facing end of
unusuai application ofa nonrigid connector and will the assembled connector should present a smooth, un-
have to he instructed accordingly. interrupted continuation of the ridge lap surface of
the pontic when the prosthesis has been completed.
Technical procedure 6. The patterns of the pontic and the premolar
retainer are connected and cast as one piece.
1. The dies and casts are fabricated and articulated as
for any FPD. 7. The sections of the FPD framework are assembled
and the gingival embrasure between the moiar and
2. Wax patterns are made for both retainers.
pontic is contoured with an abrasive separating disk.
3. The male pattern of the PDC is recessed into the
mesial surface of the pattern for the molar retainer. Figures 12 to Í5 illustrate the clinical application of
The male attachment is positioned parallel to the the PDC, which is completely concealed within the
path of insertion of the premolar retainer. FPD,

Quintessence International Volume 27, Number 8/1996 531

Zuckerman

Summary
Segmented FPDs are a well-established method re-
commended to overcotne the problems associated with Aesthetic Design
the insertion of FPDs when the abutments are severely for Ceramic Restoratioiis
misaligned. Traditional designs used to create seg-
mented FPDs were examined, and their disadvantages
were discussed.
A new design was suggested that does not have most
T he most
natrural,
esthetic results
ofthe disadvantages associated with segmented pros-
theses. Manufactured plastic patterns that can be used in dental
to create this segmented FPD design are available. ceramics can
These economical, prefabricated, burnout patterns be achieved
simplify laboratory fabrication and produce uniform, with contem-
consistent, and reliable nonrigid connectors. The
extracoronal application of an interiocking attachment porary' techniques—and this hook descrihes
for segmented FPDs provides a practical solution to a how. Investigated are the characteristics of
difficult probiem. natural dentition, tissue tnanagement, impres-
sions, occlusal records, waxing techniques,
References color, and lahorator)' techniques, including
1. Lubow RM, Cootey RL, Kaiser D. Periodontat and restorative
methods for an aesthetic ceramic margin,
aspects of molar uprighting. J Prosthet Dent I982;47:37.1. opalescence, and development ofthe dentine
2 Shillingburg HT, Hobo S. Whitsett LD. Fundamentals of Fixed mamelon. Filled with practical tips, this hook
Prosthudonties, ed 2. Chicago: Quintessence, i9Bi.
1 Zuckerman GR. Faetors that influence the meciianicai retention oí is ideal for dentists and technicians.
the complete erown. Int J Proslhodont 19SB;i; Í36-20O.
4. Zuckerman GR. Resistance form for the complète veneer crown:
Principles ofdesign and anaiiïis. Int JProsthodont t9äS;l:302-:!07. 159 pages; 292 color illus; ISBN 1 -85097-034-3
5. Rosenstiel SF. Land ME Fujimoto J Contemporary Fked Prostho-
dontics. ed I. St Louis: Mosby. 19S8
6. O'Connor RP. Caughman WF. Bemis C. Use of the split pontic
nonrigid connector with the tilted molar abutment. J Prosthet Dent Contents
1986;56:249-2;i.
7. Moulding MB, Holiand GA. Sulik WD. An alternative orientation of 1 Studies of Natural Dentition
nondgid connectors in fixed partial dentures. J Prosthet Dent
8. D 2 Dentist-Technician-Paticnt Communication
3 Tissue Management for Aesdietic
and Biological Harmony
4 Impressions artti Occlusai Records
5 Aesthetic Wax Diagnostic Control
6 Accurate Registration and Communication
of Colour Characteristics
7 Advanced Laboratory Techniques
8 Case Studies

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