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The International Journal of Periodontics & Restorative Dentistry

© 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY..
NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

375

Implant Positioning when
Replacing the Four Maxillary Incisors:
A Platform-Switched Treatment Option

Xavier Vela-Nebot, MD, DDS*/Víctor Méndez-Blanco, DDS*
Xavier Rodríguez-Ciurana, MD, PhD*/Maribel Segalá-Torres, MD, DDS*
Jaime A. Gil-Lozano, MD, DDS, PhD**

Patients do not view dental implants as an object of desire but seek a way
to replace teeth that will be as cost-effective and minimally traumatic as
possible. Nowadays, anterior fixed partial dentures can provide an esthetic
result that is difficult to distinguish from the natural dentition. Consequently,
any implant-supported prosthesis will be compared to the esthetic and
functional standards set by conventional tooth-supported restorations. The
restoration of the four maxillary incisors by means of an implant-supported
prosthesis is one of the most challenging situations in implant dentistry. The
questions of how many implants should be placed and where they should
be positioned are especially important for achieving a superior end result.
This article proposes and describes the placement of two platform-switched
implants in the central incisor positions as a means of achieving the correct
biomechanical behavior of the prosthesis, along with the best possible
esthetic results. (Int J Periodontics Restorative Dent 2011;31:375–381.)

*Private Practice, Barcelona, Spain.
** Chair, Prosthodontic Department, University of the Basque Country, Bilbao, Spain.
Correspondence to: Dr Xavier Vela-Nebot, Calle Sant Marti, 43 (Clinica Vela), 08470
Sant Celoni, Barcelona, Spain; email: headquarters@borgroup.net.

Osseointegrated dental implants
have demonstrated their reliability
and versatility in solving all types
of esthetic and functional problems
for many years. Implant-supported
restorations are considered a good
treatment option for partially edentulous patients and are well documented with prospective long-term
studies.1–4 However, restoration of
the four maxillary incisors by means
of implant-supported prostheses
can be extremely challenging, both
esthetically and biomechanically.5
After teeth are extracted from
the esthetic zone, significant volume may be lost from the alveolar
ridge. By 3 to 12 months postextraction, horizontal bone resorption may affect between 30% to
50% of the original ridge.6 Defects
associated with the inflammatory
processes, trauma, or multiple extractions may further increase bone
resorption (Fig 1).7
To avoid this, measures to minimize bone resorption should be
applied carefully throughout the
different treatment phases. Any tissue defects that occur should be
corrected by means of hard and soft

Volume 31, Number 4, 2011

© 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY..
NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

376

a

b

Fig 1    Anterior maxillary arch. Bone resorption reduces the convexity of the arch.

Fig 2    Lateral incisor position. (a) Two standard-diameter implants placed at the lateral incisor
positions. Note the occupation of the interproximal spaces by the implants. (b) Because of this
occupation, the defect had to be hidden using pink porcelain.

tissue grafts, always keeping in mind
the importance of preserving or recovering the initial pre-extraction
tissue volume.8,9
Despite the use of such techniques, the magnitude of bone loss
after extraction of the four maxillary incisors may cause the anterior
maxillary arch to lose its convexity
and become straight. When this
occurs, it may be difficult to place
prosthetically guided implants,
which should be the objective to
guarantee an esthetic end result.10
With these constraints in mind,
two questions are of paramount
importance when replacing the
four maxillary incisors: How many
implants should be placed, and
where should they be positioned?11

The anatomy of the edentulous
crest after extraction makes the
placement of four implants (one per
tooth site) problematic. Normally,
insufficient space exists between
the two canines to maintain the ideal interimplant and implant-tooth
distances.12,13 Placement of the implants closer than those distances
threatens both the hard and soft
tissues with subsequent esthetic
compromise.
The most common option is to
place two standard implants at the
lateral incisor sites and restore them
with a four-unit fixed partial denture, with two pontics replacing the
central incisors (Fig 2a). However,
when extraction of the incisors has
caused the radius of the anterior

maxillary arch to shift palatally and
become smaller, it is often impossible to place implants in the lateral
incisor positions while still respecting the need to maintain at least
2 mm of the buccal plate and remain at least 1.5 mm from the adjoining canine.13,14 All of this means
that placement is usually forced into
the interproximal area. In addition,
as the prosthetic abutments of the
fixed partial denture, the lateral incisors usually require volume augmentation. The final outcome of this is
the occupation of the interproximal
spaces by the prostheses, making it
impossible for the soft tissues to create a new papilla, with consequent
esthetic compromise (Fig 2b).11

The International Journal of Periodontics & Restorative Dentistry

© 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY..
NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

377

Fig 3 (left)    Two narrow-diameter implants
placed at the lateral incisor positions. No
occupation of the interproximal spaces by
the implants can be seen.
Fig 4 (right)    Two standard implants placed
at the central incisor positions. Again,
there is no occupation of the interproximal
spaces by the implants.

Fig 5 (left)    Platform-switching concept:
discrepancy between the diameter of the
implant platform and that of the prosthetic
abutment.

Abutment
0.65 mm 0.65 mm

Abutment
Fig 6 (right)    Interimplant bone peak
preservation when using platform-switched
implants.

Abutment

Implant

Implant

0.35 mm
Interface

Implant

To avoid this problem, Vailati
and Belser11 suggested placing two
narrow-diameter implants instead
of standard-diameter ones in the
lateral incisor positions. Because
the implants occupy less space,
the minimal implant-tooth distance
can be respected without compromising the interproximal area.
Furthermore, reducing the implant
diameter also implies a volume
reduction of the prosthetic abutments, yielding better esthetic results. This option has become the
gold standard at many prestigious
universities (Fig 3).11
The placement of two standard
implants in the central incisor positions followed by restoration with a
four-unit fixed partial denture with

two cantilever elements replacing
the lateral incisors is another approach that allows for placement of
the implants in the same position
as that of the original teeth. There
is usually better bone availability
at the central incisor position than
the lateral incisor position. The interproximal spaces can be avoided
even if alveolar ridge resorption has
occurred after tooth extraction and
no augmentation has been carried
out (Fig 4).
Implants placed in the central
incisor positions must be separated
by at least 3 mm to ensure preservation of the interimplant bone peak
that supports the soft tissue.12 Loss
of the bone peak may lead to loss
of the interimplant papilla and the

appearance of a black interdental
triangle between the central incisors
or the need for a long contact area.

A platform-switched
treatment option
The platform-switching concept was
developed in response to the major
peri-implant bone loss that has historically occurred when two-piece
implants are exposed to the oral
environment.15,16 Platform switching consists of creating a discrepancy between the diameter of the
implant platform and that of the
prosthetic abutment (Fig 5). This is
achieved, for example, by using implants with a 4.8-mm platform and

Volume 31, Number 4, 2011

© 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY..
NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

378

Fig 7    (a, c, and e) Radiographs of patients
using platform-switched implants placed at
the central incisor sites. Note the interimplant
bone peak. (b, d, and f) Final clinical aspect
with good esthetic outcomes.

a

b

c

d

e

f

a 4.1-mm abutment, which creates
a horizontal discrepancy of 0.35 mm
between the implant and abutment.
Today, the platform-switching concept can be applied to many implant
diameters and designs, adapting
the implant to the available bone.
Four-millimeter-diameter implants
and 3.2-mm abutments can be used
in narrow bone ridges, and 6-mm
implant platforms with 5-mm abutments can be used in wide ridges.
This concept can be applied with
expanded platform, cylindric, or tapered implants.

An average bone loss of 0.65
mm in both axes has been reported when using platform-switched
implants.17–19 Combining the bone
lost next to each of the two implants placed 3 mm apart allows
for maintenance of an interimplant
bone peak that will support the soft
tissues (Fig 6).18
The solution preferred by the
authors is to place two platformswitched implants in the central
incisor positions and support the
two lateral incisors with distal cantilever extensions (Fig 7). When two

standard implants are placed in the
central incisor positions, occupation of the interproximal spaces can
be avoided, even when alveolar
ridge resorption has occurred and
has not been corrected with tissue
augmentation. However, the use
of platform-switched implants also
allows for interimplant bone peak
preservation, even when less than
3 mm separates the two centrally
placed implants.18 The interimplant
papillae can thus be preserved.

The International Journal of Periodontics & Restorative Dentistry

© 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY..
NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

379

Discussion
Following extraction of the four
maxillary incisors, the associated
bone resorption can transform the
normally convex alveolar ridge into
a straight line between the canines.
This process seems to be independent of whether the implants are
placed immediately or delayed.20
Regardless of when the implants
are placed, the number used and
the positions where they are placed
will have important esthetic and
biomechanical consequences for
the restoration. If no additional
treatment is undertaken to reestablish the original ridge shape, the
four prosthetic teeth will be smaller
than initially and they will be in a
more palatal position than in the
natural dentition.
When implants are placed in
the lateral incisor positions in accordance with the buccolingual
and mesiodistal guidelines to foster an optimal restorative outcome,
they will intrude upon the interproximal spaces between the lateral and central incisors. Moreover, in
this situation, the laboratory technician will be forced to make the two
central incisors narrower than normal and the lateral incisors wider
than normal. Finally, the prosthesis
occupies the space and impedes
the formation of a natural papilla,
compromising the overall esthetic
outcome and making it necessary
to restore the soft tissues prosthetically (see Fig 2b).
When Vailati and Belser11 analyzed different options, they concluded that the most predictable solution

with the lowest esthetic risk was to
use two narrow-diameter implants
in the lateral incisor positions. By doing so, the occupation of the lateral
incisor–canine and lateral incisor–
central incisor interproximal spaces
can be avoided. Additionally, leaving the lateral incisor–central incisor
space free allows for it to be molded
with provisional restorations that can
create a satisfactory gingival architecture.
Narrow-diameter implants have
a survival rate similar to that of standard implants, but the similarities do
not extend to biomechanical behavior.21,22 When two narrow-diameter
implants are used to support a
freestanding fixed prosthesis with
three or more units, the result is an
overall increase in the stresses and
strains imposed on the surrounding
tissue.23
Mastication mainly induces vertical forces in the dentition. However, transverse forces are also
created by horizontal motion of the
mandible and the inclination of the
tooth cusps. As this occurs, a given
occlusal force may impose both
axial forces and bending moments
(the product of the force times the
length of the lever arm) on the implant.24 The axial force distributes
stress more evenly throughout the
implant, while the bending moment creates stress gradients in
the implant as well as in the bone.
To limit these loads, proper implant
positioning is of paramount importance.24 Use of a surgical template
can help to ensure proper implant
positioning. Such a template provides the surgeon with an accurate

Volume 31, Number 4, 2011

© 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY..
NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

380

D
F

Fig 8a    A long lever arm can be generated
due to the distance (D) between the force
applied to the central incisor crowns (F) and
the implants placed in the lateral incisor positions. These forces may cause screw loosening, bone resorption, and implant fracture.
Fig 8b    A short lever arm can be generated
due to the distance (D) between the force
applied to the central incisor crowns (F) and
the implants placed in the central incisor
positions because the implants are placed
closer to the site where the loads are being
applied than in the lateral position.

a

view of the ideal implant sites, as
well as the desired path of abutment
emergence and corresponding axis
in relation to the definitive prosthesis.25 When implant placement is
prosthetically guided by a template,
axial forces will predominate, and
nonaxial forces will depend on the
inclination of the tooth cusps.25
Moreover, when protrusive
movements are made, disocclusion
is supported by the central incisors,
which generate bending forces
that cause overload on the lateral
implants because of the contour
of the prosthesis. The intensity of
these bending forces is proportional to the length of the lever arm, ie,
the distance between the proximal
side of the implant abutment interface (the fulcrum) and the point
where the force is applied on the
central incisors (Fig 8a). These
forces may cause screw loosening,
bone resorption, and, worst of all,
implant fracture.23

In response to these concerns,
the authors propose placing two
platform-switched implants in the
central incisor positions. This space
may be sufficient to accommodate
the use of two wide- or standarddiameter implants because bone
volume at the central incisor sites is
usually greater than at the lateral incisor sites. To guarantee the correct
position of the implants, the use of a
surgical template is mandatory.25
When two implants are placed
in the central incisor positions, they
are placed where the loads are being applied, and the result is a reduced lever arm (Fig 8b). Moreover,
lateral movements are buttressed by
the canines, and the lateral incisors
in distal cantilever extensions are out
of occlusion. The platform-switching
concept allows for interimplant bone
peak preservation, even in cases
with less than 3 mm between implants.18 Preservation of the bone
peak is necessary to support an

D

F
b

esthetic central papilla.12 Nevertheless, Tarnow et al26 established that
2 to 4 mm (3.4 mm on average) of
soft tissue height can be expected
to cover the interimplant bone crest.
This is 1 to 2 mm less than what
is needed to duplicate the inter­
proximal papillae of adjacent teeth,
a deficiency that can be overcome
by using longer contact areas between prosthetic teeth.26
The central papilla is the only
one that does not have a symmetric mate. It is thus the only oral site
where a slight reduction in size may
be unnoticed.
One anatomical consideration
may contraindicate positioning the
implants in the central incisor positions: the status of the nasopalatal
canal. If the canal is too wide, it
may occupy the space where implants would have to be placed.5

The International Journal of Periodontics & Restorative Dentistry

© 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY..
NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

381

Conclusions
Restoration of the four maxillary incisors is an esthetic and biomechanical challenge that can be effectively
resolved by placing two platformswitched implants in the central incisor positions and supporting the two
lateral incisors with distal cantilever
extensions. When platform-switched
implants are used in this scenario,
the interimplant bone peak can be
preserved and the central papilla
maintained. The resulting esthetic
outcome will be comparable to
that achieved by placing narrowdiameter implants in the lateral incisor positions, while the biomechanical performance is superior. Implants
placed in the central incisor positions
also may minimize off-axis loading.
Additional studies are needed to
clarify the best treatment options for
complex cases.

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Volume 31, Number 4, 2011

© 2011 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY..
NO PART OF MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.



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