Prosthetic platforms in implant dentistry

1. Prosthetic Platforms in Implant Dentistry
Murillo Sucena Pita, DDS, MSc,* Rodolfo Bruniera Anchieta, DDS, MSc,Þ
Valentim Adelino Ricardo Barão, DDS, MSc,Þ Idelmo Rangel Garcia, Jr, DDS, PhD,þ
Vinicius Pedrazzi, DDS, PhD,* and Wirley Gonçalves Assunção, DDS, PhDÞ
Abstract: The use of implant-supported prosthesis to replace miss-
ing teeth became a predictable treatment. Although high success rate
has been reported, implant treatment is suitable to complications,
failures, and limitations such as peri-implant bone loss after implant
loading. Stress evaluation on the bone-abutment-implant interface
has been carried out to develop new designs of prosthetic platform
and to understand the stress distribution in this interface. Several
types of prosthetic platforms are available such as external and in-
ternal hexagon, Morse cone connection, and the concept of platform
switching. Therefore, this study aimed to critically describe the dif-
ferent options of prosthetic platforms in implant dentistry, by dis-
cussing their biomechanical concepts, clinical use, and advantages
and disadvantages. It was observed that all types of prosthetic plat-
forms provided high success rate of the implant treatment by fol-
lowing a strict criteria of indication and limitation. In conclusion, a
reverse planning of implant treatment is strongly indicated to reduce
implant overload, and the use of advanced surgical-prosthetic tech-
niques is required to obtain a long-term success of oral rehabilitations.
Key Words: Dental implants, prosthetic platforms,
implant-supported dental prosthesis, biomechanics
(J Craniofac Surg 2011;22: 2327Y2331)
The replacement of missing teeth by using implant-supported
prosthesis became an efficient and acceptable treatment option
both for partial and completely edentulous patients. The osseo-
integration concept, defined as a direct structural and functional con-
nection between bone and implant surface, provided an enhancement
of the oral rehabilitation options.1,2
Numerous attempts have been
made to improve the anchor of implants to bone such as modi-
fications on the surface, design, and prosthetic platform of dental
implants.3
Several factors are directly related to the biomechanical be-
havior of implant-prosthesis set such as implant’s location, inclina-
tion and depth on the bone. Those factors are also linked to the
design, length and diameter of implants as well as cusp inclination
and occlusal platform of prosthetic crowns. Therefore, before im-
plant insertion, surgical and prosthetic factors should be considered.
Even if a strict treatment planning has been conducted, failures might
be observed due to overloads and patient’s variations regarding the
peri-implant bone. In addition, the surgical technique and bone me-
tabolism and quality are determinant factors on the long-term success
of implant treatments.4,5
Although high success rate has been reported, implant treat-
ment is suitable to complications, failures, and limitations. Peri-
implant bone loss is expected to occur after implant insertion (0.9 mm
in the first year and 0.1 mm subsequently).6
But when the implant
is loaded, 1.5 to 2 mm of bone loss is observed.7
The local inflam-
matory process due to the gap between implant and prosthetic abut-
ment, the absence of biologic width, and the bone stress concentration
is related to the initial bone loss around the implant. Cyclic and
overloads may induce microcracks on the bone and consequently
bone resorption. The fulcrum is located on the crestal bone, which
alters the bone remodeling.8
Also, the bone anatomy leads to load
concentrations owing to the presence of a rigid cortical bone layer
externally and a porous trabecular bone internally.
Under load, natural teeth also create stress on the cortical
bone; however, the stress is reduced by the periodontal ligament.9
Whether the anchoring difference between implant and natural teeth
could create biologic problems is dependent of the load conditions
(axial and nonaxial loads) and the bone characteristics. Although
axial load is preferable to minimize implant complications, in the
posterior and excursive guide regions, implants are subjected to
oblique loads.10
Because high incidence of prosthetic screw loos-
ening and fracture has been observed, the development of different
implant designs is rational to offer better biomechanical stability of
the implant-prosthesis. Several factors can induce instability of the
screw join such as inadequate preload, screw and prosthesis design,
prosthesis misfit, occlusal overload, and bone elasticity. Clinically,
implant-supported restorations are subjected to loads that create in-
stability of the screw join such as those from centric, eccentric, ex-
cursive, interproximal, and cantilever contacts and misfit structures.11
With the increased applicability of single implant-supported
prosthesis, the implant connections were changed to avoid prosthesis
rotation. This prompted the manufactures to develop different types
of retention screws that could withstand higher torque values by
changing their material type, increasing the accuracy of the hexagon,
and creating new designs of the implant-abutment interface.10
From
the biomechanical point of view, the major difference among the
implant systems is the hexagon type; however, the influence of
implant-prosthesis interface on stress intensity under functional loads
remains unclear. In addition, the time required for functional adap-
tation of the bone to the implants may be more important than the
actual physical nature and geometry of the implants.12
SCIENTIFIC FOUNDATION
The Journal of Craniofacial Surgery & Volume 22, Number 6, November 2011 2327
From the *Department of Dental Materials and Prosthodontics, Ribeirão
Preto Dental School, Universidade de São Paulo; †Departments of Dental
Materials and Prosthodontics; ‡Surgery and Integrated Clinical, Araçatuba
Dental School, Universidade Estadual PaulistaYUNESP, São Paulo, Brazil.
Received January 18, 2011.
Accepted for publication July 24, 2011.
Address correspondence and reprint requests to Wirley Gonçalves Assunção,
DDS, PhD, Department of Dental Materials and Prosthodontics,
Aracatuba Dental SchoolYUNESP, Jose Bonifacio, 1193, Araçatuba,
São Paulo, Brazil 16015-050; E-mail: wirley@foa.unesp.br
The authors report no conflicts of interest.
Copyright * 2011 by Mutaz B. Habal, MD
ISSN: 1049-2275
DOI: 10.1097/SCS.0b013e318232a706
Copyright © 2011 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.

2. Stress evaluation of the bone-abutment-implant interface is
very important to the development of new designs of prosthetic
platforms to distribute the loads in a biologically acceptable level,
preserving the peri-implant crestal bone loss. Biomechanically, the
connections should reduce the stress on the prosthetic components
and on the bone-implant interface and provide adequate prosthetic
stability.13
For this reason, several types of prosthetic platforms are
available on the market (Fig. 1). However, the contradictions found
on the literature and the diversity of implant connection options create
doubts when choosing the most suitable connection.9
Therefore, this study aimed to critically describe the differ-
ent options of prosthetic platforms in implant dentistry, by discuss-
ing their biomechanical concepts, clinical use, and advantages and
disadvantages.
EXTERNAL HEXAGON
The external antirotational configuration under a prosthetic
platform was introduced by Branemark1,2
and became the most
popular implant design (Fig. 2). Initially, the external hexagon was
developed to facilitate the insertion of implants. By that time, full,
fixed implant-supported prosthesis was the only alternative of im-
plant rehabilitation, and the implants did not present the antirota-
tional system.14
The external hexagon system has some advantages because
it is a suitable method for 2-time surgical procedure and has anti-
rotational mechanism, reversibility, and compatibility with different
systems. On the other hand, this system presents micromovements
owing to its reduced hexagon size. In addition, its higher rotation
center promotes less resistance to rotation under lateral movements
and creates a possible gap on the implant-abutment interface, which
might lead to bone resorption. Therefore, this system is contraindi-
cated in situations of overloads.15
Under occlusal overloads that exceed the retention screw
strength limit, stresses are directly dissipated to the abutment-implant
interface. Consequently, the abutment retention screw is deformed,
which creates a space on the interface connection. Three factors are
responsible for abutment screw loosening in single external hexagon
implants: vertical overload, lateral load on the nonworking side,16
and superstructures with misfit.3
The use of gold abutment reten-
tion screw prevents its loosening because galvanized pure gold is
deformed during screw tightening, which increases its frictional re-
sistance.16
The initial preload of gold screws is significantly higher
compared with titanium screws.17 The limitations of external hexa-
gon platform became more evident when its application was ex-
panded to partial edentulous arches; therefore, in those cases, the use
of antirotational internal connections is more suitable.16
INTERNAL HEXAGON
As an evolution of the external hexagon, the internal hexagon
presents some advantages such as lower screw loosening and frac-
ture and higher load absorption. Its design promotes homogeneous
stress distribution around the implants, which reduces the stress on the
crestal bone.10
It may be explained by the taper shape of the hexagon
socket in the prosthesis and the greater depth of the internal hexagon
within the implant, which decrease the lever arm and change the
prosthesis-implant fulcrum to the middle third of the implant (Fig. 3).
This results in a better stress distribution on the bone and promotes
higher stability of the prosthesis retention screw, decreasing the risk
of screw fracture and prosthesis failure.5
Under cyclic loading, in-
ternal hexagon implants presented higher detorque values and lower
screw loosening, possibly due to the better protection of the abut-
ment screw.11
In addition to lower bone resorption on the implant neck,
internal hexagon connections promote better tactile sensation of full
settling of the abutment and improve the efficiency and the strength
of the antirotational system, which help in stress dissipation of ver-
tical loads. Under oblique loads, the lateral wall of the abutment con-
tributes to stress spreading. Furthermore, internal connections are
favorable to be used for single surgical stage and single implants and
in regions of reduced interocclusal space.15,16
However, in nonparallel multi-implantYsupported prosthesis,
the use of internal connections is limited.18
Besides, there is no
conclusive study showing that internal connection is better than
external connection.15,16
EXTERNAL HEXAGON VERSUS
INTERNAL HEXAGON
Several studies have compared the efficacy of different types
of implant-abutment connections. The internal hexagon has higher
stability versus external hexagon, which improves the clinical suc-
cess of the former. During prosthesis settling, a rotation freedom is
necessary. Because the retention screw is responsible to join the
prosthesis to the implant, overloads can promote screw loosening
and fracture in external connections.19
According to a correct treatment planning, it is necessary not
only to meet the functional and aesthetic requirement of the patient,
but also to ensure the stability of the retention screw. Internal con-
nections have better prosthesis retention and consequently higher
stability, which decrease the stress on the cervical region of the
implants and retention screws.19,20
Nevertheless, a previous study
found that the connection type did not have any effect on abutment
screw loosening and fracture under oblique cycled loading. But ti-
tanium screw presents better stability than gold screw.16
On the other hand, some observed better bone stress distribu-
tion for internal hexagon versus external hexagon under oblique load.
However, no significant difference was observed between the con-
nections under axial load.21
Recently, a photoelastic study also
FIGURE 1. Prosthetic connections in dental implantology.
FIGURE 2. External hexagon connection. FIGURE 3. Internal hexagon connection.
Pita et al The Journal of Craniofacial Surgery & Volume 22, Number 6, November 2011
2328 * 2011 Mutaz B. Habal, MD
Copyright © 2011 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.

3. showed similar results. Thus, authors suggested the use of internal
hexagon implants in cases where it is not possible to install external
hexagon implant with a large diameter because of anatomic limita-
tions.5
Contradicting the previous results, another study showed
higher stress around the implant for internal connections when com-
pared with external connections.13
In addition, the external hexagon
promoted lower stress concentration when implants were splinted to
natural teeth. This may be explained by the higher rigidity and sta-
bility of internal connections.20
A prospective clinical and radiographic study of 618 internal
hexagon implants showed minimal bone deterioration after 5 years
of prosthesis insertion. The difference of bone level was 0.09 mm
after 1 year, 0.20 mm after 3 years, and j0.26 after 5 years.22
Another
longitudinal study with 54 external hexagon implants showed a total
of 1.7 mm of peri-implant bone resorption after 10 years.23
Simi-
lar results were found in another study, in which a total of 1.8 and
1.3 mm of bone resorption was observed in the maxilla and the
mandible, respectively.24
Although several mechanical, clinical, microbiologic studies
have compared internal and external connections, the biomechanical
behavior of these connections is still controversial.15
MORSE CONE
Different from other connections, in the Morse cone design,
the abutment is joined to the implant through an internal taper con-
nection without a retention screw (Fig. 4). This connection locks the
system because of the mechanical friction between the external wall
of the abutment and internal wall of the implant, and no rotation
of the abutment is observed.3
Also, the Morse cone system is char-
acterized to eliminate the abutment-implant junction from the sub-
sulcular to the intrasulcular region,25
promoting high reliability
regarding loosening and fracture of prosthetic components26
and high
stability in long-term clinical use.27
In the Morse cone connection, the screw junction is more
resistant than that from the external hexagon, because the junction
in the former is deeper and has internal walls with a convergent
angle from 8 to 11 degrees. The internal wall of the implant supports
the abutment and decreases the stress. As a result, 30% of higher
force is necessary to disassemble the retention screw when compared
with force is necessary to assemble it.19,28
This connection improves
the flexural strength of the abutment when compared with other
conventional internal and external connections.29
Under functional loading, the mechanical instability of the
external connection promotes shaking and micromovements of the
abutment, increasing the abutment failures.3
However, screw loos-
ening of the Morse cone in single prosthesis was observed. Thus, the
use of cemented prosthesis can reduce the technical complications.30
A previous clinical study observed a success rate of 98.7% for 5439
Morse cone implants as a single restoration after 11 years of eval-
uation. For free-end implant restorations, the success rate was 97.9%.
For cases involving reduced dentition, 95.8% of success rate was
observed.31
A comparative study investigated the levels of bone resorp-
tion between Morse cone and external hexagon implants after 5 years
of investigation. The total mean bone level changes in the upper jaw
between fixture insertion and the 5-year examination were j1.74 mm
at the Morse cone implants and j1.98 mm at the external hexagon.
The corresponding values for the lower jaw were j1.06 mm for
Morse cone and j1.38 mm for external hexagon. The survival rate for
Morse cone implants was 98.4%, and for external hexagon implants,
it was 94.6%.32
In a literature review, authors found success rates
from 95.8% to 98.4% for Morse cone implants and from 94.6% to
97.2% for external hexagon. When the implants were immediately
loaded, the success rates were 97.1% and 95% for Morse cone and
external hexagon implants, respectively.33
The Morse cone design also allows higher soft tissue forma-
tion around the abutment neck even under thin soft tissue presence.34
On the other hand, the passive fit in case of multiple restorations is
harder to achieve. In addition, the compatibility with other prosthetic
systems is limited. The surgical insertion is critical, and the implants
should be placed intraosseously with no or low inclination. Thus, the
correct position of the implants is imperative so that the abutments
can be placed axially to the implants. The cost of the system is a
relative disadvantage. The bone resorption around the prosthetic
platform is related not only with the presence of gap in the implant-
abutment interface, but also with the abutment diameter reduction in
relation to the implant, which promotes the formation of soft tissue
in this area and increases the natural defense of the organism.35
PLATFORM SWITCHING
The concept of platform switching was developed to control
the peri-implant bone loss after implant insertion. This system con-
sists in the placement of smaller-diameter prosthetic components on
wider-diameter implants (Fig. 5), which improves the stress distri-
bution and decreases the peri-implant bone loss in the first year of
loading.7,36Y38
The authors stated that the bone preservation in platform
switching is due to the biologic seal against bacterial leakage, where
the surrounding soft tissue protects the crestal bone, which might
promote aesthetic conditions to the interdental papillae.37
In addition
to the biologic width provided by this concept, other factors such as
the design of the implant in the cervical region, the surface rough-
ness, the implant depth, and abutment design are involved in pre-
serving the crestal bone.39
The ability of platform switching to reduce the crestal bone
loss around 1.56 T 0.7 mm would be a major achievement in implant
dentistry. Clinical benefits such as superior aesthetics, better bone-
implant contact, and improved primary stability could be obtained
with platform switching.7
Previous study investigated the crestal bone
level after abutment insertion in 60 implants divided into 2 groups.
In the experimental group, 30 patients received implants with wide
platform and abutments with regular platform. In the control group,
patients received implants and abutments with wide platform. The
bone resorption of the mesial and distal faces of each implant was
evaluated radiographically after 1, 4, and 6 months. Mean value of
FIGURE 4. Morse cone connection.
FIGURE 5. Platform switching connection.
The Journal of Craniofacial Surgery & Volume 22, Number 6, November 2011 Prosthetic Platforms in Implant Dentistry
* 2011 Mutaz B. Habal, MD 2329
Copyright © 2011 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.

4. bone resorption on the mesial area was 2.53 mm in the control group,
whereas in the experimental group, it was 0.76 mm. On the distal
region, those values were 2.56 and 0.77 mm for the control and ex-
perimental groups, respectively. The platform switching group (exper-
imental group) exhibited statistically lower peri-implant bone loss.40
Another study investigated the use of expanded platforms
in postexodontic implants subjected to immediate loading and found
a total of 0.78 T 0.36 mm of bone loss. The probing depth did not
exceed 3 mm. Soft tissue formation was observed on the buccal
region and on the papillae. The authors concluded that the use of
platform switching promotes stability of the peri-implant bone tis-
sue and preserves the papillae and the soft tissues.41
However, this
concept presents some limitations such as the necessity of com-
ponents with similar design and enough soft tissue depth (around
Q3 mm) to achieve enough biologic width to develop an adequate
emergency profile.42,43
CONCLUSIONS
Based on the present literature review, it was concluded that
the bioengineering and biomechanical studies are important to pro-
mote the development and to investigate the different designs of
prosthetic platforms. The external hexagon is indicated for multiunit
restoration. On the other hand, the internal hexagon and the Morse
cone are more favorable in single-unit restorations and aesthetic re-
gions. The platform switching concept is adequate under reduced
prosthetic space (mesiodistal) to preserve the crestal bone and the
interdental papillae. All types of prosthetic platforms provided high
success rate of the implant treatment by following a strict criteria of
their indication and limitation. Therefore, a reverse planning of im-
plant treatment is strongly indicated to reduce implant overload, and
the use of advanced surgical-prosthetic techniques is required to
obtain a long-term success of oral rehabilitations.
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The Journal of Craniofacial Surgery & Volume 22, Number 6, November 2011 Prosthetic Platforms in Implant Dentistry
* 2011 Mutaz B. Habal, MD 2331
Copyright © 2011 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.