Immediately loaded titanium implant with a tissue-stabilizing/maintaining design (‘beyond platform switch’) retrieved from man after 4 weeks: a histological and histomorphometrical evaluation. A case report

Marco Degidi
Giovanna Iezzi
Antonio Scarano
Adriano Piattelli
Authors’ affiliations:
Marco Degidi, Giovanna Iezzi, Antonio Scarano,
Adriano Piattelli, Dental School, University of
Chieti-Pescara, Chieti, Italy
Marco Degidi, Private Practice, Bologna, Italy
Correspondence to:
Prof. Adriano Piattelli, MD, DDS
Via F. Sciucchi 63
66100 Chieti
Italy
Tel.:þ00 39 0871 3554083
Fax:þ00 39 0871 3554076
e-mail: apiattelli@unich.it
Key words: conical abutment connection, crestal bone remodeling, dental implants,
histology, immediate loading, microgap, Morse cone connection, platform switching
Abstract
Background: After implant insertion and loading, crestal bone usually undergoes
remodeling and resorption. If the horizontal relationship between the outer edge of the
implant and a smaller-diameter component (‘platform switching’) is altered, there seems to
be reduced crestal bone loss. Immediate loading allows immediate restoration of esthetics
and function, reduces morbidity, and facilitates functional rehabilitation.
Materials and methods: Three Morse cone connection implants were inserted in the right
posterior mandible in a 29-year-old partially edentulous patient. The platform of the
implant was inserted 2mm below the level of the alveolar crest. After a 1-month loading
period, the most distal mandibular implant was retrieved with a trephine bur for
psychological reasons.
Results: At low-power magnification, it was possible to see that bone was present 2mm
above the level of the implant shoulder. No resorption of the coronal bone was present. No
infrabony pockets were present. At the level of the shoulder of the implant, it was possible
to observe the presence of dense connective tissue with only a few scattered inflammatory
cells. Newly formed bone was found in direct contact with the implant surface. The bone–
implant contact percentage was 65.3 4.8%.
Conclusions: Abutments smaller than the diameter of the implant body (platform
switching) in combination with an absence of micromovement and microgap may protect
the peri-implant soft and mineralized tissues, explaining the observed absence of bone
resorption. Immediate loading did not interfere with bone formation and did not have
adverse effects on osseointegration.
Stable crestal bone levels are believed to be
critical for the long-term implant success
(Chou et al. 2004). After implant insertion
and loading, crestal bone usually undergoes
remodeling and resorption during the first
year following prosthetic restoration, in
two-piece implants (Hermann et al.
2000a). Crestal bone levels have been reported
to be usually located about 1.5–
2mm below the implant–abutment junction
(IAJ) after 1 year following implant
restoration (Lazzara & Porter 2006).
Cochran et al. (1997) and Hermann et al.
(1997, 2000b, 2001) demonstrated that
crestal bone remodels to a level about
2.0mm apical to the IAJ. Several hypotheses
have been offered to explain this remodeling.
Some investigators have related
this remodeling to a stress concentration
at the crestal level, while others believe
that the presence of a microgap and possible
microleakage and micromovement
Date:
Accepted 15 January 2007
To cite this article:
Degidi M, Iezzi G, Scarano A, Piattelli A. Immediately
loaded titanium implant with a tissue stabilizing/
maintaining design (‘beyond platform switch’) retrieved
from man after 4 weeks: a histological and
histomorphometrical evaluation. A case report.
Clin. Oral Impl. Res. 19, 2008; 276–282
doi: 10.1111/j.1600-0501.2007.01449.x
276 c 2007 The Authors. Journal compilation c 2007 Blackwell Munksgaard
could lead to a localized inflammation of
the peri-implant soft tissues (Quirynen &
Van Steenberghe 1993; Quirynen et al.
1994; Persson et al. 1996; Cochran et al.
1997; Hermann et al. 1997, 2000a, 2001;
Jansen et al. 1997; Misch et al. 2001;
Piattelli et al. 2001, 2003). The potential
influence of implant design on peri-implant
bone loss warrants additional research
(Chou et al. 2004). The loss of
crestal bone has also been reported to be
influenced by the relationship of the IAJ
to the crestal bone (Chou et al. 2004).
Hermann et al. (2001) and Piattelli et al.
(2003) have demonstrated that when the
IAJ is positioned deeper within the bone,
the resulting loss of vertical crestal bone
height increases.
When a matching implant–abutment
diameter is used, the inflammatory cell
infiltrate (abutment ICT) is located at the
outer edge of the IAJ close to crestal bone;
this close proximity may explain partially
the biologic and radiographic observations
of crestal bone loss around restored twopiece
implants (Lazzara & Porter 2006).
On the other hand, if the horizontal relationship
between the outer edge of the
implant and a smaller-diameter component
(‘platform switching’) is altered in addition
to other favorable implant design conditions,
there seems to be a reduced crestal
bone loss (Lazzara & Porter 2006). This
fact could be explained by an increased
surface area created by the exposed implant
seating surface with a reduction in the
quantity of crestal bone resorption needed
to expose a minimal amount of implant
surface to which the soft tissues can attach
(Lazzara & Porter 2006). Furthermore, the
internal repositioning of the IAJ away from
the external, outer edge of the implant and
neighboring bone decreases the effects of
the abutment ICT on surrounding tissues
(Abrahamsson et al. 1998; Lazzara &
Porter 2006). The reduced exposure and
confinement of the platform-switched
abutment ICT may result in a reduced
inflammatory effect (Lazzara & Porter
2006). Additonally, the exposed horizontal
part of the implant shoulder was also microroughened,
and this enhances the
chance of bone growth on top of this
surface.
A Morse cone connection implant (Ankylos
s, Dentsply-Friadent) has an in-built
beyond platform switching and was designed
with, among others, the following
objectives:
(1) it should allow for optimum load distribution
for permanent load stability
during functional loading;
(2) it should facilitate soft-tissue stability
due to the gap-free bacteria-proof tapered
abutment connection withmaximum
mechanical stability and the
lack of any micromovement (Nentwig
2004).
In a previous histological report of an
immediately loaded Morse cone connection
implant, retrieved from man after a
6-month loading period, we reported the
presence of newly formed bone trabeculae
at the most coronal portion on one side of
the implant; these trabeculae were surrounded
by osteoblasts actively secreting
osteoid matrix with no osteoclasts present.
We thought that the presence of this newly
formed bone in the coronal peri-implant
area was striking and we hypothesized that
it could be related to the absence of a
microgap due to the conical connection
with no bacterial colonization and leakage
at the implant–abutment interface (Degidi
et al. 2004).
Photoelastic and finite element analysis
studies have shown that the special thread
design of this implant reduces the functional
stresses at the crestal bone compared
with other implant systems (Morris et al.
2004; Nentwig 2004). Load-induced cervical
bone loss occurred in o20% of cases,
and even in these cases, the amount of
crestal bone loss was minimal (Nentwig
2004).
In a study, in 50% of the cases, X-ray
examination after 1 year of prosthetic loading
showed crestal bone at or slightly above
the level of the implant shoulder (Doring
et al. 2004).
Chou et al. (2004), in a study of over
1500 Morse cone connection implants,
reported a total overall mean loss from
implant placement to 36 months postloading
of only 0.6 or 0.2mm/year, including
the bone loss that can be attributed to
surgical trauma.
Immediate loading of dental implants
was thought to produce a fibrous repair at
the interface (Bra°nemark et al. 1977; Adell
et al. 1981; Carter & Giori 1991; Brunski
1991, 1992). Several histological reports, in
man and experimental animals, have, on
the contrary, shown mineralized tissues at
the interface in early and immediately
loaded implants (Linkow et al. 1992;
Piattelli et al. 1993a, 1993b, 1997a,
1997b, 1997c, 1998; Trisi et al. 1993;
Ledermann et al. 1999; Romanos et al.
2001; Testori et al. 2001; Romanos et al.
2002; Testori et al. 2002; Rocci et al. 2003;
Siar et al. 2003; Degidi et al. 2004; Degidi
et al. 2005a, 2005b; Traini et al. 2005a,
2005b; Neugebauer et al. 2006). Immediate
loading allows immediate restoration of
esthetics and functions, reduces the morbidity
of a second surgical intervention, and
facilitates the functional rehabilitation increasing
patient acceptance and satisfaction.
There is a need to investigate the
bone healing processes at the interface,
especially regarding which type of bone
response is present around immediately
loaded implants inserted in poorer quality
bone (Degidi et al. 2005a, 2005c). An
analysis of human biopsies of immediately
loaded implants is the best way to ascertain
the quality and quantity of the peri-implant
hard tissues (Romanos et al. 2005). The
role that implant surfaces play, especially
on the early healing processes at the interface
is also important. A sandblasted and
acid-etched surface (Friadents plus surface,
Dentsply) was obtained with a novel gritblasting
and acid-etching technique and
showed a regular microroughness with
pores in the micrometer dimension overlaying
a macroroughness structure caused
by the grit blasting. (Papalexiou et al. 2004;
Rupp et al. 2004). The spatial architecture
showed a first level of roughness of
100 mm, a second level of grooves in the
dimensions of about 12–75 mm, each of
which embraced an arrangement of smaller
round-shaped groups with diameters of
about 1–5 mm (Papalexiou et al. 2004;
Rupp et al. 2004).
The aim of this study was to evaluate the
peri-implant soft and mineralized tissues
around an immediately loaded implant,
with a conical implant abutment connection,
after a 1-month loading period.
Materials and methods
Three Morse cone connection dental
implants (ANKYLOSs plus DENTSPLYFriadent,
Mannheim, Germany) were
inserted in the right posterior mandible in
Degidi et al . Human immediately loaded implant
c
2007 The Authors. Journal compilation c 2007 Blackwell Munksgaard 277 | Clin. Oral Impl. Res. 19, 2008 / 276–282
a 29-year-old partially edentulous patient.
The platform of the implants was inserted
2mm below the level of the alveolar crest,
1mm deeper than the manufacturer’s protocol
(Fig. 1). The patient was a heavy
smoker. All the implants were immediately
loaded with a provisional resin restoration
the same day of the implant
surgery. After a 1-month loading period,
the most distal mandibular implant was
retrieved with a 5.5-mm trephine bur for
psychological reasons (Fig. 2). The patient
had developed, almost immediately after
implant insertion, an aversion to this implant,
thought that it was causing an inflammation
that could lead to cancer
development, and psychological counseling
did not obtain any results. This implant
was a 3.5 8mm implant inserted in the
D3 bone with an insertion torque of
23.8Ncm. The ISQ value was 63 at
implant insertion and 66 before implant
retrieval.
Specimen processing
The implant and surrounding tissues were
washed in saline solution and immediately
fixed in 4% para-formaldehyde and 0.1%
glutaraldehyde in 0.15M cacodylate buffer al
4 C and pH 7.4. The specimen was processed
using the Precise 1 Automated
System (Assing, Rome, Italy). (Piattelli
et al. 1997d). The specimen was dehydrated
in an ascending series of alcohol
rinses and embedded in a glycolmethacrylate
resin (Technovit 7200 VLC, Kulzer,
Wehrheim, Germany). After polymerization
the specimen was sectioned along its
longitudinal axis with a high-precision diamond
disk at about 150 mm and ground
down to about 30 mm with a specially
designed grinding machine. Three slides
were obtained. These slides were stained
with acid fuchsin and toluidine blue and
examined with a transmitted light Leitz
Laborlux microscope (Leitz, Wetzlar,
Germany) and a Zeiss fluorescence microscope
(Zeiss, Go¨ttingen, Germany).
Histomorphometry of bone-implant contact
percentage was carried out using a light
microscope (Laborlux S, Leitz) connected
to a high-resolution video camera (3CCD,
JVC KY-F55B, JVCs, Yokohama, Japan)
and interfaced to a monitor and PC (Intel
Pentium III 1200 MMX, Intels, Santa
Clara, CA, USA). This optical system
was associated with a digitizing pad (Matrix
Vision GmbH, Oppenweiler, Germany)
and a histometry software package with
image-capturing capabilities (Image-Pro Plus
4.5, Media Cybernetics Inc., Immagini &
Computer Snc, Milano, Italy).
Results
At low-power magnification, it was possible
to see that bone was present 2mm
above the level of the implant shoulder
(Fig. 3). In the first three coronal mm it
was possible to observe the presence of
lamellar cortical compact bone around the
implant (Fig. 4). In this region, many areas
of bone remodeling were present; bone
remodeling units (BMU) were also present
(Fig. 5). Areas of new bone formation were
present, with osteoblasts depositing osteoid
matrix. A rim of osteoblasts lined the
marrow spaces found at the coronal level;
these osteoblasts were depositing osteoid
matrix. At the coronal level, osteoblasts
were also found in direct contact with the
implant surface; these osteoblasts were
laying down osteoid matrix directly on
the metal surface. No resorption of the
coronal bone was present. No infrabony
pockets were present. At the level of the
shoulder of the implant, it was possible to
observe the presence of a dense connective
tissue with only a few inflammatory cells.
Newly formed bone was found in direct
contact with the implant surface. No fibrous
connective tissue was found at the
bone–titanium interface. No epithelial
downgrowth was present. No active bone
resorption was present in the middle and
apical portion of the implant perimeter and
osteoclasts were absent. All the interthread
spaces were filled by newly formed bone
with a thickness of 100–300 mm; it was
possible to observe two lines of osteocytes.
These osteocytes had their longest axis
always parallel to the implant surface. In
some portions of the implant surface, osteoblasts
were depositing osteoid matrix.
Many wide marrow spaces with many
capillaries were present in the peri-implant
bone. The bone near the implant appeared
to be moremature than the bone found at a
distance. No inflammatory cell infiltrate
was found around the implant. In the
apical portion, osteoblasts and newly
formed bone were present. No osteoclasts
Fig. 1. Radiographic aspect of the implant.
Fig. 2. The retrieved implant. The arrows show the coronal portion of the bone.
Degidi et al . Human immediately loaded implant
278 | Clin. Oral Impl. Res. 19, 2008 / 276–282 c 2007 The Authors. Journal compilation c 2007 Blackwell Munksgaard
were present. Few marrow spaces were
observed directly on the implant surface.
The bone–implant contact percentage was
65.3 4.8%.
Discussion
Only a few histological evaluations of immediately
loaded implants retrieved from
humans have been reported in the literature
(Linkow et al. 1992; Piattelli et al.
1993a, 1997a, 1997c; Trisi et al. 1993;
Ledermann et al. 1999; Testori et al.
2001, 2002; Rocci et al. 2003, 2005; Degidi
et al. 2005a, 2005b, 2005c; Romanos et al.
2005; Traini et al. 2005a, 2005b).
In the present histologic study, the aim
was to focus mainly on two aspects of the
peri-implant tissues:
(1) the soft peri-implant tissues;
(2) the aspect and characteristics of the
mineralized bone at the interface.
Because the emergence area of the
shoulder region of this implant is considerably
less than that in other systems that
use conventional implant–abutment connections,
the shoulder is positioned subcrestally
into the bone to produce an
optimal emergence profile (Doring et al.
2004). Placement of the implant deeper
into the bone does not necessarily result
in complications of the soft and hard tissues
that have been reported for other
implant systems (Doring et al. 2004). In
fact, in the present specimen it was found
that the bone had not undergone any resorption
and was still located about 2mm
above the implant shoulder.
This could be due to the positive effects
of a favorable load transmission to the bone
via the special progressive threads of this
implant, to a stable internal-tapered abutment
connection with the absence of any
microgap (Nentwig 2004) or micromovement,
and, finally, to the presence of a
thick layer of soft tissues in the narrowed
neck of the smaller-diameter abutment
(Doring et al. 2004). This collar of soft
tissue, which has a wedge-shaped cross
section, and which was found to be composed
of thick, fibrous connective tissue
with few scattered inflammatory cells,
probably provides an additional protective
function to the peri-implant bone (Doring
et al. 2004). It must, moreover, be stressed
that in this case the implants were inserted
in the posterior mandible and, probably,
the width of the ridge positively influenced
the histological result. Also the interimplant
distance was found to be a relevant
factor on crestal bone resorption. Tarnow
et al. (2000) found that the crestal bone loss
was lower for implants with a 43mm
distance between them. It can be hypothesized
that the present results would have
Fig. 4. At higher magnification, at the coronal level a rim of osteoblasts was producing osteoid matrix. Acid
fuchsin–toluidine blue. Figure on the left side magnification 50. Figure on the upper right side 100.
Figure on the right lower side 100.
Fig. 3. Immediately loaded Morse cone connection implant, inserted in the posterior mandible and retrieved
after 4 weeks. Low-power magnification on the left side. The bone–implant contact percentage was 65%. At
higher magnification, on the upper right side it was possible to see a rim of osteoblasts lining the marrow spaces
found at the coronal level: these osteoblasts were depositing osteoid matrix. At the coronal level, osteoblasts
were also found in direct contact with the implant surface: these osteoblasts were laying down osteoid
matrix directly on the metal surface. On the lower right side it was possible to observe a dense, fibrous
connective tissue with a few scattered lymphocytes. Acid fuchsin–toluidine blue. Figure on the left-side
magnification 12. Figure on the upper right-side 50. Figure on the right lower side 50.
Degidi et al . Human immediately loaded implant
c
2007 The Authors. Journal compilation c 2007 Blackwell Munksgaard 279 | Clin. Oral Impl. Res. 19, 2008 / 276–282
been different if the implants had been
placed closer together.
The surface characteristics of an implant
are important in determining the pattern of
healing under loading, especially in particularly
demanding situations such as immediate
loading.
The histological data obtained from the
present study confirm that immediate
loading did not have an adverse effect on
osseointegration, and the early bone healing
was not disturbed by the stresses transmitted
at the interface even if the implant
had been inserted in soft bone (D3). The
very high bone-to-implant contact percentage
found in the present implant (about
65%) after a healing period of only 4 weeks
is striking. This fact could be explained by
the microstructure of this surface that has
been shown to have a hierarchical surface
structure due to surface-modifying blasting
and etching processes, resulting in a wettable
surface (Rupp et al. 2004). This unique
wettability characteristic has been
hypothesized to determine an increased
adhesion to this surface of non-collagenous
proteins like sialoprotein and osteopontin,
which are the forerunners of contact osteogenesis
(Rupp et al. 2004). Moreover,
higher adsorbed amounts of fibronectin
may improve host responses such as osteoblast
adhesion (Rupp et al. 2004). At last,
the three-dimensional fibrin grid found on
this surface could produce a more favorable
structure for the in vivo three-dimensional
movement (from bone-to-implant surface)
of osteogenic differentiating cells (Di Iorio
et al. 2005).
Rocci et al. (2003) reported very high
bone–implant contact, (84.2%), with apparent
undisturbed healing in implants that
had been inserted in bone quality sites 3 or
4 and that had been biomechanically challenged.
The present results, moreover, confirm
those reported by Testori et al. (2002).
Immediately loaded splinted implants inserted
in the posterior mandible can osseointegrate
with a peri-implant response
similar to that of delayed loaded implants.
(Degidi et al. 2004, 2005a, 2005b,
2005c).
Conclusion
The use of an abutment smaller than the
diameter of the implant body (‘platform
switching’) can help to protect the periimplant
mineralized tissues. This fact
could, probably, partially explain the absent
or reduced rate of bone resorption
reported for this type of implant connection,
and observed in the present histological
case report.
The bacteria-proof seal, the lack of micromovements
due to the friction grip, and
the minimally invasive second-stage surgery
without any major trauma for the
periosteal tissues are also important factors
in preventing the cervical bone loss.
(Morris et al. 2004; Nentwig 2004). The
platform-switching concept most probably
could have a significant impact on the
implant treatment in esthetic areas. Care
should be taken in extrapolating the results
provided in this paper to the esthetic zone.
The present results show that a high
percentage of bone contact can be obtained
even in immediately loaded implants inserted
in soft bone, after a very short healing
period (4 weeks). Immediate loading did not
interfere with bone formation and did not
have adverse effects on osseointegration.
Acknowledgements: This work was
partially supported by the National
Research Council (C.N.R.), Rome, Italy,
by the Ministry of Education,
University, and Research (M.I.U.R.),
Rome, Italy, and by AROD (Research
Association for Dentistry and
Dermatology), Chieti, Italy.
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