Effect of soft tissue thickness on crestal bone loss of early loaded implants with platform switching: 1- and 5-year data

Abstract

Objectives: The aim of this retrospective study was to evaluate the effect of vertical soft tissue thickness (STT) on crestal bone loss (CBL) of early loaded implants after 1 and 5 years. Method and materials: Forty-four tapered implants with platform switching and conical connection were placed in the posterior mandible and maxilla to rehabilitate edentulous sites. STT at implant sites was divided into two groups: thin (n = 21, mean STT = 2.0 ± 0.3 mm) and thick (n = 23, mean STT = 3.0 ± 0.8 mm). The implants were loaded after 6 to 8 weeks. Survival and success rates and CBL were measured after 1 and 5 years.
Results: The survival and success rates at 1 and 5 years were 100% and 97.8%, respectively. At the 1-year follow-up, the CBL of the thin and thick gingival groups was 0.96 ± 0.49 and 0.55 ± 0.41 mm, respectively; the difference was statistically significant (P = .004). At 5 years, the CBL of the thin and thick gingiva groups increased to 1.12 ± 0.84 and 0.65 ± 0.69 mm, respectively; the difference was not statistically significant (P = .052).
Conclusion: At 1 year, the CBL was more pronounced at sites with a thin gingiva; at 5 years the difference between the groups was not statisically significantly different. Within the limitations of this study, early loading of implants with platform switched and conical connection was safe.
.

Full text

doi:##.####/j.qi.a#####2
Eect of soft tissue thickness on crestal bone loss of early
loaded implants with platform switching: 1- and 5-year data
Alper Saglanmak, DDS, PhD/Alper Gultekin, DDS, PhD/Caglar Cinar, DDS, PhD/
Serge Szmukler-Moncler, DDS, PhD/Cuneyt Karabuda, DDS, PhD
Objectives: The aim of this retrospective study was to evaluate
the eect of vertical soft tissue thickness (STT ) on crestal bone
loss (CBL) of early loaded implants after 1 and 5 years. Method
and materials: Forty-four tapered implants with platform
switching and conical connection were placed in the posterior
mandible and maxilla to rehabilitate edentulous sites. STT at im-
plant sites was divided into two groups: thin (n = 21, mean
STT = 2.0 ± 0.3 mm) and thick (n = 23, mean STT = 3.0 ± 0.8 mm).
The implants were loaded after 6 to 8 weeks. Survival and success
rates and CBL were measured after 1 and 5 years. Results: The
survival and success rates at 1 and 5 years were 100% and 97.8%,
respectively. At the 1-year follow-up, the CBL of the thin and thick
gingival groups was 0.96 ± 0.49 and 0.55 ± 0.41 mm, respect-
ively; the dierence was statistically signicant (P = .004). At
5 years, the CBL of the thin and thick gingiva groups increased to
1.12 ± 0.84 and 0.65 ± 0.69 mm, respectively; the dierence was
not statistically signicant (P = .052). Conclusion: At 1 year, the
CBL was more pronounced at sites with a thin gingiva; at 5 years
the dierence between the groups was not statisically signi-
cantly dierent. Within the limitations of this study, early loading
of implants with platform switched and conical connection was
safe. (Quintessence Int 2021;52: 2–9; doi:##.####/j.qi.a#####)
Key words: crestal bone loss, dental implants, early loading, platform switching, soft tissue thickness
During the early years of modern dental implantology, conven-
tional stress-free healing periods of implants with a machined
surface were 3 months in the mandible and 6 months in the
maxilla when inserted in type I to III bone.1 Acid-etched sur-
faces were further developed on previously machined surface
implants with the same design.2 Removal torque experiments
in tibia rabbit model3 and human histology studies4,5 showed
that a minimally roughened acid-etched surface was able to
speed up osseointegration and implant anchorage in bone as
well as increase the bone-to-implant contact in soft bone. This
led to shortening of the healing period in both the mandible
and the maxilla from 3 and 6 months respectively to 2 months
in both arches.
2
When airborne-particle abrasion and acid etch-
ing was implemented on implants, the osseointegration period
was successfully reduced from 3 to 4 months to 6 to 8 weeks in
normal bone, and to 12 weeks in soft bone.6 Implant treatment
protocols have been classied according to implantation and
loading time. Early loading in healed sites is labelled type 4B
protocol, in which functional stresses are exerted 1 to 8 weeks
after surgery7,8; it is considered as a scientically and clinically
validated protocol with survival rates of 98% at 1 year.8 It has
been clinically documented as a safe treatment modality on
certain implant systems.2,6,9 Several papers noted that certain
parameters of macrogeometry and implant surface directly
aect implant success and time of osseointegration10,11; there-
fore, extrapolation from one system to another is not straight-
forward, and careful consideration is required. Recently, Roma-
nos et al12 described a specic early loading protocol called
“moderate early loading.” After 6 weeks of healing, the authors
engaged in a demanding prosthetic protocol that involved a
temporary prosthesis left for 6 more weeks in infra-occlusion
while the patients were instructed to remain on a soft/liquid
IMPLANTOLOGY

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Saglanmak et al
diet, before providing nal implant-supported prostheses. The
complex protocol was used, after only 6 weeks of healing, so
that the capacity of the bone-implant interface was not relied
upon to withstand standard loading.
CBL around implants is a multifactorial process with multi-
ple etiology. Several factors, like the vertical distance between
the mucosal ridge and the bone crest, a parameter known as
the vertical soft tissue thickness (STT) at the implant site,13 and
height of the prosthetic abutment,14 have been identied as
aecting the early amount of crestal bone loss (CBL). Studies
dealing with STT have assessed implants loaded after more
than 2 months following surgery. To the best of the present
authors’ knowledge, there is no experimental or clinical study
comparing the eect of the gingiva thickness on early loaded
implants. A specic bone densication response has been
reported for early loaded implants compared to conventionally
and immediately loaded ones.15 Thus, it remains unclear how
bone reacts to early loading protocols in combination with ver-
tical STT. Furthermore, clinical information is lacking to deter-
mine if the change in crestal bone observed at 1 year at sites
harboring gingiva of distinct thickness13 is maintained over
time, or if this is a marked early feature and the dierence is
abated in the longer term, eg, 5 years later.
The aims of the study were therefore:
■to test the null hypothesis that STT has no eect on CBL
after 1 and 5 years when early loaded implants with a plat-
form-switching and conical connection feature were used
■to evaluate the crestal bone stability of the thin and thick
gingiva groups after 1 year and 5 years.
Method and materials
Study sample and groups
This retrospective study was conducted on patients who
attended the Department of Oral Implantology of the Faculty
of Dentistry of Istanbul University to receive implant treatment
in the posterior mandible and maxilla in accordance with the
revised Helsinki Declaration of the World Medical Association
of 2000. Data analysis was approved by the Ethical Committee
of Istanbul University Clinical Investigations (No. 421-335).
Table 1 Study population: descriptive data comparing the thin and thick soft tissue groups; the only parameter that was dierent between
the groups was the STT
Parameter P†Thin, n (%) Thick, n (%)
Study variable Sites NA 21 23
Demographic variable Age < 50 y .10 16 (36%) 11 (25%)
Age ≥ 50 y 5 (12%) 12 (27%)
Female .95 8 (18%) 10 (24%)
Male 13 (29%) 13 (29%)
Site-related variable ISQ 60–75 .19 6 (14%) 12 (27%)
ISQ ≥ 75 15 (34%) 11 (25%)
ITV 20–30 Ncm .06 15 (34%) 9 (21%)
ITV ≥ 30 Ncm 6 (14%) 14 (31%)
STT (mm) .0001* 21 (47%) 23 (53%)
Location Mandible .39 12 (27%) 17 (38%)
Maxilla 9 (21%) 6 (14%)
Diameter 3.75 mm .60 17 (38%) 16 (36%)
4.2 mm 4 (10%) 7 (16%)
Length ≤ 10 mm .70 14 (31%) 13 (29%)
> 10 mm 7 (16%) 10 (24%)
*P < .05.
†Chi-square test for categorical variables.

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Inclusion criteria
Inclusion criteria were:
■patient age above 18 years
■patient health condition corresponding to ASA 1 or 2 ac-
cording to the American Society of Anesthesiologists clas-
sication
■sites healed for at least 3 months after tooth extraction
■no need for hard or soft tissue augmentation
■written informed consent
■implants that reached an insertion torque value (ITV)
≥ 20 Ncm and an implant stability quotient (ISQ) ≥ 60
■
implants that were loaded within 6 to 8 weeks after implant
placement.
Exclusion criteria
General exclusion criteria were:
■poor general health (uncontrolled diabetes, severe kidney
disease with bone mineral disorder)
■history of radiotherapy at the head region and active che-
motherapy
■untreated periodontitis
■poor oral hygiene.
Local exclusion criteria were dictated by the ITV and ISQ values
obtained at implant seating; implants with ITV < 20 Ncm and
ISQ < 60 were excluded from this study; they were allotted a
conventional delayed loading period.
Demographics
Forty-four consecutively inserted tapered implants (C1, MIS
Implants), displaying the features of platform switching and
internal conical connection, fulfilled the inclusion criteria.
Implants were assigned to two groups according to their ver-
tical STT. In accordance with Linkevicius et al,
16
the threshold
between the thin and thick tissue groups was set at 2.5 mm.
Twenty-one implants rehabilitating nine patients entered the
thin gingiva tissue group (G1); mean STT was 2.0 ± 0.3 mm,
min. 1.6 to max. 2.4 mm. Twenty-three implants rehabilitating
11 patients entered the thick gingiva tissue group (G2); mean
STT was 3.0 ± 0.8 mm, min. 2.5 to max. 3.8, outlier 6.3 mm; the
difference between the groups was statistically significant
(P < .001). The descriptive summary of the groups is shown in
Table 1. The average age of patients was 48.2 ± 5.2 years.
Surgical and prosthetic protocol
Dental treatments including scaling and oral hygiene motiva-
tion were delivered before implant surgery. The operation was
performed under local anesthesia; prior to surgery, rinsing was
performed with a 0.12% chlorhexidine digluconate solution for
2 minutes. All implantation procedures were performed by a
1 2
Fig 1 Measurements of
the STT on a panoramic
radiograph (thin biotype).
L1, 2.01 mm; L2, 2.38 mm.
Fig 2 Measurement of
the STT on a panoramic
radiograph (thick biotype).
L1, 3.02 mm.

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Saglanmak et al
single experienced and highly skilled surgeon with more than
20 years of clinical experience in implant surgery (CK). Midcr-
estal and sulcular incisions were performed and a mucoperios-
teal ap was raised. Implants were placed in a crestal position
to rehabilitate single-splinted crowns and xed/removable par-
tial dentures, either in the mandible or the maxilla. The drilling
sequence recommended by the manufacturer was implemented
for all implants including the nal drill. The ITV at implant seating
was recorded and the ISQ was measured with the resonance fre-
quency analysis method using a transducer specic to the
implant type and diameter (Osstell Mentor, Osstell) (Table 1). A
two-stage surgical protocol was implemented; at the end of the
healing period, titanium abutments were selected and torqued
at 30 Ncm. Final cement-retained metal-fused ceramic crowns
and xed/removable partial dentures were prepared and
allowed a full occlusion: 12 single crowns, 8 splinted, and 6
xed/removable partial dentures. The mean loading time was
7.17 ± 1.2 weeks.
Variables and endpoints
At the end of surgery, implant placement was radiographically
controlled with a panoramic radiograph (Kodak 8000, Eastman
Kodak) with acquisition conditions set at 75 kV and 10 mA. This
voltage/current combination allows a better acquisition of the
soft tissue with regards to the underlying bone. After internal
calibration against the implant length, the vertical STT was
assessed by measuring the vertical distance between the bone
level at the crest and the top of the gray shadow corresponding
to the STT.
Patients were recalled annually for a clinical and panoramic
radiographic examination. The images taken at baseline and at
1 and 5 years post-loading were analyzed. Magnication, con-
trast adjustment, and internal calibration of the acquired radio-
graphs against the implant length was performed using dedi-
cated software (Image tool 3.0, UT Health San Antonio) as
previously described.17,18 STT was measured by the same exam-
iner (AS) after being trained on the software. STT and crestal
bone levels were given by the software in millimeters at the
closest tenth of millimeter.
At baseline, STT was assessed by measuring the vertical dis-
tance between the crestal bone level and the top of the gray
mark corresponding to the soft tissue (Figs 1 and 2). The crestal
bone levels at a given time point were assessed by measuring
the vertical distance between the bone level at the crest and
the rst bone-implant contact on the mesial and distal sides
(Figs 3 and 4).
Statistical analysis
Statistical analysis was performed with a commercially avail-
able software program (SPSS Statistics 21.0, IBM). Mean, stan-
dard deviation, standard error of mean, and minimum and
maximum values were calculated. Homogeneity of the various
Fig 3 Crestal bone loss at
the 5-year control (thin
biotype). P1, 0.40 mm; P2,
1.26 mm; P3, 1.24 mm; P4,
1.56 mm.
Fig 4 Crestal bone loss at
the 5-year control (thick
biotype). P1, 0.40 mm; P2,
0.37 mm.
3 4

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IMPLANTOLOGY
clinical and surgical parameters of G1 and G2 was checked with
the chi-square test (Table 1). Implants were used as the statis-
tical unit. Calculation with a power of 80%, a signicant level of
.05, and assuming a dierence between groups of 0.45 mm,
showed that the minimum sample size of each group was
n = 16. Normality of the CBL data was checked with the Shap-
iro-Wilk test; the Student t test was used to evaluate the CBL of
the groups. The paired sample t test was used for the timely
evaluation of each group. The null hypothesis was that implant
sites with thin and thick gingival tissues will display similar CBL
at the 1- and 5-year follow-up.
Results
Clinical observations
Healing was uneventful during the osseointegration period; all
implants completed the 1- and 5-year examination. One implant
in one patient of the thick gingiva group underwent a mechan-
ical complication, screw loosening rst and then ceramic chip-
ping after the 1-year control. No biologic complication includ-
ing peri-implantitis was observed during the follow-up.
Radiographic findings
The CBLs measured at the mandible and the maxilla after 1 and
5 years were not statistically dierent (Table 2). At the 1-year
control, the overall mean CBL for both groups was 0.74 ±
0.49 mm. CBL of G1 and G2 was 0.96 ± 0.49 and 0.55 ± 0.41 mm,
respectively; the dierence between the groups was statistically
signicant (P = .004) and the null hypothesis was rejected. After
5 years, the overall mean CBL for both groups was 0.87 ±
0.79 mm. CBL of G1 and G2 was 1.12 ± 0.84 and 0.65 ± 0.69 mm;
the dierence was not statistically signicant (P = .052) (Table 3)
and the null hypothesis could not be rejected. The pairwise
Table 2 Crestal bone loss mean, standard deviation (SD), and standard error (SE) measured at implants placed in the mandible and the
maxilla; the dierence at 1 and 5 years was not statistically signicant
Time point Location N Mean ± SD SE P*
1 y Mandible 29 0.80 ± 0.55 0.10 .29
Maxilla 15 0.63 ± 0.35 0.09
5 y Mandible 29 0.94 ± 0.90 0.16 .48
Maxilla 15 0.76 ± 0.53 0.13
*Signicant at P < .05, student t test.
Table 3 Crestal bone loss mean, standard deviation (SD), standard error (SE), minimum and maximum values according to the soft tissue
groups; the dierence at 1 year between the thin and thick groups was highly statistically signicant; at 5 years, the dierence was
close to signicance
Time point Group N Mean ± SD SE Min. Max. P*
1 y Overall 44 0.74 ± 0.49 0.07 −0.10 1.63 NA
Thin 21 0.96 ± 0.49 0.10 0.90 1.63 .004*
Thick 23 0.55 ± 0.41 0.08 −0.10 1.32
5 y Overall 44 0.87 ± 0.79 0.12 0 2.82 NA
Thin 21 1.12 ± 0.84 0.18 1 2.82 .052
Thick 23 0.65 ± 0.69 0.14 0 2.51
*Signicant at P < .05, student t test.
Table 4 Crestal bone loss dierence between the 1- and 5-year
controls of the STT groups; the dierence between the thin
and thick groups was not statistically signicant
Group 1–5 y dierence (mm) P*
Overall 0.13 .15
Thin 0.15 .31
Thick 0.10 .30
*Signicant at P < .05, paired sample t test.

doi:##.####/j.qi.a##### 7
Saglanmak et al
comparison of CBL increase between the two time points was
not statistically signicant (Table 4).
Discussion
To the best of the present authors’ knowledge, this is the rst
paper to address the issue of how the STT aects the CBL in the
short and longer term, up to 5 years. At the 1-year control, the
CBL measured at G1 was more pronounced than at G2, 0.96 ±
0.49 mm vs 0.55 ± 0.41 mm, and the dierence was highly statis-
tically signicant (P = .004); the null hypothesis was therefore
rejected. This is in line with other reports dealing with conven-
tionally loaded implants in which the STT was identied as a
weighty contributing factor to the crestal bone fate, whether the
implants displayed the platform-switching feature13 or not.19
Nevertheless, opposing views exist; Akcalı et al,
20
in a systematic
review, found that there was insucient evidence regarding the
superiority of thick STT over thin when it comes to minimizing
the marginal bone loss. It is possible that some other confound-
ing parameters are still missed by the community.
At the 5-year control, the CBL of both groups slightly pro-
gressed compared to the 1-year data, but not in a signicant
way (G1, P = .31; G2, P = .30). The CBL of G1 and G2 was 1.12 ±
0.84 and 0.65 ± 0.69 mm, respectively, and the dierence
between groups was close to signicance (P = .052); therefore,
in contrast to the 1-year CBL data, the null hypothesis could not
be rejected. The lack of signicance is probably due to the large
standard deviation of both groups; it may be that the cemented
retention of the prostheses contributed to a larger dispersion of
the CBL data in the longer term, especially for the thin gingiva
group where cement remains are more prone to induce apical
migration of the crestal bone.21 Another possibility is that the
CBL dierence between the groups abates with time; however,
this hypothesis should be veried over time in other studies.
Studies that investigated the eect of vertical STT on CBL
have usually set the thickness threshold between thin and thick
gingiva at 2 mm.13,19,22 This originates from the experimental
study of Berglundh et al,23 which showed that thinning a
3-mm-thick gingiva down to 2 mm led to an increased CBL. In
a rst series of studies, Linkevicius et al13,19 divided the STT into
two groups, < 2 mm and > 2 mm. In one report,13 the average
STT of the thin group was 1.51 ± 0.09 mm and average STT of
the thick group was 2.98 ± 0.08 mm; the CBL of the thin and
thick gingiva sites, respectively, was 1.65 ± 0.08 and 0.44 ±
0.06 mm on the mesial side and 1.81 ± 0.06 mm and 0.47 ±
0.07 mm on the distal side. In a more recent work, the same
authors16 divided the STT into three distinct groups; a thin gin-
giva group with STT ≤ 2.0 mm where the average STT was
1.76 ± 0.26 mm, a medium group of 2.5 mm, and a > 2.5 mm
group where the average STT was 3.91 ± 0.59 mm. The thick
gingiva group led to the lowest CBL, 0.43 ± 0.37 mm, and the
thin one to the most pronounced CBL, 1.25 ± 0.80 mm; the dif-
ference was statistically signicant (P < .001).16 The CBL of the
medium STT group was 0.98 ± 0.06 mm; it was more pro-
nounced than the CBL of the thick group (P = .0014) but statis-
tically similar to the thin one (P = .31).16 The authors concluded
that there was no dierence between the thin and the medium
STT groups.16 For this reason the threshold that discriminated
between the thin and thick STT groups was set as 2.5 mm
instead of 2.0 mm in the present study.
There is no gold standard method to precisely measure the
STT at an implant site.24 Linkevicius et al19 proposed a simple
way to measure the STT before implant placement; to raise rst
a full-thickness buccal ap but not the lingual one, then to
place a 1-mm marked periodontal probe at the bone crest in
the center of the future implant position and measure the STT
to the closest millimeter. In a more recent study,
16
these authors
used a 0.5-mm marked probe to rene their STT recording. An
even more precise measuring method has been provided by
determining the STT on biopsies taken with a dermal punch22;
however, this approach is time consuming and not clinically
convenient. Determination of soft tissue dimension from a
radiographic examination has been carried out on CBCT
scans,25 but to the present authors’ knowledge this is the rst
paper reporting on STT measured on panoramic radiographs.
This was made possible because the advantageous voltage/
current combination of the panoramic device allowed a better
acquisition of the soft tissue with regards to the underlying
bone (Fig 1). After internal calibration against the implant
length, the vertical STT was assessed by measuring the vertical
distance between the bone level at the crest and the top of the
gray shadow corresponding to the STT. Accuracy of the mea-
surements was at the tenth of millimeter, higher than STTs read
from periodontal probes with 1-mm or 0.5-mm marks.
CBL measurements are usually gained from periapical radio-
graphs using the long cone parallel technique20; however, pan-
oramic radiographs have also been implemented to assess
bone changes over time.
17,18
Software is required to compensate
the measurement errors due to the heterogenous magnica-
tion of the panoramic radiographs; various authors showed that
the method is reliable and does not dier between examin-
ers.18,26 The advantage of the panoramic radiograph in the pos-
terior area is that angulation of the lm and the implants are
kept reasonably constant if the equipment is the same, more

doi:##.####/j.qi.a#####8
IMPLANTOLOGY
than with the parallel technique using periapical radiographs.
Nevertheless, its accuracy is lower than for customized x-ray lm
holders prepared for each implant with the parallel technique.
27
The current 1- and 5-year follow-up of 44 implants docu-
ments that implants with conical connection and platform
switching feature can be successfully loaded after 6 to 8 weeks
in both the mandible and the maxilla if the ITV is ≥ 20 Ncm or
the ISQ is ≥ 60. This matter is relevant because it has been
shown that bone response to functional stress may vary accord-
ing to the loading protocol. Indeed, when an early-loaded pro-
tocol after 6 weeks was applied, Akoglan et al15 found, through
CBCT examination, a denser peri-implant bone response at the
1-year follow-up compared to immediately or conventionally
loaded implants. Therefore, CBL data that have been obtained
for conventional loading protocols against STT might not nec-
essary apply when implants are loaded at an earlier time point;
this concern is clinically relevant for the present report.
Various consensus conferences stated that the timeframe
of early loading protocols covers a span of 7 weeks from the
rst to the eighth week after implant placement.7,8 Some
authors preferably load both arches after a similar time, after
3 weeks9 or 6 to 8 weeks28,29; others discriminate between the
arches, for example 6 weeks in the mandible and 8 weeks in
the maxilla.30 It has also been suggested that longer implants
may be loaded earlier than shorter ones.31 The fact that con-
sensuses suggest a 7-week interval7,8 shows that this categori-
zation of early protocols is not based on a biologic response at
the bone-implant interface; rather, it is the result of an empir-
ical decision based on the academic necessity to distinguish
between immediate loading protocols and longer ones, which
still are inferior to conventional healing periods. In the present
study, the early loading scheme was similar in the mandible
and maxilla because this suited a patient-orientated short-
ened treatment procedure and was compatible with the inter-
nal organization of the implant rehabilitation department.
A limitation of the study is the limited numbers of implants
and patients under follow-up. In addition, the panoramic radio-
graphic examination might be less precise than periapical
radiographs taken with a customized lm holder for each
implant.
Conclusion
After 1 year of follow-up, the CBL was more pronounced at sites
with a thin gingiva, similarly to conventionally loaded implants;
at 5 years the dierence between the groups was not signi-
cantly signicant. Between 1 and 5 years, the CBL increased
slightly for both groups but did not reach signicance. Early load-
ing of implants with conical connection and a platform switching
feature within 6 to 8 weeks was safe, and no implant failed over
the 5 years of follow-up. Further comparative clinical studies with
early loaded and conventionally loaded implants are needed to
conrm the present CBL data, especially in the longer term.
Acknowledgments
Dr Serge Szmukler-Moncler is Director of Research at MIS. The
other authors have no conicts of interest to declare.
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Alper Saglanmak
Alper Saglanmak Author title, Istanbul University, Dentistry Fac-
ulty, Department of Oral Implantology, Istanbul, Turkey
Alper Gultekin Author title, Istanbul University, Dentistry Facul-
ty, Department of Oral Implantology, Istanbul, Turkey
Caglar Cinar Author title, Istanbul University, Dentistry Faculty,
Department of Oral Implantology, Istanbul, Turkey
Serge Szmukler-Moncler Author title, Research Department,
MIS Implants, City, Country
Cuneyt Karabuda Private Practice, Istanbul, Turkey
Correspondence: Dr Alper Saglanmak, Istanbul University, Dentistry Faculty, Department of Oral Implantology, Istanbul, Turkey. Email:
alper.saglanmak@istanbul.edu.tr