Platform switching and marginalbone-level alterations: the results ofa randomized-controlled trial

Luigi CanulloGiampiero Rossi FedeleGiuliano IannelloSøren Jepsen

Authors’ affiliations:Luigi Canullo, Private Practice, Rome, ItalyLuigi Canullo, S!ren Jepsen, University of Bonn,Bonn, GermanyGiampiero Rossi Fedele, Private Practice, London,UKGiuliano Iannello, Data Analyst, Rome, Italy

Correspondence to:Dr Luigi CanulloVia Nizza 4600198 RomeItalyTel.: ! 39 06 841 1980Fax: ! 39 06 841 1980e-mail: luigicanullo@yahoo.com

Key words: bone level, bone loss, dental implants, implant design, platform switching

Abstract

Objectives: This randomized-controlled trial aimed to evaluate marginal bone level

alterations at implants restored according to the platform-switching concept, using

different implant/abutment mismatching.

Material and methods: Eighty implants were divided according to the platform diameter in

four groups: 3.8mm (control), 4.3mm (test group1), 4.8mm (test group2) and 5.5mm (test

group3), and randomly placed in the posterior maxilla of 31 patients. After 3 months,

implants were connected to a 3.8-mm-diameter abutment and final restorations were

performed. Radiographic bone height was measured by two independent examiners at the

time of implant placement (baseline), and after 9, 15, 21 and 33 months.

Results: After 21 months, all 80 implants were clinically osseointegrated in the 31 patients

treated. A total of 69 implants were available for analysis, as 11 implants had to be excluded

from the study due to early unintentional cover screw exposure. Radiographic evaluation

showed a mean bone loss of 0.99mm (SD"0.42mm) for test group1, 0.82mm

(SD"0.36mm) for test group2 and 0.56mm (SD"0.31mm) for test group3. These values

were statistically significantly lower (Po0.005) compared with control (1.49mm,

SD"0.54mm). After 33 months, five patients were lost to follow-up. Evaluation of the

remaining 60 implants showed no difference compared with 21 months data except for test

group2 (0.87mm) and test group3 (0.64mm). There was an inverse correlation between the

extent of mismatching and the amount of bone loss.

Conclusions: This study suggested that marginal bone level alterations could be related to

the extent of implant/abutment mismatching. Marginal bone levels were better maintained

at implants restored according to the platform-switching concept.

It has been demonstrated that following

implant surgery, remodeling takes occurs

and is characterized by a reduction in bone

dimension, both horizontally and vertically

(Cardaropoli et al. 2006). The radiographic

marginal bone level showed a mean loss of

0.9mm at the time of abutment connec-

tion and crown placement and a further

mean loss of 0.7mm at 1 year. Similar

results were reported in a retrospective

study, which showed a range of resorption

of 2–3mm after 1 year depending on arch,

jaw region, smoking status, case type, bone

quality, surface type and implant design

(Manz 2000).

It has been suggested that this biologic

process resulting in loss of crestal bone

height may be altered when the outer

edge of the implant–abutment interface is

horizontally repositioned inwardly and

away from the outer edge of the implant

platform. This prosthetic concept has been

Date:Accepted 26 September 2009

To cite this article:Canullo L, Fedele GR, Iannello G, Jepsen S. Platformswitching and marginal bone-level alterations: theresults of a randomized-controlled trial.Clin. Oral Impl. Res. 21, 2010; 115–121.doi: 10.1111/j.1600-0501.2009.01867.x

c# 2009 John Wiley & Sons A/S 115

introduced as ‘platform switching’ and

radiographic follow-up has demonstrated a

smaller than expected vertical change in

the crestal bone height around implants

(Lazzara & Porter 2006).

Outcomes following platform switching

have also been studied histologically both

in animals and humans. Whereas, Becker

et al. (2007) did not find histological

differences in bone resorption between tra-

ditionally restored and platform-switched

implants after 28 days of healing in dogs,

Jung et al. (2008) and Cochran et al. (2009)

reported only minimal bone loss around

loaded implants with non-matching

implant–abutment diameters following a

6-month loading period. Luongo et al.

(2008) examined histologically a human

implant removed 2 months after placement

and speculated that the inward shift of the

inflammatory connective tissue zone at the

implant–abutment junction could be the

reason for bone preservation around plat-

form-switched implants. Similar conclu-

sions were drawn by Degidi et al. (2008)

who reported no resorption of the coronal

bone at a human implant that had been

retrieved after a 1-month loading period.

Using three-dimensional finite-element

models, Maeda et al. (2007) examined the

possible biomechanical advantage of plat-

form switching in an in vitro study and

suggested that by this configuration, the

stress concentration would be shifted away

from the cervical bone–implant interface.

In a controlled study with 30 patients,

Vela-Nebot et al. (2006) found a significant

reduction of mean bone loss of 0.7mm at

30 platform-switched implants compared

with 2.5mm at the 30 control implants, 6

months after abutment attachment. In a

limited number of patients, where im-

plants were placed in extraction sockets,

Canullo & Rasperini (2007) observed that

immediate loading with platform switch-

ing could provide peri-implant hard-tissue

stability with soft-tissue and papilla pre-

servation. Hurzeler et al. (2008) observed

in a preliminary study, including 15 pa-

tients who had received 14 wide-diameter

implants with platform-switched abut-

ments and eight implants with regular

diameter, less mean crestal bone resorption

(0.12 vs. 0.29mm) 1 year after final re-

storation. In another recent prospective

study with 45 patients, Cappiello et al.

(2008) showed that 12 months after load-

ing, the vertical bone loss in 75 implants

restored according to the platform-switch-

ing protocol varied between 0.6 and

1.2mm (mean: 0.95 $ 0.32mm), while

in 56 control implants with matching

abutments, bone loss was between 1.3

and 2.1mm (mean: 1.67 $ 0.37mm).

Very recently in a prospective multicenter

trial, Prosper et al. (2009) reported no bone

loss (mean: 0.04 $ 0.22mm) at 60 plat-

form-switched implants compared with 60

implants with regular abutments (mean:

0.27 $ 0.46mm) 24 months following

placement.

At present, information from studies

with a longer observation period is lacking.

Furthermore, it is not known whether

marginal bone level alterations may be

affected by the extent of implant–abutment

mismatching.

The aim of this randomized controlled

study was to assess radiographically mar-

ginal bone level alterations in implants

restored according to the platform-switch-

ing concept using different mismatching

implant–abutment diameters compared

with traditionally restored implants.

Material and methods

Study design and patient selection

Eighty consecutive implants in 31 patients

were inserted for implant-supported re-

storations in the posterior maxilla.

All patients were in general good health.

They were followed for a period of 30

months after prosthetic rehabilitation.

The exclusion criteria were:

% Sites with acute infection.

% Patients with a full mouth plaque score

and a full mouth bleeding score425%.

% Sites with o7mmwidth of bone crest.

% Sites with interproximal or buccal bone

defects.

% Smokers with 410 cigarettes/day.

% Patients with diabetes.

% Pregnant or lactating women.

% Patients with a history of bisphospho-

nate therapy.

Implants of all subjects included in the

study were randomly assigned to one of the

four treatment regimens (implant diameter

3.8, 4.3, 4.8 and 5.5mm). Random assign-

ment was performed according to pre-

defined randomization tables. A balanced

random permuted block approach, ensur-

ing that, at any point in a trial, roughly

equal numbers of participants were allo-

cated to all the comparison groups, was

used to prepare the randomization tables in

order to avoid unequal balance between the

four treatments. In order to reduce the

chance of unfavorable splits between test

and control groups in terms of key prog-

nostic factors, the randomization process

took into account the following variables:

patient’s gender, age, presence of adjacent

teeth, distal extension sites and site loca-

tion in the dental arch. Assignment was

performed using a sealed envelope.

Patients were informed about the proce-

dure but were blinded whether they re-

ceived test or control implants. A signed

informed consent form was required. The

present study was performed following the

principles outlined in the Declaration of

Helsinki on experimentation involving hu-

man subjects.

Surgical protocol

Before the surgical procedure, a full-mouth

professional prophylaxis appointment was

scheduled.

Patients received 1 g amoxicillin/clavu-

lanate 1 h before surgery and continued

with 2 g/day for 6 days (Laskin et al. 2000).

The characteristics of the site were:

% Presence of a wide ridge of bone allow-

ing the insertion of a wide platform

implant according to the Branemark

protocol.

% Absence of infection.

% Absence of bone horizontal regenera-

tive procedure requirement.

Crestal incision was performed after an-

esthesia. One to four 13mm implants

(Global, Sweden & Martina, Padua, Italy),

platform diameter of 3.8–5.5mm, were

inserted in a standardized way in the pos-

terior maxilla. A minimal distance of

2.5mm between implants and between

implants and teeth was always observed.

When required, sinus lift augmentation

was performed but the coronal part of all

implants was always placed in at least

4mm of native bone. Once the implant

site was prepared to receive a 3.8-mm-

diameter implant, surgeons’ assistants were

asked to open the sealed envelope contain-

ing the randomization. If required, the

implant site was then enlarged according

Canullo et al &Platform switching

116 | Clin. Oral Impl. Res. 21, 2010 / 115–121 c# 2009 John Wiley & Sons A/S

to the randomization, to insert awider than

3.8-mm-diameter implant. The root-

shaped implant used in this study pre-

sentedmicro-threads in the coronal portion

and a sand-blasted and acid-etched surface

in the entire length of the body.

All implants were inserted with the plat-

form at the bone level. A 3.8-mm-diameter

cover screw was used for each implant.

Tension-free suture was performed using a

5 monofilament.

Patients were instructed to have a soft

diet and to avoid chewing in the treated

area until the suture removal. Oral hygiene

at the surgical site was limited to soft

brushing for the first 2 weeks. Regular

brushing in the rest of the mouth and rinse

with 0.12% chlorexidine were prescribed

for 2 weeks. Thereafter, conventional

brushing and flossing were permitted.

After 2 weeks, sutures were removed.

Implants were allowed for a submerged

healing. Two to 3 months later, the un-

covering procedure was carried out. Only

uneventfully healed implants were ac-

cepted in this study.

Three months after the first surgery, by

performing a crestal incision just over the

area corresponding to the implant, the

cover screws were exposed and removed.

Attached keratinized mucosa was present

both on the palatal and buccal aspect

around all implants.

Subsequently, a 3.8-healing abutment

was inserted. After 1 week, a 3.8mm

coping transfer was used and an impression

was taken.

For restoration, in test and control

groups, always a 3.8 abutment was used.

In the test groups, this restoration resulted

in a mismatching of 0.25–0.85mm of

implant–abutment diameters (Fig. 1). All

restorations were a splinted single-unit

crowns in order to protect implants from

inhomogeneous loading.

Twoweeks after the re-opening procedure,

crowns were cemented using a provisional

cement (Temp Bond, Kerr, WA, USA).

Radiographical and clinical assessments

For each patient, an individual customized

digital film holder was fabricated to ensure

a reproducible radiographic analysis.

At the time of the final abutment and

crown connection, periodontal parameters

[bleeding on probing (BOP), probing pocket

depth (PPD), modified plaque index on

adjacent teeth and implants] were assessed.

Furthermore, digital periapical standar-

dized radiographs were taken to control

the perfect adaptation of the abutment on

the implant.

Every 6 months for 30 months after the

final restoration, clinical assessments were

performed in order to evaluate periodontal

parameters at implants and neighboring

(mesial and distal) teeth. Every 6 months

for 30 months after the final restoration,

periapical standardized digital radiographs

were taken in order to evaluate marginal

bone level alterations after loading (Figs 2

and 3).

A computerized measuring technique

was applied to digital periapical radio-

graphs. Evaluation of the marginal bone

level around implants was performed using

an image analysis software (Autocad 2006,

version Z 54.10, Autodesk, San Rafael,

CA, USA), which was able to compensate

radiographic distortion (Canullo et al.

2009a, 2009b). The software calculated

bone remodeling at the mesial and distal

aspects of the implants. Because each im-

plant was inserted at the bone-level crest,

the distance was measured from themesial

and distal margin of the implant neck to

the most coronal point where the bone

appeared to be in contact with the implant.

For each implant, mean values of mesial

and distal records were used.

All measurements were made and col-

lected by the same two calibrated exam-

iners, different from the implant surgeon.

For each pair of measurements, mean va-

lues were used.

Statistical analysis

Firstly, the data were checked for normal

distribution (Kolmogorov–Smirnov and

Shapiro–Wilk normality tests) and then

subjected to ANOVA. In order to evaluate

the different impact of different diameters

on bone resorption, univariate GLM test

was conducted. Bone resorption was set as

a dependent variable and the diameter of

implants and patients were selected as

independent factors. We observed that the

diameter effect was significant whereas the

patient effect was not significant.

Results

From December 2005 to September 2006,

31 consecutive patients (17 men and 14

women) were included in this study. At the

time of implant insertion, the patients

ranged in age from 36 to 78 years (mean

age: 52.1 years). Missing teeth had been

extracted due to advanced periodontitis or

endodontic failure at least 6 months before

surgery. In association with implant inser-

tion, 21 sinus lift augmentations with

a lateral window approach were carried

out using nano-structured hydroxyapatite

(Nanobone, Artoss, Rostock, Germany) as

the only bone filler.

All implants were clinically osseointe-

grated, stable and showed no sign of infec-

tion. All implants were loaded 14 weeks

after insertion. All 31 patients could be

followed up for 21 months. Eleven im-

plants in 10 patients were excluded from

the analysis because of early unintentional

cover screw exposure. Thus, a total of 69

implants in 31 patients were included for

the analysis after 21 months: 17 for test

group1, 15 for test group2, 18 for test group3and 19 for the control group. Thereafter,

five patients were lost to follow-up and 26

patients were available for the 33-months

Fig. 1. SEM image of implants of the control and test groups. According to implant platform diameter,

implants were divided into four groups: 3.8 (Control Group) with no mismatching, 4.3 (test group1) with a

mismatching of 0.25mm, 4.8 (test group2) with a mismatching of 0.05mm and 5.5mm (test group3) with a

mismatching of 0.85mm. The abutment diameter was 3.8mm in all groups.

Canullo et al &Platform switching

c# 2009 John Wiley & Sons A/S 117 | Clin. Oral Impl. Res. 21, 2010 / 115–121

evaluation of a total of 61 implants: 17 for

test group1, 13 for test group2, 14 for test

group3 and 17 for control group.

Periodontal parameters

For the duration of the study, BOP was not

detected at any implant, and PPD did not

exceed 3mm.

Radiographic results

Figure 4 displays the mean marginal bone-

level alterations for the different groups of

implants over the study period. At the last

follow-up, radiographic analysis showed a

bone resorption of 0.99mm for test group1(Time 1: 0.74mm, SD: 0.39mm; Time 2:

0.95mm, SD: 0.35mm; Time 3: 0.99mm,

SD: 0.417mm; Time 4: 0.99mm, SD:

0.42mm), 0.83mm for test group2 (Time

1: 0.64mm, SD: 0.40mm; Time 2:

0.78mm, SD: 0.35mm; Time 3:

0.82mm, SD: 0.362mm; Time 4:

0.87mm, SD:0.43mm) and 0.64mm

for test group3 (Time 1: 0.41mm,

SD: 0.28mm; Time 2: 0.51mm,

SD: 0.29mm; Time 3: 0.56mm, SD:

0.31mm; Time 4: 0.64mm, SD:

0.32mm). Control group mean value was

1.48mm (Time 1: 1.23mm, SD: 0.67;

Time 2: 1.46mm, SD: 0.53mm; Time 3:

1.49mm, SD: 0.544mm; Time 4:

1.48mm, SD: 0.42mm) (Fig. 5). For each

time point, all test groupmean values were

statistically significantly lower (Po0.005)

compared with control group values.

Furthermore, there was a significant

inverse correlation (' 0.63, Po0.001,

Pearson) between the amount of abut-

ment–implant diameter mismatching and

the extent of marginal bone loss.

Discussion

In this study, over a period of almost 3

years, it could be demonstrated that

implants restored according to the

platform-switching concept experienced

significantly less marginal bone loss than

implants with matching implant–

abutment diameters. In addition, it was

observed that marginal bone levels were

even better maintained with increasing

implant/abutment mismatching.

First limitation of this study was that

standardized radiographic evaluation only

provided information about mesial and dis-

tal bone level. Buccal and oral bone levels

were not evaluative.

One limitation of the present study de-

sign was that, not all patients could receive

all four configurations of implants/abut-

ments under study, due to limited space

in the edentulous areas. However, a possi-

ble influence of the factor patient on the

outcomes could be ruled out. In only four

patients (out of the 31 at 21-month follow-

up and 26 at the 33-month follow-up), the

order of implant types with regard to bone

loss deviated from that shown by the mean

values. More specifically, in three patients,

a 4.3mm implant experienced slightly less

bone loss than a 4.8mm implant with

wider platform, and in one patient, a

4.3mm implant showed slightly more

bone loss than a 3.8mm control implant.

In other words, in the vast majority of

patients, the marginal bone level altera-

tions observed followed the same pattern

– confirming the ranking sequence docu-

mented by the mean values.

Another limitation for the evaluation of

marginal bone level alterations is the fact

that standardized conventional radiographs

only provide information about mesial and

distal bone levels. However, it has to be

realized that this limitation applies to all

studies of this kind (Abrahamsson & Ber-

glundh 2009; Lang & Jepsen 2009).

It can be speculated that the findings of a

reduced bone loss at platform-switched

implants in the present study may be

related to their increased implant diameter

rather than to the platform. However,

comparative studies of implants with dif-

ferent diameters in relation to marginal

bone loss did not show different outcomes

(Friberg et al. 2002). Further studies

could be helpful to clarify the relevance of

Fig. 3. Periapical radiographs of a patient treated with 4.8, 4.3 and 5.5mm implants (a) at the time of implant

insertion, (b) abutment connection and (c) 33 months after surgery. Regardless of implant diameter, the

diameters of the cover screw, the healing abutment and the prosthetic abutment were always 3.8mm.

Fig. 2. Periapical radiographs of a patient treated with 3.8 and 5.5mm implants (a) at the time of implant

insertion, (b) abutment connection and (c) 33 months after surgery. Regardless of implant diameter, the

diameters of the cover screw, the healing abutment and the prosthetic abutment were always 3.8mm.

Fig. 4. Mean marginal bone-level alterations over the observation period for test and control groups.

Canullo et al &Platform switching

118 | Clin. Oral Impl. Res. 21, 2010 / 115–121 c# 2009 John Wiley & Sons A/S

wide-diameter implants rather than platform

switching in preserving marginal bone.

In the present study, implants with

micro-threads in the marginal portion

were used. The possible influence on

such a design on the marginal bone loss

was addressed in an experimental study in

dogs (Abrahamsson & Berglundh 2006).

The authors reported that the marginal

bone level was located at a more coronal

position at implants when compared with

implants without micro-threads in the

marginal portion, and suggested that the

possible positive effects may be related to

the osseous healing events after implant

placement rather than bone preservation

during function.

The unintentional perforation of sub-

merged two-stage implants during healing

can result in significant bone destruction.

Van Assche et al. (2008) showed, in a

retrospective study aimed to determine

the consequence of early cover screw ex-

posure, 2mm of mean bone re-modeling.

Therefore, in the present study, implants

with early exposition were excluded from

further analysis.

The most extensive marginal bone level

alterations were seen at the first follow-up

after 9 months, whereas, in the 2-year

observation period, thereafter, only minor

further bone loss could be observed. Pre-

vious experimental and clinical studies, in

fact, showed that the most pronounced

marginal bone level changes were identi-

fied after surgical trauma resulting from

implant installation and abutment connec-

tion, while after functional loading, only

minor signs of bone loss occurred (Bragger

et al. 1998; Astrand et al. 2004; Berglundh

et al. 2005; Broggini et al. 2006).

During the first year of loading, particu-

larly two-piece implants were frequently

associated with crestal bone loss of about

1.5–2mm (Albrektsson et al. 1986; Smith

& Zarb 1989; Jung et al. 1996). The result

of the present study, where control implants

exhibited mean marginal bone-level altera-

tions of 1.49mm are well in line with these

previous findings. Several explanations for

these observed changes in crestal bone

height have been suggested; some authors

discussed a potential role of the microgap at

the implant–abutment interface for the bac-

terial colonization of the implant sulcus

(Mombelli et al. 1987; Ericsson et al.

1995; Hermann et al. 2001a, 2001b; King

et al. 2002), while others described the

establishment of an adequately dimen-

sioned biological width to be associated

with marginal bone resorption at sites with

a thin mucosa (Berglundh & Lindhe 1996;

Hermann et al. 2000) and in conjunction

with abutment re-connection (Abrahams-

son et al. 1997). Butt–joint connections

associated with implant–abutment config-

urations with matching diameters have

been linked to inflammation, an inflamma-

tory cell infiltrate and bone loss of 1.5–

2mm (Broggini et al. 2003, 2006).

The reasons for the reduced bone loss

observed in platform-switched implants in

the present study can only be speculated

upon. The horizontal inward re-position-

ing of the implant–abutment interface has

been suggested to overcome some of the

problems associated with two-piece im-

plants. Platform switching may increase

the distance between the abutment-asso-

ciated inflammatory cell infiltrate and the

marginal bone level, and thereby decrease

its bone-resorptive effect. Also, there

might be a reduction in the amount of

marginal bone loss necessary to expose a

minimum amount of implant surface to

which the soft tissue can attach (Lazzara

& Porter 2006). These assumptions are

supported by recent animal studies (Jung

et al. 2008; Weng et al. 2008; Cochran

et al. 2009) and human histological ob-

servations (Degidi et al. 2008; Luongo

et al. 2008).

Clinical case series of immediate implants

(Canullo & Rasperini 2007; Calvo-Guirado

et al. 2009) and prospective-controlled stu-

dies have evaluated bone responses (Vela-

Nebot et al. 2006; Cappiello et al. 2008;

Hurzeler et al. 2008; Canullo et al. 2009a;

Prosper et al. 2009) as well as soft-tissue

responses (Canullo et al. 2009b) to platform-

switched implants. The magnitude of the

marginal bone level alterations observed

varied among the studies. This may be due

to different observation periods (6–24

months), implant types, study populations

and radiographic analysis methods. How-

ever, compared with control implants with

matching abutment–implant dimensions,

these studies could collectively demonstrate

statistically significantly less marginal bone

loss as assessed on radiographs at implants

restored according to the platform-switching

concept. The present study, with a longer

follow-up of almost 3 years, not only con-

firmed these data but could also – for the

first time – establish a relationship between

the extent of platform switching and the

amount of marginal bone loss. These find-

ings could possibly be attributed to a wider

space for horizontal repositioning of the

biological width and/or a better distribution

of loading stress at the bone/implant inter-

face.

Future experimental and clinical studies

will help to unravel the biological processes

involved as well as the significance of these

findings for long-term implant success.

Fig. 5. Marginal bone loss (means $ SD) in the test and control groups 9, 15, 21 and 33 months after surgery.

For each time point, all test groupmean values were statistically significantly lower compared with the control

group values (P(0.005, ANOVA, followed by Scheffe).

Canullo et al &Platform switching

c# 2009 John Wiley & Sons A/S 119 | Clin. Oral Impl. Res. 21, 2010 / 115–121

Acknowledgements: We highlyappreciated the skills and commitmentof Dr Audrenn Gautier for languagesuggestions and Dr Roberto Cocchettofor the effective help in protocol

finalization. Furthermore, the authorsare particularly grateful to Dr ValeriaCaponi, Claudia Muollo, Dr AndreaDiociaiuti, Dr Paola Cicchese and DrGiuseppe Goglia for the friendly

support in radiographic measure-ments and patient recruitment. Theauthors declare that there are noconflicts of interest. This study wasself-supported.

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