Post on 27-May-2018
gabri.grusovin@tiscali.it; r_pistilli@libero.it; fguali@tin.it; leest007@hanmail.net;
anyridge@imegagen.com; holeonemedical@libero.it; sian.matthews@megagen.org;
h.maghaireh@yahoo.co.uk; yoojaw@hanmail.net; jacopo.buti@manchester.ac.uk
Version 03/03/15
Dental implants with internal versus external connections: 1-year post-loading results
from a pragmatic multicenter randomised controlled trial
Marco Esposito, Hassan Maghaireh, Roberto Pistilli, Maria Gabriella Grusovin, Sang Taek
Lee, Federico Gualini, Jungtaek Yoo, Jacopo Buti
Marco Esposito, DDS, PhD, free lance researcher and Associated Professor, Department of
Biomaterials, The Sahlgrenska Academy at Göteborg University, Sweden
Hassan Maghaireh, BDS, MFDS, MSc, Lecturer in Implant Dentistry, University of
Manchester, UK
Roberto Pistilli, MD, Resident, Oral and Maxillofacial Unit, San Filippo Neri Hospital,
Rome, Italy
Maria Gabriella Grusovin, DDS, private practitoner in Gorizia, Italy
Sang Taek Lee, DDS, private practitioner, Suncheon, South Korea
Federico Gualini, MDS, private practitoner in Lovere and Bergamo, Italy
Jungtaek Yoo, DDS, private practitioner, DaeJeon, South Korea
Jacopo Buti, DDS, PhD, Clinical Lecturer in Periodontology, School of Dentistry, The
University of Manchester, United Kingdom
1
Correspondence to: Dr Marco Esposito, Casella Postale 34, 20862 Arcore (MB), Italy. E-
mail: espositomarco@hotmail.com
Key words: Complication, dental implant, external connection, internal connection
Running title: Internal versus external connection
Abstract
Purpose: To evaluate advantages and disadvantages of identical implants with internal or
external connections.
Materials and Methods: Two-hundred-thirty patients with any type of edentulism (single
tooth, partial and total edentulism) requiring one implant-supported prosthesis were
randomly allocated in two equal groups to receive either implants with external connection
EC) or implants of the same type but with internal connection (IC) (EZ Plus, MegaGen
Implant Co. Lld. Gyeongbuk, South Korea) at 8 centres. Due to slight differences in implant
design/components IC implants were platform switched while EC were not. Patients were
followed for 1 year after initial loading. Outcome measures were: prosthesis/implant failures,
any complication, marginal bone level changes and clinician preference assessed by blinded
outcome assessors.
Results: One-hundred-seventeen patients received 205 EC implants and 113 patients 202 IC
implants. Seven patients dropped-out with 12 EC implants and four patients with 5 IC
implants, but all remaining patients were followed up to 1-year post-loading. Three centres
did not provide any periapical radiographs. Two prostheses supported by EC implants and
one by IC implants failed. Three EC implants failed in three patients versus two IC implants
in one patient. EC implants were affected by nine complications in nine patients versus seven
complications of IC implants in seven patients. There were no statistically significant
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differences for prosthesis/implant failures and complications between the implant systems.
One year after loading, there were no statistically significant differences in marginal bone
level changes between the two groups (P=0.0629) and both group lost bone from implant
placement in a statistical significant way: 0.98 mm for the EC implants and 0.85 mm for the
IC implants. Five operators had no preference and three preferred IC implants.
Conclusions: Within the limitations given by the difference in neck design and platform
switching between EC and IC implants, preliminary short-term data (1-year post-loading) did
not show any statistically significant differences between the two connection types, therefore
clinicians could choose whatever they prefer.
Conflict of interest statement: This trial was partially funded by MegaGen Implant Co. Lld.
Gyeongbuk, South Korea, the manufacturer of the implants evaluated in this investigation,
however data belonged to the authors and by no means did the manufacturer interfere with
the conduct of the trial or the publication of the results.
INTRODUCTION
Implant-supported prostheses are an effective and reliable treatment for replacing
missing dentition. The success of implant-supported prostheses is mainly based on the
"integration" of dental implants in newly formed bone. This process is generally known as
"osseointegration". Literally thousands of new dental implant design, materials and surface
technologies are continuously developed to further improve the outcome of implant therapy,
many of them claiming superiority over competitors. There are many randomised controlled
trials comparing different dental implant made of various materials and having different
design, and surface characteristics.(2) Most of the dental implants used nowadays have a
connection which allows a stable more or less rigid connection to an abutment or directly to
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the dental prosthesis. There are connections allowing the retention via a screw of the
abutment/prosthesis and others in which the abutment is permanently cemented. Connections
usually have various shapes (such as triangles, hexagons, octagons, etc.) and other
mechanism to minimise the risk of movements and screw loosening
The connections more commonly used are the screw-retained ones, since abutments
can be removed if needed. Screw-retained connections can divided in two major groups:
external and internal connections. The external connection is characterised by a mechanism
on the top of the screw to block rotation movements which favours unscrewing. The most
widely used external connection is the "external hexagon" originally used on the Branemark
implant system. The external hexagon connection can be considered the "gold-standard" with
many manufacturers who adopted it, thought there are other types of external connections.
The internal connection is characterised by the presence of the connection mechanism inside
the implant body. There are many different types of internal connections with and without
anti-rotating mechanism and a gold standard here is not easy to identify, though the so called
"conometric" connections have many estimators.
The implant-abutment connection is believed to play an important role in the outcome
of the implant therapy and almost each dental implant manufacturer developed its own
unique connection. These connections are subjected to an aggressive commercial marketing
with many manufactures and clinicians claiming the superiority of one connection over the
others. Interesting to say, despite that osseointegrated dental implants have been in use for
almost half century, not a single well designed and conducted randomised controlled trial
(RCT) has been conducted to specifically investigate the role, if any, of different implant
connection, by evaluating implants having as the only difference their connections. Since
there are no yet any valid evidence-based clinical data evaluating whether one implant
connection could be superior to the others and whether if and how the different connection
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types could influence the clinical outcome of implant-supported rehabilitations in terms of,
complications, peri-implant marginal bone loss, aesthetics and easy to use, it would be
desirable to have RCTs evaluating these aspects. It would also be interesting to evaluate
whether the preferable connection type could be different depending on the numbers of
implants supporting the same prosthesis (single crown, 2 to 3 connected implants or more
than 3 implants).
The aim of this pragmatic multicentre randomised controlled trial (RCT) of parallel
group design was to evaluate advantages and disadvantages of identical implants with
internal or external connections. The secondary aim was to conduct subgroups analyses
between prostheses supported by one, two to three or more than three implants to see whether
one connection type could be better when different numbers of implants are used. This is the
first report in a series presenting clinical outcome at 1-year post-loading. Ideally, further
reports on this trial will be published after the completion of 5 and 10-year follow-ups. The
present article is reported according to the CONSORT statement for improving the quality of
reports of parallel-group randomised trials (http://www.consort-statement.org/).
MATERIALS AND METHODS
Any patient requiring one implant-supported prosthesis, being 18 years or older, and
able to understand and sign a written informed consent form was eligible for this trial. Only
one prosthesis per patient was to be considered for this trial which could only be supported
by the type of implants dictated by the randomization procedure. This trial was designed as a
pragmatic trial in order to be as close as possible to the clinical reality. Broad inclusion
criteria were used including, for instance, any type of bone quality, any jaw location and
heavy smokers. Clinicians were allowed to choose the treatment option they considered to be
the optimal for the patient to be rehabilitated (for instance flapless implant placement,
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immediate post-extractive implants, minor augmentation procedures at implant placement,
immediate, early or delayed loading, submerged or non-submerged techniques, etc.) at their
discretion.
Pre-operative radiographs (intra-oral, panoramic, CT scans or other radiographic
examinations at discretion of the operators) together with clinical inspection were used to
determine bone volumes. Exclusion criteria were:
general contraindications to implant surgery
irradiation in the head and neck area
immunosuppressed or immunocompromised patients,
treated or under treatment with intravenous amino-bisphosphonates
untreated periodontitis
poor oral hygiene and motivation
uncontrolled diabetes,
pregnancy or nursing
substance abusers
psychiatric problems or unrealistic expectations
lacking antagonistic occlusal surfaces at the study implant-supported prosthesis at
implant loading
acute/purulent infection in the area intended for implant placement
unrestorable with a retrievable prosthesis to allow individual implant stability assessment
(with exceptions of single implants)
participation in other studies, if the present protocol could not be properly followed
referred only for implant placement
unable to commit to 10-year follow-up.
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All patients received thorough explanations and signed a written informed consent
form prior to being enrolled in the trial to document that they understood the scope of the
study (including procedures, follow-up evaluations, and any potential risks involved), were
allowed an opportunity to ask questions pertaining to this study, and were apprised of
treatment alternatives. The study was open to qualifying patients without regard to sex or race.
Patients were categorised in three groups according to what they declared: non-
smokers, moderate smokers (up to 10 cigarettes per day), and heavy smokers (more than 10
cigarettes per day). For patients needing more than one implant-supported prosthesis, the
operator could chose which one to include in the study at the screening visit.
Patients were recruited and treated in eight private practices by experienced operators.
Five practices were in Italy (Drs Felice, Grusovin, Gualini, Pistilli and Scarano) and three in
South Korea (Drs Lee 1, Lee 2 and Yoo). Each dentist should have treated 30 patients. All
the follow-up visits were done at the respective treating centres. Originally 10 centres agreed
to participate in the study but two centres did not provide any patient data.
The investigational devices were commercially available tapered titanium screw-
shaped EZ Plus dental implants (MegaGen Implant Co. Lld. Gyeongbuk, South Korea) with
sand-blasted acid-etched surface up to the neck either with external (Fig 1a-d) or internal (Fig
2a-c) connection. The external connection was the standard external hexagon of the
Branemark System (Fig 1a-c), whereas the internal connection was an 11° morse taper
connection (Fig 2a-c) that produces a conical seal forming a cold welding between the
abutment and the implant. The only differences between the two implants apart the
connections are the presence of a bevel at the implant neck of the IC (designed to allow
platform mis-matching) which is not present in the EC design (Figs 1a and 2a) and a different
neck design for the implants with external connection of 3.3 mm diameter (Fig 1d). The neck
was designed differently in order to adapt the standard external hexagon on a small diameter
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implant. The other difference involved the abutment shape since those designed for the IC
group had to be platform switched (Fig 3 and 4). Operators were free to choose implant
lengths (7, 8.5, 10, 11.5, 13 and 15 mm) and diameters (3.3, 4, 4.5 and 5.5 mm) according to
clinical indications and their preferences.
Clinical procedures
Patients received prophylactic antibiotic therapy: 2 g of amoxicillin (or 600 mg of
clindamycin if allergic to penicillin) one hour prior to surgery and rinsed for one minute with
0.2% chlorhexidine. All patients were treated under local anaesthesia. Tooth extractions,
when needed, were performed as atraumatically as possible attempting to preserve the buccal
alveolar bone. Extraction sockets were carefully cleaned from any remains of granulation
tissue. The decision to elevate or not the flap was left to the individual clinician. The standard
implant site preparation procedure as recommended by the implant manufacturer was used.
In case of soft bone a final drill of one smaller size than the conventional procedure was used
to underprepare the implant site. During implant site preparation bone quality was
subjectively assessed and divided into hard, medium and soft. Once the implant site
preparation was completed, the operator was informed whether the implants to be placed had
to be with external or internal connections, according to a parallel-group study design with
two arms, by opening the sequentially numbered sealed envelope corresponding to the
patient recruitment number. Implants were placed with the neck flush to the crestal bone
level with the exception of post-extractive implants that were placed about two mm below
the palatal bone level and more palatally.
Clinicians were free to decide whether to load the implants immediately early or
conventionally, to submerge or to leave them non-submerged for the healing period they
decided but they had to ensure that both groups were treated in a similar way. Just after
implant placement, intraoral radiographs (baseline) were made with the paralleling technique.
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If bone levels around the study implants were hidden or difficult to estimate, a second
radiograph was made. Ibuprofen 400 mg was prescribed to be taken 2-4 times a day during
meals, as long as required. Patients were instructed to use 0.2% chlorhexidine mouthwash for
one minute twice a day for two weeks and to avoid brushing and trauma on the surgical sites.
Postoperative antibiotics were only prescribed to patients subjected to bone augmentation
procedures: 1 g of amoxicillin twice a day for six days. Patients allergic to penicillin were
prescribed 300 mg of Clindamycin twice a day for six days. Within one week all patients
were recalled and checked.
Clinicians were also free to choose screw-retained or cemented restorations with
provisional cement, to load the implants directly with definitive restorations, and whether to
use metal-ceramic or metal-composite restorations (single crowns could be also in full
ceramic). Overdentures could also be used.
Periapical radiographs of the study implants were also taken at initial loading and 1
year after loading and individual implants were tested for stability: prostheses connecting
more than one implants were removed and a torque of 20 Ncm was applied to the individual
implants, whereas stability of implant-supported crowns was tested using the handles of two
instruments.
Patients were enrolled in an oral hygiene program with recall visits planned at least
every 6 months for the entire duration of the study.
Outcome measures
This study tested the null hypothesis that there were no differences in the clinical
outcomes between the two connection types against the alternative hypothesis of a
difference. Outcome measures were:
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Prosthesis failure (primary outcome measure): whether it will not be possible to place
the prosthesis due to implant failures, secondary to implant losses or remake of a
definitive prosthesis for any reasons.
Implant failure (primary outcome measure): implant failure was defined as implant
mobility and/or any infection dictating implant removal or any mechanical failure
rendering the implant unusable, such as implant fracture or deformation of the
implant-abutment connection. The stability of each implant was measured manually
by tightening the abutment screw with a wrench delivering a torque of 20 Ncm or by
assessing the stability of single crowns using the handles of two instruments.
Any complications and adverse events (primary outcome measure) were recorded and
reported by implant types.
Peri-implant marginal bone level changes (secondary outcome measure) evaluated on
intraoral radiographs taken with the paralleling technique at implant placement, at
initial loading and 1 year after loading. Radiographs were scanned in TIFF format
with a 600 dpi resolution, and stored in a personal computer. Peri-implant marginal
bone levels were measured using the UTHSCSA Image Tool 3.0 (The University of
Texas Health Science Center, San Antonio, USA) software. The software was
calibrated for every single image using the known implant neck diameter.
Measurements of the mesial and distal bone crest level adjacent to each implant were
made to the nearest 0.01 mm and averaged at patient level and the at group level. The
measurements were taken parallel to the implant axis. Reference points for the linear
measurements were: the most coronal margin of the implant collar and the most
coronal point of bone-to-implant contact.
Operator preference (secondary outcome measure) for the connection type was
recorded at delivery of the definitive prostheses and 1 year after loading. It was
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expressed in the following way as: i) internal connection, ii) external connection, iii)
no preference. Reasons for preference were recorded.
At each center a local blind outcome assessor evaluated implant stability. The implant
type was not recognizable when assessing implant stability. One dentist (Hassan Maghaireh)
not involved in the treatment of the patients performed all radiographic assessments without
knowing group allocation, however IC implants could be identified on radiographs due to the
presence of the neck bevel and of platform switched abutments.
Methodological aspects
Prior to this study there were no clinical data from comparative data on which basing
a reliable sample size calculation. It was decided to include 30 patients at each of the 10
planned centres for a total of 300 patients, 150 patients randomised to each group.
Ten computer generated restricted random lists were created. Only one investigator
(Marco Esposito), who was not involved in the selection and treatment of the patients, knew
the random sequence and had access to the random list stored in a pass-word protected
portable computer. The random codes were enclosed in sequentially-numbered, identical,
opaque, sealed envelopes. Only after the implant sites were prepared, the envelope
corresponding to the patient recruitment number was opened and the clinician knew whether
to place an implant with internal or external connection. Therefore, treatment allocations
were concealed to the investigators in charge of enrolling and treating the patients.
All data analyses were carried out according to a pre-established analysis plan. A
dentist with expertise in statistics (Jacopo Buti) analysed the data. Differences in the
proportion of patients with prosthesis failures, implant failures and complications
(dichotomous outcomes) were compared between groups using the Fisher’s exact probability
test. Differences of means at patient level for continuous outcomes (bone levels) between
groups were compared by t-tests. Comparisons between each time points and the baseline
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measurements were made by paired tests, to detect any changes in marginal peri-implant
bone levels. Differences in radiographic marginal bone levels (continuous outcome variable)
between groups were estimated by creating two linear multilevel models at loading and 1
year changes, respectively - at 2 levels (Centre and Patient). The explicative variables used at
the Patient level were “Implant” (1=Internal Connection, 2=External Connection) and
“Baseline rx bone level” (mm). Differences among centres for dichotomous outcomes were
calculated using the chi-squared test. Pair-wise between-centres differences in mean peri-
implant marginal radiographic bone level changes (continuous outcome) were estimated
using Tukey HSD test after analysis of covariance (ANCOVA) with baseline radiographic
levels as a covariate.
A subgroup analysis, comparing the two implant connections by the following subgroups i)
single crowns; ii) prostheses supported by two to three connected implants; and iii)
prostheses supported by more than three implants, was to be conducted in the attempt to see
whether there was a preferable connection type depending on the number of implants
supporting the same prosthesis. However this was not done since no statistically significant
differences were detected between groups. We my perform this subgroup analysis at 5 year-
post-loading. All statistical comparisons were conducted at the 0.05 level of significance.
RESULTS
Two of the 10 centres never supplied any data. In total at least 331 patients were screened for
eligibility, and 101 patients were not included for the following reasons: 57 patients did not
want to participate into a clinical trial, 26 patients were referred only for implant placement;
seven patients unable to commit to a 10 years follow-up; five patients because were treated
or were under treatment with oral bisphosphonates, four patients had the implant to be
connected to other implant types; two patients for poor oral hygiene/motivation. All patients
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had their sites treated according to the allocated interventions. Eleven patients with 17
implants dropped-out before the completion of one year post loading (Table 1): with one
centre (Dr Yoo) accounting for 55% of all drop-outs.
Drop-out from the EC group:
one patient with three implants never come back for delivery of the prosthesis due to
lack of time (Dr Lee 1);
one patient with one implant died for throat cancer (Dr Scarano);
one patient with one implant moved out of the country (Dr Yoo).
Drop-out from the IC group:
one patient with one implant died just before the 1-year follow-up without having
experienced implant failures or complications (Dr Lee 1);
one patient with two implants was depressed and did not attend the follow-up but
reported no problem for the implant-supported prosthesis (Dr Grusovin);
one patient with one implant moved to another country (Dr Scarano);
three patients with one, two and three implants, respectively, did not come back for
the one year control (Dr Yoo);
two patients with one implant each did not come back for the prosthetic rehabilitation
(one patient) and for the one year control (one patient) because living too far away
from the clinic (Dr Yoo).
The data of all remaining patients were included in the statistical analyses. The main
protocol deviations are summarised in Table 2. Additional protocol deviations were:
Drs Felice, Scarano and Lee 1 did not supply any radiographic data.
Dr Scarano did not record the number and reasons of those patients screened as
potential candidates for the trial but did not match the inclusion criteria and included
more than one prosthesis per patient in 11 patients.
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Dr Lee 1 deliberately treated 20 patients instead of 30.
Dr Lee 2 did not record the number and reasons of those patients screened as
potential candidates for the trial but did not match the inclusion criteria and in
addition excluded patients of 'old age'.
Patients were recruited and implants were inserted from January 2009 to November
2011. The follow-up for all patients was 1-year post-loading.
The main baseline patient and intervention characteristics, divided by study group,
are presented in Table 3. There were no apparent significant baseline imbalances between
the two groups. In total 205 EC and 202 IC implants were placed in 117 and 113 patients,
respectively.
Two prostheses failed in the EC group (one was actually delivered with delay since
the implant was found mobile at abutment connection was successfully replaced) versus one
prosthesis (not delivered due to implant failures) in the IC group. There was not statistically
significant difference for patients experiencing prosthesis failures between groups (P=1.0000,
diff.=-0.01, 95% CI -0.05 to 0.03).
Three implants failed in three patients of the EC group versus two implants in one
patient of the IC group (Table 4). There was not statistically significant difference for
patients experiencing implant failures between groups (P=0.6217, diff.=-0.02, 95% CI -0.06
to 0.02). The following implant failures occurred at EC implants:
One patient, smoking up to 10 cigarettes per day, who received one post-
extractive implant (11.5 x 4 mm) in position 21 in soft bone which was
augmented at placement, lost the implant with its provisional crown 7 months
after placement for mobility and inflammation.
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One non-smoker patient lost one out of two post-extractive implants, in
position 35 (4 x 10 mm) at abutment connection for mobility. It was
successful replaced with another implant.
One non-smoker patient lost one out of four implants, in position 25 (4 x 10
mm) at abutment connection for mobility. The implant was not replaced and a
bar-supported overdenture was made on the three remaining implants.
The following implant failures occurred at EC implants:
One patient, smoking more than 10 cigarettes per day received two implants
(10 x 4 mm and 11.5 x 4 mm) in hard bone in position 46 and 47. The surgery
was painful and pain persisted postoperatively. After 2 weeks, the bone was
exposed and necrotic at both implants, which were removed. These implants
replaced two implants which failed previously and were not replaced.
Nine complications occurred at nine EC implants in nine patients and seven
complications at seven IC implants in seven patients (Table 5). There was not statistically
significant difference for patients experiencing complications between groups (P=0.7964,
diff.= 0.01, 95% CI -0.06 to 0.08). The following complications occurred at EC implants:
The abutment screw become loose once at single implants carrying
provisional crowns in three patients. Crowns were drilled and screw
retightened.
Loosening of the abutment screw under a provisional cross-arch prosthesis.
Screw retightened.
The abutment screw become loose once at a single implant one month after
delivery of a definitive screw-retained crown in one patient. The screw was
retightened at 30 Ncm.
15
The contact point between the implant-supported prosthesis and the adjacent
natural tooth was lost in three patients. Prostheses were unscrewed and
reshaped in the laboratory.
One implant out of two in the same patient, in position 35, was affected by
peri-implantitis at the 1 year follow-up and was surgically treated.
Subsequently the implant failed, however this failure occurred after the 1 year
follow-up and will be reported in a future publication.
IC implants were affected by the following complications:
Post-operative infection with bone exposure leading to failure of two
implants.
Loosening of one healing abutment after one week which was retightened.
The abutment screw become loose once at a single implant carrying a
provisional crown in one patient. The crown was drilled and the screw
retightened.
Loosening of the definitive crown one month after delivery. The abutment
screw was retightened at 35 Ncm.
The abutment screw become loose once on a single implant 4 months after
delivery of a definitive cemented crown in one patient. The screw was
replaced.
Loosening of one definitive crown and one definitive partial prosthesis after
three months in two patients. Screws were retightened at 30 Ncm.
Regarding radiographic peri-implant marginal bone levels, at baseline (implant
placement), there was an almost statistically significant difference (P=0.052; Table 6) of 0.1
mm with higher bone levels at IC implants. Both groups gradually lost marginal peri-implant
bone in a highly statistically significant way at loading and 1 year after loading (P<0.001;
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Table 7). At loading, patients with EC implants lost an average of 0.59 mm peri-implant
bone versus 0.54 mm for patients with IC implants (Table 7). One year after loading, patients
with EC implants lost an average of 0.98 mm peri-implant bone versus 0.85 mm for patients
with IC implants (Table 7). Multilevel analysis showed no statistically significant difference
between the two groups for peri-implant bone loss at loading (P=0.311; Table 8) and 1 year
after loading (P=0.0629; Table 9).
Operator preference: Five operators (Drs Felice, Pistilli, Yoo, Lee 1 and Gualini) had
no preference between the two connections and three operators preferred the IC connection
(Drs Scarano, Grusovin and Lee 2). Reasons to prefer the IC connection were 'simpler to
handle at abutment connection procedures' (Drs Grusovin and Lee 2) and 'smaller micro-gap
at the implant-abutment connection' (Dr Scarano).
The comparison between centres is presented in Table 10 (clinical outcomes; eight
centres) and 11 (radiographic data; five centres). There were no statistically significant
differences between centres for complications and implant failures, but there are difference
for marginal bone level changes, with Dr Pistilli and Dr Gualini losing about the double
amount of bone than the other three centres.
DISCUSSION
This is the first follow-up report of a planned series aimed at investigating which could be the
advantages and the disadvantages using internal or external connections. In order to perform
a reliable evaluation only the type of connection has to be different, all other implant
characteristics (implant material, surface characteristics and implant shape) remaining
exactly the same. The EZ Plus implant system was chosen because it almost had all the
required characteristics (the main difference were the bevel present at the coronal portions of
IC implants (Fig 2a) and the different neck of the 3.3 mm diameter EC implants (Fig 1d).
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Another reason for choosing the EZ plus systems was that the implant manufacturer was glad
to sponsor an independent conducted trial to evaluate this aspect. At 1 year post-loading, no
statistically significant differences were observed, the number of complications was low and
similar for both implant types. On one hand, due to the relatively small sample size of this
study and moreover to the short follow-up (only 1 year after loading) it would be hazardous
to conclude that there are no differences between the two connection types. On the other
hands, no statistically or clinically significant differences were observed one year after
loading. In order to draw more reliable conclusions, we need to wait for 5-year data, since the
differences which were not apparent at one year after, may become evident over time. We
decided not to implement the subgroup analysis, planned at protocol preparation, comparing
the outcomes for ì) single crowns; ii) prostheses supported by two to three connected
implants; and ii) prostheses supported by more than three implants, because lack of
statistically significant differences between the two connection type, too few prostheses
supported by more than three implants, and too short follow-up. Such analyses could be still
performed at when the 5-year data will be available.
Some comments could be done on the few complications which might be related
specifically to the connection type. The four early abutment screw loosening (three in EC and
one in IC group) reported by Dr Pistilli at single implants with provisional crowns can be
explained by the habit of the operator to screw manually the abutment screws holding
provisional crowns with torques below 10 Ncm. When placing definitive crowns the surgeon
applied a torque of 25 Ncm and no more screw loosening occurred.
The only parameter which was close to be statistically significant was the
radiographic peri-implant marginal bone levels. Indeed at baseline (implant placement), the
difference was almost statistically significant (P=0.052, Table 6). However, we are
discussing of a difference of 0.1 mm which bears no clinical relevance. One year after
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loading the statistical model used that considered also the baseline difference showed again a
P-value close to statistical significance (P=0.0629), meaning a bit more than 0.2 mm more
bone loss at EC implants, which again does not appear to be clinical relevant. Only longer
follow-ups could help us to understand whether this specific type of internal connection,
brings additional appreciable benefits over the external connection. We also need to stress
that IC implants were designed to allow platform switching, but in this case, not clinical
advantages could be clearly established by platform switching. Regarding platform
switching, contradictory results have been presented by different authors: some RCTs
showed significantly less bone loss at platform switched implants, whereas other RCTs did
not show any difference. Nevertheless, those RCTs that demonstrated a statistically
significant difference, showed a difference in favour of platform-switched implants of about
0.3 mm at 1 year post-loading which is very close to our findings. The comparisons between
various centres yielded an intriguing observation, while there were no difference for failures
and complication between the eight centres reporting this information, there was statistically
more bone loss (about the double) at two of the five centres who reported radiographic data.
We do not have an tentative explanation or a convincing hypothesis for this difference, but
some difference between treatment protocols could be present.
Five operators had no preference with regard to the internal or external connection
types, whereas three operators preferred IT implants and none ET implants. The numbers
were too low to allow for a statistical analysis, however two dentists pointed out that their
preference was justified by easier prosthetic procedures with the internal connection, which
is understandable. Actually, according to the present findings, operators can choose the
connection type, according to their preferences. It could be also hypothesised that internal
connections are more user-friendly when single implants or prosthesis supported by two or
three implants are used. On the contrary, it may be that in the presence of multiple implants,
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as when rehabilitating an edentulous jaw, the external connection could be more forgiving at
impression taking than an internal one. However, these are simply hypotheses that need to be
verified.
It is also interesting to observe that despite clinicians were left the option to
choose the time of implant loading, only one and two patients were subjected to immediate or
early loading procedures, respectively. This may suggest that immediately loading
procedures for single implants or small partial fixed prostheses are not so commonly
performed.
There are no other published randomised controlled trials comparing internal versus
external connections, so meaningful comparisons with other similar RCTs cannot be made at
the present stage.
The main limitations of the present trial are: i) the design of the two evaluated
implants was not identical but additional platform switching features were added to the IC
implants which may have slightly favoured IC implants; ii) some of the protocol deviations
and in particular the lack of periapical radiographic from three centres (80 patients in total);
and iii) the high drop-out rate from one of the centres.
Regarding the generalisation of these preliminary results, due to the pragmatic nature
of the present study design, similar results should be obtained by other operators treating
patients with similar procedures.
CONCLUSIONS
It might be imprecise to draw definitive conclusions about the role of internal and external
connections on the clinical outcome due to some minor confounding factors (different neck
design imposing platform switching at IC implants), however, no statistically significant
20
differences were observed, therefore the choice of the type of connection can be simply
based on clinician preference.
ACKNOWLEDGMENTS
Dr Pietro Felice, Antonio Scarano and Jung Sam Lee are acknowledged to have participated
in this trial.
REFERENCES
1. Brånemark P-I, Hansson BO, Adell R, Breine U, Lindström J, Hallén O, et al. Osseointegrated implants in the treatment of the edentulous jaw. Experience from a 10-year period. Stockholm: Almqvist & Wiksell International, 1977.2. Esposito M, Ardebili Y, Worthington HV. Interventions for replacing missing teeth: different types of dental implants. Cochrane Database of Systematic Reviews 2014: Chichester, UK: John Wiley & Sons, Ltd.3. Goldstein H. Multilevel statistical models. London: Edward Arnold, 2003.4. Canullo L, Goglia G, Iurlaro G, Iannello G. Short-term bone level observations associated with platform switching in immediately placed and restored single maxillary implants: a preliminary report. International Journal of Prosthodontics 2009;22:277-282.5. Guerra F, Wagner W, Wiltfang J, Rocha S, Moergel M, Behrens E, et al. Platform switch versus platform match in the posterior mandible - 1-year results of a multicentre randomized clinical trial. Journal of Clinical Periodontology 2014;41:521-529.6. Enkling N, Johren P, Klimberg V, Bayer S, Mericske-Stern R, Jepsen S. Effect of platform switching on peri-implant bone levels: a randomized clinical trial. Clinical Oral Implants Research 2011;22:1185-1192.7. Meloni SM, Jovanovic SA, Lolli FM, Pisano M, De Riu G, De Riu N, et al. Platform switching vs regular platform implants: nine-month post-loading results from a randomised controlled trial. European Journal of Oral Implantology 2014;7:257-265.
21
Table 1. Summary of drop-outs by centre, in parenthesis the reasons for dropping-out
(N = number of patients)
Felice(N=30)
Pistilli(N=30)
Scarano(N=30)
Grusovin(N=30)
Yoo(N=30)
Lee1(N=20)
Gualini (N=30)
Lee2(N=30)
Total (N=230)
EC (N=117) 0 0 1 (death) 0 1 (moved) 1 (death) 0 0 3
IC (N=113) 0 0 1 (moved) 1 (depression) 5 (did not come back) 1 (no time) 0 0 8
Table 2. Summary of protocol deviations by centre (N = number of patients)
Felice(N=30)
Pistilli(N=30)
Scarano(N=30)
Grusovin(N=30)
Yoo(N=30)
Lee1(N=20)
Gualini(N=30)
Lee2(N=30)
Total(N=230)
EC (N=117)
0 0 0 2** 0 0 2*****
1******
3*
2**
10
IC (N=113)
0 2*** 0 1* 1**** 0 1****
1*****
1* 7
*Prostheses attached to other implant types having the same connections.
**Used Ex-Feel implants with correct connection instead.
***Took panoramic and not periapical radiographs at 1 year after loading.
****Missing periapical radiograph at loading.
*****Missing periapical radiograph at 1 year after loading.
******Took unreadable panoramic instead of periapical radiograph at 1 year.
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Table 3. Patient and intervention characteristics.
EC [n=116] (%) IC [n=114] (%)Females (%) 68 (59%) 62 (54%)Mean age at implant insertion (range) 51.2 ± 14.5 (22-79) 52.4 ± 14 (20-80)Smoking up to 10 cigarettes/day (%) 21 (18%) 18 (16%)Smoking more than 10 cigarettes/day (%) 13 (11%) 19 (17%)Implants in upper jaws (%) 84 (41%) 79 (39%)Implants in lower jaws (%) 121 (59%) 123 (61%)Implants in incisor position 14 17Implants in canine position 7 15Implants in premolar position 80 66Implants in molar position 103 104Implants in hard bone 48 46Implants in medium bone 121 131Implants in soft bone 36 25Implants with 3.3 mm diameter 23 17Implants with 4 mm diameter 94 115Implants with 4.5 mm diameter 1 0Implants with 5.5 mm diameter 87 71Implants 7 mm long 0 1Implants 8.5 mm long 36 25Implants 10 mm long 50 63Implants 11.5 mm long 68 63Implants 13 mm long 51 50Post-extractive implants (%) 41 (20%) 30 (15%)Implants in augmented sites (%)* 63 (31%) 62 (31%)Implants inserted flapless (%) 99 (48%) 101 (50%)Patients with implants submerged (%) 85 (73%) 94 (82%)Single crowns (%) 59 (51%) 71 (62%)Partial fixed prostheses (%) 50 (43%) 39 (34%)Cross-arch fixed prostheses (%) 3 (3%) 1 (1%)Overdentures (%) 3 (3%) 2 (2%)Patients with implants immediately loaded (within 1 week) (%)
0 (0%) 1 (1%)
Patients with implants early loaded (between 1 week and 2 months) (%)
2 (2%) 0 (0%)
Patients with implants conventionally loaded (after 3 months) (%)
114 (98%) 112 (98%)
*Including augmented post-extractive sites at implant placement
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Table 4: Summary and comparisons expressed at implant level (N= number of
implants) of implant failures up to 1-year after loading by groups.
Felice(N=54)
Pistilli(N=57)
Scarano(N=80)
Grusovin(N=41)
Yoo(N=46)
Lee1(N=24)
Gualini(N=54)
Lee2(N=51)
Total(N=407)
EC(N=205)
2 (N=33) 0 (N=27) 0 (N=32) 0 (N=22) 0 (N=28) 1 (N=18) 0 (N=27) 0 (N=20) 3 (N=205)
IC(N=202)
0 (N=21) 0 (N=30) 0 (N=48) 0 (N=19) 0 (N=18) 0 (N=8) 2 (N=27) 0 (N=31) 2 (N=202)
p-valuea 0.5157 1 1 1 1 1 0.4916 1 1aFisher Exact test; *statistically significant differences.
Table 5: Summary and comparisons expressed at implant level (N= number of
implants) of complications up to 1-year after loading by groups.
Felice(N=54)
PistilliN=57)
Scarano (N=80)
Grusovin(N=41)
Yoo (N=46)
Lee1(N=24)
Gualini(N=54)
Lee2(N=51)
Total(N=407)
EC (N=205)
0 (N=33)
3 (N=27) 0 (N=32) 1 (N=22) 1 (N=28) 0 (N=18) 1 (N=27) 3 (N=20) 9 (N=205
IC (N=202)
0 (N=21)
1 (N=30) 1 (N=48) 3 (N=19) 1 (N=18) 0 (N=8) 1 (N=27) 0 (N=31) 7 (N=202)
p-valuea 1 0.3360 1 0.3210 1 1 1 0.0574 0.7997aFisher Exact test; *statistically significant differences.
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Table 6: Mean radiographic peri-implant marginal bone levels between groups and time
periods.
Implant placement Loading* 1 year after loading*
N Mean (SD) 95% CI N Mean (SD) 95% CI N Mean (SD) 95% CI
EC implants 75 0.18 (0.42) [0.09;0.28] 75 0.77 (0.62) [0.62;0.91] 71 1.17 (0.92) [0.95;1.39]
IC implants 73 0.07 (0.22) [0.02;0.12] 71 0.60 (0.70) [0.44;0.77] 64 0.91 (0.75) [0.73;1.10]
Difference
(SE) 95% CI
p-value
73 0.11 (0.05) [-0.01;0.21]
0.0502
*All changes from baseline (paired t-test) statistically different (P<0.001). SD = Standard
deviation; CI = Confidence interval.
Table 7: Descriptive statistics of mean changes in peri-implant marginal bone levels at
different time periods between groups.
Baseline – loading* Baseline – 1 year after loading*
N Mean (SE) 95% CI N Mean (SE) 95% CI
EC implants 75 0.59 (0.07) [0.44;0.73] 71 0.98 (0.12) [0.74; 1.22]
IC implants 70 0.54 (0.08) [0.38;0.69] 63 0.85 (0.09) [0.68; 1.03]
* Mean differences within group from paired t-test analysis; SD = Standard deviation; CI =
Confidence interval.
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Table 8: Multilevel model for the radiographic peri-implant marginal bone levels changes
between groups at loading.*Statistically significant difference; SE = Standard error; CI = Confidence interval.
Radiographic peri-implant marginal bone levels changes at loading
Term Estimate SE P-value [95% CI]
Intercept 0.47 0.18
Patient level
Baseline rx bone level -0.49 0.16 0.0017* [-0.79.;-0.18]
Implant (1=Int; 2=Ext) 0.10 0.10 0.3111 [-0.10;0.30]
Variances
u2 0.03 0.03
e 2 0.37 0.04
Theoretic model:
Loading-Bas rx = β0ij + β1ij Implant + β2ij Baseline rx bone level
u2 and e
2 indicate the variances at the Centre and at the Patient level, respectively. In the theoretic model
formula, the subscript j refers to the Centre level. The subscript i refers to the Patient level. β0ij is the 'intercept'.
SE is the standard error.
Data not provided for centres Felice, Scarano and Lee1.
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Table 9: Multilevel model for the radiographic peri-implant marginal bone levels changes
between groups at 1 year.*Statistically significant difference; SE = Standard error; CI = Confidence interval.
Radiographic peri-implant marginal bone levels changes at 1 year
Term Estimate SE P-value [95% CI]
Intercept 0.67 0.27
Patient level
Baseline rx bone level -0.82 0.19 <0.0001* [-1.20;-0.44]
Implant (1=Int; 2=Ext) 0.24 0.13 0.0629 [-0.01;0.50]
Variances
u2 0.17 0.11
e 2 0.55 0.07
Theoretic model:
1 year-Bas rx = β0ij + β1ij Implant + β2ij Baseline rx bone level
u2 and e
2 indicate the variances at the Centre and at the Patient level, respectively. In the theoretic model
formula, the subscript j refers to the Centre level. The subscript i refers to the Patient level. β0ij is the 'intercept'.
SE is the standard error.
Data not provided for centres Felice, Scarano and Lee1.
Table 10. Comparisons between study centres for the various outcome measures expressed at patient level (N= number of patients).
Felice (N=30)
Pistilli (N=30)
Scarano (N=30)
Grusovin (N=30)
Yoo (N=30)
Lee1 (N=20)
Gualini (N=30)
Lee2 (N=30)
P-value
Prosthesis failures(N=230)
1 0 0 0 0 1 1 0 0.693a
Implant failures(N=230)
2 0 0 0 0 1 1 0 0.366 a
Complications (N=230)
0 4 1 4 2 0 2 3 0.213 a
aChi-Square test
Table 11. One year radiographic peri-implant marginal bone levels changes from baseline
and pair-wise differences between centres (N = number of patients).
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Mean (SE) 95%CI p-value Between centres
Differencesa
Pistilli (N = 27) 1.17 (0.14) [0.88;1.46] <0.0001* A
Grusovin (N = 28) 0.64 (0.11) [0.42;0.87] <0.0001* B
Yoo (N = 24) 0.66 (0.16) [0.33;0.99] 0.0004* B
Gualini (N = 25) 1.55 (0.24) [1.06;2.04] <0.0001* A
Lee2 (N = 30) 0.63 (0.12) [0.39;0.87] <0.0001* B
Estimates are expressed as means (SE). *Within-centre statistically significant differences from baseline. Centres not connected by the same letter are significantly different; aanalysis of Covariance (ANCOVA) with baseline radiographic peri-implant bone level as a covariate.
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Figures
Fig 1a
Fig 1b
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Fig 1c
Fig 1d
Fig 1a-d: EZ Plus implant with external connection: a); sagittal view; b) occlusal view of the
external connection; c) sagittal section showing the external connection; d) the 3.3
mm diameter has a different neck design to have the same connection it is represented
here with the implant mount.
30
Fig 2a
Fig 2b
Fig 2c
Fig 2a-c: EZ Plus implant with internal connection: a); sagittal view; b) occlusal view of the
internal connection; c) sagittal section showing the internal connection.
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Fig 3: 1-year post-loading periapical radiograph of one Ez Plus implant with external
connection included in this study (courtesy of Dr Sang Taek Lee). Implant originally placed
with the neck level to the bone. Some marginal bone loss occurred over time.
Fig 4: 1-year post-loading periapical radiograph of 2 Ez Plus implants with internal
connection included in this study. Please note that IC implants had to be platform-switched
due to the implant design (courtesy of Dr Sang Taek Lee). Implants originally placed with
the neck level to the bone. Marginal bone levels remained virtually stable.
32