The Use of Angulated Abutments in

Implant Dentistry: Five-Year Clinical

Results of an Ongoing Prospective Study
Ashok Sethi, BDS, DGDP, MGDSRCS, DUI1/Thomas Kaus, Dr Med Dent, DDS2/Peter Sochor, ZTM3

A total of 2,261 2-stage implants was placed in 467 patients in combination with angled abutments
ranging from 0 to 45 degrees. These were observed over a period of up to 96 months, with a mean
observation time of 28.8 months. Single and multiple teeth were replaced and restored using angled
abutments. For patients who contributed multiple survival data, the data were considered dependent.
Therefore, a mean survival estimation was performed. With a certainty of 95%, an estimated mean
survival rate better than 98.6% after a 5-year observation period was calculated. The statistical com-
parison of 2 independent, randomized implant groups (with abutments angled between 0 and 15
degrees and between 20 and 45 degrees) by means of a log-rank test showed a probability of 0.84 (P
value) that the survival functions are the same for both groups. Good esthetic and functional out-
comes were observed. (INT J ORAL MAXILLOFAC IMPLANTS 2000;15:801–810)

Key words: dental abutments, osseointegrated dental implants, survival analysis

T he placement of endosseous dental implants has

become an increasingly common practice. Some
implants, especially some oral implants of the past,
rates have also been found by several other studies
and different dental implant systems.5–13
To date, there have been no long-term published
are poorly documented or have not been followed up studies that have assessed the effect of non-axial
for an adequate time period.1 It is important to use loading on the bone supporting the implants. The
an implant system that is adequately supported by anatomy of the jaws and the morphology of the
clinical reports. Well-documented implant systems residual ridges determine the orientation and angu-
such as the Brånemark (Nobel Biocare, Göteborg, lation of implant placement. Similarly, the position
Sweden) or Frialit-2 (Friadent, Mannheim, Ger- and morphology of the teeth are determined by
many) show high success rates. For follow-ups of esthetic and functional considerations. In the
more than 5 years, the Brånemark System has shown majority of situations, there is a difference between
success rates of 85% to 100% in the maxilla and 93% the long axis of the implant and the long axis of the
to 99% in the mandible.2,3 The Frialit-2 implant sys- planned tooth replacement.
tem has shown success rates of 97.6% when used for The purpose of this article was to present pre-
single-tooth replacement and 98.8% in immediate liminary results of the clinical long-term behavior
postextraction applications.4 Comparable success of implants restored using a broad range of angu-
lated abutments.

1Senior Lecturer, Department of Maxillofacial Implants, Medical

School, University of Lille 2, Lille, France.
MATERIALS AND METHODS
2Senior Lecturer, Department of Prosthodontics, University of

Tuebingen, Tuebingen, Germany. The study was designed prospectively and was per-
3Master Technician, Novadent Dental Laboratory, London, United formed at the Centre for Implant and Reconstruc-
Kingdom. tive Dentistry, London, United Kingdom. Since
Reprint requests: Dr Ashok Sethi, Centre for Implant and Recon- March 1991, 467 patients (55% female) have been
structive Dentistry, 33 Harley Street, London W1N 1DA United included in the study. These patients were provided
Kingdom. Fax: +44-207-436-8979. E-mail: asethi@dircon.co.uk with a total of 2,261 implants to replace missing

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Table 1 Distribution of Implants Placed

According to Location and Gender
No. of No. of
Gender/Arch arches implants placed
Female
Maxilla 194 831
Mandible 111 420
Male
Maxilla 168 680
Mandible 80 330
Total 553 2261

Fig 1 Cross-sectional image of a CT scan showing a maxillary

implant, in the planning stage, positioned between the labial and
palatal cortical plates. With the pre-angled abutment attached, it
lies within the prosthetic envelope defined by the radiopaque
marker on the labial surface and the mandibular incisor. The
abutment therefore emerges within the space allocated for the
restoration.

teeth with fixed restorations or to provide support Diagnostic Protocol. Clinical examination was car-
and retention for removable prostheses. The patient ried out to assess the status and the periodontal tis-
group comprised 256 females and 211 males with an sues of any remaining teeth. Clinical examination
age range from 17 to 83 years at the date of implant also included assessment of occlusal and parafunc-
surgery. The mean age was 49.6 years. The distri- tional status and the soft tissues, including attached
bution of implants placed is given in Table 1. gingiva, muscle attachments, and the lip line.
The implants used were custom-made, parallel- Radiographic examination was carried out for all
sided, commercially pure titanium screws with a patients, including an orthopantomograph and
machined surface. The implants had an internal hex other radiographs as required. Periapical radio-
and thread to provide positive location and a means of graphs were taken for assessment of detail, lateral
securing the abutment to the implant. The machined cephalographs for the assessment of bone width in
pre-angled abutments had an external hex to orient to the midline and facial profile, and computed tomo-
the implant and a screw to secure them to the implant. graphic (CT) scans for the assessment of bone vol-
These were manufactured from titanium alloy at angles ume and quality in patients requiring multiple
ranging from 0 to 45 degrees in 5-degree increments. implants, particularly in the posterior mandible.
Furthermore, CT scans were used for the assess-
Patient Selection ment of abutment angulation (Fig 1).
All patients at the Implant Centre who chose dental A diagnostic preview (via an arrangement of teeth
implants as a treatment option, or patients who in wax) was used to establish the most esthetically
were referred for implant treatment to the Centre pleasing and functionally viable tooth position. A
for Implant and Reconstructive Dentistry, were diagnostic template was fabricated over the plaster
included in the study if there were no contraindica- duplicate of the preview to outline the prosthetic
tions for implant treatment. envelope within which the abutment must fit. 14
Where inadequate bone was present, a variety of
Treatment Procedure procedures were used to augment the region, either
The treatment procedure included a diagnostic prior to the placement of implants or at the time of
phase, a pre-implant surgical phase for augmentation implant placement.
if necessary, a surgical phase for the placement and Implant Surgery. Implant Placement. Access to the
exposure of the implants in 2 stages, and a prosthetic bony ridge was obtained using remote incisions
phase. A maximum number of implants of the largest whenever possible. Remote palatal incisions were
possible dimension was placed in each arch accord- used in the maxilla, and remote buccal incisions
ing to the surgical protocol summarized below. were used in the mandible. The implant sites were

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Fig 2a Implants in situ, placed using a diagnostic template to Fig 2b Zero-degree try-in abutments are inserted into the
identify the site for the implant osteotomy. Implant angulation is implants, demonstrating the divergent angulation of the abut-
determined anatomically, with the implants placed between the ments. This is caused by the morphology of the maxilla, whose
cortical plates. base forms a smaller arc than the alveolar crest.

selected and a diagnostic template was used when-

ever appropriate. The treatment procedure was
modified on the basis of bone quality and jaw shape
according to Lekholm and Zarb.15
Osteotomies were prepared within the available
bone and between the labial and palatal cortical
plates. Internally irrigated osteotomy burs were
used in the mandible and maxilla at speeds ranging
from 1,000 to 2,000 RPM. Sterile saline was deliv-
ered by an internal cannula to the cutting edges of
the burs. 16 The burs were used to create the
osteotomy atraumatically and precisely and as a
gauge to measure the depth of the osteotomy. The Fig 2c Correctly angled try-in abutments in place, showing par-
allelism and alignment, which will facilitate the prosthetic restora-
diameter of the osteotomy was enlarged incremen- tion.
tally using gradually wider burs matched to the
implant diameters.
Bone taps were used in types 1 and 2 bone for all
implant diameters and in type 3 bone for 4.5-mm-
and 5.5-mm-diameter implants, because of the abutments ranging from 0 to 45 degrees in 5-degree
increased torque required for implant placement. increments.22 The try-in abutments corresponded
Socket formers were used in the maxilla, either by to definitive abutments and were used in conjunc-
themselves or in conjunction with ridge expanders tion with the diagnostic template (Figs 2 and 3).
and/or osteotomy burs, depending on the clinical Restorative angles and plane of orientation were
situation. In types 3 and 4 bone socket formers that evaluated for the screw-retained abutments (or
matched the implant diameter were used to create angled healing abutments) so that pre-machined
the osteotomy. For thin maxillary ridges, socket for- definitive abutments would be available at second-
mers were used in conjunction with ridge expanders stage surgery. The restorative angle and orientation
to widen narrow maxillary ridges.17 Osteotomy burs were noted on the patient record form and data
were used to determine depth and prepare the api- sheet. The wound was closed; the primary provi-
cal area in dense bone. In the posterior maxilla, sional prosthesis was then modified to compensate
where limited bone height was present, socket for- for any alteration in the gingival contours and fitted.
mers were used to raise the sinus floor to create Implant Exposure. This procedure was carried out
height, using sinus floor manipulation.18–21 This 6 months after implant placement for both
was done in conjunction with osteotomy burs. mandibular and maxillary implants. The implant
Abutment Alignment and Selection. Abutment was exposed and the cover screw was removed. The
alignment and selection were carried out during pre-angled abutments that were selected at the time
first-stage surgery (implant placement) using try-in of implant placement were seated (Fig 4), and the

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Fig 3a A try-in abutment at first-stage surgery for a single-tooth Fig 3b Multiple try-in abutment positions are verified for
replacement is selected to fit within the prosthetic envelope as mesiodistal and buccopalatal alignment using a diagnostic tem-
outlined by the diagnostic template. plate. This is to ensure adequate space for prosthetic reconstruc-
tion.

preview or try-in and allowed the transfer of tooth

form and position. The restorations were fabricated
hollow to receive the abutment and were relined at
the time of exposure. In a limited number of
patients, pre-angled healing abutments were used;
on these occasions, the provisional restoration was
appropriately modified for the transitional period.
Prosthetic Phase. Fixed restorations were fabri-
cated as single crowns supported by 1 implant, or as
a prosthesis supported by multiple implants using
Fig 4 Occlusal view of multiple definitive abutments attached splinted crowns. Most fixed restorations were
at second-stage surgery. These lie within the space allocated for cement-retained and were fabricated using conven-
each tooth of the restoration (as verified by the template) and can tional laboratory protocol for conventional cement-
be seen to be aligned with each other.
retained restorations. Thirty-eight implants sup-
ported connected restorations, and 2 single crowns
used lateral fixation screws for supplementary reten-
tion. One restoration was fabricated for screw
angle and orientation of the abutments were con- retention and was supported by 6 implants.
firmed using the template. The height of each abut- For removable restorations, a variety of protocols
ment was also assessed using the template and the was used. A total of 24 implants was placed for the
patient’s occlusion and was modified if necessary. retention of dentures; 1 implant failed and was sub-
The fixing screw was inserted through the cor- sequently replaced. Removable prostheses were
rectly aligned and seated abutment and tightened to retained using ball attachments, bar and clips, and
32 Ncm, using countertorque applied via artery for- attachments mounted on bars.
ceps. Primary stability of the implant was confirmed Implants used to stabilize traditional removable
by percussion and the absence of turning when prostheses primarily provided retention. Thus, these
rotational forces were applied to the implant while prostheses were supported by both implants and soft
tightening the screw. The hex hole of the screw was tissues. Four implants in the maxilla and 2 in the
filled with wax, and the screw access hole was sealed mandible were used for the retention of these pros-
with a glass-ionomer cement. Implant sites were theses. The number of stages varied considerably,
allowed to heal for a period of 4 weeks prior to the depending upon the mechanism used for retention.
fabrication of definitive restorations. Patient Recall. Follow-up of patients after pros-
Transitional Restorations. Transitional restorations thetic restoration was performed according to the
were fabricated from acrylic resin to provide the protocol given in Table 2. Radiographs were nor-
patients with esthetic and functional restorations, mally obtained after implant placement, 1 week
fitted at the time of abutment attachment. The after loading, at 6, 12, 18, and 24 months after
design of the restoration was based on the diagnostic placement of the definitive prosthetic restoration,

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 SETHI ET AL

and annually thereafter. To assess bone levels, peri- Table 2 Follow-up Protocol
apical radiographs were taken using the long-cone
Time since loading Procedure
technique and Rinn paralleling system (RinnXCP
film holders, Rinn Corporation, Elgin, IL). When 1 week Clinical assessment
Baseline radiographs
periapical radiographs did not provide an accurate
Oral hygiene instruction
result, orthopantomographs provided a radi- 1 month Clinical assessment
ographic overview (Planmeca PM 2002 CC Proline 3 months Clinical assessment
panoramic x-ray, Planmeca Oy, Helsinki, Finland). Oral hygiene instructions
Clinical assessment involved visual examination, 6 months Clinical assessment
Radiographs
recording of clinical parameters (bleeding on prob-
Oral hygiene instructions
ing, pocket depth, and implant mobility), as well as 12 months Clinical assessment
occlusal examination in centric relation and during Radiographs
lateral excursions. Patient feedback and any compli- Oral hygiene instructions
cations were addressed as appropriate. When neces- 18 months Clinical assessment
Radiographs
sary, oral hygiene instructions were given to ensure
Oral hygiene instructions
that a plaque-free environment could be main- 24 months Clinical assessment
tained. The ideal aid to oral hygiene was selected Radiographs
based on access. This was confirmed by plaque dis- Oral hygiene instructions
closure at each visit, and the technique was modi- Every 2-3 years Prosthesis removed for
assessment of individual implants
fied until the appropriate level of hygiene was
achieved.

Calculations and Statistics

All calculations were carried out using a personal RESULTS
computer. The data were transferred into a database
format (Microsoft Access, Microsoft, Redmond, Patients Lost to Follow-up
WA). Statistical analyses were performed with a sta- There were 467 patients with a total of 2,261
tistical program (JMP, SAS Institute Inc, Cary, NC). implants included in the study. Eighty-one patients
Because some patients contributed multiple sur- (17.3%) with a total of 379 implants (16.8%) were
vival data, dependent information from the data lost to follow-up. Fifty-five patients (11.8%) were
could not simply be excluded.23 Therefore, a mean referred patients who did not attend the recall pro-
survival estimation according to Aalen et al24 was gram and were monitored by their referring dentist.
performed using SAS software (SAS Institute Inc). Fourteen patients (3%) did not comply with
To compare survival estimates according to the requests to attend for monitoring, 8 patients (1.7%)
Kaplan-Meier method, a 1-implant-per-patient moved away from the area and were unable to
selection, supported by a randomization procedure, attend regularly, and 4 patients (0.8%) are deceased.
was performed to obtain independent information The reasons for loss of follow-up are summarized in
from the data.25 This was performed as follows: for Table 3.
each patient who contributed multiple survival data,
only 1 implant was chosen for survival analysis. In Intraoperative Complications
situations where 1 or more of a patient’s implants In the posterior mandible, no damage to the infe-
failed, only 1 of the failures was considered for rior dental nerve (IDN) took place because the
analysis. Either the failed implant that was placed depth of the osteotomy was measured to be 2 mm
first or, in cases where several failed implants were clear of the IDN. When implants were placed in
placed at the same time, only 1 of the failures was the anterior mandible, the mental foramen was
chosen by computerized randomization. In cases exposed and the osteotomies prepared so that the
where none of the implants had failed thus far, only completed osteotomy was at least 3 mm anterior to
the implant that was placed first was considered for the foramen.
analysis. A computerized randomization was per- Placement of implants in the maxilla involved the
formed when several implants had been placed at engagement of the opposing cortical plate whenever
the same time. This data selection was considered as possible. In a small but unrecorded number of
worst-case selection. Survival curves were then osteotomy preparations, the nasal or sinus floor was
compared using the log-rank test.26 inadvertently perforated. The implant length that
was selected reached only to 1.0 mm below the point
at which the perforation took place. Therefore, no

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Table 3 Patients Lost to Follow-up were more than 10 mm long. Figure 6, depicting
the frequency of diameters used, demonstrates that
Reason for loss No. of patients the majority of implants used were 3.75 mm in
Referred patients not attending recall 55 (11.8%) diameter. A disproportionately small number of 5.5-
Non-compliance 14 (3%) mm implants were used because they were only
Patient moved away 8 (1.7%)
Deceased 4 (0.8%)
recently introduced to the practice (1997).
Total 81 (17.3%)
Frequency of Abutment Angulations
The entire range of angles available was used and is
depicted in Fig 7. The majority of the angles used
ranged between 5 and 30 degrees (2,039 or 90.2%).
implants were placed into the sinus or the nasal A small number (222 or 9.8%) of 0-, 35-, 40-, and
floor, and no adverse consequences were noted. 45-degree abutments were also used. This enabled a
Because of the protocol concerning the anatomic greater number of patients to be treated without
placement of implants between the cortical plates, compromise of ideal implant placement according
very few incidences of dehiscence through the labial to available anatomic conditions.
or cortical plates were noted. These were not There were no implant or abutment failures
recorded and were not considered significant. associated with the use of angled abutments. Fur-
thermore, there was no incidence of screw loosen-
Postoperative Complications ing associated with angled abutments. The use of
Infection originating from the cover screw dead angled abutments allowed restorations to be parallel
space did occur. Twelve implants were treated by and aligned with each other. Cement-retained pros-
removing the cover screw and, while irrigating the theses could be fabricated for these patients, which
internal hex and thread, introducing an antibiotic furthermore allowed them to be connected
(gentamicin) and reinserting the cover screw. This together, providing cross-arch splinting as well as
led to uneventful healing. facilitating the management of failed implants.
Soft tissue breakdown was seen, which led to
premature exposure of 15 implants. The implants Survival Analysis
that were prematurely exposed were treated by The duration of observation since placement of the
uncovering the implants and attaching healing abut- implants was betwen 0 and 96 months, with a mean
ments, which were left unloaded for the remainder observation time of 28.8 months. Figure 8 depicts
of the 6-month healing period. None of the the distribution of implants with regard to time
implants treated in this way failed. since placement. Fifty percent (median) of all
implants were placed within 21.6 months prior to
Implant Loss the last observation. In addition, the box plot shows
A total of 2,261 implants was placed between March the 25% quartile (9.9 months) and the 75% quartile
1991 and May 1999; of these, 38 implants failed dur- (41.7 months).
ing the observation period, and 2,223 remain in situ. Figure 9 depicts the mean survival estimation
Twelve implants failed prior to exposure because of following placement, according to Aalen et al.24 For
infection, and 16 implants failed at exposure. Three each patient who contributed multiple survival data,
implants failed before prosthetic treatment could be the data were considered dependent. After an obser-
started as a result of excessive bone loss around the vation time of 60 months (5 years) after placement,
implants. The cause for this has not been deter- the calculated 95% confidence interval of the mean
mined. Two implants failed prior to completion of survival estimation according to Aalen et al24 was
the restorative phase. Five implants were lost after 99% (± 0.4%). Therefore, with a certainty of 95%,
the completion of the restorative phase, but 3 of the mean survival probability after 5 years can be
these implants were successfully replaced and con- considered better than 98.6%.
nected to the existing prosthesis. Two implants were Figure 10 depicts the survival analysis of 2
not replaced, but the restorations continue to func- selected groups of implants. A total of 467 implants
tion, since the implants were considered unnecessary was selected according to the aforementioned
for the long-term survival of the restorations. “worst-case” selection procedure. The survival
analysis according to Kaplan-Meier of implants
Frequency of Implant Lengths and Diameters with abutment angulation of more than 15 degrees
Figure 5 depicts the frequency of different implant (n = 219) was compared with implants restored with
lengths used. The majority of the implants (92%) abutments that were angulated at 0 to 15 degrees

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Fig 5 Frequency of implant lengths used in

the patient population.

320
300 293

No. of implants
249 244
216 215
200 184

123 126
101 106
100
49
31
4

7 8 9 10 11 12 13 14 15 16 17 18 19 20
Implant length (mm)

Fig 6 Frequency of implant diameters used.

1,356
1250
No. of implants

1000

750
564
500

250 180
62 99

2.75 3 3.75 4.5 5.5

Implant diameter (mm)

Fig 7 Frequency of abutment angulations

used.
471
447 437
400
No. of implants

300 267
240
200 177

100 74 80
47
21

0 5 10 15 20 25 30 35 40 45
Abutment angulation (deg)

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SETHI ET AL

Fig 8 Distribution of implants according to

time since placement (histogram and box plot
Mean with 25% and 75% quartiles).
9.9 28.6 41.7

21.6
No. of implants

Median
600

400

200

0 10 20 30 40 50 60 70 80 90 100
Time at risk since placement (mo)

Fig 9 Mean survival estimation according to

Aalen et al.24
100
90
Survival probability (%)

80
70 95% confidence interval (upper limit)
60 95% confidence interval (lower limit)
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100
Time at risk since placement (mo)

(n = 248). Statistical comparison of the groups by Goodship and coworkers have demonstrated the
means of a log-rank test showed a probability of capacity of bone to remodel in response to strain.30
0.84 (P value) that the survival functions are the To date, no long-term studies have been published
same for both groups. that have assessed the effect of non-axial loading on
the bone supporting the implants or on the compo-
nent parts transmitting these forces to the support-
DISCUSSION ing bone.31,32
The results of this study demonstrate that there
Historically, the need to change the abutment angle seems to be no difference in the survival of implants
has been recognized, as a result of the difference in based on the use of angulated abutments ranging
angulation between the bone available for implant from 0 to 45 degrees. Balshi et al have also demon-
placement and the long axis of the planned restora- strated that the survival of implants loaded via 30-
tion. However, there have been concerns expressed degree abutments is not significantly different from
about the adverse effect of non-axial forces on the implants loaded via straight abutments.31 As demon-
survival of implants. These have been investigated by strated by the present results, the survival of implants
means of photoelastic studies as well as 3-dimensional loaded via angulated abutments is comparable to
finite element computer simulations.27–29 However, other reported studies in which angulated abutments
these in vitro investigations do not address the bio- were not used or addressed.2–13
logic response of bone to functional loads.

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The protocol that was used for this study involved

the placement of implants anatomically within the 100
available bone, irrespective of the angle between the 90
long axis of the implant and proposed prosthetic
80 > 15-degree angulation (n = 219)
crown. This approach served several purposes:

Survival probability (%)

70 ≤ 15-degree angulation (n = 248)
• It enabled implants of a greater dimension 60
(length and diameter) to be placed.
50
• It enabled a greater number of patients to be
treated. 40
• It avoided surgical compromise by allowing the 30
implants to be placed between the cortical plates,
20
thus preventing perforations and dehiscences. Log-rank test P value = .84
• It allowed the permucosal site to be placed more 10
anatomically and facilitated restoration estheti- 0
cally, functionally, and phonetically. 0 10 20 30 40 50 60 70 80 90
• It improved the efficiency of the treatment by Time at risk since exposure (mo)
reducing treatment planning and clinical and lab-
oratory time. Fig 10 Survival analysis according to Kaplan-Meier. Selected
• It improved access for oral hygiene. groups are compared according to abutment angulation.

The abutments were selected at first-stage

surgery, which reduced the number of component
parts required. Alignment of each implant hex and
abutment at this stage made it possible to overcome CONCLUSION
many of the difficulties associated with the labora-
tory correction of non-aligned implants and abut- Angulated abutments may be used without compro-
ments. The planning of treatment was greatly sim- mising the long-term survival of implants. Treatment
plified, since complex surgical templates based on planning can be facilitated and implant placement
CT scans to guide the osteotomy preparation did can be carried out without surgical compromise. The
not need to be fabricated.33,34 fabrication of restorations utilizes conventional
Most importantly, there appeared to be a compa- restorative procedures. Good esthetic and functional
rable high survival rate and an esthetic and func- outcomes can be easily achieved using the protocol
tional outcome that was consistently achieved. This outlined.
may be attributable to the improved biomechanics
that result from the use of angled pre-machined
abutments, which are selected and aligned to lie ACKNOWLEDGMENT
within the prosthetic envelope to facilitate the
restorative phase. Cement-retained restorations The authors wish to acknowledge the assistance and statistical
support provided by Dr rer nat Detlef Axmann-Krcmar,
could be fabricated, which are technically easier to
Department of Prosthodontics, University of Tuebingen, espe-
fabricate than stress-inducing screw-retained cially for introducing the mean survival estimation method
restorations.35–37 according to Aalen et al to our data.
Because of the mean observation time of 29
months, less than half of the 2,261 placed implants
could be considered for the calculation of the sur- REFERENCES
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 SETHI ET AL

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