Franck Renouard
David Nisand
Authors’ affiliations:
Franck Renouard, Private Practice, Paris, France
David Nisand, Department of Periodontology,
University of Paris 7, Paris, France
Correspondence to:
Franck Renouard
Private Practice
26 Avenue Kléber
75116 Paris
France
e-mail: franck@renouard.net
Impact of implant length and diameter
on survival rates
Key words: biomechanical aspects, dental implants, implant diameter, implant length
Abstract
Introduction: Despite the high success rates of endosseous oral implants, restrictions have
been advocated to their placement with regard to the bone available in height and volume.
The use of short or nonstandard-diameter implants could be one way to overcome this
limitation.
Material and methods: In order to explore the relationship between implant survival rates
and their length and diameter, a Medline and a hand search was conducted covering the
period 1990–2005. Papers were included which reported: (1) relevant data on implant
length and diameter, (2) implant survival rates; either clearly indicated or calculable from
data in the paper, (3) clearly defined criteria for implant failure, and in which (4) implants
were placed in healed sites and (5) studies were in human subjects.
Results: A total of 53 human studies fulfilled the inclusion criteria. Concerning implant
length, a relatively high number of published studies (12) indicated an increased failure rate
with short implants which was associated with operators’ learning curves, a routine surgical
preparation (independent of the bone density), the use of machined-surfaced implants, and
the placement in sites with poor bone density. Recent publications (22) reporting an
adapted surgical preparation and the use of textured-surfaced implants have indicated
survival rates of short implants comparable with those obtained with longer
ones.Considering implant diameter, a few publications on wide-diameter implants have
reported an increased failure rate, which was mainly associated with the operators’
learning curves, poor bone density, implant design and site preparation, and the use of a
wide implant when primary stability had not been achieved with a standard-diameter
implant. More recent publications with an adapted surgical preparation, new implant
designs and adequate indications have demonstrated that implant survival rate and
diameter have no relationship.
Discussion: When surgical preparation is related to bone density, textured-surfaced
implants are employed, operators’ surgical skills are developed, and indications for implant
treatment duly considered, the survival rates for short and for wide-diameter implants has
been found to be comparable with those obtained with longer implants and those of a
standard diameter. The use of a short or wide implant may be considered in sites thought
unfavourable for implant success, such as those associated with bone resorption or previous
injury and trauma. While in these situations implant failure rates may be increased,
outcomes should be compared with those associated with advanced surgical procedure
such as bone grafting, sinus lifting, and the transposition of the alveolar nerve.
To cite this article:
Renouard F, Nisand D. Impact of implant length and
diameter on survival rates.
Clin. Oral Imp. Res. 17 (Suppl. 2), 2006; 35–51
r 2006 The Authors
Journal compilation r Blackwell Munksgaard 2006
The clinical use of several endosseous oral
implants designs has become highly predictable in recent decades.
However, their use may be restricted
where there are limitations imposed by
the geometry and volume of the alveolar
35
Renouard & Nisand . Impact of implant length and diameter on survival rates
bone. These restrictions are more common
in the posterior regions of the maxilla and
the mandible.
It is generally claimed that the best
treatment in these situations is surgical
modification of the patient’s anatomy by
bone grafting techniques, alveolar distraction or inferior alveolar nerve transposition
to allow the placement of longer and wider
implants. However, the adaptation of the
implant to the existing anatomy through
the use of short and/or narrow- or widediameter implants should now be considered as a more appropriate procedure.
In the present review, a ‘short’ implant
was defined as a device with a designed
intra-bony length of 8 mm or less, a ‘wide’
implant as one in which the stated diameter was 4.5 mm or more, and a ‘narrow’
implant as one in which this was less than
3.5 mm.
This review was conducted within the
above parameters and evaluated, through a
Medline search, the survival rate of oral
implants related to their length and diameter.
Material and methods
Studies to be included in this structured
review had to fulfill the following inclusion
criteria: (1) relevant data on implant
lengths and diameters, (2) implant survival
rates were either clearly indicated or calculable from data reported in the paper, (3)
criteria for implant failure had been clearly
defined, (4) implants were placed in healed
sites, (5) human-derived data were reported.
If more than one publication referred to
the same data, the most recent report was
used.
No restrictions were placed concerning
study design, and randomized and nonrandomized clinical trials, cohort studies, case
control studies and case reports were all
considered for inclusion in the review.
A Medline search was performed to
identify clinical articles published between
January 1990 and December 2005. The
following search terms were used: ‘dental/
oral implant’ and ‘length’, ‘diameter’,
‘shape’, and ‘short dental implant’.
In addition, a manual search of the
following journals from 1990 to 2005 was
performed: Clinical Oral Implant Re-
36 |
Clin. Oral Impl. Res. 17 (Suppl. 2), 2006 / 35–51
search, International Journal of Oral and
Maxillofacial Implants, Clinical Implant
Dentistry and Related Research, Journal
of Periodontology, Journal of Clinical
Periodontology, International Journal of
Periodontics & Restorative Dentistry.
A further manual search was conducted
through the bibliographies of all relevant
papers and review articles.
Two examiners reviewed the titles and
abstracts according to the inclusion criteria.
When necessary, the complete text of the
article was obtained for further assessment
of inclusions. Full texts of all papers that
were considered suitable for inclusion by
the two examiners were then obtained.
Disagreements between the two examiners
were resolved by discussion.
Data extracted from the review were
classified as follows:
studies dedicated to short-length implants;
studies with data available on length;
studies mainly dedicated to wide-diameter implants;
studies dedicated to narrow-diameter
implants;
studies with data available on diameter.
Results
The Medline search provided a total of 182
articles for ‘dental/oral implant’ and
‘length’, 103 articles for ‘dental/oral implant’ and ‘diameter’, 39 articles for ‘dental/oral implant’ and ‘shape’, and 102
articles for ‘dental/oral implant’ and ‘short
dental implant’ of which 67 were screened
as full text articles.
A total of 53 human studies fulfilled the
inclusion criteria and were divided as follows: 13 articles dedicated to short-length
implants, 21 articles with data available on
implant length, nine articles mainly dedicated to wide-diameter implants, seven
articles dedicated to narrow-diameter implants and eight articles with data available
on diameter.
The selected articles embodied a wide
range of approaches to study design, data
reporting, definition of terms, implant
geometry and surface, methods of statistical analysis, success and survival criteria,
and follow-up time. Consequently no
attempt was made to apply a meta-analytic
technique.
Implant length
Tables 1a and 1b display the data obtained
from the 21 articles which provided information on implant length. In most of these
studies (12), a higher failure rate was documented for shorter implants (van Steenberghe et al. 1990; Friberg et al. 1991;
Jemt 1991; Bahat 1993; Jemt & Lekholm
1995; Wyatt & Zarb 1998; Lekholm et al.
1999; Bahat 2000; Winkler et al. 2000;
Naert et al. 2002; Weng et al. 2003; Herrmann et al. 2005). The worst results with
short implants have been documented by
Wyatt & Zarb (1998) with an overall survival rate of 75% for 7-mm-long implants
(of the 12 implants placed, three were lost),
Winkler et al. (2000) with an overall survival rate of 74.4% for 7-mm-long implants
(of the 43 implants placed, 11 were lost)
and Herrmann et al. (2005) with an overall
survival rate of 78.2% for 7-mm-long implants (of the 55 implants placed, 12 were
lost).
However, only a few of these studies
analysed the statistical differences between
short and longer implants (Bahat 1993;
Jemt & Lekholm 1995; Winkler et al.
2000; Weng et al. 2003; Herrmann et al.
2005). Thus, Winkler et al. (2000) demonstrated that shorter implants tended to fail
significantly more often following uncovering and after loading than longer implants. Using logistic regression analyses,
implant length was found to be a significant factor for survival over the observation
period. In the same way, Weng et al. (2003)
reported that 60% of all failed implants
were short ( 10 mm), and that the cumulative success rate for these short implants
was significantly lower than the cumulative success rate for all implants. In the
study by Herrmann et al. (2005), a significant correlation was demonstrated between
shorter implants and failure rate. In addition, comparing the two groups of short
implants, a significant difference was
found between the 7- and 10-mm implants.
Moreover, it is of interest to note that
some of theses studies, although concluding that shorter implants had higher failure
rates than longer ones, still indicated acceptable survival rates for the former. As
such, van Steenberghe et al. (1990)
213 (732)
37 |
(35)
Patients
lost to
followup (I)
(97) at
5 years
60–144
(52.6)
(66)
(12)
440 (1022)
181 (485)
660 (1956)
60 (240)
Testori et al.
(2001)
Naert et al.
(2002)
Stellingsma
et al. (2003)
2 (8)
73 (204)
16 (39)
(30)
–
(36)
12–84
38 (123)
(120)
12–144 (64.9) –
3 (9)
124
–
3–84
(120)
16
63 (127)
12–96
4 short (8 or 11 mm)
implants to support an
overdenture in 20
patients with an
extremely resorbed
mandible. One patient
lost to follow-up and
no implant loss.
1047
306
18
341
1966
176
3
26
19 (100)
212
–
3848 (implants
10–20 mm)
192
/
–
–
–
–
–
15
26
–
–
276 –
6
/
94.3 yyn /
–
/
/
/
/
/
–
21
CSR
(%)
–
86w
92
–
719 –
122 –
480 –
210 –
770 89.1n
207 88zzz
29
93
26
814 93.4w
291 –
–
–
246 93.9z
N
10 mm
–
–
99.4 (implants
10–20 mm)
/
1091 95w
/
–
–
/
91.5zww /
100
95nn
–
–
–
–
–
97.4z
CSR
(%)
N
N
CSR
(%)
11.5 and 12 mm
13 mm
(60)
12
11 (62)
From stage 0
1 to the
connection
of prostheses
5–70 (30.3) 4
–
(12)
Follow-up
in months
(mean)
Brocard et al.
(2000)
Jemt & Lekholm
150 (801)
(1995)
Buser et al.
1003 (2359)
(1997)
Ellegaard et al.
68 (124)
(1997)
Wyatt et al.
77 (230)
(1998)
Gunne et al.
23 (69)
(1999)
Lekholm et al.
127 (461)
(1999)
Winkler et al.
(2917)
(2000)
Bahat (2000)
202 (660)
Bahat (1993)
van Steenberghe 159 (558)
et al. (1990)
Jemt (1991)
384 (2199)
Friberg et al.
889 (4641)
(1991
N patients
(N implants)
Table 1a. Studies on oral implants with information on length available
39
24
/
3
/
/
/
1
5k
/
/
/
–
/
/
N
–
–
/
–
/
/
/
100
–
/
/
/
–
/
/
/
/
–
/
/
/
/
/
–
/
19 –
/
232 –
8
138 87n
/
/
/
56 –
/
–
/
110 –
7
/
84 –
43 74.4n
101 93.5zzz
37 89w
12 75z
/
/
298 –
/
/
/
/
/
CSR
(%)
–
/
/
/
/
/
7
–
–
–
16 –
8
/
/
/
/
/
39 –
/
/
90.5zn
–
/
/
/
N
6 mm
270 94.7zy
793 94.5z
120 97.5z
389 91.4w /
/
/
–
/
/
CSR
(%)
7 mm
CSR N
(%)
8 mm
CSR N
(%)
8.5 mm
98.1z
98.5z
95.8z
CSR
(all length)
(%)
–
–
–
–
–
–
–
–
81.5z
–
94.6z
91.4
92.2
(C Success :
83.4%)
98.7
93.4 (at 10
years)
93.1z
92.6z
88.4
94z
95–100z
96.7
95.2zn
95.9z
(in bone type
II–III)
94.5z (in bone
type IV)
91.85n
71.2–92.1
–
99.4z
–
CSR
(410 mm)
(%)
95z
(10–15 mm)zz
100 (18–
20 mm)zz
80.3w (8 mm or 83.7w
less)
(12 mm or
more)
–
–
83zzz
–
–
–
–
–
–
92.6 z
(in bone type
II–III)z
86.7z (in bone
type IV)z
75.8n
–
94.5 z
(7 mm only)
–
CSR
(o10 mm)
(%)
Renouard & Nisand . Impact of implant length and diameter on survival rates
Clin. Oral Impl. Res. 17 (Suppl. 2), 2006 / 35–51
38 |
Clin. Oral Impl. Res. 17 (Suppl. 2), 2006 / 35–51
(60)
(63.6)
487 (487)
376 (1003)
–
80 (80)
(316 kk)
24–60
(4891)
(222)
16–84 (46.2) 49 (82)
(72)
Patients
lost to
followup (I)
250 (759)
493 (1179)
Follow-up
in months
(mean)
–
259
2547
49
607
–
/
–
–
/
329 –
236 –
/
95.7znnn /
–
–
/
CSR
(%)
N
N
CSR
(%)
11.5 and 12 mm
13 mm
CSR
(%)
–
–
/
81z
–
–
/
/
–
/
/
–
/
/
72 –
/
/
/
/
/
N
–
–
–
–
/
/
/
/
CSR
(%)
6 mm
55 78.2zwwwn /
143 –
/
27 74z
CSR
(%)
7 mm
CSR N
(%)
8 mm
CSR N
(%)
425 –
/
70
N
8.5 mm
159 89.9zwwwn /
1447 –
402 –
475 91z
N
10 mm
n
Significant differences between short and long implant in the same study.
wNo significant difference between short and long implant in the same study.
zOverall survival rate.
yData concerning the maxilla only.
zOnly implants 7 mm length included.
kImplants of 9 mm length.
nnOnly implants 13 mm length included (for implants 15 mm length, the success rate was 98% and 100% for implants 18 and 20 mm length).
wwOnly implants 13 mm length included (absolute survival rate);. Implants 15, 18, and 20 mm length present a 100% absolute survival rate.
zzOnly implants 3.75 mm wide included (absolute survival rate).
yyOnly implants 13 mm length included.
zzOnly implants 3.75 mm wide included (absolute survival rate).
kkIn the short-implant group (no data concerning the number of implant lost to follow-up in the long-implant group).
nnnOnly implants 3 .75 mm wide and 13 mm length were evaluated (wider implants were excluded).
wwwOnly implants 3.75 mm wide were evaluated.
CSR, cumulative survival rate.
Herrmann et al.
(2005)
Lemmerman &
Lemmerman
(2005)
Weng et al.
(2003)
Romeo et al.
(2004)
Feldman et al.
(2004)
N patients
(N implants)
Table 1a. Continued
–
93.1n
CSR
(410 mm)
(%)
96.1 (FPD)
91.1 (6 years)
CSR
(all length)
(%)
–
–
94z
Machined 91.6 Machined 93.8n –
(10 mm
included)n
Osseotite 97.7 Osseotite 98.4w
(10 mm
included)w
–
–
92.4
89 (10 mm
included) n
–
CSR
(o10 mm)
(%)
Renouard & Nisand . Impact of implant length and diameter on survival rates
Type of study
39 |
Longitudinal study
Longitudinal study
Prospective multicentre
Wyatt et al.
(1998)
Gunne et al.
(1999)
Lekholm et al.
(1999)
Retrospective
Ellegaard et al.
(1997)
TPS
Machined
Machined
Machined
Submerged
Submerged
Submerged
Machined
Machined
Machined
Nonsubmerged (93), TPS (93),
Submerged (31)
TiOblast (31)
Prospective, multicentre Nonsubmerged
Submerged
Jemt & Lekholm Retrospective study
(1995)
Buser et al.
(1997)
Submerged
Retrospective study
Bahat (1993)
Submerged
Machined
Submerged
Retrospective,
multicentre
Machined
Implant type
Submerged
Submerged/
nonsubmerge
technique
Friberg et al.
(1991)
van Steenberghe Prospective multicentre
et al. (1990)
Jemt (1991)
Retrospective study
Authors
Table 1b. Studies on oral implants with information on length available
47
12.5
50
–
26.5
–
–
100
66
87
53
87.5
50
–
73.5
–
–
/
34
13
5
Maxilla
(%)
Comments
Longer fixtures failed to a lesser extent compared with
the shorter standard implants (7-, 10-, and 13-mm long)
0.4
2.9
The edentulous patients were provided with
Brånemark implants according to routine surgical
protocol. The 7-mm implant failed more often (5.3%)
than any other size of implant in the maxilla. A
corresponding pattern was not found in the mandible
0.6 (2.7% for
2.9 (6.9%
A majority of failures associated with advanced
7 mm implant) for 7 mm)
resorption.
Length of the implants may indicate the state of jaw
bone resorption.
No relation between implant length and failures in
partially edentulous patients.
Edentulous patients frequently wore removable
dentures (preloading of implants)
–
–
7-mm implants had a higher failure rate than those of
all other length. 60% of the failing 7-mm molar
implants were the only implants in that segment of the
jaw
/
7.9–28.8
Factors of significance for implant failures in patients
were found to be age, ratio of 7-mm implants and
bone quality
5.9 (anterior)
12.2 (anterior) Analysis demonstrated a trend for better results with
4.6 (posterior) 13.3 (posterior) increasing implant length
This trend was however not statistically significant
8-mm implants were predominantly inserted in
posterior segment
7.7
2.7
The length of the implant varied between 8 and 14 mm,
with 45% being 8 mm. Most implants were placed in
the maxilla in periodontally compromised patients. A
total of three implants had failed. Two were of 8 mm
implants and one concerned a 10 mm implant
57% (of the
43% (of the
The higher failure rate documented for shorter
failed implants) failed implants) implants (25% failure of the 7-mm implants placed)
compared with longer ones may be related to
compromised placement in restricted anatomic sites.
Alternatively, the effect of the same amount of bone
loss on a short and long implant may result in dramatic
differences in their survival rates
11.6
/
Success rates reported in this study were achieved
despite the use of short implants (54% of the implants
were 7 mm) and the failure rate was similar for 7- and
10-mm implants
6.3
9.8
According to Cox regression analysis, the only
relationship between failures and implant
characteristics was seen with regard to implant length,
in that shorter implants failed more often than longer
ones
3.5
Before After Mandible
loading loading (%)
(%)
(%)
Implant failures
Renouard & Nisand . Impact of implant length and diameter on survival rates
Clin. Oral Impl. Res. 17 (Suppl. 2), 2006 / 35–51
40 |
Retrospective study
Longitudinal multicentre Nonsubmerged
Prospective multicentre
Longitudinal study
Prospective
Prospective, multicentre Submerged
Prospective
Bahat (2000)
Brocard et al.
(2000)
Testori et al.
(2001)
Clin. Oral Impl. Res. 17 (Suppl. 2), 2006 / 35–51
Naert et al.
(2002)
Stellingsma
et al. (2003)
Weng et al.
(2003)
Romeo et al.
(2004)
Nonsubmerged
Submerged
Submerged
Submerged
Submerged
Submerged
Longitudinal study
Winkler et al.
(2000)
Submerged/
nonsubmerge
technique
Type of study
Authors
Table 1b. Continued
83.7
0
–
100
19.1
37
–
93.8
16.3
0
–
0
80.9
63
–
–
/
10.1
1.6 (posterior)
2.4 (anterior)
–
6.6
–
Maxilla
(%)
47% of the
53% of the
failed implants failed implant
–
0
6.7
0.6 (posterior)
0 (anterior)
–
/
–
Before After Mandible
loading loading (%)
(%)
(%)
Implant failures
TPS (703), SLA (56) 6.2
Machined
Machined
Machined
Osseotite
TPS
Machined
Machined and
HA-coated
Implant type
Shorter implants tended to fail significantly more often
following uncovering and post-loading than longer
implants. Using logistic regression analyses, implant
length was found to be a significant factor for surviving
for the overall period of observation
As expected, the longer implants were more likely to
survive than the shorter ones. However, the failure rate
of the 7-mm-long implants was similar to that of longer
ones when the 7-mm implant was not the most distal in
a series
The implants were divided into three groups according
to their length with success rate for each group being
comparable. Implant length did not significantly
influence the results, especially for 8–12-mm implants
Short implants, defined for this report as 10 mm or
shorter, represented 31.5% (153) of the implants placed
in this investigation. There is a tendency for shorterlength ( 10 mm) machined-surface implants to fail
more often than longer implants. This tendency was
not observed for the shorter implants placed in this
study. Of the 153 short implants placed, only one 7-mm
implant, which was placed in the posterior maxilla in a
site recorded as soft bone, failed to osseointegrated. It
is possible that the difference in biologic response
between the machined implant surface and the microtextured surface is responsible for the difference in the
survival rates for short implants
A two-stage surgical intervention was performed
according to a standard protocol. The shorter the
implant length, the higher the hazard rate. Decreasing
the implant length by 1 mm increases the hazard rate
0.16 times
The objective of this report was to study the effect of
three different treatment modalities (short implants,
transmandibular implants, augmentation, and long
implants) in edentulous patients with an extremely
resorbed mandible. Differences among the three
groups were not significant. However, in terms of
discomfort and pain during the surgical phase as well
as the length of this phase, the augmentation using an
autologous bone graft from the iliac crest appeared
the least favourite option.
23.2% of all implants in the post-maxilla
CSR implants in the post-maxilla (all length) ¼ 86.2%
CSR implants 10 mm in post-maxilla ¼ 80.6%
Implant failure did not appear to be significantly
influenced by length. Only 20% of failed implants were
8-mm long
Comments
Renouard & Nisand . Impact of implant length and diameter on survival rates
reported only three failures among 120
7-mm-long implants leading to an overall
survival rate of 97.5%. Friberg et al. (1991)
in a study on 4641 implants obtained an
overall survival rate of 94.5% for 7-mmlong implants. Jemt (1991) in a study on
2199 implants reported an overall survival
rate of 95.5% (of the 270 implants placed,
12 were lost). Lekholm et al. (1999) in a
10-year prospective multicenter study reported an overall survival rate of 93.5%
for 7-mm-long implants compared with
91.5% for 13-mm-long implants.
In some of these studies, the failure rates
of short implants were similar to those of
longer ones. This finding applied to 7-mmlong implants placed in partially dentate
patients (Friberg et al. 1991), 7-mm-long
implants placed in the mandible (Jemt
1991), and when the 7-mm implant was
not the most distal in a series (Bahat 2000).
Moreover, of the nine studies which
provided data on implant length (Tables
1a and 1b), this was not reported as influencing the survival rate (Buser et al. 1997;
Ellegaard et al. 1997; Gunne et al. 1999;
Brocard et al. 2000; Testori et al. 2001;
Stellingsma et al. 2003; Feldman et al.
2004; Romeo et al. 2004; Lemmerman &
Lemmerman 2005). In a study on 2359
implants, Buser et al. (1997) reported a
91.4% cumulative survival rate for 8mm-long implants with a plasma-sprayed
surface as compared with 93.3% for 10mm-long implants and 95% for 12-mmlong implants. Feldman et al. (2004), using
dual-acid-etched implants reported a
97.7% cumulative survival rate for short
implants (implant 10 mm) as compared
with 98.4% for longer ones. However, in
the same study, short-length machinedsurfaced implants did not perform as
well against matched standard-length
machined-surfaced implants (91.6% vs.
93.8%, respectively).
Tables 2a and 2b display the data extracted from the 13 articles which are
devoted to short implants. Depending on
the definition of short implants among the
authors, these articles involved 6–13-mmlong implants. Eight of these articles (Ten
Bruggenkate et al. 1998; Deporter et al.
2000, 2001; Friberg et al. 2000; Fugazzotto
et al. 2004; Griffin & Cheung 2004; Goen
et al. 2005; Renouard & Nisand 2005) only
dealt with short-length implants. Among
the remaining five studies, the definition
n
Four multicentre study (Lekholm et al. 1994, Henry et al. 1996, Jemt et al. 1996, Friberg et al. 1997) reporting on one specific implant design constituted the basis for the research.
SLA, sandblasted and acid-etched; TPS, titanium plasma-sprayed.
6.2
6
24.5
75.5
Submerged and
nonsubmerged
Prospective study
Lemmerman &
Lemmerman
(2005)
Machined (348)
and rough
surface (655)
–
–
50
50
Machined
Submerged
Herrmann et al. Research databasen
(2005)
Feldman et al.
(2004)
Analysis of prospective
multicentre
Submerged
Machined (2597)
–
vs. Osseotite (2294)
–
–
–
Short-length dual-acid-etched implants perform as well
as standard DAE implants. Short-length machinedsurfaced implants did not perform as well against
matched standard-length machined-surfaced implants.
The performance of these short machined-surfaced
implants was especially compromised in the maxilla
and under conditions of poor-quality bone
A significant correlation was found between shorter
implants and failure rate: the failure rate for shorter
implants was 13.1%. Comparing the two groups of
short implants, a significant difference was
demonstrated between the 7- and the 10-mm implants,
respectively. When adding length as a level for the
multilevel analyses, no statistical significance regarding
any of the new combinations could be demonstrated
(jawbone quality and jaw shapes). Therefore, implant
length could indirectly be regarded as a patient-related
factor, since it is related to the bone volume present
No correlation (no effect on failure rate) was found for
implant length. Longer implants are not accompanied
by an increased success rate in this study. If anything,
the rate of failure went up about 3% with long
implants (412). This could be due to operator factors
such as longer drilling time; lesser ability of coolant to
penetrate the osteotomy; or inadvertent, increased
drilling force to get a deeper osteotomy
Renouard & Nisand . Impact of implant length and diameter on survival rates
41 |
Clin. Oral Impl. Res. 17 (Suppl. 2), 2006 / 35–51
42 |
88
95.5 (5 years)
92.3 (10 years)
/
/
100 /
100
/
100
17
/
/
100 /
100
100
87.7 /
11.2 88.8 93.3n 95.9n 95.5nw
39.7 27.5 38
62
100
99.1 99.4
23.8 /
53
47
100
100
100
/
/
100 /
95.1 /
95.1n
93.2 /
–
–
94.5z 95.8z 95.8
84.4 /
100 /
94.6 /
94.6
88
92.3
/
/
100
100
/
/
100
8
Clin. Oral Impl. Res. 17 (Suppl. 2), 2006 / 35–51
n
Overall survival rate.
wWhen the survival rate of 10-mm implants was compared with those of the shorter implants, no statistical difference was found.
zIn the posterior sextants.
FPD, fixed partial denture; RD, removable denture; CSR, cumulative survival rate; Mx, maxillae; Md, mandible; –, not reported.
6.9
7.66
9
10.26
6
8.1
8.42
7.9
7.6
/
/
/
/
/
/
/
/
5.9
1.1
100
/
/
10.5
88.5
66.6
10.1
/
/
4.3
5.5
23.9
/
/
10.1
18.4
/
81.6
/
/
/
/
17.1
/
/
/
94.5
65.6
3.9
33.3
/
1.5
/
14.1
/
/
/
/
56.8
36.7
/
/
/
/
/
/
/
42.2
/
/
/
/
0
0
15 (46)
21 (31)
0
–
–
4 (4)
6–36 (11.1)
8.2–50.3 (32.6)
12–92
12–84
9–68 (34.9)
0–84
(39.1)
24–48 (37.6)
(26)
(48)
(269)
(528)
(168)
(979)
(311)
(96)
16
24
111
236
167
979
188
85
Deporter et al. (2000)
Deporter et al. (2001)
Tawill & Younan (2003)
Nedir et al. (2004)
Griffin & Cheung (2004)
Fugazzotto et al. (2004)
Goené et al. (2005)
Renouard & Nisand (2005)
17 (68)
49 (260)
/
83
12.3
32.4
76.2
100
6.8
15.6
/
92
/
/
8.25
6.95
/
/
19.1 45.6 /
/
95
5
/
/
/
/
35.3
/
/
/
0
21
60–97 (77)
12–168 (96)
99n
94
94 (n ¼ 97%)
98.4
94
99.5
64
3
35
65
100
81.1 /
/
100 /
42.9 47.4 17.8 82.2 86.7
33
18.9
9.6
9.1
8.31
6
/
/
/
6
/
100
/
/
/
36
90
/
/
/
/
/
/
/
55
/
/
3
10
/
3 (5)
5 (9)
(28)
48 (100)
26 (67)
126 (253)
Bernard et al. (1995)
Texeira et al. (1997)
Ten Bruggenkate et al.
(1998)
Stellingsma et al. (2000)
Friberg et al. (2000)
(36)
(60)
12–84
N patients
Follow-up
(N implants) in months
(mean)
Authors
Table 2a. Studies dedicated to short implants
Patient %410 %10 %9
lost to
followup (I)
%8.5 %8
%7
%6
%5 Mean %
%
(mm) Single FPD
crown
%
RD
%
Mx
%
Md
CSR
Mx
(%)
CSR
Md
(%)
CSR
(%)
Renouard & Nisand . Impact of implant length and diameter on survival rates
of short implants included those which
were 10, 11, 12, and 13 mm long (Bernard
et al. 1995; Texeira et al. 1997; Stellingsma
et al. 2000; Tawill & Younan 2003; Nedir
et al. 2004).
Although Ten Bruggenkate et al. (1998)
recommended that short implants should
be used in combination with longer ones,
six of the above studies, reported the use of
short implants alone. Moreover, some of
the studies reported mainly on the use of
short implants to support single crowns
(Deporter et al. 2001; Fugazzotto et al.
2004; Griffin & Cheung 2004).
Nine of these studies involved texturedsurfaced implants, two either machined or
textured-surfaced implants and only two
reported data concerning machined-surfaced implants. One of the studies (Renouard & Nisand 2005) dealing with both
machined and textured-surfaced implants
indicated a trend for better results with the
use of textured-surfaced implants compared with machined ones (97.6% and
92.6% survival rates, respectively); However this trend was not statistically significant.
Four of these studies were devoted to the
treatment of the mandible, and three solely
treatment of the maxilla. Despite a reported increased failure rate of short implants in the maxilla by Ten Bruggenkate
et al. (1998) (six of 45 short implants
placed in the maxilla were lost, giving an
overall survival rate of 86.6%), acceptable
survival rates in this jaw (94.6–100%) were
reported in other studies (Deporter et al.
2000; Fugazzotto et al. 2004; Renouard &
Nisand 2005). The worst cumulative survival rate of short implants (88%) was
reported by Stellingsma et al. (2000) in
the treatment of extremely resorbed mandibles with implant-stabilized overdentures.
However, Friberg et al. (2000) reported a
92.3% cumulative survival rate after 10
years using principally short implants in
severely atrophic mandibles, supporting
fixed prostheses (45) and overdentures (4).
Out of these 13 studies, seven provide
data concerning crestal bone loss. Bernard
et al. (1995) reported an average crestal
bone loss of 0.96 mm between implant
placement and the final observation at 36
months. In contrast Ten Bruggenkate et al.
(1998) found no crestal bone loss following
abutment connection in 72% of the patients studied, 1 mm loss in 16%, 2 mm
40% (2I)
60% (3I)
44.8
Machined (56.2%) and
Ti unite (43.8%)
Renouard & Nisand (2005)
SLA, sandblasted and acid-etched; TPS, titanium plasma-sprayed.
100
Osseotite
Submerged and
nonsubmerged
Nonsubmerged
Goené et al. (2005)
bone loss in 9% and more than 3 mm of
crestal bone loss in 3%. Stellingsma et al.
(2000) claimed that no severe bone loss was
detected after a mean following time of 77
months. Deporter et al. (2001) found no
statistically significant change in the mean
crestal bone level from baseline to the end
of the observation time. Friberg et al.
(2000) reported a mean bone loss of
0.5 0.6 mm during the first year of function and losses of 0.7 0.8 and
0.9 0.6 mm after 5 and 10 years, respectively. In the study by Tawill & Younan
(2003), the mean marginal bone loss was
0.71 0.65 mm; however 8.9% of the
sites lost more than 1.5 mm (ranging from
1.6 to 3.18 mm). These results were consistent with those of Renouard & Nisand
(2005), which indicated a mean marginal
bone loss of 0.44 0.52 mm after 2 years
of function.
It is of interest to note that no specific
pattern was observed concerning the time
of failure of short implants. Apart from the
studies from Stellingsma et al. (2000) and
Goené et al. (2005) which indicated a
tendency to failure before loading.
In all, these 13 studies involved 2072
patients restored with 3173 implants (2141
6–9-mm implants) with a mean implant
length of 7.9 mm, follow-up periods of 0–
168 months (mean follow-up for the nine
studies providing this data was 47.1
months), a mean percentage of patients
lost to follow-up of 9.5% (for the 10 studies
providing this data), and a mean survival
rate of 95.9%.
Moreover, it should be noted that 46.2%
of these articles had been published
between 2003 and 2005.
55.2
30% (3I)
70% (10I)
/
66.7% (2I)
/
40% (4I)
33.3% (1I)
/
60% (6I)
TPS (50%) and SLA (50%)
HA coated
TPS and SLA
–
77.4
100
Prospective
Retrospective
Retrospective,
multicentre
Retrospective,
multicentre
Retrospective
Nedir et al. (2004)
Griffin & Cheung (2004)
Fugazzotto et al. (2004)
–
22.6
/
70.6% (12I)
/
/
50% (6I)
29.4% (5I)
/
/
50% (6I)
100
100
100
100 (with 10 mm)
Machined
Porous-sintered-surface
Porous-sintered surface
Machined
Retrospective
Prospective
Prospective
Retrospective
Friberg et al. (2000)
Deporter et al. (2000)
Deporter et al. (2001)
Tawill & Younan (2003)
/
/
/
/
12.5% (1I)
87.5% (7I)
–
Machined and TPS
Submerged and
nonsubmerged (18%)
Submerged
Submerged
Submerged
Submerged and
nonsubmerged (5%)
Nonsubmerged
Submerged
Nonsubmerged
–
57% (4I)
100% (1I)
100% (3I)
43% (3I)
/
/
–
–
–
–
–
–
TPS
HA coated
TPS
Nonsubmerged
Submerged
Nonsubmerged
Prospective
Retrospective
Retrospective,
multicentre
Retrospective
Bernard et al. (1995)
Texeira et al. (1997)
Ten Bruggenkate
et al. (1998)
Stellingsma et al. (2000)
Table 2b. Studies dedicated to short implants
Implant type
Short implant
alone (%)
Submerged/
Nonsubmerge
technique
Type of study
Authors
Short implant
with long
implant (%)
Failure
before
loading
Failure
after
loading
Renouard & Nisand . Impact of implant length and diameter on survival rates
Implant diameter
Table 3a displays the data extracted from
the nine papers, which dealt mainly with
wide-diameter implants. A higher overall
implant failure rate had been indicated by
two of these articles. The study by Eckert
et al. (2001) reported overall survival rates
of 71% and 81% in the maxilla and mandible, respectively. This failure rate was not
related to any of the specific risk factors
reviewed. In the same way, Shin et al.
(2004) obtained a cumulative survival rate
of 80.9% with wide-diameter implants (a
significantly lower success rate compared
with 87.5% for 4 mm diameter implants
43 |
Clin. Oral Impl. Res. 17 (Suppl. 2), 2006 / 35–51
44 |
Clin. Oral Impl. Res. 17 (Suppl. 2), 2006 / 35–51
Machined
Machined
Aparicio & Orozco Retrospective Submerged
(1998)
Retrospective Submerged
Retrospective Submerged
Renouard et al.
(1999)
Khayat et al.
(2001)
–
Machined
Machined
HA-coated
Retrospective Submerged
Retrospective Submerged
Krennmair &
Waldenberger
(2004)
Shin et al. (2004)
Hultin-Mordenfeld Retrospective Submerged
et al. (2004)
Anner et al.
(2005)
n
Significant differences in the same study.
wOverall survival rate.
CSR, cumulative survival rate; Mx, maxillae; Md, mandible.
Submerged
Machined
Eckert et al. (2001) Longitudinal Submerged
Case series
74 (98)
45 (185)
90 (133)
43 (45)
58 (78)
82 (128)
114 (121)
63 (85)
–
0
7 (14)
0
1–54 (23.4)
11–58 (33)
12–84
1 (1)
6
7
12–114 (41.8) 0
0–734 (286)
in days
11–21 (17)
(12)
/
/
/
/
/
45
(6 mm)
/
/
/
/
78 89.8w
64 80.9%n
/
85 71w (Mx)
81w (Md)
/
98 91.8 w
94 97.2 (Mx)
83.4 (Md)
100w /
/
/
CSR
(%)
133 97.7w
CSR N
(%)
5
121
98.3 /
(5.5 mm)
/
/
/
/
/
Patients 5 þ
lost to
N
followup (I)
16–55 (32.9) 3 (8)
14–37
N patients Follow-up
(N implants) in months
(mean)
Screw Vent 71 (131)
Machined
Case studies
Submerged/
Implants
nonsubmerged type
techniques
Submerged
Bahat &
Handelsman
(1996)
Type of
study
Table 3a. Studies dedicated to wide-diameter implant
/
97.7w
CSR
(all )
CSR
(%)
(%)
Comments
The failure rate for all of the 5-mm implants
(paired and unpaired) was 2.3%. The failure
rate for all double implants (any size) was
1.6%
/
/
–
The reason for larger failure rate in the
mandible for posterior 5-mm implants is not
known. The mean bone loss after 48 months
was 0.97 mm
/
/
91.8w
Bone loss around wide diameter implants
without a smooth collar is comparable to
that reported around standard-diameter
implants. Bone loss that occurred before
second stage surgery was observed primarily
for long implants
131
95w 95w
Only 2.5% of the implants presented crestal
(4.7 mm)
bone loss beyond the first thread. Survival
rates in the mandible and in the maxilla did
not show a statistically significant difference
/
/
71 w(Mx) The current report demonstrated a higher
81w (Md) overall implant failure rate. The failure rate
was not related to any specific risk factors
reviewed.
No relationship was noted between shorter
implants and higher failure rates
/
/
98.3
In 58 of 74 maxillary implants, a sinus lift
procedure was performed. Only two
maxillary implants lost osseintegration
/
/
–
Although, the wide implant suffered a
significantly lower success rate compared
with the standard diameter (87.5% for the
4 mm-wide and 98.2%n for the 3.75 mm-wide
diameter) implant, the 5-mm-diameter WP
implants had a much lower CSR of 73.7%
compared with an overall CSR of 100%
among the 5-mm RP implants
/
/
89.8 w
Better results were seen in the mandible
(94.5%) compared with the maxilla (78.3%).
All failures occurred within 2 years of the
first surgery. The short group (7 and 8.5 mmlength) demonstrated significantly more
failures than the long group
/
/
100w
In the present study, only one implant
presented crestal bone loss beyond the first
thread at the end of the observation period
/
N
4þ
Renouard & Nisand . Impact of implant length and diameter on survival rates
45 |
Prospective
Comfort et al.
(2005)
Submerged
Machined
Machined
Overall survival rate.
CSR, cumulative survival rate; TPS, titanium plasma-sprayed.
n
Retrospective
Vigolo et al.
(2004)
Submerged
Nonsubmerged TPS
Zinsli et al.
(2004)
Prospective
Submerged
Andersen et al. Prospective
(2001)
Machined
Nonsubmerged TPS
Hallman (2001) Prospective
Machined
Machined
Submerged
Retrospective
Submerged
and prospective
9 (23)
165 (192)
154 (298)
28 (32)
40 (182)
44 ( 52)
21 (30)
(60)
(84)
12–120
(36)
(12)
(60)
0
0
1 (2)
3 (3)
0
0
36–89 (63) 0
–
/
/
96.6
23
96n
92 (3.25 mm) –
298
3
/
/
/
/
100 (2.9 mm) –
/
/
/
96n
95.3n
96.6
–
99.4n
94.2n
52 (2.9 mm) 94.2n
/
93.3
One failure occurred after about 66
months of function. Thus, the results
show a cumulative survival rate of 93.3%
and an overall survival rate of 96.7%
During the 5-year period of this study,
two implants failed at the second surgical
phase
Of the 160 narrow implants, one failure
was registered. After 1 year of loading,
the marginal bone resorption
demonstrated a mean of 0.35 mm.12% of
the placed implants were 8-mm length
(one lost)
27 patients received 28 standarddiameter implants and 28 patients
received 32 narrow-diameter implants
with 100% and 93.8% of CSR
respectively. 2 narrow-diameter implants
were lost after 6 months but no others
failures were subsequently observed in
any of the groups. In both groups,
marginal bone loss was recorded to be a
mean of 0.4 mm.The CSR in the 2 groups
were equal despite 2 implants were lost
in the narrow-diameter group
Three implants were lost during the
healing phase. Two implant body
fractures were observed. 60 implants
have an 8-mm length (Only one was lost
due to fracture. The 5-year CSR was
98.7% and the 6-year CSR was 96.6%
No differences between the 2.9-mm and
3.25-mm implants, between small
diameter implants used for single-unit
restorations and those included in
multiple-implant restorations were
detected. 67.2% of the implants
presented a marginal bone loss between
0.6-to 1-mm at 7 years
One implant failed at abutment
connection. The mean marginal bone loss
during the first year was 0.41 mm and
between the 2nd and the 5th year,
0.03 mm
CSR Comments
(all )
CSR (%)
(%)
93.3
30
CSR (%) N
28 (3.25 mm) 93.8
160
/
/
Submerged/
Implants N patients Follow-up Patients
3.3
nonsubmerged type
(N implants) in months lost to
N
techniques
(mean)
follow-up (I)
Vigolo & Givani Retrospective
(2000)
Polizzi et al.
(1999)
Type of study
Table 3b. Studies on narrow-diameter implant
Renouard & Nisand . Impact of implant length and diameter on survival rates
Clin. Oral Impl. Res. 17 (Suppl. 2), 2006 / 35–51
46 |
Clin. Oral Impl. Res. 17 (Suppl. 2), 2006 / 35–51
surface (655)
Non submerged TPS (703)
250 (759)
SLA (56)
Submerged and Machined
376 (1003)
Nonsubmerged (348), rough-
244 (555)
49 (82)
–
(63.6)
0
16–84
(26)
/
/
/
/
/
/
/
/
/
– –
/
/
/
97
/
(at 5 year)
–
/
38 (123)
17y
6–66 (32) 5
(36)
60–144
(120)
(36–60)
5
CSR
(%)
N
4þ
/
/
–
/
–
/
74 –
157 93.1
/
33 –
/
/
/
CSR
(%)
N
CSR
(%)
3.75
N
3þ
/
/
76 95.8
/
193 –
26 100
/
–
/
–
/
470 –
146 93.2
/
434 93w
435 92.2w
91w
CSR
(all )
(%)
group (3%) and 17 of 97 (18%) in the 5-mmdiameter group. No relationship between the
marginal bone loss and implant diameter was seen
during the first year of loading. Shorter implants
showed higher failure rates, specifically within the
5-mm group (20%). In the 3.75 and 4-mm group,
Seven of the 141 implants in the 3.75-mm-diameter
group failed (5%), 2 of 61 in the 4-mm-diameter
Comments
/
/
group showed significantly less marginal bone loss
than the 3.75- and 4-mm groups
Eight implants (3.75-mm-diameter) in six patients
failed before prosthetic treatment. No differences
in success rates were noted among the implants of
different diameter. Length of the implants did not
predominated among the failures of the widerdiameter groups (6 failures with 6–8.5-mm-length
among 86 implants placed : ASR ¼ 93%) . All failures
were recorded in the maxilla. The present study
show similar low failure rates for the various
implant diameters. 10 of the 18 failure were
recorded in 2 patients. The 5-mm-diameter implant
statistically significant. The percentage of implant
failure for the 3 þ mm diameter group was higher at
each stage as compared with 4 þ mm diameter
group
In the 3.75-mm-diameter group, only long implant
failed (13–18 mm), while shorter implants (6–10 mm)
appear to influence the survival rate of restoration.
No so-called short implant (8.5 mm) failed
149 (3.3 mm) 94.6w 96.1 (FPD) Implant failure did not appear to be significantly
influenced by length and diameter
–
–
94%w
No correlation (no effect on failure rate) was found
for implant diameter
98.5
95.3w
92.6w
three of the 47 short implants failed
Shorter standard-diameter implants were lost more
often than longer ones, whereas no wider-diameter
implants whatsoever were lost
/
93.4
The failure rate of wide implant (4- and 5-mm) was
(10 years) 5% vs. 7% for the 3.75-mm implants
92.7nw 93.1w
The differences in survival for the 2 groups were
/
CSR
(%)
11 (3.25 mm) –
/
2695
/
/
61 100 (Mx) 141 95.1 (Mx) /
84.8 (Md)
94.7 (Md)
N
97.3nw /
/
/
/
CSR
(%)
4
31
93.5%w 579 96.2%w
(4.8 mm)
–
–
– –
/
/
222
/
/
97 86.3 (Mx) /
73 (Md)
N CSR N
(%)
5þ
n
Significant differences in the same study.
wOverall survival rate.
zForty-five percent of these implants were used for rescue purposes (when the standard ones were not considered suitable or did not reach initial stability).
yBased on clinical follow-up. Based on radiographic examination, 48 patients dropped out.
zImplant placement in bone of poor texture was executed utilizing an adapted bone site preparation technique.
FPD, fixed partial denture; CSR, cumulative survival rate; Mx, maxillae; Md, mandible; SLA, sandblasted and acid-etched; TPS, titanium plasma-sprayed.
(2005)
Romeo et al. Prospective
(2004)
Lemmerman & Prospective
Lemmerman
Retrospective Submerged
Garlini et al.
(2003)
Osseotite
Machined
Retrospective Submerged
Friberg et al.
(2002)z
98 (379)
Machined and (2917)
202 (660)
HA coated
Machined
127 (461)
67 (229)
(2000)
Retrospective Submerged
Machined
Machined
Winkler et al. Longitudinal Submerged
Bahat (2000)
Submerged
Retrospective Submerged
Lekholm et al. Prospective
(1999)
multicentre
Ivanoff et al.
(1999)z
Type of study Submerged/
Implants type N patients Follow-up Patients
nonsubmerged
(N implants) in months lost to
techniques
(mean)
followup (I)
Table 3c. Studies on oral implants with information on diameter available
Renouard & Nisand . Impact of implant length and diameter on survival rates
and 98.2% for 3.75 mm diameter implants).
In two of the studies, survival rates were
dependent on the location of the implant.
Hultin-Mordenfeld et al. (2004) reported a
higher implant failure rate with wide-diameter implants but better results in the
mandible (94.5%) than the maxilla
(78.3%). Aparicio & Orozco (1998) reported a cumulative survival rate of
97.2% for wide-diameter implants in the
maxilla and 83.4% in the mandible.
The remaining five studies indicated
survival rates within the limits of clinical
acceptance. As such, 528 implants with
diameters from 4.7–6 mm were placed in
392 patients, with a follow-up times of 12–
114 months (mean follow-up for the four
studies providing this data was 23.5
months). The mean number of patients
lost to follow-up was 3% for the four
studies providing this data, with a mean
survival rate of 95.6% (91.8–100%).
Bone loss around wide-diameter implants was comparable with that reported
around standard-diameter implants in most
of the studies, and no specific failure pattern could be observed.
Table 3b displays the data provided by
the seven articles, which are mainly devoted to narrow-diameter implants. All the
studies included in this structured review
have reported low failure rates with the use
of narrow-diameter implants.
Bone loss around narrow-diameter implants was within the same limits as those
reported around standard-diameter implants in most of the studies, and no
specific pattern could be drawn concerning
the time of failures.
In the study by Vigolo et al. (2004), no
differences were found between the 2.9 and
3.25-mm implants, and between small
diameter implants used for single-unit restorations and those included in multipleimplant restorations.
All together these articles involved 461
patients restored with 809 narrow-diameter implants, with follow-up periods
ranging from 12 to 120 months (mean
follow-up for the six studies providing this
data was 52.5 months), a mean percentage
of patients lost to follow-up of 1.6%, and a
mean survival rate of 95.5% (93.3–99.4%).
Table 3c displays the data obtained from
the eight articles, which provided information on implant diameter. Among them,
only two studies indicated a relationship
between implant failure and implant diameter. Ivanoff et al. (1999) reported failure
rates of 5%, 3%, and 18% for 3.75-, 4-, and
5-mm-diameter implants, respectively.
The lowest cumulative survival rates
were seen with 4- and 5-mm-diameter
implants placed in the mandible (84.8%
and 73%, respectively). On the other hand,
Winkler et al. (2000) have reported that the
percentage failure for implants with diameters 43 mm was higher at each stage as
compared with those 44 mm (the differences in survival for the two groups were
statistically significant).
In the remaining six studies implant
failure did not appear to be significantly
influenced by the diameter (Lekholm et al.
1999; Bahat 2000; Friberg et al. 2002;
Garlini et al. 2003; Romeo et al. 2004;
Lemmerman & Lemmerman 2005). As
such, in the study by Friberg et al. (2002)
the failure rates were 5.5%, 3.9%, and
4.5% for 3.75-, 4-, and 5-mm-diameter
implants, respectively.
No relationship between marginal bone
loss and implant diameter was seen in
most of the studies, which reported rather
low changes in crestal bone levels.
Discussion
This structured review has identified 13
articles dedicated to short implants, 21
with data available on implant length,
nine mainly dedicated to wide-diameter
implants, seven dealing solely with narrow-diameter implants and eight with data
available on diameter.
It should be noted, when considering the
outcome of this structured review, that the
level of evidence was somewhat weak. As
such the highest level of evidence (randomized controlled study) has not been
reached in the present analysis.
Implant length
In the light of this literature review, four
main subgroups of outcomes may be highlighted.
Some articles showed clearly that short
implants failed more often than longer ones
(Bahat 1993; Jemt & Lekholm 1995; Wyatt
& Zarb 1998; Bahat 2000; Winkler et al.
2000; Naert et al. 2002; Weng et al. 2003;
Herrmann et al. 2005).
47 |
A second group, although concluding
that failure rates increased with short implants, still provided adequate survival
rates (van Steenberghe et al. 1990; Friberg
et al. 1991; Jemt 1991; Lekholm et al.
1999).
A third group of articles reported that
implant length did not appear to significantly influence the survival rate (Buser et
al. 1997; Ellegaard et al. 1997; Gunne et al.
1999; Brocard et al. 2000; Testori et al.
2001; Stellingsma et al. 2003; Feldman
et al. 2004; Romeo et al. 2004; Lemmerman & Lemmerman 2005).
Finally, a group of articles which focused
specifically on short implants indicated
that these provided similar outcomes to
those reported for longer implants, with
survival rates of 88–100% (Bernard et al.
1995; Texeira et al. 1997; Ten Bruggenkate
et al. 1998; Deporter et al. 2000, 2001;
Friberg et al. 2000; Stellingsma et al. 2000;
Tawill & Younan 2003; Fugazzotto et al.
2004; Griffin & Cheung 2004; Nedir et al.
2004; Goené et al. 2005; Renouard &
Nisand 2005).
There were many differences in the definition of a short implant used in these 34
selected articles (Table 2a). These differences must be considered for an adequate
evaluation and comparison between the
studies.
With respect to this structured review, it
may be appropriated to define a short implant as a device with a designed intra-bony
length of 8 mm or less.
In an attempt to understand such differences in terms of survival rates among the
selected studies, several factors have been
suggested: the implant primary stability,
the practitioner’s learning curve, the
implant surface, and the quality of the
patient’s bone.
First, it is of interest to note that some of
the studies which displayed lower survival
rates with short implants used a routine
surgical protocol independent of the bone
density (Jemt & Lekholm 1995;Wyatt
& Zarb 1998; Naert et al. 2002). With
such a standard surgical protocol, which
frequently used a tapping procedure, primary stability of the freshly inserted implant may have been reduced.
More recent publications dedicated to
short implants have emphasized the use
of an adapted surgical protocol in order to
obtain adequate primary stability. As such,
Clin. Oral Impl. Res. 17 (Suppl. 2), 2006 / 35–51
Renouard & Nisand . Impact of implant length and diameter on survival rates
Tawill & Younan (2003) indicated that the
preparation of the surgical site was altered
to ensure greater primary stability in sites
of poor bone density. In the same way,
Fugazzotto et al. (2004) did not use the
countersink for implant placement and
Renouard & Nisand (2005) reported the
use of an adapted surgical protocol to enhance initial implant stability.
Moreover, the operators’ learning curves
have been proposed as a reason for the
different reported outcomes with short implants between the studies.
In the investigation by Stellingsma et al.
(2000), 17 patients were each treated with
four short (8–10 mm) implants placed in
the mandibular interforaminal region, and
restored with an overdenture. This study
reported an 88% cumulative survival rate
after a mean follow-up period of 77
months.
In 2003, the same team, in a study
comparing three modalities of treatment,
included a group of 20 patients who were
treated with the same protocol as the one
used in the previous study. This more
recent publication reported a 100% cumulative survival rate after 12 months followup. It could be argued that this reflects the
difference in the follow-up time between
the two studies, but it should be noted that
in the first study 87.5% of the failed implants were lost before loading.
Hence, it is noteworthy that articles
dedicated to short implants published
from 2003 to 2005 have reported survival
rates ranging from 94.6–99.4%.
With regards to the variations between
studies in the outcomes of treatment with
short implants, these may be explained by
differences in implant surfaces properties.
Out of the 12 studies which have documented an increased failure rate with short
implants, 11 used of machined-surfaced
implants (van Steenberghe et al. 1990;
Friberg et al. 1991; Jemt 1991; Bahat
1993; Jemt & Lekholm 1995;Wyatt &
Zarb 1998; Lekholm et al. 1999; Bahat
2000; Naert et al. 2002; Weng et al.
2003; Herrmann et al. 2005). The remaining study (Winkler et al. 2000) used
both machined-surfaced and HA-coated
implants.
In the other hand, out of the nine studies
which have indicated that implant length
did not influence the survival rate, six
(Buser et al. 1997; Ellegaard et al. 1997;
48 |
Clin. Oral Impl. Res. 17 (Suppl. 2), 2006 / 35–51
Brocard et al. 2000; Testori et al. 2001;
Feldman et al. 2004; Romeo et al. 2004)
were performed with textured-surfaced implants. One of the remaining studies (Lemmerman & Lemmerman 2005) used
mainly textured-surfaced implants. In the
same way, out of the 13 studies devoted to
short implants, nine used textured-surfaced
implants and two used either machined or
textured-surfaced implants.
In an attempt to compare the 5-year
survival rate of short machined-surfaced
and short dual-acid-etched surfaced implants, Feldman et al. (2004) demonstrated
survival rates of 91.6% and 97.7%, respectively. In this study a statistically significant difference in cumulative survival rate
was found between short machined-surfaced implants and standard machined-surfaced implants. It is noteworthy that this
difference increased dramatically in the
posterior maxilla. For the dual-acid-etched
implants, no statistically significant differences were demonstrated between shortand standard-length implants. When comparing, the cumulative survival rates in
poor bone density, Feldman et al. (2004)
demonstrated that short dual-acid-etched
implants provided better outcomes than
machined-surfaced implants (96% and
86.5%, respectively).
Additionally, Renouard & Nisand (2005)
have demonstrated a trend for better results
with the use of oxidized implants compared
with machined-surfaced implants. However, the difference of 5% was not statistically significant.
Finally, short implants have been routinely placed in anatomical sites with limited bone volume (Wyatt & Zarb 1998).
When the relationship between implant
length and available jaw bone were examined, Herrmann et al. (2005) found that
29.4% of the 7-mm implants were placed
in jaws with jaw shape E and 25.5% were
placed in jaw with jaw shape D, according
to Lekholm and Zarb’s classification.
As suggested by Friberg et al. (1991), jaw
shape and bone density must be considered
as the most influential factors in implant
survival. It should be understood that the
length of the implant, in most of the
studies reflects the state of jaw bone
resorption.
In the study by Herrmann et al. (2005),
short implants placed in combination I
bone (consisting of implants placed in jaw
shapes A, B, and C and bone qualities of 1,
2, and 3) had a failure rate of 7.3% compared with 3% for longer implants. For
combination II (jaw shapes D and E and
bone qualities of 1, 2, and 3) and IV (jaw
shapes D and E and bone density 4), the
corresponding figures were 13% (short implants) and 0% (long implants), and 78%
(short implants) and 0% (long implants).
Obviously, in combinations II and IV,
only seven long implants have been placed
in comparison with 55 short implants.
It must be noted that in such sites with
poor bone density and volume, short implants should not be compared with long
implants placed in good bone density, but
with the advanced surgical procedures
which would be required to allow the
placement of longer implants.
Hence, the 96% cumulative survival
rate obtained in poor bone density by Feldman et al. (2004), or the 94.6% obtained by
Renouard and Nisand (2005) in the treatment of severely resorbed maxilla should
not be compared with the outcomes of
long implant placed in adequate bone
density. Rather, it should be compared
with the overall survival rate of 91.5%
reported by Del Fabbro et al. (2004) in a
systematic review of implants placed in the
grafted maxillary sinus, or the implant
survival rate of 75.1% reported by Becktor
et al. (2004) in the grafted edentulous
maxilla.
Besides survival rates, when comparing
the outcomes of short implants with advanced surgical therapy, morbidity must be
evaluated as well in order to allow an
adequate comparison. It should be noted
that neurosensory disturbances were experienced by 21% of the cases treated by
inferior alveolar nerve transposition (Ferrigno et al. 2005), that post-operative complications specifically related to sinus graft
procedures affected 10% of patients
(Schwartz-Arad et al. 2004), and that complications associated with the distraction
procedure affected 75.7% of patients
(Enislidis et al. 2005).
Implant diameter
When considering narrow-diameter implants, it should be noted that all the
studies included in this structured review
have reported low failure rates. These figures could be explained by adapted and
atraumatic preparation techniques, and
Renouard & Nisand . Impact of implant length and diameter on survival rates
the careful patient selection in terms of
biomechanical conditions and bone
density. As such, narrow-diameter implants would probably have been considered in clinical situations in which spacerelated difficulties or bone availability did
not allow the use of standard-diameter
implants.
However, further studies are needed in
order to clearly define the limits of narrowdiameter implants with regards to clinical
indications, load-bearing capacity and longterm fate.
In the study by Ivanoff et al. (1999), it
was suggested that the increased failure
rate of 5-mm-diameter implants was associated with the operators’ learning curves,
poor bone density (5-mm-diameter implants were used as a ‘rescue’ implant in
45% of implant sites), implant design, and
the use of this implant diameter when
primary stability could not be achieved
with a standard-diameter implant. This
view was supported by the study of Hultin-Mordenfeld et al. (2004) in which widediameter implants were placed in unfavourable situations such as poor bone density, and compromised bone volume. As
such, in some studies a trend could be
drawn with a prevalence of early failures
(Ivanoff et al. 1999; Eckert et al. 2001; Shin
et al. 2004).
In most of the recent studies, however,
no relationship has been found between
wide-diameter implants and survival rates.
This may possibly reflect the use of newer
implant designs, more appropriate case
selection and the use of an adapted surgical
technique.
This structured review has demonstrated a
trend for an increase failure rate with short
implants and wide-diameter implants.
The highest failure rates for short implants were reported in older studies, which
were performed with routine surgical procedures independently of the bone quality,
with machined-surfaced implants and in
restricted anatomic sites with poor bone
density.
The increased failure rates of widediameter implants reported in some
studies have been mainly associated with
operators’ learning curves, poor bone density, implant designs and site preparation,
and the use of this diameter as a ‘rescue’
implant.
More recent studies which have used
surgical preparation adapted to the bone
density, textured-surfaced implants, and
modified case selection have reported survival rates for short implants and for widediameter implants which were comparable
with those obtained with long-implants
and standard-diameter implants.
In sites associated with poor bone density and jaw bone resorption, a prevalence
of short implants and/or wide-diameter
implants might be used. In these particular
situations, failure rates may be increased,
but should then be compared with the
failure rates and morbidity of advanced
surgical procedures such as bone grafting,
sinus lifting, and alveolar nerve transpositioning. Thus both survival rates and morbidity must be considered when comparing
the outcomes of short implants and advanced surgical procedures to allow adequate comparisons.
It must be noted that the levels of evidence provided by the literature are rather
low, and that further research with higher
level (randomized controlled studies),
should be performed in order to investigate
the relationships between bone density,
implant length and diameter, and survival
rates.
Becktor, J.P., Isaksson, S. & Sennerby, L. (2004)
Survival analysis of endosseous implants in
grafted and nongrafted edentulous maxillae. International Journal of Oral & Maxillofacial Implants 19: 107–115.
Bernard, J.P., Belser, U., Szmuckler, S., Martinet,
J.P., Attieh, A. & Saad, P.J. (1995) Intérêt de
l’utilisation d’implants ITI de faible longueur
dans les secteurs postérieurs: résultats d’une étude
clinique à 3ans. Médecine Buccale, Chirurgie
Buccale 1: 1–18.
Brocard, D., Barthet, P., Baysse, E., Duffort, J.F.,
Eller, P., Justumus, P., Marin, P., Oscaby, F.,
Simonet, T., Benqué, E. & Brunel, G. (2000) A
multicenter report on 1022 consecutively placed
ITI implants: a 7-year longitudinal study. International Journal of Oral & Maxillofacial Implants 15: 691–700.
Buser, D., Mericske-Stern, R., Bernard, J.P., Behneke, A., Behneke, N., Hirt, H.P., Belser, U. &
Lang, N.P. (1997) Long-term evaluation of nonsubmerged ITI implants. Part 1: 8-year life table
analysis of a prospective multicenter study with
2359 implants. Clinical Oral Implants Research
8: 161–172.
Comfort, M.B., Chu, F.C.S., Chai, J., Wat, P.Y.P. &
Chow, T.W. (2005) A 5-year prospective study on
small diameter screw-shaped oral implants. Journal of Oral Rehabilitation 32: 341–345.
Del Fabbro, M., Testori, T., Francetti, L. & Weinstein, R. (2004) Systematic review of survival
rates for implants placed in the grafted maxillary
sinus. International Journal of Periodontics and
Restorative Dentistry 24: 565–577.
Deporter, D.A., Pilliar, R.M., Todescan, R., Watson,
P. & Pharoah, M. (2001) Managing the posterior
mandible of partially edentulous patients with
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Oral & Maxillofacial Implants 16: 653–658.
Deporter, D.A., Todescan, R. & Caudry, S. (2000)
Simplifying management of the posterior maxilla
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Eckert, S.E., Meraw, S.J., Weaver, A.L. & Lohse,
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Implants 16: 208–216.
Ellegaard, B., Baelum, V. & Karring, T. (1997)
Implant therapy in periodontally compromised
Conclusions
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