Transcript
50 THE JOURNAL OF PROSTHETIC DENTISTRY VOLUME 84 NUMBER 1
The rate of success of implants in the edentulous
mouth has encouraged dentists to extend this applica-
tion to the replacement of single missing teeth. High-
ly evolved surgical techniques and the introduction of
special components for single-tooth replacements
allowed functional and esthetic improvements.
1
The
use of standard-sized or of wide-diameter implants is
suggested to allow favorable contact surface between
the bone and the implant itself.
2
Occasionally, lack of
space does not allow the dentist to place implants of
such dimensions. An adequate solution in these cir-
cumstances, when single-tooth restorations are needed
and the space is not sufficient to insert a standard or a
wide diameter implant, is the mini-implant.
From the data available in the literature, regular-
sized osseointegrated implants showed similar behavior
in the rehabilitation of totally and partially edentulous
arches and in single-tooth replacement.
1,3-20
With
regard to the rehabilitation of totally edentulous arches,
Ahlqvist et al
6
studied osseointegrated implants in 50
edentulous jaws during a 2-year observation period.
The implant survival rate was 89%in the maxillae and
97% in the mandibles. Zarb and Schmitt
7
studied,
prospectively, the 5- to 10-year results of treatment of
edentulous patients with osseointegrated implant-sup-
ported bridges. At the end of the 5- to 10-year obser-
vation period, 88.32% of the implants remained
osseointegrated and 85.04% of these implants were
used to support 43 fixed prostheses and 5 overdentures.
For rehabilitation of partially edentulous arches,
Van Steenberghe
10
evaluated the prognosis of the
osseointegration technique applied for the rehabilita-
tion of partially edentulous jaws a multicenter retro-
spective study. The observation time varied between 6
and 36 months after prosthetic reconstruction. The
success rate for the individual implants in the maxilla
and mandible was 87%and 92%, respectively. Zarb and
Schmitt
11
studied prospectively the results of osseoin-
tegrated implants placed in partially edentulous areas
in the posterior zones. One hundred five implants
were placed in 46 edentulous areas in 35 patients.
After periods of loaded service ranging from 2.6 to 7.4
years (mean 5.2 years), of the 41 implants placed in
maxillae, 40 (97.6%) remained in function, and of the
64 placed in mandibles, 59 (92.2%) remained in func-
tion, with an overall implant survival rate of 94.3%.
Zarb and Schmitt
12
also reported an average success
rate of 91.5%for implants placed in the anterior part
Clinical evaluation of single-tooth mini-implant restorations: A five-year
retrospective study
Paolo Vigolo, Dr Odont, MScD, and Andrea Givani, MD, DDS
Vicenza, Italy
Statement of problem. Placement of small diameter implants often provides a solution to space prob-
lems in implant restoration. Analysis of the success of this type of implant restoration has not been clearly
determined.
Purpose. This 5-year retrospective study presents results from 52 mini-implants for single-tooth restora-
tions placed in 44 patients from 1992 to 1994.
Material and methods. Dental records of 44 patients with 52 mini-implants placed during 1992-94
were reviewed. The implants were all placed by the same surgeon and the single-tooth custom screwed
posts with cemented crowns were positioned on the implants by the same prosthodontist.
Results. The results achieved by the mini-implant rehabilitation were similar to those reported for stan-
dard single-tooth implant restoration. Total implant survival rate was 94.2%. Two implants were lost at
second stage surgery, and another was lost after temporary loading.
Conclusion. The results suggest that single-tooth mini-implant restoration can be a successful treatment
alternative to solve both functional and esthetic problems. They may represent the preferred choice in
cases where space problems limit the use of standard or wide diameter implants. (J Prosthet Dent 2000;
84:50-4.)
a
Private Practice.
CLINICAL IMPLICATIONS
Single-tooth mini-implant restorationsdemonstrated a rateof successsimilar to those
reported bypreviousstudiesfor standard single-tooth implant restoration. Therefore, a
mini-implant mayrepresent a valid treatment alternativewhen spaceproblemsoccur.
VIGOLO AND GIVANI THE JOURNAL OF PROSTHETIC DENTISTRY
JULY 2000 51
of partially edentulous mouths both in the maxilla and
in the mandible.
With regard to single-tooth restorations, Cordioli
et al
1
reported the clinical experience of 47 patients
treated for a single-tooth replacement exhibiting a
total implant survival rate of 94.4%. Engquist et al
18
evaluated the outcome of single-tooth restorations on
Brånemark implants performed during the period
1984-1989, showing an overall survival rate of 97.6%.
McMillan et al
20
investigated the nature, timing, and
frequency of complications associated with single-
tooth implant therapy in a dental hospital and 2 den-
tal offices and they determined an implant survival rate
of 96%.
The literature provides laboratory studies that show
the different results when using different diameter
implants. I vanoff et al
21
studied the influence of diam-
eter on the integration of titanium screw-shaped
implants in rabbit tibia by means of removal torque
measurements and histomorphometry. They inserted
implants 3.0, 3.75, 5.0, and 6.0 mm in diameter and
6.0 mm long through one cortical layer in the tibial
methaphyses of 9 rabbits and allowed them to heal for
12 weeks. The implants were then unscrewed with a
torque gauge and the peak torque required to shear
off the implants was recorded. The biomechanical tests
showed a statistically significant increase of removal
torque with increasing implant diameter. Two distinct
studies have questioned the importance of implant
diameter: I n the first study,
22
the effect of diameter
and length on the pullout force required to extract
hydroxylapatite-coated implants from dog alveolar
bone was compared. After 15 weeks of integration,
implants of 3.0, 3.3, and 4.0 mm diameter and 4, 8,
and 15 mm length were pulled. The results of this
study showed that the ultimate pullout force correlat-
ed strongly to implant length, but not to diameter.
The second study
23
compared the pullout resistance of
small and large diameter (3.25 and 4.25 mm) dental
implants placed in the mandibles of 5 embalmed
humans and the relationship of these implants to bone
density. The maximum pullout force required for the
large diameter implants was 15% greater than that
required for the small diameter implants, but the dif-
ference was not significant. I n the same study, a signif-
icant positive correlation between the pull-out resis-
tance and the bone density for both the large and small
diameter implants (P<.05 and P<.01, respectively) was
noted. However, the real clinical significance of torque
and pullout tests is controversial.
The aim of this retrospective study was to collect
and summarize 5 years of clinical data on a group of
patients treated with the use of 2.9-mm mini-implants
(3i I mplant I nnovations, I nc, Palm Beach Gardens,
Fla.) for single-tooth restorations in a private clinic
environment.
MATERIAL AND METHODS
Between 1992 and 1994, 197 patients were offered
implant treatment in a private practice; a total of 638
implants were inserted. A sample group of 44 patients
(26 women and 18 men) was investigated; 8 patients
exhibited dental agenesia, 17 had lost teeth from den-
tal trauma, and 19 missed teeth as a result of caries or
periodontal disease. During the inclusion period, these
44 patients were provided with mini-implants support-
ing single restorations to replace the missing teeth.
The ages ranged from 18 to 74 years (mean age of 35).
All patients were in good health. All patients in the
sample group returned for recall and all 44 are includ-
ed in the initial and final data.
A total of 52 2.9 mm mini-implants (3i I mplant
I nnovation, I nc) were positioned after a 2-stage surgi-
cal technique (Fig. 1). The 2.9-mm implants were
chosen because no space was available for wider
implants. Because of space problems the surgeries had
to be carefully accomplished with the guidance of a
template to decrease the risk of damaging the adjacent
teeth and to reduce the difficulties in the prosthetic
phase due to poor positioning of the implant. I f an
implant had to be placed in an extraction site, a
2-month waiting period allowed esthetic healing of the
soft tissues before implant placement. Five implants
were inserted at the extraction time of traumatized
maxillary lateral incisors so as to accelerate the treat-
ment. The total number and type of teeth replaced by
implants, the length of the implants used, and the
quality of the bone
24
in the implant sites are presented
in Tables I through I I I .
At second stage surgery, the titanium healing cap
connection was made. The final restorations were fab-
ricated after conventional procedures for cemented
Fig. 1. Patient missing maxillary lateral incisor because of
agenesia. Canine in lateral position has been modified
slightly to assume morphology at lateral incisor position.
Mini-implant inserted in canine area.
THE JOURNAL OF PROSTHETIC DENTISTRY VIGOLO AND GIVANI
52 VOLUME 84 NUMBER 1
single-tooth restoration with a screw-retained abut-
ment and a cemented crown technique.
Gold-machined UCLA abutments (GUCA3, 3i
I mplant I nnovations, I nc) were used. The gold UCLA-
type abutments were screwed on top of the implant
replicas using waxing posts and wax added directly to
the gold cylinders according to standard waxing proce-
dures. The waxed-up cylinders were then invested in a
carbon-free phosphate-bonded investment (Ceramicor,
Cendres & Métaux SA, Biel-Bienne, France) and cast
with a noble alloy (Al Med, Cendres & Métaux SA). A
custom-screwed post was fabricated for all the mini-
implants (Fig. 2); the custom posts were screwed on top
of the implants in the patients’ mouths by using a
torque wrench calibrated at 30 N·cm (torque driver
CATDO, 3i I mplant I nnovations, I nc) and a provision-
al resin crown was temporarily cemented on each post
and left in the mouth for a 2-month period (temporary
cement: Temp Bond NE, Kerr I talia Sp A, Scafati, Saler-
no, I taly). This temporary phase allowed good defini-
tion and stability of the peri-implant soft tissues. This
also permitted evaluation of the occlusal scheme and to
perform the appropriate variations to the occlusal con-
tacts both static and dynamic. I n 7 patients where the
esthetic aspects were particularly important, mucogin-
gival surgeries were accomplished to improve the
appearance of the gingiva. After this initial temporary
phase, the custom posts were reprepared in the patients’
mouths to follow the matured gingival morphology;
then they were unscrewed, polished by the laboratory
technician and repositioned on the implants. Final
impressions of the mini-implant posts were accom-
plished following conventional crown and bridge tech-
niques by using custom trays and polyether material:
I mpregum F (ESPE Dental-Medizin GmbH & Co KG)
was used in the trays and Permadyne L (ESPE Dental-
Medizin GmbH & Co KG) in the syringes. Gingival
retraction was accomplished with a nonimpregnated
retraction cord (Z-Twist Gingi-Plain, Gingi-Pak, Bel-
port Co, I nc, Camarillo, Calif.). For 36 implants, regu-
lar porcelain-fused-to-metal final crowns with porcelain
occlusal were made (Fig. 3); for the remaining implants,
where the esthetic factors were of minor importance, 16
resin gold crowns with gold occlusal were constructed.
The occlusal surfaces of the crowns were designed to
avoid premature contact during lateral and protrusive
movements.
All final crowns were cemented with temporary
cement (Temp Bond NE, Kerr I talia Sp A). After pros-
thetic treatment, a follow-up program was designed
for all patients; this provided the opportunity to check
the patients every 3 months in the first year and every
6 months in the following years. All the patients regu-
larly returned to the office for recall. Five years after
the implant insertion, at the last follow-up appoint-
Table I. Site, cause of tooth loss, and number of single
teeth replaced using mini-implants
Number of
single teeth
Site Cause of tooth loss replaced
Maxilla
Central incisor Trauma 1
Lateral incisor Trauma, agenesia 14
Canine Agenesia 2
First premolar Caries, periodontal disease 8
Second premolar Caries, periodontal disease 4
Total 29
Mandible
Central incisor Trauma 5
Lateral incisor Trauma, periodontal disease 5
Canine Trauma 3
First premolar Trauma, periodontal disease, caries 5
Second premolar Trauma, periodontal disease, caries 4
First molar Caries 1
Total 23
Table II. Length of mini-implants used for single-tooth
replacement (3i Implant Innovations)
Length (mm) Number of implants
8.5 (MI 085) 1
10 (MI 100) 20
13 (MI 130) 22
15 (MI 150) 9
Table III. Bone quality at the implant sites
24
Bone quality Number of implants
Type I 12
Type II 22
Type III 14
Type IV 4
Fig. 2. Custom-screwed post on top of mini-implant at time
of final impression.
VIGOLO AND GIVANI THE JOURNAL OF PROSTHETIC DENTISTRY
JULY 2000 53
ment, all patients were seen and periodontal parameter
data were compiled on peri-implant mucosal response
(dichotomic records on 4 surfaces): supragingival
plaque, gingival inflammation, bleeding on probing,
amount of keratinized gingiva around abutment, and
probing depth from the gingival margin.
All cemented crowns were carefully removed with
the GC removal pliers (K.Y. type, GC Corporation,
Tokyo, Japan) to avoid damaging the crowns. The cus-
tom posts were unscrewed to allow the measurement
of the mucosal canal using a periodontal probe to
record the length from the marginal gingiva to the
head of the implant. I ntraoral radiographic examina-
tions were performed using the paralleling technique
and an adjusted film-holding device as suggested by pre-
vious studies.
1,25
The radiographic films were observed
using a 5× magnifying lens to precisely reveal the implant
threads and permit the measurement of marginal bone
resorption with an accuracy of ±0.3 mm. Occlusal rela-
tionships and all complications were recorded.
RESULTS
During the 5-year period of this study, 2 implants
(10 mm in length) failed at the second surgical phase.
These units were placed in the first premolar sites in
the upper maxilla (bone quality 4) in a 52-year-old
woman. Another implant (13 mm length) placed in
the lower left lateral incisor site of a 25-year-old
woman was lost 1 month after the custom post was
positioned on the implant and the temporary crown
was cemented.
One patient reported the loosening of the custom-
screwed post twice. The post was remade and the
problem did not recur. Five patients reported fracture
or loosening of the provisional resin crowns. The
problem was solved by making an accurate adjustment
to the patient’s occlusion. Seven patients reported
recurrent loosening of provisionally cemented final
crowns all with porcelain occlusal surfaces. This prob-
lem was solved by selective equilibration to achieve
optimal occlusion and to avoid contact in lateral and
protrusive movements.
The clinical evaluation of peri-implant mucosa
using periodontal indices gave satisfying results for the
implant-mucosa interfaces (Table I V). Dental plaque
was present on 12%of the considered surfaces and gin-
gival inflammation was present on only 4.5%. Kera-
tinized attached gingiva was not present in 9%of buc-
cal surfaces or in 5.5% of lingual surfaces. A mean
probing depth of 2.3 mm was recorded, less than
reported in some other studies.
1,26,27
The probing was
carefully accomplished and a low percentage of sites
(6.5%) had bleeding on probing. The mean marginal
bone resorption at the last checkup, measured with the
intraoral radiographic examination method previously
described from the apical end of the smooth collar of
the mini-implant, was 0.8 mm, with a range of 0.5 to
1.1 mm.
DISCUSSION
This 5-year retrospective study presents the results
from 52 mini-implants for single-tooth replacement
inserted in 44 patients from 1992 to 1994. All
implants were put in position by the same surgeon and
all custom-screwed posts with single cemented crowns
were positioned on implants by the same prosthodon-
tist. I n this study, the mini-implants used in single-
tooth rehabilitation exhibited a 94.2%success rate sim-
ilar to the results accomplished by regular-sized
implants in single-tooth replacement cases.
1,14-20
The mini-implant is commonly used in areas of nar-
row ridge dimension or where prosthetic space is lim-
ited.
2
This often occurs in the anterior maxillary
region, especially in situations of congenitally missing
teeth and after orthodontic treatment, wherein the
lack of space does not allow use of a regular-sized
implant. A space problem frequently results as well in
the mandibular incisors and in the maxillary premolar
and canine areas. Furthermore, the presence of thin
posterior mandibular ridges that would require bone
augmentation surgery before the insertion of standard-
sized or wide diameter implants. I n such situations,
insertion of small diameter implants would enable the
Table IV. Periodontal parameters recorded by dichotomic
records (presence or absence)
Periodontal indicesrecords Percentage
Plaque presence 12
Gingival inflammation 4.5
Bleeding on probing 6.5
Amount of facial keratinized gingiva 91
Amount of lingual keratinized gingiva 94.5
Fig. 3. Porcelain-fused-to-metal crown cemented on cus-
tom-screwed post 5 years after mini-implant insertion.
THE JOURNAL OF PROSTHETIC DENTISTRY VIGOLO AND GIVANI
54 VOLUME 84 NUMBER 1
dentist to rehabilitate the patient without preinstalla-
tion surgery.
All implants were restored with custom posts and
cemented final crowns in anticipation of achieving
more natural esthetic results. As previously said, the
occlusal scheme had to be carefully equilibrated to
avoid prematurities in eccentric movements. All our
minor prosthetic problems (fracture of the resin provi-
sional crowns, decementation of provisional resin
crowns, decementation of final crowns) were associat-
ed with occlusal prematurities. For maxillary canine
substitution, we tried to concentrate the lateral guid-
ing movements in the first premolar area. I n 1 patient,
a 2.9-mm mini-implant was positioned in the first
lower right molar site where the thin crestal ridge did
not allow the placement of a wider diameter implant.
The final restoration in that situation was a regular
porcelain-fused-to-metal crown with porcelain
occlusal: The crown shape was reduced to the dimen-
sion of a mandibular premolar to better control the
occlusal contacts of the restoration.
Only 1 patient reported the loosening of the custom-
screwed post. After closer analysis, the post showed
some casting imperfections at the hexagon level. The
post was remade and the problem did not recur. I t is
probable that the internal hexagon pattern of this type
of mini-implant reduces the risk of custom-post
unscrewing that has been reported by some authors,
with relation to standard-sized implant single-tooth
restorations.
16
CONCLUSIONS
Within the limits of this study, the following con-
clusions were drawn:
1. A success rate of 94.2%was observed. Failures
were related to poor bone quality in the recipient sites
and to occlusal problems.
2. The single-tooth mini-implant restoration can be
a valid alternative in many clinical situations in which
space problems do not permit the use of standard- or
wide-diameter implants.
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Reprint requests to:
DR PAOLO VIGOLO
VIA VECCHIA FERRIERA, 13
36100 VICENZA
ITALY
FAX NUMBER: (39)444-964545
E-MAIL:
[email protected]
Copyright ©2000 by The Editorial Council of The Journal of Prosthetic
Dentistry.
0022-3913/2000/$12.00 +0. 10/1/107674
doi:10.1067/mpr.2000.107674