An in vitro comparison of cast metal dowel retention using various luting
agents and tensile loading
H. Zeynep Ertugrul, DDS, PhD,a and Yahia H. Ismail, DMD, MS, PhDb
School of Dental Medicine, Department of Prosthodontics, University of Pittsburgh, Pittsburgh, Pa
Statement of problem. No clear consensus exists regarding the choice of luting agents for the retention of
cast metal dowels used as a treatment alternative for endodontically treated teeth with excessive loss of coronal
tooth structure.
Purpose. The purpose of this in vitro study was to investigate the retention of the dowel/luting agent/tooth
complex while applying different luting agents to cast metal dowels under vertical tensile loading.
Material and methods. Sixty extracted, noncarious mandibular premolars with roots of approximately
15-mm length were selected. For each tooth, a tapered root canal preparation was completed to a maximum
diameter of 1.60 mm and a length of 11 mm, a common clinical configuration to accommodate cast metal
dowels. Sixty cast metal dowels were fabricated for the tooth specimens and cemented with 1 of 3 luting agents
(n = 20): zinc-phosphate cement (ZPC) as a control, phosphate-methacrylate resin luting agent (PMRL,
Panavia F), and phosphate-methacrylate resin luting agent with metal dowel surfaces modified with a silane
coating technique (PMRLS, Panavia F 1 Siloc). Tensile bond strength (TBS) of the specimens was measured
with a universal testing machine at a crosshead speed of 0.5 mm/min. Data (kg) were statistically analyzed using a
1-way analysis of variance and a Scheffe multiple range test (a=.05). The homogeneity of variances was analyzed
using the Levene test.
Results. The TBS values of ZPC (34.2 6 10.54 kg) were significantly higher than PMRL (22 6 9.57 kg) and
PMRLS (21.7 6 7.64 kg). There was no significant difference between the PMRL and PMRLS groups.
Conclusion. Within the limitations of this study, the use of zinc-phosphate cement provided greater TBS for cast
metal dowels than the resin luting agent with and without the silane coating technique. The TBS values with and
without the silane coating technique were not statistically different. (J Prosthet Dent 2005;93:446-52.)
CLINICAL IMPLICATIONS
The use of cast metal dowels is common in restorative dentistry. This study demonstrated that
zinc-phosphate cement can provide superior retention for cast metal dowels relative to the
phosphate-methacrylate resin luting agent with or without the silane coating technique.
Consequently, practitioners may opt to choose zinc-phosphate cement over the other materials
tested when providing this treatment.
T
he successful restoration of an endodontically
treated tooth is an ongoing challenge for a restorative
dentist.1-3 Cast metal dowels are used as a method
for dowel-and-core fabrication, and have been used to
provide long-term tooth structure replacement for
endodontically treated teeth with moderate to severe
damage.4,5 Cast dowels are best used for single-rooted
teeth and may be fabricated directly or indirectly.4-6
The retention of a dowel in a root is critical for the
longevity and success of this treatment. Studies have
reported that design, length, and character of the surface
of endodontic dowels have an influence on their
retentive properties.2-4,7 Furthermore, the ability of
a
Postgraduate Fellow.
Professor and Director, Prosthodontic Residency Program.
b
446 THE JOURNAL OF PROSTHETIC DENTISTRY
a luting agent to retain a dowel can affect the prognosis
of a restoration.4,7 All dowels gain their definitive retention by cementation into a prepared root.2,8-10
Currently, a large variety of luting agents are available
for this purpose. Studies have provided conflicting results in regard to the performance of different types of
luting agents in retaining dowels.1,2,7,8,10-14 The ability
of different luting agents to retain dental dowels is related to the mechanical properties and durability of a luting agent, the bonding ability of a luting agent to the
surfaces being joined, and the configuration of a dowel
and prepared canal.2,15-17
The luting agents currently available for dental
restoration are zinc-phosphate, polycarboxylate, glass
ionomer, resin-modified glass ionomer, compomer,
and adhesive resin cements.4,18 Morgano and
Brackett4 showed that there are distinct advantages
and inherent disadvantages for each material category.
VOLUME 93 NUMBER 5
ERTUGRUL AND ISMAIL
Fig. 1. Cast metal dowel and core.
The authors reported that polycarboxylate and glassionomer cements provide a weak chemical bond to dentin. Polycarboxylate cements have been reported to
undergo plastic deformation after cyclic loading and
may be less retentive than zinc-phosphate and glassionomer cements.4 Glass-ionomer cements are known
to require several days and even several weeks to reach
maximum strength, making this choice unsuitable as
a cement for dowels.4,7 Resin-modified glass-ionomer
cements, although suggested for cementation of dowels, can imbibe water and expand with time.4 Zinc-phosphate cement has been the gold standard luting agent
for decades. However, resin luting agents have also
been studied extensively, and several investigations
have evaluated the retention of interradicular dowels
using adhesive resins.1,4,7-10,19 Some studies demonstrated that adhesive resin luting agents are more retentive than zinc-phosphate cement for dowels.2,7,11,14,20
However, other studies have demonstrated conflicting
results8,10,13,21 based on shrinkage stress and the difficulty in manipulating a phosphate-methacrylate resin
luting agent. Shrinkage stress results in debonding of
the luting agent from dentin and a tendency of the
bonding of phosphate-methacrylate resin cement to
fail in the root canal.10 Additionally, difficulty in manipulation, which results in the premature polymerization
of the phosphate-methacrylate resin luting agent, can
prevent a complete seating of dowels into root canals.8
In the dowel–luting agent–tooth complex, there are
several regions that may be a weak link in the outcome
of treatment, depending on the luting agent used.
These regions include the luting agent–dentin interface,
the dentin, and the luting agent–metal interface.1 With
respect to the luting agent–metal interface,1,22 metal
surfaces may be altered in a variety of ways to improve
adhesion, including airborne-particle abrasion, etching,
and silane coating.1,22-26 The silane coating technique
has been used for both noble and base alloys23,25-32
and has also been proposed for use in combination
MAY 2005
THE JOURNAL OF PROSTHETIC DENTISTRY
with phosphate-methacrylate resin luting agents.22,28,32,33
This technique pyrolytically applies a silica bonding layer
to the surface of a metal. A bifunctional silane-coupling
agent, which bonds the silanol groups of a silica layer
with the monomers of acrylic resin, is then added to
enhance bonding between the resin and metal surface.12,27,34 It was reported that a strong chemical
bond is produced between metal and resin as a result
of the silica-silane bond that promotes adhesion.22,2629,33
However, other studies indicate decreased11,12,23
or unchanged bond strengths of adhesive resin luting
agents with base metal alloys when used with silane coating.12,28,31 A silane coating technique (Siloc) has been
recently developed to simplify the regimen.34-36 It is
also applicable to both noble and base alloys and is
used to provide a chemical bond between the silica layers
coated to an airborne-particle–abraded metal surface
and a resin composite.34-41 Limited information is available about the bond strength of cast base metal dowels
with a silane coating surface treatment. The objective
of this in vitro study was to compare the retention
of cast metal dowels when cemented with a zincphosphate, a phosphate-methacrylate, and a phosphatemethacrylate resin luting agent together with a recently
developed silane coating metal surface treatment
technique.
MATERIAL AND METHODS
Sixty mandibular, noncarious premolars with root
lengths of approximately 15 mm were selected for this
study. Specimens were extracted within the last 6
months due to periodontal involvement. Teeth were
stored in a 0.1% M NaCl (0.9%) isotonic sodium chloride solution at 22°C. The crowns were separated from
the roots 1 mm above the cementoenamel junction
with a diamond-coated disk (Superflex; Edenta AG
Dentalprodukte, Au/SG, Switzerland) under constant
water spray. Root canals were widened using tapered
burs (Lindemann; Edenta AG Dentalprodukte) with
11-mm-long cutting surfaces that provided a continuous, uninterrupted taper from the apical end of the preparation with a 0.5-mm diameter to the coronal 1.6-mm
diameter opening. Root specimens were chosen from
the set of 60, and the canals were lubricated with
petrolatum. For a single specimen, a solid plastic sprue
(Williams Sprues; Williams Dental, Amherst, NY) was
trimmed so that it could easily slide into the
canal. Blue inlay wax (Blue regular inlay wax; Heraeus
Kulzer, Hanau, Germany) was introduced into the canal
followed by the sprue to register the morphology of the
root canal. A rubber loop was placed at the end of the
sprue to allow attachment to the tensile testing apparatus. Another sprue was attached to the opposite side of
the rubber loop so it was parallel to the sprue located
in the root. These 2 sprues and the rubber loop were
447
THE JOURNAL OF PROSTHETIC DENTISTRY
ERTUGRUL AND ISMAIL
Table I. Materials used in this study
Composition
Brand name
Zinc-phosphate cement
Phosphate-methacrylate cement
Silane metal surface conditioning system
Dowel metal (61.3% Ni, 26% Cr, 11% Mo,
1.5% Si, 0.1% Mn, 0.03% C)
Harvard
Panavia F
Siloc
Kera N
aligned so that the sprues and the center of the loop were
parallel. Finally, a pattern was obtained that was composed of a dowel and rubber loop. This pattern was duplicated with acrylic resin (Palavit G; Heraeus Kulzer) in
a flask. After all specimens were fabricated, this procedure resulted in 60 dowel acrylic resin patterns, each
with a loop and sprue. The dowels were evaluated for
fit in all 60 prepared teeth. The canals were lubricated
with petrolatum. The coronal aspects were reconstructed by applying the same acrylic resin with a brush.
After the acrylic resin had polymerized, the patterns
were removed from the roots. Blue inlay wax was placed
in the voids, and the pattern was reinserted in the root.
This procedure was repeated until the dowel pattern was
satisfactory. Afterwards, the coronal foundation was
shaped to a 4-mm height and a 3.7-mm diameter of
acrylic resin. In consideration of the shrinkage of acrylic
resin, the preparation depth was marked on the tapered
bur (Lindemann; Edenta AG Dentalprodukte) to verify
that the dowel was as long as the dowel space. This
length was then compared with the length of the dowels
to ensure that shrinkage was not a limitation of this
study. The acrylic resin specimens, ready for casting,
were placed into a metal casting ring (Whip Mix,
Louisville, Ky). The investment (Bellavest T; BEGO,
Bremen, Germany) was prepared using a vacuum mixer
(Motava SL; BEGO) and poured into a casting ring. The
specimens were cast using an induction casting machine
(Fornax 35K-F; BEGO). A metal alloy composed of
61.3% Ni, 26% Cr, and 11% Mo (Kera N; Eisenbacher
Dentalwaren, Oben, Germany) was used for casting because adhesive resins show higher bond strengths to
base metals relative to high noble and noble metal alloys.1,23,26 Additionally, the manufacturer of Panavia F
(Panavia F; Kuraray, Osaka, Japan) luting agent
purported that this material would adhere to Ni-Cr alloys. Ni-Cr alloys with silica coating surface treatment
systems have also been recommended for improving
bonding strength with adhesives.22,26,29-33,38 After the
casting was completed, all castings were allowed to
cool to room temperature, and the investment material
was removed from castings by airborne-particle abrasion
with aluminum oxide (250 mm). The fit of the dowel
cores in the teeth was evaluated with light finger pressure, and the cast metal dowel cores were airborne448
Manufacturer
Richter & Hoffmann Harvard Dental, Berlin, Germany
Kuraray, Osaka, Japan
Heraeus Kulzer, Hanau, Germany
Eisenbacher Dentalware, Oben, Germany
particle abraded with 250-mm aluminum oxide for
complete seating in the root canals (Fig. 1). The grain
size of 250 mm was chosen because it has been found
to produce an optimal surface for allowing a strong
bond of the base metal alloy to the silane-coated
layer.27,28
Retentive notches were placed on the outer surfaces
of the roots with an inverted cone carbide bar (Lot
05151197; Diatech Dental, Heerbrugg, Switzerland).
A mixture of autopolymerizing acrylic resin (Tru-Kit;
Harry Bosworth, Skokie, Ill) was poured into rectangular boxes with dimensions of 3 3 2 3 2 cm to form a solid
block to hold the roots during testing. Cast metal dowel
and cores seated in the prepared canal were then embedded into the acrylic resin in the boxes at the level of a cementoenamel junction while the upper sprue was
located in a surveyor (BEGO). The surveyor was used
to embed the specimens perpendicular to the base of
the boxes to ensure tensile loading occurred along the
long axis of the root canal. These 60 standardized specimens were then assigned to 3 groups of 20 specimens
each to accept a variable luting regimen. Before dowel
cementation, the root canals were etched with 35%
phosphoric acid gel (K Etchant; Kuraray) for 15 seconds, rinsed with water spray for 2 minutes, and dried
with cotton paper points. The metal surfaces were
rinsed with water and dried with compressed air before
cementation.
For the control group (ZPC), a zinc-phosphate
cement (Harvard; Herstellungs-und ertriebsgesellschaft
Richter & Hoffmann Harvard Dental, Berlin,
Germany), in the proportion 1.5/1 g/mL, was mixed
on a clean glass slab for 1.3 minutes at 20°C. Then,
zinc-phosphate cement was applied to the dowels with
a plastic instrument, and the dowels were inserted into
the roots. Next, a 5-kg constant load was applied to
the specimens for 10 minutes until the cement set.15
Finally, excess cement was removed, and each specimen
was cleaned with a moist cotton roll.
In the second group (PMRL Group), a phosphatemethacrylate resin luting agent (Panavia F; Kuraray)
was prepared according to the manufacturer’s recommendations. Equal amounts of self-etching primer
(Panavia F ED primer; Kuraray) liquids A (2-hydroxyethyl
methacrylate
[HEMA],
N-methacryloyl
VOLUME 93 NUMBER 5
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THE JOURNAL OF PROSTHETIC DENTISTRY
Table II. Statistical values of experimental data (n = 20)
Mean (kg)
Zinc-phosphate cement (Harvard)
Phosphate-methacrylate resin luting agent (Panavia F)
Phosphate-methacrylate resin luting agent 1 surface
conditioning treatment (Siloc 1 Panavia F)
34.25
22.09
21.75
SD
SE
10.54
9.57
7.64
10.78
6.86
7.35
Minimum value
Maximum value
10.98
7.01
10.26
52.09
39.33
42.21
Table III. One-way ANOVA
Source
Between groups
Within groups
Total
df
2
55
57
Sum of squares
Mean square
F ratio
F probability
1996.6312
4846.8572
6843.4885
998.3156
88.1247
11.3284
.0001
df, Degrees of freedom.
5-aminosalicylic acid [5-NMSA], 10-methacryloxydecyl
dihydrogen phosphate [MDP]) and B (5-NMSA) were
mixed together in a mixing dish, applied with a brush
inside the canal, and allowed to stand for 60 seconds.
Excess liquid was eliminated with a paper point before
completely drying the primer with a gentle air flow to
delay the polymerization process. Equal amounts of
the phosphate-methacrylate (Panavia F) paste A
(MDP, bisphenol-A-glycidyldimethacrylate [Bis-GMA],
filler, benzoyl peroxide, and photoinitiator) and B
(Bis-GMA, filler, sodium fluoride, and amine) were
then mixed for 20 seconds on the mixing plate and applied with a brush to the dowel. The dowel, covered
with cement, was inserted into the root canal. A 5-kg
constant load was applied to the specimens. The excess
cement at the margins was light-polymerized for 2 seconds with conventional halogen by means of a light
(Translux EC; Heraeus Kulzer) for easy cleanup, and removed with an explorer. The antioxidizing agent
supplied with the material was applied to the margins
of the specimens.
In the third group (PMRLS Group), a surface conditioning procedure involving the use of methacryloxypropyl trimethoxysilane (Siloc; Heraeus Kulzer) was
used. This system was recently developed by the manufacturer from the classical Silicoater system.35,36,38 This
procedure is recommended by the manufacturer for
use with all metals and has also been investigated
with adhesive luting agents23,26,32 such as phosphatemethacrylate monomers.11,12,22,25,28 Siloc Pre material,
purported to be an SiO2-reinforced polymer bond layer
by the manufacturer, was first applied uniformly with
a disposable brush on the cast metal dowel surfaces
and allowed to dry for 2 minutes. Then specimens
were placed in a ceramic holder inside the silanization
unit (Siloc oven), and Siloc Pre on the dowel surfaces
was activated at 300°C for 6 minutes. Specimens were
allowed to cool to room temperature for 4 minutes after
the Siloc Pre activation. Siloc bond, as the silane couMAY 2005
pling agent, was applied uniformly with a disposable
brush on the activated dowel surfaces and allowed to
air dry for 5 minutes. When the application of Siloc
was completed, Panavia F primer and paste were applied
as previously described for the PMRL Group. After allowing an hour for the cementation, the specimens
were returned to the isotonic NaCl solution for 15
days at 22°C. The composition, brand name, and manufacturer for the 3 luting materials and casting alloy are
listed in Table I.
Each acrylic resin block was mounted firmly to the
lower jaw of a universal testing machine (Lloyd EZ50;
Lloyd Instruments, Hampshire, England). The upper
sprue portion of the casting was connected to the upper
member of the testing machine. The prepared specimens were subjected to tensile forces along the long
axes of the dowel and tooth at a crosshead speed of
0.5 mm per minute. The force required to dislodge
each dowel was recorded in kilograms. For each of the
groups, the mean, SD, SE, and minimum and maximum
values were calculated according to the data output
obtained from the universal testing machine.
The force values (kg) were recorded when separation
was observed in the universal testing machine. Statistical
analysis was performed using 1-way analysis of variance
(ANOVA), the homogeneity of variances was evaluated
using the Levene test, and paired comparisons of the
groups were performed using the Scheffe test.
Differences were considered significant at a=.05.
RESULTS
According to the test results (Tables II and III), the
difference between the second and third groups was
not significant. Although the retentive strength of the
phosphate-methacrylate resin luting agent (Panavia F)
was found not to be significantly different than that
of phosphate-methacrylate resin luting agent with
metal dowel surfaces modified by silane coating
449
THE JOURNAL OF PROSTHETIC DENTISTRY
(Siloc 1 Panavia F), the latter resulted in a slightly lower
mean value. However, the tensile bond strength of zincphosphate cement was found to be significantly higher
than the specimens cemented with phosphate-methacrylate resin luting agent (P,.05).
DISCUSSION
Although the mode of failure measured in this investigation may not directly correspond to the clinical scenario, standardized tensile strength tests are an accepted
measure of retentive values for luting agents used with
a cement-root-dowel interface.1,2,7-11,14,15,20 For this
reason, tensile strength testing was used in this study.
The phosphate-methacrylate resin luting agent
(Panavia F), which was also used as an adhesive resin luting agent in the present study, is commonly used for
bonding cast alloys to tooth structure and has been shown
to bond to both airborne-particle abraded base metal alloys
and noble alloys.
In the studies concerning the bond strength of this
luting agent, higher bond strengths were observed for
base metal alloys than for noble metal alloys.1,22,33
This luting agent differs from existing resin composites, such as conventional resin luting agents, in
that a phosphate ester has been added to the monomer
to create a dental adhesive using both mechanical and
chemical bonding.12,18,19,24 This phosphoric-acid type
of monomer is adhesive to the oxide layer of base metals
and plays an important role in the metal-resin bond.22,23
The phosphate-methacrylate luting agent is also recommended for use with silane-coated base metal alloys.22,32
Contrary to the present study, some studies have reported significantly greater retention for cast metal dowels cemented with phosphate-methacrylate luting
agents2,8,9,11 as opposed to zinc-phosphate cement
when comparing tensile forces. For example, Chan et al2
compared the vertical retention of various luting
agents, including zinc-phosphate and phosphatemethacrylate monomer luting agents, with stainless steel
dowels and obtained higher resistance to dislodgement
by vertical tensile forces for Panavia than for zincphosphate cement.
However, there are also studies that concur with the
results of the present study.4,10,13 In an in vitro study of
phosphate-methacrylate monomer luting agents, Tjan
and Nemetz13 demonstrated that substantial voids
were present with an adhesive resin luting agent and suggested that these voids were responsible for the unexpectedly low retentive values for dowels luted with
resin luting agents. Additionally, Bouillaguet et al10
investigated microtensile bond strength between
adhesive luting agents and root canal dentin. These authors indicated that bonding for some materials, such as
dual-polymerized Panavia F, tends to fail in the intact
root canal. The polymerization shrinkage stress in the
450
ERTUGRUL AND ISMAIL
confinement of the intact root canal is reported to exceed the bond strength, causing the bond of the luting
agent in the root canals to fail.10,12 Adhesive resin luting
agents are also technique-sensitive, and there have been
reported difficulties in manipulating resin luting agents
in vitro.4,7,8,10,13,14 In a study of the retention of dowels
under tensile forces, Mendoza and Eakle8 observed no
significant difference between a non–resin-containing
luting agent and an adhesive resin luting agent
(Panavia) but mentioned difficulties in manipulating
the resin luting agent. Because of premature polymerization of the resin, some dowels did not seat in the
root canals. Although a premature polymerization was
not observed in the present study, this should be considered as a factor in evaluating bond strengths.
Some studies of microleakage indicate that zincphosphate cement caused more microleakage of dowels
and cores and other restorations than resin luting
agents.17,18 These authors report that this was due to
the greater solubility of zinc-phosphate cement.16,18
Although in the present study, higher retention values
were observed with zinc-phosphate cement, dissolution
of this type of cement should also be considered, as it
may negatively affect retention over time.
Studies have shown that the bond between resinbased luting agents and metal alloys is made considerably stronger with the use of a surface modification
procedure of metal alloys, such as silane coating.22,25,26,28-31 Silica coating not only promotes adhesion but also reduces gap formation at the resin and
metal interface.28,30 The silane coating procedure resulted in higher bond strengths with base metal alloys
than noble alloys in some studies, and using this procedure was suggested for the treatment of base metal alloys
to improve bond strengths with adhesive luting
agents.22,26,29 However, there are also some studies
that observed decreased bond strength of base metal
alloys with silane coating.12,23 Bahannan and
Lacefield12 concluded that the bond strengths between
phosphate-methacrylate resin luting agents and base
metal alloys were significantly more effective compared
to the bond strengths of silane coating. Furthermore,
the phosphate-methacrylate resin luting agents alone appeared to be easier to use. In another investigation conducted by O’Keefe et al,11 the silica coating treatment of
Ni-Cr cast dowels and cores apparently interfered somewhat with the tensile bond strength of phosphate-methacrylate resin luting agents. Both of these conclusions
support the findings of the present study, as Panavia F
showed slightly higher tensile bond strength values
than Panavia F with the Siloc surface-conditioning technique. This may be the result of the Siloc surface-conditioning technique covering the oxide layer and
decreasing the bond strength of functional monomers,
such as Panavia F, which have a high affinity for metal
oxides such as chromium, tin, and copper.23,24,34
VOLUME 93 NUMBER 5
ERTUGRUL AND ISMAIL
Although clinical recommendations can be made,
there are certain limitations to the present study that
must be considered. Complicating variables were eliminated to help simplify the analysis of data. Variables such
as temperature changes, which are common in an oral
environment, may also affect the properties of luting
agents. Additionally, the occlusal forces are much
more complex than forces applied using a simple tensile
test. Shearing, rotational, and cyclical forces are also
placed on teeth and restorations. Future research should
consist of in vitro tests that more accurately replicate the
clinical condition.
CONCLUSION
This in vitro study used tensile testing to allow for
dowel retention comparisons of a conventional zincphosphate, a phosphate-methacrylate resin, and a phosphate-methacrylate resin luting agent with the metal
dowel surfaces modified by a silane coating. Within the
limitations of this study, the tensile strength of zincphosphate cement was significantly higher than that of
the phosphate-methacrylate resin luting agent when
used with and without the silane coating treatment of
cast metal dowel surfaces. There was no significant difference observed between the tensile bond strengths
of the phosphate-methacrylate resin luting agent when
used with and without the silane coating treatment.
The cast metal dowels without silane coating surface
treatment showed slightly higher mean retentive values.
The authors thank Dr Bulent Dayangac and Dr Ibrahim
Tulunoglu, Hacettepe University, Ankara, Turkey, for their help in
the experimental phase of this study.
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Noteworthy Abstracts
of the
Current Literature
ERTUGRUL AND ISMAIL
Reprint requests to:
DR H. ZEYNEP ERTUGRUL
SCHOOL OF DENTAL MEDICINE
UNIVERSITY OF PITTSBURGH
3501 TERRACE STREET
PITTSBURGH, PA 15261
FAX: 412-648 8850
E-MAIL: [email protected]
0022-3913/$30.00
Copyright Ó 2005 by The Editorial Council of The Journal of Prosthetic
Dentistry.
doi:10.1016/j.prosdent.2005.03.001
A 10-year randomized clinical trial on the influence of splinted and
unsplinted oral implants retaining mandibular overdentures:
Peri-implant outcome
Naert I, Alsaadi G, van Steenberghe D, Quirynen M. Int J Oral Maxillofac
Implants 2004;19:695-702.
Purpose: This randomized controlled clinical trial aimed to evaluate the efficacy of splinted implants versus
unsplinted implants in overdenture therapy over a 10-year period.
Materials and Methods: The study sample comprised 36 completely edentulous patients, 17 men and 19
women (mean age 63.7 years). In each patient, 2 implants (Brånemark System, Nobel Biocare, Göteborg,
Sweden) were placed in the interforaminal area. Three to 5 months after placement, they were connected to
standard abutments. The patients were then rehabilitated with ball-retained overdentures, magnet-retained
overdentures, or bar-retained overdentures (the control group). Patients were followed for 4, 12, 60, and 120
months post–abutment connection. Group means as well as linear regression models were fitted with
attachment type and time as classification variables and corrected for simultaneous testing (Tukey).
Results: After 10 years, 9 patients had died and 1 was severely ill. Over 10 years, no implants failed. Mean Plaque
Index, Bleeding Index, change in attachment level, Periotest values, and marginal bone level at the end of the
follow-up period were not significantly different among the groups.
Discussion: The annual marginal bone loss, excluding the first months of remodeling, was comparable with
that found around healthy natural teeth.
Conclusion: The fact that no implants failed and that overall marginal bone loss after the first year of bone
remodeling was limited suggested that implants in a 2-implant mandibular overdenture concept have an
excellent prognosis in this patient population, irrespective of the attachment system used.—Reprinted with
permission of Quintessence Publishing.
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