Article by Leendert Boksman, DDS, BSc, FADI, FICD
and Glenn A. van As, BSc, DMD
The restoration of endodontically
treated teeth is often
compromised by the minimal
amount of residual tooth
structure remaining to support
and retain the final restoration.
This may be due to endodontic overinstrumentation
and flaring of the root
canal during endodontic therapy, or to
extensive structural defects from previous
restorations, or the deleterious
effects of the carious process.1 Many of
these teeth require the placement of a
post-and-core restoration for retention,
whether the tooth is restored directly
or indirectly with full or partial coverage.
The dental literature supports
the fact that a circumferential ferrule
in combination with an endodontic
post results in better long-term clinical
success for crowned, endodontically
treated teeth.2-4 However, many
of these studies looked at cemented
posts, while different ferrule designs
have little, if any, influence on the
fracture resistance of teeth with fiber
posts, with no significant change in
the resistance of teeth with fiber posts
regardless of which ferrule design is
incorporated. This unique property of
these types of posts is an additional
advantage in clinical practice.5
The gold standard for many years was
the cast gold post-and-core; however,
"given the scientific literature that
has appeared, the creation of a conventional
cast post/post core, even if
passively cemented, is useless."6 Goto
et al., when looking at crown retention,
have shown that fiber-reinforced
dowels (posts) and bonded composite
cores under fatigue loading provided
significantly stronger crown retention
than cast gold dowels and titanium
alloy dowels with composite cores.7
A four-year clinical study comparing
fiber posts and traditional cast posts
showed that the cast post group had
root fractures in 9 percent of the
sample, while fiber posts had no root
fractures.8 In a literature review by
Heydecke, it has been shown that cast
post-and-cores do not have a better
performance than direct post-and-core
restorations.9 Therefore, it seems that
the current use of cast post-and-cores
is difficult to justify.
The use of metallic posts for retention
has been studied extensively.
Stiff metallic posts work against the
natural function of the tooth, creating
zones of tension and shear, both
in the dentin and at the interfaces of
the luting cement and post.10 For teeth
restored with stainless steel posts, a
significantly lower load resulted in
failure, as compared with those teeth
restored with glass-fiber posts.11 There
is a worse mechanical performance
in teeth restored using stainless steel
posts, with a high stress concentration
due to the significant difference
between the elastic moduli of the steel and surrounding materials.11,12 The use
of fiber posts is preferable to titanium
posts as well, with teeth restored with
fiber posts exhibiting a significantly
higher resistance to fracture than with
titanium posts.13 In both static and fatigue
fracture testing under vertical or
oblique loadings, the fracture loads
of the teeth restored with fiber posts
were significantly greater than those
of teeth restored with metallic posts.14
The more rigid metallic post can transfer
more stress to the root than fiber
posts, which increases the probability
of vertical root fracture.15 Because
fiber-reinforced posts have an elastic
modulus that more closely approaches
that of dentin,16 fiber posts produce
less stress on the root dentin around
the post tip than do metal posts.17 The
nonmetallic posts comply more satisfactorily
with the requirements necessary
to provide a mechanical behavior
more similar to that of the dental
structure, the compatibility among the
mechanical properties found in these
systems and the dentin providing a
biometric behavior, reducing the risk
of failure or fracture of the root.18 If
fracture does occur, fracture with metal
posts is usually catastrophic, while
fracture of teeth restored with fiber
posts show fractures that would allow
repeated repair.19 In a literature search
looking at 1,984 abstracts on the failure
modes of post systems, Fokkinga
et al. concluded that the fiber-reinforced
post system more frequently
showed favorable failure modes compared
to metal posts.20
Many metallic posts are parallel,
which can require the removal of significant
amounts of root dentin in the
apical half, while not adapting well to
the coronal aspect of the root structure.
In contrast, an anatomical fiber
post requires minimal tooth structure
removal during canal reshaping, and
allows for greater post-to-canal adaptation
in the apical and coronal half of
the canal, with an esthetic nature. This
provides a favorable foundation for
eliminating discoloration caused by a
metallic post placed under all-ceramic
crown systems.21
As an added clinical benefit, fiber posts
can have twice the fatigue resistance
of ceramic or metal posts.22 Statistically,
as well, resin-supported polyethylene
fiber and glass-fiber dowels show
the lowest coronal leakage when compared
with stainless steel and zirconia
dowels at all time periods.23-25
Not all fiber posts are created equal.
In a study by Seefeld et al., looking
at eight types of fiber posts, the fracture
load of the tested systems ranged
from 60 to 96 N and the flexural
strength from 565 to 898 MPa. The
differences in fiber diameter ranged
from 8.2 to 21 µm and the fiber:matrix
ratio from 41 to 76 percent.26 These
fiber posts can be: zirconia enriched,
glass fiber, quartz fiber, glass fiber-zirconia
enriched, and glass fiber and
carbon fiber,27 with quartz fiber posts
recording significantly higher failure
loads.19 They can be translucent,
white, dentin or color-changing translucent,27 and for light transmission
they can be excellent, good, fair or
poor.28 Posts with a high translucency
facilitate excellent esthetic results,
eliminating show-through and discoloration
while allowing transmission
of light polymerization energy.29 Fiber
posts can be tapered, double-tapered,
parallel, parallel with a tapered end,
parallel-tapered and serrated,27 with
the double-tapered post closely imitating
the post-endodontic shape of
a radicular canal, leaving a thin and
uniform thickness of cement at the
post/canal interface. This improved
adaptation of the post promotes the
mechanical properties of the quartz
fiber/epoxy material, instead of the
weaker composite resin cement.30 The
quality, type and volume of fibers, the
way the fibers are silanated, and the
type of resin used affects the clinical
performance of these fiber posts, with
some failing in cyclic fatigue to fracture
in a few cycles and others in over
two million cycles (DT Double Taper
Light-Post radiopaque [RTD]).31
A new addition to the RTD family
of fiber posts is the Macro-Lock Illusion
post, which is fabricated with a high-percentage loading (80 percent
vol) of pretensed long continuous
translucent unidirectional quartz
fibers with epoxy resin, and is radiopaque.
Quartz crystal is the world's
purest form of silica. It is homogeneous,
non-porous,32 and has an
interface treatment of the fibers to
achieve a perfect match between the
thousands of fibers and the organic
resin matrix. Color-changing technology
allows for the post to disappear
when seated at oral temperature and
for it to be visible under water spray if
retrieval is ever necessary. The Macro-Lock Illusion post has high translucency
for good light transmission,
an elastic modulus as low as 13 GPa
(depending on the angle), and a flexural
strength of 1600 MPa. It is unique
in that it allows for micro and macro
retention of the bonded core. A recent
study by Dallari et al. showed that the
Macro-Lock post with its macro retention
reached one of the highest results
when testing the retention of quartz
fiber posts.33 No surface treatment of
the post (etch, silane, sandblasting) is
necessary before cementation.
CASE PRESENTATION
A patient presented to the office with
a failed bridge from tooth #9 to tooth
#11. The patient was advised that #11
was unrestorable and that one treatment
plan option was to place a new
5-unit bridge from #8-#12 with double
abutments on the anteriors. The preoperative
radiograph (Fig. 1) shows
a short endodontic filling requiring
retreatment,
prior to placement of a
post-and-core.
Access was difficult to negotiate at the
canal terminus. The use of ultrasonic
tips eventually removed the calcification
deep into the canal at the apex and
the tooth was re-treated endodontically.
Figure 2 shows the preoperative photograph
of the loose bridge before removal.
At removal of the bridge (Fig. 3),
it was confirmed that #11 was unrestorable,
necessitating its extraction
and the preparation of #12. Figure 4 shows the rubber dam application on
tooth #9, with the occlusal view of
the access into the canal in Figure 5.
Twisted rotary endo files were used to
remove the gutta-percha (Fig. 6), and
ultrasonic tips were used to open the
apical part of the canal (Fig. 7).
The trial cone was inserted and verified
with a trial cone radiograph
(Fig. 8). A warm vertical downpack
was achieved with the System B
(SybronEndo) and the canal was backfilled
with the Obtura II (Obtura Spartan).
The green Macro-Lock Illusion
post drill #4 (RTD) (Clinical Research
Dental) was used to create the post
space (Fig. 9). The post space depth
was measured at 15 mm on a 19 mm
root (Fig. 10). The post was inserted to
verify fit and position (Fig. 11).
Figure 12 shows a magnified view of
the Macro-Lock Illusion post seated
in the canal. The post was trimmed
with a diamond disc (Fig. 13). The
post space was etched with Ultra-Etch
(Ultradent) for 15 seconds using an
Endo-Eze tip (Ultradent) (Fig. 14) to
reach the apex of the post preparation
and inject from the apex to the
incisal, so as not to entrap any air.
The post space was thoroughly rinsed
and a purple Capillary tip (Ultradent)
was used to lightly dry the canal. A
light cure adhesive, proven to be compatible
with dual-cure cements, was
applied to the canal with a tapered
brush long enough to reach the bottom
of the post space (Fig. 15), and at
the same time the light cure adhesive
was placed on the Macro-Lock Illusion
post (Fig. 16).
The solvent was evaporated with a
light airflow and the bond cured in
the post hole and the post (Fig. 17).
A dual-cure resin cement was injected
into the canal space from the bottom
up (Fig. 18), and the post was seated
into the dual-cure cement (Fig. 19).
After curing the cement (Fig. 20),
CosmeCore (Cosmedent) was used to create the core buildup (Fig. 21),
followed by a cure of 20 seconds
(Fig. 22). CosmeCore can be used as
the dual-cure cement and the core
buildup simultaneously. Figure 23
shows preparation of the CosmeCore/Macro-Lock Illusion post-and-core for
full coverage (note the color of the
post when exposed to cold water).
Teeth #8 and #12 were prepared and
tooth #11 extracted (Fig. 24). A provisional
bridge was fabricated using
Temptation (Clinical Research Dental)
and cemented with Cling2 Temporary
Cement (Clinical Research Dental)
(Fig. 25). A final postoperative radiograph
(Fig. 26) shows the opacity of
the Macro-Lock Illusion post.
