in vitro study of the fracture resistance of endodontic teeth restored ...

IN VITRO STUDY OF THE FRACTURE RESISTANCE OF ENDODONTIC
TEETH RESTORED WITH FOUR INTRARADICULAR POST SYSTEMS
Marcé M 1 ., Bush, P 2 ., Muñoz C 3 ., Giner Ll 4 .
1. Master Prótesis Bucal y ATM, UIC. Becaria de Investigación.
2. Director, South Campus Instrumentation center. School of Dental Medicine. Buffalo, NY
3.Carlos A. Muñoz, DDS, MSD. Professor and Chair. Department of Restorative Dentistry. School of
Dental Medicine. Buffalo, NY
4.Director de Estudios de la Licenciatura de Odontología de la UIC.
Introduction: There are many kinds of intraradicular post systems for the required restoration of
endodontic teeth. Objectives: To evaluate and compare in a simulation model the fracture resistance and
kind of fracture of endodontic teeth restored with four frequently used intraradicular post systems.
Equipment, materials and methods: Forty calf incisors free from caries, cracks and fractures were
endodontically treated and distributed at random into four equal groups. Each group was restored with a
different intraradicular system: cast post and core - CrNi (group 1), prefabricated threaded titanium post
- Unimetric (group 2), prefabricated smooth titanium post with surface treatment - Dentoclic (group 3)
and prefabricated smooth glass fibre post - Dentoclic (group 4). All the specimens were subjected to
compressive force in a universal test machine (Instron 4202, University of Buffalo, Buffalo, New York),
until fracture. The results were analysed using the variable analysis test (ANOVA). Results: There were
only significant differences relating to fracture resistance between cast post and core (group 1) and glass
fibre post (group 4). With regard to the kind of fracture, teeth with higher numbers of apical fractures
were those restored with cast post and core (group 1), while teeth with fractures with a better prognosis
were those restored with glass fibre post (group 4). Conclusions: Teeth restored with glass fibre post
showed significantly lower fracture resistance values than cast post and core and similar values to
prefabricated metal post. The fractures of teeth restored with glass fibre post were largely reparable.
Key words: fracture resistance, kind of fracture, glass fibre.
INTRODUCTION
The restoration of endodontic teeth is a highly controversial subject, which has been widely reviewed by
numerous authors.
On the basis of a broad bibliographic review carried out with articles published between 1990 and 2005,
a protocol for the restoration of endodontic teeth was proposed by the Prosthesis Master of the
International University of Catalonia.
According to this protocol, which was determined on the basis of the level of destruction of the tooth,
the location of the tooth in the denture and the type of occlusal forces received by it 1, 2, 3, 4, 5 , not all teeth
which have needed endodontic treatment require the use of intraradicular posts in order to be
satisfactorily restored.
Therefore, the placing of an intraradicular post is to be recommended in those endodontic teeth which
present a maximum degree of dental problems as well as in prosthetic posts 1, 2, 5, 6 .
With the advanced technology of today, we, as clinicians, have at our disposal a wide range of dental
materials of ever-increasing quality.
In the field of intraradicular posts, there is no exception. To an increasing extent we have at our disposal
materials which fulfil the requirements presented.

The majority of authors 1, 7, 8, 9, 10, 11 opt for prefabricated fibre reinforced posts instead of traditional cast
post and cores and prefabricated metal posts, featuring high rigidity, low aesthetic value, easy corrosion
and factures of largely irreparable character 1, 6, 8 .
For prefabricated fibre reinforced posts, there is a wide range of fibre materials, namely glass fibres,
being one of those considered to be better by some authors 8, 11 . They have an elastic module similar to
dentin and can therefore transmit occlusal forces in a uniform way. They also feature good aesthetic
value, absence of corrosion, adhesive cementation and easy removal if needed 1, 8, 12, 13 .
Even so, some clinicians are still reluctant to opt for glass fibre posts, perhaps due to the lack of longterm
research into this subject.
The literature shows that there is a correlation between the fracture resistance of a tooth and the rigidity
of a post. Posts which exhibit similar rigidity to that of dentin will enhance the uniform distribution of
occlusal forces across the post and the root, decreasing the level of susceptibility to coronoradicular
11, 14, 15
fractures
The objectives of this in vitro study are the evaluation and comparison, in a simulation model, of the
fracture resistance and the type of fracture of endodontic teeth restored by means of four intraradicular
post systems which are frequently used, including a glass fibre post.
EQUIPMENT, MATERIALS AND METHODS
In order to complete this in vitro study, forty lateral calf incisors free from caries, cracks and fractures
were selected for the purpose of endodontically treating them and restoring them using four different
intraradicular post systems: cast post and core system (CrNi), threaded titanium post (Unimétric ® ),
smooth titanium post with surface treatment (Dentoclic ® . Gacd, Promodentaire, Dentoria) and a glass
fibre post (Dentoclic ® . Gacd, Promodentaire, Dentoria).
The teeth were chosen in such a way that they all presented maximum similarity with regard to their
length and breadth (Photo 1). They were carefully cleaned to remove perirradicular tissue using a scraping
curette and root-smoothing device No. 13/14 and were stored in saline solution at ambient temperature
until undergoing the study.
(Photo 1)
In order to make the dimensions uniform, the dental pieces were each cut to 23 mm from the apex by
means of a horizontal cut relative to the axial axis, to eliminate the anatomical crown, using a 40,000
rpm hand-held disc under aqueous refrigeration (Photo 2)
(Photo 2)

The radicular canals of all the teeth were prepared endodontically with the Profile rotary system using
the Crown-Down technique.
Firstly, the endodontic access was prepared using Gates Glidden drills (Maillefer ® ) No. 2, 3 and 4, at 5,
7 and 9mm from the apex respectively. Then came the K-files (Dentsplay. Maillefer) Nos. 10 to 20 and
the canals were manipulated using Profile ® files up to a working length of 22mm with a 40 calibre,
while irrigation was introduced with sodium hypochlorite at 2.5%. Once the canals had been prepared,
they were dried and filled. In order to dry the canals, paper points (Roeko ® ) and pressurised air were
used. Filling took place manually with lateral condensation using a digital condenser and gutta-percha
covered with cement (AH-Plus ® , Dentsplay DeTrey) free from eugenol.
The filled teeth were divided at random into four equal groups so that there were 10 examples per group.
Each group was restored using one of the four intraradicular systems to be studied: (Photo 3)
Group 1: cast post and core (CrNi).
Group 2: threaded titanium post (Unimetric ® . Maillefer)
Group 3: smooth titanium post with surface treatment (Dentoclic ® . Gacd, Promodentaire, Dentoria).
Group 4: glass fibre post (Dentoclic ® . Gacd, Promodentaire, Dentoria).
(Photo 3)
Group 1 Group 2 Group 3 Group 4
To maximally standardise the cemented area of the prefabricated posts and the cast posts, the radicular
canals of the different groups were all prepared at 15mm except those of the second group (Unimetric ® .
Maillefer). These were prepared at 1 mm less (14mm) because of their length. In this way it is not
necessary to cut the post-head, thereby not altering its properties. The gutta-percha of the canals was
eliminated firstly using Gates Glidden drills No. 2, 3 and 4, followed by the special drills for preparation
of each post kit. At least 5 mm of the apical gutta-percha was preserved to maintain the endodontic seal
at the apical level.
The production of the 10 cast post and cores belonging to the first group was completed using an alloy
of Cr-Ni with indirect technique by means of calcinable plastic posts and silicone type impression
addition material of medium and fluid consistency.
All the posts were cemented with the latest generation resinous cement (Rely X Unicem, 3M) according
to the manufacturer’s recommendations.

For the cementing of the intraradicular systems of the first three groups it was not necessary to complete
any type of additional preparation of the radicular canals or of the surface of the systems, as indicated by
the manufacturer.
The glass fibre posts (Dentoclic. Gacd, Promodentaire, Dentoria), which belong to group 4, were
prepared according to the manufacturer’s recommendations. Silane (Monobond-S) was applied to their
surface and left to take effect for 60 seconds and the surface was then dried with air.
The dual self-etching cement Rely X Unicem was mixed according to the manufacturer’s
recommendations for 12 seconds using the Rotomix.
All the posts were covered with a fine coating of Rely X Unicem and were inserted in a passive way,
with pressure exerted by the finger, into the dry radicular canals as far as the length established.
Subsequently the surplus was removed and each specimen was polymerised for 40 seconds using a
halogen lamp for photo-polymerisation.
To reconstruct the cores of groups 2, 3 and 4 a hybrid composite was used (Tetric Ceram). For the
conditioning of the dental structure, the surfaces of the teeth were etched with phosphoric acid at 37%
for 15 seconds, followed by washing with abundant aqueous solution, drying and dual adhesive
application (Excite), which was polymerised for 20 seconds. Then, the restorative material was applied
in layers, being polymerised for periods of 40 seconds (lamp mark), until a core with appropiate
dimensions was obtained.
In order to achieve a ferrule effect in the 40 specimens the dental margins were cut to 2mm apical of the
most coronal zone of the root. Therefore 2mm of internal dental structure remained above the margin in
the vertical sense, in the form of a ferrule.
Impressions were taken of the cores cut with monophase addition silicone in order to prepare metal caps
of Cr-Ni, which were subsequently cemented to the cores, also with Rely X Unicem, 3M cement. In the
same way, a horizontal groove was made in each cap on the palatal side, by simulating the point of
interincisive fixation, with a low-revolution, hand-held disc drill, with abundant aqueous refrigeration.
Next, a sampling cup with the dimensions of 10 x 10 x 26mm was shaped with photopolymerisable
acrylic resin (Triad ® ) and was photocured in the photopolymerisation machine (Triad ® ) for 30 seconds.
Using this model, a standardised template was made with condensation silicone (Optosil ® ), which was
used for the preparation of the 40 sampling cups, into which the teeth were inserted, leaving 2mm of the
coronal free. These were also photocured for 10 seconds each.
Before being studied in the laboratories of the University of Buffalo, all the specimens were stored for a
week in aqueous solution at 35ºC.
Once the samples had arrived in Buffalo (University of Buffalo, South Campus, Buffalo, New York,
USA), the sampling cups manufactured in Barcelona (International University of Catalonia, Sant Cugat,
Barcelona, Spain) were adapted to the dimensions required with auto-polymerisable acrylic resin
(Bosworth fastray TM ® ), to be subsequently fixed by machine (Photo 4).

(Photo 4)
The forty samples were subjected to a progressive single compressive force in Knewtons, using a
universal test machine (Instron 4202, University of Buffalo, Buffalo, New York, USA) (Photo 5), at a
constant speed of 5mm/min, under conditions of 50% humidity and a uniform temperature of 72ºF until
fracturing occurred. The compressive force was applied with a pointer, which rested on the groove made
in the caps at an angle of 135º relative to the longitudinal axis of the teeth. For this, an autopolymerisable
acrylic resin ramp (Bosworth fastray TM ® ) of 45º was made, this being placed below the
sample fixing device, resulting in an angle of 135º between the sample and the pointer (Photo 6).
(Photo 5) (Photo 6)
In order to determine the type of fracture of the specimens tested, radiographs were taken of each sample
and subsequently analysed with magnifying glasses.
Using light microscopy (Nikon SMZ-U zoom 1:10, University of Buffalo, South Campus, Buffalo, New
York, USA), the fractures of the specimens were photographed, characterising the typical kind of
fracture of each group (Photo 7)
RESULTS
Fracture Resistance
(Photo 7)

The following table contains the results obtained for each group as well as the mean value of each one of
them.
Samples
N (kN)
Group 1
(Cast post and core)
Group 2
(Unimetric)
Group 3
(Dentoclic Ti)
Group 4
(Dentoclic glass)
N=1 1.8090 1.5540 2.0050 1.4620
N=2 2.2860 1.8950 1.5760 1.7700
N=3 1.5380 1.8310 1.1210 1.4850
N=4 1.7210 1.3220 1.1630 1.6900
N=5 2.4990 1.7700 1.6300 1.5240
N=6 1.8580 1.6780 1.7730 1.5270
N=7 1.4790 1.4230 1.2340 0.9685
N=8 1.5670 1.6320 1.5970 1.6980
N=9 1.9730 1.5650 2.2990 1.6530
N=10 1.6420 1.7700 1.8560 1.6500
Mean (N) 184 164 163 154
Max. value (kN) 2.4990 1.8950 2.2990 1.7700
Min. value (kN) 1.4790 1.3220 1.1210 0.9685
Table
The results were analysed using the Statgraphics data analysis statistical program, applying the variable
analysis test (ANOVA).
2
1,9
Means and 95,0 Percent LSD Intervals
Mean
1,8
1,7
1,6
1,5
1,4
grupo 1 grupo 2 grupo 3 grupo 4
Diagram 1.
Overall, no significant differences between all the groups tested, except for groups 1 and 4 were
observed.
If the results of the prefabricated titanium posts (groups 2 and 3) are compared with the glass fibre posts
(group 4), we see that the metal posts have higher fracture resistance values but are not statistically
different from those of the glass fibre posts (Diagram 1)

Diagram 2.
Resistencia Fractura
2
1,9
1,8
1,7
1,6
1,5
1,4
Means and 95,0 Percent LSD Intervals
1 4
Grupo
Significant differences only exist with the teeth belonging to groups 1 (cast post and core) and 4 (glass
fibre), with fracture resistance values of 184N and 154N respectively (p_value = 0 0855). (Diagram 2)
Types of Fracture
After carrying out the compression tests, a radiograph of each specimen was completed and analysed
using a magnifying glass in order to ascertain the level (coronal, middle, apical) at which the dental
fracture occurred and to characterise the type of fracture (horizontal, vertical, oblique), with subsequent
determination of the reparable or irreparable character of the fractures.
On the basis of the radiographs taken, the fracture lines were outlined for each group:
Group 1 (cast post and core):
1 2 3 4 5

6 7 8 9 10
- 5 oblique fractures in the coronal radicular third.
- 5 fractures, horizontal and oblique, in the apical area of the post, corresponding to the final part of the
middle radicular third (Photo 8).
- Fractures with immediately visible aggressive edges (Photo 9). (Optical microscopy. Nikon SMZ-U
zoom 1:10, University of Buffalo, South Campus, Buffalo, New York, USA).
- Many of the posts appear doubled in the radiographs.
(Photo 8) (Photo 9)
Group 2 (Threaded titanium post. Unimetric):
1 2 3 4 5

6 7 8 9 10
- 4 fractures at coronal level, 2 horizontal and the other 2 oblique.
- 6 fractures in the middle radicular part (Photo 10), 1 horizontal and 5 oblique.
- The edges of the fractures can also be easily seen and are aggressive in character (Photo 11). (Nikon
SMZ-U zoom 1:10, University of Buffalo, South Campus, Buffalo, New York, USA),
(Photo 10) (Photo 11)
Group 3 (smooth titanium post with surface treatment. Dentoclic. Gacd, Promodentaire, Dentoria):
1 2 3 4 5

6 7 8 9 10
- 7 fractures at coronal radicular level. Two of them go down as far as 3mm intraosseous (below
acrylic). All are oblique, except for one, which is vertical.
- 3 fractures at apical level of the post, 2 are horizontal and 1 oblique (Photo 12).
- Fractures with aggressive edges but of slightly better appearance than those of the previous two groups
(Photo 13). (Nikon SMZ-U zoom 1:10, University of Buffalo, South Campus, Buffalo, New York, USA).
(Photo 12) (Photo 13)
Group 4 (glass fibre post. Dentoclic. Gacd, Promodentaire, Dentoria):

1 2 3 4 5
6 7 8 9 10
- All the fractures are observed at coronal level of the root, being of the oblique type, except for one,
which is compatible with an incomplete horizontal fracture at the level of the apex of the post,
coinciding with the middle radicular third (Photo 14).
- Fractures with edges which are almost imperceptible at first sight. They are fracture lines, not fracture
edges as in the other groups. More difficult to detect but almost all being reparable (Photo 15).
DISCUSSION
(Photo 14) (Photo 15)

To carry out this study calf teeth were chosen which had already been used in other studies, by virtue of
their exhibiting sufficient similarities to human teeth and being used by default 16, 17, 18, 19, 20 .
All of the posts in this study were cemented with resinous cement. The literature contains numerous
references, commenting that the current resinous cements improve the capacity for adhesion to the post,
exhibit greater toughness and durability, less solubility and minimum microfiltration, as well as other
1, 14, 21,
advantages, in comparison with traditional cements with a zinc phosphate or glass ionomer base
22, 23, 24, 25, 26 .
Authors such as Irie and Hecht comment that self-etching dual resin cement Rely X Unicem exhibits
greater adhesion to human and bovine dentin in comparison with other types of resinous cement.
Similarly, Sen and Bitter demonstrate in their articles that it increases the retention of fibre reinforced
posts, improving their fracture resistance, and that it is suitable for cementing metal posts 1 .
Once the teeth had been prepared, the dental margins were cut, leaving 2mm of healthy dental structure,
in the form of a ferrule 31, 32, 33, 34 , reproducing the minimum conditions for optimising the fracture
resistance of these teeth.
Fracture Resistance
Within the limitations of this study, it was possible to obtain logical results, taking into account the
characteristic rigidity of each type of post.
The resistance of the endodontic tooth is largely determined by the amount of dental structure remaining
1, 2, 3, 4, 5, 16 , but in the case of teeth with a great loss of dental support, which will require the placing of
an intraradicular post, the type of post will also determine its fracture resistance in part.
Metal posts have a high elasticity module, because they are more rigid. This gives them a greater
capacity to withstand occlusal forces before flexing until fracture, but at the same time promotes the
non-absorption by the post of the occlusal forces, transmitting them irregularly to the dental structure,
giving rise to aggressive fractures.
On the contrary, the glass fibre posts, while still not exhibiting maximum fracture resistance values, do
feature bio-mechanical behaviour similar to that of dental structure because they have a similar Young
module. Presumably, they will therefore be capable of absorbing occlusal forces and transmitting these
forces uniformly across all the structures of the system, resulting in a level of more favourable and
reparable fractures for the clinicians 1, 10, 11, 14, 15 .
In this study, the highest fracture resistance values were obtained in the posts of group 1 (Cr-Ni casts),
which are significantly higher than those found for glass fibre posts of group 4 (Dentoclic).
If we compare the values obtained in the prefabricated titanium posts belonging to groups 2 and 3 with
those obtained for the glass fibre posts, it can be observed that the former present slightly better values
than those of glass fibre, but not significantly differing from them.
These results are similar to those obtained by other authors in various in vitro studies 1, 16, 35, 36, 37 , where
greater fracture resistance values were obtained for metal posts, whether statistically significant or not.
We have found that Akkayan et al. and Cohelo Santos et al. obtained higher fracture resistance values
for glass fibre posts than for titanium posts, although these were not statistically significant.

However, the resistance values found for glass fibre posts are sufficiently high for them to be used
satisfactorily in the mouth 1, 16, 35, 36, 37, 38, 39 .
Types of Fracture
According to unanimous opinion, which is illustrated in the majority of studies carried out on this
subject 1, 7, 10, 11, 31, 40 , dental materials must feature biomechanical properties which are as similar as
possible to those found in natural dentition in order to obtain optimal functioning.
Posts with greater rigidity values than those of dentin tend not to flex, thereby transmitting the forces to
dental structure in a non-uniform way, which results in maximum expression in a fracture of aggressive
or irreparable character. On the contrary, posts which exhibit a degree of flexion similar to that of dentin
possibly have lower absolute fracture resistance values but tend to absorb the occlusal forces in part and
transmit them uniformly, reducing the level of harm in the event of fracture.
Fractures whose fracture line goes down 3mm or more from the acrylic, which simulates the osseous
level, are considered to be irreparable or irreversible. The others will be considered to be favourable
fractures by virtue of their reparable or reversible character.
The most aggressive and irreparable fractures discovered in this study and evaluated through analysis of
the radiographs with magnifying glasses occurred in teeth restored with cast post and core (group 1) and
in threaded titanium posts, Unimetric (group 2). Of these, only 4 specimens of each group suffered
fractures of a reparable character, with coronary prolongation. The other fractures, including one which
was produced at coronal level of a tooth restored with cast post and core, were irreversible because they
went down or were located 3mm intraosseous.
For prefabricated smooth titanium posts with surface treatment (Dentoclic. Gacd, Promodentaire,
Dentoria), there were fracture lines with a slightly better prognosis if compared to those found in groups
1 and 2.
This difference could be attributed to the different surface morphology, with all the posts being
cemented in a passive way.
For teeth restored with glass fibre posts, the fractures appear minimal and are generally located at
coronal level, which facilitates the recovery of the tooth if needed. Only one fracture of irreparable
character occurred.
The results obtained are consistent with those obtained by other authors 1, 7, 31, 38 .
CONCLUSIONS
Within the limitations of this study, it can be concluded that:
- Teeth restored with cast post and core (group 1) exhibit the highest fracture resistance values.

- There are no significant fracture resistance differences between teeth with cast posts and prefabricated
metal posts.
- Teeth with glass fibre posts exhibit fracture resistance values similar to those restored with
prefabricated metal posts.
- There are significant differences in fracture resistance between teeth restored with cast post and core
and glass fibre.
- Glass fibre posts lead largely to fractures of a reparable character, due possibly to the similarity in
behaviour with remaining dental structure, while teeth restored with metal posts bring about fractures of
great magnitude, almost always irreparable.
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