In vitro fracture resistance of glassfiber and cast metal posts with different lengths

Prévia do material em texto

182 Volume 101 Issue 3
The Journal of Prosthetic Dentistry Giovani et alMcLaren et al
and Snowlight (P<.001) groups.
3. The 10-mm post length groups 
had significantly higher (P<.001) 
mean initial fracture loads when com-
pared with the 5-mm post length 
groups.
4. The mode of initial failure for all 
groups was core debonding from the 
tooth.
5. The mode of ultimate failure 
for groups varied. The stainless steel 
posts had an incidence of 25% root 
fractures, while no root fractures were 
observed with fiber-reinforced posts.
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15.Saupe WA, Gluskin AH, Radke RA Jr. A 
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Corresponding author:
Dr Peter Yaman
University of Michigan School of Dentistry 
1011 North University 
Ann Arbor, MI 48109-1078 
Fax: 734-936-1597
E-mail: pyam@umich.edu
Copyright © 2009 by the Editorial Council for 
The Journal of Prosthetic Dentistry.
Clinical Implications
In situations involving small and/or curved roots, the glass-
fiber post with a smaller length represents a viable alternative 
to restore endodontically treated canines requiring prosthetic 
restoration, without decreasing the resistance to fracture.
Statement of problem. Dental fractures can occur in endodontically treated teeth restored with posts.
Purpose. The purpose of this study was to evaluate the in vitro fracture resistance of roots with glass-fiber and metal 
posts of different lengths.
Material and methods. Sixty endodontically treated maxillary canines were embedded in acrylic resin, except for 4 
mm of the cervical area, after removing the clinical crowns. The post spaces were opened with a cylindrical bur at low 
speed attached to a surveyor,resulting in preparations with lengths of 6 mm (group 6 mm), 8 mm (group 8 mm), or 
10 mm (group 10 mm). Each group was divided into 2 subgroups according to the post material: cast post and core 
or glass-fiber post (n=30). The posts were luted with dual-polymerizing resin cement (Panavia F). Cast posts and cores 
of Co-Cr (Resilient Plus) crowns were made and cemented with zinc phosphate. Specimens were subjected to increas-
ing compressive load (N) until fracture. Data were analyzed with 2-way ANOVA and the Tukey-Kramer test (α=.05). 
Results. The ANOVA analysis indicated significant differences (P<.05) among the groups, and the Tukey test revealed 
no significant difference among the metal posts of 6-mm length (26.5 N ±13.4), 8-mm length (25.2 N ±13.9), and 
10-mm length (17.1 N ±5.2). Also, in the glass-fiber post group, there was no significant difference when posts of 
8-mm length (13.4 N ±11.0) were compared with the 6-mm (6.9 N ±4.6) and 10-mm (31.7 N ±13.1) groups. The 10-
mm-long post displayed superior fracture resistance, and the 6-mm-long post showed significantly lower mean values 
(P<.001).
Conclusions. Within the limitations of this study, it was concluded that the glass-fiber post represents a viable alterna-
tive to the cast metal post, increasing the resistance to fracture of endodontically treated canines. (J Prosthet Dent 
2009;101:183-188)
In vitro fracture resistance of glass-
fiber and cast metal posts with different 
lengths
Alessandro Rogério Giovani, MS,a Luiz Pascoal Vansan, PhD,b 
Manoel Damião de Sousa Neto, PhD,c and Silvana Maria 
Paulino, PhDd 
University of Ribeirão Preto (UNAERP), Ribeirão Preto, São 
Paulo, Brazil; Faculty of Dentistry of Ribeirão Preto, University of 
São Paulo (FORP-USP), Ribeirão Preto, São Paulo, Brazil
This study was financially supported by the Brazilian agency CAPES (Coordination for Improvement of Higher Education Person-
nel), grant number PROSUP 0012/02–5. 
aPhD candidate, Department of Endodontics, University of Ribeirão Preto (UNAERP).
bAssociate Clinical Professor, University of Ribeirão Preto (UNAERP).
cAssociate Clinical Professor, Department of Restorative Dentistry, University of São Paulo (FORP-USP).
dAssociate Clinical Professor, University of Ribeirão Preto (UNAERP).
184 Volume 101 Issue 3
The Journal of Prosthetic Dentistry
185March 2009
Giovani et alGiovani et al
Endodontically treated teeth with 
extensive loss of coronal tooth struc-
ture are commonly restored with a 
post and core and a crown. Factors 
indicating this type of restoration in-
clude extensive dental caries, fracture, 
trauma, iatrogenic loss of tooth struc-
ture and pulpal pathology, as well as 
the endodontic treatment itself. In 
addition, the loss of water content in 
dentin after endodontic therapy can 
reduce tooth resilience and, conse-
quently, increase the probability of 
fracture.1,2
After endodontic treatment, the 
restoration of pulpless teeth is im-
portant to ensure successful treat-
ment outcomes. Restorations provide 
protection and reinforcement of the 
tooth, and also prevent the passage of 
microorganisms and organic liquids 
into root canals.3-5 Failures involving 
the post and the crown can result in 
fracture of the post and root, and dis-
placement or loss of retention of the 
post. Fracture of the remaining tooth 
structure is one of the most frequent 
causes of failure.4-7
Cast metal posts and cores have 
been used for many years8; however, 
there are now newer post systems 
available. Among the materials used 
for esthetic restorations, glass-fiber 
posts have gained popularity because 
of their purported favorable biome-
chanical properties.1,9 They are re-
ported to be more flexible than cast 
metal posts and allow a better dis-
tribution of forces, resulting in fewer 
root fractures.9 In addition, these pre-
fabricated posts are advantageous in 
situations in which adequate coronal 
tooth structure remains. Prefabricat-
ed posts are classified according to 
their structural composition as met-
al, ceramic, or resin reinforced with 
fibers.10,11
Some authors have reported that 
endodontically treated teeth restored 
with fiber posts show a decreased 
fracture resistance compared with 
teeth restored with metal posts.12-14 
Other authors,15,16 however, have in-
dicated that the fracture resistance of 
teeth restored with glass-fiber posts is 
equal to or greater than that of teeth 
restored with metal posts.
Studies suggest that the fracture 
susceptibility of teeth restored with 
posts may be related to factors such 
as the amount of remaining healthy 
tooth structure, which provides resis-
tance to the fracture of the tooth,4 as 
well as the characteristics of the post, 
such as the material composition,11,17 
modulus of elasticity,7,9,18 diameter,19 
and length.20 Some authors20-22 have 
indicated that the length of the post 
is related to root fracture, and that 
the post should be two thirds of the 
length of the root, or, when this can-
not be achieved, the post should have 
at least the same length as the clinical 
crown. According to Braga et al,23 if 
neither goal can be reached, the post 
must extend at least half of the root 
length. The authors observed that 
posts that extended to half of the root 
length behaved similarly to those that 
were two thirds of the root length. 
Furthermore, such posts preserve a 
greater amount of root canal filling 
material; this is important because 
the apex is an area of greater anatom-
ical complexity, with a high number of 
lateral and accessory canals.24,25
The purpose of this in vitro study 
was to evaluate the fracture resistance 
of roots with cast posts and cores and 
glass-fiber posts of different lengths 
by using a compressive test. The null 
hypothesis was that there would be 
no difference in the fracture resis-
tance of endodontically treated ca-
nines restored with different types of 
post systems of different lengths. 
MATERIAL AND METHODS
Sixty caries-free and restoration-
free human maxillary canines with 
roots of similar form were selected. 
All selected teeth had a single canal 
and straight roots measuring approxi-
mately 16 mm. The clinical crowns 
were sectioned transversally, close to 
the cemento-enamel junction, leaving 
a root length of 15 mm.
The exploration of the radicular ca-
nal was accomplished with #25 K-files 
(Dentsply Maillefer, Ballaigues, Swit-
zerland) to select the specimens that 
had a working length of 14 mm and 
an anatomical diameter of 250 µm. 
The preparation of the entrance of 
the radicular canal was accomplished 
with a flaring instrument (Endoflare 
.12, no. 25; Micro-Mega, Besançon, 
France), and the root preparation was 
accomplished with a rotary cutting in-
strument (HERO 642; Micro-Mega) 
at 300 rpm. The final instrument (#40 
master apical file; Dentsply Maillefer) 
was standardized for all specimens. 
During preparation, the canals were 
irrigated with 2 ml of 1% sodium hy-
pochlorite, alternating with 17% EDTA 
(ethylenediaminetetraacetic acid). 
Final irrigation was performed with 
10 ml of distilled water, and the ca-
nals were dried with absorbent paper 
points (Dentsply, Petrópolis, Brazil). 
Root canals were obturated by the 
warm condensation technique26 with 
gutta-percha points (Dentsply), acces-
sory gutta-percha points (Dentsply), 
and sealer (AH Plus; Dentsply). The 
plasticizing of the gutta-percha points 
was accomplished with a condenser 
(McSpadden condenser; Dentsply 
Maillefer). The extracoronal excess of 
gutta-percha was removed by using 
heated condensers (Duflex; SS White, 
Rio de Janeiro, Brazil). Vertical conden-
sation was performed with the same 
instruments, and the pulpal chambers 
were sealed with provisional cement 
(Citodur; DoriDent, Vienna, Austria). 
Specimens were immersed in distilled 
water and maintained at 37°C (±2°C) 
for a period of 36 hours. The roots 
were placed in aluminum molds (16 x 
16 x 32 mm) and embedded in acrylic 
resin (Jet; Clássico, São Paulo,Brazil) 
to maintain 4 mm of root length ex-
tending beyond the top of the acrylic 
resin. For the cervical preparation of 
the roots, a reference line was marked 
with graphite pencil at a height of 2 
mm. A diamond rotary cutting instru-
ment (3069 diamond bur; KG So-
rensen, São Paulo, Brazil) was used 
to prepare orientation notches with a 
depth of 1 mm. From these notches, 
the cervical portion of the tooth was 
prepared, resulting in a cervical termi-
nus with a square shoulder.
The specimens were divided into 
3 groups (n=20), according to their 
post lengths: group 6 mm, group 8 
mm, or group 10 mm. Each group 
was divided into 2 subgroups, accord-
ing to the post material (n=10): CPC 
(cast post and core) or GFP (glass-
fiber post). Post spaces were prepared 
with parallel-sided burs from the post 
kit (FibreKor Post; Pentron Clinical 
Technologies, Wallingford, Conn) in 
a low-speed handpiece (Dabi Atlante 
SA, Ribeirão Preto, Brazil) attached to 
a dental surveyor (Bio-Art, São Car-
los, Brazil).
For the standardization of the cor-
onal portion of the core, a standard 
mold was made in the anatomical form 
of a core of the complete crown of the 
maxillary canine tooth, which was 
cast in copper-aluminum alloy (Gol-
dent; AJE Goldent Comercial Ltda, 
São Paulo, Brazil). Beginning with 
this standard mold, 60 acetate molds 
were obtained in a plastifier (Bio-Art) 
under vacuum, and these aided in the 
fabrication of the wax patterns of the 
coronal portion of the core. 
To obtain groups CPC 6 mm, CPC 
8 mm, and CPC 10 mm, the posts 
were made by using the direct tech-
nique with acrylic resin (DuraLay; Re-
liance Dental Mfg Co, Worth, Ill) and 
prefabricated posts (Pin-Jet posts; 
Angelus Dental Solutions, Londrina, 
Brazil). The prepared posts were lu-
bricated with petroleum jelly (Un-
ião Química FTCA Nacional SA, São 
Paulo, Brazil) and, with the aid of a 
spiral drill (Lentulo bur #40; Dentsply 
Maillefer), the acrylic resin was placed 
into the prepared post space, followed 
by the insertion of the prefabricated 
plastic post. The previously made 
acetate mold was filled with acrylic 
resin (DuraLay; Reliance Dental Mfg 
Co) and placed on the post pattern, 
and the necessary finishing was per-
formed with a diamond rotary cutting 
instrument (3069 diamond bur; KG 
Sorensen). The acrylic resin patterns 
were invested in a phosphate-bonded 
investment material (Termocast; Poli-
dental, São Paulo, Brazil) and cast in 
copper-aluminum alloy (Goldent; AJE 
Goldent Comercial Ltda). The cast-
ings were airborne-particle abraded 
with 150-µm aluminum-oxide powder 
(Wilson; Polidental).
Cast posts were cemented with du-
al-polymerizing resin cement (Panavia 
F; Kuraray Co Ltd, Osaka, Japan), and 
its adhesive system (Kuraray Co Ltd). 
First, primer (Alloy Primer; Kuraray Co 
Ltd) was applied to the post. Then, 
each canal surface was acid etched 
(Ivoclar Vivadent; São Paulo, Brazil) 
for 30 seconds, rinsed with water, and 
dried with paper points (Dentsply). 
Next, 2 coats of adhesive were applied, 
followed by 20 seconds of drying and 
light polymerization with a halogen 
light (Ultralux Electronic; Dabi At-
lante SA) for 30 seconds. The unit had 
a wavelength of 350 to 500 nm and 
light intensity of 350 to 500 mv/cm2. 
The light was positioned perpendicu-
lar to the long axis of the root, and 
the distance of the light tip from the 
specimens was 2.0 mm. The cement 
(Panavia F; Kuraray Co Ltd) was ap-
plied in accordance with the manufac-
turer’s instructions. A Lentulo spiral 
instrument (Dentsply Maillefer) was 
used for the application of the cement 
inside the prepared canals, and, to 
avoid any difficulty resulting from pre-
mature polymerization of the resin ce-
ment in the canal, the pin was inserted 
immediately after the placement of 
the cement. Any excess cement was re-
moved, and the core was maintained 
under constant finger pressure for 
60 seconds. A halogen light (Ultralux 
Eletronic; Dabi Atlante SA), with a 
wavelength of 350 to 500 nm and a 
light intensity of 350 to 500 mv/cm2, 
was activated for 60 seconds. The light 
was positioned perpendicular to the 
long axis of the root, and the distance 
of the light tip from the specimens was 
2.0 mm. A waiting period of 6 minutes 
was used to allow complete polymer-
ization of the cement. An oxygen bar-
rier (Oxyguard II gel; Kuraray Co Ltd) 
was applied to the superficial margins 
for 10 minutes and then removed with 
cotton rolls and water spray.
To obtain groups GFP 6 mm, GFP 
8 mm, and GFP 10 mm, the glass-fiber 
posts were cemented with Panavia F 
cement (Kuraray Co Ltd), following 
the same protocol used for groups 
CPC 6 mm, CPC 8 mm, and CPC 10 
mm, with the exception of the primer 
application procedure. To fabricate 
the core, the tooth structure was con-
ditioned with 37% phosphoric acid 
gel (Ivoclar Vivadent) for 15 seconds, 
washed under a water stream for 20 
seconds, and dried with compressed 
air. In sequence, with the dentin wet, 
2 coats of the adhesive (Prime & Bond 
2.1; Dentsply) were applied, with an 
interval of 30 seconds between coats 
to allow for the solvent evaporation. 
Compressed air was then applied for 5 
seconds, and light polymerization was 
performed for 20 seconds with the 
halogen light (Ultralux Eletronic; Dabi 
Atlante SA). Layers of composite resin 
(Z100; 3M ESPE, St. Paul, Minn) were 
applied successively around the pre-
fabricated post, and each layer (ap-
proximately 0.5 mm thick) was light 
polymerized for 20 seconds. To obtain 
the core form, the acetate molds were 
filled with the composite resin and po-
sitioned above the coronal portions. 
The excess composite resin was re-
moved and the core was light polym-
erized for 40 seconds with the halogen 
light (Ultralux Eletronic; Dabi Atlante 
SA). After polymerization, the acetate 
molds were removed. 
For the standardization of ap-
plied force during the compressive 
test, metal crowns were made for all 
of the specimens. The specimens were 
prepared by placing a chamfer at the 
cervical shoulder with a diamond ro-
tary cutting instrument (no. 4219; KG 
Sorensen). A fine coat of petroleum 
jelly (União Química FTCA Nacio-
nal SA) was applied to the coronal 
portion of the core. Then, the crown 
patterns were made with casting wax 
(Odontofix, Ribeirão Preto, Brazil), 
invested in a phosphate-bonded in-
vestment material (Termocast; Poli-
dental), and cast in Co-Cr alloy (Resil-
ient Plus; Metalúrgica Riosulense SA, 
Santa Catarina, Brazil), according to 
184 Volume 101 Issue 3
The Journal of Prosthetic Dentistry
185March 2009
Giovani et alGiovani et al
Endodontically treated teeth with 
extensive loss of coronal tooth struc-
ture are commonly restored with a 
post and core and a crown. Factors 
indicating this type of restoration in-
clude extensive dental caries, fracture, 
trauma, iatrogenic loss of tooth struc-
ture and pulpal pathology, as well as 
the endodontic treatment itself. In 
addition, the loss of water content in 
dentin after endodontic therapy can 
reduce tooth resilience and, conse-
quently, increase the probability of 
fracture.1,2
After endodontic treatment, the 
restoration of pulpless teeth is im-
portant to ensure successful treat-
ment outcomes. Restorations provide 
protection and reinforcement of the 
tooth, and also prevent the passage of 
microorganisms and organic liquids 
into root canals.3-5 Failures involving 
the post and the crown can result in 
fracture of the post and root, and dis-
placement or loss of retention of the 
post. Fracture of the remaining tooth 
structure is one of the most frequent 
causes of failure.4-7
Cast metal posts and cores have 
been used for many years8; however, 
there are now newer post systems 
available. Among the materials used 
for esthetic restorations, glass-fiber 
posts have gained popularity because 
of their purported favorable biome-
chanical properties.1,9 They are re-
ported to be more flexible than cast 
metal posts and allow a better dis-tribution of forces, resulting in fewer 
root fractures.9 In addition, these pre-
fabricated posts are advantageous in 
situations in which adequate coronal 
tooth structure remains. Prefabricat-
ed posts are classified according to 
their structural composition as met-
al, ceramic, or resin reinforced with 
fibers.10,11
Some authors have reported that 
endodontically treated teeth restored 
with fiber posts show a decreased 
fracture resistance compared with 
teeth restored with metal posts.12-14 
Other authors,15,16 however, have in-
dicated that the fracture resistance of 
teeth restored with glass-fiber posts is 
equal to or greater than that of teeth 
restored with metal posts.
Studies suggest that the fracture 
susceptibility of teeth restored with 
posts may be related to factors such 
as the amount of remaining healthy 
tooth structure, which provides resis-
tance to the fracture of the tooth,4 as 
well as the characteristics of the post, 
such as the material composition,11,17 
modulus of elasticity,7,9,18 diameter,19 
and length.20 Some authors20-22 have 
indicated that the length of the post 
is related to root fracture, and that 
the post should be two thirds of the 
length of the root, or, when this can-
not be achieved, the post should have 
at least the same length as the clinical 
crown. According to Braga et al,23 if 
neither goal can be reached, the post 
must extend at least half of the root 
length. The authors observed that 
posts that extended to half of the root 
length behaved similarly to those that 
were two thirds of the root length. 
Furthermore, such posts preserve a 
greater amount of root canal filling 
material; this is important because 
the apex is an area of greater anatom-
ical complexity, with a high number of 
lateral and accessory canals.24,25
The purpose of this in vitro study 
was to evaluate the fracture resistance 
of roots with cast posts and cores and 
glass-fiber posts of different lengths 
by using a compressive test. The null 
hypothesis was that there would be 
no difference in the fracture resis-
tance of endodontically treated ca-
nines restored with different types of 
post systems of different lengths. 
MATERIAL AND METHODS
Sixty caries-free and restoration-
free human maxillary canines with 
roots of similar form were selected. 
All selected teeth had a single canal 
and straight roots measuring approxi-
mately 16 mm. The clinical crowns 
were sectioned transversally, close to 
the cemento-enamel junction, leaving 
a root length of 15 mm.
The exploration of the radicular ca-
nal was accomplished with #25 K-files 
(Dentsply Maillefer, Ballaigues, Swit-
zerland) to select the specimens that 
had a working length of 14 mm and 
an anatomical diameter of 250 µm. 
The preparation of the entrance of 
the radicular canal was accomplished 
with a flaring instrument (Endoflare 
.12, no. 25; Micro-Mega, Besançon, 
France), and the root preparation was 
accomplished with a rotary cutting in-
strument (HERO 642; Micro-Mega) 
at 300 rpm. The final instrument (#40 
master apical file; Dentsply Maillefer) 
was standardized for all specimens. 
During preparation, the canals were 
irrigated with 2 ml of 1% sodium hy-
pochlorite, alternating with 17% EDTA 
(ethylenediaminetetraacetic acid). 
Final irrigation was performed with 
10 ml of distilled water, and the ca-
nals were dried with absorbent paper 
points (Dentsply, Petrópolis, Brazil). 
Root canals were obturated by the 
warm condensation technique26 with 
gutta-percha points (Dentsply), acces-
sory gutta-percha points (Dentsply), 
and sealer (AH Plus; Dentsply). The 
plasticizing of the gutta-percha points 
was accomplished with a condenser 
(McSpadden condenser; Dentsply 
Maillefer). The extracoronal excess of 
gutta-percha was removed by using 
heated condensers (Duflex; SS White, 
Rio de Janeiro, Brazil). Vertical conden-
sation was performed with the same 
instruments, and the pulpal chambers 
were sealed with provisional cement 
(Citodur; DoriDent, Vienna, Austria). 
Specimens were immersed in distilled 
water and maintained at 37°C (±2°C) 
for a period of 36 hours. The roots 
were placed in aluminum molds (16 x 
16 x 32 mm) and embedded in acrylic 
resin (Jet; Clássico, São Paulo, Brazil) 
to maintain 4 mm of root length ex-
tending beyond the top of the acrylic 
resin. For the cervical preparation of 
the roots, a reference line was marked 
with graphite pencil at a height of 2 
mm. A diamond rotary cutting instru-
ment (3069 diamond bur; KG So-
rensen, São Paulo, Brazil) was used 
to prepare orientation notches with a 
depth of 1 mm. From these notches, 
the cervical portion of the tooth was 
prepared, resulting in a cervical termi-
nus with a square shoulder.
The specimens were divided into 
3 groups (n=20), according to their 
post lengths: group 6 mm, group 8 
mm, or group 10 mm. Each group 
was divided into 2 subgroups, accord-
ing to the post material (n=10): CPC 
(cast post and core) or GFP (glass-
fiber post). Post spaces were prepared 
with parallel-sided burs from the post 
kit (FibreKor Post; Pentron Clinical 
Technologies, Wallingford, Conn) in 
a low-speed handpiece (Dabi Atlante 
SA, Ribeirão Preto, Brazil) attached to 
a dental surveyor (Bio-Art, São Car-
los, Brazil).
For the standardization of the cor-
onal portion of the core, a standard 
mold was made in the anatomical form 
of a core of the complete crown of the 
maxillary canine tooth, which was 
cast in copper-aluminum alloy (Gol-
dent; AJE Goldent Comercial Ltda, 
São Paulo, Brazil). Beginning with 
this standard mold, 60 acetate molds 
were obtained in a plastifier (Bio-Art) 
under vacuum, and these aided in the 
fabrication of the wax patterns of the 
coronal portion of the core. 
To obtain groups CPC 6 mm, CPC 
8 mm, and CPC 10 mm, the posts 
were made by using the direct tech-
nique with acrylic resin (DuraLay; Re-
liance Dental Mfg Co, Worth, Ill) and 
prefabricated posts (Pin-Jet posts; 
Angelus Dental Solutions, Londrina, 
Brazil). The prepared posts were lu-
bricated with petroleum jelly (Un-
ião Química FTCA Nacional SA, São 
Paulo, Brazil) and, with the aid of a 
spiral drill (Lentulo bur #40; Dentsply 
Maillefer), the acrylic resin was placed 
into the prepared post space, followed 
by the insertion of the prefabricated 
plastic post. The previously made 
acetate mold was filled with acrylic 
resin (DuraLay; Reliance Dental Mfg 
Co) and placed on the post pattern, 
and the necessary finishing was per-
formed with a diamond rotary cutting 
instrument (3069 diamond bur; KG 
Sorensen). The acrylic resin patterns 
were invested in a phosphate-bonded 
investment material (Termocast; Poli-
dental, São Paulo, Brazil) and cast in 
copper-aluminum alloy (Goldent; AJE 
Goldent Comercial Ltda). The cast-
ings were airborne-particle abraded 
with 150-µm aluminum-oxide powder 
(Wilson; Polidental).
Cast posts were cemented with du-
al-polymerizing resin cement (Panavia 
F; Kuraray Co Ltd, Osaka, Japan), and 
its adhesive system (Kuraray Co Ltd). 
First, primer (Alloy Primer; Kuraray Co 
Ltd) was applied to the post. Then, 
each canal surface was acid etched 
(Ivoclar Vivadent; São Paulo, Brazil) 
for 30 seconds, rinsed with water, and 
dried with paper points (Dentsply). 
Next, 2 coats of adhesive were applied, 
followed by 20 seconds of drying and 
light polymerization with a halogen 
light (Ultralux Electronic; Dabi At-
lante SA) for 30 seconds. The unit had 
a wavelength of 350 to 500 nm and 
light intensity of 350 to 500 mv/cm2. 
The light was positioned perpendicu-
lar to the long axis of the root, and 
the distance of the light tip from the 
specimens was 2.0 mm. The cement 
(Panavia F; Kuraray Co Ltd) was ap-
plied in accordance with the manufac-
turer’s instructions. A Lentulo spiral 
instrument (Dentsply Maillefer) was 
used for the application of the cement 
inside the prepared canals, and, to 
avoid any difficulty resulting from pre-
mature polymerization of the resin ce-
ment in the canal, the pin wasinserted 
immediately after the placement of 
the cement. Any excess cement was re-
moved, and the core was maintained 
under constant finger pressure for 
60 seconds. A halogen light (Ultralux 
Eletronic; Dabi Atlante SA), with a 
wavelength of 350 to 500 nm and a 
light intensity of 350 to 500 mv/cm2, 
was activated for 60 seconds. The light 
was positioned perpendicular to the 
long axis of the root, and the distance 
of the light tip from the specimens was 
2.0 mm. A waiting period of 6 minutes 
was used to allow complete polymer-
ization of the cement. An oxygen bar-
rier (Oxyguard II gel; Kuraray Co Ltd) 
was applied to the superficial margins 
for 10 minutes and then removed with 
cotton rolls and water spray.
To obtain groups GFP 6 mm, GFP 
8 mm, and GFP 10 mm, the glass-fiber 
posts were cemented with Panavia F 
cement (Kuraray Co Ltd), following 
the same protocol used for groups 
CPC 6 mm, CPC 8 mm, and CPC 10 
mm, with the exception of the primer 
application procedure. To fabricate 
the core, the tooth structure was con-
ditioned with 37% phosphoric acid 
gel (Ivoclar Vivadent) for 15 seconds, 
washed under a water stream for 20 
seconds, and dried with compressed 
air. In sequence, with the dentin wet, 
2 coats of the adhesive (Prime & Bond 
2.1; Dentsply) were applied, with an 
interval of 30 seconds between coats 
to allow for the solvent evaporation. 
Compressed air was then applied for 5 
seconds, and light polymerization was 
performed for 20 seconds with the 
halogen light (Ultralux Eletronic; Dabi 
Atlante SA). Layers of composite resin 
(Z100; 3M ESPE, St. Paul, Minn) were 
applied successively around the pre-
fabricated post, and each layer (ap-
proximately 0.5 mm thick) was light 
polymerized for 20 seconds. To obtain 
the core form, the acetate molds were 
filled with the composite resin and po-
sitioned above the coronal portions. 
The excess composite resin was re-
moved and the core was light polym-
erized for 40 seconds with the halogen 
light (Ultralux Eletronic; Dabi Atlante 
SA). After polymerization, the acetate 
molds were removed. 
For the standardization of ap-
plied force during the compressive 
test, metal crowns were made for all 
of the specimens. The specimens were 
prepared by placing a chamfer at the 
cervical shoulder with a diamond ro-
tary cutting instrument (no. 4219; KG 
Sorensen). A fine coat of petroleum 
jelly (União Química FTCA Nacio-
nal SA) was applied to the coronal 
portion of the core. Then, the crown 
patterns were made with casting wax 
(Odontofix, Ribeirão Preto, Brazil), 
invested in a phosphate-bonded in-
vestment material (Termocast; Poli-
dental), and cast in Co-Cr alloy (Resil-
ient Plus; Metalúrgica Riosulense SA, 
Santa Catarina, Brazil), according to 
186 Volume 101 Issue 3
The Journal of Prosthetic Dentistry
187March 2009
Giovani et al Giovani et al
the manufacturer’s instructions. The 
crowns were airborne-particle abrad-
ed with 150-µm aluminum-oxide 
powder (Wilson; Polidental). 
All crowns were cemented with 
zinc phosphate cement (Zinc Cement; 
SS White) in a ratio of 2.0 g of phos-
phate zinc powder to 0.5 ml of liquid. 
The crowns were filled with cement, 
placed on the preparations, and con-
stant finger pressure was applied for 
60 seconds. After 10 minutes, the 
excess cement was removed with a 
dental explorer. The specimens were 
then stored in 100% relative humid-
ity, at a constant temperature of 37°C 
(±2°C), for a period of 72 hours. 
The specimens were then subject-
ed to a compressive test in a universal 
testing machine (Instron 4444; Instron 
Corp, Norwood, Mass). A device was 
used to standardize the position of the 
specimens at the base of the appara-
tus so that the load could be applied 
at an angle of 135 degrees in relation 
to the long axis of the roots. An in-
creasing oblique compressive load was 
applied on the cingulum of the pala-
tal surface (3.0 mm from the incisor 
region) by using a cylindrical-shaped 
device with a round terminus (2.7 mm 
in diameter). A crosshead speed of 1 
mm/min was applied until the root 
fractured. The set of root-post frag-
ments were removed from the acrylic 
resin, after the fracture, and observed 
under a stereoscopic magnifying glass 
(Leica Microsystems GmbH, Wetzlar, 
Germany), at x3 magnification, for 
fracture analysis. With respect to the 
location, the fracture was classified 
according to the root third in which it 
occurred: cervical, middle, or apical. 
Regarding the type, the fracture plane 
was considered in relation to the long 
axis of the root and was classified as 
longitudinal, oblique, or transverse.
The values of the forces required 
for the roots to fracture, obtained in 
N, were submitted to preliminary sta-
tistical tests using software (InStat; 
GraphPad Software, Inc, La Jolla, Ca-
lif ), to verify the normality of the dis-
tribution. The results were subjected 
to a preliminary statistical analysis. As 
the obtained values were not normally 
distributed, data were transformed to 
normalize them using the percentile-
transformed data. A 2-way ANOVA 
was performed with the transformed 
data (α=.05). The Tukey-Kramer test 
was used to verify which groups dif-
fered among themselves (α=.05).
RESULTS
The mean values of the compressive 
loads required to fracture the roots in 
each of the 6 groups are displayed in 
Table I. The ANOVA indicated signifi-
cant differences (P<.05) among the 
groups (Table II), and the Tukey-Kram-
er test (Table III) showed no statisti-
cal differences among the metal posts 
of different lengths: 6 mm (26.5 N 
±13.4), 8 mm (25.2 N ±13.9), and 10 
mm (17.1 N ±5.2). For the glass-fiber 
post group, the 8-mm posts (13.4 N 
±11.0) were statistically similar to the 
6-mm (6.9 N ±4.6) and 10-mm posts 
(31.7 N ±13.1). After the compression 
test, the post fragments were removed 
from the radicular canal for evaluation 
of the type and location of fractures. 
The fracture percentage values are 
shown in Table IV.
Table I. Mean values (SD) of strength (N) of compressive force required for root fracture
Cast post and core
Glass fiber
Mean
Groups with same superscript letter were not significantly different according to Tukey-Kramer test (P>.05).
26.5 (13.4)b,c
6.9 (4.6)a
16.75
6 mm
25.2 (13.9)b,c
13.4 (11.0)a,b
19.3
8 mm
17.1 (5.2)a,b
31.7 (13.1)c
27.4
10 mm
Post Length
Post Type
Between lengths
Between types
Between groups
Residual
Total
2
1
2
54
59
df
0.0006
0.0005
0.0032
0.0065
0.0107
0.0003
0.0005
0.0016
0.0001
Squares Squares
Sum ofSource of Mean
2.54
3.87
13.31
FVariation
8.669
5.132
.009
P
Table II. Two-way ANOVA with angle percentile-transformed data
DISCUSSION
The current study evaluated the 
resistance to fracture of roots submit-
ted to endodontic treatment and re-
stored by using cast metal and glass-
fiber posts with different lengths. The 
results of the current study support 
rejection of the null hypothesis that 
there would be no difference in the 
fracture of endodontically treated 
teeth restored with different types of 
post systems and different lengths. 
Analysis of the results indicates 
that the length of cast posts did not 
affect the resistance of the roots to 
fracture. The authors hypothesize 
that, regardless of the length, when a 
rigid cast post with a high modulus of 
elasticity is submitted to stress or an 
oblique compressive load, it does not 
absorb the energy. Rather, it transmits 
energy to a less rigid structure, in this 
case, the dentin, which has a lower 
modulus of elasticity, thus increas-
ing the fracture potential of the root.7 
Hayashi et al7 noted that the fractur-
ing of teeth restored with cast posts 
is related to the post’s stiffness. In the 
current study, the fracture location 
was predominantly in the apical re-
gion, probably because of the oblique 
compressive load transferred from the 
post to dentin in the apical region.7 
With a fracture in this location, the 
tooth is nonrestorable.7,9,18
With respectto the glass-fiber 
posts, the results indicated that the 
roots restored with the longer posts 
(10 mm) had a greater resistance 
to fracture. Posts with a modulus of 
elasticity similar to dentin, such as the 
glass-fiber post, when submitted to a 
compressive load, can better absorb 
the forces concentrated along the root, 
which may decrease the probability of 
fracture.9,18 This phenomenon may ex-
plain the results obtained in this study 
for the longer posts (10 mm), which, 
given their larger mass volume, pos-
sessed the capacity to absorb a great-
er amount of stress, rather than trans-
ferring stress to the dentin. However, 
the shorter posts (6 mm) appeared to 
concentrate the stresses in the smaller 
area of radicular dentin, with a greater 
susceptibility to fracture. 
The fracture locations for the lon-
ger glass-fiber posts (8 and 10 mm) 
were predominantly in the cervical re-
gion, which may result from a greater 
concentration of forces in this region 
due to the angle of the joint between 
the glass-fiber post and the compos-
ite resin core. As for the 6-mm posts, 
there was a greater incidence of frac-
ture in the middle region, probably 
because of the smaller mass volume of 
these posts, which resulted in a lower 
absorption of forces and their more 
efficient transfer to the dentin.
The 6-mm and 8-mm glass-fiber 
posts correspond, respectively, to 40% 
and 53.3% of the radicular length of 
15 mm measured in this study. These 
lengths should be between one third 
and one half of the radicular length 
only in situations that do not allow the 
Table III. Tukey-Kramer test, between groups
Table IV. Percentage of fractures in relation to location of root fracture according to post type and length
Cast post and core, 6 mm
Cast post and core, 8 mm
Cast post and core, 10 mm
Glass-fiber post, 6 mm
Glass-fiber post, 8 mm
Glass-fiber post, 10 mm
Groups with same superscript letter were not significantly different according to Tukey-Kramer test (P>.05).
26.5ab
25.2ab
17.1bc
6.9c
13.4bc
31.7a
Means
13.22
Critical Value (α=.05) Post Type
Cervical
Middle
Apical
0
10
90
6 mm
0
10
90
8 mm
0
30
70
10 mm
30
70
0
6 mm
60
40
0
8 mm
70
30
0
10 mm
Length
Post Type
Cast Metal Glass Fiber
Place of
Fracture
186 Volume 101 Issue 3
The Journal of Prosthetic Dentistry
187March 2009
Giovani et al Giovani et al
the manufacturer’s instructions. The 
crowns were airborne-particle abrad-
ed with 150-µm aluminum-oxide 
powder (Wilson; Polidental). 
All crowns were cemented with 
zinc phosphate cement (Zinc Cement; 
SS White) in a ratio of 2.0 g of phos-
phate zinc powder to 0.5 ml of liquid. 
The crowns were filled with cement, 
placed on the preparations, and con-
stant finger pressure was applied for 
60 seconds. After 10 minutes, the 
excess cement was removed with a 
dental explorer. The specimens were 
then stored in 100% relative humid-
ity, at a constant temperature of 37°C 
(±2°C), for a period of 72 hours. 
The specimens were then subject-
ed to a compressive test in a universal 
testing machine (Instron 4444; Instron 
Corp, Norwood, Mass). A device was 
used to standardize the position of the 
specimens at the base of the appara-
tus so that the load could be applied 
at an angle of 135 degrees in relation 
to the long axis of the roots. An in-
creasing oblique compressive load was 
applied on the cingulum of the pala-
tal surface (3.0 mm from the incisor 
region) by using a cylindrical-shaped 
device with a round terminus (2.7 mm 
in diameter). A crosshead speed of 1 
mm/min was applied until the root 
fractured. The set of root-post frag-
ments were removed from the acrylic 
resin, after the fracture, and observed 
under a stereoscopic magnifying glass 
(Leica Microsystems GmbH, Wetzlar, 
Germany), at x3 magnification, for 
fracture analysis. With respect to the 
location, the fracture was classified 
according to the root third in which it 
occurred: cervical, middle, or apical. 
Regarding the type, the fracture plane 
was considered in relation to the long 
axis of the root and was classified as 
longitudinal, oblique, or transverse.
The values of the forces required 
for the roots to fracture, obtained in 
N, were submitted to preliminary sta-
tistical tests using software (InStat; 
GraphPad Software, Inc, La Jolla, Ca-
lif ), to verify the normality of the dis-
tribution. The results were subjected 
to a preliminary statistical analysis. As 
the obtained values were not normally 
distributed, data were transformed to 
normalize them using the percentile-
transformed data. A 2-way ANOVA 
was performed with the transformed 
data (α=.05). The Tukey-Kramer test 
was used to verify which groups dif-
fered among themselves (α=.05).
RESULTS
The mean values of the compressive 
loads required to fracture the roots in 
each of the 6 groups are displayed in 
Table I. The ANOVA indicated signifi-
cant differences (P<.05) among the 
groups (Table II), and the Tukey-Kram-
er test (Table III) showed no statisti-
cal differences among the metal posts 
of different lengths: 6 mm (26.5 N 
±13.4), 8 mm (25.2 N ±13.9), and 10 
mm (17.1 N ±5.2). For the glass-fiber 
post group, the 8-mm posts (13.4 N 
±11.0) were statistically similar to the 
6-mm (6.9 N ±4.6) and 10-mm posts 
(31.7 N ±13.1). After the compression 
test, the post fragments were removed 
from the radicular canal for evaluation 
of the type and location of fractures. 
The fracture percentage values are 
shown in Table IV.
Table I. Mean values (SD) of strength (N) of compressive force required for root fracture
Cast post and core
Glass fiber
Mean
Groups with same superscript letter were not significantly different according to Tukey-Kramer test (P>.05).
26.5 (13.4)b,c
6.9 (4.6)a
16.75
6 mm
25.2 (13.9)b,c
13.4 (11.0)a,b
19.3
8 mm
17.1 (5.2)a,b
31.7 (13.1)c
27.4
10 mm
Post Length
Post Type
Between lengths
Between types
Between groups
Residual
Total
2
1
2
54
59
df
0.0006
0.0005
0.0032
0.0065
0.0107
0.0003
0.0005
0.0016
0.0001
Squares Squares
Sum ofSource of Mean
2.54
3.87
13.31
FVariation
8.669
5.132
.009
P
Table II. Two-way ANOVA with angle percentile-transformed data
DISCUSSION
The current study evaluated the 
resistance to fracture of roots submit-
ted to endodontic treatment and re-
stored by using cast metal and glass-
fiber posts with different lengths. The 
results of the current study support 
rejection of the null hypothesis that 
there would be no difference in the 
fracture of endodontically treated 
teeth restored with different types of 
post systems and different lengths. 
Analysis of the results indicates 
that the length of cast posts did not 
affect the resistance of the roots to 
fracture. The authors hypothesize 
that, regardless of the length, when a 
rigid cast post with a high modulus of 
elasticity is submitted to stress or an 
oblique compressive load, it does not 
absorb the energy. Rather, it transmits 
energy to a less rigid structure, in this 
case, the dentin, which has a lower 
modulus of elasticity, thus increas-
ing the fracture potential of the root.7 
Hayashi et al7 noted that the fractur-
ing of teeth restored with cast posts 
is related to the post’s stiffness. In the 
current study, the fracture location 
was predominantly in the apical re-
gion, probably because of the oblique 
compressive load transferred from the 
post to dentin in the apical region.7 
With a fracture in this location, the 
tooth is nonrestorable.7,9,18
With respect to the glass-fiber 
posts, the results indicated that the 
roots restored with the longer posts 
(10 mm) had a greater resistance 
to fracture. Posts with a modulus of 
elasticity similar to dentin, such as the 
glass-fiber post, when submitted to a 
compressive load, can better absorb 
the forces concentrated along the root, 
which may decrease the probability of 
fracture.9,18 This phenomenon may ex-
plain the results obtained in this study 
for the longer posts (10mm), which, 
given their larger mass volume, pos-
sessed the capacity to absorb a great-
er amount of stress, rather than trans-
ferring stress to the dentin. However, 
the shorter posts (6 mm) appeared to 
concentrate the stresses in the smaller 
area of radicular dentin, with a greater 
susceptibility to fracture. 
The fracture locations for the lon-
ger glass-fiber posts (8 and 10 mm) 
were predominantly in the cervical re-
gion, which may result from a greater 
concentration of forces in this region 
due to the angle of the joint between 
the glass-fiber post and the compos-
ite resin core. As for the 6-mm posts, 
there was a greater incidence of frac-
ture in the middle region, probably 
because of the smaller mass volume of 
these posts, which resulted in a lower 
absorption of forces and their more 
efficient transfer to the dentin.
The 6-mm and 8-mm glass-fiber 
posts correspond, respectively, to 40% 
and 53.3% of the radicular length of 
15 mm measured in this study. These 
lengths should be between one third 
and one half of the radicular length 
only in situations that do not allow the 
Table III. Tukey-Kramer test, between groups
Table IV. Percentage of fractures in relation to location of root fracture according to post type and length
Cast post and core, 6 mm
Cast post and core, 8 mm
Cast post and core, 10 mm
Glass-fiber post, 6 mm
Glass-fiber post, 8 mm
Glass-fiber post, 10 mm
Groups with same superscript letter were not significantly different according to Tukey-Kramer test (P>.05).
26.5ab
25.2ab
17.1bc
6.9c
13.4bc
31.7a
Means
13.22
Critical Value (α=.05) Post Type
Cervical
Middle
Apical
0
10
90
6 mm
0
10
90
8 mm
0
30
70
10 mm
30
70
0
6 mm
60
40
0
8 mm
70
30
0
10 mm
Length
Post Type
Cast Metal Glass Fiber
Place of
Fracture
188 Volume 101 Issue 3
The Journal of Prosthetic Dentistry Kious et alGiovani et al
optimal length, two thirds of the root, 
to be obtained.22,23 When the length 
of 10 mm was used for the glass-fiber 
posts (66.6%, or two thirds, of the 
root length), the force required for 
the fracture of these posts was signifi-
cantly greater than that required for 
the 6-mm-long posts. The 8-mm post 
showed an intermediate value which 
was statistically similar to the values 
for the 6-mm and 10-mm posts. As in 
the present study, Braga et al,23 work-
ing with glass-fiber and cast posts of 
different lengths, obtained satisfac-
tory results for the 8-mm glass-fiber 
posts with respect to retention. Thus, 
considering that the 8-mm glass-fiber 
posts have demonstrated values simi-
lar to the 6- and 10-mm posts, with 
respect to both fracture strength 
and retention, their use can be rec-
ommended for situations in which 
the length of two thirds cannot be 
reached, for example, in situations in-
volving curved roots. Based on these 
results, the recommendation of Shil-
lingburg et al20 that the intraradicular 
post be two thirds of the root length 
should be modified to suit the new 
prefabricated posts and adhesive ma-
terial systems.
This current study has some limita-
tions, such as the type of testing used, 
that is, a single cycle to failure, which 
does not represent the intraoral con-
dition. Intraorally, teeth are subjected 
to cyclic loading through mastication 
and are immersed in a wet environ-
ment that is subject to chemical and 
thermal changes. The study also evalu-
ated maxillary canines, and, therefore, 
the results can be applied only to that 
group of teeth. Furthermore, cement 
pressure was not standardized, as only 
finger pressure was used.
It is also important that clinicians 
consider the various types of materi-
als available for post systems, as well 
as their mechanical properties. Future 
research is necessary to clarify the ef-
fects of different lengths of new post 
systems on the resistance to fracture. 
Finally, further investigations using a 
similar study design, but with a simu-
lated periodontal ligament, should be 
used to compare the different esthetic 
post systems.
CONCLUSIONS
Within the limitations of this in 
vitro study, the following conclusions 
were drawn:
1. In relation to the length, cast 
posts did not differ significantly in 
terms of the compressive load re-
quired to fracture the root (P=.17). 
2. The 10-mm-long glass-fiber 
group demonstrated significantly 
higher values of fracture resistance, 
and the 6-mm-long glass-fiber group 
showed the lowest values for the force 
resulting in root fracture; these groups 
were significantly different from each 
other (P<.001). 
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Corresponding author
Dr Silvana Maria Paulino
R: Florêncio de Abreu, 1201, apto. 92 - Centro
Ribeirão Preto
São Paulo
BRAZIL
141015-060
Fax: +55-16-39311072
E-mail: silvana.paulino@gmail.com 
Copyright © 2009 by the Editorial Council for 
The Journal of Prosthetic Dentistry.
Clinical Implications
As long as restorations are seated in a timely manner, all of the prod-
ucts evaluated in this study demonstrate acceptable film thicknesses.
Statement of problem. A luting cement must maintain a minimum film thickness over a sufficient period of time to 
allow seating of indirect restorations. The performance of newer luting cements in this regard has not been evaluated. 
Purpose. The purpose of this study was to compare the film thicknesses of 6 luting cements, 2 resin-modified glass 
ionomer (FujiCEM and RelyX Luting Plus), 2 composite resin (Panavia 21 and RelyX ARC), and 2 self-adhesive resin 
(Maxcem and RelyX Unicem) cements, over 3 minutes. 
Material and methods. The film thickness (µm) of each cement (n=7) was determined at room temperature at 1, 2, 
and 3 minutes after the start of mixing, according to the testing method set forth in ISO Standard 9917. Means of all 
cements were compared at the 2-minute interval, and means at the 1- and 3-minute intervals for each were compared 
to the mean for the same cement at 2 minutes, using 1-way analyses of variance (ANOVA) and Tukey-Kramer multiple 
comparison tests (α=.05).
Results. Except for 1 resin-modified material at 3 minutes, a point beyond its specified working time, all materials 
produced film thicknesses under 30 µm at 3 minutes and under 26 µm at 2 minutes. 
Conclusions. All of the materials tested meet the ISO standard of 25-µm maximum film thickness for up to 2 minutes 
after mixing. (J Prosthet Dent 2009;101:189-192)
Film thicknesses of recently introduced 
luting cements
Andrew R. Kious, DDS,a Howard W. Roberts, DMD, MS,b and 
William W. Brackett, DDS, MSDc
School of Dentistry, Medical College of Georgia, Augusta, Ga; 
USAF Dental Corps, Great Lakes, Ill
The views expressed in the article are those of the author and do not reflect the official policy or position of the US Air Force, De-
partment of Defense, or the US Government.
aAssistant Professor, Department of Oral Rehabilitation.
bColonel, USAF Dental Corps; Director, Dental Biomaterials Evaluation, USAF Dental Evaluation and Consulting Service, Great 
Lakes, Ill. 
cProfessor, Department of Oral Rehabilitation.
Indirect restorations have been 
demonstrated to be effective, with 
clinical studies reporting a survival 
rate for single crowns of greater than 
90% over 8-10 years, using current 
techniques.1,2 Luting agents, because 
they join indirect restorations to their 
preparations, are critical to their ef-
fectiveness.3 In addition to possessing 
the low solubility and high ultimate 
strength necessary for long-term re-
tention of restorations, these materi-
als must also maintain a minimal film 
thickness over a long enough interval 
that restorations can be seated com-
pletely. 
Currently, 3 classes of luting 
agents, resin-modified glass ionomer, 
composite resin, and self-etching res-
in, are considered to be viable clinical 
options. In the past, composite resin 
cements have demonstrated a greater 
film thickness than other cements,4,5 
which is reflected in current ISO stan-
dards that require a film thickness 
at the time of seating of no greater 
than 25 µm for water-based luting 
cements,6 and no greater than 50 µm 
for resin-based cements.7
In recent years, self-adhesive resin 
luting cements have been introduced, 
and composite resin and resin-modi-
fied glass ionomer cements reformu-
lated, but little information on the film 
thicknesses of these materials has been 
reported. The Council on Scientific 
	In vitro fracture resistance of glassfiber and cast metal posts with different lengths
	MATERIAL AND METHODS
	RESULTS
	DISCUSSION
	CONCLUSIONS
	REFERENCES