CLINICAL DENTISTRY AND RESEARCH 2015; 39(3): 87-94 Original Research Article
INFLUENCE OF BONE LEVEL, POST LENGTH AND FERRULE
HEIGHT ON FRACTURE RESISTANCE OF METAL AND GLASS-FIBER
POSTS
Cem Şahin, DDS, PhD
Associate Professor, School of Dental Technology,
Vocational School of Health Services, Hacettepe University,
Ankara, Turkey
Simel Ayyıldız,DDS, PhD
Associate Professor, Department of Prosthodontics,
Center for Dental Sciences, Gülhane Military Medical Academy,
Ankara, Turkey
ABSTRACT
Background and Aim: Dentin-post combination subjected to
complex occlusal forces may result undesired fractures even after
a successful treatment. The aim of this study was to evaluate
whether the durability of glass-fiber posts are improved comparing
with metal posts.
Material and Methods: One hundred sixty freshly extracted caries
free upper second premolar teeth with one root canal were selected
for this study. The crowns were cut off 2 mm coronal from the
cement-enamel junction to obtain straight roots. The samples were
embedded into 6 mm or 8 mm depth acrylic resin with 5 cm radius to
mimic bone level. To perform fracture resistance test each, specimen
was settled in a special metal holder and loaded until fracture. Data
were analyzed using Sample T-test, Kruskal Wallis and Dunn’s tests.
Results: Mean fracture resistance of fiber-post samples
(1280.07±191.48 N) were significantly higher than metal-post
samples (1157.19± 160.26 N) (p=0.01). Mean fracture resistance
of samples in the 8 mm bone was 1270.2±168.6 N, while it was
1167.0±190.1 N at 6 mm group. Effect of ferrule to fracture
resistance was found to be significantly higher at “2 mm” compared
with “0 mm” height (p=0.03). There was no correlation between
fracture types and post types at different bone levels. There was no
correlation between fracture types and bone levels.
Conclusion: Fracture occurrence is independent from bone levels
and post length. To obtain the most resistant restoration ferrule
Correspondence
establish is doubtless. Increasing the post length with apical care
will contribute to the success.
Cem Şahin DDS, PhD
Clin Dent Res 2015: 39(3): 87-94
School of Dental Technology,
Vocational School of Health Services,
Hacettepe University
06100 Sıhhiye
Keywords: Post Core Restorations, Glass Fiber Posts, Apical
Fractures
Ankara, Turkey
Phone: + 90 505 335 30 92
Fax: + 90 312 310 27 30
E-mail: [email protected]
Submitted for Publication: 07.09.2015
Accepted for Publication : 11.16.2015
87
CLINICAL DENTISTRY AND RESEARCH 2015; 39(3): 87-94
Orjinal Araştırma
KEMİK SEVİYESİ, POST UZUNLUĞU VE FERRUL YÜKSEKLİĞİNİN
METAL VE CAM-FİBER POSTLARIN KIRILMA DAYANIMLARINA
ETKİSİ
Cem Şahin
Doç. Dr. Hacettepe Üniversitesi, Sağlık Hizmetleri Meslek Yüksekokulu,
Diş Protez Teknolojisi,
Ankara, Türkiye
ÖZ
Amaç: Kompleks okluzal kuvvetlere maruz kaldığında başarılı bir
dentin-post kombinasyonunda dahi beklenmedik kırıklar görülebilir.
Post uzunluğu kökün 3’te 2’ine ulaştıkça stres kırığı riski artar. Bu
Simel Ayyıldız
Doç. Dr. GATA Diş Hekimleri Bilimleri Merkezi,
Protetik Diş Tedavisi Anabilim Dalı,
Ankara, Türkiye
çalışmanın amacı uygulama ve bağlanma avantajlarıyla geliştirilen
cam fiber postları metal postlarla karşılaştırmaktır.
Materyal ve Metod: Yüzaltmış adet çürüksüz tek köklü üst 2.
premolar dişler çalışmaya dahil edildi.kronlar mine-sement sınırının
2 mm coronalinden elmas diskler kullanılarak kesildi. Örnekler kemiği
taklit eden 6 ve 8 mm derinliğinde ve 5 cm çapında akril blokların
içerisine gömüldü. Kırma testi için örnekler yer düzlemine 45°’lik
açıyla hazırlanmış olan metal taşıyıcı içerisine yerleştirildi. Veriler,
Sample t test, Kruskall Wallis ve dunn’s testi kullanılarak analiz edildi.
Bulgular: Fiber post örneklerin ortalama kırılma dayanımları
(1280.07±191.48 N) metal post örneklerden (1157.19± 160.26
N) belirgin olarak yüksek bulundu (p=0.01). 8 mm kemik içerisindeki
örneklerin ortalama kırılma dayanımları 1270.2±168.6 N bulunurken
bu değer 6 mm kemik içerisinde 1167.0±190.1 N olarak tespit edildi.
Kırılma dayanımına 2 mm ferrulun etkisi 0 mm’ye oranla belirgin olarak
farklı bulundu (p=0.03). Farklı kemik yükseklikleri içerisinde kırık türleri
ve post türleri arasında istatistiksel bir korelasyon bulunamamıştır.
Sonuç: Kırık oluşumu kemik seviyesi ve post uzunluğundan
bağımsızdır. Dayanımı artırmak için ferrul planlaması gereklidir. Apical
stress oluşturmadan post boyunu uzatmak başarıya katkı sağlar.
Sorumlu Yazar
Clin Dent Res 2015: 39(3): 87-94
Cem Şahin
Hacettepe Üniversitesi, Diş Hekimliği Fakültesi,
Sağlık Hizmetleri Meslek Yüksekokulu,
Diş Protez Teknolojisi,
Anahtar Kelimeler: Post-Core Restorasyonlar, Cam Fiber
Postlar, Apikal Kırıklar
06100 Sıhhiye Ankara, Türkiye
Telefon: + 90 505 335 30 92
Fax: + 90 312 310 27 30
E-mail: [email protected]
88
Yayın Başvuru Tarihi : 09.07.2015
Yayına Kabul Tarihi : 16.11.2015
FRACTURE RESISTANCE OF METAL AND FIBER POSTS
INTRODUCTION
MATERIALS AND METHODS
Dentinal volume loss during essential root canal and coronal
One hundred sixty freshly extracted caries free upper second
premolar teeth with one root canal were selected for this
study. The crowns were cut off 2 mm coronal from the cementenamel junction using a diamond disc to obtain straight roots.
Pulp tissues were instrumented with Hedstrom files (Dentsply,
Maillefer, Ballagues, Switzerland). Rotary instruments (VDW,
Munich, Germany) with crown down technique at 250 rpm
were used to prepare root canals to size F3 at a certain
working length of 1 mm coronal from apex. After irrigating
with 2 ml 2.5% sodium hypochlorite, the root canals were filled
with gutta percha and AH plus (DeTrey Dentsply, Konstanz,
Germany) using lateral condensation technique. The samples
were then randomly divided into subgroups and arranged for
the experimental process as shown in table 1. Preparations of
ferrules of half of the samples (2-mm) were accomplished at
this stage and zero-ferrule samples were cut from cementenamel junction.
To prepare post spaces in the root canals of all the samples
matching fiber post drills with 1.3 coronal and 0.7 apical
diameter and 3.44 conicity were used (3M ESPE, Saint
Paul, USA). Spaces were irrigated with the 3% sodium
hypochlorite solution and were dried with paper points.
For metal posts negative molds of the post spaces were
obtained using a high viscosity impression material. One
technical assistant fabricated all the wax patterns and
then casting process was performed with conventional
techniques using Co-Cr based alloy. Metal posts were
designed to mimic fiber-glass (RelyX, 3M ESPE, UK.)
prefabricated posts for standardization. Post lengths were
measured using a digital micrometer (Insize IP54 Electronic
Point Micrometer, Insize Co., LTD, USA) and adjusted into
their post level position as shown in Figure 1.
Both metal and fiber post surfaces were etched using
orthophosphoric acid (37%) for debris removal and then
immersed into ultrasonic cleaners. The posts were seated
into the post spaces using self–adhesive resin cement
(RelyX Unicem Aplicap, 3M ESPE, Germany) according to
manufacturer’s recommendations. Halogen light curing
unit was used for polymerization of the resin from coronal
part of the post for 40 seconds. To etch the occlusal part
of the samples, ortho-phosphoric acid was used for 10
sec. Cylindrically shaped core parts of all specimens with
5 mm diameter and 4 mm length (Figure 1) were built up
using light-polymerized posterior composite resin (Filtek
P60, 3M ESPE, Saint Paul, USA) according to manufacturer’s
recommendations.
preparation after endodontic treatment to reconstruct the
teeth with post and core fabrication is unavoidable which
weakens the teeth structure.1, 2 Therefore the dentin-post
combination subjected to complex occlusal forces may result
undesired fractures even after a successful treatment.3
Current clinical post-core procedures are based on one of
two systems; prefabricated or casted posts. Prefabricated
or casted metal posts have an effect of durability because
of their structure; however they transfer most of the stress
to weakened root canal and dentin which may provoke
unrestorable fractures. On the other hand non-metallic post
materials fabricated with carbon-fiber reinforcement principle
may be less durable because of their own structure
represent similar elasticity characteristics to dentin.
3, 6, 7
4, 5
but
They also
have better vision and application advantages over metal
posts. As the integrity of post material with root canal dentin
forming a solid entire is achieved, this feature may be favorable
for endodontically treated teeth under occlusal loads.
Durability and long-term survival are the primary goal
of a post-core restoration with endodontic treatment.
Treatment modalities based on biological and physical
principles have been improved for years. Post length is
assumed to have significant role at retention and fracture
resistance.8, 9 However as the post length approaches to
two-thirds of the root, stress fracture risk increases.10
Supragingival part of remaining teeth is defined to be the
most important feature to resist fracture against lateral,
vertical and oblique forces called as ferrule effect.11 To
achieve the best benefit of ferrule is suggested to be at
least 1.5 mm high from gingival level.12 The contribution
of the existence of ferrule to fracture resistance has been
discussed by many researchers.13-16
To date many studies were conducted concerning bone
level, ferrule effect, adhesive materials or techniques,
structure and properties of post materials or post/canal
lengths separately; however few of them were constituted
combining all the mentioned parameters in one study.
The aim of this study was to evaluate whether the durability
of glass-fiber posts are improved with the application and
luting advantages comparing with metal posts, which are
widely known to have strength priority, at different bone
levels, ferrule effect and canal depth.
89
90
8 mm
6 mm
Bone level
1320.55±152.55
Metal post+2 mm ferrul+8 mm dept
1471.42±134.34
Fiber post+2 mm ferrul+8 mm dept
1185.73±112.28
1295.37±123.39
Fiber post+2 mm ferrul+6 mm dept
Metal post+2 mm ferrul+6 mm dept
1322.68±145.07
Fiber post+0 mm ferrul+8 mm dept
1190.02±152.56
1219.60±170.73
Fiber post+0 mm ferrul+6 mm dept
Metal post+0 mm ferrul+8 mm dept
1186.10±105.20
Metal post+2 mm ferrul+8 mm dept
1156.68±152.22
1026.02±113.27
Metal post+2 mm ferrul+6 mm dept
Metal post+0 mm ferrul+6 mm dept
1131.08±173.20
1338.37±220.91
Fiber post+2 mm ferrul+8 mm dept
Metal post+0 mm ferrul+8 mm dept
1200.43±194.99
Fiber post+2 mm ferrul+6 mm dept
1061.34±162.68
1267.38±216.72
Fiber post+0 mm ferrul+8 mm dept
Metal post+0 mm ferrul+6 mm dept
1125.34±141.31
Fiber post+0 mm ferrul+6 mm dept
Mean
1329.45
1200.2
1156.4
1144.9
1461.15
1346
1348.25
1230.9
1205.35
1007.5
1113.7
1062.6
1389.75
1199.1
1322.2
1127.9
median
1522.1
1307.9
1490.2
1426
1624.4
1404.7
1482.7
1474.2
1304.6
1209
1401
1291.2
1634.2
1433.3
1522.5
1323.3
maximum
Fracture Resistance (N)
1066.4
1004.6
1008.1
979.3
1259.5
1084.3
974.4
973.2
993.3
893
919.2
799.5
992.4
918.5
792.4
922.2
minimum
Table 1. Sub-groups of the experiment; treatment type, bone level and fracture resistance and fracture types in the study.
9
8
9
7
8
7
7
5
8
9
8
9
7
7
6
7
90%
80%
90%
70%
80%
70%
70%
50%
80%
90%
80%
90%
70%
70%
60%
70%
Coronal
-
-
-
2
-
1
-
2
-
-
1
-
1
1
-
-
Dentin
20%
10%
20%
10%
10%
10%
Apical
1
1
1
1
2
2
3
3
1
1
1
1
1
2
2
3
10%
10%
10%
10%
20%
20%
30%
30%
10%
10%
10%
10%
10%
20%
20%
30%
Post-core
(restorative)
Fracture Type
1
1
1
2
10%
10%
10%
20%
Dentin+Post
CLINICAL DENTISTRY AND RESEARCH
FRACTURE RESISTANCE OF METAL AND FIBER POSTS
Figure 1. Shematic view of the samples prepared showing the
dimensions, bone levels and restoration design.
The samples were then embedded into 6 mm or 8 mm depth
acrylic resin with 5 cm radius to mimic bone level around the
endodontically treated teeth (Figure 1).
To perform fracture resistance test each specimen was
settled in a special metal holder with 45° angle inclination
to load direction. Compressive load with a crosshead speed
of 1 mm/min through the corner of the core was applied
using a universal testing machine (Lloyd LRX, West Sussex,
UK) until the fracture occur.
Bone levels divided the structure into two as coronal and
apical. Failures occurring more occlusally from ferrule were
accepted as post-core (restorative) fractures.
Statistical analysis was performed using SPSS software.
Independent Sample-T test was used to determine the
statistical differences between 6 mm and 8 mm bone
level groups. The difference between eight subgroups was
analyzed using Kruskal Wallis test and multiple comparisons
were performed by Dunn’s tests. Modes of failures were
statistically analyzed using Chi-square test to determine
correlation between bone levels, post types and failure
modes. P<0.05 was considered as significant.
RESULTS
The data were transferred to a personal computer. After
the mechanical loading the mode of failures were recorded.
Dentin fractures were classified as; Dentin (coronal or
apical), post-core and post+dentin fractures as shown in
the Table 1.
Mean fracture values and the fracture types were shown in
table 1. Figure 2 shows the subgroups of treatment type –
fracture data distribution at 6 and 8 mm bone levels.
Mean fracture resistance of fiber-post samples
(1280.07±191.48 N) were significantly higher than metalpost samples (1157.19± 160.26 N) (p= 0.01).
Mean fracture resistance of samples in the 8 mm bone was
1270.2±168.6 N, while it was 1167.0±190.1 N at 6 mm
group. The difference was statistically significant (p= 0.01).
When all the subgroups were evaluated according to fracture
resistance data independent from bone levels “fiber+2 mm
ferrule+8 mm depth” group showed the highest mean
value (1383.40±154.65) while “metal+0 mm ferrule+6 mm
depth” group did the lowest (1096.21±167.41).
Fracture values at “2 mm ferrule group” of fiber-post
samples were 5-9% higher than “0 mm ferrule group” and
2-5% higher in “2 mm ferrule group” of metal than “0 mm”
in 6 mm bone level. Data was same for both groups (3-5%)
in 8 mm bone level.
The most resistant group in 6 mm bone was “fiber post+2
mm ferrul+8 mm depth” (1338.3±220.9) while the “metal
post+2 mm ferrul+6 mm depth” was the least (1026±113.2).
The difference between them was statistically significant
(p= 0.012).
Statistically significant difference in 8 mm bone level was
also obtained between the highest mean fracture value
at “fiber post+2 mm ferrul+8 mm depth” (1471.4±134.3)
group and the lowest mean value at “metal post+0 mm
ferrul+6 mm depth” (1156.6±152.2) group (p= 0.03).
Mean fracture resistance of samples with 8 mm post length
regardless from bone level and post type was significantly
higher than (1278.75±189 N) 6 mm posts (1158.75±177.2
N) (p= 0.02). The samples with 8 mm post length in 8 mm
bone exhibited the most resistant fracture data.
Effect of ferrule to fracture resistance was significantly
higher at “2 mm” compared with “0 mm” height (p= 0.03),
there was no statistically significant difference between
the mean fracture data of “0 mm” (1134.78±141.1 N) and
“2 mm” (1179.6±139.5 N) ferrule samples in metal post
groups. On the other hand the difference was statistically
significant in fiber post groups (1326.4±175.2 N at “0 mm”,
1233.75±166.7 N at “2 mm”) (p= 0.02).
Chi-square test revealed that coronal post fracture incidence at
metal groups was higher than fiber groups; the difference was
not significant. Post fractures without dentin were observed to
91
CLINICAL DENTISTRY AND RESEARCH
Figure 2. Sub-groups of treatment type – fracture data distribution
be higher at fiber groups even at 6 or 8 mm bone levels. There
was no correlation between fracture types and post types at
both 6 mm and 8 mm bone levels. There was no correlation
between fracture types and bone levels.
DISCUSSION
This in-vitro study revealed that fiber posts fracture
resistance with proper length may be improved with
adhesive contribution. Mean fracture resistance of fiber
groups were significantly higher than metal groups. This
data may be due to modulus of elasticity of fiber-posts
which is closer to the dentin.17 Fiber posts with adhesive
interaction may be improving the fracture resistance by
distributing the applied forces to its components owing to
its material specialties.
New fiber post materials other than metal ones was first
introduced to dental practice at the end of the 20Th century.18
According to mechanical tests it was observed that these
materials were showing similar physical properties to dentin
especially about elasticity.19 This phenomenon reminded
researchers to use fibers in post-core restorations instead of
metal which was unsuccessful about absorbing the forces
causing dentinal or apical fractures. However fiber posts
were more favored by distributing the stress between post
and the dentin. It is widely accepted that cast metal posts,
without distortion in its composition, transfer the occlusal
forces directly to dentin which is not sufficiently tough to
resist.20 On the other hand many researches claim that the
design of the post is another reason for apical fractures
that tapered posts transfer the occlusal forces to the apical
portion.21-23 Therefore they offer posts with double tapered
92
mold which hinders apical fractures. However we used
tapered shaped posts in our study which may have proned
to higher apical fracture data.
Investigators claim that irreparable root fractures occurred
at groups with metal posts and reparable fractures with
fiber posts.24 However such fractures were observed both
at metal and fiber post groups in our study. Additionally,
conversely to common; apical fracture incidences of metal
posts were lower than fiber posts. This may be due to
the thickness of metal posts that were fabricated with
the dimensions similar to fiber posts for standardization
protocol. Such dimension of metal posts which is less than
1-1.5 mm may have resulted an unexpected elastic behavior.
It is known that there is no specified post length about postcore restorations. However there may be a lot to commend
over this situation. In this study the post lengths were at least
longer than half of the root. Most of them were almost 2/3 of
the root. Evaluating the fracture data in this study, it can be
observed that the values were all higher than 1000 N which is
over masticatory forces. Therefore it can be assumed that the
samples were conformable about this type of rehabilitation.
Franco et al.25 concluded that the post length was not an
effective determinant on apical fractures. Conversely in our
study we observed that the incidence of apical fracture (closer
to cement-enamel junction) at shorter samples were higher
than longer samples. The data was only 2 for 8-mm while it
was 6 for 6-mm groups. Therefore if the apical fractures are
accepted as irreparable, in this study such affair occurred
more at 6 mm post length samples of all subgroups. On the
other hand fracture data increased as the surface area of the
adhesive increase, this may be another indicator of the integrity
FRACTURE RESISTANCE OF METAL AND FIBER POSTS
of post material with root dentin by adhesive contribution
regardless from the post material. A self-adhesive cement was
used for the experiments, however, self-adhesive systems may
be less effective while etching the dentin covered with thick
smear layer formed during drilling, than etch and rinse systems
which dissolves the smear layer using strong phosphoric acids.
According to the micromorphological investigations etching
the dentin before bonding stage improves the adhesive quality
by dissolving the smear layer completely and reaching into the
dentinal tubules26, 27 therefore fracture data may change with
the adhesive system alterations. On the other hand dual-cured
resin cements which were especially developed for intracanal
luting provide benefits of both the self and light-cured
materials. Despite the polymerization advantage without
light, they may be more prone to fracture because of their
ingredients to introduce flowability which is needed especially
while using at post cementation.
Increasing the ferrule height from “0” to “2” mm in 6 mm bone
level groups, fracture values of fiber posts were increased
5-10% while the increase was 2-5% at metal pots. This may
be attributed to the surface area increase which cement
material may adhere forming an entire structure with the
fiber post as mentioned before. On the other hand in 8
mm bone level the ratio was the same for both fiber and
metal post samples. Therefore within the limitations of this
study it may be concluded that increasing the post length
regardless from the material and independent from apical
seal will contribute to fracture resistance in vitro.
Higher fracture values were observed at longer post
materials in 8 mm bone levels. At higher bone levels it may
be assumed that the apical fractures may be avoided by
proper treatment protocol, however in our study other than
expected, according to statistical analysis there were no
correlation between fracture types and bone levels.
Fractures which occurred occlusal from ferrule were
accepted as post type fractures and within the limitations
of this study this type of fractures were widely observed
during the mechanical tests. One of the reasons might
be the result of the composite material which was not
supported with dentin. It may be a definitive factor whether
the post material was supported with dentinal structure
or not. The post material may have been forced to rotate
around a lever-effect like point that is formed as a result
of junction of different structures (dentin and composite
material) which have different elastic properties. On the
other hand there were no correlation between post types
and bone levels according to statistical correlation.
It can be observed in this study that as the post length
increased regardless from sub determinants the resistance
increased. However it should be hardly reminded that apical
leakage is also one of the restorative failures that must be
eliminated. It is accepted that at least 4 to 6 mm apical seal is
needed for a proper infrastructure.28 Therefore to restrict the
length of the post material may become an obligation. In such
situation the integration of post material and the dentin come
into prominence to overcome this possible adversity.
In our study we did not evaluate the residual wall thickness of
the dentin. Scotti et al.29 concluded that the wall thickness is
ineligible parameter at fracture resistance of endodontically
treated teeth and it should be more than 2 mm. However in our
study the wall thickness of the samples was approximately 1.5 to
2 mm. Therefore unexpected fracture may have occurred during
mechanical tests that this estate may have altered the obtained
fracture data. Another determinant that was not evaluated is
periodontium; a specialized soft tissue that supports the teeth
in the alveolar bone and acts as a suspension mechanism which
compensates much of the centric and eccentric occlusal forces.
Within the limitations of this study because of absence of the
periodontium almost all the applied force was transferred to
samples dependent to the structures of materials used. Therefore
it should not be omitted that the data of this in vitro study may
differ with the clinical outcomes.
CONCLUSION
Within the limitations of this study it can be concluded that
the fracture occurrence is independent from bone levels
and post length. To obtain the most resistant restoration
ferrule establish is doubtless. Increasing the post length
with apical care would contribute to the success.
ANCKNOWLEDGEMENT
We, the authors, would like to thank to Associate Prof. Dr.
Özgür Uyanık from Hacettepe University Department of
Endonontics, for his technical support.
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