Biological
aim for root canal treatment is to prevent and/or eliminate apical
periodontitis. This elimination can be achieved by means of chemo-mechanical
debridement of the root canal followed by final obturation. Ideal role for root
canal filling material is to disinfect and seal  the canal apically, laterally and coronally.
Ideally root filling material should be dimensionally stable, easily
insered into root canals,biocompatible, radiopaque, sterile, bactericidal
(or prevent from bacterial growth), easiily removed and must not stain tooth
structure. Filling material for root canal  should strengthen the remaining root structure
as well. (1)

At
present, gutta percha along with sealer is considered as the best remedy for
root canal filling. Sealers are capable of filling the voids between gutta-percha
cones and the gaps between gutta-percha and dentinal canal walls . Sealing of apical
and lateral gaps in the root canal system and adaptation to the dentinal canal
walls are the favourable condition of ideal sealers.  In cases such as, thinning and weakening of root
canal walls may occur due to excessive pressure during root canal cleaning and
shaping, over-instrumentation, removal of intracanal post, previous root canal
treatment, internal root resorption or dehydration due to the application of
irrigating solutions. As a result, resistance of root canals of the tooth to
functional loads may decrease and the roots become more susceptible to fracture.
Therefore, standard principles must be followed during filling the root canals.Root
canal sealers which are capable of bonding to root dentin can increase the
fracture resistance of endodontically treated teeth. (2)

The
fracture susceptibility of endodontically treated teeth are  more common when compare to the vital teeth.
The reasons most often reported are -:

1.      Water
loss upto 11%

2.      Loss
of collagen cross-linking due to mechanical debridement

3.      Excessive
lateral pressure application during obturation

4.      Removal
of radicular tooth structure during cleaning and shaping

The
amount of remaining sound tooth structure and methods of canal preparation
directly helps to the strength of root canal treated tooth. From mechanics of
fracture point of view, the presence of structural defects, cracks, or canal
irregularities play a major role in determining fracture strength , because an
applied stress may be exponentially amplified at the tip of those defects. Influencing
factors for potential fracture susceptibility involves the dentin thickness,
radius of canal curvature as well as3 external root morphology. (3)

The
use of Gutta-percha with root canal sealers for obturating root canals has
remained the standard of care in endodontics, despite their inability to achieve
fluid impervious seal along the dentinal wall of the root canal. Experimentally
Both total-etch and self-etch adhesives techniques are found to reduce apical
as well as coronal leakage as it seals intra-radicular dentin just before the
obturation of root canals with gutta-percha.S till these techniques have
limitation due to  lack of
copolymerization between the methacrylate-based dentin adhesives, the epoxy
resin or zinc oxide eugenol-based root canal sealer, and gutta-percha. (3)

Resin-based
dental materials have been proposed in the dentistry to reinforce an
endodontically treated tooth with the use of adhesive sealers in the root canal
system. However,studies says that till date bonding agents and resins have
problems in working properties, radiopacity and lack of re-treatability when
used for endodontic purposes. In recent years, new endodontic obturation
material Resilon based on polyester chemistry which contains bioactive and
radiopaque fillers has been developed and tested.The performance and handling
of this material are similar to Gutta-percha. In addition, when used in
conjunction with a resin-based sealant or bonding agent it forms a mono-block
within the canals that bonds to the dentinal walls very well and strengthen the
walls against fracture. (3)

The
risk factors for fracture predilection in endodontically treated teeth are -:
(4)

1.
Chemical factors:  include effects of
endodontic irrigants and medicaments on dentine

2.
Microbial factors: include effects of bacteria-dentin interaction

3.
Dentin factors: include effects of tooth structural loss

4.
Restorative factors: include effects of post and core restorations

5.
Age factors: include effects of age changes in dentin

Thus,
it would be advantageous if the root canal obturation could reinforce the tooth
and decrease the incidence of root fractures as well. The type of root canal
sealer using for endodontic therapy may affect root fracture resistance and the
pattern of root fracture. (3)

As
we know conventional root canal sealers do not bond strongly to dentin and
gutta-percha, they do not behave as mechanically homogenous units with the root
dentin. The classical mono-block concept for sealing and reinforcing the root
canal space was rek4ndled with the advent of bondable root filling materials
that are advocated as alternatives to conventional gutta-percha. There is
thought that adhesion and mechanical interlocking between the material and root
canal dentin will strengthen the remaining tooth structure, and thus reduce

fracture
 risk. (4)

 Resilon obturating material
is a synthetic polymer-based material (introduced in 2004) performs similar
qualities to gutta-percha and has the same handling characteristics. Thus, this
material could be considered as replacement for gutta-percha. A tight adhesion
between Resilon cone and resin-based sealer form a ‘mono-block’ and has potential
to strengthen the walls against fracture and decrease the micro-leakage.
Resilon was used to reinforce an endodontically treated tooth through the use
of adhesive sealers in the root canal system. However, for a dental material to
reinforce the tooth, the material should bond to dentin very well. So, an
essential attribution for a good dentin adhesive system is the adhesive’s ability
to wet and infiltrate dentin. (4)

In
current years, root canal  obturation
material which is based on polyester chemistry and containing  radiopaque and bioactive fillers has been
developed as well as tested. Resilon performs 
as  gutta-percha. When resilon used
in conjunction with  resin-based sealant
and bonding agent, it forms a mono-block within  root canals that bonds to wall of dentin.
Because of  resin core, sealant and
dentin-  wall all are  ‘attached’ , therefore  they have potential to strengthen dentinal
walls against  tooth fracture. (5)

Resilon
is supplied in the same ISO sizes and shapes (in cones and/ or pellets) as gutta-percha.
According to manufacturer, this may be used with any other obturation technique
(eg. lateral compaction, thermo-plasticized, in carrier or  injectable). In cone form, the flexibility of
this material is similar to  gutta-percha.
Based on polyester polymers, Resilon contains bioactive glass with radiopaque
fillers (barium sulphate and bismuth oxy-chloride ) with approx. 65% of filler
content. This can be softened in presence of heat and also dissolved with many solvents
such as chloroform. This property allows the use of  retreatment techniques non-healing  cases. Due to it is a resin-based system,
resilon is compatible with current restorative techniques in which posts and
cores are placed with resin bonding agents. (6)

 Hence, the aim of this study is Comparative
Evaluation of Fracture Resistance of Root Obturated with Resilon and
Gutta-Percha Using Two Different Techniques: An in Vitro Study.