Operative dentistry aje qualtrough, jd satterthwaite la morrow, pa brunton

Gutta-percha
Gutta-percha has been used for more than 100 years. It is a form of
rubber mixed with zinc oxide and other agents. Although not ideal, 
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Chapter 3
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Principles of endodontics


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its advantages are that it is inert, is dimensionally stable, is non-
allergenic, antibacterial, non-staining, radiopaque, compactable, may
be softened by heat and organic solvents and may be removed from
the canal.
Filling techniques
There are various techniques. These may be divided into:
• Solid gutta-percha techniques
• Softened gutta-percha techniques
Gutta-percha may be softened using either heat or solvents
Solid core techniques
Solid core techniques may utilise a single cone of gutta-percha or may
employ lateral condensation of multiple cones of gutta-percha. For
these methods, a gutta-percha cone is selected to match the size of the
apical preparation, i.e. a master cone of the same size as the master
apical file is chosen. Although a master cone is selected to match the
size of the master apical file, the apical preparation may be larger than
the nominal size due to the filing action of the file. Therefore, the
selected master cone may, in fact, be a loose fit. In order to achieve 
a good friction fit (termed ‘tug-back’), the tapered master cone is
shortened slightly so that it has a slightly larger diameter at its end.
Several trial fits may be necessary to obtain the required tug-back at
the correct length.
In the single cone method, the gutta-percha cone is selected to
match the canal preparation dimension. Although this is a quick 
technique, the main disadvantage is that only canals of circular
dimension may be adequately filled and this rarely represents the true
clinical situation. Should this method be used in non-circular canals,
there will not be a three-dimensional fill.
In the lateral condensation technique (the favoured method for
solid core techniques), a master gutta-percha cone, corresponding 
to the apical preparation dimension, is placed in position, alongside
which are condensed additional accessory gutta-percha points. The
advantage is that the canal may be filled in all dimensions, the final
material being a mass of gutta-percha points joined by a thin layer 
of sealant material. This is, however, a technique-sensitive method, it
can be time consuming and is not appropriate in cases of internal
resorption, for example. It must also be remembered that filling of 
lateral canals by sealant cannot be guaranteed.
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A gutta-percha point of the same size as the master apical file
should wedge slightly at 0.5–1.0 mm short of the full working length
and a ‘dry run’ root filling radiograph is useful to confirm its position.
Measurement of a spreader (a tapered, blank, pointed instrument
used to push the gutta-percha to one side) to 2 mm short of the work-
ing length ensures that apically directed pressure will not result in
overextension of the gutta-percha.
The walls of the canal to 2 mm short of the apex should be 
coated with an even, thin film of sealant and this also facilitates 
placement of the master gutta-percha point by acting as a lubricant.
Controlled placement of the coated master cone allows extrusion 
of excess sealer in a coronal direction before it is seated with firm 
pressure and a twisting action. Insertion of either a hand or finger
spreader to the depth indicated by the stop, alongside the master
cone, pushing it to one side and oscillating and withdrawing the
spreader results in creation of space for the placement of additional
wedging or lateral cones. When excess filling material at the base of
the pulp chamber has been seared off using a hot ‘plastic’ instrument
to the level of the canal orifice, a check root filling radiograph should
be carefully assessed to confirm that the root has been adequately
obturated.