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

Posterior teeth
The restoration of root-filled posterior teeth is complicated by the
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axial stress placed on any restoration distal to the canines. The prepa-
ration of the access cavity and removal of the roof of the pulp 
chamber acts to increase the stresses at the base of the cusps during
function and predisposes these cusps to fracture. In addition, in most
root-filled posterior teeth, removal of caries and defective restorations
will have resulted in disruption of the marginal ridge, which further
weakens the tooth. The overall result of this is that the compromised
cuspal tissue cannot withstand the ‘wedging’ forces developed during
function and is liable to fracture
13
.
When restoring endodontically treated posterior teeth, considera-
tion needs to be given to the high risk of cuspal fracture. Although
some protection may be given to weakened cusps by placing a
bonded restoration
14
, in any tooth in which the existing restoration
and access cavity combined involves more than the occlusal sur-
face, some form of cuspal protection is required. As discussed in
Chapter 5, although cuspal coverage may be provided with a direct
restoration, practically this need is best served by provision of an 
indirect restoration that overlays the cusps at risk of fracture. Thus
most endodontically treated posterior teeth require restoration with a
suitable core followed by provision of an indirect restoration such as 
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Chapter 4
Fig. 4.2
Direct restoration of (a) posterior and (b) anterior root filled teeth (Am 
=
amalgam, GP 
= gutta-percha, Co = composite, RmGIC = resin-modified glass-ionomer
cement).
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a crown or cuspal coverage inlay.
The choice of core restoration depends primarily on the amount of
coronal dentine available to assist in retention of the core, or, more
exactly, an assessment of the quantity of sound coronal dentine that
will remain following subsequent preparation for the indirect restora-
tion. It is of interest that the amount of residual coronal dentine is
often overestimated in the clinical setting
15
.
Teeth requiring endodontic treatment have typically lost tooth
structure (due to previous restorations and/or current caries): further
loss of coronal dentine is necessary for endodontic access. As a result,
there is often a lack of coronal dentine in which to prepare retentive
features without compromising the strength of the remaining tooth
structure. Nayyar and his co-workers described a technique whereby
2–3 mm of the coronal root filling is removed and an amalgam core
placed to fill not only the coronal preparation, but also to fill the 
pulp chamber and extend into the roots
16
. Utilisation of the radicular 
portion of the tooth in this way provides good retention and resist-
ance without the need to remove any more coronal tooth structure
(Fig. 4.2). In the initial report, a very high success rate was reported.
This technique has been widely adopted and is also suitable for 
premolars as well as molars. Although it is usual to remove root-
filling material from the coronal aspect of the root, in situations in
which there is a large pulp chamber, extension of the amalgam into
this space alone is sufficient. A core of this type will function well even
when as little as one sound cusp remains and careful application 
of this technique can overcome problems related to limited retention
of a direct core, while reducing the need for placement of an intra-
radicular post and associated problems.
The main disadvantage of this technique is the difficulty of
endodontic retreatment and the lack of any ‘sealing’ material between
the root filling and the coronal restoration. The latter problem may be
overcome if the technique is used with resin-modified glass-ionomer
cement (RmGIC) as the core material, though a significant amount 
of coronal dentine must remain, as RmGIC is a weaker material and
less suitable for use as a structural core.
If there is little remaining coronal dentine, then further retention 
for the core will need to be provided by the placement of an intra-
radicular post. If some coronal dentine remains to provide some 
support, then a direct post in conjunction with a corono-radicular
direct core should be placed. If very little coronal dentine remains
then a cast post (indirectly constructed) should be provided. If a cast
post is to be provided and more than one canal needs to be utilised 
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to provide retention, as the canals are likely to be divergent, the core
should be constructed in more than one piece (i.e. two or three,
depending on how many intra-radicular posts are placed). Such a core
is termed a ‘split core’.