The choice between provision of an intra-coronal or extra-coronal
restoration is usually straightforward. When an indirect restoration is
indicated owing to problems in achieving a functional result with
direct materials or when a stronger material than those available
for direct restoration is needed, then an intra-coronal restoration is
an obvious choice. However, this presupposes that the axial walls of
the tooth are intact and are not prone to fracture. If the axial walls of
a tooth are substantially broken down and in need of restoration, then
an extra-coronal restoration would be better suited.
There are, however, situations in which the decision is less straightforward,
for example large preparations that span from one proximal
area to another, leaving thin and tall unsupported cusps. Placement
of an intra-coronal restoration would result in wedging forces and
predispose the remaining cusps to fracture. Although a bonded
restoration could be placed in the hope that the bond would protect
the cusps, this is not as reliable as providing cuspal coverage, i.e. a
reinforcing extra-coronal element to the restoration. This may simply
be done by placing an inlay that also overlays the occlusal surface
and a little of the axial surface (Fig. 5.2). However, as the size of such
restorations increases, the difficulty also increases and placement
of restorations with both intra-coronal and extra-coronal elements
becomes more problematic – excess expansion of the investment
during casting affects the fit of intra-coronal elements and conversely
too little expansion of investment or shrinkage of resin composite/
ceramic will affect the fit of extra-coronal elements. In many cases
provision of an extra-coronal restoration is more reliable, particularly
if the preparation is complex.
