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.
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