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

INTRA/EXTRA-CORONAL RESTORATION
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 straight-
forward, 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.
PARTIAL-COVERAGE RESTORATIONS
Advantages of partial-coverage restorations include:
• Preservation of tooth structure due to part of the clinical crown not
being reduced, though the requirement for additional features for
POOC06 02/18/2005 04:36PM Page 133

---

134


Chapter 6
retention/resistance (described on p. 145) may demand more
removal. However, this is likely to be at the expense of the core
rather than healthy tooth structure.
• Natural landmarks more likely to be preserved and this may 
aid preparation and also aid laboratory construction (easier to 
visualise the emergence profile).
• Margins are more likely to be supragingival and hence it will be
easier to obtain an impression and to finish/polish margins as well
as perform maintenance.
• Better seating on cementation as the axial walls are not covered to
such an extent, thus expression of excess cement is easier than with
full-coverage restorations.
• Access for pulp testing is maintained.
• Maintained vitality more likely.
Disadvantages of partial-coverage restorations include:
• Limited retention and resistance form.
• Aesthetic limitations.
• Technically demanding.