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

Rotary gingival curettage
Rotary gingival curettage is the term used to describe the simultane-
ous preparation of the tooth and removal of the inner part of the sulcal
epithelium. There is little or no tactile feedback during this procedure,
which is obviously traumatic to the gingivae and therefore leads to
apical relocation of marginal tissues. In addition the frank haemor-
rhage that occurs with this technique requires control in order to take
an impression, which can usually only be achieved with a material
that is hydrophilic, such as reversible hydrocolloid. Visualisation of
the preparation margin is also difficult and uncertain. This technique
should not be used routinely and is largely historical.
METHODS OF CONSTRUCTION
There are a number of ways in which indirect restorations, constructed
extra-orally, may be made. The most common methods utilise an 
indirect pattern, though computer-aided design and computer-aided
machining techniques (CAD/CAM) may be employed, as may a
direct pattern.
Indirect pattern
Once a preparation has been completed, an impression is taken to
record fine detail. An impression of the opposing arch is also taken.
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Chapter 6
The impression is disinfected and sent to the dental laboratory where
a gypsum-based plaster is poured into the impression to make a
model. The restoration is either made directly on a model of the tooth
formed from phosphate-bonded gypsum (termed a refractory die) 
for resin composite or ceramic, or is made on a model formed from
die-stone (Type IV) for metal restorations (by investing and casting a
wax pattern). Due to the number of separate steps involved in this
process and the potential for inaccuracies at several stages (e.g. distor-
tion of the impression, expansion of gypsum products) it is technique
sensitive. However, this method of construction is well established
and each stage well understood, and as the pattern for the restoration
and/or restoration itself is made in controlled conditions, a high level
of accuracy can be achieved.
Direct pattern
An alternative to forming a pattern in the laboratory from a replica of
the preparation is to form a pattern directly intra-orally from the tooth
itself. This is usually only appropriate for metal restorations, when 
a pattern is made either in casting wax or acrylic. This method has
obvious advantages in that as fewer stages are involved compared
with an indirect pattern, then the potential for errors is small and
accuracy of fit is high. However, the pattern should be invested as
soon as possible after it has been formed to avoid distortion. This
method is technically demanding to perform, especially if occlusal
surfaces are involved and is therefore only suitable for small restora-
tions. It is particularly suited for creating patterns for post-retained
cores.