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

Surface finish
The threaded or screw post has been in use for the longest time
26,27
.
Although increased retention is provided, care must be taken during
insertion to avoid fracture of the root or post. Photoelastic studies
have demonstrated high levels of residual stress with threaded posts
in both loaded and unloaded states, and as such the increased 
retention afforded by use of threaded posts must be weighed against
the potential for creating stress fracture of roots. Some studies 
have shown that posts with larger threads are less passive and such
posts, especially if tapered, are more likely to be involved in root 
fractures
28,29
.
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The provision of serrations or roughening can increase the surface
area of a post. Smooth posts demonstrate the lowest retentive values,
while sandblasting smooth surfaces doubles their retentive value. 
The retentive value of smooth and sandblasted posts can be further
increased by the addition of circumferential grooves, but such features
may weaken the post itself.
Post material
Custom cast metal posts (type III yellow gold, base metal alloys or 
silver–palladium alloys) are the only universal way of achieving 
accurate adaptation to all root canal configurations, but as discussed
above are not as retentive as parallel posts. Prefabricated post systems
may utilise a burnout replica to construct a one-piece cast post and
core or a wrought post onto which a core is cast. A wrought post is
stronger than a cast post for a given diameter. However, wrought
posts with cast-on cores are not consistently more resistant to fracture
30
.
The strength advantage afforded by wrought gold is lost during 
casting; however a complete casting with fewer voids is more likely,
especially with smaller diameters. The use of differing metals in such
a situation offers the potential for corrosion and this may even lead 
to root fracture due to build up of pressure from corrosion products,
especially if the post contains tin
31
. Wrought posts are also generally
more expensive.
Direct intra-radicular posts are designed to be cemented into the
tooth and a core built up intra-orally. Prefabricated wrought metal
posts offer the advantage of superior strength compared with cast
posts, particularly in diameters less than 1.5 mm, and they are also
clinically convenient. As well as wrought gold, direct posts may be
composed of titanium, stainless steel or newer materials such as 
fibre posts (posts with a resin matrix and carbon or quartz fibre) or
ceramic.
A post fabricated from carbon-fibre reinforced epoxy resin became
commercially available in 1992
32
, and several fibre posts are now
available, with quartz fibres being the most common. It is claimed that
the physical properties of such posts are similar to that of dentine,
although it has been suggested that the flexibility of the post in situ
will not match that of the root, even if the elastic modulus is the same,
due to the influence of the cement layer and core
33
. There also remains
disagreement as to whether a stiffer post leads to more even distribu-
tion of stress or whether a post with low stiffness is preferred
34
.
Increased longevity of the restoration is claimed due to the decrease
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in stress concentration
35
, though there is no clinical evidence to sup-
port this statement. There are a number of large studies showing a
reduction in incidence of root fracture when fibre posts are compared
with more rigid posts
36–38
and thus it is wise to consider placement 
of a fibre post to retain a core in situations in which the root is 
at significant risk of fracture (e.g. a short root, short post and thin
radicular dentine). However, there are few well controlled clinical
studies and no reliable randomised controlled trials
39
, though this is
an area of research interest at present and more data may soon be
available.
In response to the need for a post possessing optical properties 
compatible with an all-ceramic crown, an all-ceramic post has been
developed. The post is made from zirconium polycrystals and has a
high flexural strength and fracture toughness. Although designed for
use with a composite core, a technique has been described to combine
the post with a pressed glass core. Due to the brittle nature of these
posts, they are extremely difficult to remove.