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

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Chapter 2
Fig. 2.5
Typical position of a dentine pin.
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locked and self-threading) have been used to retain dental restora-
tions. Although cemented and friction-locked pins have certain
advantages, all but a few of the pins presently used in clinical practice
are of the self-threading type. These are relatively simple to use 
and are the most retentive. A wide variety of self-threading pins are
available, a typical dentine pin system comprises a twist drill with a
matching pin, which is usually threaded and self-tapping (i.e. cuts its
own thread on insertion). It is usual that both drill and pin have a latch
grip enabling them to be used in a conventional handpiece. Some pins
consist of a simple length of threaded pin, while others have features
such as a shoulder stop (to control depth of insertion) and altered
shapes for more mechanical retention of the restorative material.
Although the use of dentine pins has an advantage over prepara-
tion features in that less removal of sound tooth structure is required,
it has long been recognised that their use also has considerable 
problems. The stress produced within the dentine during placement
of a dentine pin causes cracking and subsequent weakening. Errors
during placement are not uncommon and may result in perforations
into the pulpal space or the periodontal ligament with subsequent
problems. An additional problem may occur due to the mismatch of
the modulus of elasticity of the pin and the restorative material. This,
combined with the lack of homogeneity of the restorative material
due to pin placement, may cause localised stress concentrations dur-
ing load and a subsequent predisposition to failure (i.e. pins weaken
rather than reinforce or strengthen restorations). This can be a prob-
lem with amalgam and more so with polymeric restorative materials
where such a mismatch will be even larger. Obviously, the more pins
that are placed, the greater the risks.
Given the routine use of bonding agents with polymeric restorative
materials, the additional use of dentine pins with these materials 
is questionable as the disadvantages would seem to outweigh any
advantages. In addition if an adhesively retained restoration is supple-
mented with dentine pin placement, catastrophic bond failure may go
unnoticed and rapidly progressing caries is then a risk.
There is a lack of clinical data on survival of large amalgam restora-
tions placed with or without pin retention
32,33
. There are however,
some studies that suggest that large amalgam restorations placed
without the use of dentine pins, but using preparation features as
described above have equal strength, resistance and longevity to those
restorations placed with pin retention. It is becoming apparent that
supplementary retention/resistance is probably not as essential as
was once thought, and when necessary can be achieved without the
Principles of direct intervention


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use of dentine pins and their potential problems. For very large
restorations, the placement of a dentine pin can aid in stabilising the
amalgam during removal of the matrix band and during finishing. In
this way dentine pins may be useful for a particularly large amalgam
restoration that is otherwise retained by preparation features as
described above.