F05.
Identify the problems that a clinician may encounter when he or she uses a resin
to restore lesions in which the margins are all or partially on the root
surface.
A
few years ago, enamel bonding worked well, while dentin bonding was a major
problem. With modern materials, though, it is now possible to produce quite
reliable bonds to dentin, particularly on young dentin with exposed dentinal
tubules. However, it is still somewhat unpredictable when we try to bond to
sclerotic dentin.
Restoring
a tooth with margins on the root surface can often be associated with the
presence of sclerotic dentin. Root surface lesions are more frequently seen on
elderly patients than younger, and abfraction and/or toothbrushing often cause
these lesions. In addition, it may also be difficult to keep the cervical margin
free from saliva contamination during placement of the restoration.
When
a cervical restoration is placed in the above example, it is rather easy to bond
to the incisally located enamel, while the dentin bond formation, particularly
in the cervical region, is much more unpredictable. As a result, the material
often separates from the cervical margin when the composite is cured. Therefore,
to secure retention, small cervical retention grooves can be used, combined with
a rather broad incisal enamel bevel. Incremental build-up is also recommended to
reduce shrinkage. As soon as the restoration has been finished and polished, the
surface and surrounding margins are lightly etched (5 s) rinsed and coated with
a so-called single-bottle dentin bonding agent. By coating the margins with such
a material, capillarity forces will pull the resin into any potential gap formed
during curing and polishing.
(Courtesy
of J. Perdigao)
The
above picture shows a debonded margin. Because of polymerization shrinkage, the
composite has debonded from the margin.
