Dentin/Adhesive Interface in Teeth - Structural Interfaces and Attachments in Biology - page 131

Fig. 7.1 Radiographic image of primary teeth on right side .( a ) The arrow denotes carious lesion
on the proximal surface of mandibular right first primary molar. ( b ) The arrow denotes the
composite restoration on first primary molar. ( c ) Radiographic image of primary teeth on right
side, 2 years after figure ( b ). The arrow denotes the failed class II composite restoration because of
extensive decay
placed in 8-12-year-old children, the primary reason for failure of both materials
was secondary decay; secondary decay was 3.5 times higher in composite
restorations [ 4 ].
In moderate-to-large class II composite restorations, secondary decay is most
often localized gingivally (Fig. 7.1 ). Secondary decay at the gingival margin is
linked to failure of the bond between the tooth and composite and increased levels
of the cariogenic bacteria, Streptococcus mutans, at the perimeter of these materials
[ 20 , 21 , 41 ]. For clarification, class I restorations involve the biting surface only
while class II restorations involve the biting surface and one or more proximal
surfaces.
As described earlier, the composite is too viscous to bond directly to the tooth
surface. A low viscosity adhesive is used to form a bond between the tooth and
composite. Acid etching leads to effective mechanical bonding at the interface
between enamel and adhesive, but bonding to dentin has been fraught with
challenges and problems.
Clinicians frequently find very little enamel available for bonding at the gingival
margin of class II composite restorations and thus, the bond at the gingival margin
depends on the integrity of the seal formed with dentin. Under clinical conditions,
one can frequently detect a separation between the composite material and the
tooth surface at the gingival margin [ 38 ]. These marginal gaps have been related
to technique-sensitive and unreliable bonding between the adhesive and dentin
[ 38 , 42 ].
At the vulnerable gingival margin, the adhesivemay be the primary barrier between
the prepared tooth and the surrounding environment. A failed adhesive means that
there are gaps between the tooth and composite. Bacterial enzymes, oral fluids, and
bacteria can infiltrate these gaps, and this activity will lead to recurrent decay,
hypersensitivity, pulpal inflammation, and restoration failure [ 2 , 17 , 23 , 40 , 43 ].
The lack of durable dentin adhesives is considered one of the major problems with
the use of composites in direct restorative dentistry [ 44 ].