Class III cavity
Location:
Proximal surfaces of incisors and canines without weakened or lost incisal edge
Material:
Composite
Glass ionomer (rather exceptionally, only if the cavity edges are not in the enamel, it is impossible to
keep the working field dry – e.g. in handicapped patients)
Gaining access to the carious lesion:
Ball diamond or ball bur. We penetrate the carious lesion from the oral side, and guide the
preparatory instrument obliquely from the adjacent tooth in order to minimize loss of tissues. We
can keep enamel unsupported by dentin vestibulary.
Fig. 1: A carious lesion and the direction of the preparatory instrument
Fig. 2: Initiation of the preparation
Fig. 3 a, b: Prepared cavity
We bevel the enamel at the outlines of the cavity by means of a diamond flame or pointed bur with
fine grit – red code. We create a retentive border ca 1 mm wide.
Fig. 4: Retentive border
MAKING OF THE FILLING
We work with a matrix – a transparent polyester band which is sealed by a wedge.
Fig. 5: Matrix (a transparent band sealed by a wedge)
The principle of retention of composite filling is a micromechanical bond (microretention) during
which the composite material gets into microscopic spaces in enamel and dentin that have been
prepared by ortophosphoric acid etching (35-37%). After securing a dry field, we apply the etching
gel with content of acid – 20 s on enamel, 10 s on dentin. Then we wash the gel away and dry any
excessive water. The next step is application of primer – it mediates the bond between composite
and dentin. After its application and blowing, we apply the bond (it is identical with the organic
compound of the composite, but it does not contain any filler). It flows into the microscopic
unevennesses of enamel, dentin tubules and the colagen fibres of demineralized dentin. We blow it
into a thin layer and polymer it by curing – with the light of polymerisation lamp. Then the composite
is deposited in layers of ca 1 mm thick and their polymerisation follows. We begin from the oral side,
the matrix can be pressed by a finger to the oral part of the tooth during application of the first layer.
Both primer and bond are applied with special brushes.
Fig. 6 a: The primer wets dentin and prevents the collapse of collagen fibres
Fig. 6 b: The bond flows into the microscopic unevennesses and copolymerises with the composite
In the end, we treat the filling by very fine diamond burs (yellow code) and polish it with rubber tools
and polishing discs. The transition between the filling and the tooth must be smooth. There are more
concepts for composite polishing. Besides rubber tools, we can use special brushes, some of which
have abrasive particles incorporated in them, others are used in combination with polishing pastes.
Good tools are also flexible discs.