A REVISED UNDERSTANDING OF THE CARIES LESION
In recent times the term “Minimal Intervention
Dentistry” has been coined to describe a new approach
to the treatment of early carious lesions.
It is now clearly acknowledged that caries is a bacterial
disease and treatment should therefore revolve primarily
around overcoming the infection.
It will then often be possible to interrupt the process
and actually heal an early lesion prior to cavitation
of the surface of the crown of the tooth.
If this action is too late, or unsuccessful and the
enamel surface is damaged to the degree that it may
continue to retain plaque, then some degree of surgical
intervention will become necessary to restore the smooth
surface once more.
But it is suggested that any surgical intervention should
be as minimally invasive as possible and should provide
only for the removal of completely demineralised infected
tooth structure.
Remaining, partially demineralised enamel and dentine,
should be retained and remineralised wherever possible.
This will lead to extensive preservation of natural
tooth structure and, in turn, will minimise aesthetic
problems and at least slow down the need for replacement
of failed restorations.
| The
pattern of attack of the carious lesion and its
speed of progress through the enamel and dentine
has been understood for many years but has not
been taken into account in designing techniques
for the repair of a lesion.The
purely surgical approach to caries control, as
taught by GV Black, has been the standard of
care but is now recognised as being far too destructive
to be used as the first line of defence. |
Click
images to view fullsize |
 |
figure1 |
It is inefficient because it does not cure the disease
and the major problem is that it leads to a continuing
process of replacement dentistry wherein the cavity
just gets larger, the restoration is subjected to
an
increasingly heavy load and the tooth gets weaker.
It is now recognised that it is quite
possible to heal a lesion on the enamel surface providing it has not progressed. For the enamel surface, providing it has not progressed to surface breakdown and cavitation. As long as the surface is smooth, it can be remineralised through the use of fluoride and/or casein phosphopeptides with amorphous calcium phosphate nanocomplexes (CPP-ACP). The latter will penetrate into the porosities in demineralised enamel and effectively restore the white spot lesion to the full depth of the lesion.
For demineralised dentine, providing there is still some level of mineral attached to the collagen matrix, it is sufficient to isolate the lesion from further bacterial activity with a bioactive restorative material, and it will remineralise to a considerable degree.
This means that the old GV Black principle of “extension for prevention” is no longer valid and natural tooth structure should be preserved and retained as far as possible.
It must be noted that, in permanent teeth, it may take up to four years for demineralisation to penetrate the full thickness
of the proximal enamel and develop surface cavitation,
and a further four years to reach the pulp.
Progress may be far quicker through a
fissure because of the potential for forcing bacteria
laden saliva and plaque down into the fissure under
the stress of mastication.
It is not suggested that the minimal
intervention approach is any easier than the traditional
surgical techniques but it is far more conservative
of tooth structure and offers the possibility of far
greater longevity for the dentition in general.
There is no longer a need to sacrifice natural tooth
structure through the preparation of relatively large
cavities based upon the theory of “extension
for prevention”.
The evidence required for the adoption of this new
philosophy has been accumulating for a number of
years
and the principles have been utilised in enough practices
to suggest that they are sound.
There have been many articles in the scientific literature
over the last 20 years suggesting greater emphasis
on preventive measures and modified cavity designs
and there are now at least four text books (Wilson & McLean
1988,
Mount, Hume 2nd Edition, 2005
, Roulet, Degrange 2000,
Mount 2002
)
covering the subject in some detail.
It is understood that no restorative material can
be regarded as permanent, and that there may, in time,
be further breakdown of either tooth structure or
restoration.
Any restored lesion is at risk of becoming larger,
at least because the remaining tooth structure will
be weakened by cavity preparation.
With each replacement, the cycle is likely to move
faster to the next stage of breakdown and replacement.
Significantly, any alteration to the occlusal anatomy
of a tooth, through placement of a restoration, may
lead to changes in occlusal harmony.
Even a minor change in occlusal anatomy can lead to
the introduction of undue stress on remaining cusp
inclines, to the development of splits at the base
of a cusp, to deflective inclines and to functionally
opening contacts - all of which will speed the decline
of the occlusion and may lead to periodontal problems
as well.
It is logical, therefore, to retain as much of the
original tooth crown as possible in the first place
and deal with a lesion in need of repair in a very
conservative manner.
New Classification
The concept of minimal intervention cavity designs
is not difficult to accept and visualise even in the
presence of the traditional GV Black classification.
After all, the latter is a classification of cavities
wherein the cavity design is specified for each lesion
in the expectation that amalgam will be the primary
material of choice for restoration. It is suggested
that, if minimal intervention is to be adopted as
a philosophy, there is a need for an entirely new
classification that will identify lesions rather than
cavities. It is neither necessary nor desirable to
specify any particular design for the cavity that
may have to be prepared. In the first place it is
best to identify a lesion before it becomes cavitated
so that it can be subjected to treatment by remineralisation
and subsequently kept under observation until healed.
Following loss of surface integrity and cavitation
there will be a need for surgical intervention. The
cavity should then be designed simply to eliminate
surface cavitation and to ensure that the restorative
material will properly seal the margins against any
potential microleakage.
There has always been a problem with the GV Black
classification because it identifies a lesion regardless
of size and prescribes the required cavity design.
Replacement simply extends the cavity outline but
does not define the changes. This problem of the enlarging
cavity is taken into account with the proposed new
approach, to the advantage of both the patient and
the profession.
The following classification was first proposed in
an article in Quintessence International in 1997 and
subsequently enlarged upon in a text book (Mount and
Hume 1998) and then modified in other articles and
a Letter to the Editor (Quint. Int 2000; 31: 375).
It is repeated here so that the subsequent discussion
on possible variations in cavity design will be better
understood.
Below is a diagrammatic representation of the proposed
classification and the following is an explanation
of the number system that is used.
Lesion Site
figure8
|
|
Carious
lesions occur in only three different sites on
the surface of the crown of a tooth. |
Site 1 - the pits and fissures on the occlusal
surface of
posterior teeth and similar defects on otherwise
smooth enamel surfaces.
Site 2 - the contact areas between any pair of
teeth, anteriors
or posteriors.
Site 3 - the cervical areas related to the gingival
tissues
including exposed root surfaces. |
Lesion Size
A neglected lesion will continue to extend as an area
of demineralisation in relation to one of the Sites
noted above.
As it extends so the complexities of restoration will
increase.
The sizes that can be readily identified are as follows:
| Size 0 |
|
The initial lesion at any Site that
can be identified but has not yet resulted
in surface cavitation – it may be possible
to heal it. |
| Size 1 |
The smallest minimal lesion requiring operative
intervention.
The cavity is just beyond healing through remineralisation. |
| Size 2 |
A moderate sized cavity. There is still sufficient
sound tooth structure to maintain the integrity
of the remaining crown and accept the occlusal
load. |
| Size 3 |
The cavity needs to be modified and enlarged
to provide some protection for the remaining crown
from the occlusal load.
There is already a split at the base of a cusp
or, if not protected, a split is likely to develop. |
| Size 4 |
The cavity is now extensive following loss of
a cusp from a posterior tooth or an incisal edge
from an anterior. |
It is acknowledged that it is not possible
to ask the profession to simply abandon the GV Black
system and adopt this proposal over night.
After all, 90% of all restorations placed at present
will be placed using Black’s principles.
If the proposals offered here are adopted then the
proportion of these “over-extended” cavities
will decline over time but it may be many years before
the new system becomes universal.
In the meantime it will be essential to teach both
classifications in parallel.
It is suggested that this should not pose a problem
for either teaching or recording of lesions.
All that will be needed is an understanding of the
principles espoused by both systems and a clear explanation
to students or converts.
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