International Dental Journal (2006) 56, 82-91

In the presence of improved methods of identification and treatment of lesions on the exposed surfaces of teeth, it should now be acknowledged that the GV Black “classifica-tion of carious cavities” is out of date. This paper describes a new system, proposed in 1997, discussed broadly throughout the profession, and eventually modified. The system has been adopted in several regions around the world as being a useful corollary to the current developing concept of minimal intervention dentistry. It is now desirable to adopt a new approach to the identification and recording of the lesions caused by both caries and non-carious tooth loss. A major advantage arising from its adoption would be that it would encourage the profession to minimise the amount of normal healthy tooth structure that is often sacrificed in pursuit of the cavity designs as suggested by Black. The authors are members of a Project Group of the FDI Science Committee, and this paper explains the concept and offers justification for the adoption of the system.

© 2006 FDI/World Dental Press0020-6539/06/02082-10

A proposal for a new classification of lesions of exposed tooth surfaces

Key words: Caries, cavity preparation, dental materials, classification

G J Mount Adelaide, AustraliaM J TyasMelbourne, Australia.E S DukeTemple, USAJ J Lasfargues and R Kaleka Paris, FranceW R Hume San Francisco, USA

The foundations for modern operative dentistry were laid down at the beginning of the last century, mainly by GV Black, through his pioneering text, Operative Dentistry which was first published in 19041. Within this text Black set out a ‘cavity classification’ that served as a guide for the surgical removal of caries lesions and restoration of the diseased tooth to full anatomical form. The classifi-cation was based upon the site of caries lesions divided into five separate classes and for each lesion there was a cavity design prescribed. The numerical system em-ployed was based upon the perceived frequency of the occurrence of each of the lesions. Black was aware that different materials would be appropriate for restoration of lesions arising from similar situations. For example, at that time, a cavity prepared for the restoration of an

approximal lesion on an anterior tooth would be re-stored with silicate cement or gold foil whereas a similar lesion on the approximal surface of a posterior tooth would be restored with amalgam or a gold inlay and these choices would lead to variations in cavity design. Thus, the profession learned to use this classification, not only for the caries lesions themselves, but also for the cavities prepared to receive restorations.

Therefore, it has become common usage to identify lesions by their location as well as by the rather rigid cavity designs prescribed for restoration.

Identification of lesions was based upon topogra-phy, and was therefore static, and did not take into ac-count the dynamic nature of the caries lesion. Largely because he advocated “extension for prevention” the

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cavity design for even the initial lesion was relatively extensive. Even the early white spot lesion was likely to be treated surgically and there was no way of recording the increasing size or complexity of a restoration when the lesion extended more deeply into the crown of the tooth. In recent years several authors2-4 have suggested modified classifications designed to identify the stages of progress of a cavity as it enlarges through the enamel and extends deeper into dentine, but it seems none have been universally accepted.

Whilst there was considerable logic displayed in the construction of Black’s system, it was developed at a time when the understanding of caries was in its infancy and surgical removal of the lesion and placement of a restoration was the only possible alternative to extrac-tion. The role of bacteria in the initiation and progress of caries had only recently been suggested5,6, the con-cept of bacterial plaque was in its infancy, the potential effects of the fluoride ion had not been discovered7 and the materials available for restoration were limited to gold, amalgam and silicate cement. Very importantly, radiographs, good illumination and magnification were not available, so it was not possible to identify a caries lesion until it was, by modern standards, reasonably ad-vanced. In spite of these limitations the profession has continued to allow Black’s classification to be the prin-cipal guide within the discipline of operative dentistry, and it remains the only accepted method of recording the presence of caries lesions, a purpose for which it is now ill suited8.

Over the last 50 years there has been considerable progress in the understanding of caries and many changes in restorative materials and techniques. The disease is now known to be bacterial in origin leading to a progressive demineralisation of tooth structure. It is strongly related to changes in lifestyle which affect the oral environment and can be reversed and healed in its early stages9,10. There can be several stages to the treatment of the disease, some of them involving nei-ther surgical removal of tooth structure nor restoration placement. A classification that does not prescribe any specific treatment would be valuable in encouraging change within the profession towards more conserva-tive, and therefore more ethical, treatment of caries than was possible in GV Black’s day.

For many years now it has been possible to identify the changes in lifestyle that lead to modifications to the oral environment that will, in turn, lead to the initiation of the disease, as well as the potential for non-carious tooth loss. However, the profession has continued to use identification of caries lesions as its first line of diagnosis. It is logical to assume that all the ingredients for the disease have been present for some time prior to demineralisation and cavity formation so it is apparent that elimination of the disease should be the profession’s first responsibility. Identification of the earliest sign of cavity formation is then the second responsibility.

However, the profession has denied itself the means of recording such disease status through the continuing use of a classification with limited capacity.

Present concepts of the reversible nature of caries, in its earliest stages, through ion migration both out of and back into enamel and dentine, are fundamental to its proper treatment. It is now well recognised that early lesions can be remineralised, providing surface cavitation has not yet occurred and this applies equally to enamel11 and dentine12. Recognition and elimination of the disease process, in the earliest stages, preferably before surface demineralisation, is therefore desirable for the optimal and ethical provision of care.

Following surface cavitation, lesions will generally re-quire surgical preparation and restoration to recreate the smooth surface of the crown and thus prevent further plaque accumulation. The range of available restorative materials is now greater than it was in Black’s time and some of them adhere well to tooth structure, and there-fore do not allow microleakage13,14. The size of the le-sion will markedly influence material choice. In the early stages of cavitation when the lesion is small, it is only necessary to recreate the smooth surface of the tooth in the immediate area to facilitate proper plaque control. Surgical intervention should be minimal and bioactive adhesive restorative materials utilised to avoid needless sacrifice of sound tooth structure15. At the same time it is recognised that a large part of a day’s work for the average practitioner is ‘replacement dentistry’, wherein older restorations have failed and need to be repaired or replaced. The cavity design has already been defined, at least to some extent, and the selection of the restora-tive material may be limited because of the cavity size. Treatment options vary markedly, dictated largely by the size of the lesion, by the diminishing strength of the remaining tooth structure, or by the need to restore and maintain the occlusal table.

These modifications to both materials and therapy argue strongly against continuing use of the Black classification, because that is generally interpreted as a description of the cavity design required for the treat-ment of a moderately advanced caries lesion. It includes neither the minimal initial lesion that does not yet re-quire surgical intervention, nor the extensively broken-down tooth where complex techniques and materials are needed for long-term restoration. It is time for the introduction of a new system that will record lesions rather than cavities, and specify both site and size. A new system should identify the extent of the caries lesion or the non-caries tooth loss, without defining the cavity design or the selection of the restorative material to be placed. This paper proposes such a classification.

The Classification

The following is a description of a proposed new “Clas-sification of Lesions of the Exposed Tooth Surfaces”16,17.

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It is important to note that this is a classification of lesions rather than of surgically prepared cavities and does not specify, in any way, the cavity design required to deal with any particular situation. It is based upon the positions on the tooth surface that are likely to become carious (Figure 1), and the size or extent to which the lesion has progressed. It recognises the potential growth pattern of a neglected lesion, and extends to recognition of the problems posed when an old restoration requires replacement (Table 1).

Under normal circumstances lesions occur in only three sites on the exposed surface of a tooth, that is, at those sites subject to the accumulation of plaque or erosion and abrasion.

Therefore the first parameter for the classification is identification of the three sites: • Site 1 - pits, fissures and minor defects on exposed

enamel surfaces of all teeth.• Site 2 - approximal enamel surfaces immediately cer-

vical to the contact area between any pair of adjacent teeth.

• Site 3 - the cervical one-third of the crown around the full circumference of any tooth or, following gingival recession, the exposed root surface.For the new lesion that has not previously been

subject to treatment, it is possible to define stages as the lesion progresses2,3. For all lesions, including situations where old restorations are being replaced, it is possible to define five sizes as the lesion progresses in extent and complexity. For Table 1 the term ‘size’ is used but

it is understood that this word will not necessarily be universally acceptable because it may not be easily trans-lated into other languages. The actual terminology used is not as important as the principle that is proposed, so it is accepted that there may be variations in the words used in different languages.

The following identifies the five different sizes that can be clearly defined regardless of the actual terminol-ogy that is used :• Size 0 – the earliest lesion that can be identified,

and represents the initial stage of demineralisation, such as a ‘white spot lesion’ or an early erosion le-sion, where surgical treatment will probably not be required.

• Size 1 - minimal surface cavitation with involvement of dentine, just beyond the possibility of treatment by remineralisation alone.

• Size 2 - moderate loss of tooth structure. Cavita-tion has progressed further than minimal and the remaining tooth structure is sound, well supported by dentine and not likely to fail under normal oc-clusal load.

• Size 3 - the lesion is enlarged beyond moderate. A cusp or incisal corner is sufficiently weakened that some level of protection for remaining tooth struc-ture is required.

• Size 4 - extensive caries, erosion or trauma has lead to bulk loss of tooth structure. A cusp or an incisal edge has already been lost or root structure is in-volved on two or more adjacent surfaces.

Table 1 A diagrammatic representation of the new classification so that the user can visualise the relationship of the Site and Size concept for the description of lesions of the crown of a tooth

Size

No cavity 0 Minimal 1 Moderate 2 Enlarged 3 Extensive 4

Site

Pit/fissure 1 1.0 1.1 1.2 1.3 1.4

Contact area 2 2.0 2.1 2.2 2.3 2.4

Cervical 3 3.0 3.1 3.2 3.3 3.4

Figure 1.

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DiscussionThis proposed classification has now been described and discussed in a number of publications16-22. The appropri-ate management of a lesion depends upon many factors including the state of the oral environment, the health of the salivary flow, efficiency of oral hygiene proce-dures and lifestyle factors for each individual patient. However, the most probable approach to dealing with each Site and Size is discussed in the following examples. They are offered simply to help to explain the concept, without any attempt to show an exhaustive selection of cavity designs or treatment methods. The primary concept of minimal intervention dentistry is based upon elimination of the disease followed by treatment of the lesion, as required, with retention, as far as pos-

sible, of all tooth structure that is not directly involved in the lesion. There have to be exceptions to this, but they should be minimal. One of the most serious short-comings of the Black system is that it was based upon “extension for prevention”, and therefore the crown of the tooth was almost invariably weakened by cavity preparation. With the present knowledge of methods for both control of the disease and remineralisation of tooth structure, this particular basic principle must be abandoned in favour of “prevention of extension”.

Thus it is apparent that a Size 0 lesion will probably not be treated surgically, but most likely will be managed through elimination of the disease followed by reminer-alisation. Identification of a Size 1 lesion suggests opera-tive management using a minimal intervention approach

Table 2 A table showing a direct comparison between the standard GV Black classification and the new classification which is recommended for modern operative dentistry.

New Classification Equivalent Black Classification

Site 1 – Pits, fissures and smooth surfaces Class I – Pits & fissuresSize 0 – fissure seal Not classified

Size 1 – minimal surgery Not classified

Size 2 – equivalent to Black Class 1 Class I

Size 3 – requires protection for maining tooth structure Class I

Size 4 – lost cusp or similar Class I

Site 2 – contact area, all teeth Class II – contact area, posteriorsSize 0 – surface demineralisation Not classified

Size 1 – beyond remineralisation Not classified

Size 2 – moderate involvement Class II

Size 3 – requires protection of remaining tooth structure Class II

Size 4 – bulk loss of tooth structure Class II

Class III – contact area, anteriors

Not classified

Not classified

Class III

Not classified

Class IV – incisal edge lost, anteriorsNot classified

Not classified

Not classified

Class IV

Site 3 – cervical third Class V – cervical thirdSize 0 – surface demineralisation not classified

Size 1 – minimal intervention not classified

Size 2 – more extensive Class V

Size 3 – approximal root surface Class II

Size 4 – two or more surfaces Class V

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with adhesive restorative materials, glass-ionomer being the preferred primary choice because of its potential for bioactivity21. If the occlusal load is considered to be excessive, the lamination technique may be indicated, in which glass-ionomer is overlaid and protected with resin composite22.

For Size 2, 3 and 4 lesions, clinical decisions will be required based upon the location of the lesion, the position of the tooth within the arch and the expected occlusal load.

A surgical approach will invariably be required but the most important factor in restoration is that the le-sion be sealed against further ingress of bacteria or their nutrients. The choice of material will necessarily remain broad, and will include glass-ionomer, resin composite, amalgam, porcelain, gold inlays or crowns, and the cavity design will depend upon this choice. Initially, the cavity outline should be defined by the removal of all tooth structure that is beyond remineralisation, keeping in mind that partially demineralised enamel and dentine can be remineralised, at least to some degree (11,12), and can be efficiently supported by adhesive restorative materials. Subsequent modifications to the cavity design will be dictated by the strength of the remaining tooth structure, the need for protection from occlusal load, and the choice of material. One important requirement of a restoration is that the surface of the crown be made smooth again, thus enhancing the efficiency of oral hy-giene routines and minimising further plaque accumula-tion; partially demineralised enamel surrounding a lesion need not necessarily be removed provided it is smooth and can be remineralised. Also, partially demineralised ‘affected’ dentine on the floor of the cavity can be sealed against further bacterial microleakage23 and therefore retained. The longevity of remaining tooth structure is of paramount importance because enamel and dentine are finite structures, generally aesthetic and not easily replaced. Therefore they need to be retained as far as possible. Logically, longevity of the restorative material is of equal importance to retention of natural tooth structure.

Site 1, Size 0

The lower molar in Figure 2 shows the problem that presents so commonly with posterior teeth. The fissure system is convoluted and complex and it is difficult to determine the extent of dentine involvement. In this example the enamel is stained in part, and using the Black system it would be a Class 1 and the entire fissure system involved in the cavity design. However, if car-ies activity can be eliminated and the patient rendered disease free, it will be classified in the proposed system as a Site 1, Size 0, and kept under observation only. It must be remembered that the occlusal fissure system is under constant load from mastication and bacteria laden plaque is easily forced into the depths and can-

not be removed. Thus if there is any doubt about the level of caries activity, the fissures can be protected by placement of a sealant.

Site 1, Size 1

The two teeth shown in Figure 3 demonstrate the classic quandary when the patient becomes caries active. The first step should always be to evaluate the oral environ-ment for the level of caries risk. On the assumption this is low then it may be sufficient to classify the fissures of the second molar as Size 0 and place a sealant or maintain observation only. On the other hand, there is some degree of cavitation in the distal fissure on the first molar and, even though it may not show radiographi-cally, the case may be regarded as a Size 1 lesion and limited surgical treatment may be required. Neither the cavity design nor the restorative material to be used are specified, but logically the material will be adhesive and the remaining fissures will be sealed at the same time as restoring any prepared cavity.

Site 1, Size 2

The lesion in the first molar (Figure 4) was initially thought to be Site 1, Size 1. Thus, entry was very con-servative, but it became apparent that the lesion had progressed for some distance through the lingual fissure and the cavity had to be enlarged to gain full access. The record should therefore be modified to Site 1, Size 2.

Site 1, Size 3

The lesion that is classified as a Site 1, Size 3 (Figures 5 and 6) will be moderately extensive when first identified. It may arise from the need to replace a failed restoration with faulty margins or secondary caries but, in this case, it was an advanced new lesion. It was initially classified as Site 1, Size 2. However, following surgical explora-tion it was apparent that the disto-buccal cusp required support and protection from occlusal stress and thus it was finally classified Size 3.

Site 1, Size 4

As with the previous classification, the lesions in this category are generally the result of serious neglect or else they arise through the need to replace a failed res-toration. This case (Figures 7 and 8) presented as a new lesion and it was apparent from the initial examination that the distal cusps were so weakened that they would require replacement. As much tooth structure as pos-sible was retained but the complete disto-lingual cusp was reduced sufficiently to allow a full rebuild with the restorative material.

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Figure 2.

Figure 3. Figure 4.

Figure 5. Figure 6.

Figure 7. Figure 8.

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Site 2, Size 0

Lesions within this classification occur in relation to the contact areas between adjacent teeth, both anteriors and posteriors, and are generally not under occlusal load. They may therefore be well advanced into dentine be-fore there is surface cavitation (Figure 9). The greatest risk to these lesions is posed by examination for their presence with a sharp probe, because this is likely to damage the demineralised surface and create a cavity. They can be identified by either radiographs or transil-lumination, but the first step should be to investigate the level of caries risk within the oral environment. All possible measures should be undertaken to eliminate the disease prior to instituting surgical procedures. Up to the point where surface cavitation has occurred, it is possible for the lesion to remineralise and heal, so the use of a surgical approach should be at least delayed while preventive and remineralising measures are under-taken. It has been shown that, depending upon the level of caries risk, progress may be rather slow and it may take up to 3-4 years for the lesion to progress through the full depth of the enamel24. This suggests that con-trol of the bacterial population with chlorhexidine and applications of fluoride in conjunction with casein phosphopeptide and amorphous calcium phosphate may well control the lesion and remineralise it25. Careful steps should be taken to try to evaluate surface integrity before deciding on the classification. It may be possible to gain sufficient separation between the teeth to obtain a limited elastomer impression of the approximating surfaces26. If cavitation has developed, it is no longer possible to completely control plaque accumulation and the classification will be Size 1 and surgical measures will generally be required.

Site 2, Size 1

Figure 10 shows a typical Site 2, Size 1 lesion, and some limited form of surgical intervention is required to restore the smooth surface of the tooth and facilitate plaque control. The design of the surgical approach will be dictated by the position and extent of the lesion on the approximal surface, and the strength of the remain-ing marginal ridge, at the time of diagnosis. The most important aspect in cavity design will be to retain as much of the original tooth structure as possible. There are no fixed rules or designs and the choice of material remains optional.

Several minimal intervention approaches, designed to retain maximum amounts of tooth structure, have been tested such as internal tunnel and slot preparations, or an approximal approach, and each of these will have their indications and contraindications18. These preparations can be applied to both anterior and posterior lesions and only the operator will be in a position to decide on the most appropriate.

Site 2, Size 2

This may be a new lesion but in many cases it will be a replacement following failure of a previous Black designed restoration. The case demonstrated in Figures 11 and 12 was an extensive amalgam restoration that had failed around the margin, probably the result of poor placement of the material. The cavity has been cleaned and extended conservatively with the inten-tion of restoring it again with amalgam. Note that the demineralised ‘affected’ dentine remains on the axial wall and this will be covered with a glass-ionomer lin-ing with the expectation that it will remineralise27. The remaining crown of the tooth appears to be substantial and based on sound dentine and therefore capable of accepting occlusal load and there is no need to protect any of the remaining cusps.

Site 2, Size 3

Figures 13 and 14 show an old amalgam in an extracted tooth. The provisional classification was Site 2, Size 2. However, having removed the old restoration and defined the extent of the underlying lesion, it became apparent that the remaining cusps on both the buccal and the lingual aspects could not withstand further oc-clusal load and required protection. The classification should therefore be Site 2, Size 3.

In the finished cavity design both buccal and lin-gual cusps have been bevelled out to allow substantial coverage and protection28. The final step of providing retention with slots at the buccal and lingual walls of the approximal box is being undertaken with a small tapered steel bur. The choice of material for a restoration as extensive as this remains in the hands of the operator.

Site 2, Size 4

It is apparent in this case (Figure 15) that a relatively small traditional Black Class II amalgam, involving the occlusal and distal surfaces only, has weakened the buc-cal cusp of the first bicuspid sufficiently to lead to its complete loss. This is a typical Site 2, Size 4 classification and it is apparent that the only really satisfactory long term restoration will be placement of a full crown.

Site 3, Size 0 or 1

The Site 3 lesion may present the operator with a number of options. The Size 0 lesion will often be a relatively simple non-carious loss of enamel or dentine and will not require restoration or protection. Alter-natively, there may be early signs of demineralisation (Figure 16). Providing the disease has been controlled, it may be sufficient to polish the demineralised area and prevent progression by periodic applications of fluoride or other materials for remineralisation25.

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Mount et al.: A proposal for a new classification of lesions of exposed tooth surfaces

Figure 9. Figure 10.

Figure 11. Figure 12.

Figure 13. Figure 14.

Figure 15. Figure 16.

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The Site 3, Size 1 lesion on the first bicuspid is fur-ther demineralised and lacks aesthetics, and this would imply removal of at least some of the softened dentine from around the margin so that adhesion to sound dentine can be achieved. There will also be decisions to be made concerning the lesion on the second bicuspid (Figure 16). It appears to be free of demineralisation but it may be hypersensitive or it may be regarded as unaesthetic. On the other hand, in the absence of active disease, there may be no need for a restoration.

Site 3, Size 2

Often the Site 3, Size 2 lesion will be the result of res-toration breakdown or secondary caries. In Figure 17 there are two traditional Black Class V resin composite restorations in the upper central and lateral incisors. These have apparently been added to and repaired at least once and are showing further signs of failure, so replacement is required.

These lesions may also be new active caries, and if so they usually represent a high level of caries activity. Treatment should commence with strenuous efforts to overcome the disease first, possibly including placement of transitional restorations, before attempting a defini-tive restoration.

Site 3, Size 3

The usual Site 3, Size 3 lesion (Figure 18) will be an approximal root surface lesion on either anterior or posterior teeth because of the additional complexity of restoration placement. Root surface caries always arises under conditions of high caries activity and the disease should be treated first, because it may be pos-sible to remineralise the dentine and avoid surgical intervention.

Generally, the area of demineralisation will be confined to the dentine surface. The lesion is not im-mediately apical to the contact area otherwise it would be classified as a Site 2 lesion and probably approached from the occlusal surface.

Site 3, Size 4

This is a complex lesion (Figure 19) similar to the Size 3 category. However, two or more adjacent surfaces of the tooth are now involved, hence the Size 4 classifica-tion in recognition of the additional complexity. In this case there is an old restoration on the lingual surface that shows signs of failure, as well as a temporary restoration on the approximal surface. There is also a failing resin composite restoration at the buccal gingival margin and all three lesions may well be treated with a single restoration.

Figure 17.

Figure 18. Figure 19.

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Mount et al.: A proposal for a new classification of lesions of exposed tooth surfaces

ConclusionIt is suggested that the clinical application of the proposed classification should be regarded as simple, straightforward and logical. It consists of a simple nu-merical system for recognition of caries lesions from the smallest initial lesion to the most advanced and complex. It fits well with modern methods of compu-terised record keeping and should be readily understood by auxiliary personnel. A change over period will be es-sential and it is suggested that it should be recognised in parallel with the Black system during this period. Even if Black style cavity designs were abandoned im-mediately, it will be many years before the last of these is seen clinically.

Currently the major problems with the Black system are that it is not designed to recognise the initial lesion

prior to cavitation, and it is not possible to identify the increasing complexity of restoration of the exposed tooth surface as the lesion progresses in size. In addi-tion it implies, at a minimum, a relatively extensive cav-ity preparation, designed for non-adhesive restorative materials and embodying the principles of “extension for prevention”. Both the profession and our patients require a new approach designed specifically to preserve natural tooth structure.

Note

The views expressed in this paper are those of the au-thors and do not reflect the opinions of the US Veterans Administration or any other government agency in the USA or elsewhere.

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Correspondence to: Dr G J Mount, 13 MacKinnon Parade, North Adelaide, South Australia 5006. Email: gjmount@ozemail.com.au