G. V. Black's Classifications of Tooth Decay

To standardize the classification of cavities between dentists, a gentleman by the name of Greene Vardiman Black devised a system to identify caries in 1869. G.V. Blacks nomenclature is based mainly on the location of caries. Black also published a series of papers that discuss how dental caries should be treated given the type of cavity present.[2]

Six Caries Classifications[1]

1. Class I Caries - These types of caries are found on the occlusal (biting) surfaces of the posterior (back) teeth. Occlusal surfaces have pits and fissures thus this type of caries is also known as pit-and-fissure caries. Pit-and-fissures as the name implies, are irregular surfaces of the teeth that resulted from imperfect coalescence of enamel during the development of the tooth crown. The bristles of toothbrushes often cannot effectively reach the bottom part of pits-and-fissures. As such, plaque builds up and will damage the tooth to create a Class I cavity. 

• Detecting Class I caries is sometimes a bit tricky. A "catch" after the dental explorer is passed on the occlusal surfaces, is an indication of a class I caries. However, deep fissures that do not have caries can also give the dentist the feel that there is a "catch" in the explorer. That's why it takes good tactile sense and ocular inspection to make a very accurate diagnosis. 

2. Class II Caries - These are cavities that involve the occlusal surfaces and the proximal area (the area that is in contact with another tooth) of an affected tooth. With this type of caries, more than one surface of the tooth is affected.

• Class II caries are also detected the same way as Class I caries although it is a bit challenging to pass the explorer on proximal areas. Bitewing radiographs are very helpful diagnostic aids. They tell the dentist if the proximal area has caries by way of the presence of radiolucent areas. 

3. Class III Caries - Caries that involve only the proximal area of anterior (front) teeth are classified as Class III Caries. This type affects the smooth-surface of a tooth, or the surface that is facing the lips, the palate (for upper teeth) or the tongue (for lower teeth). Class III caries happen in areas that are not habitually cleaned and constantly covered with plaque. 

• Class III caries are usually very easy to detect. They show areas of cavitation and brown-black discoloration that can be seen immediately. The explorer is ran on the facial and lingual proximal surfaces to check for cavities. 

4. Class IV Caries - If caries affects the proximal area and the incisal (cutting) surface of anterior teeth, then it is classified as Class IV.

• The process of detecting class IV caries is also the same as class III. 

5. Class V Caries - Class V caries are those that are found near the gingival (gums) area of the tooth. It also affects a smooth surface.

• To detect class V caries, the explorer is run through the facial or lingual aspects of teeth from the cervical (near the gum) to the coronal (near the crown) surface. An indication that there is class V caries is a "catch". 

Class VI Caries - The tip of the cusps of posterior teeth can also have caries. If that is the case, they are classified as Class VI caries. Note that unlike Class I caries that originate from pits-and-fissures, Class VI caries affects a smooth-surface.

• To check for Class VI caries, the explorer is passed through the cuspal inclines and tips. 

Root Surface Caries
Root surface caries are not classified under any of the six classes. As the name implies, they occur on the cementum of the tooth that's always covered in plaque. Cementum being less mineralized than enamel, is more prone to demineralization caused by caries. Root surface caries progresses rapidly also because of the same reason, that's why it should be treated immediately. It is prevalent in the older population as the elderly frequently experience gingival recession.

[1] Roberson, T., Heymann, H., & Swift Jr., E. (2006). Sturdevant's art and science of operative dentistry. Missouri: Mosby 
[2] Wolff, M., Allen, K., & Kaim, J. (2007). A 100-year journey from GV Black to minimal surgical intervention. Compendium of Continuing Education in Dentistry, 28(3), 130-134.
[3] Awadalla, H., Ragab, M., Bassuoni, M. Fayed, M., & Abbas, M. (2011). A pilot study of the role of green tea use on oral health. International Journal of Dental Hygiene, 9(2), 110-116. 
[4] Ferrazzano, G., Cantile, T., Quarto, M., Ingenito, A., Chianese, L., & Addeo, F. (2008). Protective effect of yogurt extract on dental enamel demineralization in vitro. Australian Dental Journal, 53(4), 314-319. 
[5] Gutkowski, S. (2008). Minimal intervention. RDH, 28(6), 88-117.