CARIES OF THE ENAMEL

A HISTOPATHOLOGICAL STUDY OF CARIES OF THE HUMAN ENAMEL OPERATING BENEATH APPARENTLY SOUND AND INTACT ENAMEL SURFACES

¹ Division of Operative Dentistry, Section of Oral Pathology, College of Dentistry, University of California, San Francisco, Calif.

The development of the carious lesion in enamel of the human has been followed from the earliest microscopic stages to the final cavitation of the surface. Several distinct types of penetration by microorganisms have been described. Another type of slowly progressing caries (restricted caries) has been studied. The gross appearance of the surface lesion is that of a brown-stained spot on the intact enamel surface of a tooth. The following observations were made.

1. In undecalcified ground sections the brown stain may extend to the dentinoenamel junction and may involve the dentin.

2. In this type of lesion the spherical microorganisms have long since penetrated the surface and have established a central focus of infection within the enamel.

3. A microscopic plaque overlies the stained carious surface of the tooth. The plaque consists of an amorphous background in which filamentous organisms form a dense mat and have a characteristic parallel arrangement to one another.

4. In the deeper part approximating the disintegrating tooth surface these filamentous forms are seen to project themselves directly into the surface lesion so as to appear partly within the degraded organic mass.

5. These organisms apparently make their appearance following the establishment of the superficial carious process. Morphologically the primary invaders have a spheroidal appearance.

6. The macroscopic appearance of the surface lesion is that of a hard, intact enamel surface. The microscopic observation is that the area of organic degradation may have had its initiation from multiple portals of entry on the tooth surface.

7. With deeper penetration of the infection, a central focus of infection is established and multiple irregular channels spearhead in all directions beneath an uninvolved surface so that islands of apparently uninfected matrix are isolated by the anastomosing of these channels. These invading organisms are of the spheroidal type.

8. Concomitantly with the spearheading tracts, the peripheral matrix of the central focus undergoes progressive disintegration, leaving a shell of uninvolved enamel on the surface of the tooth.

9. The infected organic matrix takes on a more intense acidophilic staining reaction when compared with the normal surrounding matrix. This increased staining reaction is the earliest indication of a pathological change in the matrix.

10. The increase in acceptance of the dye is closely followed by a progressive loss of structural detail; when the alteration is advanced, the matrix becomes almost homogenous in appearance.

11. The spheroidal appearing microorganisms are found in greater abundance at the perimeter of the central focus where the organic rods have begun to undergo a definite degradation and solution.

12. In the center of the focus where the breakdown of the organic rods is nearing completion, relatively few organisms are to be found.

13. The infection, having reached the dentino-enamel junction, then extends laterally along this structure on the enamel side, opening up the dentinal extremities of the rods and inter-rod intervals and thus establishes retrograde spread.

14. The lateral spread of the focus is at first confined to the enamel, and only when disintegration is advanced does the dentin become involved. This characteristic spread is due, in part, to the nature and mineralization of the dentinoenamel junction.

15. The first microorganisms to invade the dentin are of the same spheroidal type as those seen in the early invasion and spearheading of the enamel lesion.

16. The spheroidal forms first penetrate along the lateral walls of the dentinal tubule but are found in the center of the tubule only after the dentinal fibril has become affected.

17. The microorganisms associated with the carious lesion and the character of this lesion are essentially the same in both the enamel and dentin structures. The greater content of organic material in the dentin accounts for the greater rapidity of the breakdown.

18. When the degradation of the enamel matrix in the central focus is in its final stage, there is a variation in the morphological types of organisms present. The spheroid types no longer predominate, and threadlike forms are found in greater numbers.

19. The appearance of the thread forms in the central focus points to the possibility that these organisms may have more than a casual relationship to the carious process.

We believe that these observations of the carious process operating beneath apparently unbroken and intact enamel surfaces further advance our original hypothesis: that dental caries is fundamentally a degradation of the organic matrix of the enamel resulting from the enzymatic action of microorganisms, rather than a simple acid decalcification and removal of the inorganic salts.

This article has been cited by other articles:

				V. HURST, H. E. FRISBIE, J. NUCKOLLS, and M. S. MARSHALL In Vitro Studies of Caries oof the Enamel in the Syrian Hamster Science, January 9, 1948; 107(2767): 42 - 44. [PDF]