Zones of enamel caries
• The early (submicroscopic) lesion
• Phase of nonbacterial enamel crystal destruction
• Cavity formation
• Bacterial invasion of enamel
Early submicroscopic lesion:
In early lesion, earliest visibility changes appear as white opaque spot on the surface of tooth and adjacent to contact point other than this chalking white appearance the enamel is hard and smooth on appearance . This caries is known as Incipient caries.
1. Translucent zone : 1st observable changes occur in this translucent zone. It appears as by formation of submicroscopic spaces or by pores . locate at the prism boundaries and other junctional sites such as on the stiae of retjius.Here 1% demineralization occur.
2. Dark zone : It lies adjacent to translucent zone .It is defined as positive zone because it is always present. This zone is formed by demineralization and here 2-4% demineralization occur .
3.Body of the lesion: It lies between surface zone and body of the lesion . Here greatest amount of demineralization occur. Here 5% demineralization occur near the periphery and 25 % demineralization occur on the centre of the lesion .
4 . Surface zone : When it is examined by polarized microscope , micro radiography shows relatively unaffected . The greater resistance of this layer may be due to greater amount of remineralization or may be due to greater concentration of surface enamel.
Once bacteria have penetrated the enamel they reach the amelodentinal junction and spread laterally to undermine the enamel. This has three major effects. First, the enamel loses the support of the dentine and is therefore greatly weakened. Second, it is attacked from beneath . Third, spread of bacteria along the amelodentinal junction allows them to attack the dentine over a wide area . Thus the primary lesion provides the bridgehead for the attack on enamel, but undermining of the enamel determines the area of a cavity. Clinically this is frequently evident when there is no more than a pinhole lesion in an occlusal pit, but cutting away the surrounding enamel shows it to be widely undermined.As undermining of the enamel continues, it starts to collapse under the stress of mastication and to fragment around the edge of the (clinically obvious) cavity. By this stage, bacteria damage to the dentine is extensive.
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