Pathophysiology of Dental Caries.

Carious lesion dynamics are dependent predominantly on the availability of fermentable sugars, other environmental conditions, bacteria, and host factors. Our current understanding of the microorganisms involved in the initiation and progression of caries is still rather incomplete. The most relevant acidogenic-aciduric bacterial species known to date are Streptococcus mutans, bifidobacteria, and lactobacilli. Whereas mutans streptococci are initiators, bifidobacteria and lactobacilli are more enhancers for progression. Boosters for microbial activity are specific environmental conditions, such as the presence of fermentable dietary sugars and the absence of oxygen. Based on these conditions, the necrotic and/or contaminated zone fulfils all criteria for disease progression and has to be removed. For those deep lesions where the pulp vitality is not affected, a selective removal of the contaminated leathery dentine should take place as this approach lowers the risk of regrowth of the few embedded microbial cells here. In repelling the microbial attack and repairing damage, the host has developed several ingenious strategies. A major resistance to carious lesion progression is mounted by the dentine-pulp tissues. The signalling molecules and growth factors released upon dentine demineralisation upregulate the odontoblast activity and act as sensor cells. After carious stimulation, odontoblasts initiate an inflammatory reaction by producing chemokines and synthesise a protective tertiary dentine. After the destruction of these cells, the pulp still has a high capacity to synthesise this tertiary dentine thanks to the presence of adult stem cells within the pulp. Also, in addition to the systemic regulation, the pulp which is located within inextensible the confines of the dentine walls has a well-developed local regulation of its inflammation, regeneration, and vascularisation. This local regulation is due to the activity of different pulp cell types, mainly the fibroblasts, which secrete soluble molecules that regulate all these processes.