Dentine and Pulp 4

Dentine lesion

This is a ground longitudinal section of a tooth showing a region where reactionary events have occurred within the dentine underlying a fissure caries lesion within the enamel. Note how the lesion in the dentine spreads wider than that visible in the overlying enamel because of the arrangement of the enamel prisms around the fissure and because of some lateral spread at the ADJ.

Sclerotic dentine: Sclerotic (or translucent) dentine arises because the dentinal tubules have been completely occluded by the laying down of additional peritubular dentine within the tubules by the odontoblasts. This occurs either as a general aging process or (as in this case) as a defensive mechanism in response to some overlying trauma (the caries lesion in enamel). This process only occurs if the progress of the lesion is slow enough to allow the cells to fill-in the tubules in good order. In this particular case initially the odontoblasts were able to accomplish this, hence the significant amounts of sclerotic dentine. However, subsequently the cells could not maintain this form of defence and withdrew their cell processes, leaving behind empty tubules (which during the grinding process fill with air and debris and appear black). This is a 'dead tract'.

Dead tract: If the odontoblast cannot mount an 'ordered' defence by producing sclerotic dentine then it will withdraw its cell process (or indeed may be killed) leaving an empty tubule which during the grinding process fills with air and debris and thus appears black. The odontoblast will (if still extant) attempt to seal the pulpal end of the tubule with reparative (or irregular secondary) dentine. If the odontoblasts are killed then this process is completed by sub-odontoblastic cells which produce a bone-like material.