Pulpal Reaction to Tooth Preparation

In the recent past, high speed cutting instruments have largely been employed in cutting cavities and preparing teeth for crowns. Adequate cooling of the burs is essential to prevent injury to dentin and also to underlying odontoblastic region of the pulp. The water spray should reach at the site of cutting and bur. Light pressure with intermittent cooling can minimize temperature increase.

When the cooling is inadequate, the injury leads to displacement of odontoblastic nuclei into the dentinal tubules. The odontoblasts appear disorganized. The cooling, if missing, or excessive pressure is utilized constantly the burning of dentin becomes evident. Many a times, the smear layer may obturate the opening of the tubules and reduce the extrusion of contents of dentinal fluids.

It is established that such flow of fluid, later, is helpful in formation of peritubular dentin. The disturbance and redistribution of the cellular constituents, if continued, leads to degeneration of odontoblastic processes. This might form the base for formation of ‘dead tracts’ and subsequently formation of tertiary dentin.

Displacement of odontoblastic nuclei

Burning of dentin due to inadequate cooling or blunt cutting instrument, during tooth preparation

Gentle grinding over the dentin leads to increased blood flow. Grinding halfway into the dentin causes much more increase in blood flow. However, grinding in the inner half leads to decrease in blood flow. The blood flow has been seen as decreasing after crown preparation, since the inner thickness of dentin might not be more than 1.0 mm.

The displacement of odontoblastic nuclei into the dentinal tubules has been established. Earlier, ‘aspiration of odontoblastic nuclei’ was considered the phenomenon, but recently the accepted phenomenon is found to be the ‘displacement of odontoblasts’. The cavity depth or the remaining dentin thickness has always been the key factor in such reactions. A number of morphologic changes occur including intracellular disorganization of the odontoblasts. This can lead to disruption of odontoblastic layer. The exact mechanism of such movements might not be fully understood, however, mechanical distortion of the dentin can be the cause.

The alternative means of cavity preparation such as air abrasion and laser cavity preparation also affects the pulp. The generation of heat with the use of lasers is more detrimental than air abrasion technique.