Factors Influencing Pulpal Response

The risks of pulpal response associated with any dental material depend to a large extent on its ability to diffuse through dentin and accumulate in the pulp. It has been established that materials, which may not be toxic at low concentrations become toxic at high concentrations. Pulp reactions to the same irritant may vary not only between different persons but also between different teeth in the same mouth, and between opposing teeth of the similar anatomic form. Factors influencing pulpal response are:

a) Dentin Permeability

The rate of permeation of substances through dentin depends upon a number of factors like:

i) Location: Dentin permeability varies in different areas of the same tooth e.g., it increases towards the pulpal side. This is because both the tubule diameter and the number increase towards the pulp chamber.

ii) Dentin Diffusion Surface Area: This is a product of tubule diameter and number, which directly influences the wetness and hence the hydrolytic dissolution of the restorative material.

iii) Smear Layer: The presence of the 1-5 μm thick smear layer reduces permeability.

iv) Intratubular Contents: The intratubular contents such as mineral deposits, collagen fibrils, proteins etc. may reduce permeability.

v) The Concentration and Solubility of the Diffusing Solutes: The substances with high molecular weight and size are less penetrating than the substance with low molecular size and weight. Solutes that are water soluble would show a rapid rate of penetration.

vi) Patency of the Dentinal Tubules: Sclerotic dentin is less permeable than the physiological tubular dentin.

vii) Reparative Dentin: In case where reparative dentin has been formed previously, the response of the pulp is less, because reparative dentin reduces the penetration and movement of the tubular contents.

viii) Remaining Dentin Thickness: Effective remaining dentin thickness of 2.0 mm provides an adequate insulating barrier against almost all the techniques and restorative materials.

b) Dentin Pretreatments

Preconditioning of dentin by acids (etchants and conditioners) might increase dentin permeability by removing smear layer and enlarging tubule orifices. The effect depends upon the concentration and the duration for which the etchant/ conditioner is applied.

c) Age of the patient

It is usually accepted that the inflammatory response of the older persons is slightly more extensive and the secondary dentin formation is slightly less than in the younger person. The older pulps have a far less defensive capacity in resolving a lesion and resisting infection. However, certain authors have shown that age differences do not affect the pulpal response of human teeth.