Secondary dentin is dentin that is formed and deposited in response to a normal or slightly abnormal stimulus after the complete formation of the tooth.
There is a considerable variation in the composition of primary and secondary dentin. The dentinal tubules that make up dentin are generally irregular in secondary dentin and deposits contain less calcium phosphorous and collagenous matrix per unit volume than the primary dentin. Secondary dentin is less mineralized and contains 6-10 % more mineral than primary dentin.
There are generally two types of secondary dentin produced as a result of different stimuli. The two types of secondary dentin are Physiological secondary dentin and Reparative secondary dentin.Physiological secondary dentin
This type of dentin is a regular uniform layer of dentin around the pulp chamber that is laid down throughout the life of the tooth as a result if physiological factors generally thought to be age and tooth eruption. This type of secondary dentin is produced more slowly than primary dentin.Reparative secondary dentin
Reparative secondary dentin is the dentin that forms around the pulp chamber as a result of irritation or attrition which is a form of tooth wear. Attrition is tooth-to-tooth contact which results from occlusal function such as Bruxism and can cause loss of tooth structure. This gradual traumatic process stimulates the development of natural protective measures such as secondary dentin.