One of the important factors in determining the dentinal bonding is collagen. This process lies in the dentinal tubule. The smear layer prevented all the sealers from penetrating dentinal tubules. Gradually however, the tubules obturate and lead to dentinal sclerosis. This diminishes the ability for dental caries to progress within the dentinal tubules. The three dimensional configuration of the dentinal tubules is genetically determined. The structure of the dentinal tubules contributes to both its porosity and its elasticity. This interaction may be essential in the invasion of dentinal tubules by "P. gingivalis". Dentinal dysplasia is another disorder of dentin. Fluid movement inside the dentinal tubules may be away from or towards the pulp. It is believed that potassium ions diffuse along the dentinal tubules to inactivate intradental nerves. Smear layer will fill the orifices of the dentinal tubules, hence forming smear plugs. Dentinal tubules are irregular and are bigger in diameter. Resorption continues up the dentinal tubules into the tooth crown. It has better structural integrity and forms a thicker, more localized dentinal bridge.