Editing Tooth decay (section)

====Tertiary dentin====
{{See also|Tertiary dentin}}
In response to dental caries, there may be production of more dentin toward the direction of the pulp. This new dentin is referred to as tertiary dentin.<ref name="cate152"/> Tertiary dentin is produced to protect the pulp for as long as possible from the advancing bacteria. As more tertiary dentin is produced, the size of the pulp decreases. This type of dentin has been subdivided according to the presence or absence of the original odontoblasts.<ref name="transdentinal">{{cite journal |vauthors=Smith AJ, Murray PE, Sloan AJ, Matthews JB, Zhao S |title=Trans-dentinal stimulation of tertiary dentinogenesis |journal=Advances in Dental Research|volume=15 |pages=51–4 |date=August 2001 |pmid=12640740 |doi=10.1177/08959374010150011301|s2cid=7319363 }}</ref> If the odontoblasts survive long enough to react to the dental caries, then the dentin produced is called "reactionary" dentin. If the odontoblasts are killed, the dentin produced is called "reparative" dentin.

In the case of reparative dentin, other cells are needed to assume the role of the destroyed odontoblasts. [[Growth factor]]s, especially [[TGF beta|TGF-β]],<ref name="transdentinal"/> are thought to initiate the production of reparative dentin by [[fibroblast]]s and [[Mesenchymal stem cell|mesenchymal]] cells of the pulp.<ref name="summit14">Summit, James B., J. William Robbins, and Richard S. Schwartz. "Fundamentals of Operative Dentistry: A Contemporary Approach." 2nd edition. Carol Stream, Illinois, Quintessence Publishing Co, Inc, 2001, p. 14. {{ISBN|0-86715-382-2}}.</ref> Reparative dentin is produced at an average of 1.5&nbsp;μm/day, but can be increased to 3.5&nbsp;μm/day. The resulting dentin contains irregularly shaped dentinal tubules that may not line up with existing dentinal tubules. This diminishes the ability for dental caries to progress within the dentinal tubules.