Pulpitis is the inflammation of the dental pulp mostly caused by bacterial invasion following dental caries. The pulp is limited from expanding due to it being enclosed by the hard, mineralized dentin. This can be advantageous and protective but also be possibly destructive. Inflammation may remain reversible or proceed to irreversible pulpitis and necrosis depending on the balance kept between microbial invasion and immune system. The pulp-dentin complex works together as functional unit. Odontoblasts, which are found at the pulp-dentin interface, are the first line of defense. In addition, in their role for forming dentin, they use pattern recognition receptors (PRRs), specifically Toll-like receptors (TLRs) to recognize bacteria, so therefore act as immune sentinel cells. Fibroblasts, dendritic cells, macrophages, and dental pulp stem/progenitor cells (DPSCs) are other types of pulp cells that help the body fight off infections.