The dentinal fluid is an integral part of tooth structure. The fluid transport system of the tooth is important for the nourishment of tooth by supplying various nutrients and innervating the entire dentin. Dentinal fluid originates from the terminal capillaries in the pulp and diffuses into DEJ along with periodontoblastic space. The pulpal interstitial fluid is under positive tissue pressure that tends to move dentinal fluid from the pulp through any dentinal tubules that are not sealed peripherally by enamel. The carious dentinal exposure may lead to change in the composition of the dentinal fluid. The most postoperative sensitivity is caused by fluid shifts that occur across normal dentin that is either too thin or poorly sealed. Dentinal fluid can be used for pulpal diagnosis using molecule markers found in fluid as in normal function, the composition of the dentinal fluid is controlled by the odontoblasts. So this literature attempted to put insight into less talked about a topic that is dentinal fluid which is actually "The Life Line of the Teeth"