Review Article http://doi.org/10.18231/j.ijohd.2019.042 International Journal of Oral Health Dentistry, October-December, 2019;5(4):184-190 184 Polymerase chain reaction (PCR) – A review with its pertinency to dentistry Sumit Kumar Yadav 1 , Achla Bharti Yadav 2* , Neal Bharat Kedia 3 , Gunjan Kedia 4 , Kunal Kumar 5 1,2 Reader, 3 Professor, 4 Senior Lecturer, 5 Senior Resident, Dept. of Oral Pathology, 1,2 DJ College of Dental Sciences & Research, Uttar Pradesh, 3,4 Buddha Institute of Dental Sciences & Hospital, Patna, Bihar, 5 Patna Medical College and Hospital, Patna, Bihar, India *Corresponding Author: Achla Bharti Yadav Email: drachlabharti@gmail.com Abstract Advances in molecular technologies over recent years have a profound impact on diagnostic pathology. These techniques utilize DNA, RNA and enzymes that interact with nucleic acids to understand biology at a molecular level. They will also provide a complementary approach to traditional methods of histopathological analysis in the future. Various molecular techniques are now being widely used throughout the world including polymerase chain reaction (PCR), hybridization methods, flow cytometry, tissue microarray and laser capture microdissection (LCM). Among these PCR is one of the most common diagnostic modality with high specificity, sensitivity and variety of applications. It will significantly impact three major areas: specific diagnosis, prognosis determination and prediction of response to therapy. Therefore, it has a great potential to become a standard procedure in diagnostic surgical pathology. The application of PCR in the context of dentistry is also presented here, along with the basics of PCR and its fundamental aspects. Keywords: Applications, Dentistry, Inhibitors, Oral cancer, Polymerase Chain reaction, Tumor biology. Introduction Recent advances in molecular and genetic biology have revolutionized the study of DNA, RNA, and proteins, obtained from various diagnostic specimens to elucidate the complex mechanisms involved in the pathogenesis of diseases. 1,2 In the field of oral and maxillofacial biology and medicine, study at the molecular level is essential for the diagnosis, prognosis, and treatment of diseases, as well as for understanding the development of normal and abnormal tissues/organs. 3 The development of PCR, an acronym for Polymerase Chain Reaction is one of the most substantial technical advances in the field of molecular genetics for the in vitro amplification of DNA. 4 In PCR, nucleic acid primers are hybridized to a target nucleic acid sequence to allow the enzymatic copying and subsequent amplification of the sequence of interest. 5 The discoverer of the technique Dr. Kary Mullis, said “lets you pick the piece of DNA you’re interested in and have as much of it as you want”. 4 The present paper is an attempt to review the basics and fundamental aspects of PCR along with the applications, particularly in the context of oral pathology. Review Historical background PCR was thought to be conceived by Dr. Kary Mullis in 1983 while working at the Cetus Corporation in Emeryville, CA. However, some pioneering work was also done by Gobind Khurana in 1971 who described a basic principle of replicating a piece of DNA using two primers. 6,7 In 1993Kary Mullis was awarded the Nobel Prize for the discovery of PCR. In Mullis's original PCR process, the enzyme DNA polymerase extracted from the bacterium E. coli was used which gets destroy at high temperature and the enzyme had to be replenished after the heating stage of each cycle. Mullis's original PCR process was proved to be inefficient since it required a great deal of time, vast amounts of DNA-Polymerase enzyme and continual attention throughout the PCR process. 7,8 The milestone in the field of molecular research and creditable for universal adoption of PCR was the isolation of a heat stable (up to 95°C) enzyme Taq polymerase from extreme thermopile bacterium 'Thermus aquaticus' (1989). 7-9 David Gelfand and his associates at Cetus, purified and subsequently cloned this polymerase, allowing a complete PCR amplification to be done without opening the reaction tube. 7 The discovery of Taq polymerase has facilitated the development of automated PCR machines which takes about five minutes for each cycle and is programmed to control the repetitive stages of heating and cooling. 7,9 Reaction mixture Amplification of DNA requires following main components: 4,8-10 1. DNA template, or cDNA which contains the region of the DNA fragment to be amplified; 2. Enzyme Taq polymerase (DNA polymerase) which copies the region to be amplified; 3. Pair of oligonucleotides that may serve as primers for DNA synthesis, that are complementary to the beginning and end of the DNA fragment to be amplified; 4. Equimolar concentrations of the four deoxynucleotide triphosphates (dATP, dCTP, dGTP, dTTP) with which to construct the new DNA strands; 5. Appropriate buffer containing MgCl2 to optimize DNA polymerase activity. Principle of PCR 4,8-13 PCR is an in vitro enzymatic amplification of a specific DNA sequence to obtain large number of DNA copies by means of an exponential rate. It is composed of the following major stages: A. Denaturation: The double-stranded DNA (ds-DNA) is isolated from the material under study (target DNA)