ATP as a Biomarker for the Caries Infection

ATP stands for adenosine triphosphate and is the energy molecule in all living cells. In the mouth, ATP provides the opportunity to measure bacterial load and biofilm activity levels as they relate to health. ATP bioluminescence testing is the method for rapidly measuring the quantity of microorganisms through the detection of adenosine triphosphate. ATP is quantified by measuring the light produced through its reaction with the naturally occurring firefly enzyme “luciferase” using a luminometer, a very sensitive light measuring device. ATP testing has been used in a variety of health and biologic testing methods since the 1960s but has only in the last 10 years been adapted to dentistry and dental caries diagnosis.

One of the primary issues related to dental microbiological testing has been the sheer number of bacterial species implicated in the disease process. Until recently, dental caries was thought to be a fairly simple disease. It was thought to be caused primarily by two bacteria, Mutans streptococci and Lactobacillus^1,2 and required only refined sugar and tooth structure to occur. The traditional disease model was supported by an abundance of scientific studies linking Mutans streptococci and Lactobacillus levels to caries risk in children.^{3, 4} But as the field of biofilm research developed, a broader, more complex picture became apparent. More bacteria were implicated in the disease process by different researchers worldwide.⁵ Now oral biofilms can be studied with forensic-type precision by identifying the bacteria with the 16S gene sequence of their rRNA.⁶ This has added additional species to the growing list of bacterial species now implicated in the dental decay process.^{7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18}

Recent biofilm research based on 16S gene sequence DNA evidence is also broadening the picture of dental caries. It is clear now that some of the previous paradigms on the microbiology of dental caries were wrong.^{15, 20} The mouth represents a unique environment in the body for biofilms. The teeth are the only nonshedding surfaces in the body, so the biofilms on the teeth tend to be more complex and microbiologically diverse than previously thought.²¹ While more than 700 bacterial phylotypes could potentially be found in the human mouth, a healthy individual only has around 113 different bacterial species, while a high caries-risk individual has an average of 94, presumably because fewer bacteria are capable of surviving the low pH conditions consistent with the disease.²²

Based on the biofilm disease model, with a large number of different species of bacteria participating in the disease process and high (100 times) usage of ATP being one of the common “fingerprints” of aciduric bacteria, a better metric of assessment is ATP testing.²³ The survival of acidogenic/aciduric (cavity-causing) bacteria depends on their ability to produce enough ATP to effectively transport the H+ (acidic) ions out of the cell, thereby maintaining intracellular neutrality necessary for survival.²⁴ The concept of ATP bioluminescence has been tested with strong positive correlation values in dental caries risk assessment and fits the nonspecific bacterial biofilm model.²³

Even with all of this evidence, one common misconception is that all patients with current decay will test high with ATP bioluminescence testing. The reality is high levels of bacteria are not always the primary factor driving dental decay. Dental caries is a multifactorial pH dysfunction disease. For some patients, a highly destructive diet may be the primary driver. For others, it may be poor-quality saliva or poor saliva flow making them more susceptible. The purpose of ATP testing is not to identify “bacterial challenge” or “biofilm challenge” as the sole factor responsible for a patient’s disease, but rather either include it as one of the multiple factors associated with a patient’s condition when making treatment, restorative, and cosmetic recommendations, or eliminate it, allowing patients and practitioners to focus on other factors involved.

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